Abstract
Abstract. Coarse dead wood is an important component of forest carbon stocks, but it is rarely measured in Amazon forests and is typically excluded from regional forest carbon budgets. Our study is based on line intercept sampling for fallen coarse dead wood conducted along 103 transects with a total length of 48 km matched with forest inventory plots where standing coarse dead wood was measured in the footprints of larger areas of airborne lidar acquisitions. We developed models to relate lidar metrics and Landsat time series variables to coarse dead wood stocks for intact, logged, burned, or logged and burned forests. Canopy characteristics such as gap area produced significant individual relations for logged forests. For total fallen plus standing coarse dead wood (hereafter defined as total coarse dead wood), the relative root mean square error for models with only lidar metrics ranged from 33 % in logged forest to up to 36 % in burned forests. The addition of historical information improved model performance slightly for intact forests (31 % against 35 % relative root mean square error), not justifying the use of a number of disturbance events from historical satellite images (Landsat) with airborne lidar data. Lidar-derived estimates of total coarse dead wood compared favorably with independent ground-based sampling for areas up to several hundred hectares. The relations found between total coarse dead wood and variables quantifying forest structure derived from airborne lidar highlight the opportunity to quantify this important but rarely measured component of forest carbon over large areas in tropical forests.
Highlights
Intact and disturbed tropical forests play a critical role in the global carbon cycle (Pan et al, 2011)
The airborne lidar data used in this study were collected between 2012 and 2015, covered a total area of 14 870 ha, and overlapped with 103 coarse dead wood (CDW) transects (48 km of total length sampled within 6 months of the lidar airborne campaigns)
Intact forests grouped by site had an average total CDW of 42.4 (±19.7) Mg ha−1
Summary
Intact and disturbed tropical forests play a critical role in the global carbon cycle (Pan et al, 2011). From 1990 through 2007, tropical forests contributed about 46 % of the global carbon sink (Schimel et al, 2015). The largest remaining area of tropical forest in the Amazon region contains about 50 % of the carbon stored in all tropical forests or about 60 Pg C in the living aboveground biomass pool (Saatchi et al, 2011; Baccini et al, 2012). The Brazilian Amazon retains about 80 % of its original forest cover (PRODES-INPE, 2016) and while deforestation rates in Brazil have decreased by about 70 % since 2004 (PRODES-INPE, 2016), forest degradation processes including logging, fire, and fragmentation continue to deplete carbon stocks.
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