Fine-scale patch mosaic of developmental stages in Northeast American secondary temperate forests: the European perspective
Conceptual models that describe temperate forest dynamics differ substantially between Europe and America. In Europe, the concept of the forest cycle describes a sequentially shifting fine-scale mosaic of patches in different phases of forest development. In North America, the descriptive concept is largely based on severe coarse-scale disturbances that repeat in a cyclic fashion and restart the succession of the whole forest stand from initiation through to ‘old-growth,’ neglecting the within-stand dynamics on the patch level. Here, we investigate fine-scale stand structures across European and North American forests by applying the European concept of forest developmental phases to all stands. The patches of four major forest developmental stages were recognized and delineated by the spatially explicit rule-based classification system implemented in GIS, which employs stem position maps of live and dead trees for analysis. The basic quantitative characteristics of identified patch structures in the N. American stands, as the Mean Patch Size of the mosaic (between 760 and 890 m2), were comparable with European old-growth stands, although mosaic complexity was higher in the latter. We demonstrated that in addition to the large-scale forest cycle assumed by N. American conceptual models there simultaneously exist finer-scale patch dynamics described by the European conceptual model. We also demonstrated that the occurrence of the Steady State stage was promoted by higher local tree species richness, which may explain the abundant occurrence of this stage in N. American secondary stands. The Steady State stage of the European model might represent an important commonality across both paradigms.