Use of time-series satellite data to identify mesquite response to stress as an indicator of ecosystem health

TitleUse of time-series satellite data to identify mesquite response to stress as an indicator of ecosystem health
Publication TypeConference Paper
Year of Publication1995
AuthorsMouat D.A., Lancaster J., Kuehl R.O., Whitford WG
Conference NameWildland Shrub Symposium
Date PublishedMay 23-25, 1995
Abstract

Since the late nineteenth century the Jornada Experimental Range has undergone change from grassland to a mixed shrubland ecosystem, and could be considered in less healthy condition as a result. The phenological response of mesquite dominated ecosystems to environmental stressors was analyzed through the use of high temporal resolution satellite data and environmental stressor data. Four mesquite and four grassland sites with variable composition and cover were selected, along with concomitant precipitation, grazing history and herbicide treatment as major stressors. Satellite data for the period 1987 through 1993 from the Advanced Very High Resolution Radiometer (AVHRR) were used to calculate the Normalized Difference Vegetation Index (NDVI), which is a measure of vegetation greenness. Values for NDVI from between 12 and 14 images at approximately 17-day intervals for each year from mid March through early October, were plotted on a site-by-site basis, and smoothed to produce NDVI temporal profile curves., Metrics calculated from these curves include the intergration of the area under the curve, the ratio of spring to summer of NDVI, the duration of maximum photosynthetic activity, and the date of NDVI, value for green-up and brown-off. Species composition and cover data, and soil color and texture were collected on a sample of field sites, and from aerial photography. Values were obtained for summer, winter and year-round stocking rates, for current year annual, spring and summer rainfall, and for herbicide treatment.  The data were analyzed to investigate differences between sites and years, and associated between stressors and NDVI response. The NDVI temporal profile curves of mesquite shrub sites are clearly distinct from other ecosystems it is possible to test the hypothesis that the temporal and spatial variability of degraded shrublands is lower than that of grasslands or shrub-grass ecosystems.