Periodic forest blowdowns are a major disturbance regime in West and Central Amazon. In this vast region, blowdowns can influence floristic composition and tree species diversity. However, to date, the legacy of blowdowns on tree community biomass balance and its interactions with taxonomical attributes during recovery from disturbances has not been assessed. We show that blowdowns can persistently affect biomass stocks and balance for decades. To do so, we studied an old-growth forest as control, and three disturbed forests varying in time since the last blowdown event (from 4 to 27 years). For each disturbed forest, we estimated tree mortality caused by blowdowns employing Spectral Mixture Analysis on Landsat images. We monitored tree species composition and forest dynamics in 596 subplots established along transects spanning a 0-70% tree mortality gradient. Each plot was surveyed at least two times. We applied a locally parameterized biomass estimation model for estimating biomass (dry) of ca. 13,000 trees belonging to 275 genera and at least 1,017 species.
Results/Conclusions
Blowdowns produced changes in biomass stocks, with reductions persisting for at least 27 years in areas with greatest tree mortality intensity (174.3 ± 141.0 Mg ha-1). Biomass gain rates 7 years after disturbance (8.1 ± 2.3 Mg ha-1 y-1) were almost double those found in our old-growth control forest (4.6 ± 0.2 Mg ha-1). Between 10 and 27 years after disturbance, pioneer and mid-successional species made up a greater proportion of biomass stocks and gain. The most important explanatory biomass gain mechanisms were tree growth, recruitment and resprouting, respectively. When randomly sampling from our data set a community representing the entire tree mortality gradient and time since-disturbance interval, 20 genera accounted for 73% of the total biomass gain. These 20 genera accounted for only ca. 12% of the genera richness of this community but were represented by 193 species (i.e., ca. 40% of the total species richness) from dfferent successional groups. Our findings emphasize the importance of blowdowns on defining structural and floristic attributes of Central Amazon forests. Moreover, we show that in these forests, resilience to natural disturbances is enhanced by shifts in functional composition. The biomass balance is influenced by demographic changes in genera and species, which are driven by the tree mortality regime.