Abstract
We report large-scale estimates of Amazonian gap dynamics using a novel approach with large datasets of airborne light detection and ranging (lidar), including five multi-temporal and 610 single-date lidar datasets. Specifically, we (1) compared the fixed height and relative height methods for gap delineation and established a relationship between static and dynamic gaps (newly created gaps); (2) explored potential environmental/climate drivers explaining gap occurrence using generalized linear models; and (3) cross-related our findings to mortality estimates from 181 field plots. Our findings suggest that static gaps are significantly correlated to dynamic gaps and can inform about structural changes in the forest canopy. Moreover, the relative height outperformed the fixed height method for gap delineation. Well-defined and consistent spatial patterns of dynamic gaps were found over the Amazon, while also revealing the dynamics of areas never sampled in the field. The predominant pattern indicates 20–35% higher gap dynamics at the west and southeast than at the central-east and north. These estimates were notably consistent with field mortality patterns, but they showed 60% lower magnitude likely due to the predominant detection of the broken/uprooted mode of death. While topographic predictors did not explain gap occurrence, the water deficit, soil fertility, forest flooding and degradation were key drivers of gap variability at the regional scale. These findings highlight the importance of lidar in providing opportunities for large-scale gap dynamics and tree mortality monitoring over the Amazon.
Highlights
We report large-scale estimates of Amazonian gap dynamics using a novel approach with large datasets of airborne light detection and ranging, including five multi-temporal and 610 singledate lidar datasets
We aimed to answer the following research questions: (Q1) How are static and dynamic canopy gaps related in tropical forests and which gap definition best represents this relationship? (Q2) How do canopy gap dynamics derived from airborne lidar data vary across the Brazilian Amazon forests? (Q3) What landscape- and/or regional-scale factors drive gap variability in the Brazilian Amazon? (Q4) Does large-scale dynamic gaps estimates reproduce known spatial patterns of field-plot tree mortality estimates across the Amazon?
We showed the opportunities for tree mortality estimates and monitoring based on the lidar gap dynamics
Summary
We report large-scale estimates of Amazonian gap dynamics using a novel approach with large datasets of airborne light detection and ranging (lidar), including five multi-temporal and 610 singledate lidar datasets. While topographic predictors did not explain gap occurrence, the water deficit, soil fertility, forest flooding and degradation were key drivers of gap variability at the regional scale These findings highlight the importance of lidar in providing opportunities for large-scale gap dynamics and tree mortality monitoring over the Amazon. Kill the trees through the physiological mechanisms of carbon starvation and hydraulic failure, the interactions with biotic agents, and the modifications in plant structure that provoke stem breakage[2] All this knowledge has been originated from field observations over a few hundred-forest sites in the Amazon, but we still lack tools for monitoring tree mortality over a large scale. In the Amazon, this mode of death represents approximately 39–55% of the total mortality but, on average, it is not significantly distinguished from the standing dead mode of d eath[22,23,24]
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