The Greening and Browning of the San Juan Mountain Range: Trend Analysis of Landscape Change using Landsat Imagery

Katherine C. Cavanaugh, Gettysburg College
Rutherford V. Platt, Gettysburg College

This research was presented at the 2016 American Association of Geographers' Annual Meeting in San Francisco, CA, March 29 - April 2, 2016.


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 'greeness,' is often used to measure changes in the vegetative characteristics of a landscape. Using a trend analysis of NDVI, I will answer the following research question: 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 changes in climate)? 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 is 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.