Gilles Le Moguédec

Fagacées: a tree-centered growth and yield model for sessile oak (Quercus petraea L.) and common beech (Fagus sylvatica L.)

Abstract• IntroductionFagacées is a growth model that has been developed for pure Oak or Beech stand management in even-aged high forests and coppice with standards forests. It has been calibrated for the plain forests of northern France.• ObjectivesThis paper presents all the characteristics of this model: general structure, equations, and parameters. It can be classified as a distance-independent tree-centered model. Its main originality is that tree growth is organised according to a top–down organisation.• ResultAt first, the growth is computed at the stand level. Then it is allocated between the individual trees. The paper presents and discusses successively these two parts. In addition, the model delivers the stem profile of each tree: rings and compartments within the stem. Some other additional modelling that have been defined for batch mode purposes are also briefly presented.

Increase in male reproductive success and female reproductive investment in invasive populations of the harlequin ladybird Harmonia axyridis.

Reproductive strategy affects population dynamics and genetic parameters that can, in turn, affect evolutionary processes during the course of biological invasion. Life-history traits associated with reproductive strategy are therefore potentially good candidates for rapid evolutionary shifts during invasions. In a series of mating trials, we examined mixed groups of four males from invasive and native populations of the harlequin ladybird Harmonia axyridis mating freely during 48 hours with one female of either type. We recorded the identity of the first male to copulate and after the 48 h-period, we examined female fecundity and share of paternity, using molecular markers. We found that invasive populations have a different profile of male and female reproductive output. Males from invasive populations are more likely to mate first and gain a higher proportion of offspring with both invasive and native females. Females from invasive populations reproduce sooner, lay more eggs, and have offspring sired by a larger number of fathers than females from native populations. We found no evidence of direct inbreeding avoidance behaviour in both invasive and native females. This study highlights the importance of investigating evolutionary changes in reproductive strategy and associated traits during biological invasions.

A generalized self-thinning relationship for multi-species and mixed-size forests

IntroductionThe self-thinning relationship established by Reineke in 1933 assumes a relationship between the number of stems and the quadratic mean diameter in fully stocked pure stands. This rule is extensively used for management purposes, but it has been initially calibrated for pure, even-aged stands for relatively few species.ObjectivesHere, we extend this relationship to mixed-species and mixed-size forests through a generalized modeling approach. Reineke’s rule can be seen as a particular case of this generalized approach. Resource sharing is taken as a starting point; thus, both site fertility and diameter heterogeneity are taken into account.DiscussionCalibration on actual inventories is made on a dataset of 82 French stands. The theoretical relationship is successfully adjusted for species in which enough data were available, namely, common beech (Fagus sylvatica L.), oak (Quercus petraea [Mattuschka] Liebl and Quercus robur L.), and Norway spruce (Picea abies [L.] Karst).ConclusionSelf-thinning exponents obtained for beech and oak (1.86 and 1.76, respectively) can be used in the mixed-species equation that we developed. These results encourage calibrating the parameters for other species if appropriate data are available.

Approach to the estimation of red heart occurrence in Fagus sylvatica based on geometric relationships between branch scar development and knot dimensions

Abstract The effect of branch scars on the initiation and occurrence of red heart in beech (Fagus sylvatica L.) was studied on 17 trees with red heartwood and 14 trees with no discoloured heartwood, all of which were selected from a 120-year-old high-forest stand in Germany. Logistic regression was used to predict the probability of red heart occurrence for a given tree. The model was based on individual probabilities derived from geometric relationships between scar and knot morphologies, and integrated the diameter at breast height. Using this model, 27 of 31 trees were correctly classified, and the two groups of trees were clearly distinguished by probabilities below 0.25 and above 0.85 (with one exception). Given the constitution of the model, only 17 of 616 scars were found to initiate red heart formation, and the parameters of mechanistic variables were strongly correlated. The results suggest specifying the relationship between scars, knots and red heart, and extending the scope of the model.

Integrating mixed-effect models into an architectural plant model to simulate inter- and intra-progeny variability: a case study on oil palm (Elaeis guineensis Jacq.)

Three-dimensional (3D) reconstruction of plants is time-consuming and involves considerable levels of data acquisition. This is possibly one reason why the integration of genetic variability into 3D architectural models has so far been largely overlooked. In this study, an allometry-based approach was developed to account for architectural variability in 3D architectural models of oil palm (Elaeis guineensis Jacq.) as a case study. Allometric relationships were used to model architectural traits from individual leaflets to the entire crown while accounting for ontogenetic and morphogenetic gradients. Inter- and intra-progeny variabilities were evaluated for each trait and mixed-effect models were used to estimate the mean and variance parameters required for complete 3D virtual plants. Significant differences in leaf geometry (petiole length, density of leaflets, and rachis curvature) and leaflet morphology (gradients of leaflet length and width) were detected between and within progenies and were modelled in order to generate populations of plants that were consistent with the observed populations. The application of mixed-effect models on allometric relationships highlighted an interesting trade-off between model accuracy and ease of defining parameters for the 3D reconstruction of plants while at the same time integrating their observed variability. Future research will be dedicated to sensitivity analyses coupling the structural model presented here with a radiative balance model in order to identify the key architectural traits involved in light interception efficiency.

Characterizing Tropical Tree Species Growth Strategies: Learning from Inter-Individual Variability and Scale Invariance

Understanding how tropical tree species differ in their growth strategies is critical to predict forest dynamics and assess species coexistence. Although tree growth is highly variable in tropical forests, species maximum growth is often considered as a major axis synthesizing species strategies, with fast-growing pioneer and slow-growing shade tolerant species as emblematic representatives. We used a hierarchical linear mixed model and 21-years long tree diameter increment series in a monsoon forest of the Western Ghats, India, to characterize species growth strategies and question whether maximum growth summarizes these strategies. We quantified both species responses to biotic and abiotic factors and individual tree effects unexplained by these factors. Growth responses to competition and tree size appeared highly variable among species which led to reversals in performance ranking along those two gradients. However, species-specific responses largely overlapped due to large unexplained variability resulting mostly from inter-individual growth differences consistent over time. On average one-third of the variability captured by our model was explained by covariates. This emphasizes the high dimensionality of the tree growth process, i.e. the fact that trees differ in many dimensions (genetics, life history) influencing their growth response to environmental gradients, some being unmeasured or unmeasurable. In addition, intraspecific variability increased as a power function of species maximum growth partly as a result of higher absolute responses of fast-growing species to competition and tree size. However, covariates explained on average the same proportion of intraspecific variability for slow- and fast-growing species, which showed the same range of relative responses to competition and tree size. These results reflect a scale invariance of the growth process, underlining that slow- and fast-growing species exhibit the same range of growth strategies.

Using a chain of models to simulate the distribution between quality clusters of a set of boards coming from a sessile oak (Quercus petraea Liebl.) resource. Validation of the simulations

Taking sessile oak as an example, this paper initially presents a method to predict the final production (quantity and quality) coming from a forest resource when two sets of data are available. The data sets are from two models: measured or simulated ring width profiles from pith to bark of the constituent trees as well as a mixed model for the basic wood properties which are used to grade the boards into quality clusters. The second part of the paper contains a validation for the proposed method. Simulations are used to predict two basic wood properties (volumetric swelling coefficient and wood density) in the trees of a forest resource in relation to the ring width profile of each tree. The simulations are used to compute a map of these two basic properties in each plank derived from the trees. A quality index derived from this map of basic wood properties in the boards is then used to allocate the planks to quality clusters. The basic wood properties considered in this paper are modelled with linear mixed models. Since computation of the plank properties or definition of the grading rule can use several properties simultaneously, the models used to simulate the basic properties are joint models. Modelling jointly several properties with a mixed model consists of defining a covariance structure between the random effects of the model. Such a model can be substantial in terms of parameters and computational resources required, thus we compared three kinds of joint models. The simplest one is not quite a joint model but is simply obtained from the juxtaposition of independent models, one for each of the two properties taken into consideration. We also defined a model with a moderate covariance structure between the two properties, and lastly, we used a third model with a full covariance structure. Simulations of volumetric swelling coefficient, wood density and the resulting board grading were carried out with each of these three models. All give results roughly in accordance with the observations, but the two “truly” joint models give better results than the simplest model.

Using terrestrial laser scanning data to estimate large tropical trees biomass and calibrate allometric models: A comparison with traditional destructive approach

Summary 1.Calibration of local, regional or global allometric equations to estimate biomass at the tree level constitutes a significant burden on projects aiming at reducing Carbon emissions from forest degradation and deforestation. The objective of this contribution is to assess the precision and accuracy of Terrestrial Laser Scanning (TLS) for estimating volumes and aboveground biomass (AGB) of the woody parts of tropical trees, and for the calibration of allometric models. 2.We used a destructive dataset of 61 trees, with diameters and AGB of up to 186.6 cm and 60 Mg respectively, which were scanned, felled and weighed in the semi-deciduous forests of eastern Cameroon. We present an operational approach based on available software allowing to retrieve TLS volume with low bias and high accuracy for large tropical trees. Edition of the obtained models proved necessary, mainly to account for the complexity of buttressed parts of tree trunks, which were separately modelled through a meshing approach, and to bring a few corrections in the topology and geometry of branches, thanks to the AMAPStudio-Scan software. 3.Over the entire dataset, TLS derived volumes proved highly reliable for branches larger than 5 cm in diameter. The volumes of the remaining woody parts estimated for stumps, stems and crowns as well as for the whole tree proved very accurate (RMSE below 2.81% and R² above of 0.98) and unbiased. Once converted to AGB using mean local specific wood density values, TLS estimates allowed calibrating a biomass allometric model with coefficients statistically undistinguishable from those of a model based on destructive data. Un-edited Quantitative Structure Model (QSM) however lead to systematic overestimations of woody volumes and subsequently to significantly different allometric parameters. 4.We can therefore conclude that the non-destructive TLS approach can now be used as an operational alternative to traditional destructive sampling to build the allometric equations, although attention must be paid to the quality of QSM model adjustments to avoid systematic bias. This article is protected by copyright. All rights reserved.

Reduced population size can induce quick evolution of inbreeding depression in the invasive ladybird Harmonia axyridis

Understanding biological invasion is currently one of the main scientific challenges for ecologists. The introduction process is crucial for the success of an invasion, especially when it involves a demographic bottleneck. A small introduced population is expected to face a higher risk of extinction before the first stage of invasion is complete if inbreeding depression, caused by the expression of deleterious alleles, is important. Changes in mating regimes or in population size can induce the evolution of deleterious allele frequencies, either by selection or by drift, possibly resulting in the purging or the fixation of such alleles within the population. The harlequin ladybird Harmonia axyridis became invasive on several continents following a scenario including at least one event of demographic bottleneck. Although native populations suffered from severe inbreeding depression, it was greatly reduced in invasive ones suggesting that deleterious alleles were purged during the invasion process. In this study, we performed an experiment designed to manipulate the effective population size of H. axyridis across successive generations to mimic contrasting introduction events. We used the measurement of two fitness-related phenotypic traits in order to test (1) if inbreeding depression can evolve at the time-scale of an invasion; and (2) if the changes in inbreeding depression following a bottleneck in laboratory conditions are compatible with the purging of deleterious alleles observed in this species. We found that two generations of very low population size are enough to induce a substantial change in inbreeding depression. Although the genetic changes mostly consisted in fixation of deleterious alleles, purging did also occur, sometimes simultaneously with fixation.

Low functional but large soil-related variations in growth trajectories characterise the widespread Neotropical tree Cecropia obtusa Trecul (Urticaceae)

1. Trait-environment relationships have been described at the community level across tree species. However, whether interspecific trait-environment relationships are consistent at the intraspecific level is yet unknown. Moreover, we do not know how consistent is the response between organ vs whole-tree level. 2. We examined phenotypic variability for 16 functional leaf (dimensions, nutrient, chlorophyll) and wood traits (density) across two soil types, Ferralitic Soil (FS) vs. White Sands (WS), on two sites for 70 adult trees of Cecropia obtusa Trecul (Urticaceae) in French Guiana. Cecropia is a widespread pioneer Neotropical genus that generally dominates early successional forest stages. To understand how soil types impact resource-use through the processes of growth and branching, we examined the architectural development with a retrospective analysis of growth trajectories. We expect soil types to affect both, functional traits in relation to resource acquisition strategy as already described at the interspecific level, and growth strategies due to resource limitations with reduced growth on poor soils. 3. Functional traits were not involved in the soil response, as only two traits -leaf residual water content and K content-showed significant differences across soil types. Soil effects were stronger on growth trajectories, with WS trees having the slowest growth trajectories and less numerous branches across their lifespan. 4. The analysis of growth trajectories based on architectural analysis improved our ability to characterise the response of trees with soil types. The intraspecific variability is higher for growth trajectories than functional traits for C. obtusa, revealing the complementarity of the architectural approach with the functional approach to gain insights on the way trees manage their resources over their lifetime. Soil-related responses of Cecropia functional traits are not the same as those at the interspecific level, suggesting that the effects of the acting ecological processes are different between the two levels. Apart from soil differences, much variation was found across sites, which calls for further investigation of the factors shaping growth trajectories in tropical forests.Environment-driven interspecific functional variability has been convincingly described across Amazon lowland tree species. However, functional variability has rarely been addressed at the intraspecific level, especially through one key environmental driver such as soil composition. In this study, we assess whether patterns of soil-dependent interspecific variability are retained at the intraspecific level. We examined phenotypic variability for 16 functional leaf (dimensions, nutrient, chlorophyll) and wood traits (density) across two soil types, Ferralitic Soil (FS) vs. White Sands (WS), and on two sites for 70 adult trees of Cecropia obtusa Trécul (Urticaceae) in French Guiana. Cecropia is a widespread pioneer Neotropical genus that generally dominates forest early successional stages. We also examined the architectural development through a temporal-scaled retrospective analysis and lifespan-level growth trajectories, in order to evaluate the role of soil phenotypic variability. Cecropia’s unique features, such as simple architecture and growth markers allowed us detailed description of temporal-scaled retrospective analysis of development. Functional trait responses to soil types were weak, as only two traits, namely petiole length and leaf area, exhibited significant differences between the two soil types. Soil effects were stronger on growth trajectories and tree architectural development, with WS trees having the slowest growth trajectories-underlined by smaller internode length-, smallest trunk heights and diameters for a given age, and less numerous branches. Soil-related functional traits did not mirror the divergence usually found at the interspecific level. By integrating a dynamic approach based on retrospective analysis of architectural development to the functional approach to understand tree ecology, here, we demonstrate how an improved understanding of environmental effects on tree phenotypic variance can be captured.ABSTRACT Trait-environment relationships have been described at the community level across tree species. However, whether interspecific trait-environment relationships are maintained at the intraspecific level is yet unknown. We examined phenotypic variability for 16 functional leaf (dimensions, nutrient, chlorophyll) and wood traits (density) across two soil types, Ferralitic Soil (FS) vs. White Sands (WS), on two sites for 70 adult trees of Cecropia obtusa Trecul (Urticaceae) in French Guiana. Cecropia is a widespread pioneer Neotropical genus that generally dominates forest early successional stages. To understand how soil types impact resource-use through the processes of growth and branching, we examined the architectural development with a retrospective analysis of growth trajectories. Functional trait responses to soil types were weak, as only two traits -leaf residual water content and K content- showed significant differences across soil types. Soil effects were stronger on growth trajectories and tree architectural development, with WS trees having the slower growth trajectories -mediated through smaller internode length-, smaller trunk heights and diameters for a given age, and less numerous branches across their lifespan. The analysis of growth trajectories based on architectural analysis improved our ability to detect the effects of soil types compared to measured functional traits. Intraspecific variability is higher for growth trajectories than functional traits for C. obtusa, revealing the higher sensitivity of the architectural approach in comparison to the functional approach in the case of C. obtusa. Soil-related response of Cecropia functional traits is not homologous to the community-level environmental filtering, suggesting that the effects of the acting ecological processes are different between the two levels.