Friday, November 16, 2018
The Selection Committee is proud to announce Erik Andersen and Martha Gebhardt as the 2017 finalists and 41st Awardees of the William G. McGinnies Graduate Scholarship in Arid Lands Studies. Erik's research focuses on how plant invasions affect demography and distributions of breeding birds in semiarid grasslands, while Martha's research uses remotely sensed data from an open-access data platform to quantify the impacts of shrub encroachment on nutrient dynamics at The Santa Rita Experimental Range (SRER) in southeastern Arizona.
The William G. McGinnies Graduate Scholarship in Arid Lands Studies is given each year to a student in honor of the founder of the Office of Arid Lands Studies, Dr. McGinnies. The intent of the McGinnies Graduate Scholarship is to provide additional support to graduate students whose dissertation research concerns physical and biological processes in the world's arid and semiarid lands.
To learn about how Erik and Martha's research is extending the legacy of Dr. William G. McGinnies, please read the abstracts from their research:
Plant Invasions Affect Demography and Distributions of Breeding Birds in Semiarid Grasslands by Erik Andersen
Arid and semiarid grasslands, which comprise a significant portion of the global grassland biome, are imperiled from an array of anthropogenic impacts that have altered composition of plant communities. Encroachment by woody plants and invasions by nonnative grasses have reduced habitat for many grassland-associated species, including grassland birds, which have declined more rapidly than any other group of birds across North America. We established 140 plots that spanned gradients in cover of woody plants and nonnative grasses in grasslands of southeastern Arizona and evaluated how these plant invasions affected species richness, density, habitat selection, and nesting success of breeding birds. Encroachment by woody plants influenced breeding birds strongly, with distributions and densities of most grassland-obligate species decreasing sharply as woody cover increased. As encroachment progressed, overall density of birds increased as shrub-associated species were recruited. Species richness increased with encroachment, plateauing when woody cover reached ~25%, where losses of grassland-associated species surpassed gains in shrub-associated species. Effects of invasions by nonnative grasses on density and nest success of grassland obligates were mixed. For some bird species, nonnative grasses decoupled the cues they used to select breeding habitat from the resources associated with those cues over evolutionary time. For these species, areas invaded by nonnative grasses might function as ecological traps by attracting individuals away from areas of high-quality habitat into areas where reproductive success is lower. Understanding how plant invasions affect native birds in grasslands can benefit conservation and restoration efforts by identifying achievable targets for control of nonnative grasses and shrubs that threaten imperiled grassland species.
Shrub Encroachment Alters Ecosystem Processes: Linking Imaging Spectroscopy and Microbial Biogeochemistry by Martha Gebhardt
Arid and semi-arid grasslands are undergoing prolific changes in vegetation due to woody shrub encroachment that causes large-scale shifts in biogeochemistry. Nitrogen-fixing mesquites, a common shrub to invade these areas, fundamentally alters ecosystem processes by changing plant community diversity, net primary productivity, and soil functioning. Although the spread and proliferation of these shrubs is well documented, uncertainties related to landscape-scale biogeochemical consequences and spatial patterns associated with shrub invasion remain. This information is needed to quantify the effects of vegetation changes on nutrient cycling, soil functioning, and other ecosystem services. This project offers a novel approach to answering these questions by combining remotely sensed data from an open-access data platform to infer foliar chemistry with in situ measures of plant and soil biogeochemistry to quantify the impacts of shrub encroachment on nutrient dynamics at The Santa Rita Experimental Range (SRER) in southeastern Arizona. This study explores how hyperspectral data can be used to quantify changes in ecosystem services due to differences in vegetation chemistry and associated belowground processes across a landscape. These data are used to investigate the link between soil nutrients, topography and the abundance of shrubs and grasses; the potential effects of shrub encroachment on landscape-scale nutrient dynamics; and the utility of imaging spectroscopy to inform management practices through remote monitoring. SRER is an ideal location to investigate these questions because of the long-term data on vegetation and soil dynamics and the National Ecological Observatory Network (NEON) airborne observation platform, which offers a unique opportunity to map patterns of plant species, litter inputs and microbial-mediated biogeochemical cycling across the landscape. Scaling of plant and microbial interactions to landscape and regional scales is essential to sustainable land management worldwide.
Images: Martha Gebhardt (left) and Erik Andersen (right)