A process-based model of old field succession linking ecosystem and community ecology

This paper presents a mechanistic model of plant succession to simulate the growth of natural vegetation during long fallow periods in traditional cropping systems of the high tropical Andes. The vegetation is described as a multilayer mixture of species in competition for light and soil nitrogen. In each layer leaves are randomly distributed. The model predicts growth and biomass production of each species, and takes into account carbon and nitrogen cycling through plants and soil. It uses a daily time-step with meteorological data as forcing variables. It considers six species with four organs: leaves, stems, seeds and roots. It simulates photosynthesis; growth and maintenance respiration; carbon allocation; nitrogen uptake, fixation and remobilization; tissue mortality; and seed dispersion and germination. Our simulations show among other results that: (1) it may be difficult to detect changes in the amount of soil nitrogen during fallow periods, because simulated changes in soil nitrogen are lower than the spatial variability of the measurements; (2) how the initial seed pool and resource availability affects the pattern of succession and the dominant or co-dominant late successional species; and as a consequence (3) higher soil nitrogen availability may not always result in higher ecosystem productivity. The implication of these modeling results for the management of long fallow cropping systems is also discussed.