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Humus is the place of key tree nutrition processes. However, it remains a compartment of the ecosystem still under studied for all major nutrients and beneficial elements other than C and N. Thus, in a context of increasing pressure on forests, it matters to understand the dynamics of the elements from their input into the humus to their output towards the soil. The aims of this thesis are: (1) to identify the mechanisms and factors responsible of the major element dynamics (C, N, P, K, Ca, Mg, Mn, S, Si, Al and Fe), (2) to determine the relationships between these elements and (3) to specify the place of the humus in tree nutrition. To answer these objectives, a conceptual model based on the identification of humus inputs and outputs and the possible mechanisms present at the humus level was elaborated. The results of this thesis suggest that the element output fluxes depends on processes and reactions accelerating or delaying their release from the humus. The element release rates in the soil depend on their forms in the humus inputs (soluble, organic molecules, biominerals) and their location in the plant tissues (leaf blade vs. vein) supplying the humus. The element dynamics is also influenced by recycling reactions within the humus, such as biotic or abiotic precipitation through testate amoebae (Si, P, Ca and Mn), precipitates around hyphae (Ca, Mn, P, and K) or amorphous Si precipitates. These reactions control the mean residence times of the elements and their leaching gradient below the humus: the most soluble and least immobilized elements will be leached more rapidly and will have lower residence time. The release of these elements below the humus is another important factor that affects the availability of these elements to trees. During the growing season, when the trees upatke soil solution, less than 25% of K and P are released from humus. The ability of the soil to hold the elements produced during periods of senescence and dormancy is fundamental to ensure the sustainability of the ecosystem. In this thesis, the particles leaving the humus were quantified for the first time. In addition to their role on pedogenesis and the dynamics of C, this particle flux below the humus could increase the cation-exchange capacity of the soil and its ability to hold these leached elements during the dormant period.; L’humus est le siège de processus clés pour la nutrition des arbres. Cependant, il reste un compartiment de l’écosystème encore peu étudié pour l’ensemble des nutriments et éléments bénéfiques autre que C et N. Ainsi, dans un contexte où les pressions exercées sur les forêts augmentent depuis quelques années, il est important de comprendre la dynamique comparée des éléments de leur arrivée dans l’humus à leur sortie dans le sol. Les objectifs de cette thèse sont (1) d’identifier les mécanismes et les facteurs responsables de la dynamique des éléments majeurs (C, N, P, K, Ca, Mg, Mn, S, Si, Al et Fe), (2) de déterminer les relations entre ces éléments et (3) de préciser la place de l’humus dans la nutrition de l’arbre. Pour répondre à ces objectifs, un modèle conceptuel basé sur l’identification des flux entrant et sortant de l’humus et des possibles mécanismes présents dans le niveau de l’humus a été élaboré. Les résultats obtenus dans cette thèse suggèrent que la dynamique des éléments et leur disponibilité pour l’arbre à la sortie de l’humus dépendent d’un ensemble de processus et réactions accélérant ou retardant leur départ de l’humus. Les vitesses de libération des éléments dans le sol dépendent de leurs formes dans les entrées de l’humus (soluble, molécules organiques, biominéraux), de leur localisation dans les feuilles (limbe vs. nervure) et des tissus des végétaux plus ou moins facilement dégradables alimentant l’humus. La dynamique des éléments est également influencée par des réactions de recyclage à l’intérieur de l’humus, comme des précipitations biotiques ou abiotiques. Les éléments être utilisés par les amibes à thèques (Si, P, Ca et Mn), précipités autour des hyphes (Ca, Mn, P, et K) ou encore être précipité sous forme de plage amorphes (Si). Ces réactions contrôlent les temps moyens de résidence des éléments : les éléments les plus solubles, localisés dans des tissus plus dégradables et les moins recyclés seront lessivés plus rapidement et auront des temps de résidence plus bas. La période libération des éléments sous l’humus intervient sur leur disponibilité pour l’arbre de ces éléments. En période de végétation où les éléments sont directement disponibles pour les arbres, moins de 25% de K et P sont libérés. La capacité du sol à retenir les éléments produits en période de sénescence et de dormance sera fondamentale pour assurer la pérennité de l’écosystème. Lors de cette thèse, les particules en sortie de l’humus ont été quantifiées pour la première fois. Outre le rôle sur la pédogenèse en général et la dynamique du C, ce flux particulaire sous l'humus pourrait augmenter la capacité d’échanges cationique des sols et sa capacité à retenir ces éléments lessivés en période de dormance.

International audience; AbstractKey messageA remote sensing-based approach was implemented to detect the effect of a late spring frost on beech forests in the Mediterranean mountain region. The analysis of spatio-temporal variability of frost effects on normalised difference vegetation index (NDVI) highlighted the distribution of the canopy damage across the forest according to geomorphic factors such as slope, aspect, and altitude.ContextIncreased intensity and frequency of extreme temperatures such as late spring frosts and heat waves represent the main drivers affecting forest ecosystem structure and composition in the Mediterranean region.AimsThe main objective of this study was to evaluate the effects of a late spring frost disturbance, which occurred during spring 2016 in southern Italy, through the assessment of the spatial pattern of the damage to the beech forest canopy associated with the peak decrease in normalised difference vegetation index (NDVI), and the analysis of the NDVI temporal recovery after this frost disturbance.MethodsThe forest areas affected by frost were detected through the NDVI differencing technique based on Landsat 8 (OLI/TIRS) imagery time series. The influence of local geomorphic factors (i.e., aspect, elevation, and slope) on forest NDVI patterns was assessed by means of a generalized additive model (GAM).ResultsA rather counterintuitive NDVI patterns emerged according to the forest exposition, with NDVI significantly higher on the north facing areas than the southerly ones. The main canopy damage occurred at about 1250 m and reached up to 1500 m asl, representing the altitudinal range affected by the frost disturbance. Finally, the full canopy recovery occurred within 3 months of the frost event.ConclusionThe analysis of seasonal Landsat 8 image time series related to local geomorphic factors, such as aspect, slope, and altitude, and plant phenology on a frost event date, contributed to highlight the NDVI spatio-temporal variation and canopy recovery of a Mediterranean mountain beech forest.

International audience; This study evaluates the performances of the new version (v.5.1) of 3D-CMCC Forest Ecosystem Model (FEM) in simulating gross primary productivity (GPP), against eddy covariance GPP data for 10 FLUXNET forest sites across Europe. A new carbon allocation module, coupled with new both phenological and autotrophic respiration schemes, was implemented in this new daily version. Model ability in reproducing timing and magnitude of daily and monthly GPP fluctuations is validated at intra-annual and inter-annual scale, including extreme anomalous seasons. With the purpose to test the 3D-CMCC FEM applicability over Europe without a site-related calibration, the model has been deliberately parametrized with a single set of species-specific parametrizations for each forest ecosystem. The model consistently reproduces both in timing and in magnitude daily and monthly GPP variability across all sites, with the exception of the two Mediterranean sites. We find that 3D-CMCC FEM tends to better simulate the timing of inter-annual anomalies than their magnitude within measurements' uncertainty. In six of eight sites where data are available, the model well reproduces the 2003 summer drought event. Finally, for three sites we evaluate whether a Published by Copernicus Publications on behalf of the European Geosciences Union. 480 A. Collalti et al.: Validation of 3D-CMCC Forest Ecosystem Model (v.5.1) more accurate representation of forest structural characteristics (i.e. cohorts, forest layers) and species composition can improve model results. In two of the three sites results reveal that model slightly increases its performances although, statistically speaking, not in a relevant way.

International audience; Substituting renewable forms of energy for fossil fuels is a real challenge in developed countries and fuel wood will undoubtedly have an important role to play in forested areas. However, fuel wood harvesting may deplete nutrients in forest ecosystems and adversely affect site fertility in the long term. We compared the cost of compensatory fertilising and liming operations between whole-tree harvesting and traditional stem-only harvesting. We worked in beech (Fagus sylvatica L.) stands in eastern France and two site fertility classes (high and low). We used a growth model to calculate the nitrogen, calcium, potassium, magnesium and phosphorus contents of fine woody debris (FWD, diameter < 7 cm) and compared the benefits of selling this fine wood for energy to the cost of compensatory fertilising and liming. We showed that compensating and liming are more expensive than the profits derived from selling fine fuel wood, except when fuel wood prices rise considerably. This was mainly due to the high proportion of bark in FWD compared with other tree compartments. Indeed, bark is especially rich in nutrients such as nitrogen and phosphorus, which were the most costly nutrients to replace. Our study highlights the importance of considering the environmental costs of fuel wood production at the stand scale. Whenever fertilisation or liming is necessary, we recommend compensating at least for calcium and magnesium, two nutrients that account for a very small part of the costs. In any case, fertilisation should only be used if long-term site fertility has been compromised.

Soil carbon dioxide (CO2) efflux is an important component of the carbon (C) cycle but the biological and physical processes involved in soil CO2 production and transport are not fully understood. To improve our knowledge, we present a new approach to measure simultaneously soil CO2 concentrations and efflux, and their respective isotopic signatures (C-13-CO2). To quantify soil air (CO2)-C-13 and (CO2)-C-12 concentrations, we adapted a method based on CO2 diffusion from soil pores into tubes with a highly gas-permeable membrane wall. These tubes were placed horizontally at different depths in the soil. Air was sampled automatically from the tubes and injected through a diluting system into a tuneable diode laser absorption spectrometer. The CO2 and C-13-CO2 vertical profiles were thus obtained at hourly intervals. Our tests demonstrated the absence of fractionation in the membrane tubes for C-13-CO2. Subsequently, we set up field experiments for two forest soils, which showed that natural soil CO2 concentrations and C-13-CO2 were not affected significantly by the measurement system. While C-13-CO2 in air-filled pores below 5cm was constant over 3days, we observed large diurnal variations in C-13-CO2 efflux. However, the average difference between the two measurements was close to -4.4 parts per thousand, which supports steady-state diffusion over this 3-day period. This new method seems to be a very effective way to measure the C-13-CO2 profile of the soil atmosphere, and demonstrates that the fractionation that occurs during diffusion is the main transport process that affects the C-13-CO2 of the soil CO2 efflux on a daily timescale while advection may account for within-day variations.

An unbiased partitioning of autotrophic and heterotrophic components of soil CO2 efflux is important to estimate forest carbon budgets and soil carbon sequestration. The contribution of autotrophic sources to soil CO2 efflux (FA) may be underestimated during the daytime as a result of internal transport of CO2 produced by root respiration through the transpiration stream. Here, we tested the hypothesis that carbon isotope composition of soil CO2 efflux (dFS) in a Eucalyptus plantation grown on a C4 soil is enriched during the daytime, which will indicate a decrease in FA during the periods of high transpiration. Mean dFS of soil CO2 efflux decreased to -25.7 parts per thousand during the night and increased to -24.7 parts per thousand between 11:00 and 15:00 h when the xylem sap flux density was at its maximum. Our results indicate a decrease in the contribution of root respiration to soil CO2 efflux during the day that may be interpreted as a departure of root-produced CO2 in the transpiration stream, leading to a 17 parts per thousand underestimation of autotrophic contribution to soil CO2 efflux on a daily timescale.

Soils contain the largest carbon (C) reservoir on Earth, but the mean residence time (MRT) of soil C is often poorly estimated, despite its importance for assessing the efficiency with which soils may serve as a sink for atmospheric C. The objective of this study was to evaluate how the structure of simple models of soil C dynamics affects the MRT determined from isotope-mixing experiments, using data from field studies with either artificial labelling (FACE) or C3/C4 vegetation change. We first highlighted theoretically how non-steady-state conditions and the model structure (one single, two successive, or two parallel C pools) can have an impact on the MRT assessment. We then tested these different model structures against published data on the dynamics of different soil organic matter separates and their constituents. Our findings indicated that many of the reviewed studies assumed wrongly that the system was at steady state or could be described by a single-pool approach. To select the correct model, exact knowledge of C input rates and several data points are needed from the beginning of the experiment. For steady-state conditions an apparent temporal change of MRT computed from a single-pool model is thus a clear indicator that a two-pool approach must be chosen. The errors made by the wrong choice of model varied with the length of the experiment and usually resulted in an over-estimate of MRT by a factor of 1.15 for some data published on physical size separates, but by a factor of up to 11 for individual microbial biomarkers such as muramic acid.

International audience; Root respiration consumes an important part of the daily assimilated carbon but the magnitude of this component of forest net ecosystem exchange and its partitioning among the different energy demanding processes in roots are still poorly documented. 5-month old Eucalyptus cuttings were grown in a greenhouse in pot filled with coarse sand. They were fertilized with three different amounts of a slowrelease fertilizer with the doses of 8, 24 and 48 g of nitrogen per plant. Root respiration was measured using an infrared gas analyser by perfusing air through the pot on 9 plants per treatment on three dates 14 days apart. Measure of root respiration of the three treatments over time was made in order to obtain a large range of growth and nutrient uptake. Root respiration normalized at 22°C ranged from 0.09 to 0.23 gC d−1 for the three treatments during all the experiment. It was well predicted with a model that includes root growth rate and root nitrogen content. The nitrogen related maintenance coefficient was negatively correlated to the root nitrogen concentration suggesting a decrease in protein turnover with increasing fertility. Growth rate of fine root in a virtual stand was simulated using age-related allometric equations and further used to estimate root respiration in the field. Simulated root respiration increased over time from 0.39 to 3.14 gC m−2 d−1 between 6 and 126 months assuming a turnover of 2 yr−1 for fine roots. The major fraction of simulated root respiration in the field (78–92%) was used for the maintenance of the existing biomass.

Temporal variations of carbon isotope composition of soil CO2 efflux (FS and δ13 CFS) at different time scales should reflect both temporal variations of the climate conditions that affect canopy functioning and temporal changes in the relative contribution of autotrophic respiration to total FS. A tunable diode laser spectrophotometer (TDLS) was installed in the Hesse forest (northeast of France) early during the 2007 growing season to determine the seasonal and daily variability in δ13 CFS. This method, based on the measurement of the absorption of an infrared laser emission at specific wave lengths of the 13 CO2 and 12 CO2, allows the continuous monitoring of the two isotopologues. The concentrations of the two isotopologues in FS were continuously monitored from June to November 2007 using chamber method and Keeling plots drawn from nocturnal accumulation of CO2 below the canopy. These TDLS measurements and isotope ratio mass spectrometer based Keeling plots gave very similar values of δ13 CFS, showing the reliability of the TDLS system in this context. Results were analysed with regard to seasonal and daily changes in climatic and edaphic variables and compared with the δ13 CofCO2 respired by roots, litter and soil incubated under controlled conditions. Pronounced daily as well as seasonal variations in δ13 CFS were recorded (up to 1.5‰). The range of variation of δ13 CFS was of the same order of magnitude at both diurnal and seasonal scales. δ13 CFS observed in the field fluctuated between values of litter and of root respiration recorded during incubation, suggesting that temporal (and probably spatial) variations were associated with changes in the relative contribution of the two compartments during the day and during the season.

International audience; Half-hourly measurements of the net exchanges of carbon dioxide and water vapor between terrestrial ecosystems and the atmosphere provide estimates of gross primary production (GPP) and evapotranspiration (ET) at the ecosystem level and on daily to annual timescales. The ratio of these quantities represents ecosystem water use efficiency. Its multiplication with mean daylight vapor pressure deficit (VPD) leads to a quantity which we call "inherent water use efficiency" (IWUE*). The dependence of IWUE* on environmental conditions indicates possible adaptive adjustment of ecosystem physiology in response to a changing environment. IWUE* is analyzed for 43 sites across a range of plant functional types and climatic conditions. IWUE* increases during short-term moderate drought conditions. Mean annual IWUE* varied by a factor of 3 among all sites. This is partly explained by soil moisture at field capacity, particularly in deciduous broad-leaved forests. Canopy light interception sets the upper limits to canopy photosynthesis, and explains half the variance in annual IWUE* among herbaceous ecosystems and evergreen needle-leaved forests. Knowledge of IWUE* offers valuable improvement to the representation of carbon and water coupling in ecosystem process models.

International audience; The effects of climate changes on carbon and water fluxes are quantified using a physiologically multi-layer, process-based model containing a carbon allocation model and coupled with a soil model (CASTANEA). The model is first evaluated on four EUROFLUX sites using eddy covariance data, which provide estimates of carbon and water fluxes at the ecosystem scale. It correctly reproduces the diurnal fluxes and the seasonal pattern. Thereafter simulations were conducted on six French forest ecosystems representative of three climatic areas (oceanic, continental and Mediterranean areas) dominated by deciduous species (Fagus sylvatica, Quercus robur), coniferous species (Pinus pinaster, Pinus sylvestris) or sclerophyllous evergreen species (Quercus ilex). The model is driven by the results of a meteorological model (ARPEGE) following the B2 scenario of IPCC. From 1960 to 2100, the average temperature increases by 3.1 °C (30%) and the rainfall during summer decreases by 68 mm (−27%). For all the sites, between the two periods, the simulations predict on average a gross primary production (GPP) increase of 513 g(C) m−2 (+38%). This increase is relatively steep until 2020, followed by a slowing down of the GPP rise due to an increase of the effect of water stress. Contrary to GPP, the ecosystem respiration (Reco) raises at a constant rate (350 g(C) m−2 i.e. 31% from 1960 to 2100). The dynamics of the net ecosystem productivity (GPP minus Reco) is the consequence of the effect on both GPP and Reco and differs per site. The ecosystems always remain carbon sinks however the sink strength globally decreases for coniferous (−8%), increases for sclerophyllous evergreen (+34%) and strongly increases for deciduous forest (+67%) that largely benefits by the lengthening of the foliated period. The separately quantified effects of the main variables (temperature, length of foliated season, CO2 fertilization, drought effect), show that the magnitude of these effects depends on the species and the climatic zone.

A forest ecosystem model (CASTANEA) simulating the carbon balance (canopy photosynthesis, autotrophic and heterotrophic respirations, net ecosystem exchange, wood and root growth) and the water cycle (transpiration, soil evaporation, interception, drainage and soil water status) is tested with data from a young beech forest (Fagus sylvatica L.). For this purpose, the model validity is assessed by comparison between net CO2 and H2O fluxes simulated and measured by the eddy flux technique over one year. In addition, most of the sub-models describing the processes mentioned above are tested using independent measurements from the same forest stand: tree growth, branch photosynthesis, wood and soil respirations, sap flow and soil water content. Most of the input parameters (both weather and plant characteristics) are measured in the same experimental site (i.e. Hesse forest) independently of the validation dataset (none has been fitted to match the output data, except rainfall interception parameters); some are from other beech sites or from literature. Concerning the radiative transfer, the model reproduces the measured exponential PAR extinction and provides a good estimate of the net radiative budget, except during winter. At the branch scale, simulated photosynthesis and transpiration of sun-leaves are close to the measurements.We show also, using model simulations, that the seasonal decrease of measured net photosynthesis at the branch level could be explained by a decrease in leaf nitrogen content during the leafy season. At stand scale, a good correlation was obtained between simulated and observed fluxes both on a half-hourly basis and on a daily basis. Except at the end of the leafy season, the model reproduces reasonably well the seasonal pattern of both CO2 and H2O fluxes. Finally, even if there are some discrepancies between model estimations and fluxes measured at stand scale by eddy covariance, the model simulates properly both annual carbon and water balances when compared with the sum of the measured local fluxes. The remaining differences question the scaling up process when building such a model and the spatial footprint of eddy fluxes measurements.

A forest ecosystem model (CASTANEA) is developed with the aim to bridge the gap between soil–vegetation–atmosphere (SVAT) and growth models. A physiologically multi-layer process-based model is built, completed with a carbon allocation model and coupled with a soil model. CASTANEA describes canopy photosynthesis and transpiration, maintenance and growth respiration, seasonal development, partitioning of assimilates to leaves, stems, branches, coarse and fine roots, evapotranspiration, soil heterotrophic respiration, water and carbon balances of the soil. Net primary productivity (NPP) is calculated as the difference between gross photosynthesis and plant respiration. The net ecosystem exchange (NEE) between soil-plant system and atmosphere is calculated as the difference between gross photosynthesis and total respiration (soil + plants). The meteorological driving variables are global radiation, rainfall, wind speed, air humidity and temperature (either half-hourly or daily values). A complete description of the model parameterization is given for an eddy flux station in a beech stand (Hesse, France). A parametric sensitivity analysis is carried out to get a classification of the model parameters according to their effect on the NEE. To determine the key input parameters, a +10% or −10% bias is applied on each of the 150 parameters in order to estimate the effect on simulated NEE. Finally 17 parameters, linked to photosynthesis, vegetative respiration and soil water balance, appear to have a significant effect (more than 2.5%) on the NEE. An uncertainty analysis is then presented to evaluate the error on the annual and daily NEE outputs caused by uncertainties in these input parameters. Uncertainties on these parameters are estimated using data collected in situ. These uncertainties are used to create a set of 17,000 simulations, where the values of the 17 key parameters are randomly selected using gaussian random distributions. A mean uncertainty of 30% on the annual NEE is obtained. This uncertainty on the simulated daily NEE does not totally explain the discrepancies with the daily NEE measured by the eddy covariance technique (EC). Errors on daily measurements by EC technique and uncertainty on the modelling of several processes may partly explain the discrepancy between simulations and measurements.

Thèse soutenue le 26 février 2004 N° d'ordre : 2932 Co-directeurs de thèse : Forgeard, F. Maître de Conférence - Université de Rennes I Nys, C. Directeur de recherches - INRA de Nancy. [Unité Biogéochimie des Ecosystèmes Forestiers] Bibliog. : 293-307 Annexes : 311-370 Diffusion du document : totale Diplôme : other; Dans le contexte de la menace de l'élévation de la teneur en CO2 atmosphérique, quelle est la capacité de stockage de carbone de la hêtraie de plaine acidophile de l'Ouest de l'Europe ? La démarche consiste à travailler à l'échelle du peuplement, en compartimentant les stocks et les flux de carbone, et en suivant leurs évolutions au cours de la révolution forestière, à l'aide de l'outil chronoséquentiel. La biomasse arborescente est le déterminant majeur de la capacité de stockage. Les pertes de carbone sont principalement dues aux exportations de bois et à la respiration de l'écosystème. Le rôle du sous-bois semble non négligeable. Le peuplement de hêtres est un puits croissant de carbone dont la capacité de stockage s'amoindrit en vieillissant. Les pratiques sylvicoles et les tempêtes altèrent cette fonction. La capacité de stockage de la hêtraie est donc fonction de l'âge moyen des peuplements. Cette fonction puits peut être améliorée par la modélisation de la gestion sylvicole.

International audience; - Forest management requires a dense forest road system which combines truck roads and skidding tracks. However, harvesting machines cause damage to forest stands and soils. The aim of this study is to examine the consequences skidding tracks have on net nitrogen mineralization and vegetation composition compared to adjacent forest stands. A beech forest on limestone as well as beech and Norway spruce forests on acidic soils were investigated in south Lower Saxony, Germany. Along the wheel tracks the net nitrogen mineralization is markedly reduced compared to the undisturbed stands. Although nitrogen mineralization is found to be low especially along the wheel tracks, ruderal plants with high nitrogen indicator values have established themselves. Along the skidding tracks, numerous species from fringe and ruderal communities, grasslands and wet sites occur while the stands are dominated by typical forest plant species. Therefore, species diversity is higher along the skidding tracks than in the adjacent stands.; - Minéralisation d'azote et végétation le long de lignes de débardage. Une gestion forestière durable nécessite un système de desserte forestière dense par des chemins et des lignes de débardage. La circulation d'engins forestiers lourds cause des dégâts parfois importants au sol et aux peuplements forestiers. Une hêtraie calcicole ainsi qu'une hêtraie et une pessière sur des stations acidiclines ont fait l'objet de la présente étude dont l'objectif est l'appréciation des conséquences de la circulation sur la minéralisation d'azote ainsi que sur la végétation. Par rapport à des peuplements voisins non perturbés, la minéralisation d'azote nette dans les ornières est sensiblement ralentie. Malgré ce fait, de nombreuses espèces des ourlets et des milieux ouverts ("espèces rudérales"), présentant un besoin élevé d'azote, apparaissent le long des lignes de débardage. Les peuplements fermés sont caractérisés par des espèces forestières typiques. Ainsi, on constate une plus grande diversité d'espèces le long des lignes de débardage.

International audience; All the macrofauna were sampled in the litter and deep soil of thirteen beechwoods, situated within the same geographical and geological area (the central Ardenne), but with different humus types: mesotrophic mull, dystrophic mull, moder and dysmoder. The analysis of data for 21 saprophagous taxa in 96 sampling units showed that the mesotrophic mull community was characterized not only by Lumbricidae (anecic, endogeic and some epigeic species), but also by many other epigeic taxa, pertaining mainly to Diplopoda, Isopoda and Gastropoda. By contrast, Elaterid larvae were one of the few taxa that were abundant in moder and dysmoder soils. The results from the Ardenne, with regard to the high density and diversity of the saprophagous macrofauna in forest mull, have confirmed other results in the literature, which gives them a large significance. The results also emphasize the interest of experimental studies dealing with interactions between different saprophagous species, during the process of formation of forest mull.