The interaction of land-use legacies and hurricane disturbance in subtropical wet forest: twenty-one years of change

Disturbance shapes plant communities over a wide variety of spatial and temporal scales. How natural and anthropogenic disturbance interact to shape ecological communities is highly variable and begs a greater understanding. We used five censuses spanning the years 1990-2011 from the 16-ha Luquillo Forest Dynamics Plot (LFDP) in northeast Puerto Rico to investigate the interplay of human land-use legacies dating to the early 20th century and two recent hurricanes (Hugo, 1989 and Georges, 1998). The LFDP is a landscape mosaic comprised of an area of mature subtropical wet forest and three areas of secondary forest with differing past land-use intensities. We examined the degree to which hurricane disturbance-effect and subsequent community recovery varied across past land-use classes. We expected areas with greater intensity of human land use to be more affected by hurricane disturbance therefore exhibiting greater initial damage and longer successional recovery times. Structurally, areas of secondary forest contained smaller trees than old-growth areas; hurricanes caused widespread recruitment of shrubs and saplings that thinned with time since the first hurricane. Species richness of the plot declined over time, mostly due to the loss of rare species, but also due to the loss of some heliophilic, pioneer species that became abundant after the first hurricane. Species composition differed strongly between areas of secondary and mature forest, and these differences were largely constant over time, except for an increase in compositional differences following the second hurricane. An indicator species analysis attributed this pattern to the longer persistence of pioneer species in areas of greater past land-use intensity, likely due to the more open canopy in secondary forest. When secondary forest areas of differing past land-use intensity were considered separately, few species of low community rank were found as indicators. When these areas were combined, more and higher-ranked species emerged as indicators, creating ecologically meaningful indicator species combinations that better captured the broad-scale plant community response to past land use. Our findings support the idea that effects of past land use can persist for decades to centuries following land-use abandonment, illustrating the importance of land-use legacies in shaping regenerating tropical secondary forests.