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under climate and human pressure
Modeling of plant growth
Overview
A dynamic vegetation model (DVM) is dynamic in time and space. It computes explicitly various physical, biogeochemical and ecological processes like soil hydrology, vegetation physiology or nutrient budget. For this reason, but depending on the scale of its application, it needs some adaptations, e.g. to plant species, to dispersion characteristics. In addition, it could be upgraded with new processes, e.g. with some germination aspects or the translation into ecosystem services.
The inputs of the model are soil texture, plant constants, monthly or daily climate variables (air temperature, precipitation, percentage of sunshine hours, air relative humidity and wind speed), and CO2 partial pressure. The outputs are numerous: parameters of water budget, energy, plant growth, etc. (see diagram below). Therefore, it is possible to observe the vegetation changes under the various hypotheses.
The model used at continental scale with a 20 km resolution grid already simulated a mix of savannas and tropical rain forest on the selected region. The increase of resolution to the kilometer and the use of the new fire module will directly enhance the precision of the simulation. Gains will also come with the upgrades, the local adaptations and the inclusions of crops.
Objectives
A first goal is to adapt the model and use it to simulate the growth of the five selected species in the framework of the rest of the vegetation also grown by the model.
Once ready, the model can be coupled with the ABM to quantify the ecosystem services.
Then, through various scenarios (climate combined with socio-economic) for the future, the coupled models can simulate how ecosystem services could evolve and if the forest would be able of regeneration.
Approach
The adaptation of local flora is done by creating local BAGs. The method consists in establishing lists of plant species representative of the various habitats. For each species, one looks for occurrences (coordinates or localities) in atlases, flora or online databases like GBIF. The coordinates permit to obtain bioclimatic limits which produce the BAGs through discriminant analysis. These objects make the background vegetation for modelling in which the five selected tree species are grown. The model simulate the growth of the BAGs and of the five species under the various hypotheses of climate change and CO2 partial pressure. The BAGs are necessary to produce competition for space and resources (light and water in the current version of the model). Otherwise, the five species alone would occupy all the allowed virtual space. The background vegetation is computed through the BIOME routine, which compares the net primary productivities and leaf area indices of the differents BAGs present on the grid cell. It thus adds the information of the vegetation type and allows to map this information. Some species are able to grow in savannas or secondary forest or else. In addition, it is possible to impose an additional human stress like fire. The model integrate some effect of the fauna. The ABM is used to derive control of hunting since it provokes defaunation particularly of large animals, a supposed limiting factor of forest regeneration according to literature.
Diagram showing the different processes considered by the dynamic vegetation model.
From Dury, M., Hambuckers, A., Warnant, P., Henrot, A., Favre, E., Ouberdous, M., Francois, L., 2011.
Iforest-Biogeosciences and Forestry 4, 82-99.