PARENT SESSION
Contributed Oral Session 11: Invasive Species: Arid Lands
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal
Community and ecosystem impacts of Pennisetum ciliare (Buffelgrass) in the Sonoran Desert, Sonora, Mexico.
Lyons, Kelly 1, 1 Trinity University, San Antonio, TX, U.S.A.
ABSTRACT- In the last five decades P. ciliare has been actively introduced in southwestern U.S. and northern Mexico to improve desert rangelands. In the Plains of Sonora subdivision of the Sonoran Desert, P. ciliare readily spreads from converted grasslands into intact native vegetation. Newly established individuals of P. ciliare in intact desert are most often found under tree-shrub complexes where native diversity is highest. Conversion of native shrubland to P. ciliare grassland and spread of the species into intact desert vegetation results in an apparent decline in native herbaceous species. Our goal was to assess the impact of P. ciliare grassland conversion and the species' establishment in intact desert on the native flora. We also aimed to elucidate the mechanism of competition between the invasive exotic and native species through study of limiting resources. In summer 2002, we established a 2x2x2 factorial experiment with P. ciliare removal, nitrogen addition and land use history as factors. We also included a procedural control to account for disturbance created through P. ciliare removal. The experiment was established in a randomized, complete, block design spanning converted P. ciliare grassland and intact desert. In winter 2002-03, we found that P. ciliare removal had a positive effect on native species cover while nitrogen addition had the opposite effect. P. ciliare fitness was unaffected by nitrogen addition, a finding we attribute to low rainfall. In both converted grassland and intact desert P. ciliare removal did not alter available NO3 and NH4. Nonetheless, P. ciliare removal had a significantly positive effect on net nitrogen mineralization rates. We were unable to detect significant differences in soil water content between P. ciliare removal treatments and controls. Competition of P. ciliare with the native herbaceous species likely occurs through utilization of limiting resources, slowing of nutrient cycling and occupation of space.
Key words: Pennisetum ciliare, non-indigenous, sonora, mexico, grassland