Date of Award

January 2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Earth System Science & Policy

First Advisor

Jeffrey VanLooy

Abstract

Tallgrass prairies are one of the rarest ecosystems on the planet as up to 99% of their historical extent has been converted to agriculture. Once a prairie is converted there is often a loss of ecosystem services such as soil retention, carbon storage, water quality and a loss of biodiversity. It can take centuries to restore a native prairie after conversion has taken place. The Sheyenne National Grassland is managed by the U.S. Forest Service and contains the largest publicly owned tract of tallgrass prairie remaining in North America making it a highly valuable for conservation.

Ordinary least squares regression was implemented to evaluate statistically significant trends at a per pixel basis in selected Vegetation Indices (VI) between the years of 1984 and 2011 on the Sheyenne National Grassland. VIs included NDVI, NDII RGR and SWIR32. Additionally, a Composite Index which sought to combine information from the original four indexes was created to evaluate the usefulness of combining indexes. A random forest regression model was also used to evaluate which independent variables were the most useful in predicting VI values through time.

Between 1984 and 2011 the NDVI and NDII have increased while the RGR and SWIR32 have decreased. This indicates that greenness and wetness have increased through time while stress and non-photosynthetic vegetation have decreased. It is likely that the increase in NDVI is driven by a complex relationship between the influence of climate change and cattle grazing on the relative abundance of C3 and C4 plants. It is hypothesized that continuously stocked cattle grazing has reduced the vigor and competitive ability of native C4 grasses which competitively releases C3 grasses that are more tolerant of grazing and are primarily invasive. In addition to the competitive release of cattle grazing, C3 establishment is promoted through increased spring precipitation which has increased over the last century.

Download

Share

COinS