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United States Department of Agriculture

Agricultural Research Service

Title: Response of Individual Bouteloua Gracilis (Gramineae) Plants and Tillers to Small Disturbances

Authors
item Fair, J - COLORADO STATE UNIVERSITY
item Peters, Debra
item Lauenroth, W - COLORADO STATE UNIVERSITY

Submitted to: American Midland Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 22, 2000
Publication Date: January 1, 2001
Citation: FAIR, J.L., PETERS, D.C., LAUENROTH, W.K. RESPONSE OF INDIVIDUAL BOUTELOUA GRACILIS (GRAMINEAE) PLANTS AND TILLERS TO SMALL DISTURBANCES. AMERICAN MIDLAND NATURALIST. 2001. V. 145(1). P. 147-158.

Interpretive Summary: We examined the effects of small disturbances on tiller and plant survival of blue grama, the dominant species in shortgrass steppe rangelands. The importance of soil texture, grazing by cattle, disturbance type, and severity were evaluated. Two disturbance types (covering or removing tillers) and three severities (50, 75, and 90% of the plant killed) were used to represent effects of cattle fecals, harvester ants, and burrows of small animals. Survival of remaining tillers was not affected by soil texture or grazing intensity, but was affected by disturbance type and severity. Plants that were partially covered showed a 33% increase in tiller number for all levels of severity from August (1991) to June (1992). No net change in tiller number was found for partially removed or control plants. The ability of blue grama plants to survive even with 90% tiller mortality indicates that small disturbances must kill entire plants before gaps in resource space are produced and successional dynamics are initiated. Because seedling establishment by blue grama occurs infrequently, the ability of this species to survive partial plant mortality is important to its continued dominance in the presence of these small, but frequent disturbances.

Technical Abstract: We evaluated effects of small disturbances that kill parts of individual plants on plant survival by measuring tiller survival for the perennial bunchgrass, Bouteloua gracilis (H.B.K.) Lag ex Griffiths (blue grama). The importance of soil texture, grazing by cattle, disturbance type, and severity were evaluated. Two disturbance types (covering or removing tillers) and three disturbance severities (50, 75, and 90% tiller mortality) were used to represent effects of natural disturbances in shortgrass communities (cattle fecal pats, nest sites of Western harvester ants, burrows of small animals). Tiller survival through time was not affected by soil texture or grazing intensity, but was affected by disturbance type and severity. Plants that were partially covered showed a 33% increase in tiller survival for all levels of severity from August (1991) to June (1992). No net change in tiller number was observed for partially removed or control plants. The number of tillers produced was small, but significant (avg=20 tillers/plant), which suggests that B. gracilis plants do not contain independent tillers, but consist of integrated physiological units (IPUs). The lack of plant mortality even with 90% tiller mortality indicates that small disturbances must kill entire plants before gaps in resource space are produced, and gap dynamics are initiated that result in the recovery of an individual B. gracilis plant. Because recovery through seedling establishment by B. gracilis occurs infrequently, the ability of this species to survive after partial plant mortality is important to its continued dominance of shortgrass steppe communities in the presence of these small, but frequent disturbances.

Last Modified: 12/21/2014