Forest succession in tropical hardwood hammocks of the Florida keys: Effects of direct mortality from Hurricane Andrew

A tree species replacement sequence for dry broadleaved forests (tropical h ardwood hammocks) in the upper Florida Keys was inferred from species abund ances in stands abandoned from agriculture or other anthropogenic acitiviti es at different rimes in the past. Stands were sampled soon after Hurricane Andrew, with live and hurricane-killed trees recorded separately; thus it was also possible to assess the immediate effect of Hurricane Andrew on sta nd successional status. We used weighted averaging regression to calculate successional age optima and tolerances for all species, based on the specie s composition of the pre-hurricane stands. Then we used weighted averaging calibration to calculate and compare inferred successional ages for stands based on (1) the species composition of the pre-hurricane stands and (2) th e hurricane-killed species assemblages. Species characteristic of the earli est stages of post-agricultural stand development remains a significant com ponent of the forest for many years, but are gradually replaced by taxa not present, even as seedlings, during the first few decades. This composition al sequence of a century or more is characterized by the replacement of dec iduous by evergreen species, which is hypothesized to be driven by increasi ng moisture storage capacity in the young organic soils. Mortality from Hur ricane Andrew was concentrated among early-successional species, thus tendi ng to amplify the long-term trend in species composition.