The Greening and Browning of the San Juan Mountains of Colorado: Trend Analysis of Forest Vegetation Using Landsat Imagery

Katherine C. Cavanaugh, Gettysburg College

Environmental Studies Senior Honors Thesis

Description

The forested areas within the San Juan Mountain Range in Southwestern Colorado are affected by factors such as temperature, precipitation, wildfire, and forest treatments. Changing social and environmental conditions may be altering forested vegetation in ways that were not historically observed. The Normalized Difference Vegetation Index (NDVI), an index of 'greenness,' is often used to measure changes in the vegetative characteristics of a landscape. Using a trend analysis of NDVI, the following research questions will be assessed: Has there been long term 'greening' or 'browning' of forest vegetation in the Colorado San Juan Mountain Range from 1984-2014? To what extent is greening/browning associated with disturbances (e.g. forest treatments and fire) versus environmental conditions (e.g. vegetation type and elevation)? To evaluate and detect these changes, Breaks for Additive Seasonal and Trend method (BFAST) was applied to NDVI derived from 30 years of Landsat Imagery. While there was no overall change in NDVI within the forested vegetation types of the study area, Rocky Mountain aspen forests and woodlands experienced the greatest amount of browning, and Southern Rocky Mountain piñion-juniper forests experienced the greatest amount of greening. These results are consistent with the negative effects of Sudden Aspen Decline (SAD) on Apsen Forests, and also with the effects of decreased wildfire occurrences on Piñion-Juniper Forests. Furthermore, browning was more prominent in areas of higher elevations, which is consistent with changing temperature and precipitation averages that are contributing to declines in higher elevation forest health. Aside from ponderosa pine forests, all vegetation types were browning within wildfire burned areas, which is consistent with the structure of historical tree stands. Ponderosa pine forests experienced slight browning within broadcast burning treatment areas, and slight greening within thinning treatment areas relative to reference zones.

 
Apr 29th, 4:30 PM Apr 29th, 6:15 PM

The Greening and Browning of the San Juan Mountains of Colorado: Trend Analysis of Forest Vegetation Using Landsat Imagery

CUB Ballroom

The forested areas within the San Juan Mountain Range in Southwestern Colorado are affected by factors such as temperature, precipitation, wildfire, and forest treatments. Changing social and environmental conditions may be altering forested vegetation in ways that were not historically observed. The Normalized Difference Vegetation Index (NDVI), an index of 'greenness,' is often used to measure changes in the vegetative characteristics of a landscape. Using a trend analysis of NDVI, the following research questions will be assessed: Has there been long term 'greening' or 'browning' of forest vegetation in the Colorado San Juan Mountain Range from 1984-2014? To what extent is greening/browning associated with disturbances (e.g. forest treatments and fire) versus environmental conditions (e.g. vegetation type and elevation)? To evaluate and detect these changes, Breaks for Additive Seasonal and Trend method (BFAST) was applied to NDVI derived from 30 years of Landsat Imagery. While there was no overall change in NDVI within the forested vegetation types of the study area, Rocky Mountain aspen forests and woodlands experienced the greatest amount of browning, and Southern Rocky Mountain piñion-juniper forests experienced the greatest amount of greening. These results are consistent with the negative effects of Sudden Aspen Decline (SAD) on Apsen Forests, and also with the effects of decreased wildfire occurrences on Piñion-Juniper Forests. Furthermore, browning was more prominent in areas of higher elevations, which is consistent with changing temperature and precipitation averages that are contributing to declines in higher elevation forest health. Aside from ponderosa pine forests, all vegetation types were browning within wildfire burned areas, which is consistent with the structure of historical tree stands. Ponderosa pine forests experienced slight browning within broadcast burning treatment areas, and slight greening within thinning treatment areas relative to reference zones.