Increasing biomass carbon stocks in trees outside forests in China over the last three decades

Z D Guo,R A Birdsey,Y D Pan,H F Hu,J Y Fang

doi:10.5194/bg-11-4115-2014

Abstract

Abstract. Trees outside forests (TOF) play important roles in national economies, ecosystem services, and international efforts for mitigating climate warming. Detailed assessment of the dynamics of carbon (C) stocks in China's TOF is necessary for fully evaluating the role of the country's trees in the national C cycle. This study is the first to explore the changes in biomass C stocks of China's TOF over the last three decades, using the national forest inventory data in six periods from 1977 to 2008. According to the definition of the forest inventory, China's TOF could be categorized into three groups: woodlands, shrubberies, and trees on non-forest land (including four-side greening trees, defined in the article, and scattered trees). We estimated biomass C stocks of woodlands and trees on non-forest land by using the provincial biomass-volume conversion equations derived from the data of low-canopy forests, and estimated the biomass C stocks of shrubberies using the provincial mean biomass density. Total TOF biomass C stock increased by 62.7% from 823 Tg C (1 Tg = 1012 g) in the initial period of 1977–1981 to 1339 Tg C in the last period of 2004–2008. As a result, China's TOF have accumulated biomass C of 516 Tg during the study period, with 12, 270, and 234 Tg in woodlands, shrubberies, and trees on non-forest land, respectively. The annual biomass C sink of China's TOF averaged 19.1 Tg C yr−1, offsetting 2.1% of the contemporary fossil-fuel CO2 emissions in the country. These estimates are equal to 16.5–20.7% of the contemporary total forest biomass C stock and 27.2% of the total forest biomass C sink in the country, suggesting that TOF are substantial components in China's tree C budget.

Highlights

Contrary to popular perception, trees and forests are not synonymous; trees alone do not make up forests, and trees are not found only in forests (Long and Nair, 1999)
Based on the up-to-date national forest inventory data starting in the late 1970s, this study aims to explore the temporal changes and regional distributions of biomass C stocks for each trees outside forests (TOF) group and for total TOF between 1977 and 2008
Total TOF biomass C stock increased by 62.7 % from 823 Tg C in the initial period of 1977–1981 to 1339 Tg C in the last period of 2004–2008, with a net accumulation of 516 Tg C (Table 2)

Summary

Introduction

Trees and forests are not synonymous; trees alone do not make up forests, and trees are not found only in forests (Long and Nair, 1999). Trees outside forests (TOF) have begun to attract more and more attention with growing acknowledgements of their potential economic importance and political interest in their environmental services (de Foresta et al, 2013). Because TOF are typically splintered among the categories of agroforestry, urban and rural forestry, and other sectors, they tend to be left out of forest statistics, natural resource assessments, policy, and legislation (de Foresta et al, 2013). The concept of “Trees Outside Forests” first appeared in 1995 to indicate trees growing outside the forest and not Published by Copernicus Publications on behalf of the European Geosciences Union A major challenge for a better evaluation of trees and their services globally is to improve our understanding of the status and dynamics of all tree resources, including TOF (FAO, 2001; de Foresta et al, 2013).

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