Long-term fragmentation effects on the distribution and dynamics of canopy gaps in a tropical montane forest

Fragmentation alters forest canopy structure through various mechanisms, which in turn drive subsequent changes to biogeochemical processes and biological diversity. Using repeated airborne LiDAR (Light Detection and Ranging) mappings, we investigated the size distribution and dynamics of forest canopy gaps across a topical montane forest landscape in Hawaii naturally fragmented by lava.100 yr ago. The combined effects of long-term isolation were evaluated using edge-proximity patterns in the distribution of gaps identified in year 1 ("existing gaps"). In addition, using the data from year 2, we investigated patterns in the loss of canopy ("new gaps") and regrowth of canopy ("filled gaps"). The size distributions of the three gap types were modelled using the power-law exponent, k. We found that fragmentation has resulted in some large changes in gap dynamics, with both the total area of gaps and the relative proportion of large existing gaps increased with distance to fragment edge. In models of powerlaw distribution scaling, k estimates decreased to asymptotic values within 20 m of fragment edges for existing gaps. The size distributions of new and filled gaps were surprisingly similar. However, the total area of filled gaps was less than that of new gaps, and this difference was greatest near fragment edges. From these results, we conclude that fragmentation may be capable of continuously altering gap-phase dynamics of a forest for more than a century.