Abstract
Canopy gaps created by wind-throw events, or blowdowns, create a complex mosaic of forest patches varying in disturbance intensity and recovery in the Central Amazon. Using field and remote sensing data, we investigated the short-term (four-year) effects of large (>2000 m2) blowdown gaps created during a single storm event in January 2005 near Manaus, Brazil, to study (i) how forest structure and composition vary with disturbance gradients and (ii) whether tree diversity is promoted by niche differentiation related to wind-throw events at the landscape scale. In the forest area affected by the blowdown, tree mortality ranged from 0 to 70%, and was highest on plateaus and slopes. Less impacted areas in the region affected by the blowdown had overlapping characteristics with a nearby unaffected forest in tree density (583±46 trees ha−1) (mean±99% Confidence Interval) and basal area (26.7±2.4 m2 ha−1). Highly impacted areas had tree density and basal area as low as 120 trees ha−1 and 14.9 m2 ha−1, respectively. In general, these structural measures correlated negatively with an index of tree mortality intensity derived from satellite imagery. Four years after the blowdown event, differences in size-distribution, fraction of resprouters, floristic composition and species diversity still correlated with disturbance measures such as tree mortality and gap size. Our results suggest that the gradients of wind disturbance intensity encompassed in large blowdown gaps (>2000 m2) promote tree diversity. Specialists for particular disturbance intensities existed along the entire gradient. The existence of species or genera taking an intermediate position between undisturbed and gap specialists led to a peak of rarefied richness and diversity at intermediate disturbance levels. A diverse set of species differing widely in requirements and recruitment strategies forms the initial post-disturbance cohort, thus lending a high resilience towards wind disturbances at the community level.
Highlights
Natural disturbances varying in size are suggested as major driver of tree species substitution across space and time, influencing vegetation structure, composition and diversity in forest ecosystems [1,2,3,4]
Study sites We conducted the research at the Estacao Experimental de Silvicultura Tropical (EEST) (2u619S, 60u209W) of the Instituto Nacional de Pesquisas da Amazonia (INPA) and adjacentcontiguous area (ZF2), which is administered by the Superintendencia da Zona Franca de Manaus (SUFRAMA) (2u569S, 60u269W), Amazonas, Brazil (Figure 1a)
Our structural measures confirm a correlation between DNPV and tree mortality, and indicate that vegetation damage was partially controlled by topography
Summary
Natural disturbances varying in size are suggested as major driver of tree species substitution across space and time, influencing vegetation structure, composition and diversity in forest ecosystems [1,2,3,4]. Widespread tree mortality associated with blowdowns is more prevalent in the Central and Western Amazon than the Eastern Amazon [12,13,14]. This has revived a classical question [1,5,15,16] on the ecological importance of large canopy gaps (2000 m2) and how these influence forest dynamics and tree diversity patterns at the landscape scale [11,14,17,18,19,20]
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