In tropical rainforests, interspecific variation in leaf- and wood functional traits represents the spectrum of tree life-history strategies, from shade-intolerant “pioneers” to shade tolerant late successional species. Several studies have invoked functional trait variation across understory light gradients to infer mechanisms of tree species co-existence. While it remains untested, it may be expected that pronounced differences in disturbance regimes across large biogeographical scales may also drive community-level patterns in traits. For instance, in Caribbean rainforests where large-scale disturbances with multi-decadal return intervals (i.e. hurricanes) drive forest dynamics, one may expect tree floras to primarily express “pioneer” leaf and wood traits, such as high maximum photosynthetic rates (Amax) and low wood density (Dt).
Results/Conclusions
In comparing leaf and wood functional traits across two forest types (hurricane disturbed forests in Dominica, West Indies, versus seasonally dry Panamanian rainforests), we found no evidence for disturbance-mediated shifts in trait values. Common tree species from Dominican and Panamanian forests exhibited similar ranges and distributions of Amax, leaf nitrogen (N), leaf mass per area (LMA), and Dt. However, an interesting pattern unique to hurricane-disturbed forests in Dominica was the ecophysiological traits of 2 near-endemic dominant species, Amanoa caribaea (Euphorbiaceae) and Tapura latifolia (Dichapetalaceae). Both species are restricted to a small range in the Lesser Antilles from St. Lucia to Guadaloupe, and between them constitute on average 21.1% of total forest basal area (11.0 m2 ha-1). When compared to 13 additional common Dominican species comprising on average 51.2% of forest basal area (27.6 m2 ha-1), A. caribaea and T. latifolia consistently showed traits which bracketed the “shade tolerant” end of trait axes. For example, Amax values for A. caribaea and T.latifolia were 3.15 and 3.09 mmol m-2 s-1, respectively, and only one species (Licania ternatensis (Chrysobalanaceae), considered a “regional endemic”) showed lower Amax. Similarly, A. caribaeaand T. latifolia exhibited 2 of the 3 lowest values for foliar N, and 2 of the 3 highest values for LMA and Dt. Overall, our results suggest severe disturbance regimes may not give rise to community-specific functional trait distributions. However, our results regarding the ecophysiology of dominant near-endemic tree species in Dominican rainforests may provide some insight as to processes structuring Caribbean rainforests. Specifically, our results suggest that possibly tree species resistant or resilient to hurricane damage, and not fast-growing pioneers thriving in disturbed areas, may evolve locally and dominate in hurricane-disturbed rainforest canopies.
