Cécile Cézanne
email: cecile.cezanne@gredeg.cnrs.fr

Olivier Sautel
email: olivier.sautel@gredeg.cnrs.fr

The Human Capital-Intensive Firm and Coordination:

Redefined Integration and Disintegration by

OLIVIER SAUTEL AND CECILE CEZANNE

The aim of this paper is to reconsider the link between integration and disintegration. We argue that the conception of this link depends on the way one defines the firm and its coordinating role. We focus on studying the human capital-intensive firm. We explain that coordination by this kind of firms consists in coordinating productive tasks. The role of the firm is to coordinate the specialization of complementary resources and the division of labour. We show that integration and disintegration must be differentiated by the tools they give to the firm to effectively govern productive assets. (JEL: D23, L22, L23)

1 Introduction
Vertical integration is one of the main issues of the analysis of industrial organization. In an historical perspective, the literature has often put the emphasis on successive movements of vertical integration and disintegration [START_REF] Chandler | The Visible Hand: The Managerial Revolution in American Business[END_REF][START_REF] Langlois | The Vanishing Hand: The Changing Dynamics of Industrial Capitalism[END_REF] 1 . This tendency to historically contrast integration with disintegration can be explained in an analytical way.

Since the seminal work of [START_REF] Coase | The acquisition of Fisher Body by General Motors[END_REF] on the existence and the nature of the firm, many economists have interpreted the link between integration and disintegration as the consensual opposition between hierarchy and market [START_REF] Williamson | Markets and Hierarchy[END_REF](WILLIAMSON, , 1985;;[START_REF] Klein | Vertical Integration, Appropriable Rents, and the Competitive Contracting Process[END_REF].

Economists describe integration and disintegration as alternative means to coordinate productive activities. In an institutional perspective, the division of labour is ensured, on the one hand, by hierarchies, and by the price system, on the other hand. Integration and disintegration are the two polar modes of coordinating economic agents. The perception of vertical disintegration as the analytical opposite of integration is based on the vision of the firm as a combination of physical assets commonly owned. As modelled by the Incomplete Contracts Theory, the ownership of physical assets determines a planed coordination by firms whereas the non-ownership corresponds to a spontaneous coordination by markets.

The traditional theory of the firm based on the property rights perspective as formalized by HART AND [START_REF] Hart | Property Rights and the Nature of the Firm[END_REF] and HART [1995] can be criticized by taking into account the importance of human assets in the production process of firms (RAJAN AND ZINGALES, 2000; ROBERTS AND [START_REF] Roberts | Stakeholder Interests, Human Capital Investment and Corporate Governance[END_REF]MINEFI, 2005). BLAIR [1995, p. 292] states "a knowledge company's primary resource and principal competitive advantage is the knowledge that its employees possess …". Abilities, skills and knowledge developed both by internal workers and external stakeholders of the firm characterize a significant corporate added value of innovative strategies of the productive entity. For example, business services firms in data-processing and in telecommunications produce 72% of the added-value of the French sector of Information and Communication Technologies (SESSI, 2005). It indicates that firms built around agents' resources produce 72% of the added-value of the sector. By comparison, the production of computers represents only 3% of the added value of the same industry. These data suggest that human capital-intensive firms tend to be more and more important in economic activity.

The aim of this paper is to re-consider the link between vertical integration and disintegration on the basis of an understanding of modes of coordination within the human capital-intensive firm.

We focus on analyzing entrepreneurial firms whose productive activity is built around the human capital of its key partners. One can say this case is a restrictive one but we believe it concerns numerous firms. Especially, it concerns business service firms.

On the basis of an original vision of the human-capital-intensive firm, we suggest a new definition of the relationship between integration and disintegration, overcoming the traditional dichotomic vision. A change in the central subject of coordination (human assets rather than physical assets) involves reconsidering modalities of coordination (specialization of tasks rather than property of assets). It thus involves re-examining the link between integration and disintegration (integration and disintegration are not viewed as two opposite institutional modes of coordination). We argue that integration and disintegration must be differentiated by the tools they give to the firm so that it can effectively govern the productive specialization of its human assets.

The outline of the paper is as follows. Section 2 describes the dichotomic conception of the link between vertical integration and disintegration. The alternative "hierarchy/market" as the mode of coordination is based on a vision of the firm exclusively defined as a structure of property rights. Section 3 questions the relevance of this vision developed by the Incomplete Contracts Theory by examining the problem of coordination in a human capital-intensive firm. The hierarchical organization, power stakes and the model of governance of a firm based on its human assets lies on the management of the specialization of agents rather than the allocation of property rights. On the basis of this enriched vision of the coordinating role of the human capital-intensive firm, we propose in section 4 a new analysis of integration and disintegration. We conclude that the relationship between integration and disintegration must be understood as a combination of instruments available to a unique mode of coordination, the specialization of agents within the functional boundaries of the firm.

2 The Firm as a Legal Structure of Property Rights

Questioning the Foundations of Contractual Theories of the Firm

Scholars have long ignored the firm as a very important agent of the economic analysis. They focused on studying market and described it as the only and optimal mode of coordination of economic activities. The seminal article of [START_REF] Coase | The acquisition of Fisher Body by General Motors[END_REF] bases the existence of the firm on market informational imperfections. And Coase justifies the superiority of the firm by emphasizing the price system fails to coordinate effectively economic activities. Economic institutions, like corporations, would be able to save some transaction costs due to productive activities [START_REF] Coase | The acquisition of Fisher Body by General Motors[END_REF][START_REF] Williamson | Markets and Hierarchy[END_REF]WILLIAMSON, , 1985)). Besides, the tendency of firms to create market value through productive transactions matters as far as two dimensions are concerned.

The surplus-sharing, on the one hand, and uncertainty concerning the realization of this surplus, on the other hand, are the two main problems arising from the productive activity of firms.

Later research (GROSSMAN AND HART, 1986; HART AND [START_REF] Hart | Property Rights and the Nature of the Firm[END_REF] explains transactions costs are due to a problem of strategic expropriation of relational quasi-rents: this is the so called hold-up risk induced by underinvestments. The Incomplete Contracts Theory focuses on efficiency considerations and incentives structures to deal with hold-up problems. More precisely, the Incomplete Contracts Theory comes down to two main assumptions:

-The coordination of two agents in a productive transaction amounts to a problem of incentives; what only matters is how to encourage agents to make efforts and how to solve the corresponding hold-up problem; -The hold-up problem can be overcome by giving the set of residual rights of control to a unique agent. This solution supposes this agent legally appropriates the assets of the firm.

In other words, the firm is defined as a combination of assets legally and commonly owned. The Incomplete Contracts Theory considers ownership as the way to address potential holdups and incentives alignment in a world of incomplete contracting and divergent interests (HOLMSTROM AND ROBERTS, 1998).

In this context, vertical integration is associated with a need of planed coordination in the production process. Vertical integration is the organizational solution to buffer hold-up threats. Reciprocally, vertical disintegration can be viewed as a spontaneous coordination by markets where assets remain separately owned. The analytical link between vertical integration and disintegration is considered in a bipolar way: sometimes the firm, sometimes the market, is privileged in order to coordinate industrial activities. This analysis seems not to be pertinent in regard to the current industrial context. The last twenty years have been characterized by a large movement of vertical disintegration [START_REF] Langlois | The Vanishing Hand: The Changing Dynamics of Industrial Capitalism[END_REF][START_REF] Leiblein | An Empirical Examination of Transaction-and Firm-level Influences on the Vertical Boundaries of the Firm[END_REF]. Many stages of the production process are outsourced so that inter-firms relationships have greatly and rapidly increased. In 2003, 81% of French firms of more than 20 employees declared keeping up at least one cooperation relationship; 70% of these firms communicated that this kind of relationships was durable (more than five years) (SESSI, 2005). Besides, inter-firms relationships have changed in the way companies are linked. A lot of work on the emergence of the network-firm testifies the recent growth of market relations [START_REF] Langlois | The Vanishing Hand: The Changing Dynamics of Industrial Capitalism[END_REF][START_REF] Baudry | La question des frontières de la firme : Incitation et coordination dans la firme réseau[END_REF][START_REF] Frigant | Vanishing hand versus systems integrators -Une revue de la littérature sur l'impact organisationnel de la modularité[END_REF]. Yet, disintegration does not necessarily correspond to a new development of anonymous and spontaneous market relationships. Industrial restructuring has come with a strengthening of the influence of leader firms in the economic system. This monopolization process does not suggest a return of market coordination; it rather highlights the structuring role of big firms in the organization of markets.

This apparent "paradox" can be understood by re-founding the nature and the role of the firm. More precisely, we must go beyond the vision of the firm as a combination of fixed assets commonly owned. In this perspective, we can overcome the traditional dichotomic conception of the relationship between vertical integration and disintegration. We propose to explain integration and disintegration as two different modalities of a same coordination process controlled by the firm. To do so, we show that the firm effectively governs its productive activity and actively organizes the division of tasks with different tools given by vertical integration and disintegration.

Two perspectives can be explored to develop this argument by questioning the two main assumptions stated above. First, the contractual problem of rents expropriation is not the only one. The historical controversy around General Motors -Fisher Body case [START_REF] Coase | The acquisition of Fisher Body by General Motors[END_REF][START_REF] Klein | Vertical Integration as Organizational Ownership: the Fisher Body -General Motors Relationship Revisited[END_REF][START_REF] Freeland | Creating Hold-up through Vertical Integration: Fisher Body Revisited[END_REF][START_REF] Casadesus-Masanell | The Fable of Fisher Body[END_REF] illustrates, for example, that vertical integration is especially chosen in order to coordinate the production process. The contractual aspect is of secondary importance in the choice of vertical integration. For Christensen, VERLINDEN AND [START_REF] Christensen | Disruption, Disintegration and the Dissipation of Differentiability[END_REF], the choice of the institutional form depends on a need of explicit technological coordination between agents. This choice varies with the degree of innovation of the goods produced. As a result, questioning the first assumption stated above corresponds to an external criticism of the Incomplete Contracts Theory. The coordination challenge is not a problem of incentives alignment. The nature of the coordination problem must be revised. Yet, this line of attack is not the issue of this paper. Next, the second assumption can be critically examined but in an internal way. The hold-up problem and more globally investments incentives issues are recognized as central questions.

It is however possible to discuss that the firm, as a set of physical assets under common ownership, is up to solve these problems. This is the argumentation of MASKIN AND [START_REF] Maskin | Two Remarks on Property-Rights Literature[END_REF]: without referring to the firm, complete private contracts can be re-established to ensure incentives alignment. In this context, there's no raison d'être to the firm. The internal criticism can be addressed in another way. In this paper, we suggest that the firm is the solution to the hold-up problem but not as a unified structure of property rights. The role of the firm is obviously to regulate the hold-up problem but in a different way, on the basis of an active and enriched coordination of the specialization of agents. This conception of the coordinating role of the firm results from dealing with the management of human assets in a contractual theory of the firm.

Rethinking the Hold-Up Problem: the Importance of Specific Human Capital

In the contractual framework, the hierarchy is a solution to the hold-up problem, given the opportunistic nature of human actors and the specificity of fixed assets required for efficient production. As an authority of coordination, the firm motivates agents who take part in the productive activity. However, the contractual framework focuses on the notion of ownership of physical and transferable assets. Such an approach of the firm argues away the possibility of a hold-up based on human capital, because of hypotheses which seem questionable. In the Incomplete Contracts Theory, the power due to the existence of specific human assets affects neither the design of incentives systems nor the coordination of productive activities. Therefore, the Incomplete Contracts Theory overshadows the assumption of a hold-up problem arising from human assets. It takes into account the human dimension but in a very restrictive way. Human assets are always subordinated to the development of physical assets. For example, the transfer of physical assets necessarily induces the transfer of human assets. Corporate knowledge does not depend on a unique individual but on a set of partners [START_REF] Klein | Vertical Integration as Organizational Ownership: the Fisher Body -General Motors Relationship Revisited[END_REF]. In this context, the problem of quasi-rents expropriation arising from human capital disappears via the assumption of knowledge dispersion.

Moreover, when property rights on physical capital are reallocated, the control of human capital is indirectly but concomitantly altered. The level of skills, abilities and competencies reached by employees necessarily depends on a fixed capital specific to the firm. It follows that the possibility that a worker attempts to expropriate a part of organizational rents is ruled out. Human capital is only valuable when it is combined to a firm-specific physical asset. In this perspective, when property rights are redistributed, workers simultaneously "transfer" their specific human capital. Workers follow the reorganizing movement and carry on their productive effort in the same previous conditions. HART [1989] notes that control of physical capital can lead to control of human assets in the form of organizational capital.

Yet, we believe it is difficult to subordinate the importance of human assets to physical assets. Competition has increased, technological change has been advancing at a stronger pace and finance has been made more widely available. In this context, innovation has gained momentum and has been facilitated. Innovation usually requires workers whose human capital is specialized and specific to the firm employing them. Indeed, innovation race is necessarily conducted by valuable human capital at each stage of the production process. In this dynamic perspective, human capital has become more central in the productive activity of firms. Moreover, the development of specific human assets is strategic because according to BLAIR [1995, P. 231] "much of the wealth-generating capacity of most modern firms is based on the skills and knowledge of the employees and the ability of the organization as a whole to put those skills to work for customers and clients". And, the great ability of human capital to capture rents makes the traditional Incomplete Contracts Theory no longer tenable. Human capital takes on intrinsic importance, beyond its complementarities with physical capital. Thus, the way to control incentives relative to human capital does differ from the way to control incentives relative to physical one.

In this paper, we propose to adapt the existing theory of the firm to an emblematic case of a human capital-intensive firm and to analyze the different methods developed to discipline human capital in this firm. Human capital, because of its immaterial and non-transferable nature, can be appropriated neither by the firm nor by any stakeholders in the firm. Indeed, referring to Grossman, Hart and Moore terminology, an agent can not promise his residual rights of control on his human capital to others through an incomplete contract for a long period. Human capital is not alienable so that contracts on its management do not give the same residual rights of control as contracts on physical capital. GIBBONS [2005] notes that two kinds of rights coexist: alienable rights on physical assets and inalienable rights on human assets. Therefore, human capital-intensive firms can not be satisfactorily defined in terms of structure of property rights. The focus on the theory of the firm must shift to studying the economic nature (and not the legal nature) of organizations (RAJAN AND ZINGALES, 2001). The vision of the firm as a combination of physical assets commonly owned must be abandoned for an improved conception of the firm based on the specialization of human assets. It is a question of reconsidering control and incentives mechanisms over assets critical to the productive activity of the firm. Thus, we analyse the coordination of human assets and the coordination of their complementarities by exploring the organization, the operating and the governance of the human capital-intensive firm.

3 The Human Capital-Intensive Firm: Hierarchical Organization, Power Relationships and Corporate Governance

The Critical Resource Theory: the Firm as a 'Nexus of Specific Investments

The human capital-intensive firm must be viewed as a set of specific and mutually dependant tangible and intangible resources. This approach refers to multiple developments, and inter alia, the Resource-Based View of the firm [START_REF] Rumelt | Toward a Strategic Theory of the Firm[END_REF][START_REF] Wernerfelt | A Resource-Based View of the Firm[END_REF]; PRAHALAD AND HAMEL, 1990; PETERAF, 1993). PENROSE [1959] defines the firm as a core of capacities and unique resources. [START_REF] Aoki | The Co-operative Game Theory of the Firm[END_REF] characterizes the organization as a long term combination of specific resources. However, RAJAN AND ZINGALES [1998, p. 405], developing the Critical Resource Theory, model the entity as 'a collection of commonly owned critical resources, talents, and ideas, and also the people who have access to those resources'. More precisely, ZINGALES [2000, p. 1645] states that the firm represent a "web of specific investments built around a critical resource". It would result from the combination of three distinct phenomena: power, access to resources and complementarity, which all correspond to original mechanisms crucial to understand the firm built around its key human assets.

On the basis of the Critical Resource Theory, we present a simple vision of the hierarchical organization, the division of tasks and power relationships within an entrepreneurial human capital-intensive firm. A firm builds its productive activity on a critical resource owned by the entrepreneur. This resource is decisive for the firm insofar as it enhances the development of its production process. In addition, the critical resource is a source of power for the entrepreneur who possesses it. The entrepreneur can influence his employees' human capital, and he acquires power through the control (not ownership) over his own resource. If we actually regard entrepreneur's critical resource as a key human capital (talent, skills, etc.), economic power arises from an intangible and non-transferable capital non-imitable in an instantaneously way. In this situation, the hierarchical organization gets power thanks to the ability of the entrepreneur to cause an accumulation of specific investments. In order to reach this objective, the entrepreneur needs to control access to his critical resource and to build complementarities between his critical resource and employees' human capital. Unlike the Incomplete Contracts Theory, no contract is signed on the allocation of property rights because we consider a firm whose production process is based on human capital. We argue that a non-contractual2 agreement is rather done by giving access to the critical resource of the firm. The entrepreneur provides specialized stakeholders with an access to the firm or to his critical resource (i.e. its human capital) so that they can get power if they specialize themselves. In fact, by investing in human capital, stakeholders get power because they become decisive in the activity of the firm. The entrepreneur assigns access rights so that stakeholders who get access to the critical resource have the possibility to use or to work with it (RAJAN AND ZINGALES, 1998). The regulation of access corresponds to a coordinating mechanism alternative to ownership. Considering a firm typically built around its human assets, access is provided either through an employment relationship or through a cooperation agreement 3 . Once co-specificity exists between specific human assets, specialized workers adjust their investments in order not to jeopardize the joint value they can create together. Consequently, as this situation makes them dependent on the entrepreneur, employees choose to realize firm-specific investments because they know their reward will be greater if they control the critical resource of the firm. Through regulated access, an entrepreneur can shape a nexus of specific investments capable of producing more than any competitor with a similar resource hardly starting the production process. Indeed, the web of specific investments, built over time, cannot be instantaneously reproduced. The more agents specialize, the more power is maintained and increased so that at some point, the firm becomes the nexus of specific investments itself. The firm becomes the critical resource itself. Therefore, it can increase the value of the growth opportunities of the firm.

In this framework, power comes from control over human capital critical for the production process of the firm. Control over immaterial and inalienable critical capital does not refer to ownership. Control over critical capital rather involves the possibility of using or working with it. The stakeholder who is granted access does not acquire an additional residual right of decision; he can enhance his value by specializing, that is, by being a crucial "factor" in the production process of the firm. Access represents a power stake for the different stakeholders.

On the one hand, by giving access to his critical resource, the entrepreneur arbitrates his power. First, he improves market valorisation of the firm. The firm has a competitive advantage on its real and/or potential competitors. As a nexus of specific investments in human capital, it cannot be imitated instantaneously. Second, the entrepreneur enhances his power within the firm on the specialized employees. As he is the only agent to control the inalienable rights of control on his critical resource, the entrepreneur is the key element of the complementarity between human assets in the production process. Nevertheless, the entrepreneur looses some negotiation power by giving up a part of the control of the firm to stakeholders who are granted access to the critical resource.

On the other hand, stakeholders who are granted access control the nexus of critical resources so that they multiply their outside opportunities. First, specialization provides employees with a potential additional value: by accumulating knowledge and competencies within the firm they worked, employees improve the outside value of their human capital. Specialized employees systematically enhance their outside value because human capital is more "readjustable" than physical capital. For example, engines to paint cars cannot be transferred in a firm of the data-processing business service sector. Whereas, a computer scientist working within a business service firm can be employed in a company of the car industry, either in a similar position or for another job, without important losses of value. In fact, specialized human capital is adaptable. Yet, as human capital is non-reproducible instantaneously, it can be costly for specialized employees to value their human capital outside. There remain some costs of search for a new job, some costs relative to the supply of a weaker salary, or some costs of adaptation to the critical resource of the new firm that employs them (even if this firm has same characteristics as the previous one). In order to get back a high negotiation power within the new firm, employees must co-specialize to the members of the new production team. However, their investment efforts would be weaker thanks to the similar competences and capabilities and experience they have acquired in the first firm. Second, employees have also the residual right to leave the firm. By using and working with it, employees can control the critical resource of the entrepreneur. Control over the critical resource is de facto an economic source of power for central employees. This power generates in turn surplus that depends on the importance of firm-specific investments made. Thus, the regulation of access is a privileged means to promote specific investments. The regulation of access can be a more motivating mechanism and a superior mode of allocation of power than ownership in the particular case of the human capital-intensive firm.

Whereas ownership legally associates physical assets to a firm, complementarities join human assets within a team production. More precisely, by controlling access over his critical resource, the entrepreneur has the power to set and manage the collection of productive factors of which emerge synergies (ALCHIAN AND [START_REF] Alchian | Production, Information Costs, and Economic Organization[END_REF]. The human capitalintensive firm can be viewed as a team organization which supports productive specialization. Stakeholders federate their efforts and make their skills co-specialize in a team production.

Therefore, team work is essential in a firm considered as an authority of coordination. Indeed, via the regulation of access, synergies between employees arise from a team work where each stakeholder is decisive because of the specific investments he makes (BLAIR AND STOUT, 1999; RAJAN AND ZINGALES, 2001). Moreover, a critical resource is all the more crucial it is combined to the individual capabilities of other team members who are engaged in a particular task (BLAIR, 1995[START_REF] Blair | Firm-Specific Human Capital and Theories of the Firm[END_REF]. Control over critical resources depends on the recognition of this manifestation.

The organization of the human capital-intensive firm and the corresponding allocation of power highlight potential conflicts of interest between stakeholders. Power relationships have to be controlled through an organizational mode of governance adapted to the human capitalintensive firm.

The Governance of the Human Capital-Intensive Firm: Main Objectives and Main Tools of Coordination

Originally, corporate governance issues arise from the separation between ownership and control (BERLE AND [START_REF] Berle | The Modern Corporation and Private Property[END_REF]. In our framework4 , the separation between ownership and control is about time. First, ownership, i.e. the legal source of power, provides the entrepreneur with the right to determine access to the critical resource now and in the future. Indeed, as he owns the initial critical resource of the firm, he has some exclusive residual rights of control. The right to forbid some agents to use or work with resources is part of his rights of decision. Secondly, control only gives to the owner the right to determine current access. Then, control may temporarily enhance the economic power of the owner. Critical resources, that cannot be owned but only controlled, even for the time being, give the same residual rights of control as ownership does. Specialized workers are key agents who increase power by investing specifically in their human capital. Altogether, the structural organization of the firm and the internal division of labour are an expression of power relationships and found a model of governance of the human capitalintensive firm: the owner of the critical resource does not need that other stakeholders excessively develop their human capital because they wish organizational rents will be protected. In a symmetric way, stakeholders search for enriching their tasks and for making firm-specific investments. By specializing and by accumulating knowledge and competencies, stakeholders make themselves indispensable in the firm and enhance their outside value.

As the distinctive value of human capital-intensive firms comes from resources that cannot be easily appropriated, the boundaries of the firm are often altered. Stakeholders can leave the firm with their human capital; so they can leave the firm with a part of the firm. Specialized employees get a negotiation power through mutual dependencies they have created.

Negotiation power relies on the ability of stakeholders to make firm-specific investments: the more internal and external stakeholders specifically invest, the more rents to share within the coalition will be significant. Moreover, the accumulation of power in the hands of many stakeholders deteriorates their investment behavior. In this context, the risk of hold-up is high and the organizational structure of the firm can be changed. By ensuring them an equitable and attractive rent-sharing, the entrepreneur encourages the stakeholders to continue investing in the future. Because the possibility of renegotiation jeopardizes long-term commitments, growth prospects are crucial in making the promise of future rents credible. If growth prospects diminish, then key stakeholders may lose the incentives to specialize. These stakeholders may be encouraged to leave the firm, changing its organizational form. In other words, specialized stakeholders can expropriate a large fraction of the value of the firm by developing their outside opportunities5 . As power and rents are not concentrated but diffused, even outside the legal boundaries of the firm (as is the case for subcontractors essential for the firm), the main objective of corporate governance is to protect the integrity of the firm. In fact, the major corporate governance problem comes down to "how to prevent conflicts among stakeholders from paralyzing or even destroying the firm" [START_REF] Zingales | In Search of New Foundations[END_REF](ZINGALES [ , p. 1648]]).

Capital structure can be used to motivate the owners of critical resources to go on making firm-specific investments. Outside equities can lock-in relationships between stakeholders so that the firm can appropriate a fraction of rents generated and can protect its long-term viability. The solution consists in associating key stakeholders (employees, suppliers, customers, etc.) to the financial capital structure of the firm [START_REF] Hege | L'évaluation et le financement des start-up Internet[END_REF]. The role of these funds would be to preserve the firm as a nexus of specific investments, by making stakeholders' interests converge. This modality to govern within the firm would reduce potential sources of conflicts. Moreover, the generalized award of stock options to employees remains an important trend in corporate governance in order to compensate and thus in order to retain employees (HOLMSTROM AND [START_REF] Holmstrom | Corporate Governance and Merger Activity in the United States: Making Sense of the 1980s and 1990s[END_REF][START_REF] Oyer | Why Do Some Firms Give Stock Options to All Employees?: An Empirical Examination of Alternative Theories[END_REF]. While rights of control associated with ownership may have diminished, the role of ownership in coordinating stakeholders may have increased (RAJAN AND ZINGALES, 2000). Another privileged instrument of corporate governance could be a better board representation of decisive stakeholders (HILLMAN, KEIM AND LUCE, 2001). Finally, setting up a system of job rotation could reduce hold-up problems in the human capital-intensive firm [START_REF] Halonen-Akatwijuka | Organizational Design, Technology and the Boundaries of the Firm[END_REF]).

As we focus on the human capital-intensive firm, investigations have to study mechanisms which give to the firm the power to motivate, to control, and to retain specific human capital in order to maximize its value. In the Critical Resource Theory, power comes from the control of critical resources within the firm. In these circumstances, the main objective is to provide stakeholders with incentives to continue their relationship with the firm so that the firm can get wealth indispensable for its productive activity. Thus, the governance of the human capital-intensive firm is based on a particular representation of the acquisition, the allocation and the exercise of power. Stakeholders are not only viewed as agents with divergent interests. Stakeholders are also and above all considered as complementary critical resources that enhance the value of the firm and ensure its durability. At the same time, such a "disciplinary" system of corporate governance (to control and to incite) is necessary for competitive firms to capture growth opportunities.

As we admit that specific human capital is central in many firms, we have attempted to develop a revised survey of the nature and the governance of the human capital-intensive firm. This approach inspires a new perception of the relationship between vertical integration and disintegration. In fact, taking into account an enlarged coordinating role of the firm, we argue that integration and disintegration can be viewed as different ways for the firm to coordinate the specialization of agents.

Revisiting the Relationship between Integration and Disintegration

The vision we develop of the human capital-intensive organization highlights three characteristics of the coordinating role of the firm:

-The role of the firm is rather an organizational role than a legal one. The power of the firm does not depend on its legal structure. It relies on the active capacity of the firm to organize the division of labour. The role of the firm consists in managing a whole combination of complementarities between knowledge, skills and capabilities. Actually, the firm does not only aim to deal with traditional hold-up problems; -The central role of the firm is to organize productive activities. Coordination within the firm does not only suppose that a unique agent holds all the residual rights of control. The firm requires a set of coordinating instruments in order to handle the specialization of agents; -The firm can extend its coordinating role to agents who work outside its legal boundaries. These three features are crucial to understand the nature of the link between vertical integration and disintegration. First, vertical disintegration must be viewed as an organizational choice. Vertical disintegration does not stand for mere markets. When a firm collaborates with a legally independent agent, the two parties need, as for employees within the firm, to specialize their human capital; the two parties need to access to the critical resource. Consequently, access would constitute the privileged mode of the governance of the firm built around its specific human capital. We argue this is true both for human capital inside and outside the legal boundaries of the firm. Second, the relationship between integration and disintegration can be formally re-examined on the basis of economic coordination issues. In fact, the objective of pooling the efforts of complementary agents involves redefining the link between integration and disintegration. Assets specificity always causes an economic dependency between agents. Agents are valuable insofar as they are working together. Yet, a risk of strategic exploitation of the relationship can arise from this economic dependency. In the Incomplete Contracts Theory, the allocation of property rights neutralizes the negative effects of the economic dependency by introducing a legal dependency. Ownership makes agents subordinate to each other6 . Thus, the legal dependency or independency (which means integration or disintegration) represents the core of the coordinating role of productive activities. In the Incomplete Contracts Theory, integration and disintegration symbolize the two traditional poles of organizing economic activities. The focus on the human capital-intensive firm modifies the way to study the mutual and economic dependency between agents. The economic dependency cannot be solved by introducing a legal dependency because human capital cannot be legally appropriated in a privative way. That is why specialization, regulated by access to a critical resource, becomes the main coordinating tool. Besides, the issue of coordinating specialized stakeholders relates to agents inside and outside the firm. The coordinating role of the firm goes through its legal boundaries. The firm has to control relationships with its key employees, but also with its key suppliers, clients, subcontractors, etc. The firm coordinates the specialization of agents in the limits of its economic (or functional) boundaries. Therefore, integration and disintegration do not stand for hierarchy and market; integration and disintegration are two coordinating methods which differ as far as the governance of the specialization of agents is concerned.

They characterize two states of organizing production and coordinating the specialization of agents and resources by the firm (GIBBONS, BAKER AND [START_REF] Gibbons | Relational Contracts and the Theory of the Firm[END_REF]. Figure 1 illustrates this theoretical shifting in the way to explain the relationship between integration and disintegration. The firm is the superior institution to coordinate productive activities. Indeed, intra or inter-firms transactions are always coordinated by the firm. Contracts are not the only means to coordinate productive transactions. Coordination often occurs upstream the contracting scheme when the firm sets up the division of labour. Consequently, we do not describe the ownership of assets as an aim and a solution per se. Owning or not specific assets becomes integrated with a larger objective, the coordination of tasks which is materialized by a preliminary choice of division of labour.

Figure 1

Changing the link between integration and disintegration Third, as the coordinating role of the firm operates beyond its boundaries, it would be possible to exclude the notion of legal boundaries. We do not conclude to such an extreme interpretation. The permanent coordinating role of the firm, beyond its legal boundaries, does not exclude the question of the allocation of property rights. The allocation of property rights is not the final objective of the coordinating activity of the firm; it is rather an instrument to manage the specialization of agents. Actually, integration (i.e. the choice of an employment

Management of specialization

Unique coordinating mode

Source: Authors relationship) and disintegration (i.e. the choice of a cooperation relationship) do not develop the same instruments to deal with the specialization of agents. In this context, for example, RAJAN AND ZINGALES [2001] show that the hierarchical position is an essential tool in order to encourage employees to specialize. Nevertheless, this kind of incentive can only affect agents within the firm. Incentives methods based on wages can also be developed to motivate workers to make specific investments. When the firm needs somebody to specialize in a particular and temporary task, it will ask rather for an outsider. It is actually easier to have a cooperation relationship with an agent not legally linked with the firm. Reciprocally, an external stakeholder would not fear to invest in a "useless" capital in the mid-term. The legal status (integration or disintegration) does not represent the core of the problem of coordination; the legal status of the institutional forms rather assumes an instrumental weight.

The question of ownership only occurs in a second period, with regard to a first objective of productive specialization of agents. Consequently, integration and disintegration can be effectively distinguished on the basis of their respective capacity to regulate the specialization of agents. Lastly, such an original vision of the relationship between integration and disintegration opens up several research prospects. First, it is possible to find an analytical status to interfirms relationships. In the Transaction Costs Theory, inter-firms relationships only exist as hybrid forms (WILLIAMSON, 1985). In fact, the existence of inter-firms relationships is simply justified by the will to combine hierarchical devices and market mechanisms. Their existence is not properly justified. In our framework, the firm is viewed as a nexus of specific investments in human capital. Thus, inter-firms relationships are in keeping with the general need for firms to look for innovative and competitive skills non-reproducible instantaneously. When these skills result from a combination of human assets developed in another firm, interfirms relationships is the unique institutional mode of transaction. Second, we avoid analyzing historical movements of integration and disintegration as alternations between firm and market to coordinate industrial activities. We do not believe that a same productive activity follows, over time, fundamentally different logics of coordination. The link between integration and disintegration must be re-interpreted on the basis of the common objective of controlling the specialization of agents. Third, the notion of regulation of access gives new foundations to explain the current increase of inter-firms cooperations. We argue that interfirms cooperations stand out as an adapted way to govern the specialization of tasks in a context of the growing importance of human capital in the production process of firms. The role of firms is always to coordinate productive specialization despite institutional changes (from the big integrated firm to the network-firm). Fourth, the perimeter of the role of the firm cannot be modelled on the legal boundaries of the firm. Thus, the question of corporate activity must be thoroughly studied. As we focus on analyzing the firm built around its human capital, the ownership of assets does not delimitate the functional boundaries of the firm. Today, the boundaries of the firm are established in an organizational way by setting the limits of the activities coordinated by the firm. It is a question of better figuring out what the productive activity aims in order to precisely determine the group of agents that create value. The definition of the boundaries of the firm involves understanding the process of the specialization of tasks within the firm. Therefore, the traditional Incomplete Contracts Theory must be overcome so that one can re-examine the productive dimension of the firm, beyond incentives issues.

Conclusion

Our paper re-examined the link between vertical integration and disintegration. We found that the nature of this link is determined by the way we define the coordinating role of the firm. The Incomplete Contracts Theory presents vertical disintegration as the perfect counterfactual to vertical integration. In this perspective, the Incomplete Contracts Theory defines the firm as a combination of physical assets commonly owned. The firm is only understood as an answer to the hold-up problem. By studying the human capital-intensive firm, we show that the coordinating role of the firm needs to be reconsidered. The role of the firm is not limited to solve the problem of the expropriation of organizational rents. In order to capture growth opportunities, the firm has to control complementarities between agents who realize specific human capital investments. In this context, the Incomplete Contracts Theory must be extended towards two directions: developing new mechanisms ensuring incentives alignment and dealing with the division of productive tasks. Actually, the division of labour must be set as the foundation of the problem of ensuring incentives alignment. This active coordinating role of the firm transforms the perception of the relationship between integration and disintegration. We advance that the firm ensures the division of tasks beyond its legal boundaries. Thus, the division of tasks concerns all agents directly employed by the firm but also all its key specialized stakeholders. Consequently, we conclude that integration and disintegration must be viewed as two different modes for the firm to coordinate the specialization of human assets within its economic (or functional) boundaries. In other words, integration and disintegration must be differentiated by the tools they give to the firm so that it can effectively govern the productive specialization all over its economic boundaries.

During a same period, the thesis of massive adoption of a unique organizational form has been criticized by LAMOREAUX ET AL.[2003]. These authors explain that the modes of vertical organization do vary from firm to firm and from industry to industry.

The regulation of access includes not only access rights to the critical resource, but also the cooperation of the person being specialized to. Moreover, the regulation of access is not only a momentary action but a process that cannot be continuously verified by courts (RAJAN ANDZINGALES [1998, p. 403]).

The common (separate) ownership of assets is not viewed as the corollary of vertical integration (disintegration). Corollary, an employment relationship would correspond to integration and a cooperation relationship to disintegration. Analyzing the boundaries of the human capital-intensive firm involves considering the relevance of employment relationships vis-à-vis cooperation relationships with external stakeholders.

In this paper, we analyse the case of an entrepreneurial firm based on its human assets. Results would approximately be the same in a managerial enterprise built around its human assets except the fact ownership and control would be assumed by two kinds of agents, shareholders, on the one hand, and managers, on the other hand.

This hold-up manifestation is significant because 71% of the firms recorded in the Inc 500 list would have been founded by talented employees that have imitated or only changed a growth opportunity built by the firm employing them before[START_REF] Bhide | The Origin and the Evolution of New Businesses[END_REF].

Besides, the owner of physical assets can escape from the economic dependency.


Bernard Prévosto
email: bernard.prevosto@cemagref.fr

Yogan Monnier

Christian Ripert

Catherine Fernandez

Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development?

Keywords: Thinning, Seedling growth, Soil water content, Pinus halepensis, Winter deciduous oak, Evergreen oak

The use of shelterwoods to favour the development of natural or underplanted seedlings is common in temperate forests but rare in the pine forests of the Mediterranean area. Our aim was to assess the use of shelterwoods in Aleppo pine (Pinus halepensis) woodlands in southern France to promote the survival and growth of two co-occurring oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex.

Twelve Aleppo pine stands were selected and differentially thinned to create a light shelterwood (G = 32 m 2 /ha, irradiance 13%), a medium shelterwood (G = 19 m 2 /ha, irradiance 33%) and a dense shelterwood (G = 10 m 2 /ha, irradiance 52%). A total of 1248 sowing points, half composed of Q. pubescens and half of Q. ilex, were then set up in these three conditions. Seedling survival and growth were monitored for three years and plant stress was assessed by measuring predawn leaf potential and photosynthetic performance through the F v ⁄F m ratio. Soil moisture was also recorded at two depths during two growing seasons.

Survival was high for both species in all three conditions due to three consecutive wet years. The lowest survival was recorded for Q. pubescens in the dense shelterwoods. Growth in diameter and height increased from the dense to the light shelterwoods. Shrubs developed more strongly in the light shelterwood, and increasing shrub cover enhanced height growth. Photosynthetic performance was lowest for Q. pubescens in dense shelterwoods and highest in light shelterwoods, whereas the reverse was true for Q. ilex. The lowest predawn potentials were recorded in the dense shelterwoods even though higher soil water content values were measured in this treatment during the summer drought.

We show that light shelterwoods were more beneficial to growth than denser ones, indicating control by light availability during the three years of the study. However, as lower soil moisture and faster understorey development were also recorded in this condition, more extended observation is needed to determine whether this benefit persists in subsequent years.

Introduction

Aleppo pine (Pinus halepensis Mill.) is one of the major pine species in the Mediterranean basin due to its high colonizing capacity and remarkable adaptation to the environmental constraints of the Mediterranean area. However, its spread has also been largely promoted by human action. For instance, in the Iberian Peninsula 43% of the P. halepensis forest results from afforestation [START_REF] Vélez | Fire prevention in Aleppo pine forests[END_REF] and 80% of the plantations were initiated with this species in Israel [START_REF] Ginsberg | Restoring biodiversity to pine afforestations in Israel[END_REF]. In southern France, Aleppo pine has also largely developed in recent decades -its present cover is estimated at 250 000 ha -mainly by natural colonisation after the collapse of the traditional agricultural system in the 1950s.

Aleppo pine woodlands, either planted or naturally established, have long been considered as a favourable habitat to promote a natural transition towards vegetation dominated by broadleaved species. This assumption has mainly been supported by the intermediate successional status of Aleppo pine forests between shrub or herbaceous vegetations and late-successional hardwoods [START_REF] Barbéro | Pines of the Mediterranean Basin[END_REF][START_REF] Pausas | Pine and oaks in the restoration of Mediterranean landscapes of Spain: New perspectives for an old practice -a review[END_REF]). However, this supposed facilitating process is currently a subject of debate. In semi-arid Mediterranean areas, manipulative studies show a negative impact of P. halepensis cover on the late successional woody species [START_REF] Maestre | Does Pinus halepensis facilitate the establishment of shrubs under semi-arid climate? For[END_REF][START_REF] Bellot | Afforestation with Pinus halepensis reduces native shrub performance in a Mediterranean semiarid area[END_REF]. Similarly, [START_REF] Maestre | Are Pinus halepensis plantations useful as a restoration tool in semiarid Mediterranean areas? For[END_REF] in a review study emphasize the negative consequences of Aleppo pine forests on spontaneous vegetation, water use and soil losses. By contrast, in more humid conditions, observational data suggest a positive influence of Aleppo pine on latesuccessional broadleaved species [START_REF] Lookingbill | Spatial pattern of Quercus ilex and Quercus pubescens recruitment in Pinus halepensis dominated woodlands[END_REF][START_REF] Zavala | Constraints and trade-offs in Mediterranean plant communities: the case of Holm oak-Aleppo pine forests[END_REF]. In addition to climatic and other abiotic conditions, the structure of the pine overstorey in relation with understorey development also seems to play a role in the successful establishment of late-successional ligneous species. Assessing how pine plantations could successfully promote the recovery of the native vegetation along biotic and abiotic gradients in southern Spain, [START_REF] Gómez-Aparicio | Are pine plantations valid tools for restoring Mediterranean forests? An assessment along abiotic and biotic gradients[END_REF] showed the negative influence of dense, closed overstorey. By contrast, moderate densities were favourable to species recruitment, suggesting the existence of facilitative interactions.

Although the role of Aleppo pine stands on the successional ligneous vegetation is controversial, experience with Aleppo pine overstorey manipulations is particularly scant in the Mediterranean area. Typically, the shelterwood regeneration method is commonly used in temperate forests to favour the establishment and growth of late-successional tree species (e.g. [START_REF] Gemmel | Development of oak and beech seedlings planted under varying shelterwood densities and with different site preparation methods in southern Sweden[END_REF][START_REF] Agestam | The effects of shelterwood density and site preparation on natural regeneration of Fagus sylvatica in southern Sweden[END_REF]), but has seldom been tested in the Mediterranean conifer forests [START_REF] Rodríguez-Calcerrada | Ability to avoid water stress in seedlings of two oak species is lower in a dense understory than in a medium canopy gap[END_REF]. In the shelterwood treatment, the degree of openness of the overstorey is used to control light availability and so influence the growth of naturally established or underplanted broadleaf seedlings (Beaudet andMessier 1998, Coll et al., 2003). Changes in microclimatic conditions and in water regime are other direct consequences of the presence of shelterwoods [START_REF] Madsen | Natural regeneration of beech (Fagus sylvatica L.) with respect to canopy density, soil moisture and soil carbon content[END_REF]. Shelterwoods also control the development of the ground vegetation that can compete with tree seedlings for light, water and nutrients [START_REF] Nambiar | Competition for water and nutrients in forests[END_REF]Sands 1993, Davis et al. 1999) and can thus severely limit seedling development [START_REF] Löf | Establishment and growth in seedlings of Fagus sylvatica and Quercus robur: influence of interference from herbaceous vegetation[END_REF].

Our objective was to assess how successfully shelterwoods could be used in Aleppo pine forests to promote survival and growth of introduced seedlings. For this purpose we designed an experiment in which Aleppo pine stands underwent different degrees of thinning. Treatments effects were then assessed by analysing the changes in abiotic and biotic environmental factors and the performance of oak seedlings established in the different conditions obtained. We hypothesized that (i) dense shelterwoods would produce the conditions most detrimental to seedling survival and growth, (ii) lower seedling performance in dense shelterwoods would be linked to lower light and soil water availability and (iii) ground vegetation would benefit from pine canopy openness and thereby limit seedling growth.

Materials and methods

Study area

The experimental site was located in a protected natural area near the Étang de Berre, a coastal lagoon adjacent to the Mediterranean Sea west of the city of Marseille in southern France.

The landscape of this area is covered by Aleppo pine forests, shrublands (garrigues) and some residual agricultural areas. The mean annual temperature is 14.5 °C and the annual rainfall is 406 mm (computed over the period 1961-1996). We note that during the three years of the experiment, rainfall was largely higher than the mean, with respective values of 779, 697 and 662 mm in 2008, 2009 and 2010. The experiment was set up on a flat area (mean altitude 130 m). This area had previously been used as cropland and divided up into small fields bounded by stone walls, the remains of which were still visible. The current vegetation was dominated by Aleppo pine, which had become naturally established after land abandonment, forming closed stands 40 to 50 years old that had not been affected by wildfires at least during the past four decades. The dominant layer was composed of Aleppo pine, the evergreen holm oak (Quercus ilex L.) was present in the subcanopy layer, the shrub layer was dominated by Q. coccifera L., Q. ilex, Rosmarinus officinalis L., Phyllerea angustifolia L. and the herb layer was scant. Q. pubescens Wild. (a deciduous co-occurring oak) did not form woodlands close to the study area and only individual trees could be found. At a broader regional scale, Q. ilex was found preferentially in drier site conditions and poorer soils, but Q. pubescens and Q. ilex had overlapping ranges and coexisted in many habitats. Owing to the long history of anthropogenic disturbances in this area, it was not clear from the current distributions of the two oak species what the relative contributions of environmental factors and human actions were.

The soils had developed on a calcarenite bedrock composed of sandy limestone material and fossil shells. Alteration of this bedrock had led to calcareous soils, composed of a first organic layer 5-10 cm thick and a second sandy loam layer 20-40 cm thick.

Thinning experiment and acorn sowing

We selected 12 abandoned fields with a dense cover of pine on which we set up twelve 25 m × 25 m plots (one plot/field). We then applied one of the three thinning treatments to each plot in October 2007: (i) heavy thinning removing 2/3 of the basal area, to give light shelterwood (Light Shelterwood LS), (ii) moderate thinning removing 1/3 of the basal area (Medium Shelterwood MS) and (iii) no thinning (Dense Shelterwood DS). Plots were inventoried before and after the thinning by recording girth at breast height of all trees >1.30 m and thinning was practised from below.

Acorns from Q. ilex and Q. pubescens were collected in November 2007 using different sites and several trees per site for each oak species. Sites were located near the experimental stand and in comparable ecological site conditions. Non-viable acorns were eliminated by the floating method and visual screening. Acorns were sown at sowing points of three acorns. The three acorns were laid flat in a small hole (10 cm × 10 cm, 4 cm deeep), covered with 2 cm of soil, a wire mesh (same dimensions, 0.6 cm mesh size, to prevent predation by small rodents) and covered by a further 2 cm layer of soil. The wire mesh had been previously left for 24 h in an acid solution to favour its corrosion.

The sowing points were arrayed in each plot in 8 rows of 13 points each. They were spaced 1 m apart from each other on the row, alternating Q. ilex and Q. pubescens. The distance between rows was 2 m. A total of 104 sowing points of three acorns per plot were installed (half Q. ilex and half Q. pubescens) in late November 2007, forming a grand total of 1248 sowing points for the whole experiment. During spring 2008 we observed signs of predation by rodents on Q. pubescens seedlings only and a protection net (height 40 cm, mesh size 0.8 cm) was accordingly placed around all the Q. pubescens sowing points.

Environmental factors: light, soil moisture and soil temperature

In July 2008, light measurements were made on clear days using five solarimeter tubes per plot (300-3000 nm, Delta-T Device), leaving two tubes in full light conditions. The light transmittance was then computed by averaging the below/above ratios per plot and per treatment. Light quality was measured in nine plots (three plots per treatment) using a spectrometer (Spectro-Vio C5210-C5220, Korea Materials & Analysis Corp. K-MAC). Measurements were taken at five locations per plot. The red-far red ratio (R:FR) was computed as the ratio of photon irradiance at 660 nm to the photon irradiance at 730 nm. Following [START_REF] Aphalo | Effects of light quality on growth and N accumulation in birch seedlings[END_REF], transmission of light in the blue region was taken as the ratio of photon irradiance at 450 nm under the canopy to photon irradiance in full light conditions.

Soil water content (SWC) was measured at different time intervals during the 2009 and 2010 growing seasons using a TDR profile probe (PR2, Delta-T Devices) equipped with five electronic sensors arrayed at fixed intervals. The probe was inserted in an access tube driven into the soil, and we took the average of three readings at each location by rotating the probe through 120°. Nine plots distributed among the three thinning treatments were equipped with four access tubes per plot. Owing to soil stoniness, access tubes were installed at ranging depths. Thus for each tube the depth at which SWC was measured varied and soil water measurements were finally used for only the two soil depth classes 10-30 cm and 30-50 cm. Soil temperature was measured at three dates during summer 2009 by inserting a probe (Wet2, Delta-T Devices) in the upper soil layer (10 cm depth). At each date, six sampling points distributed along a transect were measured per plot, and three measurements were made per point.

Vegetation measurements

The emerged seedlings were counted in June 2008 and surviving seedlings were recorded and measured (height and stem base diameter) at the end of each year from 2008 to 2010. Some apparently dead seedlings, with no green leaves and brittle stems, were able to recover and resprout after the summer period, and were therefore counted as alive. The soil surface was characterized at the same time inside a 25 cm-radius hoop centred on the sowing point. Cover of bare soil, litter, grass species and shrub was estimated using an abundance dominance coefficient derived from the Braun-Blanquet method: 1 presence, 2 < 5%, 3 = [5-25%], 4 = [25-50%], 5 = [50-75%], 6 = [75-100%]. For subsequent computations, the midpoint of each class was used. Mean shrub height was measured during the last growing season using 15 points per plot distributed along five transects. Shrub cover was also visually estimated at plot scale.

Fluorescence and leaf water potentials

Measurements of fluorescence were made to estimate the photosynthetic performance of the plants in the different treatments. Measurements were made each month in 2009 from May to October in the morning (9:00-11:00). We used a portable fluorimeter (Pocket Pea, Hanstech Instruments) and leafclips to allow dark adaptation of the sampled leaf (minimum time 30 min). Ten Q. pubescens and ten Q. ilex seedlings were sampled in each plot (one measurement per seedling) and used for all the measurements. Maximal (F m ) and minimal (F 0 ) fluorescence were used to calculate maximum efficiency of the photosynthetic energy conversion of photosystem II (

F v ⁄F m = [F m -F 0 ] ⁄F m ).
To determine the water status of the seedlings during the summer period, predawn leaf water potential was measured on 16 July 2008 after a short period of dryness and on 15 September 2009 after a long period of dryness. A total of 16 seedlings per species and per treatment were sampled. Before sunrise (solar time 3:30-5:00), a leaf was cut from the oak seedling, placed in a plastic bag and transported in an icebox for immediate in-field measurement with a pressure chamber (PMS/1000, PMS Instrument).

Data analysis

Differences between treatments and species and the interaction between these two factors were analysed using two-way analyses of variance (ANOVA) followed by a Tukey post hoc test. Before ANOVAs, assumptions of normality and homoscedasticity were checked. Mathematical transformations of data were used when necessary to correct deviations from normality and heterogeneity of variances. When these conditions could not be met the nonparametric Kruskall-Wallis test was used (soil water content and seedling survival). For seedling survival, to detect which of the treatments differed significantly at a confidence level of 95%, we used the Nemenyi test [START_REF] Nemenyi | Distribution-free multiple comparisons[END_REF]. Statistical analyses were performed using Statgraphics Centurion XV (StatPoint Inc.) and R software (R development Core Team, 2005).

Results

Stand characteristics after thinning

The treatments deeply modified stand characteristics (Table 1). The heavy thinning (LS treatment) produced stands with an open tree layer cover providing a light transmittance of 52%. By contrast, light transmittance was reduced by about 20% in the MS treatment and by 40% in the unthinned stands (DS treatment) with respective light transmittance values of 33% and 13%. Light quality was also modified, as we noted decreasing R:FR and blue light ratios from the light to the dense shelterwoods.

In relation to these contrasting light availability values, the stands in the LS treatment exhibited a more developed shrub cover than those of the MS treatment, whereas shrub cover was sparse in the stands of the DS treatment. Shrub cover was mainly composed of Q. coccifera, which represented 47%, 61% and 77% of the total shrub cover in the LS, MS and DS treatments respectively, and secondarily by Q. ilex. Mean shrub height significantly increased from LS to DS. Litter cover, mainly pine needles, was highest in the DS treatment and lowest in the LS treatment, although differences were not significant. Herbaceous cover was nil in the stands before thinning and negligible three years after thinning.

Soil water content and soil temperature

Soil water content (SWC) followed the same general pattern during the growing season for the two years and the different treatments (Fig. 2). SWC peaked in spring and then decreased sharply with the drop in rainfall in late spring, reaching a minimum in late summer. It then rose again with the return of autumnal rain. However, SWC values in autumn remained lower than those recording in spring even after heavy rainfall such as in September 2009 (113 mm in two days). In the upper soil layer, SWC was lower in the DS treatment than in the other two treatments in spring and early summer, whereas in summer SWC tended to be lowest in the LS treatment and highest in the MS treatment, although differences were not significant. In the deeper soil layer, trends were more marked between the treatments in the summer period: SWC was lowest in the LS treatment and highest in the DS treatment, SWC in the MS treatment being close to the values of the DS treatment.

Soil temperature (Fig. 3) during the summer period was appreciably higher under the opened pine cover of the LS treatment than in the other two treatments. We found no differences between DS and MS during that period.

Oak seedling survival and growth

Three years after treatment application, seedling survival was higher for Q. ilex than for Q. pubescens in the DS (Kruskall-Wallis test, P < 0.001) and MS treatments (P < 0.001), but not in the LS treatment (P = 0.82). As shown in Fig. 1,Q. pubescens survival was appreciably lower under the dense shelterwood than under the two other shelterwood types. By contrast, differences in survival among the treatments were less marked for Q. ilex, although survival was higher in the medium shelterwood treatment at all dates. We did not find any effect of shrub cover on survival (data not shown), although growth was affected (see below).

Stem diameter and height significantly increased from the DS treatment to the LS treatment for both species (Fig. 4), and Q. pubescens growth was lower than Q. ilex growth in all three treatments. By contrast, the height-diameter ratio decreased from the DS to LS treatments, the Q. ilex seedlings being more slender (tall and thin) than the Q. pubescens seedlings in MS and LS (F = 22.02, P < 0.001 and F = 29.45, P < 0.001).

Concerning the influence of shrub cover on seedlings dimensions in the MS and LS treatments, we did not find any effect on stem diameter (P = 0.60 and P = 0.16 for Q. pubescens and P = 0.39 and P = 0.23 for Q. ilex). However, shrub cover influenced height in both species (Fig 5), seedlings being taller with increasing shrub cover. This effect was more marked in the LS treatment, where shrubs were more abundant.

Fluorescence and leaf water potential

Maximal photochemical efficiency of PSII (F v ⁄F m ) showed a decrease for both species during the summer period (Fig. 6). Nevertheless, the responses of the two oak species were remarkably different according to the treatment. For Q. pubescens, lowest values were recorded in the DS treatment, and similar values were recorded in the MS and LS treatments. Conversely, for Q. ilex, highest values were found in the DS treatment, and lowest values in the LS treatment, values in the MS treatment lying between these extremes.

Predawn leaf water potentials were lower in Q. pubescens than in Q. ilex for the two dates, but the difference was significant only in September 2009, when the seedlings experienced a major drought stress (ψ pd = -5.09 Mpa for Q. pubescens and ψ pd = -4.16 Mpa for Q. ilex in all treatments, P < 0.001). The lowest potentials were recorded in the DS treatments for both species and both dates (Fig. 7). Potentials in the MS treatment were significantly lower than those in the LS treatment in July 2008 only.

Discussion

Light and soil water availability

Not surprisingly, light availability was correlated with degree of thinning. This resource was primarily controlled by the upper pine cover, as the shrub layer was weakly developed at the beginning of the experiment and the shelterwood treatments had generated a light resource gradient. Along with light availability, light quality was modified, an alteration also noted by Gasque and Garcia-Fayos (2004) under Aleppo pine cover. Unexpectedly, soil water content was similar or slightly lower in the dense shelterwoods than in the two other shelterwood types in the upper layer only and before the summer period. By contrast, in the deeper layer, SWC was significantly higher during the summer period in the dense shelterwoods. This result is at variance with the finding of [START_REF] Bellot | Afforestation with Pinus halepensis reduces native shrub performance in a Mediterranean semiarid area[END_REF] who observed a negative effect of Aleppo pine on soil moisture in SE Spain, particularly in the 0-10 cm layer, an effect that increased with tree density. However, [START_REF] Maestre | Does Pinus halepensis facilitate the establishment of shrubs under semi-arid climate? For[END_REF] did not report any such negative effect in the 0-20cm soil layer between microsites located under Aleppo pine canopy and open areas without vegetation. [START_REF] Koechlin | Effects of pioneer trees on soil moisture content in Mediterranean old fields[END_REF] also found a negligible effect of Aleppo pine on the soil water balance in the 0-15 cm soil layer in southern France.

In this experiment, unlike the above studies, deeper layers were measurednd, which showed showed that that SWC in the upper layers did not necessarily reflect SWC of in the deeper layers. The moderate reduction of SWC in the 10--30 cm layer recorded before the drought period in the dense shelterwoods can be explained by rainfall interception by the closed pine canopy. However, during the drought period, the more pronounced decrease in soil moisture recorded in the light shelterwood treatment could be the result of: (i) a greater more soil evaporation due to a higher temperature, as recorded in this study, (ii) a greatertranspiration from the more abundant understorey and, (iii) a limited transpiration of the upper pine canopy due to stomatal closure, as Aleppo pine has been shown to reduce its transpiration sharply during drought periods [START_REF] Schiller | Water balance of Pinus halepensis Mill. Afforestation in an arid region[END_REF]. In a study comparing a thinned vs. an unthinned P. ponderosa stand in Arizona, [START_REF] Simonin | The influence of thinning on components of stand water balance in a ponderosa pine forest during and after extreme drought[END_REF] showed that the importance of the understory evapotranspiration was greater in thinned than in unthinned plots, and increased during extreme drought, when overstory transpiration was low. Similarly, [START_REF] Kurpius | Partitioning of water flux in a Sierra Nevada ponderosa pine plantation[END_REF] found that soil evaporation accounted for about 50% of the total stand evaporation during summer and autumn in a P. ponderosa plantation in California. In a semiarid Aleppo pine stand of in southern Israel, Raz-Yaseef et al (2010) reported soil evaporation fluxes in sun-exposed areas double those in shaded areas, and higher soil water content in the latter areas than in the former areas during the drying season. Differences in soil moisture between the light shelterwood treatment and the other treatments were greater in the deeper layer. This result might be due to preferential water uptake by the understorey at this depth, but further investigations is needed to confirm this hypothesis.

Oak seedling survival and growth

Oak survival after 3 years was shown to vary markedly for Q. pubescens only, survival being appreciably reduced under the dense shelterwood. This result is in line with the lower tolerance to shade of Q. pubescens compared with Q. ilex and with the higher physiological stress undergone by the seedlings of this species in such conditions (see below). In previous experiments conducted under a light pine cover in the same area and with the same species [START_REF] Prévosto | Diversification of Pinus halepensis by sowing Quercus ilex and Quercus pubescens acorns: testing the effects of different vegetation and soil treatments[END_REF], we reported a much lower survival rate of the seedlings one year after emergence, and Q. pubescens was more strongly affected than Q. ilex (survival of 16% and 53%, respectively). However, unlike the earlier study, the present experiment benefited from three consecutive 'wet' years, which explains, in part, this much higher survival. Regeneration dynamics of Mediterranean species have been shown to depend strongly on the recruitment peaks that occur in sporadic 'wet' years [START_REF] Gómez-Aparicio | Microhabitats shift rank in suitability for seedling establishment depending on habitat type and climate[END_REF][START_REF] Franklin | Shade avoidance[END_REF].

Supporting our initial assumption, growth in height and diameter for both species was enhanced by canopy openness, related to higher light availability. In the most shaded conditions of the dense shelterwoods, reduced light was the main factor limiting growth, although soil water content was comparable (in the upper soil layer) or even higher (in deeper soil layers) during the summer drought period. The observed pattern of growth increase with light is consistent with previous studies in the Mediterranean area (e.g. [START_REF] Sánchez-Gómez | Performance of seedlings of Mediterranean woody species under experimental gradients of irradiance and water availability: trade-offs and evidence for niche differentiation[END_REF][START_REF] Pérez-Ramos | Seedling growth and morphology of three oak species along field resource gradients and seed mass variation: a seedling age-dependent response[END_REF], although others found that intermediate light conditions were the most growth-enabling (e.g. [START_REF] Puerta-Piñero | Irradiance and oak seedling survival and growth in a heterogeneous environment[END_REF][START_REF] Quero | Relating leaf photosynthesis rate to whole plant growth: drought and shade effects on four seedlings of four Quercus species[END_REF]. These results also confirm the predominant successional status of Q. ilex after pine colonisation in this area, Q. ilex outperforming Q. pubescens in both survival and growth under all three stand conditions.

In shade conditions, seedlings of both species were slender (tall and thin) compared with seedlings growing in stronger light conditions, as shown by the decreasing values of the height-diameter ratio from dense to light shelterwoods. In the dense shelterwoods light is less abundant and its spectral quality is changed, with reduced values of red-far red and blue light ratios. These modifications lead to stimulation of plant elongation typical of shade avoidance [START_REF] Franklin | Shade avoidance[END_REF].

The influence of shrubs in oak tree species establishment has been seldom studied under afforested conditions. Here, shrubs had no effect on the survival of oak seedlings, whereas clear facilitative effects are usually found in open conditions due to reduction of water stress and direct radiation [START_REF] Castro | Benefits of using shrubs as nurse plants for reforestation in Mediterranean mountains: A 4-year study[END_REF][START_REF] Gómez-Aparicio | Differential light responses of Mediterranean tree saplings: linking ecophysiology with regeneration niche in four cooccurring species[END_REF][START_REF] Smit | Facilitation of Quercus ilex recruitment by shrubs in Mediterranean open woodlands[END_REF]. The role of the shrub layer in attenuating the extreme climatic conditions prevailing in open areas (e.g. high radiation, high or low temperatures) were probably weaker here, as this role was played primarily by the pine canopy. Shrub cover only enhanced height elongation, and this effect was more pronounced under the light shelterwoods. Shrubs, by physically preventing lateral expansion of the seedlings and by modifying light availability and quality, enhanced stem elongation, but left growth in diameter unchanged. We note that shrubs may also limit damage by rodents, as noted on Q. pubescens seedlings at the beginning of the experiment, but this protective effect was not investigated here, and deserves further work. 4.3 Plant stress: leaf potential and F v ⁄F m Plant stress was measured using leaf water potential and photoinhibition values as indicators. Lower leaf water potentials were found lower under the closed than under the more open pine canopies, in line with previous studies [START_REF] Rodríguez-Calcerrada | Summer field performance of Quercus petraea (Matt.) Liebl and Quercus pyrenaica Willd seedlings, planted in three sites with contrasting canopy cover[END_REF][START_REF] Franklin | Shade avoidance[END_REF][START_REF] Robson | Summer drought impedes beech seedling performance more in a sub-Mediterranean forest understory than in small gaps[END_REF], but at variance with the higher soil water content recorded in the closed shelterwoods during the summer period. The beneficial effects of wetter soil in such conditions did not therefore outweigh the negative effects of reduced light availability. The low light environment in the closed stands leads to carbon limitation and probably an enhanced biomass allocation to shoots rather than roots compared with a higher light environment (e.g. [START_REF] Mcconnaughay | Biomass allocation in plants: ontogeny or optimality? A test along resource gradients[END_REF]. Limited growth, probably unfavourable biomass allocation and stronger competition by pine roots [START_REF] Ricard | Do understory saplings respond to both light and below-ground competition? A field experiment in a north-eastern hardwood forest and a literature review[END_REF] could result in a lower capacity of seedling to face summer drought in dense pinewoods. In a previous experiment conducted in central Spain on Quercus seedlings planted below a dense P. sylvestris L. stand and a medium canopy gap, [START_REF] Rodríguez-Calcerrada | Ability to avoid water stress in seedlings of two oak species is lower in a dense understory than in a medium canopy gap[END_REF] found a higher degree of water stress (i.e. lower pre-dawn leaf water potentials) in the seedlings of the dense stand despite similar soil moisture contents in both sites. related to photoinhibition, i.e. reduction of the photosynthetic capacity [START_REF] Farquhar | Photosynthesis and gas exchange[END_REF]. For both oak species, F v ⁄F m values remained high (above 0.75), indicating a relatively mild photoinhibition, and showed a decrease during the summer season. This decrease was probably due to water stress, as the values increased again after the first major rainfall. Reduction of F v ⁄F m can result from different types of stress acting alone or combined, and previous studies have shown that water stress can enhance photoinhibition, although its effects are species-specific, year-and season-dependent and vary with the type of leaf monitored and the time of day (e.g. Prietro et al., 2009;[START_REF] Valladares | Interactions between water stress, sun-shade acclimatation, heat tolerance and photoinhibition in the sclerophyll Heteromeles arbutifolia[END_REF]. Photoinhibition in Q. ilex seedlings was highest in the light shelterwoods where light availability was highest and lowest in the other treatments. In Mediterranean environments, increasing light intensities usually overstretch the capacity for orderly energy dissipation by the photosynthetic system, resulting in enhanced photoinhibition [START_REF] Long | Photoinhibition of photosynthesis in nature?[END_REF]. However, this explanation does not hold for Q. pubescens, as photoinhibition was higher in the darker environment. This difference between the two oaks may arise because the Q. pubescens was subjected to more severe water stress in closed stands. [START_REF] Méthy | Drought and photosystem II activity in two Mediterranean oaks[END_REF], studying photochemical efficiency (F v ⁄F m ) of Q. ilex and Q. pubescens to drought showed that F v ⁄F m decreased sharply with predawn leaf water potential < 4 Mpa. Below potentials of -4 to -4.5 Mpa, Q. pubescens underwent more severe damage than Q. ilex, probably because of greater sensitivity to cavitation [START_REF] Damesin | Co-occurrence of trees with different leaf habit: a functional approach on Mediterranean oaks[END_REF][START_REF] Tyree | Summer and winter embolism in oak: impact on water relations[END_REF]. Higher water stress, in addition to lower tolerance to shade, could thus explain the contrasting behaviour of the deciduous Q. pubescens compared with the evergreen Q. ilex.

Conclusion

Our results suggest that the growth -and to a lesser extent the survival -of the two cooccurring Mediterranean oak species are mainly driven by light availability under shelterwoods. However, it would be too easy and too early to conclude that light shelterwoods Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology andManagement, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043 (i.e. heavily thinned stands) are to be preferred to denser ones in all situations. Our results show that light shelterwoods also lead to lower soil water content during the summer period and to enhanced growth of the ground vegetation. Seedlings were not impacted by such detrimental factors, i.e. less soil water availability and more competition by vegetation, but this finding is mitigated by at least two considerations. First, the positive effect on height growth of the shrub vegetation has to be considered in the light of the moderate development of the shrub vegetation three years after thinning. In subsequent years, shrub vegetation is likely to develop faster and so could affect seedling growth negatively. Also, in the presence of more competitive species such as grasses (e.g. Brachypodium retusum in our area), strong development of the ground vegetation under light shelterwoods could be more detrimental to the underplanted seedlings than recorded in this study (Prévosto et al., 2010). Second, the three years of this study were 'wet' years and therefore not representative of the general Mediterranean climate, in which 'dry' years are usually considered as major bottlenecks for the vegetation dynamics.

Observations over longer periods are thus needed to determine whether the beneficial effects on seedling development provided by light shelterwoods are lasting, or whether intermediate situations are to be preferred, as usually advocated in the literature [START_REF] Gómez-Aparicio | Are pine plantations valid tools for restoring Mediterranean forests? An assessment along abiotic and biotic gradients[END_REF][START_REF] Paquette | Survival and growth of under-planted trees: a meta-analysis across four biomes[END_REF].

Table 1 .

 1 Stand dimensions, light values and vegetation covers (mean value, SD in brackets) for the three treatments. Shrub height and cover values are given 3 years after treatment application. Letters indicate statistical differences between treatments (P < 0.05, Tukey test).

  Fig.2

  Fig.3

  Fig. 4

  Fig. 7

Time since emergence (month) Nb of seedlings/point

  Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? ForestEcology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043 Number of seedlings per sowing point (mean ± SE) against time since emergence (time 0 = June 2008). Open circles: Light Shelterwood, grey circles: Medium Shelterwood, black circles: Dense Shelterwood. Letters indicate statistical differences for the last date between treatments (P < 0.05, Nemenyi test). Soil temperatures measured at three dates in the three treatments. Letters indicate differences between treatments (Tukey test, P < 0.05). LS: light Shelterwood, MS: Medium Shelterwood, DS: Dense Shelterwood. Dimensions of the 3-year old oak seedlings for the three treatments (mean values + SE) A) seedling stem base diameter, B) seedling height, C) height / stem diameter ratio.Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043 Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043

	Figure captions Fig. 1
	2.8 Figure 1. Figure 2. Soil water content during years 2009 (April-October) and 2010 (May-November) Q. pubescens at two depths for the three treatments: Light Sheterwood (open circles), Medium Shelterwood (grey circles) and Dense Shelterwood (black circles). Rainfall values are indicated by vertical black bars. Arrows indicate significant differences between treatments for a given date (P < 0.05, Kruskal-Wallis test) 0 4 8 12 16 20 24 28 32 1.2 1.6 2.0 2.4 a a b Time since emergence (month) Nb of seedlings/point 0 4 8 12 16 20 24 28 32 1.2 1.6 2.0 2.4 a a,b b Figure 3. Figure 4. Figure 7. Leaf predawn potential at two dates for Q. pubescens (white bar) and Q. ilex (grey 2.8 Q. ilex
	bar) by treatment. LS: light Shelterwood, MS: Medium Shelterwood, DS: Dense Shelterwood.
	Letters indicate significant differences between treatments for a given species (P < 0.05,
	Tukey test)

White bars correspond to Q. pubescens and black bars to Q. ilex. Letters indicate significant differences (P < 0.05) between treatments for a given oak species (Tukey test). DS: dense shelterwood, MS: medium shelterwood, LS: light shelterwood Figure 5. Influence of shrub cover in classes on height for the Medium Shelterwood and Light Shelterwood treatments (mean ± SE). Black circles refer to Q. ilex and white circles to Q. pubescens. In each treatment, influence of shrub cover classes on height for a given species is indicated by P value.

Figure 6. F v ⁄F m ratio (mean ± SE) measured at different dates during summer and early autumn 2009 for A) Q. pubescens B) Q. ilex. Treatments: Light Shelterwood (open circles), Medium Shelterwood (grey circles) and Dense Shelterwood (black circles). Stars indicate statistical differences between treatments (Kruskal-Wallis test): P < 0.05 (*), P < 0.01 (**), P < 0.001 (***), NS: not significant.

  Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043

  Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043

C

  Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043 Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043

		Fig. 6
		0,84								0,84
	Fv/Fm Q. pubescens	0,76 0,78 0,8 0,82	***		*	*	**	**	Fv/Fm Q. ilex	0,76 0,78 0,8 0,82			*	*	*	**
		0,74								0,74
		16-Jun	6-Jul	26-Jul	15-Aug	4-Sep		24-Sep	14-Oct	16-Jun	6-Jul	26-Jul	15-Aug	4-Sep	24-Sep	14-Oct

NS

Prevosto B.,

  Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043

Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043

Acknowledgements

This study was supported by the French Ministry of Agriculture (MAP-DGPAAT) and the Fume European project (7 th Framework Programme). The authors are especially grateful to Aude Corbani, Gautier de Boisgelin, Roland Estève, Aminata N'Daye and Willy Martin for data collection. Prevosto B., Monnier Y., Ripert C. and Fernandez C. (2011) Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development? Forest Ecology and Management, 262, 1426-1433. author-produced version of the final draft post-refeering Original publication available at www.elsevier.com/locate/foreco -doi:10.1016/j.foreco.2011.06.043

MS treatment

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LS treatment

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