Do ungulates facilitate native and exotic plant spread? Seed dispersal by cattle, elk and deer in northeastern Oregon

Large domestic and native ungulates have the potential to disperse large quantities of seeds throughout the landscape. Many studies have found that ungulates are capable of dispersing seeds but few quantify the relative importance of ungulate dispersal across the landscape. We investigated the potential for cattle, elk, and deer to disperse native and exotic plants in two different western North American ecosystems in northeast Oregon. We collected fecal samples of cattle, elk and deer that had been deposited during the current growing season. In the greenhouse we monitored the density and species richness of seedlings that germinated from the fecal samples. All three species act as seed dispersers for native and exotic plants. Cattle fecal pats had a higher species richness and density of exotic grasses germinating compared to the other ungulates; elk had a higher species richness and density of native and exotic forbs compared to the other ungulates. We then projected the number of seeds that each animal could disperse during a growing season. We predict that cattle disperse more than an order of magnitude more seeds than elk and deer per animal. Cattle, elk and deer interact with the landscape in different ways and this can have important ramifications for plant communities at local and regional scales. (C) 2007 Elsevier Ltd. All rights reserved.