Simulating the response of mixed broadleaved forests to changes in climate conditions: disentangling the relative importance of various abiotic factors

Forests will face in the future unprecedented climatic conditions that are expected to impact them in various and sometimes opposite ways. The fertilizing effect of rising atmospheric CO2 concentrations and nitrogen deposits added to the lengthening of the vegetation period due to warmer temperatures are likely to increase forest productivity. These effects could be offset or even reversed by the increase of drought frequency and severity that trigger stomatal closure and can even lead to tree death. Due to the complex interactions between these factors, their spatial variability and the uniqueness of their combinations, the future forest response to climate change cannot be deducted only from observational studies or environmental manipulation experiments. Here, we use HETEROFOR, an individual and mechanistic tree growth model recently developed and evaluated to simulate the gross primary production of diverse mixed broadleaved forest according to different climatic scenarios. Among the model outputs, a drought index accounting for both the length and the magnitude of the stand hydric deficit is calculated. First, these simulations are conducted with atmospheric CO2 concentration values maintained constant, then with those from the IPCC scenarios. The results of these simulations are finally used to assess the impact of the various abiotic stressors and their interactions on forest productivity. In a second step, a second set of simulations is launched to assess the impact of the soil properties and of the stand composition, structure and density on tree growth by interchanging soil and forest structures subjected or not to different thinning intensity

Which benefits in the use of a modeling platform : the VSoil example

In the environmental community the need for coupling the models and the associated knowledges emerged recently. The development of a coupling tool or of a modeling platform is mainly driven by the necessity to reate models accounting for multiple processes and to take into account the feed back between these processes. Models focusing on a restricted number of processes exist and thus the coupling of these numerical tools appeared as an efficient and rapid mean to fill up the identified gaps. Several tools have been proposed : OMS3 (David et al. 2013) ; CSDMS framework (Peckham et al. 2013) ; the Open MI project developed within the frame of European Community (Open MI, 2011). However, what we should expect from a modeling platform could be more ambitious than only coupling existing numerical codes. We believe that we need to share easily not only our numerical representations but also the attached knowledges. We need to rapidly and easily develop complex models to have tools to bring responses to current issues on soil functioning and soil evolution within the frame of global change. We also need to share in a common frame our visions of soil functioning at various scales, one the one hand to strengthen our collaborations, and, on the other hand, to make them visible by the other communities working on environmental issues. The presentation will briefly present the VSoil platform. The platform is able to manipulate concepts and numerical representations of these processes. The tool helps in assembling modules to create a model and automatically generates an executable code and a GUI. Potentialities of the tool will be illustrated on few selected cases

Luberon2 user manual - A forest demo-genetic simulation software on Capsis

Luberon2 is a forest dynamics model with heritable trait variation to simulate the joint effects of natural evolutionary processes including stochastic disturbance, thinning and cutting, and genetic diversity in monospecific stands: it is a demo-genetic agent-based model (Oddou-Muratorio et al, 2020; Lamarins et al, 2022). The current version runs either for cedar (Cedrus atlantica), Douglas fir (Pseudotsuga menziesii), Norway spruce (Picea abies), and larch (Larix sp.). Fir species (Abies sp.) are planned. Using a graphical interactive environment or a script mode, it can be used with various levels of expertise for communication, teaching, training or research purposes. The model is developed on the Capsis modeling platform, available upon request. This user manual contains a synthetic presentation of the model and more detailed documentation on the model. Some sections can be skipped depending on the level of use of the model: (1) simple simulations using pre-existing input files; (2) development of ad-hoc input files for personalized simulations; (3) advanced use of all parameters’ flexibility; (4) extension of the model or re-use of parts of the code. Luberon2 is continuously evolving, the latest version of the user-manual and a quick tutorial to the graphical interface are available on the Capsis website

HETEROFOR 1.0: a spatially explicit model for exploring the response of structurally complex forests to uncertain future conditions. I. Carbon fluxes and tree dimensional growth.

International audienceGiven the multiple abiotic and biotic stressors resulting from global changes, management systems and practices must be adapted in order to maintain and reinforce the resilience of forests. Among others, the transformation of monocultures into uneven-aged and mixed stands is an avenue to improve forest resilience. To explore the forest response to these new silvicultural practices under a changing environment, one need models combining a process-based approach with a detailed spatial representation, which is very rare.We therefore decided to develop our own model (HETEROFOR) according to a spatially explicit approach describing individual tree growth based on resource sharing (light, water and nutrients). HETEROFOR was progressively elaborated through the integration of various modules (light interception, phenology, water cycling, photosynthesis and respiration, carbon allocation, mineral nutrition and nutrient cycling) within CAPSIS, a collaborative modelling platform devoted to tree growth and stand dynamics. The advantage of using such a platform is to use common development environment, model execution system, user- interface and visualization tools and to share data structures, objects, methods and libraries.This paper describes the carbon-related processes of HETEROFOR (photosynthesis, respiration, carbon allocation and tree dimensional growth) and evaluates the model performances for a mixed oak and beech stand in Wallonia (Belgium). This first evaluation showed that HETEROFOR predicts well individual radial growth and is able to reproduce size-growth relationships. We also noticed that the more empirical options for describing maintenance respiration and crown extension provide the best results while the process-based approach best performs for photosynthesis. To illustrate how the model can be used to predict climate change impacts on forest ecosystems, the growth dynamics in this stand was simulated according to four IPCC climate scenarios. According to these simulations, the tree growth trends will be governed by the CO2 fertilization effect with the increase in vegetation period length and in water stress also playing a role but offsetting each other

Radiative transfer modeling in structurally complex stands: towards a better understanding of parametrization

Key message : The best options to parametrize a radiative transfer model change according to the response variable used for fitting. To predict transmitted radiation, the turbid medium approach performs much better than the porous envelop, especially when accounting for the intra-specific variations in leaf area density but crown shape has limited effects. When fitting with tree growth data, the porous envelop approach combined with the more complex crownshape provides better results. When using a joint optimization with both variables, the better options are the turbid medium and the more detailed approach for describing crown shape and leaf area density. Context : Solar radiation transfer is a key process of tree growth dynamics in forest. Aims : Determining the best options to parametrize a forest radiative transfer model in heterogeneous oak and beech stands from Belgium. Methods : Calibration and evaluation of a forest radiative transfer module coupled to a spatially explicit tree growth model were repeated for different configuration options (i.e., turbid medium vs porous envelope to calculate light interception by trees, crown shapes of contrasting complexity to account for their asymmetry) and response variables used for fitting (transmitted radiation and/or tree growth data). Results : The turbid medium outperformed the porous envelope approach. The more complex crown shapes enabling to account for crown asymmetry improved performances when including growth data in the calibration. Conclusion : Our results provide insights on the options to select when parametrizing a forest radiative 3D-crown transfer model depending on the research or application objectives

A demo‐genetic model shows how silviculture reduces natural density‐dependent selection in tree populations

International audienceBiological production systems and conservation programs benefit from and should care for evolutionary processes. Developing evolution‐oriented strategies requires knowledge of the evolutionary consequences of management across timescales. Here, we used an individual‐based demo‐genetic modelling approach to study the interactions and feedback between tree thinning, genetic evolution, and forest stand dynamics. The model combines processes that jointly drive survival and mating success—tree growth, competition and regeneration—with genetic variation of quantitative traits related to these processes. In various management and disturbance scenarios, the evolutionary rates predicted by the coupled demo‐genetic model for a growth‐related trait, vigor, fit within the range of empirical estimates found in the literature for wild plant and animal populations. We used this model to simulate non‐selective silviculture and disturbance scenarios over four generations of trees. We characterized and quantified the effect of thinning frequencies and intensities and length of the management cycle on viability selection driven by competition and fecundity selection. The thinning regimes had a drastic long‐term effect on the evolutionary rate of vigor over generations, potentially reaching 84% reduction, depending on management intensity, cycle length and disturbance regime. The reduction of genetic variance by viability selection within each generation was driven by changes in genotypic frequencies rather than by gene diversity, resulting in low‐long‐term erosion of the variance across generations, despite short‐term fluctuations within generations. The comparison among silviculture and disturbance scenarios was qualitatively robust to assumptions on the genetic architecture of the trait. Thus, the evolutionary consequences of management result from the interference between human interventions and natural evolutionary processes. Non‐selective thinning, as considered here, reduces the intensity of natural selection, while selective thinning (on tree size or other criteria) might reduce or reinforce it depending on the forester's tree choice and thinning intensity

Luberon2 user manual - A forest demo-genetic simulation software on Capsis

Luberon2 is a forest dynamics model with heritable trait variation to simulate the joint effects of natural evolutionary processes including stochastic disturbance, thinning and cutting, and genetic diversity in monospecific stands: it is a demo-genetic agent-based model (Oddou-Muratorio et al, 2020; Lamarins et al, 2022). The current version runs either for cedar (Cedrus atlantica), Douglas fir (Pseudotsuga menziesii), Norway spruce (Picea abies), and larch (Larix sp.). Fir species (Abies sp.) are planned. Using a graphical interactive environment or a script mode, it can be used with various levels of expertise for communication, teaching, training or research purposes. The model is developed on the Capsis modeling platform, available upon request. This user manual contains a synthetic presentation of the model and more detailed documentation on the model. Some sections can be skipped depending on the level of use of the model: (1) simple simulations using pre-existing input files; (2) development of ad-hoc input files for personalized simulations; (3) advanced use of all parameters’ flexibility; (4) extension of the model or re-use of parts of the code. Luberon2 is continuously evolving, the latest version of the user-manual and a quick tutorial to the graphical interface are available on the Capsis website

Luberon2 user manual

Luberon2 is a forest dynamics model with heritable trait variation to simulate the joint effects of natural evolutionary processes including stochastic disturbance, silviculture, and genetic diversity in monospecific stands: it is a demo-genetic agent-based model. The current version runs either for cedar (Cedrus atlantica) or for Douglas fir (Pseudotsuga menziesii), other species choices are planned. Using a graphical interactive environment or a script mode, it can be used with various levels of expertise for communication, teaching, training or research purposes. The model is developed on the Capsis modeling platform, available upon request. This user manual contains a synthetic presentation of the model and more detailed documentation on the model. Some sections can be skipped depending on the level of use of the model: (1) simple simulations using pre-existing input files; (2) development of ad-hoc input files for personalized simulations; (3) advanced use of all parameters’ flexibility; (4) extension of the model or re-use of parts of the code. Luberon2 is continuously evolving, the latest version of the user-manual and a quick tutorial to the graphical interface are available on the Capsis website

How much genetic selection for growth can result from silviculture ? A new demo-genetic simulation approach

International audienceThe genetic composition of forest stands dynamically evolves driven by the combination of natural processes and management practices. Evolution-oriented forest management consists in understanding and stewarding these combined processes to enhance short-term adaptation and productivity while maintaining long-term evolvability.Silviculture is a sequence of practices, each having multiple possible genetic impacts, depending one on the other. Moreover, silvicultural practices interact with demographic changes due to other natural causes like environment changes. All these dependencies and interactions make an analytical approach of the resulting evolutionary dynamics, based on quantitative genetics, very complex. Here, we developed a demo-genetic simulation approach of this issue.Previous demo-genetic models in forest systems mainly focused on the possible impacts of silviculture on the overall (neutral) gene diversity. Here we focus on the selection effects on growth. We coupled a quantitative genetics model to a growth dynamics model calibrated for Cedrus atlantica, and simulated various scenarios of silviculture, using the CAPSIS simulation platform (http://capsis.cirad.fr/capsis/help_en/luberon2).We compared the effect of various management practices on (i) the growth, (ii) the genetic quality and (iii) the evolutionary potential of the stand. We show that different silviculture sequences may result in very different levels of selection intensity for growth, which have different impacts on the dynamics of genetic means and variances from one generation of trees to the next. We also show the importance of all stages of interventions, including those in the juvenile stage, on the final genetic impacts. Finally, we show that the effective genetic impacts of a given silviculture guideline are highly influenced by pragmatic choices in the forest and by local disturbance regimes.This work should be considered as a “proof of concept” showing that demo-genetic models coupling forest dynamics, quantitative genetics, silviculture practices and natural disturbances are feasible. Such models provide a powerful approach to investigate the potential genetic impacts of silviculture and guide evolution-oriented forest management. We are currently extending this approach to other species and other contexts