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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 shortterm
(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 (583646
trees ha21) (mean699% Confidence Interval) and basal area (26.762.4 m2 ha21). Highly impacted areas had tree density
and basal area as low as 120 trees ha21 and 14.9 m2 ha21, 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.
