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

Anastasios Mazis,Julie A Fowler,Jeremy Hiller,Yuzhen Zhou,Brian D Wardlow,David Wedin,Tala Awada

doi:10.1016/j.ecolind.2021.108159

Anastasios Mazis, Julie A Fowler + Show 5 more

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https://doi.org/10.1016/j.ecolind.2021.108159

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Journal: Ecological Indicators	Publication Date: Aug 31, 2021
Citations: 5	License type: cc-by

Affiliation: University of Nebraska–Lincoln

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 (CIred edge) performed best when tested against biomass, and chlorophyll content and fluorescence (Fv/Fm), 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.

Highlights

Grasslands and savannas cover approximately 25% of the terrestrial ecosystem (Lemaire et al, 2011) and contribute to around 35% of the terrestrial net primary production (NPP; Chapin et al, 2011), providing significant provisioning, support ing, regulating, and cultural ecosystem services (Zhao et al, 2020)
For mixed medium density and dense P. ponderosa stands, inter-annual variation was most pronounced at the 100–200 cm soil depth, while for the dense J. virginiana, the change was observed throughout the soil profile (0–300 cm), suggesting different patterns of soil moisture uptake by trees from the soil profile (Eggemeyer et al, 2009)
Similar to findings by Coultrap et al (2008), our study showed that chlorophyll content of the herbaceous vegetation in the dense J. virginiana and P. ponderosa stands was significantly lower compared to the open grasslands, demonstrating the impacts of the woody species on resource availability, i.e., light and water, and in turn on photosynthetic ability and primary production of the herbaceous vegetation (Rossatto et al, 2018)

Summary

Introduction

Grasslands and savannas cover approximately 25% of the terrestrial ecosystem (Lemaire et al, 2011) and contribute to around 35% of the terrestrial net primary production (NPP; Chapin et al, 2011), providing significant provisioning (e.g., livestock and forage), support ing (e.g., biodiversity, carbon sequestration and nurtient cycling), regulating (e.g., flood control and water infiltration), and cultural (e.g., spiritual, recreational, educational and aesthetic) ecosystem services (Zhao et al, 2020). The native Juniperus spp. encroachment into the Great Plains, especially J. virginiana (eastern redcedar) and J. ashei (ashe juniper), are an example of a widespread phenomenon driven by a complex anthropogenic-environment interac tion (e.g., fire suppression and overgrazing). This encroachment is resulting in grasslands degradation, loss of biodiversity, and shifts in key ecosystem services (Twidwell et al, 2013; Msanne et al, 2017). This includes a decline in species diversity and net primary production (Ratajczak et al, 2012), and changes in the hydrological and biogeo chemical cycles (Awada et al, 2013), with economic impacts on live stock production and ranching operations (Throop et al, 2012), and an increase in human health problems due to pollen production (Leis et al, 2017)

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