Southwest Montana Sagebrush Canopy Cover Classification

A land cover type classification of SW Montana was completed during the summer of 2001 for Region One of the US Forest Service. Land cover types were mapped using Landsat TM images and training examples of different land cover types. First, each Landsat image (30 meter pixels) was run through an image segmentation process to delineate the image into "ground-feature" regions. A variable minimum map unit was used based on the level of spectral diversity in a moving window. The image segmentation regions varied in size from 0.09 ha to 200 ha with an average size of 5 ha. Each region was attributed with TM band and topographic values based on the average of pixels within the region. Then, training data was used to run a supervised classification of the regions. Each region was compared to the training data set, and the 12 nearest training data (based on euclidian distance in spectral space) were used to determine the land cover type. Due to limited amounts of rangeland training data, sagebrush and other xeric shrub types were mapped as a combined type. The initial rangeland types mapped were:

3130 very low cover grasslands (10-34% grass)
3150 low/moderate cover grasslands (35-64% grass)
3170 moderate/high cover grasslands (>= 65% grass)
3610 willow and mesic shrubland
3625 sagebrush and xeric shrubland

The BLM Dillon Resource Area office wanted to try a re-classification of SW Montana for sagebrush canopy cover groups. Xeric shrublands in SW Montana are primarily dominated by Mountain Big Sagebrush (Artemisia tridentata-vas), Wyoming Big Sagebrush (Artemisia tridentata-wym), Basin Big Sagebrush (Artemisia tridentata-tri), Low Sagebrush (Artemisia arbuscula), Rabbit brush (Chrysothamnus nauseousus), and Moutain Mahogany (Cercocarpus species). Sagebrush and xeric shrub patches range from 5-60% canopy cover. Sagebrush also varies from continuous cover to dense patches mixed with open grass. First, Mountain Mahogany was separated from the sagebrush and xeric shrubland group. Then, 5 sagebrush canopy cover groups were created. The new rangeland types became:

3130 very low cover grasslands (10-34% grass)
3150 low/moderate cover grasslands (35-64% grass)
3170 moderate/high cover grasslands (>= 65% grass)
3301 mountain mahogany 3550 very low cover sagebrush/low cover grass (5-14% sagebrush & 10-24% grass)
3560 very low cover sagebrush/moderate cover grass (5-14% sagebrush & >= 25% grass)
3380 low cover sagebrush (15-24% sagebrush)
3390 moderate cover sagebrush (25-34% sagebrush)
3395 high cover sagebrush (> 35% sagebrush)
3610 willow and mesic shrubland

The new rangeland types required additional training data for the supervised classification. The BLM provided Daubenmire transect data and the Montana Heritage Program provided sagebrush survey data for SW Montana. A series of supervised classifications were performed and then maps were created for field checking the classifications. During the field checks additional training data were collected using the classified maps. The final result was a region grid with 30 land cover types mapped, five of them being different levels of sagebrush canopy cover.

The metadata for the project contains a full description of the mapping process, accuracy results, and a description of attributes in the region grid.

blmsilc3z.shtml - Click to view metadata

Project completion date: February 28,2002

Principal Investigator	Roland L. Redmond
GIS Analyst	Chip Fisher

Funded by the Bureau of Land Management, Montana State Office