Canopy analysis as a technique to characterize defoliation intensity on Sandhills range.

Abstract

Characterization of relationships between grazing and vegetation responses is difficult. Rapid and accurate measurement of pasture canopy characteristics would help clarify these relationships if canopy changes are directly related to grazing variables. The objectives of this study were (1) to evaluate use of the LI-COR LAI-2000 for quantification of changes in canopy density and architecture in response to defoliation by cattle, (2) to determine if changes in leaf area index (LAI) measured with the LAI-2000 are related to stocking rate, and (3) to determine advantages and drawbacks of the LAI-2000 for monitoring grazing impacts on canopy density and architecture. Leaf area index and mean foliage tilt angle were measured before and after defoliation by cattle (Bos taurus L.) in June, July, and August under 9 grazing treatments on Nebraska Sandhills range. Differences in LAI could be attributed to certain grazing treatments at various points throughout the season. Grazing treatment had little impact on mean foliage tilt angle. Change in LAI (delta LAI) had a significant negative relationship with stocking rate (P < or = 0.0001). The relationship detected for delta LAI versus stocking rate predicted LAI reductions of between 0.14 and 0.40 for the range of stocking rates studied; stocking rate accounted for 62% of the decrease in LAI caused by grazing. When configured for the Sandhills canopy, the LAI-2000 provided a rapid and precise method for quantification of the degree of defoliation associated with grazing.