PARENT SESSION
Poster Session #46: Riparian Ecology.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Livestock herbivory impacts on woody species in a central Arizona riparian area.

GREEN, DOUGLAS^*,1, FENNER, PATTI², ¹ Arizona State Univeristy East, Mesa, AZ² U.S. Forest Service, Scottsdale, AZ

ABSTRACT- Populus fremontii (Fremont cottonwood) and Salix gooddingii (Goodding willow) are important native woody species of many Arizona riparian systems. To determine the impact of livestock grazing on community dynamics of P. fremontii and S. goodingii in April of 1999 we tagged 410 trees located in 10 greenline communities along the Verde River in central Arizona, USA. Livestock are grazed on this reach as part of a winter grazing program and are generally removed by April of each year. The utilization limit of woody riparian species is set at 40% of the grazeable meristems. At each tagged tree we measured overall height, diameter, distance from the tag to the sediment surface, and utilization twice each year. By September of 2001, 216 trees were left in the study group. Utilization ranged from 23.4% in 1999 to less than 1% in 2001. Growth of grazed P. fremontii was 39.4, 50.5, and 34.5 cm in 1999, 2000, and 2001 respectively; while ungrazed P. fremontii grew 34.3, 48.2 and 34.0 cm during the same time periods. During the study period, grazed S. gooddingii grew 35.6 cm in 1999, 29.9 cm in 2000, and 23.1 cm in 2001; ungrazed S. gooddingii grew 32.1, 27.8, and 23.5 cm over the same time periods. Differences in growth between grazed and ungrazed trees were not significant for either species in any year. Based on our results, livestock grazing does not appear to significantly impact height growth of P. fremontii or S. gooddingii along this reach of the Verde River.

KEY WORDS: riparian, grazing, Populus fremontii, Salix gooddingii