DISTURBANCE INTENSITY AND ABOVE- AND BELOWGROUND HERBIVORY EFFECTS ON LONG-TERM (14Y) RECOVERY OF A SEMIARID GRASSLAND

Authors: Peters, Debra; LAYCOCK, WILLIAM - UNIVERSITY OF WYOMING; LAUENROTH, WILLIAM - COLORADO STATE UNIVERSITY

Submitted to: Ecology of Plant Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Large amounts of rangeland have been affected by white grub infestations resulting in loss of forage availability. We have little understanding of how other components of rangelands, such as grazing by cattle, affect plant recovery on areas killed by grubs. We studied recovery of shortgrass steppe ecosystems over a 14 year period on grub-kill patches that were grazed or ungrazed. Grazing did not affect the rate and pattern of recovery, a resul similar to effects of grazing on other aspects of these ecosystems. We found the most important effect of grazing was a greater mortality of plants from grubs compared to plant mortality in ungrazed areas. Recovery of native rangeland on areas killed by grubs was faster than for other types of disturbances similar in size to grub-killed patches. These results are important since they indicate that white grubs have large, yet short- term effects on shortgrass communities, and that recovery of plants is not affected by grazing. Management options that include changing grazing patterns are not needed for rangeland recovering after white grub infestation.

Technical Abstract: The importance of disturbance intensity and herbivory by cattle and white grubs to recovery of shortgrass steppe ecosystems in Colorado was evaluated over 14 years. Disturbance intensity was defined by survival of the dominant grass species after an outbreak of root feeding activity by white grubs. Sixteen patches of vegetation consisting of 4 pairs of adjacent ungrazed-grazed by cattle locations with 2 replicates that were recently affected by white grubs were selected in 1977. Disturbance intensity was determined in 1977 by the area in each patch that contained live tillers of B. gracilis. Permanent plots were located within and outside of each patch. Plant basal cover and density by species were estimated at time of peak aboveground biomass in 6 different years on each plot. Successional dynamics on patches was similar to areas affected by other types of disturbances, however, rate of recovery was faster for patches affected by grubs. Grazing by cattle was infrequently important to plant recovery. Disturbance intensity was important to recovery of B. gracilis. For ungrazed patches, initial conditions were important to recovery of B. gracilis for as many as 14 years. For grazed patches, initial conditions decreased and grazing increased in importance through time. Persistence of shortgrass ecosystems in spite of disturbances with different intensities are determined at least in part by characteristics of disturbances interacting with the ability of plants to respond and in part by the evolutionary history of the system. Although white grubs affect shortgrass communities infrequently, they have large and important effects on plant community structure through time and represent an important class of disturbance defined by intensity.