Wednesday, August 8, 2007

PS 45-78: Resilience of grasslands to grazing across an elevation gradient in the southern interior of British Columbia

Lauchlan H. Fraser1, Cameron N. Carlyle2, Roy Turkington2, and Don Thompson3. (1) Thompson Rivers University, (2) University of British Columbia, (3) Federal Government of Canada

Recovery of grasslands from disturbance occurs on a decadal scale; consequently, assessing their resilience is difficult. Cattle exclosures which have been constructed in dry grasslands in the southern interior of British Columbia over the past 80 years provide an opportunity to measure resilience.  We selected 50 exclosures.  The sizes of the exclosures varied but were no smaller than 400 m2.  Some exclosures date back to the 1920's, but most were built between the 1960's to 1990's.  This study tested two hypotheses critical to the management of grasslands: (1) The resilience of rangelands will increase with primary productivity; (2) Dominant vegetation both influences the resilience of grasslands and indicates recovery.  Through the measurement of plant species richness, diversity, community composition, primary productivity, soil characteristics and seed banks in the 50 exclosures of different ages we could determine the most probable factors influencing the resilience of rangelands to disturbance caused by cattle grazing. Using multivariate community analysis and regeneration indexes we compared grasslands within exclosures to those which are unfenced. We found that resilience was affected by elevation such that low-elevation, drier grassland was less resilient to grazing disturbance than high-elevation grassland of higher productivity.