Linking stochasticity to determinism of woody plant recruitment in a mosaic landscape: A spatially explicit approach

Here, we investigate small-scale spatial variation of environmental factors potentially influencing woody-plant establishment for 3 years (2004, 2005 and 2006) along a heterogeneous landscape. Environmental variables of over 2883 potential microsites were sampled in different landscape units with a spatially explicit design, and seeds of four tree species were sown at the different microsites. We used spatial-analysis techniques to quantify spatial heterogeneity of the environment surrounding the seeds, and to relate seedling and sapling survival to the spatial structure of environmental factors studied. Most environmental variables showed aggregated spatial patterns among landscape units. However, survival showed random spatial patterns in most of the cases, although it may depend on year-to-year variation of precipitation. Thus, spatial patterns of survival were random under both wet and dry conditions, while aggregated patterns emerged under intermediate conditions. Aggregated survival, if detected, was better explained by the environmental variables studied as plant age increased. In addition, the spatial consistency found across demographic stages, represents hotspots of recruitment, for which direct identification would be critical for restoration activities. Our results showed a balance between stochasticity at early stages and environmental determinism at later stages, showing, behind the idiosyncratic character of plant recruitment, stronger general rules at sapling stages.