RESUMO
Liverworts and mosses are a major component of the epiphyte flora of tropical montane forest ecosystems. Canopy access was used to analyse the distribution and vertical stratification of bryophyte epiphytes within tree crowns at nine forest sites across a 3400 m elevational gradient in Peru, from the Amazonian basin to the high Andes. The stable isotope compositions of bryophyte organic material (13C/12C and 18O/16O) are associated with surface water diffusive limitations and, along with C/N content, provide a generic index for the extent of cloud immersion. From lowland to cloud forest δ13C increased from -33 to -27, while δ18O increased from 16.3 to 18.0. Epiphytic bryophyte and associated canopy soil biomass in the cloud immersion zone was estimated at up to 45 t dry mass ha-1, and overall water holding capacity was equivalent to a 20 mm precipitation event. The study emphasizes the importance of diverse bryophyte communities in sequestering carbon in threatened habitats, with stable isotope analysis allowing future elevational shifts in the cloud base associated with changes in climate to be tracked.
Assuntos
Biodiversidade , Biomassa , Briófitas/química , Isótopos de Carbono/análise , Isótopos de Oxigênio/análise , Altitude , Florestas , PeruRESUMO
Understanding demographic transitions may provide the key to explain the high diversity of tropical tree communities. In a faunally intact Amazonian forest, we compared the spatial distribution of saplings of 15 common tree species with patterns of conspecific seed fall, and examined the seed-to-sapling transition in relation to locations of conspecific trees. In all species, the spatial pattern of sapling recruitment bore no resemblance to predicted distributions based on the density of seed fall. Seed efficiency (the probability of a seed producing a sapling) is strongly correlated with distance from large conspecific trees, with a >30-fold multiplicative increase between recruitment zones that are most distant vs. proximal to conspecific adults. The striking decoupling of sapling recruitment and conspecific seed density patterns indicates near-complete recruitment failure in areas of high seed density located around reproductive adults. Our results provide strong support for the spatially explicit predictions of the Janzen-Connell hypothesis.