Spatial and Temporal Trends in Vegetation Index in the Bonanza Creek Experimental Forest.

Becky Baird

M. S. Thesis
June 2011
University of Alaska Fairbanks

ABSTRACT

Climate has warmed substantially in boreal Alaska since the mid-1970s.  The direct effects of rising temperatures on sub-Arctic ecosystems are already being seen in the form of drought stress, increased fire frequency and severity, and increased frequency and severity of herbivorous insect outbreaks. These effects of climate change are having a direct impact on the vegetation of the boreal forest and leading to a decreased remotely sensed vegetation index (NDVI), as observed by some studies.  The vegetation index, is an effective proxy for plant photosynthesis on a landscape scale, and therefore, an appropriate measure to examine landscape-scale changes in vegetation due to climate change effects.  The overarching goal of my research was to assess the change in vegetation index at Bonanza Creek Experimental Forest, using a combination of remote sensing and field sampling to examine associated patterns in plant communities. 
My project consists of two main parts:  creating a landcover classification through field sampling and incorporating the field data into a map using satellite imagery and examining trends in the vegetation index using 11 Landsat TM and ETM+ images from 1986-2009.  By using Landsat imagery and doing a landcover classification of my study area I was able link changes in vegetation index to specific plant communities on the landscape. 
Vegetation at Bonanza Creek Experimental Forest was sampled using the relevé approach to collect floristic and environmental data at 85 sites throughout the study area.  The floristic data was classified using non-metric multidimensional scaling, leading to the classification of six upland and seven floodplain plant communities. 
We used Landsat TM and ETM+ images, spanning a period of 23 years, to link temporal vegetation index (NDVI) trends, in an interior Alaska boreal forest, to landscape features and plant communities.  What we found was a significant decline in NDVI throughout the study site and similar declining trends in various landscape positions, topographic classes, and plant communities.  There were two recently burned areas in the study site and we found an increase in NDVI following each of the two burns.