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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #284393
Title: Indirect measurement of leaf area index in sagebrush-steppe rangelands

Author
item Finzel, Julie
item Seyfried, Mark
item Weltz, Mark
item Kiniry, James
item JOHNSON, MARI-VAUGHN - Natural Resources Conservation Service (NRCS, USDA)
item LAUNCHBAUGH, KAREN - University Of Idaho

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2011
Publication Date: 3/15/2012
Citation: Finzel, J.A., Seyfried, M.S., Weltz, M.A., Kiniry, J.R., Johnson, M.V., Launchbaugh, K.L. 2012. Indirect measurement of leaf area index in sagebrush-steppe rangelands. Rangeland Ecology and Management. 65:208-212.

Interpretive Summary: Leaf area index (LAI) is defined as the one-sided area of leaves above a unit area of ground. It is a fundamental ecosystem parameter that is a required input of process-based plant growth and biogeochemical models. Direct measurement of LAI is the most accurate method, but is destructive, time-consuming, and labor-intensive. LAI is highly variable in time and space on sagebrush-steppe rangelands, and a rapid nondestructive method is desirable to understand ecosystem processes. The point-intercept method is a non-destructive method and has been demonstrated to provide accurate data on sagebrush. A limitation of the point-intercept method is that it is time-consuming. The Accupar ceptometer (Decagon Devices, Pullman, WA) is also a nondestructive method that is faster than point-intercept but has not been evaluated on sagebrush-steppe rangelands. The objective of this study was to evaluate the ceptometer for measurement of LAI in sagebrush-steppe rangelands. Ceptometer and point-intercept LAI data were evaluated at six sites in sagebrush-steppe rangelands. We found that the ceptometer measured LAI was significantly different from point-intercept measured LAI and was consistently greater than point-intercept LAI data. We also found that the ceptometer data were much more variable than the point-intercept and, there was minimal relationship between the two techniques. The much greater ceptometer LAI values were at least partly was due to its inability to distinguish the difference between woody stems and leaves.

Technical Abstract: Leaf area index (LAI) is defined as the one-sided area of leaves above a unit area of ground. It is a fundamental ecosystem parameter that is a required input of process-based plant growth and biogeochemical models. Direct measurement of LAI is the most accurate method, but is destructive, time-consuming, and labor-intensive. LAI is highly variable in time and space on sagebrush-steppe rangelands, and a rapid nondestructive method is desirable to understand ecosystem processes. The point-intercept method is a non-destructive method and has been demonstrated to provide accurate data. A limitation of the point-intercept method is that it is time-consuming. The Accupar ceptometer (Decagon Devices, Pullman, WA) is also a nondestructive method that is faster than point-intercept but it has not been evaluated on sagebrush-steppe rangelands. The objective of this study was to evaluate the ceptometer for measurement of LAI in sagebrush-steppe rangelands. Ceptometer and point-intercept LAI data were collected at six sites in sagebrush-steppe rangelands and the values were compared. We found that: 1) ceptometer measured LAI was significantly different from point-intercept measured LAI (p < 0.005), 2) ceptometer LAI data were consistently greater than point-intercept LAI data, 3) ceptometer data were much more variable than the point-intercept data based on standard deviations and, 4) the overall correlation between the two methods was very weak (r2 = 0.15). The much greater ceptometer LAI values were at least partly was due to the large woody component of the vegetative cover. We attribute the high variability of ceptometer measured LAI to high instrument sensitivity of the angle of the instrument relative to the sun.