Ecophysio-optical traits of semiarid Nebraska grasslands under different Juniperus virginiana and Pinus ponderosa canopy covers

Authors

Anastasios Mazis, University of Nebraska-LincolnFollow
Julie A. Fowler, University of Nebraska-Lincoln
Jeremy Hiller, University of Nebraska-LincolnFollow
Yuzhen Zhou, University of Nebraska - LincolnFollow
Brian Wardlow, University of Nebraska - LincolnFollow
David A. Wedin, University of Nebraska - LincolnFollow
Tala Awada, University of Nebraska - LincolnFollow

Document Type

Article

Date of this Version

2021

Citation

Ecological Indicators 131 (2021) 108159

doi:10.1016/j.ecolind.2021.108159

Comments

This is an open access article under the CC BY license

Abstract

Despite conservation efforts in the U.S. Great Plains, woody species have continued to expand at an unprecedented rate, threatening key ecosystem services and resilience. Cross-scale monitoring of these grasslands is key to successful integrative management strategies. In this study we measured plant optical traits derived from hyperspectral proximal sensing techniques with a field spectrometer, coupled with field-based measurements, including fluorescence and chlorophyll content, to determine the impacts of Juniperus virginiana and Pinus ponderosa expansion on grasslands health in Nebraska Sandhills, and investigated the use of optical-based approaches as indicators of successful monitoring of grasslands. Our results showed that higher woody species cover in grasslands was associated with lower soil moisture, decline in forbs, shrubs, and grasses cover and productivity, as well as herbaceous chlorophyll content and fluorescence, compared to non-invaded grasslands. We derived 13 vegetation indices (VIs) from optical-based methods and validated them against traditional handheld measurements of plant ecophysiological traits and vegetation biomass and composition. VIs, including Normalized Difference Vegetation Index (NDVI), Water Index (WI) and Chlorophyll Index at red edge (CI_{red edge}) performed best when tested against biomass, and chlorophyll content and fluorescence (F_v/F_m), suggesting their potential use for assessing grasslands vegetation health. We demonstrate that optical-based approaches can serve as efficient non-invasive tools that can be part of multi-scale successful integrative management strategies.