Patch dynamics and community metastability of a subtropical forest: compound effects of natural disturbance and human land use

Where large disturbances do not cause landscape-wide mortality and successional change, forested ecosystems should exhibit landscape metastability (landscape equilibrium) at a scale equal to the dominant patch size of disturbance and recovery within the landscape. We investigated this in a 16-ha contiguous plot of subtropical wet forest in Puerto Rico, the Luquillo Forest Dynamics Plot (LFDP), which experienced two major hurricanes during the 15-year study and has a land use history (logging and agriculture 40 or more years hence) that differs in intensity between two areas of the plot. Using he LFDP as our landscape, we studied the spatial pattern of community change through time (3-5 year intervals) by calculating community dissimilarity between tree censuses for two size classes of trees (1 to < 10 cm DBH and a parts per thousand yen10 cm DBH) in quadrats ranging in size from 0.010-1 ha and for the entire landscape, i.e., plot or land use type. The point at which the decline in community dissimilarity with quadrat size showed maximum curvature identified the dominant patch size (i.e., point of metastability). For canopy trees a parts per thousand yen10 cm dbh, there was no evidence that the community experienced landscape-wide successional changes in either land use type, and we found a consistent patch size of community change around 0.1 ha (range 0.091-0.107). For the understory tree and shrub community (1 to < 10 cm dbh) there was some evidence of landscape-wide community changes over time in response to hurricane damage, apparently driven by interactions with the dominant canopy species, whose composition varied with land use intensity, and their species-specific susceptibility to hurricane damage.