Evaluating Success of Alternative Restoration Methods for Riparian Willows: Seeding and Ungulate Exclosures

摘要

Riparian willows provide important ecosystem functions, however, in some locations they have been degraded due to over-browsing by wild and domestic ungulates. Fires can also have a detrimental effect on riparian vegetation, but have positive effects by creating bare soil necessary for willow seed germination. Both active and passive methods of restoration are common, but questions related to willow seed production are not welt studied. We examined two questions: 1) Are bare soil patches created by wildfire suitable for willow seedling establishment? and 2) How has aerial seed rain changed since the establishment of exclosures to limit access of ungulates to willow stands? Working in montane riparian areas in Rocky Mountain National Park (USA), we seeded 1 m~2 plots on bare soil patches created by a wildfire and monitored germination and survival. Seeds germinated in 46% of the plots and the number of seedlings ranged from 1 to 591. Plots with higher average growing season soil moisture had greater numbers of seedlings and seedling survival rates. In a nearby unburned valley, we assessed aerial seed rain biweekly using traps established at the same locations as a previous study in 2000. Five years after the establishment of exclosures, aerial seed rain was lower than in the pre-fence year 2000. We conclude that fire could trigger willow seeding establishment and controlled burns used as a viable option for restoration. In addition, five years of fencing is insufficient to reestablish willow seed rain after a period of heavy browsing.