Abstract
Tropical forests are subject to seasonal hurricanes resulting in cycles of canopy opening and deposition of litter, followed by periods of recovery and canopy closure. Herein, we review two studies of litter-based communities in Puerto Rico; (i) a survey of bromeliad invertebrates in three montane forest types along an elevational gradient in 1993–1997, during a period of canopy recovery after two severe hurricanes, and the results compared with those from a resurvey in 2010, and (ii) a large scale canopy trimming experiment in the lower montane (Tabonuco) forest designed to simulate an hurricane event, and to separate the effects of canopy opening from debris deposition. Measurements of changes in invertebrate community parameters and decay rates of litter were made in a litter bag experiment as part of this major experiment. As the canopy closed, during the periods of study, bromeliad density reduced, especially in the Tabonuco forest. This was associated with a decline in both alpha and gamma invertebrate diversity, which appears to have involved the loss of rarer species. In the Tabonuco forest, two endemic bromeliad specialists were not found during resampling in 2010, though the most common species were remarkably stable over the two decades. Canopy opening significantly altered the diversity, biomass, and composition of litter communities, irrespective of litter deposition. It particularly reduced organisms responsible for comminution of litter and increased the activity of fungivores and microbiovores. Both studies showed that canopy disturbance, either indirectly or directly, adversely affects invertebrate diversity and detrital processing.
Highlights
Caribbean forests are shaped by hurricanes that cause structural damage to the canopy through defoliation, branch, and tree falls, with consequential changes in light regime, microclimate, and increased heterogeneity in the understorey [1]
We review the changes in two litter-based invertebrate communities, one in bromeliads in three forest types along an elevational gradient following canopy recovery after two severe hurricanes, and forest floor litter invertebrates in an experimental canopy trimming experiment (CTE), designed to simulate a hurricane in the Caribbean island of Puerto Rico
In forests the canopy is of prime importance in circulation of nutrients
Summary
Caribbean forests are shaped by hurricanes that cause structural damage to the canopy through defoliation, branch, and tree falls, with consequential changes in light regime, microclimate, and increased heterogeneity in the understorey [1]. There is evidence of generally increasing liana abundance and biomass in New World forests due to increasing forest disturbance, fragmentation, and elevated atmospheric CO2 [2] This increase in lianas can add to shading and result in decreased tree diversity, recruitment, growth, and survival [2], and could reduce understorey bromeliad density. The trees are tall, the canopy is dense, with thin, large, simple, or compound leaves, and little understorey in the mature forest, except in riparian areas. It has the highest diversity of tree species of the three forests. The effects of canopy disturbance on litter invertebrates may be direct, as a result of changes in litter and soil moisture, temperature, nutrient resources, and light regime, as a consequence of canopy opening and litter deposition, or indirect, through changes in the forest affecting the distribution of bromeliads, and their invertebrate communities
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