Land Use Increases the Correlation between Tree Cover and Biomass Carbon Stocks in the Global Tropics

Manan Bhan,Steffen Fritz,Simone Gingrich,Karl-Heinz Erb,Sarah Matej

doi:10.3390/land10111217

Abstract

Tree cover (TC) and biomass carbon stocks (CS) are key parameters for characterizing vegetation and are indispensable for assessing the role of terrestrial ecosystems in the global climate system. Land use, through land cover change and land management, affects both parameters. In this study, we quantify the empirical relationship between TC and CS and demonstrate the impacts of land use by combining spatially explicit estimates of TC and CS in actual and potential vegetation (i.e., in the hypothetical absence of land use) across the global tropics (~23.4° N to 23.4° S). We find that land use strongly alters both TC and CS, with stronger effects on CS than on TC across tropical biomes, especially in tropical moist forests. In comparison to the TC-CS correlation observed in the potential vegetation (biome-level R based on tropical ecozones = 0.56–0.90), land use strongly increases this correlation (biome-level R based on tropical ecozones = 0.87–0.94) in the actual vegetation. Increased correlations are not only the effects of land cover change. We additionally identify land management impacts in closed forests, which cause CS reductions. Our large-scale assessment of the TC-CS relationship can inform upcoming remote sensing efforts to map ecosystem structure in high spatio-temporal detail and highlights the need for an explicit focus on land management impacts in the tropics.

Highlights

Terrestrial vegetation plays a pivotal role in the global carbon cycle by absorbing, sequestering and releasing vast amounts of carbon each year [1,2]
Using evidence from existing data products, our analysis extends the investigation of the Tree cover (TC)-carbon stocks (CS) relationship to the global tropics
Our findings provide empirical evidence of the landscape-level TC-CS relationship across tropical biomes and describe the impacts of land use on the relationship

Summary

Introduction

Terrestrial vegetation plays a pivotal role in the global carbon cycle by absorbing, sequestering and releasing vast amounts of carbon each year [1,2]. The modification of naturally-occurring vegetation through land use is a major driver of global change [3]. The relationship between these two parameters can be considered as a function of environmental conditions and stand age: an initial linear relationship as a tree-bearing stand grows, followed by a saturation of TC while biomass accumulation continues over time, such that a given stand with high TC can be associated with a range of biomass stocks [4,5,6,7]. We hypothesize that in closed forests, the correlation between TC and CS is poor, while in open forests and other wooded lands, the correlation is stronger

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