Jean-Luc Danger
email: jean-luc.danger@telecom-paristech.fr

Sylvain Guilley

Shivam Bhasin

Maxime Nassar

Laurent Sauvage

Overview of Dual Rail with Precharge Logic Styles to Thwart Implementation-Level Attacks on Hardware Cryptoprocessors -New Attacks and Improved Counter-Measures --Invited Paper at SCS'2009

Keywords: Side Channel Attacks, Fault Attacks, Dual-rail with Precharge Logic (DPL), Differential Power Analysis

The security of cryptographic implementations relies not only on the algorithm quality but also on the countermeasures to thwart attacks aiming at disclosing the secrecy. These attacks can take advantage of the secret leakages appearing through the power consumption or the electromagnetic radiations also called "Side Channels". This is for instance the case of the Differential Power Analysis (DPA) or the Correlation Power Analysis (CPA). Fault injections is another threatening attack type targeting specific nets in a view to change their value. The major principle to fight the side-channel attack consists in making the power consumption constant. The Masking method allows the designer to get a power consumption which has a constant mean and a variance given by a random variable. Another manner is the Hiding method which consists in generating a constant power consumption by using a Dual-rail with Precharge phase Logic (DPL). This paper presents an overview of the various logic styles that have been promoted in the last six years, with an emphasis on their relative advantages and drawbacks.

I. INTRODUCTION

Many modern cryptographic algorithms are theoretically robust and immune from practical cryptanalysis in the "black box" model. However, some methods can be deployed to break the security by attacking the physical implementation of virtually any algorithm. These attacks can be mounted by merely observing or perturbing the targeted system. Observing the activity of the system and its correlation with potential guesses can yield sensible information. Such attacks are better known as Side Channel Attacks (SCAs). When a device is perturbed such that it yields a non-nominal output, this together with expected output can lead to the secret key. Such attacks are called Differential Fault Analyses (DFAs [START_REF] Biham | Differential Fault Analysis of Secret Key Cryptosystems[END_REF], [START_REF] Piret | A Differential Fault Attack Technique against SPN Structures, with Application to the AES and KHAZAD[END_REF]).

The advantages of SCAs are that the system is made to operate in its comfort zone. In such condition, it is difficult to detect that some devices may be observing the activity of the target. To defeat SCA efficiently, the countermeasures have at least to be submitted at the logic level. Dual-rail with Precharge Logic (DPL) is a class of countermeasures which aims at making the device activity constant and independent of data processed.

In this paper, we propose an overview of the main DPL styles with a focus on their vulnerabilities against both the Side-Channel and the Fault attacks.

The rest of the article is organized as follows. Section II presents the DPL countermeasure at logical level and the major vulnerabilities incurred by the backend. Then the Sec. III describes how the vulnerabilities are addressed by the already evaluated logic styles in either FPGA or ASIC. The Sec. IV explains how some optimizations and original solutions can be found using specific technologies. A synoptic comparison between the known logic styles is drawn in Sec. V. Finally, conclusions and perspectives are discussed in Section VI.

II. DPL PRINCIPLE, BUILT-IN DFA RESISTANCE, AND LATENT SIDE-CHANNEL VULNERABILITIES

A. Information Hiding Rationale

The aim of dual-rail with precharge logic (DPL) is to hide the internal circuit's activity from a prospective attacker. If any sensitive variable update occurs with a constant activity, it is likely that all side-channels also are. Therefore, the measurable quantity from an attacker's point of view is independent from any secret value. The protocol of the DPL consists of two phases: precharge and evaluation. The precharge phase allows to start new computations from a known electrical state. It thus prevents unexpected transitions between two computation steps. The dual-rail signalization of the data is conveyed by two wires for each Boolean variable: NULL = (0, 0) or (1, 1) while in precharge and VALID ∈ {(0, 1), (1, 0)} while in evaluation. Therefore, every evaluation consists in the transition of exactly one wire ((0, 0) → (0, 1) or (0, 0) → (1, 0)). If the design is adequately balanced, which transition actually occurred is indiscernible by an attacker.

B. DPL Built-in DFA Resistance

Single bit faults are inefficient against DPL because they turn a VALID data into a NULL token, that propagates and leads to a non exploitable error since it hides the faulted value. This is the typical scenario described in the seminal paper [START_REF] Selmane | WDDL is Protected Against Setup Time Violation Attacks[END_REF], introducing the intrinsic immunity of DPL against some classes of DFA.

Highly multiple faults ((1, 0) ↔ (0, 1)) generate randomly a large quantity of NULL values along with some more unlikely but devastating bit-flips. However, as NULL values are systematically propagated, they proliferate very quickly after some combinatorial logic layers traversal. And as they have the nice property to contaminate VALID values, the risky coherent bit-flips (simultaneous 0 * → 1 and 1 * → 0 in one dual-rail couple) has a great chance to be jammed through the propagation towards the algorithm output. This absorption property is all the more efficient as the number of NULL generated by the multiple faults is high. Therefore, the only way to inject a poisonous fault is to stress the circuit sufficiently enough to have multiple faults, without nonetheless creating too many faults so as to leave a chance for them not to be absorbed during their percolation towards the outputs.

C. Vulnerabilities w.r.t. Side-Channel Attacks

Although perfectly sound at logical level, DPL ends up to be concretely implemented in physical devices. Now, the logical description of DPL ignores any timing and capacitance's notions.

Regarding the timing, three unbalanced behaviors can occur. On the way from the precharge to the evaluation, and viceversa, there can exist:

1) spurious transitions, referred to as glitches, that negate the hypothesis of activity constantness, and 2) early evaluation effects. It takes place if the gate switching depends on the difference between the arrival time of the inputs. 3) technological bias. This flaw comes from the imbalance between the dual signals. It can be caused by the manufacturing dispersion, the place-and-route stage or merely the types og gate driving the true and false networks. This biais could be exploited by an attacker who measures the signal emanating from one wire of a pair. The cross-coupling is another issue, still unexploited but probably also endangering the security of DPL designs.

The next section III studies how these latent flaws have been addressed by some existing DPL logics, whereas the section IV illustrates technology-dependent optimizations or innovative solutions.

III. DPL FAMILIES BASED ON STANDARD CELLS

A. WDDL

Wave Dynamic Differential Logic (WDDL [START_REF] Tiri | A Logic Level Design Methodology for a Secure DPA Resistant ASIC or FPGA Implementation[END_REF]) meets all the logical constraints of a DPL. The initial state is propagated by a wave of (0, 0) couples through the netlist thanks to the use solely of positive gates. The fact that exactly one half of the gates evaluate results from the duality between the true and false networks. In addition, the positivity of WDDL ensures the absence of glitches in the complete netlist. Notice that WDDL with gates propagating the NULL spacer but without being positive is easily broken in practice, as explained in [START_REF] Guilley | Evaluation of Power-Constant Dual-Rail Logic as a Protection of Cryptographic Applications in FPGAs[END_REF]. However, as shown in [START_REF] Suzuki | Security Evaluation of DPA Countermeasures Using Dual-Rail Pre-charge Logic Style[END_REF], [START_REF]An Analysis of Leakage Factors for Dual-Rail Pre-Charge Logic Style[END_REF], WDDL is prone to early evaluation and early precharge. The Early Evaluation (EE) effect comes from the difference of delay between two variables of a same gate. Fig. 1 illustrates the EE flaw when variable a is in advance to variable b. In this case the output does not switch at the same time.

Moreover, the dual networks are not necessarily balanced, since the transistor structure of x → f (x) and of x → f (x) differ. Those two issues have made possible some attacks on WDDL circuits, as described for instance by the authors of WDDL themselves in an ASIC [START_REF] Tiri | Prototype IC with WDDL and Differential Routing -DPA Resistance Assessment[END_REF] or independently in an FPGA [START_REF] Sauvage | Successful Attack on an FPGA-based WDDL DES Cryptoprocessor Without Place and Route Constraints[END_REF]. Therefore, either incremental improvements or radically novel strategies have shown up.

B. MDPL

Masked Dual-rail with Precharge Logic (MDPL [START_REF] Popp | Masked Dual-Rail Pre-charge Logic: DPA-Resistance Without Routing Constraints[END_REF]) is an attempt to fix the otherwise imbalance of WDDL. The assumption is that, in some conditions, it can be difficult to constrain a router to balance the differential interconnect. Indeed, the two solutions available in the literature, namely the fat wire [START_REF] Tiri | Place and Route for Secure Standard Cell Design[END_REF] and the backend duplication [START_REF] Guilley | The "Backend Duplication" Method[END_REF] methods, apply primarily to ASICs. The transposition to FPGA is possible, albeit with less fine-grain control over the result [START_REF] Guilley | Place-and-Route Impact on the Security of DPL Designs in FPGAs[END_REF]. For this reason, MDPL proposes to swap the true and the false routes randomly, so as to emancipate from the fatal routing unbalance. By the same token, it makes up for the structural unbalance of the dual pair of gates. The only gates involved in the logic are majority functions, both for the true and the false networks. Nonetheless, MDPL fails to provide a solution to the early evaluation and precharge of WDDL.

C. DRSL

The primary focus of Dual-rail Random Switching Logic (DRSL [START_REF] Chen | Dual-Rail Random Switching Logic: A Countermeasure to Reduce Side Channel Leakage[END_REF]) is to make the evaluation and the precharge gates data-independent. For this reason, one pairwise unanimity gate1 computes the validity of all inputs prior to allowing the gate from delivering any result, thus avoiding the EE flaw. On the contrary, the unanimity makes it possible for the overall DRSL logic to always anticipate the precharge. However, in the original design of DRSL, the functions are not required to be positive. The example of the AND function is sketched in Fig. 2(a). Hence the presence of data-dependent glitches in the return to precharge phase. We carried out an extensive simulation of the DRSL AND gate when it returns to precharge. It happens that the DRSL AND gate glitches iff a ⊕ b = 1, irrespective of the mask value.

a T b T m T b F m F a F q T q F 1 × T prop 1 × T prop pre a T b T m T m F b F a F uni q T q F 1 × T prop (a) (b)
Two solutions can be imagined to patch the glitching problem of DRSL. The first one consists in adding buffers to delay the signals so as to balance the paths within the DRSL gate. Another option consists in implementing DRSL in positive logic, as shown in Fig. 2(b). This solution has a cost in CMOS logic, because inverting gates are smaller than noninverting ones (actually realized in practice by the composition of an inverting gate with an inverter [START_REF] Weste | CMOS VLSI Design: A Circuits and Systems Perspective[END_REF]). However, this is not constraining in FPGA. A loss in area is nonetheless expected, as the functionality can only consist in positive gates, thereby limiting the degree of freedom of the the logic synthesizers. In this case, the new logic, that we name DRSL+, consists in MDPL augmented with a synchronization by an unanimity cell.

Another attack against DRSL is presented in [START_REF] Saeki | Security Evaluations of MRSL and DRSL Considering Signal Delays[END_REF]. Actually, this attack puts forward a vulnerability that is common to all masked DPL styles. The idea is that the masking of the gates allows to make up for the routing unbalance. However, the mask signal is itself differential and therefore unbalanced. As it is not balanced (since this is the hypothesis when resorting to masked DPL), it paradoxically opens the door to an attack on itself.

D. STTL

Secure Triple Track Logic (STTL [START_REF] Soares | Evaluating the robustness of secure triple track logic through prototyping[END_REF]) eludes any glitching risk by waiting to evaluate and to precharge until all the inputs are either valid or NULL. This incurs useless delays in the return to precharge phase, which is however only detrimental to performance, not to security. The main drawback of STTL is the requirement to route one synchronization signal slower than the dual-rail, while granting a balanced routing within the dual-rail pair. However, the known methods to balance signals (fat wire and backend duplication) operate on a full netlist, and are therefore difficult to adapt on heterogeneous netlists, in which single-ended and dual-rail signals are mixed up.

E. BCDL

Balanced Cell-based Differential Logic (BCDL) [START_REF] Danger | Circuit de cryptographie programmable -Logique BCDL (Balanced Cell-based Differential Logic)[END_REF] improves on STTL by accelerating the precharge phase, thanks to a global signal. As BCDL design allows to squeeze the precharge step, BCDL can compute about 80% faster than DRSL because the precharge is global.

Furthermore, as the global signal is, by design, faster than data signals, BCDL is free from the flaw identified in DRSL. Additionally, BDCL is a truly differential logic. BCDL and STTL can be seen as equivalent at the netlist level: input synchronization logic (either C-elements or unanimity gates) can be factored in STTL to the detriment of the systematic addition of a third routing resource.

F. WDDL Variants

Some variants of WDDL have also been devised to ease the balance of the WDDL networks. However, as already explained in the subsection devoted to MDPL, it is known that balancing the WDDL interconnect does not solve the early evaluation (EE) inherent to this logic. Nevertheless, we introduce them here because some of these logics have unexpected positive side-effects on their security w.r.t the EE.

1) DWDDL: Double WDDL (DWDDL) is introduced in [START_REF] Yu | Secure FPGA circuits using controlled placement and routing[END_REF] to counterbalance one unbalanced network with a dummy dual one. Although this solution is sound in theory, other efforts have been deployed to reduce the overhead associated with the further duplication of hardware in DWDDL. In [START_REF] Guilley | Place-and-Route Impact on the Security of DPL Designs in FPGAs[END_REF], the design of a substitution box (sbox) in WDDL, similar to the WDDL in BDD-style presented in [START_REF] Akishita | A Practical DPA Countermeasure with BDD Architecture[END_REF], allows for a separation between the true and false halves, thus allowing for a copy-and-paste of the two halves, that are thus guaranteed to have the same backend.

2) WDDL with Divided backend duplication: Divided backend duplication [START_REF] Baddam | Divided Backend Duplication Methodology for Balanced Dual Rail Routing[END_REF] attempts to go one step further by being applicable to any kind of logic (not only the sboxes), has roughly speaking the same overhead as WDDL, while being completely separable in the meantime. Basically, the true/false separation is achieved by preventing the inversions to be replaced by dual wires crossing. However, in a view to keep the precharge propagation to the NULL state, the inverters can be inhibited when in precharge: they are implemented as XNORs with the precharge signal. However, this alteration comes at the cost of two vulnerabilities insertion. If the precharge is concomitant to the clock, then glitches are going to occur due to races between the signals in a non-positive logic. If the precharge is asserted in an individual clock period, then the precharge state does not guarantee anymore a constant number of toggles at evaluation stage.

3) IWWDL: Eventually, Isolated WDDL (IWWDL) [START_REF] Mcevoy | Isolated WDDL: A Hiding Countermeasure for Differential Power Analysis on FPGAs[END_REF] is a different strategy to separate a WDDL netlist. Here, inverters are kept but potential glitches are stopped by systematically inserting one register after it. This strategy is expensive in terms of area and requires a redesign of the controller. Additionally, the design becomes much more pipelined, which requires much higher clock frequencies to maintain an acceptable throughput. However, the benefit of this approach is to stop also the propagation of the EE wave. Apart from the very poor performance of IWDDL, this method is however very strong from a pure security standpoint. Only one point is questionable: isn't the complete separation of the netlist opening the door to well located EMA attacks, that can record selectively the activity from only one half of the netlist, thus defeating the activity constantness property. This issue is all the more stringent as the netlist is much larger in IWDDL than in WDDL, because of the large quantity of registers added for the pipeline.

4) WDDL w/o EE: WDDL w/o EE is a logic style dedicated to FPGA that removes the EE without computing a rendezvous. Instead, each functional half gate receives the true and false inputs, and decides to output the VALID value only when all the inputs are VALID. This behavior can be achieved by a purely combinatorial gate [START_REF] Bhasin | Combined SCA and DFA Countermeasures Integrable in a FPGA Design Flow[END_REF]. The detailed rationale behind the "WDDL w/o EE" style is the following:

• The gate outputs NULL{0,1} when the inputs are NULL{0,1} or transitional from this value.

• The gate outputs VALID only when all the inputs are VALID.

• In case of inconsistent values w.r.t. the DPL convention, the gate outputs an arbitrary NULL value. This logic does not evaluate early by design, and propagates errors: if any input is stuck to NULL or if the input is out of specifications, then the output always remains to NULL too. In addition, this logic does not generate glitches even if the functionality is not positive, and can be inverting. Therefore, the synthesis is more optimized than for plain WDDL.

IV. TECHNOLOGICAL SPECIFIC DPL STYLES

A. Full Custom Optimizations

In 2002, Kris Tiri introduces the "Sense Amplifier Based Logic" (SABL) logic style [START_REF] Tiri | A Dynamic and Differential CMOS Logic with Signal Independent Power Consumption to Withstand Differential Power Analysis on Smart Cards[END_REF], [START_REF] Verbauwhede | A Dynamic and Differential CMOS Logic with Signal-Independent Power Consumption to Withstand Differential Power Analysis[END_REF], which aim is to make power consumption independent of both the logic values and the sequence of the data. It is therefore the first DPL proposal. Its principle consists in combining Differential and Dynamic Logic (DDL) like in the "Dynamic Cascode Voltage Switch Logic" (DCVSL) style, while fixing second order asymmetry in the gate (especially for complex logic functions), due to parasitic capacitance [START_REF] Rabaey | Digital Integrated Circuits[END_REF]. This allows to decorrelate the power consumption from the inputs. In 2006, Marco Bucci et al. [START_REF] Bucci | Three-Phase Dual-Rail Pre-charge Logic[END_REF] show that the balance of DPL gates can be improved by adding a systematic discharge after the evaluation. The resulting computations are thus based on a ternary pace: (1) pre-charge, (2) evaluation and (3) post-discharge. When applied to SABL, simulations reveal that a gain of two-order of magnitude is obtained in terms of balance.

SecLib is a full-custom logic style depicted in Fig. 3 introduced in 2004 by Sylvain Guilley et al. [START_REF] Guilley | CMOS Structures Suitable for Secured Hardware[END_REF]. This logic is based on an quasi-delay insensitive asynchronous primitives, that are balanced to provide constant evaluation and precharge time and dissipation. Specially crafted transistor-level symmetry grants SecLib a higher resistance level to attacks than WDDL, albeit at a high cost in terms of silicon area [START_REF] Guilley | Secured CAD Back-End Flow for Power-Analysis Resistant Cryptoprocessors[END_REF], [START_REF]Security Evaluation of a Balanced Quasi-Delay Insensitive Library[END_REF], [START_REF] Guilley | Security Evaluation of WDDL and SecLib Countermeasures against Power Attacks[END_REF].

Synchronization C 00 C 01 C 10 C 11 C C C C A 0 B 0 A 0 B 1 A 1 B 0 A 1 B 1 3OR Y 0 3OR Y 1 Computation gnd Y gnd C B A SNOR SNOR SNAND Y . = 3OR(A, B, C) . = A + B + C
In [START_REF] Duflot | Device Forming a Logic Gate for Minimizing the Differences in Electrical or Electromagnetic Behavior in an Integrated Circuit Manipulating a Secret[END_REF], Loïc Duflot et al. describe an optimization for SecLib. The core idea, detailed by Fabien Germain's PhD [START_REF] Germain | Towards cryptographic security using dedicated integrated circuits design methodologies[END_REF], is to balance the computation thanks to conflict logic after an input configuration decoding stage.

In 2005, SABL and "Dynamic Current Mode Logic" (Dy-CML) [START_REF] Allam | Dynamic current mode logic (DyCML), a new low-power/high-performance logic family[END_REF] are compared by Franc ¸ois Macé et al. [START_REF] Macé | A Design Methodology for Secured ICs Using Dynamic Current Mode Logic[END_REF]. In DyCML, only one of the output nodes is discharged during the precharge phase. This leads to better performances, such a reduction by 80 % of the power delay product and by 50 % of the power consumption. In addition, DyCML is assessed to be more resistant to DPA than SABL.

Recently, Francesco Regazzoni et al. explore the resistance of "MOS Current Mode Logic" (MCML) against DPA [START_REF] Regazzoni | A Simulation-Based Methodology for Evaluating DPA-Resistance of Cryptographic Functional Units with Application to CMOS and MCML Technologies[END_REF], [START_REF] Regazzoni | Evaluating Resistance of MCML Technology to Power Analysis Attacks Using a Simulation-Based Methodology[END_REF], [START_REF] Regazzoni | A Design Flow and Evaluation Framework for DPA-Resistant Instruction Set Extensions[END_REF] up to simulated attacks. Preliminary results show that MCML has a strong potential for protecting circuits.

B. Asynchronous Logic

Some asynchronous logic styles operate in a DPL mode. If the netlist and their layout is additionally balanced, asynchronous styles can be a candidate for secure computing [START_REF] Bouesse | DPA on Quasi Delay Insensitive Asynchronous Circuits: Concrete Results[END_REF], [START_REF] Bouesse | DPA on Quasi Delay Insensitive Asynchronous Circuits: Formalization and Improvement[END_REF], [START_REF] Hassoune | Dynamic differential self-timed logic families for robust and low-power security ICs[END_REF]. In addition to the protection against side-channel attacks, asynchronous logics are also more tolerant to the environmental variations, which makes them inherently more difficult to attack with faults injections.

C. Reversible Differential Logic

Reversible logic is a means to compute without loosing energy at any step. This implies that any moment of the computation, the operations may be reversed. Two precursors in this field of research were Tommaso Toffoli [START_REF] Toffoli | Reversible Computing[END_REF] and Edward Fredkin [START_REF] Fredkin | Conservative Logic[END_REF].

They proved that the concept of reversible computing was indeed realizable physically, provided that the function to implement is logically reversible. Basically, they demonstrated that any bijection can be mapped onto a reversible physical system. However, two difficult issues were left uncovered by their works:

1) a generic synthesis method for arbitrary bijections, and also an algorithm to provide the most compact netlist, is still be found, and 2) an integrable electronic system suitable for the implementation of reversible logic is laking. Indeed, the only concrete example illustrating Toffoli & Fredkin's work was the famous albeit unpractical "Billiard Ball" model, that cannot extend to thousands of interactions, as required by our modern computational needs. The first question has received some answers [START_REF] Kerntopf | A new heuristic algorithm for reversible logic synthesis[END_REF], [START_REF] Wille | Fast exact Toffoli network synthesis of reversible logic[END_REF]. Regarding the second point, it has been covered by some researchers, for instance in this article [START_REF] Vos | Reversible Computing: from Mathematical Group Theory to Electronical Circuit Experiment[END_REF]. In this paper, the authors describe some implementations in CMOS for representative reversible logic gates.

V. DPL STYLES COMPARISON

Table I draws up a comparison of the main DPL styles, in terms of principle, design constraints and performance, highlighting most of the known advantages (masking, synchronization) and drawbacks (primitives and back-end constraints, and technological bias) of such countermeasures.

Masking allows to greatly reduce the technological bias, but also results in a significant increase of area. As a matter of fact, it requires at least a transformation of 2-input operations into 3-input majority function (MDPL) or into a 4-input RSL gate (DRSL).

Synchronization on both precharge and evaluation is mandatory to avoid glitches and early propagation effects.

Primitive constraints induce a higher complexity, by reducing the panel of usable functions (like in WDDL where only positive functions are allowed), or by binding the designer to use specific functions that can be more area-consuming or slower than basic ones (Seclib, MDPL, DRSL).

Back-end constraints generate extra design work as the P/R stage has to meet specific requirements to achieve a good balance between the T and F networks. It can also cause a loss of performance, like in STTL where the synchronisation signal must be manually made slower than the others, by adding delay elements between each gates, in order to ensure that it always switches last.

Technological bias corresponds to the imbalance between the True and False networks. It encompasses the load, interconnect and CMOS structure differences. This is a significant source of information leakage, and must therefore be as low as possible to ensure a perfectly secure countermeasure.

VI. CONCLUSIONS

In this article, we presented the different DPL logic styles aiming at Hiding the cryptoprocessors activity to thwart the side-channel attacks. Although the DPL logic is based on an elegant manner to obtain secure implementations, flaws exist at logical and physical level. The different logic styles are more or less able to counteract these negative effects but often with an higher complexity or back-end design. This paper permits the understanding of the main DPL style and draws a comparison between them in order to help the pros and the cons analysis. Research on new DPL styles is still active to improve the robustness and keep a good compromise with complexity and performances requirements.

Figure 1 .

 1 Figure 1. WDDL AND gate with the Early Evaluation flaw.

Figure 2 .

 2 Figure 2. (a) Genuine DRSL AND gate and (b) Glitch-free variant.

Figure 3 .

 3 Figure 3. Schematic of the QDI secured (aka SecLib) AND gate (left) and its internal 3OR architecture (right).

Table I DPL

 I PERFORMANCE AND SECURITY FEATURES OVERVIEW. place&route † M AJ stands for the majority gate:M AJ(a, b, c) . = a • b + b • c + c • a.‡ ni is the maximum number of inverters amongst all combinatorial paths.

	Logic Mask	Synchro	Constraints	Tech Speed
			Pre Eval Primitives	Back-end	Bias
	WDDL	no	positive	balanced	high	< 1 /2
			funct only place&route
	MDPL	yes	M AJ †	no	no	< 1 /2
	STTL	no	no		delay on	very	< 1 /4
					sync signal	low
	DRSL	yes	no		no	no	< 1 /2
	Seclib	no	specific lib	back-end	very	< 1 /2
					duplication	low
	IWDDL no	no		netlist post-processing	low < 1 2•n i	‡
	BCDL	no	no		balanced	low	> 1 /2

The pairwise unanimity Boolean gate performs the following computation:(x T , x F , y T , y F , . . . , z T , z F ) → (x T + x F ) • (y T + y F ) • . . . • (z T + z F ).


Marie Larrieu
email: marie.larrieu2@gmail.com

Christophe Vaschalde
email: c.vaschalde@mosaiquesarcheologie.com

Jérôme Kotarba
email: jerome.kotarba@inrap.fr

Carole Puig
email: c.puig@free.fr

Jérôme Ros
email: jerome.ros@umontpellier.fr

Forest exploitation in the plains of early medieval northern Catalonia: Anthracological review

Keywords: charcoal analysis, woodland exploitation, wood fuel, wood trade, Middle Ages, regional review

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

The Early Middle Ages: a turning point in rural landscape dynamics

In the north-western Mediterranean (Mediterranean France, Catalonia), the Early Middle Ages were a period of major change, both regarding landscape structuration and how animal and plant resources were exploited. In fact, the 5 th -6 th centuries saw a restructuration of rural settlements around emerging centers of power, whether political or religious, around new agglomerations and around areas with particular agricultural potential (hills, terraces, wet depressions), favoring the emergence of new trade networks and new dynamics in land use (e.g. [START_REF] Wickham | Framing the Early Middle Ages, Europe and the Mediterranean[END_REF][START_REF] Schneider | Dynamiques spatiales et transformations de l'habitat en Languedoc méditerranéen durant le haut Moyen Âge (VIème-IXème s.)[END_REF][START_REF] Schneider | Cités, campagnes et centres locaux en Gaule narbonnaise aux premiers siècles du Moyen Age (Ve-IXe s.) : une nouvelle géographie, de nouveaux liens[END_REF][START_REF] Schneider | De la fouille des villages abandonnés à l'archéologie des territoires locaux. L'étude des systèmes d'habitat du haut Moyen Age en France méridionale (Ve-Xe siècle) : nouveaux matériaux, nouvelles interrogations[END_REF][START_REF] Ripart | Représentation et gestion de l'espace dans l'Occident médiéval, V-XIIIe siècle[END_REF][START_REF] Ros | Approches croisées de l'occupation et de l'exploitation des campagnes roussillonnaises durant le haut Moyen Âge (Ve -VIIIe siècles)[END_REF].

Over the last few decades, the boom in bioarchaeological research in the north-western Mediterranean made it possible to document these new dynamics, highlighting the continuities and breaks with the Roman era. For example, regarding breeding and meat consumption, this period saw a change in the frequency of exploited taxa, a global decrease in the bone dimensions of the main domestic species as well as changes in mortality patterns (e.g. [START_REF] Forest | A propos de la corpulence des bovins en France durant les périodes historiques[END_REF][START_REF] Duval | Évolution et diversité de la forme du cochon entre l'âge du Fer et la période moderne en Gaule et en France[END_REF][START_REF] Colominas | From Vilauba to Vila Alba: Changes and continuities in animal and crop husbandry practices from the Early Roman to the beginning of the Middle Ages in the north-east of the Iberian Peninsula[END_REF][START_REF] Ros | Approches croisées de l'occupation et de l'exploitation des campagnes roussillonnaises durant le haut Moyen Âge (Ve -VIIIe siècles)[END_REF][START_REF] Mureau | Construction of chrono-stratigraphic samples (CSS) as a support for taxa quantification in zooarchaeology: an example of the use of this new unit of analysis in the Languedoc region (southern France) from Late Antiquity to the High Middle Ages (3-12th c. AD)[END_REF], proving changes in livestock management. Regarding plant production, archaeobotanical research reveals that early medieval agriculture in the north-western Mediterranean was based on a greater diversity of plant species than in the Roman period, particularly in cereal production, with a boom in certain spring (millets) and acid/poor soils (rye) crops. The hypothesis is that early medieval peasants were looking for a certain form of food security, possibly linked to their greater autonomy and the preponderance of small and medium-sized farms (e.g. [START_REF] Ruas | Aspects of early medieval farming from sites in Mediterranean France[END_REF][START_REF] Ros | Approches croisées de l'occupation et de l'exploitation des campagnes roussillonnaises durant le haut Moyen Âge (Ve -VIIIe siècles)[END_REF]Ros et al. in press).

Changes in livestock farming practices, pastoralism and the opening up of new land for the development of new crops are all factors that can lead to important changes in woodland landscapes. Nonetheless, so far in this region, woodlands have been unevenly studied from a bioarchaeological point of view, despite their central role in the economy and daily practices of medieval rural populations.

Forest history in the plains of the medieval north-western Mediterranean: a brief review

In the north-western Mediterranean, palynology provides relatively little information about the vegetation of the Early Middle Ages, as sediments associated with this period are very rarely preserved. Some insights have been gained from pollen sequences from the Marais des Baux in Provence [START_REF] Andrieu-Ponel | Towards the reconstruction of the Holocene vegetation history of Lower Provence : two new pollen profiles from Marais des Baux[END_REF], Marsillargues [START_REF] Planchais | Palynologie lagunaire de l'étang de Mauguio. Paléoenvironnement végétal et évolution anthropique[END_REF], the lido of the Etang de Thau [START_REF] Court-Picon | Paléoenvironnements littoraux depuis 8000 ans sur la bordure occidentale du Golfe du Lion: le lido de l'étang de Thau (carottage SETIF, Sète, Hérault)[END_REF] and the lower valleys of the Hérault and Aude rivers [START_REF] Dolez | Évolution des paysages végétaux en Languedoc durant l'Holocène : apports de la palynologie à l'étude des milieux et des agrosystèmes[END_REF]. More often than not, these studies provide information on local and regional vegetation at the scale of the Sub-Atlantic, without being able to detail the evolution of vegetation during the Early Middle Ages. The Sub-Atlantic was globally characterized by increasing human pressure, resulting in a decrease in forest taxa and an increase in cultivated taxa (most often Olea sp., sometimes Juglans sp.), with some exceptions. For example, at Sète and in the Marais des Baux, a period of resurgence of forest taxa (Quercus pubescens in particular) and a decline in taxa indicative of cultivation has been detected (Court-Picon et al.

2010).

Thanks to the precise dating of archaeological layers, anthracology can provide a more detailed analysis of the evolution of vegetation in the Early Middle Ages. In Languedoc and Provence, between the 5 th and 7 th c., vegetation seems to have evolved differently depending on the locality. Around Dassargues (Languedoc), on the Vidourle plain, L. Chabal [START_REF] André | Habitat et environnement autour de l'étang de l'Or au premier millénaire. Approches pluridisciplinaires[END_REF]Chabal 1997, p. 132-133) hypothesized that the alluvial ash-hornbeam grove had regenerated, echoing a similar but slightly earlier dynamic identified around the pottery workshops at La Quintarié in Clermont-l'Hérault between the 4 th and 6 th c. [START_REF] Fabre | Anthracologie et techniques artisanales : l'économie des combustibles dans l'atelier de La Quintarié et ses résonances en paléo-économie forestière[END_REF].

Mise en forme : J. ROS (23/11/2023) Coastal and/or lagoon settlements appear to have opened the vegetal landscape during the same period. At Bourbou, the sclerophyllous oak woodland exploited for five centuries by potters saw pine trees develop around the 5 th -6 th c. [START_REF] Chabal | Evidence of palaeogeographic constraints on woodlands on the shores of a coastal lagoon during Antiquity: charcoal analysis of the Prés-Bas villa and Le Bourbou (Loupian, Hérault)[END_REF]. In Camargue, where the landscape was much more wooded than it is today, pine trees began to decline in favor of tamarisk from the 4 th to 5 th c., possible result of greater human pressure combined with changes in the sedimentary environment and soil salinity [START_REF] Chabal | Étude anthracologique de la Capelière et synthèse sur l'histoire des boisements en Camargue, de l'âge du Fer au début du Moyen Âge[END_REF]. At Marignane, on the shores of the Etang de Berre, the most mesophilic taxa are a minority within a vegetation dominated by sclerophyllous oak, and disappear definitively after the 7 th c. [START_REF] Vaschalde | Marignane, place de l'Olivier, îlot I1 (Bouches-du-Rhône). Paysage et économie végétale d'un habitat de l'étang de Berre (V e -XII e siècles)[END_REF].

In Catalonia, charcoal studies are pretty rare in rural contexts for this period (e.g. Euba Rementeria and Palet-Martinez 2010) and are only just beginning to take off in urban contexts [START_REF] Vila Moreiras | Paisatge vegetal i gestió del combustible a la plana occidental catalana entre el neolític i l'edat mitjana: estat de la qüestió des de l'anàlisi antracològica[END_REF][START_REF] Bianco | The evolution of wood fuel exploitation in the El Born Market site (Barcelona, Spain) during the 15th-18th centuries starting from charcoal analysis[END_REF][START_REF] Bianco | Multi-site archaeobotanical analysis reveals wood-fuel supply, woodland impact and Mise en forme : J. ROS (23/11/2023) land use around Roman urban centres: The case of Barcino (Barcelona, NE Iberia)[END_REF]. Around l'Esquerda, anthracological studies have identified a few cultivated taxa, in a mainly mesophilous woodland (Cubero i Corpas 2011).

In the north-western Mediterranean, anthracological data are rarer between the 8 th and 10 th -11 th c. The few available sites in Camargue suggest that the process of replacing pine trees with tamarisk continued [START_REF] Chabal | Étude anthracologique de la Capelière et synthèse sur l'histoire des boisements en Camargue, de l'âge du Fer au début du Moyen Âge[END_REF], attesting to a strong anthropisation of the environment, also documented in the 9 th -10 th c. at Augery de Corrège [START_REF] Durand | Les paysages médiévaux du Languedoc (X e -XII e siècles)[END_REF]. At Marignane, an abrupt but momentary opening of the sclerophyllous oak woodland gave way to Ericaceae scrub around the 10 th c. [START_REF] Vaschalde | Marignane, place de l'Olivier, îlot I1 (Bouches-du-Rhône). Paysage et économie végétale d'un habitat de l'étang de Berre (V e -XII e siècles)[END_REF], possibly linked to the development of agropastoral and/or craft activities [START_REF] Durand | Le charbonnage des Ericacées méditerranéennes: approches croisées archéologiques, anthracologiques et historiques[END_REF]. The end of the Marignane sequence is characterized by a regeneration of the sclerophyllous oak woodland tree which, given the persistence of the settlement, seems to be linked to a change in practices rather than to human abandonment. In Languedoc, signs of the opening up of the vegetation environment (cultivated taxa in particular) are evident as early as the 8 th -9 th c. [START_REF] Figueiral | L'apport de l'archéobotanique à la compréhension des habitats médiévaux du Mas de Roux (Castries)[END_REF][START_REF] Figueiral | Exploitation du bois de feu pendant le haut Moyen Âge d'après les charbons de bois de la zone orientale[END_REF][START_REF] Tarrou | L'habitat rural du haut Moyen Âge en France (V e -XI e siècles): dynamiques du peuplement, formes, fonctions et statuts des établissements[END_REF], which leads us to reconsider the extent of the changes observed in the vegetation in the 11 th c. [START_REF] Durand | Les paysages médiévaux du Languedoc (X e -XII e siècles)[END_REF][START_REF] Durand | Natural Sciences (4th-11th century)[END_REF].

Across the area, the pace of research is uneven, and depends largely on local archaeological dynamism, the sensitivity to palaeoenvironmental issues, and the presence of dedicated bioarchaeologists. Over the last decade, the French department of Pyrénées-Orientales, which corresponds to the northern fringe of medieval Catalonia, has been the focus of significant bioarchaeological activity. Carpological and zooarchaeological studies have focused particularly on the medieval period, leading to the production of several reviews (e.g. Ros 2020; [START_REF] Ros | Approches croisées de l'occupation et de l'exploitation des campagnes roussillonnaises durant le haut Moyen Âge (Ve -VIIIe siècles)[END_REF], which confirm the rise of new agropastoral trends and the opening up of new areas for agriculture. However, anthracological studies have long remained ad hoc, despite a corpus of sites that have yielded substantial quantities of charcoal. This significant potential prompted us to carry out the present study, aimed at documenting the composition and state of the early medieval forests in this region.

Material and method

Regional setting

This study focus on the coastal plains of the eastern Pyrénées (French department of the Pyrénées-Orientales), surrounded by the Corbières hills and the lagune of Salses (north), the Pyrenees mountains (west), the Albères hills (south) and the Mediterranean Sea (east) (Fig. 1). The plains are crossed by four west-east oriented coastal rivers: the Agly, the Têt, the Réart and the Tech. Archaeological and geomorphological surveys, as well as medieval written sources indicate that this hydrography has changed over the millennia, but that the valleys were pretty stable during the Roman and early medieval periods [START_REF] Marichal | La transformation du milieu géomorphologique de la plaine du Roussillon et ses conséquences sur son occupation. Premiers résultats[END_REF][START_REF] Calvet | Les cours d'eau des Pyrénées orientales depuis 15 000 ans : état des connaissances et perspectives de recherches[END_REF][START_REF] Puig | Approche chronologique comparée de l'occupation humaine en bordure des étangs de l'intérieur en Roussillon, de la Protohistoire au Moyen Âge. Etangs et marais. Les sociétés méridionales et les milieux humides, de la Protohistoire au XIXe siècle[END_REF][START_REF] Carozza | Impact du petit âge glaciaire sur les plaines alluviales méditerranéennes françaises : apport de la géoarchéologie) l'évolution du bassin du Roussillon[END_REF]). In the past, a greater quantity of wetland areas existed in the plains, drained between the end of the medieval and the beginning of the modern period [START_REF] Puig | Approche chronologique comparée de l'occupation humaine en bordure des étangs de l'intérieur en Roussillon, de la Protohistoire au Moyen Âge. Etangs et marais. Les sociétés méridionales et les milieux humides, de la Protohistoire au XIXe siècle[END_REF]). Among the sites we studied, some were located near these wetlands during the Early Middle Ages (Fig. 1).

In this region, the geological substrate is pretty much the same everywhere, but with dominant limestone in the north, and schists in the south [START_REF] Servant | Carte pédologique de France au 1/100 000, Argelès-sur-Mer Perpignan, Notice explicative[END_REF]. The local vegetation includes elements from the thermo-, meso-and supramediterranean levels [START_REF] Gaussen | Végétation de la moitié orientale des Pyrénées : sol, climat[END_REF][START_REF] Gaussen | Les forêts du Roussillon[END_REF], dominated by mixed evergreen (Quercus ilex) and pubescent (Q. pubescens) oak forest.

According to the average annual rainfall, sub-sectors are distinguished, notably the drier coastal fringe (averages below 600 mm) and the inland area (subhumid type with higher rainfall). The drier coastal fringe is populated by evergreen oak formations, as well as Aleppo pine (Pinus halepensis), lentisk (Pistacia lentiscus) and kermes oak (Quercus coccifera) formations, and, mixed with pubescent and pedunculate oaks on deep soils, cork oak (Q. suber) forests. These species are absent in the inland area, where pubescent oak is more frequently mixed with evergreen oak.

Corpus of archaeological sites

Although their geographical position differs, all of the settlements have yielded archaeological structures testifying to medieval rural occupations, covering a chronology ranging from the 5 th to the 10 th c. AD. (Tab. 1). These settlements were uncovered within the framework of preventive archaeology operations, following various land development projects such as the construction of a TGV line, a high school, and the installation of photovoltaic panels in the field. As a result of these operations, various structures were uncovered (Fig. 2) [START_REF] Kotarba | LGV 66, liaison ferroviaire Perpignan Le Perthus[END_REF][START_REF] Kotarba | Ortaffa, Pyrénées-Orientales, projets de parcs photovoltaïques[END_REF][START_REF] Kotarba | Le Boulou RD 618 -Le Pilà et Plà de Molàs, vestiges de la Protohistoire, de l'époque romaine républicaine et du Moyen Âge au piémont des Albères, rapport final d'opération[END_REF][START_REF] Jandot | Les sites ruraux médiévaux des Vignes de l'Espérance (Banyuls-dels-Aspres, Pyrénées-Orientales)[END_REF][START_REF] Puig | A l'origine du village roussillonnais : Taxo-d'Avall, premiers éléments d'enquête[END_REF]. No evidence of habitation as such was found, but numerous silage areas and planting pits were discovered, notably at sites 1, 2, 5 and 6 (Fig. 1). The numerous storage structures, associated with ovens and hearths, indicate that the settlements correspond to farms with areas of domestic activity. The excavated contexts mainly correspond to accumulation contexts: pits, shafts and silos filled with domestic waste. Sites 4, 5 and 8 have the particularity of having yielded domestic ovens and oven reject pits, some of whose levels were rich in concentrated charcoal fragments. The interpretation of this corpus requires precautions, due to its heterogeneous nature. The sites were not excavated by the same teams, and the studied area and the quantity of studied samples also vary (Tab. 1). These differences in sampling can lead to biases, which must be taken into account for any subsequent analysis.

Sampling and sieving protocol

For all sites, sediment samples were taken for archaeobotanical analysis, in volumes ranging from 3 to 100 liters per sample. Water sieving and/or manual flotation on fine mesh (0,5 mm) were carried out, in order to recover bioarchaeological remains. Some samples, intended solely for charcoal study, were sieved on mesh sizes ranging from 2 mm to 4 mm, avoiding the collection of small-sized charcoal fragments that are difficult to identify [START_REF] Kabukcu | Sampling and quantitative analysis methods in anthracology from archaeological contexts: Achievements and prospects[END_REF].

Identification

The anthracological study was carried out by different specialists on 32 samples. The charcoal fragments were identified on the basis of the observation of the anatomical structure of the wood in three observation planes (transverse, longitudinal tangential and longitudinal radial).

Identification was carried out using a reflection microscope with dark-bright field and x100, x200 and x500 magnification, with the help of reference atlases [START_REF] Jacquiot | Atlas d'Anatomie des Bois des Conifères[END_REF][START_REF] Jacquiot | Atlas d'anatomie des bois des Angiospermes[END_REF][START_REF] Schweingruber | Anatomie europäischer Hölzer[END_REF][START_REF] Vernet | Guide d'identification des charbons de bois préhistoriques et récents[END_REF]) and the reference collection of the bioindicator platform of the Institut des Sciences de l'Évolution de Montpellier (UMR 5554).

The final matrix shows 5,910 observed charcoal fragments.

Results

Representativeness of the results

The results as a whole form a picture of past vegetation that needs to be interpreted taking into account the limitations of the material. The contexts of wood deposits among the studied sites are diverse, some coming from pits, others from ovens. These concentrated deposits are linked to domestic activity: they provide partial palaeoenvironmental information, complementing the interpretations from material issued from scattered deposits. The anthracological information between the different sites is uneven: some sites provided less than 200 identified fragments (site 4), while others have more than 1,000 (sites 5, 7). Taking these limitations into account allows us to provide the most reliable and accurate palaeoenvironmental interpretation possible. The total anthracological corpus (Appendix 1) is based on 5,910 observed charcoals, allowing the identification of 44 taxa, including 40

Angiosperms and 4 Gymnosperms. The presence of stage 1 to 5 vitrification [START_REF] Mcparland | Is vitrification in charcoal a result of high temperature burning of wood[END_REF][START_REF] Vaschalde | Fours à chaux et chaufourniers en france méditerranéenne du moyen âge à l'époque moderne. Approche interdisciplinaire autour des techniques, des savoir-faire et des artisans[END_REF], of nodes, and pieces of bark prevented or limited identification. In the corpus, this represents 9,2% of the observed fragments, with 0,4% undetermined gymnosperms, 8,2% undeterminable, 0,1% undetermined, 0,2% knots and 0,3% pieces of bark.

Composition of the assemblages and woodland identification

The presented diagram (Fig. 3) is synchronic, providing information on the plant assemblages identified over the Early Medieval period (5 th -10 th c. Rosaceae Maloideae. These taxa can be found in the wild in the above-mentioned groups (edge, matorral, shrub formation, riparian), as well as being cultivated.

A group of alluvial forest taxa is identified, composed of Ulmus sp., Fraxinus sp., Corylus sp.

and Tilia sp. This assemblage can be found in major riverbeds and is distinct from the Salix sp., Populus sp. and Alnus sp. assemblages found in minor riverbeds. Pinus t. sylvestris, Fagus sylvatica and Abies alba are species with a mountain affinity. Their discovery in the plains may be evidence of the occasional presence of a few individuals (residual pine colonies, beech trees descending under mesophilic conditions) (Quézel and Médail 2003b). The species proportions are colored according to the vegetation assemblage to which they are assimilated: yellow=mattoral, green=oak forest, orange=pre-forest/hedgerow boundary, pink=potentially cultivated taxa, blue=alluvial/riparian forest, purple=mountain taxa. Site number refers to table 1.

Structuring the corpus

The two dimensions of the "Correspondence Factor Analysis" (Fig. 4) are defined by axis 1 (37,8% inertia) and axis 2 (23% inertia). A third dimension is taken into account, whose axis has an inertia of 18% (Appendix 2). Only the two dimensions that explain a maximum of variance are described here.

DISCUSSION

This anthracological review provides a micro-regional overview of shrub and tree cover during the Early Middle Ages in the plains of northern Catalonia. It allows proposing a model, in the form of an east-west transect, the diagram and the CFA showing different states of vegetation. A gradient of vegetation is observed from the coast to the foothills, with a transition from Ericaceous scrub to sclerophyllous oak forest, then to deciduous oak forest (Fig. 5). This gradient could be explained by: 1) natural factors (different edaphic conditions, altitude) favoring a layering of vegetation, or 2) the strong role of anthropic pressure, with different modes of exploitation depending on the location. The current distribution of potential vegetation and the geography of this area invalidate the first hypothesis: all the sites are located at an altitude of between 10 and 100m, which is too low to explain a bioclimatic layering of vegetation [START_REF] Ozenda | Sur les étages de végétation dans les montagnes du bassin Méditerranéen[END_REF][START_REF] Quézel | Les chênes sclérophylles en région méditerranéenne[END_REF]. The hypothesis of a strong anthropic influence is supported by palynological data, documenting clearings on the plains around 3000 BC, prior to those on the mountains [START_REF] Planchais | Analyses polliniques du remplissage holocène de la lagune de Canet (plaine du Roussillon, département des Pyrénées-Orientales)[END_REF]. For the same period, a greater exploitation of the coastal plains that gradually extended inland has also been documented in the Languedoc [START_REF] Durand | La forêt languedocienne (fin VIII e siècle-XI e siècle)[END_REF]) and the Camargue [START_REF] Chabal | Étude anthracologique de la Capelière et synthèse sur l'histoire des boisements en Camargue, de l'âge du Fer au début du Moyen Âge[END_REF]).

To interpret these differences in the composition and state of the forest cover, we therefore need to carry out a detailed analysis, following the groups highlighted by the CFA (Fig. 4).

For ease of reading, we propose a spatial reconstruction of the vegetation cover documented by the anthracological analysis (Fig. 6).

Role of human pressures in lowland areas: the opening of the matorral and riparian zones

Although the vegetation exploited by the inhabitants of Pujals and Taxo les Gavarettes appear similar, they seem to be in a different state (Fig. 3, 4) that may be explained by differences in landscape management and, more generally, by differences in human pressure on the surrounding land. Pujals inhabitants exploit a relatively dense Ericaceous scrub, with a high proportion of Arbutus unedo (Mesléard andLepart 1989, 1991), and a well-preserved riparian forest, as shown by the presence of alder [START_REF] Gaussen | Les forêts du Roussillon[END_REF]. The documented woodland, beyond being denser and better preserved, could have even been in the process of being closed.

Recolonization of woody species is indeed possible when pastoral pressure decreases, favoring young shoots (and Fabre 2011). Between the Gallo-Roman period and the Middle Ages, this type of dynamic caused by pastoral abandonment was identified at the site of Lunel-Viel in Languedoc, and between the 3 rd and 5 th c., a decrease in agricultural and grazing land [START_REF] Devroey | Catastrophe, crise et changement social: à propos des paradigmes d'interprétation de développement médiéval (500-1100)[END_REF]) is thought to have led to the regeneration of oak woodland in certain regions of Gaul (Durand and Leaveau 2004). At Pujals, the woodland composition suggests little anthropogenic impact or a potential decline in agro-pastoral activity, but data from earlier phases would be needed to confirm this dynamic.

On the other hand, at Taxo les Gavarettes, the scrubland appears to be less dense (higher proportion of Erica) and the presence of willow and poplar, more heliophilous, indicates an open riparian zone [START_REF] Rameau | Flore forestière française : guide écologique illustré, 3, Région méditerranéenne[END_REF]. This open wooded landscape dominated by Erica scrub is echoing the pollen sequence of Marsillargues in Languedoc, where a peak of Erica arborea associated with a decline in the sclerophyllous oak forest indicates an opening of the environment around the 9 th century [START_REF] Durand | Les paysages médiévaux du Languedoc (X e -XII e siècles)[END_REF]. At Taxo, Quercus coccifera/ilex and Q. suber (Fig. 3) are evidence of a sclerophyllous oak woodland and a cork oak forest in a vestigial state following a major opening up [START_REF] Molinier | La forêt face aux incendies[END_REF]. This opening up can be explained by repeated cutting to obtain fuel and/or of burning to open up agro-pastoral areas [START_REF] Durand | La forêt languedocienne (fin VIII e siècle-XI e siècle)[END_REF], which favours Erica sp. (Mesléard andLepart 1989, 1991).

The significant anthropic pressure exerted on the wooded environment can be explained by the site's agricultural and/or craft vocation, as evidenced by the huge silage area (2,000 silos) and the discovered ovens, the function of which has yet to be documented [START_REF] Puig | A l'origine du village roussillonnais : Taxo-d'Avall, premiers éléments d'enquête[END_REF]).

In the Mediterranean, the Erica genus has been exploited, maintained and perhaps even cultivated for charcoal-making since protohistoric times [START_REF] Durand | Le charbonnage des Ericacées méditerranéennes: approches croisées archéologiques, anthracologiques et historiques[END_REF][START_REF] Durand | Le charbonnage en fosse : approche ethnoarchéologique d'une pratique méconnue dans le Rif marocain[END_REF]. Prized by blacksmiths, this charcoal was also used in domestic contexts [START_REF] Gaucher | Le site de l'impasse Turcan. Artisanat et entrepôt aux abords du port de la ville antique de Forum Iulii (Fréjus, Var)[END_REF]. Although there is no evidence of charcoal-making at Taxo les Gavarettes, it seems clear that Ericaceae had a special status there.

Variable human pressure in inland areas: on oak woods and alluvial forests

Some of the sites, located further inland, appear to have developed a fuel economy based on the exploitation of oak woods and alluvial forests. Although these sites all correspond to modest scale rural occupations, whose economy is centered on farming and livestock rearing, their impact on the forest landscape seems to vary, suggesting differences in pressure on the surrounding environment.

Among these sites, Camps de la Ribera (site 4) and Vignes de l'Espérance (7) are structured around Quercus coccifera/ilex (most probably Q. ilex) (Fig. 4). At Camps de la Ribera, the results are issued from a single kiln (Appendix 1). Given the nature of the only studied context, the large proportion of evergreen oak certainly reveals a strong human selection, and therefore results have scarce paleoenvironmental value (Kabucku and Chabal 2021). At Vignes de l'Espérance, sclerophyllous oaks are accompanied by Quercus deciduous, Acer sp.

and Phillyrea/Rhamnus alaternus (Fig. 3). This composition bears witness to a stage in the dynamics of competition between holm oak and white oak, already documented in Protohistoric and Ancient Languedoc [START_REF] Thiébault | Characterization and Palaeoecological Charcoal Assemblages during Late and Post-Glacial Phases in Southern France[END_REF][START_REF] Chabal | Les potiers, le bois et la forêt à l'époque romaine, à Sallèles d'Aude (Ier -IIIe s[END_REF]). In the north-western Mediterranean, human pressure (e.g. repeated clear-cutting) tends to favor the holm oak, which grows back more vigorously thanks to its permanent foliage [START_REF] Espelta | Resprouting Dynamics[END_REF].

This phenomenon is reflected anthracologically by an increase in the frequency and dominance of holm oak in the studied assemblages [START_REF] Chabal | Les potiers, le bois et la forêt à l'époque romaine, à Sallèles d'Aude (Ier -IIIe s[END_REF]), as at Vignes de l'Espérance. This anthropogenic pressure is confirmed by the presence of other taxa (e.g.

Erica sp., Cistus sp.), identified by both anthracological and carpological remains [START_REF] Ros | ans d'agriculture en Roussillon : Productions végétales, pratiques et terroirs protohistoriques, antiques et médiévaux[END_REF].

At Vignes de l'Espérance, the opening of the environment is thought to have been favored by pastoral pressure and the exploitation of wood for fuel [START_REF] Machado Yanes | Analyse anthracologique des sites d'époque wisigothique sur la ligne LGV : Toulouges Baltasà, Canohès Manresa et Ponteilla Les Bagueres[END_REF]. The presence of Corylus sp. and Fraxinus sp. also testifies to the existence of a sparse alluvial woodland, benefiting from the moisture of the streams flowing into the Tech [START_REF] Leroyer | Environnement et anthropisation du milieu durant l'âge du Bronze dans le Bassin parisien : l'apport des données polliniques et de la modélisation du couvert végétal[END_REF].

In sites 1 to 3 (Baltasà, Manresa, Les Baguères 56) and 8 (Le Pilà), the forest landscape is dominated by Quercus deciduous, probably Q. pubescens (Fig. 4), in mixed woodlands also populated by Q. coccifera/ilex, as well as Buxus sempervirens for sites 2 and 3 (Fig. 3). Ulmus sp., in association with Fraxinus sp., forms a mesophilic alluvial plain forest [START_REF] Chabal | Forêts et sociétés en Languedoc (Néolithique final, Antiquité tardive)[END_REF][START_REF] Dufour | Forêts riveraines des cours d'eau et ripisylves : spécificités, fonctions et gestion[END_REF]. The wooded landscape is therefore little degraded, but the ratio between evergreen and deciduous oaks suggests that the oak forest is beginning to be exploited. The deciduous oak forest has been exploited (coppiced?) for a sufficiently short period of time and/or not intensively enough for Quercus ilex to be dominant, and the alluvial forest is maintained and provides fuel. This type of forest, richer in elm than ash, is similar to the dense alluvial forests identified in the medieval Camargue [START_REF] Chabal | Étude anthracologique de la Capelière et synthèse sur l'histoire des boisements en Camargue, de l'âge du Fer au début du Moyen Âge[END_REF].

Despite the numerous wetlands that existed in the vicinity of sites 1 to 3 in the Middle Ages, the anthracological samples reveal little trace of riparian tree strata. This is a cause for concern, as it has been suggested that lands along the water's edge were exploited for local agricultural production (millets, flax cultivation and retting) and livestock rearing (production of bedding and fodder) [START_REF] Ros | Approches croisées de l'occupation et de l'exploitation des campagnes roussillonnaises durant le haut Moyen Âge (Ve -VIIIe siècles)[END_REF]. The exploitation of the riparian forest, prior to total clearing, leads to a vegetation dominated by Salix sp. [START_REF] Dufour | Forêts riveraines des cours d'eau et ripisylves : spécificités, fonctions et gestion[END_REF]. In these sites, the total absence of willow and the presence of monocotyledonous charcoal (perhaps reed or cane), and seeds and stems of seasonal to permanent amphibian taxa suggest the existence of a very open wetland [START_REF] Ros | ans d'agriculture en Roussillon : Productions végétales, pratiques et terroirs protohistoriques, antiques et médiévaux[END_REF], raising the question of how long these areas had been exploited, and potentially cleared before the medieval period. In contrast, site 8, located on the banks of the Tech river, delivered a wide variety of riparian taxa, indicating the existence of substantial woodland near the river.

Finally, the presence of fruit taxa (e.g. Rosaceae, Olea europaea, Vitis vinifera) in various sites raises the question of their status, as evidence of the openness of the area (pre-forest edges and/or hedgerows) or the existence of local arboriculture.

Exchange networks between the plains and mountains

While most of the sites used local species, Pujals stands out for its exceptional proportion of Pinus t. sylvestris (20% of the studied fragments), making it the second most important taxon of the site (Fig. 3). Other taxa with mountain affinities, such as Fagus sylvatica and Abies alba, were also identified in the same samples, raising the question of their origin.

The presence of these taxa in lowland sites, particularly in Languedoc, has sometimes been interpreted as a sign of their presence at low altitude [START_REF] Chabal | Forêts et sociétés en Languedoc (Néolithique final, Antiquité tardive)[END_REF][START_REF] Durand | Les paysages médiévaux du Languedoc (X e -XII e siècles)[END_REF][START_REF] Puertas | Perception palynologique de la gestion du paysage autour de la cité protohistorique de Lattara (Lattes, France)[END_REF], mountain species being able to exceed their range in cooler/humid conditions (Quézel et Médail 2003b). However, Pujals stands out from these sites: the very high quantity of Pinus t. sylvestris charcoal fragments is an anomaly compared with the other medieval sites of the region. If this is a mountain import, the question arises as to the form and role of the imported elements. Pinus sylvestris can be used as timber [START_REF] Davasse | Anthracologie et espaces forestiers charbonnés. Quelques exemples dans la moitié orientale des Pyrénées[END_REF][START_REF] Chabal | Apports récents de l'anthracologie a la connaissance des paysages passés : performances et limites[END_REF], then be reused as fuel, as well as the waste from its manufacture. However, no elements of this type (posts, beams) were identified during the excavations. The initial nature (e.g. green wood, dead wood, architectural wood) of the Pujals pine charcoal could be revealed through entomoanthracological analyses, as certain insects only thrive in certain types of wood [START_REF] Toriti | Traces of Common Xylophagous Insects in Wood Atlas of Identification -Western Europe[END_REF]). Although we cannot confirm that pine was imported from the mountains, it is known by textual archives that during the Late Middle Ages, the Tech river had a role in transporting mountain wood to the plains, for dyeing factories [START_REF] Verna | L'industrie au village. Essai de micro-histoire (Arles-sur-Tech, XIVe et XVe siècles)[END_REF].

At Pujals, other resources are likely to have been imported from the mountain hinterland, in particular rye (Secale cereale). This cereal, which flourished in the eastern Pyrenees from the Late Imperial period onwards, was extremely sporadic and discreet on the early medieval plain, whereas it was systematic in the high-altitude sites [START_REF] Ros | ans d'agriculture en Roussillon : Productions végétales, pratiques et terroirs protohistoriques, antiques et médiévaux[END_REF]Ros et al. in press). At Pujals, the discovery of samples made up of thousands of rye caryopsis, with no other evidence of local harvesting or processing (straw waste, crop weeds), is another anomaly, reinforcing the idea that the consumed plant resources were of allochthonous origin.

Zooarchaeological data does not allow us to confirm or refute this hypothesis, due to the lack of strontium analyses to characterize the local nature of the consumed meat resources. To date, Pujals faunal remains provide evidence of a trade with the coast, notably through the discovery of marine shellfish (cockles, mussels and oysters) [START_REF] Ros | Approches croisées de l'occupation et de l'exploitation des campagnes roussillonnaises durant le haut Moyen Âge (Ve -VIIIe siècles)[END_REF]. Pujals subsistence economy is therefore based on different supply networks, stretching from the mountains to the coast. This raises questions about the site status: is it a site with a particular socio-economic status because of its activities, or the origin of its inhabitants? Or was it a trading site, precursor of a trading economy that did not really take off in Roussillon until the 10 th -12 th c.?

CONCLUSION

This regional compilation has revealed a variable use and state of forest landscapes, depending on the location of the sites. On the coastal fringe, the woodland is very open, in the form of Ericaceae scrub, certainly due to the intensity of local anthropic pressure, whether agricultural, pastoral or artisanal. It remains to be determined whether the Roman occupations on the plains, and in particular the nearby urban agglomeration of Ruscino, played a role in the state of the forests inherited by the early medieval populations or if the opening were caused by the restructuration of rural settlements between the 5 th and the 7 th c. Inland, we observe contrasting situations, with mixed oak woodland and alluvial forest providing most of the fuel used at the various sites. Globally, the local populations did not appear to be evolving in a completely open, deforested landscape, inheriting relatively unspoilt woodland landscapes, although there were signs at several sites that the environment was opening up.

At Pujals, the evidence of a network of exchanges with the mountains and the coast is a unique feature that needs to be studied in greater depth. Isotope analyses of domestic faunal remains would reveal whether these plain-mountain relationships were also expressed through transhumance.

Among the research prospects, two will be explored in the coming years. The first will be to Preliminary anthracological analyses have revealed that in the oldest urban contexts, the fuel mainly consisted of Ericaceae [START_REF] Dimanche | Impact de l'essor urbain sur les boisements forestiers méditerranéens au Moyen Âge : le cas de Perpignan[END_REF]. It now remains to be seen whether fuel management for the growing population was carried out in a reasoned way over the long term, or whether it led to total deforestation of the plain, leading to the establishment of commercial networks enabling the city to be supplied regularly and adequately.

Fig. 1 :

 1 Fig. 1: Distribution of the archaeological sites of the corpus and restitution of disappeared wetlands (from Puig 2009).

Tab. 1 :

 1 Corpus of archaeological sites including an anthracological study. "L" = liter, "-" = no data.

Fig. 2 :

 2 Fig. 2: Types of contexts that provided anthracological remains in the archaeological sites (site number refers to table 1).

Fig. 3 :

 3 Fig. 3: Synchronic anthracological diagram produced in Excel 2003 ACACIA macro (Nourissier et al. 2016).

Fig. 4 :

 4 Fig. 4: Correspondence Factor Analysis (CFA) (60.8% variance) of species occurrences identified from charcoal fragments (blue dots) for each site (red dots). Dark blue taxa are represented, but are not included in the CFA to maintain clarity of representation. Site number refers to table 1.

Fig. 5 :

 5 Fig. 5: Restitution of the gradient of vegetation observed from the coast to the foothills. Site number refers to table 1.

Fig. 6 :

 6 Fig. 6: Spatial reconstruction of forest cover in the plains of northern Catalonia during the Early Middle Ages.

  study earlier phases (Roman period, Second Iron Age) to determine the origin of the forest opening identified on the coastal fringe. The aim will be to determine whether these open Ericaceae formations and degraded riparian zones are a consequence of protohistoric human activity, the expansion of the villae model during the High Empire, or the new rural dynamics of the Early Middle Ages. A second area of research will be to determine how the forest environment changed over the course of the Middle Ages in this region. During the 10 th c., the city of Perpignan took on a central role in northern Catalonia, and experienced a dazzling demographic boom, the consequences of which on the landscape have been little explored.

N°Settlement Locality Studied area Dating Number of sample Sample volume (L) Number of context Context type Archeozoology

	Mise en forme : J. ROS (23/11/2023)
										Type of studies and references
											Carpology	Anthracology
	1	Baltasà	Toulouges	6 hectares	6th-7th c. A.D.	1	700	1	1 well	Ros et al. 2020	-	Machado & Fabre 2011
	2	Manresa	Canohès	7000 m²	6th-8th c. A.D.	7	830	6	4 silos, 1 oven, 1 pit	Ros et al. 2020	Ros et al. 2020 Machado & Fabre 2011
	3	Les Bagueres 56	Ponteilla	-	6th-8th c. A.D.	2	700	2	2 pits	Ros et al. 2020	Ros et al. 2020 Machado & Fabre 2011
	4	Camps de la Ribera	Ponteilla	-	8th-9th c. A.D.	3	30	2	1 oven, 1oven decharge pit	-	Ruas in Ros 2020 Machado & Fabre 2009
									2 hearths, 3
	5	Taxo les Gavarettes	Argelès-sur-Mer	-	5th-10th c. A.D.	1 1	1 1 0	8	silos, 2 oven, 1	-	Ros 2020	Vaschalde unpub
									circulation level
	6	Pujals	Ortaffa	6 hectares	5th-8th c. A.D.	4	49	4	4 pits	Ros et al. 2020	Ros et al. 2020	-
	7 Vignes-de-l'Espérance Banyuls-dels-Aspres	-	Early Middle Ages	4	40	2	2 pits	-	Ruas in Ros 2020	Fabre unpub
	8	Le Pilà	Le Boulou	800 m²	Early Middle Ages	3	128	2	1 oven, 1 oven decharge pit	-	Ros 2020	Poirier 2009

  The predominance of deciduous and evergreen oaks is characteristic of the Mediterranean mixed oak forest[START_REF] Braun-Blanquet | La Chênaie d'Yeuses méditerranéenne (Quercion ilicis)[END_REF] Quézel and Médail 2003 a, b). This mixed oak woodland has different facies depending on the associated species. The holm oak can form, with Acer campestre, A. monspessulanum, Fraxinus sp., Corylus avellana and Tilia platyphyllos, a supramediterranean, thermophilic, mesoxerophilic and acidicline linden-ash-maple forest. In a more humid bioclimate, on deep draining soils, deciduous oak forests (probably Quercus pubescens) develop(Quézel and Médail 2003 a, b).The deciduous oaks associated with Buxus sempervirens found in sites 2 and 3 form boxwood oak forests, often in the form of coppice, or coppice under forest[START_REF] Rameau | Flore forestière française : guide écologique illustré, 3, Région méditerranéenne[END_REF]. The dominant taxa in sites 5 and 6 are Arbutus unedo and Erica sp. In site 5, 62% of fragments were identified as Erica sp. and 10% as Arbutus unedo, and at site 6, 21% were Arbutus unedo and 12% Erica sp. These taxa, together with Juniperus sp., Lamiaceae, Fabaceae, Cistaceae, Cistus sp., and Pistacia sp. form a matorral. Erica arborea and Arbutus unedo are pioneer taxa, characteristic of the maquis, which is the siliceous facies of the matorral,

). Oak woodland species dominate for sites 1 to 4, 7 and 8. Deciduous oaks dominate at site 1 with 21%, and at site 3 with 42%.

Conversely, evergreen oaks (Quercus suber, Q. coccifera/ilex) dominate in sites 2 and 4: 36,2% and 66% of identified fragments. whereas the garrigue (Juniperus sp, Cistus sp, Pistacia lentiscus, Rhamnus alaternus, Quercus coccifera, Fabaceae, Lamiaceae, Buxus sempervirens) develops in calcareous conditions

[START_REF] Rameau | Flore forestière française : guide écologique illustré, 3, Région méditerranéenne[END_REF]

.

Many fruit trees are found in the assemblage: Ficus carica, Vitis vinifera, Olea europaea, Juglans regia, Rosaceae t. Rubus fructicosus, Rosaceae t. Crataegus, Rosaceae Prunoideae,

  The spatial representation of the variable points makes it possible to draw a cloud of points divided into three sub-clouds. The first group is located in the positive pole of axis 1 and negative pole of axis 2. It consists of sites 5 and 6, whose assemblages are mainly based on the taxa Erica sp. and Arbutus unedo. They are accompanied by Populus/Salix towards site 5, and Alnus towards site 6. Two of the taxa have a littoral affinity, namely Myrtus communis and Pinus t. halepensis/pinea, and Myrtus may belong to scrubland vegetation. For site 6, the taxa Juglans regia, Fagus sylvatica, and Pinus t. sylvestris are added to the assemblage. These taxa are classified as additional variables, so that their rarity does not distort the CFA to the point of rendering it unreadable. The second group is drawn in the negative pole of axis 2. It represents the assemblage of site 7, which is similar to site 4 due to the strong contribution of Quercus evergreen. The dominant variables in this assemblage are Quercus evergreen,

	campestre (3,8%), Acer cf. monspessulanum (3,6%), Arbutus unedo (7%), Rosaceae
	Prunoideae (10,6%), Quercus evergreen (4,7%), Phillyrea/Rhamnus alaternus (4%) for the
	negative pole. The mixed sclerophyllous oak woodland taxa (Acer sp., Quercus deciduous)
	and pre-forest taxa (Phillyrea/Rhamnus alaternus, Arbutus unedo, Rosaceae Prunoideae) are
	found in opposition to the taxa of boxwood deciduous oak, edges (Rosaceae t. Crataegus) and
	mesophilic (Ulmus sp.) woodlands.

Site number refers to table

1

.

Axis 1 represents the largest deviation from independence. The variables (Appendix 3) that contribute most to its inertia are: Erica sp. (31%), Arbutus unedo (32,7%), Populus/Salix (4,5%), Alnus sp. (4,5%), which cluster in the positive pole, and Quercus evergreen (13,2%), Quercus suber (3,4%) in the negative pole. This axis thus allows us to oppose the taxa of sclerophyllous oak forests to the taxa characteristic of maquis and riparian vegetation. For axis 2, the contributing variables are Quercus deciduous (23,8%), Buxus sempervirens (5,5%), Ulmus sp. (5,5%) and Rosaceae t. Crataegus (8,2%) for the positive pole, and Acer cf.

Rosaceae Prunoideae, Acer cf. campestre, Phillyrea/Rhamnus alaternus. This group is structured around sclerophyllous oak and maple taxa, which is supported by the less contributing variable Acer cf. monspessulanum. In the third group are the positive poles of axis 1 and 2. Sites 1 to 3 and 8, structured around the variables Quercus deciduous, Buxus sempervirens, Rosaceae t. Crataegus and Ulmus sp. The assemblages of these sites are thus characterized by mesophilic oak woodland and pre-forest edge species.

ACKNOWLEDGEMENTS

This research could not have been possible without the work carried out over many years by various institutions, companies and colleagues working in Roussillon, in particular the Departmental Archaeological Service of Pyrénées-Orientales, Inrap, Acter, as well as the many archaeologists whose implication was essential to constitute the archaeobotanical corpus. We would also like to thank Allowen Evin (ISEM), whose support made it possible to carry out this work and produce this paper.

Funding: This project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 852573, PI: A. Evin).

Mise en forme : J. ROS (23/11/2023)