Submitted to: Wildland Shrub Symposium Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2006
Publication Date: 6/6/2006
Citation: Moffet, C.A., J.B. Taylor, D.T. Booth. 2006. Very large scale aerial (VLSA) imagery and addressin post-fire bitterbrush recovery [abstract]. Shrublands Under Fire: Distubance and Recovery in a Changing World. Fourteenth Wildland Shrub Sympsium. p. 49. Interpretive Summary: Evaluating the effects of management activities on vegetation in extensive rangelands with traditional methods requires much time and effort. Very large scale aerial (VLSA) imagery is an efficient tool for collecting the data required to evaluate these effects. We analyzed VLSA imagery collected from a survey of the U. S. Sheep experiment station along with soil and 68 years of fire history data to test whether VLSA imagery can be used to evaluate the effect of fire on bitterbrush recovery. The relationship between post-fire recovery interval and bitterbrush cover and density were similar to those previously reported in the literature for eastern Idaho and indicate that analysis of VLSA imagery is an effective method for evaluating the impact of fire history on bitterbrush recovery.
Technical Abstract: Very large scale aerial (VLSA) imagery is an efficient tool for monitoring extensive rangelands. The near 1-mm resolution imagery is sufficient for identification of many species. The shrub bitterbrush (Purshia Tridentata Purch DC) can be consistently identified in images obtained from a U. S. Sheep Experiment Station (USSES) VLSA survey (2005). Bitterbrush is an important browse species for domestic livestock and wild ungulate species. Bitterbrush response to fire varies among ecotypes. For example, some ecotypes are susceptible to fire, but in eastern Idaho bitterbrush often re-sprouts from the root crown after fire. Researchers at the USSES in eastern Idaho have been conducting fire research since the 1930’s, and fire history on the 11,000 ha Headquarters property is well known. In 2005, a total of 705 VLSA images (fixed-wind aircraft; altitude above ground level = 100 m; 3 x 4 m image; pixel width = 1.1 mm) were obtained on an equally spaced grid encompassing the entire Headquarters. Using our GIS database, we classified soil and fire history for the center point of each image. A subset of images (n = 263) was selected that included only range sites having up to 10 % bitterbrush composition in the historic climax plant community description. For each image, current post-fire recovery interval was calculated from the fire history data, and bitterbrush density and cover were measured. These data were used to determine the relationships between post-fire recovery interval and bitterbrush density and cover. Bitterbrush cover in the images with no recorded history of fire during the past 68 yr (22 % of all images) was 1.54 % and the density was 1,180 plant/ha. Areas with a post-fire recovery interval between 8 and 68 yr (62 % of all images) had bitterbrush density (840 plant/ha) and cover (1.19 %) that were not significantly different from areas with no fire history. Images with a post-fire recovery interval less than 8 yr (16 % of all images) exhibited significantly less bitterbrush cover (0.38 %) and density (222 plants/ha). These results are consistent with other observations of post-fire bitterbrush recovery in eastern Idaho and indicate that analysis of VLSA imagery is an effective method for evaluating the impact of fire history on bitterbrush recovery.