Evaluating the potential of the SORTIE forest succession model for spatio-temporal analysis of small-scale disturbances

Abstract

Ecologists and forest managers both recognize the importance of detailed spatio-temporal knowledge on local small-scale disturbances (SSD) dynamics and impacts. However, a large proportion of the knowledge about SSD is based on temporally short data sets, and on non-spatial analysis. SORTIE, a stochastic and mechanistic spatially explicit and individual-based forest succession model, is particularly well suited for simulating SSD and overcoming traditional field studies limitations. Our main goal is to investigate the potential of SORTIE for spatio-temporal analysis of SSD. More specifically, we intend to evaluate the model sensitivity to initial conditions, and to assess the impact of introduced minor disturbances on the species densities. We hypothesize that SORTIE will generate realistic species dynamics within the range of tested scenarios. We performed simulations over a period of 1000 years using two different initial spatial configurations (Random and Aggregated) and fifteen replicates. For each replicate we extracted, at each time step of 5 years, the species local spatial structure with the use of the Ripley's K statistic. The resulting time series periods and trends were compared between initial condition scenarios by performing phase coherence and regression analysis. In another set of simulations, SSD of different sizes (500, 800 and 1100 m 2) were introduced at two distinct time steps (400 and 600 years). Species density time series were analyzed again in terms of periodicity and trend. Results indicate a sensitivity to initial conditions limited to the first 300 years, and a very similar species local spatial structure between the scenarios after that period. Also, statistical tests revealed that the species densities are not sensitive to single introduced SSD, for all SSD sizes and moments of disturbance. These conclusions suggest that SORTIE can be a valuable complementary tool to SSD field studies.