Catherine Collet - Academia.edu (original) (raw)

Papers by Catherine Collet

Forest Ecology and Management, 2014

Context: Growth partitioning among trees in forest stands is pivotal to silviculture, making it c... more Context: Growth partitioning among trees in forest stands is pivotal to silviculture, making it crucial to understand its control by factors such as stand development, stand density, or thinning. Since growth partitioning primarily depends on the partitioning of environmental resources among individuals, climatic change further calls for extending this framework to explicit climatic factors. Recent debate on adapting management to such changes also requires larger density gradients to be encompassed. Methods: We primarily aimed to investigate the effects of stand density and climatic factors on growth partitioning, in even-aged stands of sessile oak and Douglas-fir, two species currently managed under contrasted silvicultural regimes. We used two original permanent plot networks designed to explore effects of large density gradients, from open-grown to self-thinning situations. Growth partitioning was assessed on basal area growth, using both the growth dominance index, and the within-stand size-growth relationship. Their dependence on stand density, age, thinning, and climatic predictors was modeled statistically. A one-at-a-time sensitivity analysis of these models was performed to evaluate the magnitude of the effect of each predictor on growth partitioning. Simulations of the effect of extreme climatic conditions on stand growth, and on dominant, intermediate and close-to-suppressed trees growth were also performed. Results: For both species, stand density was found to strongly increase growth partitioning toward the biggest trees. Stand growth in sessile oak was reduced by high summer soil water deficit, with a particularly severe growth reduction for suppressed trees, suggesting asymmetric belowground competition for water in this species. In Douglas-fir, a stand growth reduction was found for high summer temperatures, with an increase in growth dominance that suggested a higher temperature-driven stress for suppressed trees. In addition, age slightly increased/decreased growth dominance in sessile oak/Douglas-fir, respectively. Conclusions: Growth dominance and size-growth relationships offered complementary insight into growth partitioning. Stand density appears to be the major driver of growth partitioning. Climatic factors were also shown to significantly affect growth partitioning, with species differences, in addition to stand density and ageing. These results suggest to maintain stands at medium density levels to reduce rotation length and minimize risk of exposure to extreme climatic events.

Forest Ecology and Management, 2011

In order to better understand the structure and composition of forest plant communities, we aimed... more In order to better understand the structure and composition of forest plant communities, we aimed to predict the abundance of understory herbaceous species locally at the stand level and according to different environments. For this, we seeked to model species distributions of abundance at a regional scale in relationship with the local stand structure (canopy openness) and regional soil resources (soil pH).

Forest Ecology and Management, 2010

Canopy closure and soil characteristics are commonly used to explain regeneration distribution at... more Canopy closure and soil characteristics are commonly used to explain regeneration distribution at local and regional scales, although very few studies take both factors into account. The combination of environmental variables defined at broad and local scales is necessary to provide regeneration distribution models with a small resolution (tree scale) that are valid on a large spatial scale (regional scale). Our aim was to quantify how gap partitioning among tree species at the seedling stage varies across large soil and stand type gradients. Regeneration inventories performed 5 years after gap creation were used to analyse the combined effects of soil type, stand type, and position within canopy gaps on the regeneration development of eight western European broadleaved species: Acer campestre, Acer pseudoplatanus, Betula pendula, Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Quercus sp., and Salix caprea. A clear pattern of gap partitioning among the eight species was observed. All species had higher density at the gap edge except birch and willow showing the highest presence in gap centres. For all species, the probability of presence of tall seedlings (height > 0.5 m) increased from gap edge to gap centre. Small seedlings presented the opposite trend except birch and willow. Soil pH influenced probability of presence for each species, but did not affect the pattern of gap partitioning among species. Both local (location within the gap) and regional (soil pH and stand type) scale factors affect recruitment distribution and are thus necessary to predict seedling distribution. The models developed may be used to determine the optimal gap size in order to obtain a given species composition according to soil and stand type conditions.

Ecography, 2013

ABSTRACT In recent years, there has been increasing interest in modelling of species abundance da... more ABSTRACT In recent years, there has been increasing interest in modelling of species abundance data in addition to presence data. In this study, we assessed the similarities and differences between presence-absence distributions and abundance distributions along similar environmental gradients, derived, respectively, from presence-absence and abundance data. Moreover, we examined the possibility of using presence-absence distribution models to derive abundance distributions. For this purpose, we used Braun-Blanquet abundance scores for 243 vascular species at 10 996 French forest sites. Species distribution models were used to analyse the link between the patterns of occurrence, low abundance and high abundance for each species with regard to mean annual temperature, June water balance, and soil pH. For each species, differences in the modelled distributions were characterised by the ecological optimum and ecological amplitude. A comparison of the presence-absence and abundance distributions for all species revealed similar optima and different amplitudes along the three ecological factors. An abundant-centre distribution was observed in environmental space, with species abundance being greatest at the optimal conditions and lower at less favourable conditions of the species occurrence response. Geographical habitat mapping also shows centred, high-abundance suitability within the presence habitat of each species. We conclude that species distribution models derived from presence-absence data provide useful information about the ecological optima of abundance distributions but overestimate the range of habitats suitable for high species abundance. This study demonstrates the utility of presence-absence data for ecologist and conservation biologist when they are interested in the optimal conditions of high species abundance.

Annals of Forest Science - ANN FOR SCI, 2001

In order to analyze the growth dynamics of beech seedlings growing under contrasting canopy condi... more In order to analyze the growth dynamics of beech seedlings growing under contrasting canopy conditions, a beech stand in which two types of canopy opening (canopy release or gap creation) had been applied in 1995 was selected. Three and four years after the canopy had been opened, 113 naturally regenerated seedlings were sampled in gaps or under the canopy. The effects of canopy opening and seedling age on annual height and diameter growth were analyzed using mixed models. Under closed canopy, average annual seedling height and diameter increments were 1.2 cm and 0.18 mm, respectively. Diameter growth increased in the first year after the canopy had been opened, and exhibited considerable inter-annual variation related to climatic conditions. Conversely, height growth did not increase immediately after canopy opening, but increased regularly in the following years. Four years after the gap had been created, annual seedling height and diameter growth were 9.5 cm and 0.49 mm respectively in the gaps, and 3.8 cm and 0.21 mm respectively under released canopy. Age did not affect the dynamics of seedling growth. gap / shade tolerance / natural regeneration / Fagus sylvatica L. / mixed model Résumé -Effets de l'ouverture du couvert sur la croissance en hauteur et en diamètre de semis naturels de hêtre. La dynamique de croissance de jeunes semis de hêtre poussant dans les conditions de couvert contrastées a été étudiée dans un peuplement à base de hêtre dans lequel deux types d'ouverture du peuplement ont été réalisés. En 1995, un simple relevé de couvert a été effectué dans l'ensemble du peuplement et des trouées ont été ouvertes dans certaines parties. En 1998 et 1999, 113 semis naturels de hêtre ont été récoltés sous couvert ou dans les trouées. Les effets combinés de l'ouverture du couvert et de l'âge des semis sur la croissance en hauteur et en diamètre des semis ont été analysés à l'aide de modèles linéaires mixtes. Les semis sous couvert présentaient un accroissement annuel en hauteur de 1,2 cm et un accroissement annuel en diamètre de 0,18 mm. La croissance en diamètre a augmenté dès la premère année après l'ouverture du couvert et a ensuite montré de fortes variations inter-annuelles liées à des variatons climatiques. En revanche, l'augmentation de la croissance en hauteur à la suite de l'ouverture du peuplement n'a pas été immédiate, et a continué de manière progressive dans les quatre années suivantes. Quatre ans après l'ouverture du peuplement, les accroissements annuels en hauteur en en diamètre étaient de 9,5 cm and 0,49 mm respectivement pour les semis dans les trouées et de 3,8 cm and 0,21 mm respectivement pour les semis sous relevé de couvert. La croissance des semis n'est pas apparue liée à l'âge. trouée / tolérance à l'ombrage / régénération naturelle / Fagus sylvatica L. / modèle mixte Ann. For. Sci. 58 (2001) 127-134 127

Forest Ecology and Management - FOREST ECOL MANAGE, 1998

The objective of this research was to evaluate the influence of vegetation control on the microcl... more The objective of this research was to evaluate the influence of vegetation control on the microclimate (light, air temperature, vapor-pressure deficit (VPD)) and on the growth of young planted, sessile oak seedlings. Three types of vegetation control, creating a range of above-ground interaction intensity, were compared. In the open treatment, vegetation was chemically controlled and was maintained at a low height; in the closed treatment, vegetation was manually controlled and a few dominant individuals that overtopped the oak seedlings were cut; and in the sheath treatment, the vegetation in a 0.5-m diameter circle around each seedling was manually cut to a height equal to three quarters of the total seedling height. In all treatments, a strong reduction of incoming radiation was observed, as well as an increase in air temperature and VPD during the day, and a decrease in daily PET, compared to the reference located 4 m above the vegetation. However, the neighboring vegetation did not modify the microclimate around the seedling to a level that could have induced a significant reduction in seedling photosynthesis and, thus, in seedling growth. Seven years after planting, seedlings were shortest in the open treatment and tallest in the closed treatment (334, 372, 378 cm in the open, sheath and closed treatments, respectively). Seedlings in the open treatment allocated proportionally more biomass to diameter increment than to height growth, compared to seedlings in the sheath and closed treatments. The seedlings averaged 1.77, 1.10 and 1.00 forks in the open, sheath and closed treatments, respectively, and the average height of the lowest fork was 171, 206 and 226 cm in the same treatments. The reduction of the number of forks per seedling was not related to a reduction of the appearance of new forks, but rather to a reduction in the persistence of the existing forks. These changes in stem allometry and in fork development seemed to be related to the lateral shade afforded by the vegetation.

Botany-botanique - BOTANY, 1996

Growth characteristics and water uptake were compared on two forest grass species (Agrostis stolo... more Growth characteristics and water uptake were compared on two forest grass species (Agrostis stolonifera L. and Deschampsia cespitosa (L.) Beauv.) to evaluate their potential competitive effects on young forest seedlings. The two grass species were grown in large containers under two watering regimes (regular irrigation that maintained the soil at field capacity or seasonal water stress). Spring regrowth occurred earlier in Deschampsia than in Agrostis. During the summer, under irrigated conditions, Agrostis had higher values of leaf and tiller appearance rates than Deschampsia. Under water-stressed conditions, leaf and tiller appearance rates decreased sharply for both species during the desiccation period, and regrowth was much more pronounced in Agrostis than in Deschampsia after rewatering. Observations of the root systems indicated that Deschampsia developed deeper roots than Agrostis. Despite these differences, evapotranspiration in the irrigated and in the dry treatments were similar for both grasses. In the water-stressed treatments, soil water potential decreased rapidly under both grasses and was slightly lower in Agrostis than in Deschampsia. Although the two grasses had similar soil water uptake, differences in the overall competitive effect of the two grasses on forest tree seedlings might appear because of differences in their phenology, their recovery from drought, and the development of their root system.

European Journal of Forest Research, 2011

By increasing resource availability, canopy opening enhances tree recruitment as well as the deve... more By increasing resource availability, canopy opening enhances tree recruitment as well as the development of neighbouring vegetation. The proliferation of early successional and highly competitive vegetation may have dramatic consequences on seedling establishment. However, differences in competitive abilities have been shown among the plant growth forms commonly encountered in forests. We may thus expect that vegetation management leading to control of different plant growth forms would have different consequences on tree seedling growth and development. To test this hypothesis, we analysed the effects of an intensity gradient of four vegetation control treatments (untreated, coppice control, coppice and non-tree plant control, and coppice, non-tree and pioneer (tree) plant control) on plant species richness and natural tree regeneration in three post-storm sites. Higher plant species richness and a better natural tree regeneration were observed in the more intensive treatments that significantly improved the balance of the relative abundance of tree species. Suppressing the more competitive vegetation, mainly Rubus fruticosus and graminoids, led to the recruitment and growth of tree species sensitive to competition and good tree species diversity. Practical recommendations in terms of vegetation control relative to tree regeneration and plant species richness are given.

European Journal of Forest Research, 2014

ABSTRACT This study aimed at evaluating alternative methods to ensure regeneration success in tem... more ABSTRACT This study aimed at evaluating alternative methods to ensure regeneration success in temperate low-mountain forest stands by (1) estimating the effects of seed availability, competition from the adult stand and from neighbouring vegetation and interaction with the litter layer on seedling density, and by (2) comparing the effects of various silvicultural methods on regeneration success. The experiment was conducted in a monospecific beech (Fagus sylvatica) stand and a mixed silver fir-beech (Abies alba, Fagus sylvatica) stand with contrasted vegetation communities, in north-east France. Different methods of soil preparation, i.e. chemical (herbicide), mechanical (surface hoeing and deep scarification using light-weight machines) and biological (cover crops after surface hoeing) methods, were applied along a canopy opening gradient. After soil preparation (in 2009), vegetation colonisation and tree seedling density were monitored once a year from 2010 to 2013. Results were similar for the two sites. Seedling density the first year indicated a predominant effect of seed availability and soil scarification over potential competitive effects of adult stand and neighbouring vegetation. Despite continuous vegetation colonisation after soil preparation, seedling density remained stable over the 4 years of the experiment. For each of the 4 years, seedling density increased with canopy cover. Seedling density was higher after mechanical soil preparation than after herbicide application. Cover crops (following surface hoeing) appeared as the best method, ensuring both the lowest vegetation colonisation and the highest seedling density.

Trees, 2014

Key message Density was more important in shaping crown structure than neighbor species identity.... more Key message Density was more important in shaping crown structure than neighbor species identity. Both species showed high crown plasticity at alternative levels, which may explain species coexistence in mixed broadleaved forests with functionally similar species. Abstract Understanding crown response to local competition is essential to predicting stand development in mixed stands. We analyzed data from an 8-year-old field experimental plantation mixing two species according to a crossed gradient of density and species proportion to quantify the effect of a broad range of local neighborhood conditions on the development of young trees at multiple crown levels. We used Fagus sylvatica and Acer pseudoplatanus, as two model deciduous species. They are considered functionally equivalent at the young stages, but with contrasting architectural patterns. For both species: (1) changes in density explained more of the variation on crown development than species proportion (2) much of the effect of competition was accounted for by variables at the stem level, while branch and leaf development within crowns were not directly altered by competition. Both species were able to modify their crowns at the stem level to compete with intra-and inter-specific neighbors: Acer and Fagus were taller with a highest proportion of Fagus as neighbors; Fagus displayed a lower crown base when the proportion of Fagus decreased, while Acer had a lower crown base when the proportion of Fagus around it increased. Both species showed common shapes in allometric relationships but contrasting responses at alternative crown levels. Acer exhibited broader intra-specific variation in its height-diameter relationship and in its crown length, while Fagus displayed higher individual variation of branch development and leaf area than Acer. This study demonstrates that differences in crown development strategy of each species in response to changes in local neighborhood conditions are an important factor in maintaining species coexistence in broadleaved forests and designing mixtures that persist over time.

Revue Forestière Française, 2011

Annals of Forest Science, 2010

• In mixed-species forest stands, large losses in tree species diversity often occur during the r... more • In mixed-species forest stands, large losses in tree species diversity often occur during the regeneration phase. In a former coppice-with-standards, we investigated whether the limiting stage in the recruitment process of advance regeneration is the immediate seedling response to canopy release. Experimental canopy gaps were opened and the survival and growth of advance seedlings (Fagus sylvatica, Acer pseudoplatanus, Acer campestre, Acer platanoides) growing in the gaps or under closed canopy were monitored for three years. • All species responded positively and rapidly to canopy release. Survival was not affected by gap opening. Diameter increment after gap opening was similar across species, and height increment was greater for Acer platanoides and for Acer pseudoplatanus. Post-release diameter and height growth were mainly determined by pre-release seedling size. Competition from neighbouring seedlings did not affect growth in the three years following canopy opening. • In the recruitment process of F. sylvatica and Acer sp. advance regeneration, the recovery from canopy release did not appear as a limiting step that would filter against some species. Pre-release size was the main factor accounting for post-release growth and is probably a major determinant of long-term seedling dominance. • Dans les peuplements mélangés, une forte réduction de la diversité spécifique a lieu au cours de la phase de régénération. Nous avons examiné dans un ancien taillis-sous-futaie dans quelle mesure la réponse immédiate des semis à l’ouverture du couvert adulte pouvait limiter le recrutement de semis préexistants. Des trouées ont été ouvertes dans le couvert, et la survie et la croissance de semis préexistants (Fagus sylvatica, Acer pseudoplatanus, Acer campestre, Acer platanoides), situés dans les trouées ou bien sous couvert fermé, ont été suivies pendant trois années. • Les quatre espèces ont répondu positivement et rapidement à l’ouverture du couvert. La survie n’a pas été affectée par l’ouverture. Pour les semis dans les trouées, l’accroissement en diamètre était similaire pour les quatre espèces et l’accroissement en hauteur était plus important pour Acer platanoides et Acer pseudoplatanus. La croissance en hauteur et en diamètre après ouverture étaient principalement déterminées par les dimensions des semis avant ouverture. La compétition exercée par les semis voisins n’a pas affecté significativement la croissance dans les trois années qui ont suivi l’ouverture. • La période d’acclimatation des semis aux nouvelles conditions après ouverture de la canopée n’est pas apparue comme un stade limitant le recrutement des semis préexistants de Fagus sylvatica, Acer sp., ni comme un filtre vis-à-vis de l’une des quatre espèces. Les dimensions initiales des semis constituaient le facteur principal expliquant la croissance après ouverture, et probablement un facteur explicatif important pour la dominance future des semis vis-à-vis de leurs voisins.

Trees, 2002

Beech (Fagus sylvatica L.) seedlings growing under contrasting canopy closure conditions (gaps vs... more Beech (Fagus sylvatica L.) seedlings growing under contrasting canopy closure conditions (gaps vs closed canopy) were collected in a naturally regenerating stand of northeastern France. Seedling morphology [total height, basal diameter, number of growth units (GUs), length of GUs] and anatomy (width of the pith and width of the annual rings at seedling base and at various levels along the stem) were described. Seedling ages, as estimated by counting the number of rings at seedling base and by counting the number of GUs along the stem, were compared. Seedling age ranged between 1 and 19 years. The best method for determining the age of seedlings with reduced growth appeared to be GU counting, whereas the best method for determining the age of actively growing seedlings was ring counting. No effect of seedling age on any parameter of seedling growth was found. The degree of canopy closure strongly affected seedling growth. Seedlings sampled in gaps were larger and allocated more biomass to secondary than to primary growth, compared to seedlings sampled under closed canopy. However, the increase in secondary growth relative to primary growth was only significant when analysing annual growth increment (GU length and ring width) and was not statistically significant when comparing seedling final size (total height and basal diameter).

Plant and Soil, 2006

A dynamic 3D model of root system development was adapted to young sessile oak seedlings, in orde... more A dynamic 3D model of root system development was adapted to young sessile oak seedlings, in order to evaluate the effects of grass competition on seedling root system development. The model is based on a root typology and the implementation of a series of developmental processes (axial and radial growth, branching, reiteration, decay and abscission). Parameters describing the different processes are estimated for each root type. Young oak seedlings were grown for 4 years in bare soil or with grass competition and were periodically excavated for root system observation and measurements (topology of the root system, length and diameter of all roots with a diameter greater than 0.3 mm). In the fourth year, 40 cmÂ20 cmÂ20 cm soil monoliths were excavated for fine root measurement (root density and root length). Root spatial development was analysed on a sub-sample of roots selected on four seedlings. The model was a guideline that provided a complete and consistent set of parameters to represent root system development. It gave a comprehensive view of the root systems and made it possible to quantify the effects of competition on the different root growth processes. The same root typology was used to describe the seedlings in bare soil and in grass. Five root types were defined, from large tap roots to fine roots. Root system size was considerably reduced by grass competition. Branching density was not affected but the branch roots were always smaller for the seedlings grown in competition. Reiteration capacity was also reduced by competition. Cross sectional areas before and after branching were linearly related with a scaling coefficient close to 1, as predicted by the pipe model theory. This relationship was not affected by grass competition.

Plant and Soil, 2000

Dynamic models of root system development and architecture integrate various developmental proces... more Dynamic models of root system development and architecture integrate various developmental processes and let simulate multiple dynamic interactions. They are recognised as valuable tools to study the soil-plant-atmosphere continuum. In the recent years, some models have emerged from fractal descriptions. Others arose from developmental approaches but most efforts met little success for genericity. Among the difficulties with models are their growing complexity and they inability to detail evenly all important mechanisms often due to a deficit of independent and suitable data for model testing. We propose here a generic model called 'Root Typ' dedicated to quantitative and global analyses of root system architectures and simplified representation of architectural diversity. It aims at (i) detailing evenly a large range of developmental processes, (ii) generalising the concept of root type and (iii) representing in a very simplified way soil effects on developmental processes. The model implements several developmental processes including: root emission, axial and radial growth, sequential branching, reiteration, transition, decay and abscission, which are all discussed in details. Finally, it's ability to mimic a diversity of root architectures is tested against representative root systems depicted in the book of Kutschera (1960) which represents an independent database collected on a large number of plant species and soil conditions, and gives an overall synthetic view upon root systems.

Forest Ecology and Management, 1997

The objective of this study was to determine if various morphological components of height growth... more The objective of this study was to determine if various morphological components of height growth were sensitive to environmental factors (i.e., grass root competition, frost and shading) and to see if these components could be used to quantify the effect of environmental stress on the height growth of sessile oak (Quercus petraea Liebl.) seedlings. The following components were measured: number of flushes produced on the main stem, length of the growth unit (GU) developed during each flush, annual GU length, number of nodes per GU, and state of the terminal bud of each GU. The number of flushes produced was reduced by all environmental treatments. The annual GU length was positively related to the number of flushes produced. Grass competition reduced GU length in each flush and therefore reduced annual GU length. On the other hand, partial shading increased GU length in each flush and annual GU length. Number of nodes was not apparently affected by environmental factors and was positively related to GU length. Where factors that affect terminal bud mortality were partially controlled (i.e., in grass competition and shading experiments), mortality rate was low (5% for GUs of the first flush in grass competition experiment), but in the frost experiment terminal bud mortality rate was higher (64% for GUs of the first flush). The sensitivity of the different morphological components to environmental factors and the quantification of the effects of the factors using generalized linear models were discussed.

Forest Ecology and Management, 2010

Forest Ecology and Management, 2010

European Journal of Forest Research, 2013

ABSTRACT The objective of the study was to analyse to which extent horizontal crown plasticity re... more ABSTRACT The objective of the study was to analyse to which extent horizontal crown plasticity reduces inter-tree competition at stand scale, and how it relates to species growth strategy. Two components of crown plasticity defined at the individual tree level (crown shape distortion, CSD and crown displacement relative to stem, CRD) were analysed and their relative importance in the reduction of competition was quantified. Inter-tree competition at stand scale was estimated using spatial pattern analysis and crown overlap estimation. Measurements were performed in a mixed broadleaved stand of Western Europe. Crown plasticity was shown to regularise the spatial distribution of crowns in comparison with the corresponding stems and to reduce inter-tree competition by optimising space occupation. A significant reduction in crown overlap was observed, mainly due to CRD and secondarily to CSD. At the species level, CSD and CRD were positively correlated. In addition, both were negatively correlated with species shade-tolerance scores. In particular, three European temperate tree species showed contrasting responses, which were related to their known specific ecological strategies. Fagus sylvatica, known to be a highly shade-tolerant species, showed large crowns, low CSD and CRD, indicating a low plasticity and suggesting a strong competitive ability. At the opposite, Quercus sp., known to be clearly less shade-tolerant, exhibited a reduced growth, associated with high CSD and CRD, indicating high crown plasticity and probably a lower competitive ability. For this species, plasticity could be described as passive. Last, Carpinus betulus, known to have a relatively good shade-tolerance, showed a contrasting behaviour with high CSD and CRD and a strong presence in the stand, suggesting high crown plasticity and a good competitive ability. In that case, plasticity was described as rather adaptive.

Forest Ecology and Management, 2014

Context: Growth partitioning among trees in forest stands is pivotal to silviculture, making it c... more Context: Growth partitioning among trees in forest stands is pivotal to silviculture, making it crucial to understand its control by factors such as stand development, stand density, or thinning. Since growth partitioning primarily depends on the partitioning of environmental resources among individuals, climatic change further calls for extending this framework to explicit climatic factors. Recent debate on adapting management to such changes also requires larger density gradients to be encompassed. Methods: We primarily aimed to investigate the effects of stand density and climatic factors on growth partitioning, in even-aged stands of sessile oak and Douglas-fir, two species currently managed under contrasted silvicultural regimes. We used two original permanent plot networks designed to explore effects of large density gradients, from open-grown to self-thinning situations. Growth partitioning was assessed on basal area growth, using both the growth dominance index, and the within-stand size-growth relationship. Their dependence on stand density, age, thinning, and climatic predictors was modeled statistically. A one-at-a-time sensitivity analysis of these models was performed to evaluate the magnitude of the effect of each predictor on growth partitioning. Simulations of the effect of extreme climatic conditions on stand growth, and on dominant, intermediate and close-to-suppressed trees growth were also performed. Results: For both species, stand density was found to strongly increase growth partitioning toward the biggest trees. Stand growth in sessile oak was reduced by high summer soil water deficit, with a particularly severe growth reduction for suppressed trees, suggesting asymmetric belowground competition for water in this species. In Douglas-fir, a stand growth reduction was found for high summer temperatures, with an increase in growth dominance that suggested a higher temperature-driven stress for suppressed trees. In addition, age slightly increased/decreased growth dominance in sessile oak/Douglas-fir, respectively. Conclusions: Growth dominance and size-growth relationships offered complementary insight into growth partitioning. Stand density appears to be the major driver of growth partitioning. Climatic factors were also shown to significantly affect growth partitioning, with species differences, in addition to stand density and ageing. These results suggest to maintain stands at medium density levels to reduce rotation length and minimize risk of exposure to extreme climatic events.

Forest Ecology and Management, 2011

In order to better understand the structure and composition of forest plant communities, we aimed... more In order to better understand the structure and composition of forest plant communities, we aimed to predict the abundance of understory herbaceous species locally at the stand level and according to different environments. For this, we seeked to model species distributions of abundance at a regional scale in relationship with the local stand structure (canopy openness) and regional soil resources (soil pH).

Forest Ecology and Management, 2010

Canopy closure and soil characteristics are commonly used to explain regeneration distribution at... more Canopy closure and soil characteristics are commonly used to explain regeneration distribution at local and regional scales, although very few studies take both factors into account. The combination of environmental variables defined at broad and local scales is necessary to provide regeneration distribution models with a small resolution (tree scale) that are valid on a large spatial scale (regional scale). Our aim was to quantify how gap partitioning among tree species at the seedling stage varies across large soil and stand type gradients. Regeneration inventories performed 5 years after gap creation were used to analyse the combined effects of soil type, stand type, and position within canopy gaps on the regeneration development of eight western European broadleaved species: Acer campestre, Acer pseudoplatanus, Betula pendula, Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Quercus sp., and Salix caprea. A clear pattern of gap partitioning among the eight species was observed. All species had higher density at the gap edge except birch and willow showing the highest presence in gap centres. For all species, the probability of presence of tall seedlings (height > 0.5 m) increased from gap edge to gap centre. Small seedlings presented the opposite trend except birch and willow. Soil pH influenced probability of presence for each species, but did not affect the pattern of gap partitioning among species. Both local (location within the gap) and regional (soil pH and stand type) scale factors affect recruitment distribution and are thus necessary to predict seedling distribution. The models developed may be used to determine the optimal gap size in order to obtain a given species composition according to soil and stand type conditions.

Ecography, 2013

ABSTRACT In recent years, there has been increasing interest in modelling of species abundance da... more ABSTRACT In recent years, there has been increasing interest in modelling of species abundance data in addition to presence data. In this study, we assessed the similarities and differences between presence-absence distributions and abundance distributions along similar environmental gradients, derived, respectively, from presence-absence and abundance data. Moreover, we examined the possibility of using presence-absence distribution models to derive abundance distributions. For this purpose, we used Braun-Blanquet abundance scores for 243 vascular species at 10 996 French forest sites. Species distribution models were used to analyse the link between the patterns of occurrence, low abundance and high abundance for each species with regard to mean annual temperature, June water balance, and soil pH. For each species, differences in the modelled distributions were characterised by the ecological optimum and ecological amplitude. A comparison of the presence-absence and abundance distributions for all species revealed similar optima and different amplitudes along the three ecological factors. An abundant-centre distribution was observed in environmental space, with species abundance being greatest at the optimal conditions and lower at less favourable conditions of the species occurrence response. Geographical habitat mapping also shows centred, high-abundance suitability within the presence habitat of each species. We conclude that species distribution models derived from presence-absence data provide useful information about the ecological optima of abundance distributions but overestimate the range of habitats suitable for high species abundance. This study demonstrates the utility of presence-absence data for ecologist and conservation biologist when they are interested in the optimal conditions of high species abundance.

Annals of Forest Science - ANN FOR SCI, 2001

In order to analyze the growth dynamics of beech seedlings growing under contrasting canopy condi... more In order to analyze the growth dynamics of beech seedlings growing under contrasting canopy conditions, a beech stand in which two types of canopy opening (canopy release or gap creation) had been applied in 1995 was selected. Three and four years after the canopy had been opened, 113 naturally regenerated seedlings were sampled in gaps or under the canopy. The effects of canopy opening and seedling age on annual height and diameter growth were analyzed using mixed models. Under closed canopy, average annual seedling height and diameter increments were 1.2 cm and 0.18 mm, respectively. Diameter growth increased in the first year after the canopy had been opened, and exhibited considerable inter-annual variation related to climatic conditions. Conversely, height growth did not increase immediately after canopy opening, but increased regularly in the following years. Four years after the gap had been created, annual seedling height and diameter growth were 9.5 cm and 0.49 mm respectively in the gaps, and 3.8 cm and 0.21 mm respectively under released canopy. Age did not affect the dynamics of seedling growth. gap / shade tolerance / natural regeneration / Fagus sylvatica L. / mixed model Résumé -Effets de l'ouverture du couvert sur la croissance en hauteur et en diamètre de semis naturels de hêtre. La dynamique de croissance de jeunes semis de hêtre poussant dans les conditions de couvert contrastées a été étudiée dans un peuplement à base de hêtre dans lequel deux types d'ouverture du peuplement ont été réalisés. En 1995, un simple relevé de couvert a été effectué dans l'ensemble du peuplement et des trouées ont été ouvertes dans certaines parties. En 1998 et 1999, 113 semis naturels de hêtre ont été récoltés sous couvert ou dans les trouées. Les effets combinés de l'ouverture du couvert et de l'âge des semis sur la croissance en hauteur et en diamètre des semis ont été analysés à l'aide de modèles linéaires mixtes. Les semis sous couvert présentaient un accroissement annuel en hauteur de 1,2 cm et un accroissement annuel en diamètre de 0,18 mm. La croissance en diamètre a augmenté dès la premère année après l'ouverture du couvert et a ensuite montré de fortes variations inter-annuelles liées à des variatons climatiques. En revanche, l'augmentation de la croissance en hauteur à la suite de l'ouverture du peuplement n'a pas été immédiate, et a continué de manière progressive dans les quatre années suivantes. Quatre ans après l'ouverture du peuplement, les accroissements annuels en hauteur en en diamètre étaient de 9,5 cm and 0,49 mm respectivement pour les semis dans les trouées et de 3,8 cm and 0,21 mm respectivement pour les semis sous relevé de couvert. La croissance des semis n'est pas apparue liée à l'âge. trouée / tolérance à l'ombrage / régénération naturelle / Fagus sylvatica L. / modèle mixte Ann. For. Sci. 58 (2001) 127-134 127

Forest Ecology and Management - FOREST ECOL MANAGE, 1998

The objective of this research was to evaluate the influence of vegetation control on the microcl... more The objective of this research was to evaluate the influence of vegetation control on the microclimate (light, air temperature, vapor-pressure deficit (VPD)) and on the growth of young planted, sessile oak seedlings. Three types of vegetation control, creating a range of above-ground interaction intensity, were compared. In the open treatment, vegetation was chemically controlled and was maintained at a low height; in the closed treatment, vegetation was manually controlled and a few dominant individuals that overtopped the oak seedlings were cut; and in the sheath treatment, the vegetation in a 0.5-m diameter circle around each seedling was manually cut to a height equal to three quarters of the total seedling height. In all treatments, a strong reduction of incoming radiation was observed, as well as an increase in air temperature and VPD during the day, and a decrease in daily PET, compared to the reference located 4 m above the vegetation. However, the neighboring vegetation did not modify the microclimate around the seedling to a level that could have induced a significant reduction in seedling photosynthesis and, thus, in seedling growth. Seven years after planting, seedlings were shortest in the open treatment and tallest in the closed treatment (334, 372, 378 cm in the open, sheath and closed treatments, respectively). Seedlings in the open treatment allocated proportionally more biomass to diameter increment than to height growth, compared to seedlings in the sheath and closed treatments. The seedlings averaged 1.77, 1.10 and 1.00 forks in the open, sheath and closed treatments, respectively, and the average height of the lowest fork was 171, 206 and 226 cm in the same treatments. The reduction of the number of forks per seedling was not related to a reduction of the appearance of new forks, but rather to a reduction in the persistence of the existing forks. These changes in stem allometry and in fork development seemed to be related to the lateral shade afforded by the vegetation.

Botany-botanique - BOTANY, 1996

Growth characteristics and water uptake were compared on two forest grass species (Agrostis stolo... more Growth characteristics and water uptake were compared on two forest grass species (Agrostis stolonifera L. and Deschampsia cespitosa (L.) Beauv.) to evaluate their potential competitive effects on young forest seedlings. The two grass species were grown in large containers under two watering regimes (regular irrigation that maintained the soil at field capacity or seasonal water stress). Spring regrowth occurred earlier in Deschampsia than in Agrostis. During the summer, under irrigated conditions, Agrostis had higher values of leaf and tiller appearance rates than Deschampsia. Under water-stressed conditions, leaf and tiller appearance rates decreased sharply for both species during the desiccation period, and regrowth was much more pronounced in Agrostis than in Deschampsia after rewatering. Observations of the root systems indicated that Deschampsia developed deeper roots than Agrostis. Despite these differences, evapotranspiration in the irrigated and in the dry treatments were similar for both grasses. In the water-stressed treatments, soil water potential decreased rapidly under both grasses and was slightly lower in Agrostis than in Deschampsia. Although the two grasses had similar soil water uptake, differences in the overall competitive effect of the two grasses on forest tree seedlings might appear because of differences in their phenology, their recovery from drought, and the development of their root system.

European Journal of Forest Research, 2011

By increasing resource availability, canopy opening enhances tree recruitment as well as the deve... more By increasing resource availability, canopy opening enhances tree recruitment as well as the development of neighbouring vegetation. The proliferation of early successional and highly competitive vegetation may have dramatic consequences on seedling establishment. However, differences in competitive abilities have been shown among the plant growth forms commonly encountered in forests. We may thus expect that vegetation management leading to control of different plant growth forms would have different consequences on tree seedling growth and development. To test this hypothesis, we analysed the effects of an intensity gradient of four vegetation control treatments (untreated, coppice control, coppice and non-tree plant control, and coppice, non-tree and pioneer (tree) plant control) on plant species richness and natural tree regeneration in three post-storm sites. Higher plant species richness and a better natural tree regeneration were observed in the more intensive treatments that significantly improved the balance of the relative abundance of tree species. Suppressing the more competitive vegetation, mainly Rubus fruticosus and graminoids, led to the recruitment and growth of tree species sensitive to competition and good tree species diversity. Practical recommendations in terms of vegetation control relative to tree regeneration and plant species richness are given.

European Journal of Forest Research, 2014

ABSTRACT This study aimed at evaluating alternative methods to ensure regeneration success in tem... more ABSTRACT This study aimed at evaluating alternative methods to ensure regeneration success in temperate low-mountain forest stands by (1) estimating the effects of seed availability, competition from the adult stand and from neighbouring vegetation and interaction with the litter layer on seedling density, and by (2) comparing the effects of various silvicultural methods on regeneration success. The experiment was conducted in a monospecific beech (Fagus sylvatica) stand and a mixed silver fir-beech (Abies alba, Fagus sylvatica) stand with contrasted vegetation communities, in north-east France. Different methods of soil preparation, i.e. chemical (herbicide), mechanical (surface hoeing and deep scarification using light-weight machines) and biological (cover crops after surface hoeing) methods, were applied along a canopy opening gradient. After soil preparation (in 2009), vegetation colonisation and tree seedling density were monitored once a year from 2010 to 2013. Results were similar for the two sites. Seedling density the first year indicated a predominant effect of seed availability and soil scarification over potential competitive effects of adult stand and neighbouring vegetation. Despite continuous vegetation colonisation after soil preparation, seedling density remained stable over the 4 years of the experiment. For each of the 4 years, seedling density increased with canopy cover. Seedling density was higher after mechanical soil preparation than after herbicide application. Cover crops (following surface hoeing) appeared as the best method, ensuring both the lowest vegetation colonisation and the highest seedling density.

Trees, 2014

Key message Density was more important in shaping crown structure than neighbor species identity.... more Key message Density was more important in shaping crown structure than neighbor species identity. Both species showed high crown plasticity at alternative levels, which may explain species coexistence in mixed broadleaved forests with functionally similar species. Abstract Understanding crown response to local competition is essential to predicting stand development in mixed stands. We analyzed data from an 8-year-old field experimental plantation mixing two species according to a crossed gradient of density and species proportion to quantify the effect of a broad range of local neighborhood conditions on the development of young trees at multiple crown levels. We used Fagus sylvatica and Acer pseudoplatanus, as two model deciduous species. They are considered functionally equivalent at the young stages, but with contrasting architectural patterns. For both species: (1) changes in density explained more of the variation on crown development than species proportion (2) much of the effect of competition was accounted for by variables at the stem level, while branch and leaf development within crowns were not directly altered by competition. Both species were able to modify their crowns at the stem level to compete with intra-and inter-specific neighbors: Acer and Fagus were taller with a highest proportion of Fagus as neighbors; Fagus displayed a lower crown base when the proportion of Fagus decreased, while Acer had a lower crown base when the proportion of Fagus around it increased. Both species showed common shapes in allometric relationships but contrasting responses at alternative crown levels. Acer exhibited broader intra-specific variation in its height-diameter relationship and in its crown length, while Fagus displayed higher individual variation of branch development and leaf area than Acer. This study demonstrates that differences in crown development strategy of each species in response to changes in local neighborhood conditions are an important factor in maintaining species coexistence in broadleaved forests and designing mixtures that persist over time.

Revue Forestière Française, 2011

Annals of Forest Science, 2010

• In mixed-species forest stands, large losses in tree species diversity often occur during the r... more • In mixed-species forest stands, large losses in tree species diversity often occur during the regeneration phase. In a former coppice-with-standards, we investigated whether the limiting stage in the recruitment process of advance regeneration is the immediate seedling response to canopy release. Experimental canopy gaps were opened and the survival and growth of advance seedlings (Fagus sylvatica, Acer pseudoplatanus, Acer campestre, Acer platanoides) growing in the gaps or under closed canopy were monitored for three years. • All species responded positively and rapidly to canopy release. Survival was not affected by gap opening. Diameter increment after gap opening was similar across species, and height increment was greater for Acer platanoides and for Acer pseudoplatanus. Post-release diameter and height growth were mainly determined by pre-release seedling size. Competition from neighbouring seedlings did not affect growth in the three years following canopy opening. • In the recruitment process of F. sylvatica and Acer sp. advance regeneration, the recovery from canopy release did not appear as a limiting step that would filter against some species. Pre-release size was the main factor accounting for post-release growth and is probably a major determinant of long-term seedling dominance. • Dans les peuplements mélangés, une forte réduction de la diversité spécifique a lieu au cours de la phase de régénération. Nous avons examiné dans un ancien taillis-sous-futaie dans quelle mesure la réponse immédiate des semis à l’ouverture du couvert adulte pouvait limiter le recrutement de semis préexistants. Des trouées ont été ouvertes dans le couvert, et la survie et la croissance de semis préexistants (Fagus sylvatica, Acer pseudoplatanus, Acer campestre, Acer platanoides), situés dans les trouées ou bien sous couvert fermé, ont été suivies pendant trois années. • Les quatre espèces ont répondu positivement et rapidement à l’ouverture du couvert. La survie n’a pas été affectée par l’ouverture. Pour les semis dans les trouées, l’accroissement en diamètre était similaire pour les quatre espèces et l’accroissement en hauteur était plus important pour Acer platanoides et Acer pseudoplatanus. La croissance en hauteur et en diamètre après ouverture étaient principalement déterminées par les dimensions des semis avant ouverture. La compétition exercée par les semis voisins n’a pas affecté significativement la croissance dans les trois années qui ont suivi l’ouverture. • La période d’acclimatation des semis aux nouvelles conditions après ouverture de la canopée n’est pas apparue comme un stade limitant le recrutement des semis préexistants de Fagus sylvatica, Acer sp., ni comme un filtre vis-à-vis de l’une des quatre espèces. Les dimensions initiales des semis constituaient le facteur principal expliquant la croissance après ouverture, et probablement un facteur explicatif important pour la dominance future des semis vis-à-vis de leurs voisins.

Trees, 2002

Beech (Fagus sylvatica L.) seedlings growing under contrasting canopy closure conditions (gaps vs... more Beech (Fagus sylvatica L.) seedlings growing under contrasting canopy closure conditions (gaps vs closed canopy) were collected in a naturally regenerating stand of northeastern France. Seedling morphology [total height, basal diameter, number of growth units (GUs), length of GUs] and anatomy (width of the pith and width of the annual rings at seedling base and at various levels along the stem) were described. Seedling ages, as estimated by counting the number of rings at seedling base and by counting the number of GUs along the stem, were compared. Seedling age ranged between 1 and 19 years. The best method for determining the age of seedlings with reduced growth appeared to be GU counting, whereas the best method for determining the age of actively growing seedlings was ring counting. No effect of seedling age on any parameter of seedling growth was found. The degree of canopy closure strongly affected seedling growth. Seedlings sampled in gaps were larger and allocated more biomass to secondary than to primary growth, compared to seedlings sampled under closed canopy. However, the increase in secondary growth relative to primary growth was only significant when analysing annual growth increment (GU length and ring width) and was not statistically significant when comparing seedling final size (total height and basal diameter).

Plant and Soil, 2006

A dynamic 3D model of root system development was adapted to young sessile oak seedlings, in orde... more A dynamic 3D model of root system development was adapted to young sessile oak seedlings, in order to evaluate the effects of grass competition on seedling root system development. The model is based on a root typology and the implementation of a series of developmental processes (axial and radial growth, branching, reiteration, decay and abscission). Parameters describing the different processes are estimated for each root type. Young oak seedlings were grown for 4 years in bare soil or with grass competition and were periodically excavated for root system observation and measurements (topology of the root system, length and diameter of all roots with a diameter greater than 0.3 mm). In the fourth year, 40 cmÂ20 cmÂ20 cm soil monoliths were excavated for fine root measurement (root density and root length). Root spatial development was analysed on a sub-sample of roots selected on four seedlings. The model was a guideline that provided a complete and consistent set of parameters to represent root system development. It gave a comprehensive view of the root systems and made it possible to quantify the effects of competition on the different root growth processes. The same root typology was used to describe the seedlings in bare soil and in grass. Five root types were defined, from large tap roots to fine roots. Root system size was considerably reduced by grass competition. Branching density was not affected but the branch roots were always smaller for the seedlings grown in competition. Reiteration capacity was also reduced by competition. Cross sectional areas before and after branching were linearly related with a scaling coefficient close to 1, as predicted by the pipe model theory. This relationship was not affected by grass competition.

Plant and Soil, 2000

Dynamic models of root system development and architecture integrate various developmental proces... more Dynamic models of root system development and architecture integrate various developmental processes and let simulate multiple dynamic interactions. They are recognised as valuable tools to study the soil-plant-atmosphere continuum. In the recent years, some models have emerged from fractal descriptions. Others arose from developmental approaches but most efforts met little success for genericity. Among the difficulties with models are their growing complexity and they inability to detail evenly all important mechanisms often due to a deficit of independent and suitable data for model testing. We propose here a generic model called 'Root Typ' dedicated to quantitative and global analyses of root system architectures and simplified representation of architectural diversity. It aims at (i) detailing evenly a large range of developmental processes, (ii) generalising the concept of root type and (iii) representing in a very simplified way soil effects on developmental processes. The model implements several developmental processes including: root emission, axial and radial growth, sequential branching, reiteration, transition, decay and abscission, which are all discussed in details. Finally, it's ability to mimic a diversity of root architectures is tested against representative root systems depicted in the book of Kutschera (1960) which represents an independent database collected on a large number of plant species and soil conditions, and gives an overall synthetic view upon root systems.

Forest Ecology and Management, 1997

The objective of this study was to determine if various morphological components of height growth... more The objective of this study was to determine if various morphological components of height growth were sensitive to environmental factors (i.e., grass root competition, frost and shading) and to see if these components could be used to quantify the effect of environmental stress on the height growth of sessile oak (Quercus petraea Liebl.) seedlings. The following components were measured: number of flushes produced on the main stem, length of the growth unit (GU) developed during each flush, annual GU length, number of nodes per GU, and state of the terminal bud of each GU. The number of flushes produced was reduced by all environmental treatments. The annual GU length was positively related to the number of flushes produced. Grass competition reduced GU length in each flush and therefore reduced annual GU length. On the other hand, partial shading increased GU length in each flush and annual GU length. Number of nodes was not apparently affected by environmental factors and was positively related to GU length. Where factors that affect terminal bud mortality were partially controlled (i.e., in grass competition and shading experiments), mortality rate was low (5% for GUs of the first flush in grass competition experiment), but in the frost experiment terminal bud mortality rate was higher (64% for GUs of the first flush). The sensitivity of the different morphological components to environmental factors and the quantification of the effects of the factors using generalized linear models were discussed.

Forest Ecology and Management, 2010

Forest Ecology and Management, 2010

European Journal of Forest Research, 2013

ABSTRACT The objective of the study was to analyse to which extent horizontal crown plasticity re... more ABSTRACT The objective of the study was to analyse to which extent horizontal crown plasticity reduces inter-tree competition at stand scale, and how it relates to species growth strategy. Two components of crown plasticity defined at the individual tree level (crown shape distortion, CSD and crown displacement relative to stem, CRD) were analysed and their relative importance in the reduction of competition was quantified. Inter-tree competition at stand scale was estimated using spatial pattern analysis and crown overlap estimation. Measurements were performed in a mixed broadleaved stand of Western Europe. Crown plasticity was shown to regularise the spatial distribution of crowns in comparison with the corresponding stems and to reduce inter-tree competition by optimising space occupation. A significant reduction in crown overlap was observed, mainly due to CRD and secondarily to CSD. At the species level, CSD and CRD were positively correlated. In addition, both were negatively correlated with species shade-tolerance scores. In particular, three European temperate tree species showed contrasting responses, which were related to their known specific ecological strategies. Fagus sylvatica, known to be a highly shade-tolerant species, showed large crowns, low CSD and CRD, indicating a low plasticity and suggesting a strong competitive ability. At the opposite, Quercus sp., known to be clearly less shade-tolerant, exhibited a reduced growth, associated with high CSD and CRD, indicating high crown plasticity and probably a lower competitive ability. For this species, plasticity could be described as passive. Last, Carpinus betulus, known to have a relatively good shade-tolerance, showed a contrasting behaviour with high CSD and CRD and a strong presence in the stand, suggesting high crown plasticity and a good competitive ability. In that case, plasticity was described as rather adaptive.