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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #238158
Title: Comparison of three vegetation monitoring methods: Their relative utility for ecological assessment and monitoring

Author
item GODINEZ-ALVAREZ, H - Universidad Nacional Autonoma De Mexico
item Herrick, Jeffrey - Jeff
item MATTOCKS, MICHELLE - New Mexico State University
item Toledo, David
item Van Zee, Justin

Submitted to: Ecological Indicators
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2008
Publication Date: 3/1/2009
Citation: Godinez-Alvarez, H., Herrick, J.E., Mattocks, M., Toledo, D.N., Van Zee, J.W. 2009. Comparison of three vegetation monitoring methods: Their relative utility for ecological assessment and monitoring. Journal of Ecological Indicators. 9:1001-1008.

Interpretive Summary: Scientists, students and land managers all need reliable, repeatable methods to measure vegetation cover and composition. Many different methods are used, but there is relatively little information on whether the results from different methods are comparable. In this study, we compared 3 different methods for measuring vegetation cover relative to: 1) interchangeability of data, 2) precision, 3) cost, and 4) value of each method based on its potential to generate multiple indicators. Foliar cover by species (the proportion of the soil surface covered by a vertical projection of a plant) was measured in five plant communities in the Chihuahuan Desert using 3 common methods: line-point intercept, grid-point intercept, and ocular estimates. Line- and grid-point intercept provide similar estimates of the number of species. These estimates were lower than those based on ocular estimates, but there were no differences in the precision of the number of species detected. Precision of cover estimates with line-point intercept was higher than for ocular estimates. Time requirements for the three methods were similar, despite the fact that the point-based methods provided many more indicators (including multiple vegetation layers) than ocular estimates. Results suggest that point based methods provide interchangeable data with higher precision than ocular estimates. Moreover these methods can be used to generate a much greater number of indicators that are more directly applicable to a variety of monitoring objectives, including soil erosion and wildlife habitat.

Technical Abstract: Vegetation cover and composition are two indicators commonly used to monitor terrestrial ecosystems. These indicators are currently quantified with a number of different methods. The interchangeability and relative benefits of different methods have been widely discussed in the literature, but there are few published comparisons that address multiple criteria across a broad range of grass- and shrub-dominated communities, while keeping sampling effort (time) approximately constant. This study compared the utility of three field sampling methods for ecological assessment and monitoring: line-point intercept, gridpoint intercept, and ocular estimates. The criteria used include: (1) interchangeability of data, (2) precision, (3) cost, and (4) value of each method based on its potential to generate multiple indicators. Foliar cover by species was measured for each method in five plant communities in the Chihuahuan Desert. Line- and grid-point intercept provide similar estimates of species richness which were lower than those based on ocular estimates. There were no differences in the precision of the number of species detected. Estimates of foliar cover with line- and grid-point intercept were similar and significantly higher than those based on ocular estimates. Precision of cover estimates with line-point intercept was higher than for ocular estimates. Time requirements for the three methods were similar, despite the fact that the point-based methods included cover estimates for all canopy layers and the soil surface, while the ocular estimates included only the top canopy layer. Results suggest that point-based methods provide interchangeable data with higher precision than ocular estimates. Moreover these methods can be used to generate a much greater number of indicators that are more directly applicable to a variety of monitoring objectives, including soil erosion and wildlife habitat.