Document Type

Article

Publication Date

2023

Abstract

Eastern redcedar (ERC) (Juniperus virginiana L.) is the most rapidly spreading woody species in the Northern Great Plains due to fire suppression, planting in windbreaks, and overgrazing. Its encroachment has converted already fragmented and/or degraded grassland into woodland, and there is concern that it may negatively impact grassland-obligate/dependent avian species. In this study, I evaluated avian community composition between ERC-encroached and non-encroached grasslands in eastern South Dakota. Six sites each of encroached grassland and non-encroached grassland were selected. Bird surveys were conducted by performing point counts placed equidistantly along a transect for two years. Presence and abundance of each species observed/heard were recorded. In 2021, 47 species were observed/heard between both site types, with 32 in non-encroached sites and 42 in encroached sites. In 2022, 63 species were observed/heard between both site types, with 37 in non-encroached sites and 51 in encroached sites. Species richness, evenness, and Shannon-Wiener diversity index were higher at encroached sites in both years. Jaccard’s Species Similarity Indices between encroached and non-encroached sites ranged from 44.19% to 61.36% across two years. Non-encroached sites were dominated by grassland-obligate/dependent species like Sedge Wren (Cistothorus platensis), Bobolink (Dolichonyx oryzivorus), Western Meadowlark (Sturnella neglecta), Grasshopper Sparrow (Ammodramus savannarum), and Savannah Sparrow (Passerculus sandwichensis), while encroached sites were dominated by transitional/woodland species such as Clay-colored Sparrow (Spizella pallida), American Goldfinch (Spinus tristis), Eastern Kingbird (Tyrannus tyrannus), Brown-headed Cowbird (Molothrus ater), and Yellow Warbler (Setophaga petechia). My results demonstrate that ERC encroachment shifts communities from grassland-obligate/dependent species to transitional/woodland species. Higher diversity metrics on encroached sites are likely temporary, as they appear due to heterogeneity of the transition phase between two distinct habitat types. With grasslands being among the world's most threatened and important ecosystems and their passerines serving as ecosystem health indicators, my results amplify the importance of slowing ERC encroachment.

Publisher

South Dakota State University

Rights

Copyright © 2023 Jay Holm

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