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United States Department of Agriculture

Agricultural Research Service

Title: Detecting Fragmentation of Cover in Desert Grasslands Using Line Intercept

Authors
item Kuehl, Robert - UNIVERSITY OF ARIZONA
item Mcclaran, Mitchel - UNIVERSITY OF ARIZONA
item Van Zee, Justin

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 2001
Publication Date: January 1, 2001
Citation: KUEHL, R.O., MCCLARAN, M.P., VAN ZEE, J.W. DETECTING FRAGMENTATION OF COVER IN DESERT GRASSLANDS USING LINE INTERCEPT. JOURNAL OF RANGE MANAGEMENT. 2001. V. 54(1). P. 61-66.

Interpretive Summary: Changes in the amount or spatial distribution of grass plants are thought to be indicative of the stability of desert grasslands. This study assessed, through simulation, the sensitivity of statistical properties for distance between plants (fetch length), measured with a line intercept transect, to changes in the spatial distribution and amount of plant cover. Simulated plots were created with four different grass covers with random and fragmented spatial distribution, then fetch lengths were measured on two random transects in those plots. The accuracy of the fetch length method was verified by its similarity to a commonly used point-to-plant sampling procedure. In both random and fragmented plant distributions, both fetch length and point-to-plant measurement methods accurately estimated changes in percent grass cover. The results suggest the evaluation of changes over time at a monitoring site could use fetch lengths measured along a line intercept transect, which is a simpler and more rapid method than point-to-plant methods, to detect changes in both absolute and spatial arrangement of plant cover.

Technical Abstract: Changes in the amount or spatial distribution of grass plants are thought to be indicative of the stability of desert grasslands. This study assessed, through simulation, the sensitivity of statistical properties for distance between plants (fetch length), measured with a line intercept transect, to changes in the spatial distribution and amount of plant cover. Monitoring plots, 30 X 30 m, were simulated for 1, 2.5, 5, 10, and 15% grass cover with random and fragmented spatial distribution. Fetch lengths were measured on 2 randomly placed 30 m transects. In addition to the median and interquartile range, the asymmetry of the sampling distributions was measured with a ratio [(maximum-median)/(median-minimum)] that would identify the presence of at least one large, open space. The accuracy of the fetch length method was confirmed by the similarity of its sampling distribution to that for the well-known, random point-to-plant sampling procedure. In both the fetch length and the point-to-plant measures, the median and interquartile range increased with decreasing cover for random and fragmented distribution. The asymmetry estimate increased sharply with increasing cover for the fragmented distribution, but asymmetry was nearly constant with increasing cover for the random distribution. The results suggest the evaluation of changes over time at a monitoring site could use fetch lengths measured along a line intercept transect to detect changes in both absolute and spatial arrangement of cover.

Last Modified: 4/19/2014
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