Tree allometric equations for estimation of above, below and total biomass in a tropical moist forest: Case study with application to remote sensing
利用树的异速生长方程估计热带潮湿森林地上生物量、地下生物量以及总生物量：案例研究与遥感应用
ABSTRACT: The unavailability of site-specific allometric equations to estimate forest biomass has promoted the use of general equations in tropical moist forests which may result to errors in the estimates. The aim of this study was to develop site-specific allometric equations to estimate biomass of trees in tropical moist forests of Cameroon. For this study, 237 trees (1D121 cm) obtained by destructive method were used to develop allometric equations for the estimation of aboveground biomass. Allometric equations to estimate belowground and total biomasses were developed with 25 trees and 13 trees respectively. Trunk and crown biomass estimators were also developed in this study using 96 sample trees. Predictor variables considered were diameter, tree height, wood density and crown diameter. 237 and 235 trees were also used to develop regressions equations to estimate tree height and crown diameter respectively. For remote sensing applications, this study developed allometric equations to estimate aboveground biomass using crown diameter as predictor variable. Comparison of our biomass data to existing models showed that the equation of Djomo et al. (2016) provided the best estimator of total and mean biomass. Our study contributes to site-specific allometric equations and to the knowledge of belowground, above, trunk, crown and total biomass, which lack in most of the biomass data in tropical moist forests. Also, adding allometric equations with application to remote sensing, this study is a significant input for the implementation of REDD in Central Africa.
摘要：在热带潮湿地区缺乏定点异速生长方程估计森林生物量的方法促进了普通方程的使用，但普通方程会引起估计误差。本文研究的目的是发展定点异速生长方程来估计喀麦隆热带潮湿地区的生物量。此研究中，以破坏性方法获得的237棵树用于地上生物量的估算，25棵树用于地下生物量的估算，13棵树用于总生物量的估算。同时，96棵样本树用于树干和树冠生物量的估计。所考虑的预测变量有直径、树高、木材密度以及冠幅。237棵树和235棵树分别用于估计树高和冠幅的回归方程的探究。在遥感应用中，本研究以冠幅作为预测变量进行异速生长方程地上生物量的估计。对现有模型模拟生物量的比较中发现，Djomo等人2016年提供的方程最适用于总生物量和平均生物量的估计。我们的研究提供了定点异速生长方程以及大多数热带潮湿森林缺失的地下生物量、地上生物量、树干生物量、树冠生物量和总生物量的数据。同时，将异速生长方程与遥感应用相结合，对非洲中部实施REDD 是重大的投入。
1. Introduction
Cameroonrsquo;s forests which belong to Congo basin forest, cover about 190,000 km2 (FAO, 2011) and represents about 42% of the national territory. These forests are characterized by a remarkable plant biodiversity, making it the second richest country in Atlantic Central Africa (Mareacute;chal et al., 2013). However, human activities such as deforestation for agriculture and human settling, forest degradation due to logging, forest fires impact each year this forest cover (Hairiah et al., 2011). According to FAO (2010), a rate of 0.94% was lost per year during the period 1990–2000, 1.02% during the period 2000–2005 and 1.07% during the period 2005–2010. East and South region are the most forested area of the country constituted essentially by moist evergreen or semi-deciduous forest(Letouzey, 1985). As countries try to fulfil their commitments regarding the aim of reducing greenhouse gas emissions (GHG), it becomes necessary and urgent to better understand how the forest sector contributes to climate change mitigation (Kurz et al., 2016). Forests are the largest terrestrial carbon sink (Zianis, 2008) and they have absorbed about 25% of global emissions from fossil fuel combustion during the last twenty years (Le Queacute;reacute; et al., 2015). The study of Stephens et al. (2007)showed that tropical forests absorb 1.4 billion metric tons of carbon dioxide out of a total global absorption of 2.5 billion. Photosynthesis is the process used by plants to absorb carbon dioxide present in the atmosphere which are stored as carbon compounds in the plants (Brown and Pearson, 2005; Basuki et al., 2009).
- 引言
喀麦隆地区的森林属于刚果盆地森林，占地190000平方千米，覆盖了42%的国家领土。这些森林显著的植被多样性使喀麦隆成为大西洋中部非洲植被第二丰富的国家。然而，人类活动比如农业和人类定居带来的森林砍伐、伐木造成的森林退化、森林火灾，都在影响着喀麦隆地区每年的森林覆盖率。根据FAO 2010年的数据，森林覆盖率在1990-2000年以0.94%的速率下降，2000-2005年的速率为1.02%，2005-2010年的下降速率是1.07%。东部和南部是这个国家森林最茂盛的地区，主要由湿润常绿林和半落叶森林组成。由于各国试图履行他们减少温室气体排放的承诺，所以更好的理解森林对气候变化缓解的作用就显得尤为重要。森林是最大的陆地碳汇，在过去20年间森林大约吸收了25%的由石油燃料燃烧产生的全球排放量。Stephens et al. (2007)的研究表明，热带森林在全球吸收25亿吸收量中吸收了1.4亿公吨的二氧化碳。植被利用光合作用吸收大气中的二氧化碳并以碳化物的形式存储在植被中。
Tropical forests represent approximately 33% of global land area(FAO, 2011), and contain more carbon per unit area than any other land cover type (Hairiah et al., 2011). Despite the strong carbon dioxide absorption rate of these forests which represents about 1.3 Pg C yr-1 (Lewis et al., 2009), they are increasingly exposed to degradation and deforestation representing about 20% of global emission (Canadell et al., 2009). As a result, forests have become a major issue of international negotiations to fight against climate change. Therefore, it has become necessary to make precise estimate of the carbon content in these forests in order to determine a reliable policy for the implementation of REDD (Reducing Emissions from Deforestation and Forest Degradation and foster conservation, sustainable management of forests, and enhancement of forest carbon stocks).
热带森林大约占全球陆地面积的33%, 并且单位面积的碳含量比其他土地覆盖类型高。尽管这些森林的二氧化碳吸收率很高约为1.3 Pg C yr-1，他们也日益遭受着森林退化和森林砍伐的影响，大约为全球排放量的20%。由此，森林已经变成对抗气候变化的重要国际谈判内容。因此，为了制定可靠的实施REDD （减少森林砍伐和森林降解带来的排放，促进保护，森林可持续管理和增强森林碳储量）政策，精确估计森林碳含量变得十分重要。
