Forest expansion or fragmentation? Discriminating forest fragments from natural forest patches through patch structure and spatial context metrics.

In forest-grassland mosaics, patches can result from two processes: forest expansion over grassy ecosystems and forest fragmentation. We tested the hypothesis that patches produced by these processes differed in structure and spatial context in a forest-grassland mosaic in the southern Brazilian highlands. We compared a present-day land cover map with a past vegetation map to identify natural forest patches and forest fragments. Patches were described according to structure (size, core area and shape metrics) and spatial context (distance from roads and urban areas, edge contrast). Principal component analyses were used to examine gradients of patch types, and differences were tested by analysis of variance with randomization test. We found 878 natural patches and 214 fragments. Natural forest patches, riparian forest patches and forest fragments differed in structure and spatial context. In comparison to natural forest patches, fragments tend to be larger, with larger core areas, and more irregular and complex in shape. Fragments are situated in a different spatial context, tending to be closer to roads and urban areas and to present higher edge contrast. Riparian natural forest patches are similar to natural forest patches, except for shape. The smaller area and regular shape of natural patches probably result from the mechanisms involved in nucleus formation in the grassland matrix and from current grassland management. Natural patches are less exposed to some anthropogenic stresses, since most of them remain in a native grassland matrix context. Our results show that inferring process from pattern is not trivial, because different processes - forest expansion and forest fragmentation - may lead to either distinct or similar patterns of patch shape and spatial context. Studying patch structure and spatial context may then provide further insight into understanding changes in vegetation pattern at landscape scale, and in disentangling the effects of concurrent processes. [ABSTRACT FROM AUTHOR]