Correlation of WorldView-3 spectral vegetation indices and soil health indicators of individual urban trees with exceptions to topsoil disturbance

Abstract

Increasing recognition of the potential ecosystem services provided by urban forests suggests a need to examine soil quality under urban conditions. Soil quality assessment tools are presently mostly applied in agricultural production, but these approaches must also be evaluated in the urban context. This proof-of-concept exploratory study evaluates whether Worldview-3 spectral vegetation indices (SVIs) generated for individual tree crown (ITC) objects can be correlated to soil health attributes measured in the field in Metro Boston, Massachusetts, USA. While similar studies have completed such analysis for agricultural crops, none have done so for urban trees. The statistical analysis by Pearson correlation and principal component analysis (PCA) showed that SVIs, specifically the Normalized Difference Vegetation Index (NDVI), correlated significantly and positively with bulk density (BD) (r = 0.536) and soil luminance (r = 0.562) and negatively with CO2 respiration (r = −0.536), active fungi and active bacteria (r = −0.401), and total carbon (r = −0.548). The negative correlations with parameters commonly considered positive for soil health in agricultural settings may indicate strong perturbation at the urban soil surface level; they also suggest soil health attributes measured at this study’s 0–15 cm sampling depth may not be satisfactorily indicative of tree health as measured by SVIs. This study evidences the ground truthing of satellite-based urban SVIs, including their relationships with soil health attributes at the individual tree level.