Vincent Zoma

Wendpanga Manassé Congo

Foundations of the regional integration of the West African economic and monetary union (WAEMU)

Keywords: regional integration, West Africa, WAEMU

After the independences, most of the countries of Africa in general and West Africa specially opted to unite within the framework of regional integration. It is in this context that the West African Economic and Monetary Union (WAEMU) was created in 1994. Moreover, beyond the African continent or even on this continent, there is a variable geometry in the process of regional integration of setting up. Thus, the present article, based on a documentary research aims to surround the foundations or the main logics which favored the creation of the WAEMU which wants to be a space of regional integration. Overall, it emerges from this investigation that the establishment of this regional integration institution is based on historical, political and economic foundations linked to endogenous factors in the region and exogenous factors related to the influence of the former colonial power and especially global economic challenges.

Introduction

After the independences, it appeared that the "balkanization" of Africa in general and of West Africa particularly constituted a factor of vulnerability. This not only limited the possibilities of internal economic growth, but also reduced the weight of Africa in world trade (H. Dicko, 2005) [START_REF] Dicko | The Common Market of the West African Economic and Monetary Union: Realities and Prospects[END_REF] . Indeed, the partition of Africa is the result of the meeting held in Berlin from November 15, 1884 to February 26, 1885 by the United States and the States of Europe, at the end of which a act consecrating the fragmentation or division of the African continent between the colonial powers has been signed (S. Diouf, 2005) [START_REF] Diouf | Legal integration in Africa: The example of UEMOA and OHADA[END_REF] . It's in this context that M. Ropivia (1994) [START_REF] Ropivia | Geopolitics of integration in Black Africa[END_REF] explains that balkanized African states can only visibly flourish in a context of self-centered economic development if they unite by integrating geographically. Still in this same sense, A. Diouf (2006) [START_REF] Diouf | Africa: regional integration in the face of globalization[END_REF] precise that willy-nilly, Africa must live, like the whole of our planet, at the time of what is called globalization. In other words, M. Ghadhi (2009, p.18) asserts that "obviously, the more time passed, the more the elites in power realized that individually considered, no State could on its own get out of the lasting crisis in which everyone was struggling. The need for unity was felt". Thus, in view of the multiple challenges of development in the context of globalization, most African States and those of West Africa have opted to unite in the process of regional integration defined within the framework of this study as "the process by which States unite, by conceding part of their sovereignty to a supranational body having the competence to exercise its policy in a well-determined space on the basis of a consensus in order to achieve predefined objectives" (V. Zoma, 2015, p. 16) [START_REF] Zoma | Regional integration and land use planning: the case of WAEMU. Master's thesis in geography[END_REF] . Concerning West Africa specifically, P. Kippré (2006, p.39) [START_REF] Kippré | Regional integration and rural development in West Africa[END_REF] recalls that "regional integration is part of the movement of ideas that Pan-Africanism has aroused in West Africa since its origins and throughout the twentieth century". It's in this context that alongside the Economic Community of West African States (ECOWAS) created in 1975, more recently, the States of West Africa proceeded to the creation of the West African Economic and Monetary Union (WAEMU) in 1994. Furthermore, N. Mareï and Y. Richard (2018) [START_REF] Mareï | Dictionary of the regionalization of the world[END_REF] points out that there is a variable geometry in the process of implementing regional integration around the world. According to these authors, "regional integration is a perennial, multifaceted and spatially dynamic phenomenon" (N. Mareï and Y. Richard, 2018, p.24) [START_REF] Mareï | Dictionary of the regionalization of the world[END_REF] . This article, based on documentary research, aims to identify the main foundations of regional integration within the WAEMU space. It emerges from this investigation that West African regional integration led by WAEMU is based on historical, political and economic foundations.

Historical foundations or the advent of WAEMU

According to M. Ballogoun (2000) [START_REF] Ballogoun | WAEMU customs union: short-term impact on Benin's foreign trade[END_REF] , before 1994, economic integration and monetary integration between the countries that make up the current WAEMU were governed by two separate agreements. These are the treaty of the West African Monetary Union (WAMU) adopted in 1962 and that of the Economic Community of West Africa adopted in 1975. These documents were intended, for the first, to to achieve monetary integration and the second to promote trade and sectoral cooperation between member countries. These treaties had not made it possible to achieve the objectives set. Thus, in March 1990, the countries of the Union asked the Governor of the Central Bank of West African States (CBWAS) to submit to them an economic integration plan. This need to consolidate WAMU was felt strongly following the economic and financial crisis that member countries were facing at the end of the 1980s. In this context, M. Ballogoun (2000, op.cit.) [START_REF] Ballogoun | WAEMU customs union: short-term impact on Benin's foreign trade[END_REF] adds that since June 1991 under the instigation of France with the support of the European Union, the project of the creation of WAEMU has materialized on January 10, 1994 in Dakar, Senegal on the eve of the devaluation of the currency of the Franc of the French Community of Africa (FCFA), thus succeeding the WAMU created in 1962. Its constitutive act entered into force on the August 1st of the same year after ratification by its seven member states. Thus, the treaty establishing the WAEMU was born on January 10, 1994 in Dakar two days before the devaluation of the FCFA (F. Cissé, 2008) [START_REF] Cissé | Economic integration in West Africa: from independence to interdependence[END_REF] . It was signed by their Excellencies, Nicéphore Dieudonné Soglo (President of the Republic of Benin), Blaise Compaoré (President of Burkina Faso), Daniel Kablan Duncan (Prime Minister of Ivory Coast), Alpha Omar Konaré (President of the Republic of Mali), Ousmane Mahamané (President of the Republic of Niger), Abdou Diouf (President of the Republic of Senegal), and Joseph Kokou Koffigoh (Prime Minister of the Togolese Republic). The WAEMU created, was to "ensure in the future a stronger coherence between the monetary policy of the Union and the budgetary and economic policies of its Member States" (WAEMU, 2010, p.5). Its "devices relate to the rules for issuing money, the centralization of foreign exchange reserves as well as the free circulation of monetary signs" (Cissé F., 2008, p.16, op.cit) [START_REF] Cissé | Economic integration in West Africa: from independence to interdependence[END_REF] . WAEMU has its headquarters in Ouagadougou in Burkina Faso and has as its main objective the construction of a harmonized and integrated economic space, within which is ensured total freedom of movement of persons, capital, goods, services and factors of production, as well as the effective enjoyment of the right of exercise and establishment for the liberal professions, of residence for citizens throughout the Community territory. It is an institution whose mission is to achieve the economic integration of the Member States, through the strengthening of the competitiveness of economic activities within the framework of an open and competitive market and a rationalized legal environment. and harmonized (WAEMU, 2022) [START_REF] Sekongo | WAEMU facing the challenges of sub-regional integration[END_REF] . Eight coastal and Sahelian States, including seven French-speaking and one Portuguese-speaking, linked by the use of a common currency, the FCFA (linked to the euro by a fixed parity) and benefiting from common cultural traditions, currently make up the Union. Map 1 identifies the member states of the current WAEMU.

Map 1: WAEMU Member States

Map 1 shows the WAEMU member states. The Union is made up of eight countries (Benin, Burkina Faso, Côte d'Ivoire, Mali, Niger, Senegal, Togo and Guinea-Bissau) which covers an area of 3,506,126 km2 and has 123.6 million inhabitants (WAEMU, 2022). WAEMU is part of a larger whole in West Africa which is the Economic Community of West African States (map n°2).

Map 2: WAEMU and ECOWAS member countries

As shown in Map 2, of the 15 ECOWAS countries, 8 belong only to WAEMU. The Union of these 8 countries is represented by a logo symbolizing growth, union, solidarity and complementarity between the coastal States and the Sahelian States (Figure 1). This logo represents two and elliptical shapes which, despite their specificities, intertwine to express two strong notions: the solidarity and complementarity of the States and peoples of the Union. This solidarity and this complementarity are ready to be released in a movement of continuous ascent which will lead to the economic, social and cultural development of our respective populations. The energy of the lianas of the forest harmonizes with the warm and vivacious vibrations of the Sahel to produce the sphere of happiness illustrating the characteristics and objectives of WAEMU. Natural resources and material (lower 1/2 blue sphere), intellectual resources (1/2 gold sphere). The white circle expresses the peace, serenity and stability that must remain the anchor points of the Union's integration process (WAEMU, 2022). The construction of this Union undoubtedly has political foundations.

Source: WAEMU,2022

Political foundations of WAEMU

In general, the integration of Africa has always been one of the objectives for many African leaders such as George Patmore, William Edward Burghardt Dubois or Marcus Garvey, etc., as well as for pan-Africanists such as Kwame Nkrumah who, in his book Africa Must Unite, already advocated African unity (V. Zoma, 2019) [START_REF] Zoma | Transport and regional integration in the WAEMU area, road transit of goods from Mali and Niger via Burkina Faso[END_REF] . Regarding West Africa, as it has already been mentioned, "regional integration is part of the movement of ideas that pan-Africanism has aroused in West Africa since its origins and throughout the 20th century" (P. Kippré, 2006, p.39, op.cit) [START_REF] Kippré | Regional integration and rural development in West Africa[END_REF] . Indeed, the day after their accession to national sovereignty, West African countries opted for the establishment of a set of mechanisms allowing them to remove the barriers established by the colonial powers in their space and to strengthen their solidarity. Thus, was born on May 12, 1962, the West African Monetary Union (WAMU). It is an organization whose arrangements relate to the rules for issuing money, the centralization of foreign exchange reserves and the free circulation of monetary signs. On May 21, 1970, the West African Economic Community (WAEC) was created. Its aim was to achieve economic integration in West Africa. Subsequently, on May 28, 1975, the Economic Community of West African States (ECOWAS) was created with the main objective of promoting cooperation and integration in order to create an economic and monetary union for all West African countries without exception. This institution provided for the establishment of a single West African currency by 2020. However, the idea of integration has not always appealed to all West African political leaders in the same way. There was often a lack of solidarity between them. For example, the inequalities between certain States in the region were visible after their accession to independence. Ivory Coast and Senegal seemed to be the wealthiest in the region. To resolve these differences, the heads of state embarked on a pan-Africanist or federalist policy. But Presidents Félix Houphouët Boigny [START_REF] Buabua | The integration of African States within the African Union: study of its effectiveness with regard to the European practice of integration[END_REF] and Léopold Sédar Senghor [START_REF] Cissé | Economic integration in West Africa: from independence to interdependence[END_REF] did not approve of this initiative because their countries risked becoming the source of supply for other countries. It is in this perspective that the WAEMU report (2017) reveals that for thirty-two years, there has been convergence between three forces to block the process of integration between the countries of the old French West Africa (FWA). The first was the policy of France, which preferred to deal with small separate states, rather than with a coherent whole. This is not surprising; it is the logic of the "Defferre Law" which continued. With independence proclaimed, it was necessary to set up a management tool for the single currency, which was the CFA franc, created in 1945 as the Franc of the "French Colonies of Africa" and the issuing institute was set up place in 1955. From 1958, the acronym CFA means "French Community of Africa". Since 1962, the CFA franc has been managed by the Central Bank of West African States (CBWAS) and is the currency of the West African Monetary Union (WAMU). CBWAS headquarters were in Paris until 1978 and then in Dakar. WAMU did not include Guinea Bissau and Mali, which only joined in 1984. It is important to note that maintaining the headquarters of this institution in Paris for sixteen years illustrates the strong dependence of the system on the Bank of France (V. Zoma, 2019, op.cit) [START_REF] Zoma | Transport and regional integration in the WAEMU area, road transit of goods from Mali and Niger via Burkina Faso[END_REF] . Still according to the WAEMU report (2017, op.cit), the second force would be the policy of Ivory Coast, which exactly coincided with that of France. Félix Houphouët-Boigny showed great consistency and consistency in his ideas. Considering that Ivory Coast alone represents 80% of the area's investment capacity, he absolutely wanted to avoid any system that could lead to the idea of sharing. He wanted to confine the Union to the strict monetary domain and to maintain the parity of the CFA franc at 50 cents for one franc. The third was not a strength but rather a sum of weaknesses because between 1962 and 1994, the States of the zone experienced about ten putchs and multiple political crises which monopolized the attention of those responsible for the problems interiors. Basically, it suited many people to let France solve the economic and monetary problems. In this context, Félix Houphouët-Boigny occupies the central place and he will block any reform during his lifetime. The Ivorian president died on December 7, 1993 and WAEMU was established on January 10, 1994 with headquarters in Ouagadougou (V. Zoma, 2019, op.cit) [START_REF] Zoma | Transport and regional integration in the WAEMU area, road transit of goods from Mali and Niger via Burkina Faso[END_REF] . Overall, West African sub-regional integration is above all a political issue in the sense that the various integration policies emanate from the will of the Heads of State. This is why the division of competences between the Union and the States requires clarification (WAEMU, 2018). The competences of the WAEMU are defined in such general terms that it can take care of everything or nothing. The only clearly Community areas are those of currency and foreign trade. For everything else, this structure is supposed to define and implement policies in the most varied fields but without ever defining a field specific to the action of this integration institution (WAEMU, 2018, op.cit.). Along the same lines, D. Buabua (2007) notes that integration is the merging of certain state powers into a supra-state or supra-national body. It can be seen as the function of a supra-state structure which aims to gradually unify mechanisms appropriate to the economy, or even the political system of the Member States. The founding treaty laid down the guidelines for integration into WAEMU. Indeed, it created within this organization a kind of transfer of competence in the sense that it grants to the institutional bodies of this institution the means of their missions. The Member States have thus "abandoned" in theory their sovereignty for the benefit of this organization, they have today built a field of affinity of common interest which constitutes their integrated space. But this community is not a federal state, because it is made up of independent states united voluntarily, built from bottom top in full respect of the decision-making power of the different parties united in the supreme power, always exercised in common. The transfer of competence has resulted in the existence of bodies, mechanisms and legal powers that are superimposed on national systems. In other words, the WAEMU treaty stipulates that the Conference of Heads of State and Government defines the main policy orientations of this structure and adopts, whenever the need arises, acts whose respect is imposes on all the bodies as well as on the authorities of the Member States. In accordance with the provisions of the treaty, it appears that the States agree to transfer to the Union all regulatory power in the areas where the treaty and the acts intervene (A. Sekongo, 2013). The WAEMU Commission is responsible for implementing the decisions taken by the Conference of Heads of State. And, since the creation of this organization, this Commission has been led by five (06) presidents who are respectively, Ousmane Seck from Senegal (1995-1996), Moussa Touré from Senegal (1996-2004), Soumaïla Cissé from Mali (2004 -2011), Cheikhe Hadjibou Soumaré from Senegal (2011-2017), Abdallah Boureima from Niger (2017-2021) and since May 2021 the Senegalese Abdoulaye Diop. The WAMU was not a sub-regional institution which accentuated its efforts on the monetary aspect. But since its "rebirth" in 1994 under the name WAEMU or West African Economic and Monetary Union, it deals with economic issues in order to help its Member States to face the challenges of globalization.

Economic foundations of WAEMU

The global economic context has been marked for decades by the tendency of countries to integrate into the global economy through the creation or the strengthening of regional groupings. This strategy explains the realization of projects to create structures such as the West African Economic and Monetary Union. According to J. Igué (1995), regional integration responds to the need to be able to amortize territorial facilities by offering them new market opportunities. This problem has reappeared on a triple constraint. These are the heavy indebtedness of the Member States of the region, the generalization of the Structural Adjustment Program (SAP) and the devaluation of currencies as a consequence of the adoption of the SAP. In addition to these three constraints there is the need to change the socio-economic environment marked by autocratic powers and catastrophic economic management in an atmosphere of low productive capacities. To overcome these difficulties, the political authorities of the countries believe that only the creation of a larger regional economic space can provide good answers. For example, the devaluation of the FCFA which took place on January 11, 1994 was accompanied by the creation of a form of regional integration, the WAEMU, which is grafted on to already existing experiences (V. Zoma, 2019, op.cit) [START_REF] Zoma | Transport and regional integration in the WAEMU area, road transit of goods from Mali and Niger via Burkina Faso[END_REF] . This is the reason why the treaty establishing WAEMU, signed in Dakar on January 10, 1994, should not only provide the common currency (the CFA Franc) with the real foundation that determines its consolidation and sustainability, but also to accelerate the process of regional integration. This is a strategy that will enable the economies of the Member States to meet the challenges of contemporary economic changes, namely globalization and international competitiveness (M. Ballogoun, 2000, op.cit) [START_REF] Ballogoun | WAEMU customs union: short-term impact on Benin's foreign trade[END_REF] . This vision (of the creation of WAEMU) was born in the 1990s from the need for greater harmonization of economic policies (R. Lavergne, 1996), from the collapse in the prices of raw materials which are important sources export earnings (WAEMU, 2010, op.cit). One of the factors underlying this vision is the real appreciation of the CFA franc, under the combined effect of the rise of the French franc and the downward adjustment of the exchange rates of neighboring countries outside the Franc Zone. These previously mentioned factors caused the rapid deterioration of the main macroeconomic and financial indicators, plunging the Union into a deep crisis. For these reasons, as early as 1990, WAMU member countries expressed their desire to go beyond monetary union by integrating the Economic Union. It was obvious that monetary regulation mechanisms had to be complemented by economic reforms to ensure the cohesion of the Union and lay the foundations for sustainable growth. To this end, the member states of WAEMU have come together with the aim of promoting their economic and social development, through the harmonization of their legislation, the unification of their internal markets and the implementation of policies common sectors in the essential sectors of their economies (WAEMU, 2010 op.cit). The process of economic integration then takes place in six stages, as M. Ballogoun points out (2000, op.cit) [START_REF] Ballogoun | WAEMU customs union: short-term impact on Benin's foreign trade[END_REF] . Firstly, it takes into account the preferential customs area, which is an area within which customs duties on trade between member countries are lowered to a level significantly lower than those applied to trade with third countries. The second is the free trade area. Its main characteristic is the total abolition of customs duties between member countries, which nevertheless remain in control of their customs policy with regard to third countries. Then there is the customs union, which is a free trade area reinforced by the adoption by the members of a Common External Tariff. There is also the common market, which is a space within which there is complete freedom of movement of goods and factors of production. This implies a certain harmonization of economic policies, with a view to preventing distortions prejudicial to the full exercise of competition. It follows the economic union which is the most advanced stage of economic integration in the strict sense which supposes a thorough harmonization even the standardization of the economic policies of the member countries, in addition to the institution of the common market. These stages end with the establishment of economic and monetary union, which represents the most complete form of economic integration, adding to the achievements of economic union the advantages of a currency and a monetary policy unique. WAEMU in its treaty enshrines this completed degree of integration in West Africa. These steps are intended to facilitate the free movement of people and goods within the community area. About this free movement of people and goods in this area, H. Kane (2010) quotes Mr. Soumaïla Cissé, former president of the Union Commission in these terms: "the free movement of people and goods is the key to integration. Heads of state are aware of this. For successful integration, people will have to feel free to move around" (H. Kane, 2010, p.3). The principle of the free movement of persons and goods brings together several other principles which all aim to boost the economy of the WAEMU space. To this end, the free movement of persons, according to the provisions of the Treaty, means that any national of this Community area has the right to move freely from one Member State to another without any hindrance. It includes the right of residence, the right of establishment, and the freedom to provide services. The principle of the free movement of goods is one of the pillars of the realization of the common market (H. Kane, 2010, op.cit). It implies the free movement of goods as well as the free movement of capital within the community area.

Conclusion

This study on the process of regional integration within the West African Economic and Monetary Union (created in 1994), shows that regional integration in this area is essentially based in the same time on historical, political and economic foundations. Historically, the current WAEMU was essentially built on the former colonial space which is French West Africa (FWA) following several attempts at general regrouping such as the West African Monetary Union (WAMU). ) in 1962, the West Africa Economic Community (WAEC) in 1970, and more recently the Economic Community of West African States (ECOWAS) in 1975 which is still also a regional integration space in West Africa. The attempts or the will to move towards regional integration in Africa is the result of a combination of political factors linked, among other things, to the declared will of certain political leaders in the region, such as Kwame Nkrumah, whose will to go to Integration has been recognized on the African continent. But this desire will come up against or be slowed down by other leaders in the region such as the Ivorian and Senegalese presidents of the time (Félix Houphouët Boigny and Léopold Sédar Senghor) who did not share the same vision of the way or the form as the integration should take. This obstacle accompanied by the influence of the former colonial power of most member countries of the current WAEMU will undoubtedly slow down or even influence the process of establishing regional integration in this part of the world. However, the economic challenges and the weaknesses of the new independent States in terms of governance will lead to the establishment of WAEMU, especially in the context of the devaluation of the currency of these countries (the FCFA) and especially with the death of the first president of the Ivory Coast.

Fig 1 :

 1 Fig 1: WAEMU logo


Yohan Pillon

Time and tempo of diversification in the flora of New Caledonia

Keywords: Biodiversity hotspots, island biogeography, Pacific, palms, serpentine, speciation rate, ultramafic soils

New Caledonia is well-known for its rich and unique flora. Many studies have focused on the biogeographic origins of New Caledonian plants, but rates of speciation on the island have scarcely been investigated at all. Here we use dated phylogenies from selected published studies to evaluate the time and tempo of diversification in New Caledonia. The 12 plant lineages investigated all seem to have colonised the island less than 37 My ago, when New Caledonia re-emerged after a period of inundation. The timing of these arrivals is spread across the second half of the Cenozoic. Speciation rates are not particularly high and are negatively correlated with lineage age. The palms have the fastest speciation rates and also the most recent arrival times. The lineage ages of rainforest plants suggest that this ecosystem has been present for at least 6.9 My. The New Caledonian flora seems to represent a relatively old community which may have reached a dynamic equilibrium. Colonisation by new immigrants has been possible until relatively recently and diversity-dependent processes may still be affecting the diversification rates of the earlier colonisers. Further studies on the diversification of large plant clades with exhaustive sampling should help to clarify this.

INTRODUCTION

New Caledonia is an archipelago in the south-west Pacific, well-known for its rich and distinctive flora. It is considered as one of the major biodiversity hotspots of the planet [START_REF] Myers | Biodiversity hotspots for conservation priorities[END_REF] and has attracted major interest in biogeographical studies. The genus Nothofagus Blume (Nothofagaceae) exemplifies well the different phases of progress in phylogeographical studies, based first on cladograms built up from morphological data [START_REF] Hill | The evolutionary history of Nothofagus (Nothofagaceae)[END_REF], then on molecular data [START_REF] Manos | Systematic of Nothofagus (Nothofagaceae) based on rDNA spacer sequences (ITS): taxonomic congruence with morphology and plastid sequence[END_REF] and most recently using molecular clocks (Cook & Crisp, 2005).

New Caledonia is a continental island that drifted away from Australia in the late Mesozoic (ca. 80 My ago) and has been isolated since then (Pelletier, 2006). The island was then submerged under deep sea during the first half of the Cenozoic as shown by the deposit of Paleocene-lower Eocene pelagic limestone [START_REF] Paris | Geology of the New Caledonia region and its implications for the study of the New Caledonian biodiversity[END_REF][START_REF] Picard | L'archipel néo-calédonien, 300 millions d'années pour assembler les pièces d'un puzzle géologique[END_REF]Pelletier, 2006). Reemersion of the island occurred about 37 My ago [START_REF] Cluzel | Upper Eocene unconformity and pre-obduction events in New Caledonia[END_REF] when the island was uplift and the ophiolitic nappe overthrust that is the origin of the ultramafic soils. These soils, including serpentine in the strict sense, have several characteristics that are limiting to plant/ low fertility (low N, P, K); high Mg/Ca ration, high concentration of heavy metals (Co, Cr, Ni, etc.), low water-holding capacity and increased susceptibility to fire [START_REF] Proctor | Vegetation and soil and plant chemistry on ultramafic rocks in the tropical Far East[END_REF].

Although evidence for immersion of the island have been available for a long time, most biologist have favoured until recently the hypothesis of the persistence of the New Caledonian biota since its separation from Australia and throughout the Cenozoic. This conviction is increasingly challenged as biologists begin to take into account evidence from geological studies (some of which were published some time ago), that indicate that New Caledonia was submerged from the end of the Cretaceous to the mid-Cenozoic and emerged only ca. 37 My ago. The presence of nearby islands during the early Cenozoic that could have served as refugie cannot be excluded although evidence are lacking (Pelletier, 2006). The debate is still running on the vicariant [START_REF] Ladiges | New Caledonia-Australia connections: biogeographic patterns and geology[END_REF] or entirely long-distance dispersal [START_REF] Grandcolas | New Caledonia: a very old Darwinian island?[END_REF] origins of the New Caledonian biota, but the latter concept is gaining increased support. Indeed, as more molecular clock analyses are becoming available, no study has provided firm evidence for a colonisation of any terrestrial organism prior to 37 My (reviewed in [START_REF] Grandcolas | New Caledonia: a very old Darwinian island?[END_REF][START_REF] Cruaud | Testing the emergence of New Caledonia: fig wasp mutualism as a case study and a review of evidence[END_REF]. It seems likely that biologists have been mislead by the abundance of "early branching" plant lineages in New Caledonia and the erroneous assumption that they persist in their ancestral area (Crisp & Cook, 2005;[START_REF] Crisp | Hypothesis testing in biogeography[END_REF]. A large number of plant lineages present in New Caledonia and once thought to be "archaic" (Winteraceae, Monimiaceae, Atherospermataceae, etc.) belongs to the Magnolianae and more specifically Laurales. These clades have been shown to be over-represented in New Caledonia, possibly because of an exaptation ("pre-adaptation") to ultramafic soils [START_REF] Pillon | Ultramafic soils and species sorting in the flora of New Caledonia[END_REF]. Therefore their abundance may be better explained by ecological factors rather than biogeography, and the same may also be true for Conifers, which are exceptionally diverse on the island [START_REF] De Laubenfels | Gondwanan conifers on the Pacific Rim[END_REF].

Whether we consider the New Caledonia biota to date back to the split from Australia in the Cretaceous or to its re-emergence in the mid-Cenozoic, it is not known if the vegetation has been the same throughout. Furthermore, although the island has been inhabited by plants for a long time, it can still be a land of immigration, as dispersal over long distances can also occur within a continent [START_REF] Galley | The Cape element in the Afrotemperate flora: from Cape to Cairo?[END_REF][START_REF] Gehrke | The scramble for Africa: pan-temperate elements on the African high-mountain[END_REF]. For example, although Africa has been geologically stable for a long time, it is widely accepted that the Cape flora is relatively recent and probably developed after the establishment of a Mediterranean climate [START_REF] Richardson | Rapid and recent origin of species richness in the Cape flora of South Africa[END_REF][START_REF] Linder | Evolution of diversity: the Cape flora[END_REF]. The Cenozoic history of New Caledonia is still poorly understood. It is not clear for example how its mountain range has changed with time.

New Caledonia was once entirely covered by ultramafic rocks (Pelletier, 2006) and it is not known at what rate this terrain may have weathered and fragmented. Because of the abundance of these poorly fertile soils, New Caledonia may be considered as an old, climatically buffered, infertile landscape (OCBIL, Hopper, 2009) along with the Cape flora or the South-West Australia, however its climatic stability remains to be proven. There is some evidence that Quaternary climatic oscillations may have affected the New Caledonian flora [START_REF] Pintaud | Chorology of New Caledonian palms and possible evidence of Pleistocene rain forest refugia[END_REF][START_REF] Pillon | Reticulate evolution on a mosaic of soils: diversification of the New Caledonian endemic genus Codia (Cunoniaceae)[END_REF], but this require further studies. The main vegetations of New Caledonia include rainforest, sclerophyll forest, savanna (a secondary vegetation mostly dominated by Melaleuca quinquenervia (Cav.) S.T. Blake)) and maquis [START_REF] Jaffré | The relationship between ecological diversity and floristic diversity in New Caledonia[END_REF]. The maquis is a typical scrubby vegetation found on ultramafic soils which may have been dependant on the onset of a climate favourable to a certain fire-regime [START_REF] Jaffré | Impact des feux de brousse sur les maquis lignoherbacés des roches ultrabasiques de Nouvelle-Calédonie[END_REF]. It is not known how old each of these vegetation types are and their occurrence is highly tight to climate and geology.

If so-called "ancient" lineages may have received more attention in the study of New Caledonian biogeography, there may be something to learn from more recently diverged lineages which may actually be older than expected. First, they represent the largest proportion of the flora in terms of numbers of species and also as ecologically dominant species. Furthermore, the fact that they diversified in New Caledonia (vs. a monotypic group) implies that their crown diversification can be dated. The latter provides a more reliable minimum age for the origins of the New Caledonia biota. Thus, as New Caledonia is now widely acknowledged as a 'museum of biodiversity', we investigate here how old it is as a cradle of biodiversity. We selected here a taxonomically diverse set of studies that satisfy a number of criteria (described below) in order to develop relatively unambiguous evidence. This study aims not to be extensive in terms of its coverage of taxa, but to develop reasonably reliable estimates of the age of the vegetation and the tempo of diversification in the New Caledonian flora.

METHODS

A literature search was carried out to identify any studies on New Caledonian seed plant phylogenetics and was largely based upon the author's knowledge accumulated over years. Only the studies satisfying the following criteria were retained: 1) the group investigated must be the result of single colonization event and must contain more than one species; 2) to ensure that the most basal split in this clade is contained in the study, all (or almost all) the species of each clade must be included, or all the endemic genera it contains must be included and 3) estimates of the stem age and the crown age of the clade endemic to New Caledonia must be provided. If molecular clock studies may contain methodological problems and uncertainty that can greatly affect age estimation [START_REF] Graur | Reading the entrails of chickens: molecular timescales of evolution and the illusion of precision[END_REF]), the compilation of multiple studies should reduce the impact of such confounding factors.

The stem age (the age of the divergence between the endemic clade and its non-New Caledonian sister lineage, preferably continental) provides a conservative estimate of the earliest time of the group's arrival in New Caledonia (Figure 1). At the other extreme, the crown age provides a conservative estimate of the latest time of arrival of this group in New Caledonia, and also the latest date of the first diversification event. Thorough sampling of the clade is therefore important as the absence of some basal taxa could lead to a significant under-estimate of crown age. Because extinction may have erased intermediate nodes in the land of origin or in New Caledonia, it is not possible to determine when the dispersal/vicariant event took place between the stem-age and the crown-age, nor when the clade started to diversify in New Caledonia (Figure 1). Some attention must be paid to the sister-clade, which, especially in the case of an island endemic group (rather than continental, but see figure 1), may actually represent an ancient dispersal out of New Caledonia.

To develop an estimate of the mean diversification rate of each clade in New Caledonia, we use equation 4 from [START_REF] Magallón | Absolute diversification rates in angiosperm clades[END_REF] which utilises species numbers and crown age. Although these are rather simplistic estimates, the aim of this study was to compare diversification rates in New Caledonia with those in other areas and this was done by applying the same calculation for all clades considered. We used mean or median age for speciation rate calculation as age range were not available for many studies, and we aimed at comparing speciation rate between groups rather than estimate precisely speciation rate for individual groups. We also included data (crown age and species number) from a number of radiations in New Zealand (reviewed in [START_REF] Linder | Plant species radiations: where, when, why?[END_REF] and recalculated mean diversification rate with the same equation to compare with New Caledonia as well as a few groups from the Mascarenes and from Hawai'i. We compared species richness, crown age and diversification rate between New Zealand and New Caledonian clade with a Mann-Whitney test. Correlation between species richness, crown age and diversification rate within New Caledonia were tested with a Spearman rank test.

NEW CALEDONIAN LINEAGES INCLUDED Arecoid Palms

The palm flora of New Caledonia comprises several lineages within Arecoideae, that are all trees and that are mainly found in rainforests [START_REF] Pintaud | Chorology of New Caledonian palms and possible evidence of Pleistocene rain forest refugia[END_REF]. We follow here the classification of [START_REF] Pintaud | A revision of the palm genera (Arecaceae) of New Caledonia[END_REF] and use the dated tree of [START_REF] Papadopulos | Speciation with gene flow on Lord Howe Island[END_REF].

The endemic genera Clinosperma Becc.-Cyphokentia Brongn. (6 species) form a monophyletic group that diverged from its sister group from Australia and New Guinea 6.1

My ago and has a crown age of 3.3 My. The endemic genera Burretiokentia Pic.Serm.-Cyphophoenix H.Wendl. ex Hook.f. (9 species) diverged from their widely-distributed, mostly Oceanic sister-group 4.5 My ago and have a crown age of 2.6 My. The endemic genera Chambeyronia Vieill. and Kentiopsis Brongn. (6 species) diverged from their sister group (mostly from Australia and New Guinea) 5.1 My ago and have a crown age of 2.0 My.

The endemic genus Basselinia s.l. (Basselinia Vieill. and Alloschmidia H.E. Moore) was not included because of doubt on its monophyly. In the analysis of Papadopulos (2011), Basselinia s.l. is not recovered as monophyletic as Hedyscepe H.Wendl. & Drude (Lord Howe Island) is nested within it. This study includes a single species of Basselinia s.s., which itself may not be monophyletic (Baker et al. unpublished in Pintaud & Baker, 2008). Therefore there is no reliable estimate of the crown age of Basselinia in a broad or a narrow sense, but its stem age is likely not older than 5.3 My, that is the age of the divergence between the clade formed by Basselinia s.l. and Hedyscepe from its sister group. Similarly, the following two genera where excluded: Actinokentia Dammer (a single species was included in the phylogenetic analysis of [START_REF] Papadopulos | Speciation with gene flow on Lord Howe Island[END_REF] and Cyphosperma H.Wendl. ex Hook.f. (a non-endemic genus with a single endemic species).

Kermadecia-Sleumerodendron (Proteaceae)

The genera Kermacedia Brongn. & Griseb. and Sleumerodendron Virot are two endemic genera of large rainforest trees containing together 5 species [START_REF] Virot | Flore de la Nouvelle-Calédonie et Dépendances[END_REF].

Sleumerodendron is the sister group of Kermadecia + Turrillia A.C.Sm. [START_REF] Mast | A smaller Macadamia from a more vagile tribe: inference of phylogenetic relationships, divergence times, and diaspore evolution in Macadamia and relatives (tribe Macadamieae; Proteaceae)[END_REF], the latter genus, endemic to Vanuatu and Fiji, most likely represents a secondary dispersal event from New Caledonia to these two archipelagos. The divergence between the clade containing these three genera and their sister group, the genus Euplassa Salisb. from South America is dated to 11.4 My (8.1-15.6, [START_REF] Mast | A smaller Macadamia from a more vagile tribe: inference of phylogenetic relationships, divergence times, and diaspore evolution in Macadamia and relatives (tribe Macadamieae; Proteaceae)[END_REF], the age of the crown clade is estimated at 9.8 My (4.9-11.4). Diversification for this clade was calculated only for the New Caledonian species and the dispersal to Vanuatu-Fiji was ignored in this calculation.

Dracophyllum (Ericaceae)

In New Caledonia, the genus Dracophyllum Labill. contains 9 endemic species [START_REF] Wagstaff | Origin, diversification, and classification of the Australasian genus Dracophyllum (Richeeae, Ericaceae)[END_REF] of shrubs or sometimes small trees. It is present mostly in maquis on ultramafic soils [START_REF] Virot | Flore de la Nouvelle-Calédonie et Dépendances[END_REF]. In an analysis containing all New Caledonian species, [START_REF] Wagstaff | Origin, diversification, and classification of the Australasian genus Dracophyllum (Richeeae, Ericaceae)[END_REF] date the divergence of the New Caledonian clade from its Australian sister group to 6.7 My (4.0-9.7 My, Bayesian estimate) and the crown age to 5.2 My (2.6-7.2).

Pycnandra (Sapotaceae)

The genus Pycnandra Benth. is currently recognised as the largest endemic genus of the New Caledonian flora [START_REF] Morat | The taxonomic reference base "FLORICAL" and characteristics of the native vascular flora of New Caledonia[END_REF] with 57 species of trees and shrubs of diverse ecology. In an analysis containing all but eight taxa, [START_REF] Swenson | Phylogenetic and generic limits in the Niemeyera complex of New Caledonian Sapotaceae: evidence of multiple origins of the anisomerous flower[END_REF] found a basal split within the genus between the two clades BDCE and FGH. In an analysis of Chrysophylloideae, [START_REF] Bartish | Vicariance or long-distance dispersal: historical biogeography of the pantropical subfamily Chrysophylloideae (Sapotaceae)[END_REF]

Metrosideros (Myrtaceae)

The genus Metrosideros Banks ex Gaertn. (Myrtaceae) is a genus of shrubs and trees with 18 species in New Caledonia [START_REF] Dawson | Myrtaceae -Leptospermoideae[END_REF], found mostly in high-elevation maquis and forest. All New Caledonian species have been included in molecular phylogenetic analysis [START_REF] Wright | Phylogenetic analyses of New Caledonian Metrosideros and Carpolepis (Myrtaceae) from nrDNA (ITS) sequences[END_REF], and a dating of the phylogeny is provided in Papadopulos et al. Caledonian species, Metrosideros oreomyrtus Däniker is phylogenetically isolated and is therefore not very informative by itself. An alternative scenario may be that all New Caledonian Metrosideros descend from a single colonizer, and that multiple events of dispersal to other Pacific islands obscured its biogeographical history. If we considered the smallest clade including all New Caledonian Metrosideros, its crown age is 37.1 My and its stem-age 42.2 My. In statistical analyses on diversification rate, Metrosideros was considered as three distinct clades (three colonization events) as similar results were obtained if a single colonisation event was considered.

Nothofagus (Nothofagaceae)

The genus Nothofagus is represented in New Caledonia by a clade of five endemic species of rainforest, which have all been included in a phylogenetic analysis [START_REF] Sauquet | Testing the impact of calibration on molecular divergence times using a fossil-rich group: the case of Nothofagus (Fagales)[END_REF]. The crown age of this clade is estimated to 16.5 My (6.7-27.5, figure 2 of [START_REF] Sauquet | Testing the impact of calibration on molecular divergence times using a fossil-rich group: the case of Nothofagus (Fagales)[END_REF] and the divergence from the New Guinea sister group is estimated to 25.4 My (13.7-39.1).

Araucaria (Araucariaceae)

The genus Araucaria Juss. is represented in New Caledonia by 13 species of emergent trees in rainforest, maquis and coastal formations [START_REF] De Laubenfels | Flore de la Nouvelle-Calédonie et Dépendances[END_REF]. The divergence between the New Caledonian Araucaria and their sister group A. heterophylla (Salisb.)

Franco, endemic to Norfolk Island is dated to 14.4 My (26.6-6 My , [START_REF] Biffin | Did Kauri (Agathis: Araucariaceae) really survive the Oligocene drowing of New Zealand?[END_REF]. AFLP (Amplified Fragment Length Polymorphism) data [START_REF] Gaudeul | AFLP markers provide insights into the evolutionary relationships and diversification of New Caledonia Araucaria species (Araucariaceae)[END_REF] suggests that within the New Caledonian clade the coastal group containing A. columnaris, A. luxurians and A. nemorosa is sister to the rest (including A. rulei). The divergence between A. columnaris Hook. and A. rulei F.Muell. is dated to 4.8 My (2.4-10.8) and corresponds therefore to the crown age of New Caledonian Araucaria. It is possible that A. heterophylla represent a case of dispersal from New Caledonia, and the stem-age of New Caledonian Araucaria would then be the divergence between the clade formed by the New Caledonian Araucaria and A. heterophylla, and A. cunninghamii (Australia, New Guinea) which is dated to 21.6 My (10.8-38.4).

Dacrydium (Podocarpaceae)

The genus Dacrydium Lamb. is represented in New Caledonia by a clade of four endemic species of shrubs and trees, growing in rainforest, maquis or on the banks of rivers and lakes [START_REF] De Laubenfels | Flore de la Nouvelle-Calédonie et Dépendances[END_REF]. All four species have been included in a phylogenetic analysis [START_REF] Keppel | Diversification history anf hybridisation of Dacrydium (Podocarpaceae) in remote Oceania[END_REF] and the crown age is estimated to 5.5 My (no range provided).

The divergence from its Fijian sister group is estimated to 9.6 My (2.9-18.9). It is possible that the two Fijian species are the result of a dispersal event from New Caledonia, and the actual stem-age of the New Caledonian Dacrydium may actually be the age of the divergence between the New Caledonian-Fijian clade and its South-East Asia sister group: 15.4 My (7.1-27.9). colonization of these plants is more recent than the separation of New Caledonia from Australia and simultaneous or posterior to the re-emersion of the island ca. 37 My ago [START_REF] Cluzel | Upper Eocene unconformity and pre-obduction events in New Caledonia[END_REF]. So far, therefore, all evidence is consistent with colonisation of New Caledonia by long-distance dispersal over water, as well as with a post-emersion origin of the flora, in agreement with the observations reviewed by [START_REF] Grandcolas | New Caledonia: a very old Darwinian island?[END_REF] and [START_REF] Cruaud | Testing the emergence of New Caledonia: fig wasp mutualism as a case study and a review of evidence[END_REF]. This data does not provide evidence for survival of these clade on putative islands around New Caledonia during early Cenozoic, but do not allow to rule allow out this hypothesis. The colonisation of the plant lineages is concomitant with the overall cooling of the climate in the Oligocene and Miocene (igure 2, [START_REF] Zachos | Trends, rythms, and aberrations in global climate 65 Ma to present[END_REF], although the colonisation is not markedly simultaneous across lineages. Events of colonisation of New Caledonia are spread across the second half the Cenozoic, suggesting that the island was still able to be invaded by new migrants long after the arrival of the first lineages. Because of the limited number of observations and the coarse estimation of the time of colonisation (large intervals between stem an crown ages), it is not possible to determine if there has been a particular time when more colonisation events occurred or when any simultaneous onset of diversification was triggered. Only the ages observed for Pycnandra and possibly Metrosideros are congruent with an immediate colonisation of New Caledonia after emergence. An early arrival of Metrosideros would be consistent with its high dispersal capacity and its ability to grow on barren soils including young lava flow [START_REF] Drake | Seed dispersal of Metrosideros polymorpha (Myrtaceae): a pioneer tree of Hawaiian lava flows[END_REF].

Interestingly, when considering the two conifer group included in this study, both Araucaria (4.8 My) and Dacrydium (5.5 My) have a younger crown age than the average Angiosperms lineages studied (9.7 My). This is consistent with the conclusions of [START_REF] Nagalingum | Recent synchronous radiation of a living fossil[END_REF] and Crisp & Cook (2011) that extant Gymnosperms are not living fossils and therefore cannot be used as evidence for the persistence over a long period of time of the New Caledonian flora.

Synchronous arrivals of palm clade

A striking observation is the almost simultaneous independent colonisation of New Caledonia by the Arecoid palms lineages, where the short time separating the stem-age and crown-age allows quite precise estimation of the time of arrival of these lineages. A somewhat similar pattern is observed in Metrosideros but not so clearly. This may be explained by the appearance of key-innovations in the common ancestor of these palms, possibly high dispersal capacity or features that allow them to outcompete other plants occupying the same niche. Island) and it can be accepted that they were among the earliest colonizers. It is possible that the New Caledonian environment was either not suitable for palms before relatively recently, or that the current Arecoid palms have displaced a cortege of palms previously present, of which Saribus could be a survivor.

Age of New Caledonian ecosystems

The crown age of Pycnandra,) may be used to provide a conservative estimate of the latest arrival time of the first plants in New Caledonia. There are too few lineages included in the present study to reasonably date the different vegetations of New Caledonia. However the crown age of groups restricted to a given ecosystem can be considered to provide a conservative minimum age for the presence of these ecosystems.

Considering the lineages restricted to rainforest, the crown age of Nothofagus is estimated to 16.5 My (6.9-27.5) , the crown age of Kermadecia-Sleumerodendron to 9.8 My (4.9-11.4), and all Arecoid palm lineages in New Caledonia are younger than this, the oldest having a crown age of 3.3 My. Therefore, in a conservative approach, it seems likely that rainforest has been present on New Caledonia for at least 6.9 My, but probably more. None of the lineages investigated here is restricted to maquis, although Dracophyllum is present mostly in this ecosystem. Its crown age is 5.2 My (2.6-7.2) and this could be considered a minimum age for this ecosystem. Data would be desirable for clades restricted to maquis such as Dubouzetia Pancher ex Brongn. & Griseb., Greslania Balansa or Thiollierea Montrouz.

Diversification rate

Diversification rates were relatively modest, ranging from 0.080 in clade B of Metrosideros (or 0.059 if Metrosideros is considered as a single clade) to 0.58 in Burretiokentia-Cyphophoenix, what is much lower than that observed in rapid plant radiation [START_REF] Valente | Unparalled rates of species diversification in Europe[END_REF]. On average, speciation rates were lower than in New Zealand (0.236 vs. 0.516). However no significant difference was found between the two archipelagos regarding species-richness (p=0.15, Mann-Withney test), crown age (p=0.3) and diversification rates (p=0.17). New Caledonian palms have a similar diversification rate to the Mascarenes endemic clade Acanthophoenix-Tectiphiala. New Caledonian Metrosideros have a higher diversification rate than the New Zealand ones, but lower than the Hawaiian ones.

Across the New Caledonian clades we found no significant correlations between species number and crown age (p=0.69, Spearman rank test), a nearly significant positive correlation between species number and diversification rate (p=0.056), and a significant negative correlation between diversification rate and crown age (p=0.00079). Therefore, species-richness within a clade does not seem to be explained by greater age or may be not by higher diversification rate. The fact that the youngest clades are the ones that diversify fastest and the absence of correlations between species richness and clade age suggests a slowing down of diversification in the older clade, i.e. perhaps the occurrence of density-dependant diversification [START_REF] Rabosky | Density-dependent diversifcation in North American wood warblers[END_REF][START_REF] Rabosky | Ecological limits on clade diversification in higher taxa[END_REF]. A slowing down in diversification rate has indeed been observed in Pycnandra and also in several New Caledonian animal lineages [START_REF] Espeland | Diversity dynamics in New Caledonia: towards the end of the museum model?[END_REF].

New Caledonia, an old community Diversification rate in New Caledonia seems to be relatively low. It is possible the flora reached saturation some time ago and that the new species are only replacing species as they go extinct. [START_REF] Gillespie | Island biogeography of remote archipelagoes[END_REF] considered that the oldest Hawaiian islands particularly Kaua'i (4.7 My) may already have reached equilibrium, whereas in the youngest islands, Hawai'i and possibly Maui, the species number is still growing. It is also possible that the considerable isolation of this archipelago strongly limits the number of colonisers, and so these may have had more opportunity to diversify. Although the New Caledonia vegetation has existed for at least 23 My (crown-age of Pycnandra) and equilibrium may have been reached shortly after this, colonisation seems to have been possible for a long time after this, e.g. the youngest clade of this study (Burretiokentia-Cyphophoenix) arrived no earlier than 4.5 My (stem age). Compared to other oceanic islands, often of volcanic origin, New Caledonia may have a relatively old flora, allowing equilibrium to have been reached [START_REF] Macarthur | The theory of island biogeography[END_REF]. As time passed, extinction created phylogenetically isolated taxa but new species still appeared and others invaded the system. The continuous arrival of new taxa that compete with previous settlers could explain why there are no dramatic examples of adaptive radiation today in New Caledonian plants compared to those in other islands, whether these either never existed or they suffered extinction through competition. The apparent faster diversification rates in New Zealand may be explained by its relatively recent orogenesis and the origin of the alpine biome which could have triggered a recent burst of diversification [START_REF] Linder | Plant species radiations: where, when, why?[END_REF].

Compared to other areas that underwent intense diversification, the ten largest genera of the New Caledonia flora encompass 18.9% of the species compare to 29.1% in south-west Australia [START_REF] Hopper | The Southwest Australian floristic region: evolution and conservation of a global hot spot of biodiversity[END_REF], 21.4% in the Cape Floristic Region [START_REF] Goldblatt | Plant diversity of the Cape region of southern Africa[END_REF] and 32.3% in Hawai'i [START_REF] Wagner | Manual of the flowering plants of Hawai[END_REF]. Even of those genera may not form a monophyletic clade in each of these areas (but likely so in Hawa'i, [START_REF] Baldwin | Hawaiian angiosperm radiations of North American origin[END_REF], they are probably composed of one main radiation and this comparison gives an idea of the diversification opportunity of a small collection of closely related plant clades that exploit their environment in a similar. So, in the floras of Hawa'i, south-west Australia and the Cape, some large radiations seem to represent a much greater proportion of the flora.

It is possible that some rapidly-diversifying clades tend to take over a community on settlement but, as time passes, more immigrants arrive and diversify and this gradually decreases the representation of the earlier fast-diversifying clades. This may be a manifestation of the density-dependant diversification effect that becomes stronger as the community approaches equilibrium. The flora of Hawai'i is still young because of the recent volcanic origins of these islands. Meanwhile, the floras of Cape Province and of south-west Australia underwent turnover as their climates became drier in the Cenozoic [START_REF] Hopper | The Southwest Australian floristic region: evolution and conservation of a global hot spot of biodiversity[END_REF][START_REF] Dupont | Climate-driven rampant speciation of the Cape flora[END_REF]. Explosive radiation is expected by the neutral theory as a new community arises or if some dramatic change (e.g. climate) cause large-scale extinction [START_REF] Hubbell | The Unified Neutral Theory of Biodiversity and Biogeography[END_REF]. It is possible that New Caledonia has reached a greater degree of maturity than the three flora mentioned above. This may not be a matter simply of community age, it may take more time for a large community such as those of the Cape Flora or of south-west Australia to reach equilibrium, and the stability of the physical environment of a community is also difficult to determine over long periods.

Towards the study of large radiation in New Caledonia

This study suffers from the inclusion of several clades that have only a small number of species. One can expect that larger clades may also be older ones and also ones that diversify fastest. Pycnandra (57 species), the largest endemic genus included in this study, although probably the oldest coloniser in the groups investigated, does not have the highest diversification rate. At this stage, this is the largest endemic clade whose monophyly has been tested and confirmed with molecular phylogenetics. Further attention to the extensive New Caledonian radiations is therefore required. However there do not seem to be many larger radiations than Pycnandra. There are very few occurrences of endemic genera forming monophyletic clades outside the palms, and none of these is species rich. Only three genera have more species than Pycnandra in New Caledonia: Phyllanthus L. (108 endemic species), Psychotria L. (ca. 80 species, all endemic) and Syzygium Gaertn. (69 endemic species). New Caledonian Syzygium are not monophyletic and are composed of several independent clades [START_REF] Biffin | Molecular systematics of Syzygium and allied genera (Myrtaceae): evidence from the chloroplast genome[END_REF], which may not exceed Pycnandra in size. This seems to be relatively common in the large New Caledonia genera, as the same pattern has been observed in Planchonella Tiegh. [START_REF] Swenson | Molecular phylogeny of Planchonella (Sapotaceae) and eight new species from New Caledonia[END_REF], Diospyros L. [START_REF] Duangjai | A multi-locus plastid phylogenetic analysis of the pantropical genus Diospyros (Ebenaceae), with an emphasis on the radiation and biogeographic origins of the New Caledonian endemic species[END_REF] and probably Pittosporum Banks ex Gaertn. [START_REF] Chandler | Molecular and morphological agreement in Pittosporaceae: phylogenetic analysis with nuclear ITS and plastid trnL-trnF sequence data[END_REF]. Some genera such as Eugenia L., Tapeinosperma Hook.f., Myrsine L. or Elaeocarpus L. require further investigation. As for Psychotria, multiple colonisations are likely, although most species may belong to a single monophyletic clade of ca. 75 species (L. Barrabé, pers. comm.).

Phyllanthus also colonised New Caledonia on multiple occasions [START_REF] Kathriarachchi | Phylogenetics of tribe Phyllantheae (Phyllanthaceae; Euphorbiaceae sensu lato) based on nrITS and plastid matK DNA sequence data[END_REF], and it is not clear yet if there is one predominant radiation on the island within that genus. Therefore, there seem to be very few, if any, instances of large, explosive radiation within the New Caledonia flora.

CONCLUSION

As new studies on New Caledonian plants continue to be published, none have yet provided firm evidence for the persistence of vegetation throughout the Cenozoic but, instead, are congruent with a colonisation postdating the re-emersion of the island in the mid-Cenozoic. The occurrence of relict lineages seems to be misleading. The only firm evidence for the persistence of some lineages since the Cretaceous could come from fossils or a radiation in which the crown age pre-dates the re-emersion of the island (Crisp et al., 2011).

Plant lineages seem to have been able to colonise New Caledonia throughout the second half the Cenozoic and, so far, there is no evidence that there has been a particular time when colonisation has been more frequent or when diversification of multiple clades started simultaneously. Diversification rate seems to have been relatively slow and there is no correlation between clade age and species-richness. This suggests that density-dependent processes dominate. The New Caledonian flora may thus be a community that has reached equilibrium, albeit still dynamic. Further studies on large plant radiations may shade some light on the ecological parameters that triggered speciation, the trend of diversification rate over time, the importance of climatic oscillations or the principal mode of speciation (sympatric vs. allopatric).

(

  supplementary data, 2011) that include both subgenera Mearnsia and Metrosideros. The clade A contains M. punctata J.W.Dawson, M. humboldtiana Guillaumin, M. nitida Brongn. & Gris, M. engleriana Schltr., M. microphylla (Schltr.) J.W.Dawson, M. tetrasticha Guillaumin and M. cherrieri J.W.Dawson (7 species) diverged from its sister group M. ochrantha A.C.Sm. (Fiji) + M. boninensis (Hayata ex Koidz.) Tuyama (Bonin islands) 16.6 My ago, and the age of the crown is 13.7 My. Meanwhile, Metrosideros whitakeri J.W.Dawson, M. dolichandra Schltr. ex Guillaumin, M. porphyrea Schltr., M. longipetiolata J.W.Dawson and M. brevistylis J.W. Dawson (5 species) form clade B, which diverged from its sister group clade D (New Zealand) 21.7 My ago and the crown is dated to 11.5 My. Metrosideros paniensis J.W. Dawson, M. operculata Labill., M. cacuminum J.W.Dawson, M. rotundifolia J.W.Dawson and M. patens J.W.Dawson (clade C, 5 species) diverged from the New Zealand sister clade 29.9 My year ago and the crown age is date to 8.4 My. The last New

  The relative youth, and the similar ages of the different lineages of the New Caledonia Arecoid palms, which comprise all palms of the archipelagos except Cocos nucifera L. and Saribus jeanneneyi (Becc.) C.D.Bacon & W.J.Baker is striking. Palms from various clades have shown clear abilities to colonise distant islands (Mascarenes, Hawai'i, Lord Howe

Figure 1 .

 1 Figure 1. Inferring time of colonisation and onset of diversification from dated phylogeny. For

Figure 2 .

 2 Figure 2. Estimated intervals of arrivals and first events of diversification of nine selected

  included members of the Swenson et al. clades, D, G and H, thus allowing a reliable estimate of crown age: 23.6 My (18.3-29.7). The divergence between Pycnandra and its sister group Niemeyera prunifera F.Muell. from Australia is dated to 35.8 My (no deviation provided).

Table 1 .

 1 Speciation rates for various clades of New Caledonian plants and a comparison with other regions. Alternative stem-age are given in parenthesis for Araucaria and Dacrydium (see methods). See text for references for species numbers, crown and stem ages, and for complete age range.

	Clade	Species	Stem age	Crown	Diversification
		number	(My)	age	rate
				(My)
	New Caledonia
	Clinosperma-Cyphokentia	6	6.1	3.3	0.33
	Burretiokentia-Cyphophoenix	9	4.5	2.6	0.58
	Chambeyronia-Kentiopsis	6	5.1	2	0.55
	Kermadecia-Sleumerodendron 5	11.4	9.8	0.093
	Dracophyllum	9	6.7	5.2	0.29
	Pycnandra	57	35.8	23.6	0.14
	Metrosideros A	7	16.6	13.7	0.091
	Metrosideros B	5	21.7	11.5	0.080
	Metrosideros C	5	29.9	8.4	0.11
	Metrosideros (one clade)	18	42.2	37.1	0.059
	Nothofagus	5	25.4	16.5	0.056
	Araucaria	13	14.4 (21.6) 4.8	0.39
	Dacrydium	4	9.6 (15.4)	5.5	0.13
	New Zealand
	Abrotonella	20		4.2	0.55
	Chionochloa	22		5	0.48
	Forsteria	7		6	0.21
	Gentianella	30		2.05	1.32
	Hebe	100		3.9	1.00
	Myosotis	34		8.35	0.34
	Pachycladon	8		2.25	0.62
	Scleranthus	3		4.45	0.091
	Metrosideros D	5		25.2	0.036
	Hawai'i
	Lobeliads	126		13.2	0.31
	Cyrtandra	53		5.2	0.63

Non-New Caledonian lineages

To compare speciation rate, we used all of the eight New Zealand lineages analysed in the study by [START_REF] Linder | Plant species radiations: where, when, why?[END_REF], plus a clade of New Zealand Metrosideros (see below). We also used as a comparison the two largest plant radiations of the Hawaiian archipelago: the Hawaiian Lobeliads (126 species, crown-age of 13.2 My, [START_REF] Givnish | Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae)[END_REF] [START_REF] Percy | Progressive island colonization and ancient origin of Hawaiian Metrosideros (Myrtaceae)[END_REF]. We also considered a group of Metrosideros Banks ex Gaertn. from New Zealand (clade D), including M. parkinsonii Buchanan, M. fulgens Sol. ex Gaertn., M.perforata (J.R.Forst. & G.Forst.) Druce, M. carminea W.R.B.Oliv., M. diffusa (G.Forst.) Sm. and M. colensoi Hook. f., of which the crown clade is dated to 25.2 My [START_REF] Papadopulos | Speciation with gene flow on Lord Howe Island[END_REF]. Finally we added a clade of Arecoid palms endemic to the Mascarenes: Acanthophoenix H. Wendl.-Tectiphiala H.E.Moore (4 species) of which the crown clade is dated to 1.7 My [START_REF] Papadopulos | Speciation with gene flow on Lord Howe Island[END_REF].

DISCUSSION

Timing of colonisation

For all clade included in this study, colonization seems to have happen around 37 My (emergence of New Caledonia) or after (table 1, figure 2). The oldest stem age are found in Pycnandra (35.8 My),Nothofagus (25.4 My,