Revisiting the interaction of land use and the environment in a Puerto Rican subtropical wet forest

Background/Question/Methods

The Luquillo Forest Dynamics Plot (LFDP) has provided many insights into the successional dynamics of Caribbean wet forests as they respond to natural disturbance and a history of logging and subsistence agriculture.  Established in 1990, following Hurricane Hugo, the LFDP has been surveyed approximately every five years since, most recently in 2011.  Two major hurricanes have struck the LFDP; Hurricane Hugo in 1989, and Hurricane Georges in 1998.  Data from 1990 indicated a strong influence of land use history on species composition of secondary forest.  Clear patterns in species distribution reflect significant tree felling and farming in the northern two-thirds of the plot, where Casearia arborea dominates, and light disturbance from selective logging in the southern area, where old-growth species such as Dacryodes excelsa are abundant.  We revisited the interaction of past-human land use, tropical forest succession and hurricane disturbance.  Does the land-use signal get stronger, weaker or remain constant over time?  Addressing this question should help determine the future of tropical secondary forests with a history of human land use.  We used multivariate methods to determine how the strength of the land-use signal changed over time and the changes in species abundance explaining these differences.

Results/Conclusions

A Multiple Response Permutation Procedure (MRRP) showed the land-use signal to weaken following Hurricane Hugo (1990 – 1995), then become stronger (as indicated by the magnitude of A from the MRRP) after Hurricane Georges (in the census completed in 2000). The magnitude of the signal then weakened (indicated by a diminishing value of A) again through the last two censuses.  Thus, hurricanes reinforce the land-use signal in the LFDP over the short-term.  Differences in indicator species were found with respect to land use, with anthropogenically-associated pioneer species displaying higher indicator values in the high land-use region, and another suite of pioneer and native forest species being strong indicators in the low land-use area.  We conclude that land-use legacies remain a key driver in community composition and structure in Puerto Rican forests, with hurricanes disturbances playing a key role in maintaining these differences over the short-term.  This is despite simulation models that suggest these land-use history differences will become diminished over longer periods of time.