Tracking herbivory from space: a multi-scale remote sensing approach to mapping vegetation biomass and assessing impacts of caribou on vegetation

Orndahl, Kathleen Marie (2022) Tracking herbivory from space: a multi-scale remote sensing approach to mapping vegetation biomass and assessing impacts of caribou on vegetation. Doctoral thesis, Northern Arizona University.

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Abstract

Arctic and boreal ecosystems are warming over three times faster than the rest of the planet. This warming has contributed to significant changes in vegetation community structure and function over the past half century. Changes in vegetation have downstream impacts – affecting nutrient cycling, fire regimes, climate feedbacks and wildlife. Wildlife are acutely affected through alteration of habitat and forage quantity and quality. However, animals also impact vegetation through grazing and trampling. Therefore, they influence the trajectory of vegetation change in Arctic/boreal environments, and play a large role in determining ecosystem responses to climate change. Thus, it is crucial to monitor changes in vegetation across large spatiotemporal scales, especially as they relate to fluctuations in animal populations. Vegetation does not respond uniformly to warming or herbivory, nor does it respond only in two dimensions. Therefore, comprehensive understanding of vegetation change requires monitoring that 1) is parsed by ecologically meaningful taxonomic groups, and 2) incorporates a third dimension e.g. height or biomass. We mapped a 35-year time series of plant functional type aboveground biomass (AGBPFT) across Alaska and northwest Canada at 30m resolution using a multi-scale approach that incorporated field harvest data, unmanned aerial vehicle (UAV) imagery and Landsat seasonal spectral composites. Using a similar product, we assessed the impacts of a growing migratory caribou herd on changes in PFT top cover. We found incorporating UAV imagery improved AGB estimates for some PFTs (deciduous shrubs), but not others. Our AGBPFT maps reveal widespread increases in deciduous (37%) and evergreen shrub (7%) biomass, and decreases in graminoid (14%) and lichen (13%) biomass from 1985-2020. Fire was an important driver of changes in the study area, with the largest changes in biomass associated with historic fire perimeters. We did not find evidence that caribou herbivory stymied Arctic shrub expansion, as deciduous shrub cover increased even in areas with high caribou spatial density. However, we found faster rates of graminoid and lichen decline where caribou spatial density was highest. This suggests increasing caribou populations might lead to density-dependent forage reduction across critical habitat. Our results illustrate the driving trends in vegetation change occurring across the Arctic/boreal region and show that climate-induced shifts in vegetation may be influenced by caribou-plant interactions across the circumpolar region.

Item Type:	Thesis (Doctoral)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	aboveground biomass; Arctic; caribou; plant functional type; remote sensing; unmanned aerial vehicles
Subjects:	T Technology > TP Chemical technology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of Engineering, Informatics, and Applied Sciences > School of Informatics, Computing, and Cyber Systems
Date Deposited:	13 Jun 2023 17:21
Last Modified:	13 Jun 2023 17:21
URI:	https://openknowledge.nau.edu/id/eprint/6010

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