Seasonal Spectral Separation of Western Snowberry and Wolfwillow in Grasslands with Field Spectroradiometer and Simulated Multispectral Bands

Irini Soubry,Xulin Guo

doi:10.3390/environments8070060

Abstract

Woody plant encroachment (WPE), the expansion of native and non-native trees and shrubs into grasslands, has led to degradation worldwide. In the Canadian prairies, western snowberry and wolfwillow shrubs are common encroachers, whose cover is currently unknown. As the use of remote sensing in grassland monitoring increases, opportunities to detect and map these woody species are enhanced. Therefore, the purpose of this study is to identify the optimal season for detection of the two shrubs, to determine the sensitive wavelengths and bands that allow for their separation, and to investigate differences in separability potential between a hyperspectral and broadband multispectral approach. We do this by using spring, summer, and fall field-based spectra of both shrubs for the calculation of spectral separability metrics and for the simulation of broadband spectra. Our results show that the summer offers higher discrimination between the two species, especially when using the red and blue spectral regions and to a lesser extent the green region. The fall season fails to provide significant spectral separation along the wavelength spectrum. Moreover, there is no significant difference in the results from the hyperspectral or broadband approach. Nevertheless, cross-validation with satellite imagery is needed to confirm the current results.

Highlights

Grasslands are among the largest ecosystems in the world, providing important ecologic and economic services [1]; they face multiple threats from climate change and human activity, which can lead to their degradation [2]
Rather noticeable is the lack of absorption for wolfwillow in the blue region (350–500 nm), which could be explained by the grey-blue appearance of its leaves (Figure 1)
The shortwave infrared (SWIR) reflectance for western snowberry decreases slightly from spring to summer, and increases again during fall, whereas it increases throughout the seasons for wolfwillow

Summary

Introduction

Grasslands are among the largest ecosystems in the world, providing important ecologic and economic services [1]; they face multiple threats from climate change and human activity (e.g., conversion to cropland, biodiversity loss, expansion of invasive species), which can lead to their degradation [2]. Woody plant encroachment (WPE) has become an important issue for grasslands in recent years. It is related to the expansion of native and non-native trees and shrubs into grasslands [3], and has been connected to changes in primary productivity, nutrient cycling, energy flow, the structure and function of the ecosystem [3]; these all lead to issues in rangeland management and livestock production. WPE occurs in the grasslands of the south-central and southwestern

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Results

Conclusion