Multi-scale analysis on species diversity within a 40-ha old-growth temperate forest

In order to better explore the maintenance mechanisms of biodiversity, data collected from a 40-ha undisturbed Pinus forest were applied to the Individual Species–Area Relationship model (ISAR) to determine distribution patterns for species richness. The ecological processes influencing species abundance distribution patterns were assessed by applying the same data set to five models: a Log-Normal Model (LNM), a Broken Stick Model (BSM), a Zipf Model (ZM), a Niche Preemption Model (NPM), and a Neutral Model (NM). Each of the five models was used at six different sampling scales (10 m × 10 m, 20 m × 20 m, 40 m × 40 m, 60 m × 60 m, 80 m × 80 m, and 100 m × 100 m). Model outputs showed that: (1) Accumulators and neutral species strongly influenced species diversity, but the relative importance of the two types of species varied across spatial scales. (2) Distribution patterns of species abundance were best explained by the NPM at small scales (10 m–20 m), whereas the NM was the best fit model at large spatial scales. (3) Species richness and abundance distribution patterns appeared to be driven by similar ecological processes. At small scales, the niche theory could be applied to describe species richness and abundance, while at larger scales the neutral theory was more applicable.