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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #223400

Title: Line-point intercept, grid-point intercept, and ocular estimate methods: their relative value for rangeland assessment and monitoring

item Herrick, Jeffrey - Jeff
item Toledo, David
item Van Zee, Justin

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/30/2007
Publication Date: 1/26/2008
Citation: Godinez-Alvarez, H., Herrick, J.E., Mattocks, M., Toledo, D.N., Van Zee, J.W. 2008. Line-point intercept, grid-point intercept, and ocular estimate methods: Their relative value for rangeland assessment and monitoring [abstract]. Society for Range Management Meeting, Building Bridges: Grasslands to Rangelands, January 26-31, 2008, Louisville, Kentucky. p. 2380. 2008 CDROM.

Interpretive Summary:

Technical Abstract: We compared the utility of three methods for rangeland assessment and monitoring based on the number of species detected, foliar cover, precision (coefficient of variation) and time required for each method. We used four 70-m transects in 15 sites of five vegetation types (3 sites/type). Point intercepts were recorded every 1 m along each transect (280 points/site). Five one square meter quadrats (for ocular and grid-point) were located on each transect (20 quadrats/site). Grid-point intercepts were recorded in 16 points evenly distributed in each quadrat (320 points/site). Foliar cover estimates based on line-point and grid-point intercept methods were similar and correlated based on Spearman’s correlations (r =0.96, p<0.0001). Ocular estimates were poorly correlated with other methods, although they were significant (Line-point: r =0.62, p=0.007; Grid-point: r =0.70, p=0.002). The relationship between foliar cover estimated with line-point and ocular estimates varied with vegetation type. The number of species detected per site by line-point (17 ± 2) and grid-point (16 ± 2) intercept methods was significantly lower than the number detected by ocular estimates (21 ± 2). The time required for line-point (23 ± 2 min) was less than for grid-point intercept (31 ± 3) and ocular estimates (27 ± 4). The coefficient of variation (n=15 sites) was lower for the line point (32%) than for grid-point (37%) or ocular (49%). This study supports others indicating that ocular estimates are more effective for detecting species, while line-point intercept and grid-point provide more precise cover estimates. These results suggest that when assessing the effects of conservation practices (e.g. CEAP), methods should be selected based on objectives (e.g. biodiversity vs. cover). The results also suggest that species area curves can be used to estimate total species using any of the methods. Future analyses will include comparisons with ground and aerial photography.