Controls over aboveground forest carbon density on Barro Colorado Island, Panama

J. Hall,H. C. Muller-Landau,K. Dahlin,G. P. Asner,M. van Breugel,J. Mascaro

doi:10.5194/bg-8-1615-2011

Abstract

Abstract. Despite the importance of tropical forests to the global carbon cycle, ecological controls over landscape-level variation in live aboveground carbon density (ACD) in tropical forests are poorly understood. Here, we conducted a spatially comprehensive analysis of ACD variation for a continental tropical forest – Barro Colorado Island, Panama (BCI) – and tested site factors that may control such variation. We mapped ACD over 1256 ha of BCI using airborne Light Detection and Ranging (LiDAR), which was well-correlated with ground-based measurements of ACD in Panamanian forests of various ages (r2 = 0.84, RMSE = 17 Mg C ha−1, P < 0.0001). We used multiple regression to examine controls over LiDAR-derived ACD, including slope angle, forest age, bedrock, and soil texture. Collectively, these variables explained 14 % of the variation in ACD at 30-m resolution, and explained 33 % at 100-m resolution. At all resolutions, slope (linked to underlying bedrock variation) was the strongest driving factor; standing carbon stocks were generally higher on steeper slopes. This result suggests that physiography may be more important in controlling ACD variation in Neotropical forests than currently thought. Although BCI has been largely undisturbed by humans for a century, past land-use over approximately half of the island still influences ACD variation, with younger forests (80–130 years old) averaging ~15 % less carbon storage than old-growth forests (>400 years old). If other regions of relatively old tropical secondary forests also store less carbon aboveground than primary forests, the effects on the global carbon cycle could be substantial and difficult to detect with traditional satellite monitoring.

Highlights

Tropical forests play a critical role in the global carbon cycle, storing an estimated 350 Pg of carbon in their aboveground biomass – more than any other biome (Fischlin et al, 2007)
To ensure that our Light Detection and Ranging (LiDAR) data were calibrated to forests of all possible carbon densities on and beyond BCI, we conducted additional LIDAR measurements over mapped plots in nearby Agua Salud (Neumann-Cosel et al, 2010), which contains a matrix of grasslands, active pasture, and young to moderateaged forests that have recently reverted from pasture
Our model indicated that slope angle was the single most important parameter controlling aboveground carbon density on the island

Summary

Introduction

Tropical forests play a critical role in the global carbon cycle, storing an estimated 350 Pg of carbon in their aboveground biomass – more than any other biome (Fischlin et al, 2007). Given the pressing importance of quantifying tropical forest carbon balance, ecologists have recently improved carbon monitoring techniques in several areas, including development of generalized tree allometry theory (Chave et al, 2005; Niklas, 2006), assembly of global wood density databases (Chave et al, 2006; Swenson and Enquist, 2007), and improved methods to quantify carbon stored in poorly sampled pools such as lianas, small trees, and necromass (Hughes et al, 1999; Schnitzer et al, 2006; Chao et al, 2009). Lagging far behind improved field methodology, is our understanding of fundamental ecological controls over aboveground carbon density (ACD) at landscape scales in tropical forests. Without an improved understanding of these controls, changes in ACD will be difficult to interpret – much

Objectives

Methods

Results

Conclusion