Impact of a tropical forest blowdown on aboveground carbon balance

K C Cushman,Carlo Zgraggen,Sassan S Saatchi,Orlando Vargas,Benedikt Imbach,James R Kellner,Carlos E Silva,John T Burley

doi:10.1038/s41598-021-90576-x

Abstract

Field measurements demonstrate a carbon sink in the Amazon and Congo basins, but the cause of this sink is uncertain. One possibility is that forest landscapes are experiencing transient recovery from previous disturbance. Attributing the carbon sink to transient recovery or other processes is challenging because we do not understand the sensitivity of conventional remote sensing methods to changes in aboveground carbon density (ACD) caused by disturbance events. Here we use ultra-high-density drone lidar to quantify the impact of a blowdown disturbance on ACD in a lowland rain forest in Costa Rica. We show that the blowdown decreased ACD by at least 17.6%, increased the number of canopy gaps, and altered the gap size-frequency distribution. Analyses of a canopy-height transition matrix indicate departure from steady-state conditions. This event will initiate a transient sink requiring an estimated 24–49 years to recover pre-disturbance ACD. Our results suggest that blowdowns of this magnitude and extent can remain undetected by conventional satellite optical imagery but are likely to alter ACD decades after they occur.

Highlights

Field measurements demonstrate a carbon sink in the Amazon and Congo basins, but the cause of this sink is uncertain
70.5 ha in secondary forest 31–66 years old in 2019; Fig. 1; Supplementary Fig. 2). By comparing these measurements to previously collected airborne lidar and inventory plot data, we identified multiple lines of evidence that indicate the disturbance was unprecedented in the previous 20 years of annual field measurements[20]. These measurements are used to address three main questions: 1) what is the impact of the blowdown disturbance on aboveground carbon density (ACD) and forest structure? 2) what is the estimated recovery time of the forest to its pre-disturbance ACD? 3) to what extent can similar events be detected by conventional remote sensing observations for large scale monitoring applications?
Impact of disturbance on ACD and forest structure. We found that this blowdown disturbance caused substantial losses to ACD and changes to forest structure

Summary

Introduction

Field measurements demonstrate a carbon sink in the Amazon and Congo basins, but the cause of this sink is uncertain. This blowdown event caused largescale disturbance in forest structure, creating > 600 new gaps along trails alone, according to local field surveys (Supplementary Fig. 1)[19]. We collected ultra-high-density drone lidar data after the disturbance to quantify canopy structure and aboveground carbon density (ACD) over 103.5 ha of forest

Results

Conclusion