Developing General Equations for Urban Tree Biomass Estimation with High-Resolution Satellite Imagery

Jindong Wu

doi:10.3390/su11164347

Abstract

Urban trees provide various important ecological services, the quantification of which is vital to sustainable urban development and requires accurate estimation of tree biomass. A limited number of allometric biomass equations, however, have been developed for urban species due to the prohibitive cost. Remote sensing has provided cost-effective means for estimating urban forest biomass, although the propagation of error in the estimation process is not well understood. This study aimed to offer a baseline assessment of the feasibility of estimating urban tree biomass with remote sensing-based general equations applicable to broad taxonomic groups by conducting a large urban tree inventory on a university campus. The biomasses of 191 trees of seven species from the inventory, separated into two categories (i.e., evergreen and deciduous), were calculated exclusively with urban-based species-specific allometric equations. WorldView-2 satellite imagery data were acquired to retrieve normalized difference vegetation index (NDVI) values at the location, crown, and stand levels. The results indicated that biomass correlated with NDVI in varying forms and degrees. The general equations at the crown level yielded the most accurate biomass estimates, while the location-level estimates were the least accurate. Crown-level spectral responses provided adequate information for delivering spatially explicit biomass estimation.

Highlights

Urban landscapes are projected to continue to expand at unprecedented rates, increasing by 38.6 million hectares between 2010 and 2060 in the U.S alone [1]
At the crown and stand levels, logarithmic relationships were found significant between transformed dry weight biomass (DWB) and normalized difference vegetation index (NDVI)
DWB could be described as an exponential function of NDVI at the location level and as a power function of NDVI at the crown and stand levels

Summary

Introduction

Urban landscapes are projected to continue to expand at unprecedented rates, increasing by 38.6 million hectares between 2010 and 2060 in the U.S alone [1]. As a basic element of urban-suburban environments, trees cover a significant area in cities. Rapid urbanization and population growth present a major cause of concern to the sustainability of cities [4]. The recently adopted United Nations’ New Urban Agenda recognized the importance of urban greenspace in fostering social integration, economic growth, and environmental amelioration, and proposed a series of implementation plans for sustainably augmenting its social, economic, and environmental values [7]. Greenspace cover, including trees and grass, is considered one of the most significant sustainability indicator variables [8]. A number of large cities in the U.S, have initiated tree planting projects to restore their urban forests [9,10]

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Discussion

Conclusion