Quantifying Structural Vegetation Change on Arctic Tundra: A Multi-Decadal Study Integrating Remotely Sensed Imagery and Traditional Field Measurements

Author

Anna M. MoserFollow

Year of Award

2024

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geography (Cartography and GIS Option)

Department or School/College

Geography

Committee Chair

Dr. Anna Klene

Commitee Members

Dr. John Kimball, Dr. Carl Seielstad

Keywords

remote sensing, climate change, Arctic, photogrammetry, vegetation, tundra

Subject Categories

Geographic Information Sciences | Physical and Environmental Geography | Remote Sensing

Abstract

Arctic regions have experienced an amplified rate of climate warming in recent decades, contributing to well-documented increases in tundra vegetation productivity. Satellite remote sensing has historically played a crucial role in detecting and quantifying trends at regional and biome scales; however, coarse resolution imagery has proven insufficient for capturing fine-scale variability in vegetation response. Considering the spatial heterogeneity of tundra vegetation, high resolution, plot-scale remote sensing observations are necessary. This study couples traditional field measurements with high-resolution unmanned aerial vehicle (UAV) imagery and plane-based aerial photos to quantify changes in vegetation on the North Slope of Alaska over a 28-year period.

In-situ field measurements of vegetation characteristics were recorded in 1995 at a series of plots across the North Slope. Measurements were repeated in 2021 and 2023, revealing substantial increases in the overall mean canopy height and overall mean maximum shrub height, both of which doubled over the study period. Graminoid and deciduous shrub cover generally increased across the plots, with decreases in bryophytes and litter. Canopy height models (CHMs) for each site were previously derived by Ellenson 2022 from stereo color-infrared aerial photographs captured in 1995. High resolution UAV imagery of the sites was collected in 2023 and used to replicate the established photogrammetric processing workflow to generate CHMs at varying resolutions. The 2023 CHMs generally were more accurate in capturing both the mean measured canopy height and the variability in distribution of heights. Maximum shrub height was underestimated by CHMs at all resolutions for 2023. Both estimated canopy and maximum shrub heights consistently increased as pixel resolution increased for all plots, revealing a trend that necessitates further research to establish best practices for determining optimal spatial resolution of CHMs. Differences in microtopography and surface hydrology appear to be the primary drivers of plot-level shifts in species distribution and consequent variations in canopy heights at the sites included in this study. Both quantitative and qualitative findings from this study are consistent with the results of similar studies in northern Alaska, confirming that canopy heights are rapidly increasing, and that site conditions play a significant role in determining heterogeneous patterns of species distribution and productivity. This study contributes to ongoing monitoring efforts of warming-induced vegetation trends in Northern Alaska, demonstrating the value of plot-scale remote sensing observations in characterizing local vegetation response.

Recommended Citation

Moser, Anna M., "Quantifying Structural Vegetation Change on Arctic Tundra: A Multi-Decadal Study Integrating Remotely Sensed Imagery and Traditional Field Measurements" (2024). Graduate Student Theses, Dissertations, & Professional Papers. 12347.
https://scholarworks.umt.edu/etd/12347