Efficacy of Riparian Revegetation Projects in the Inland Pacific Northwest

Riparian areas have been severely damaged by the combined impacts of grazing, river regulation, development and other types of land use, so that many no longer provide key ecosystem functions and services. Revegetation is a common riparian restoration practice, but there is little information available on whether revegetation projects are effective. I reviewed the efficacy of riparian revegetation projects conducted in the inland Pacific Northwest (iPNW) between 1984 and 2007 based upon the Pacific Northwest Salmon Habitat Project (PNHSP) database. I found that 10% of the stream restoration projects in the iPNW included riparian revegetation (1,340 projects), and 11% of those projects (151 projects) indicated they had monitored their results. I was unable to demonstrate that riparian revegetation projects conducted in the iPNW during this period were successful. The main reason for this was a lack of monitoring; just 151 (11 percent) of 1,340 restoration projects in the Pacific Northwest Salmon Habitat Project database that included revegetation also included monitoring. Despite extensive efforts I was only able to obtain monitoring reports for 36 of these projects, indicating that even when projects are monitored the results are often either not published or not readily available. Of the projects for which monitoring results were available: 1) most (89%) did not define quantitative success criteria, so it was not possible to determine whether project goals had been achieved; 2) a wide variety of monitoring techniques was used, making it difficult to identify trends or make comparisons among projects; 3) almost all (97%) were monitored for less than five years, which is not long enough to determine the true effectiveness of revegetation. Despite the lack of effective monitoring, project practitioners in the iPNW have learned a great deal about the factors influencing the outcome of revegetation efforts. The two operational factors identified most frequently in the 36 monitoring reports were the need to select plant material and planting techniques that are well suited to the site, and the need for ongoing maintenance to reduce impacts due to environmental factors such as herbivory, plant competition, moisture, erosion/flooding/scour, and coarse substrate. Project practitioners use a range of techniques to reduce the effects of these environmental factors. Follow up discussions with restoration practitioners identified additional factors affecting project outcomes including: 1) providing sufficient budget for the revegetation component of the project; 2) conducting an in-depth site assessment prior to project implementation; 3) taking an interdisciplinary team approach to restoration; 4) integrating ecological concepts from research into revegetation studies; and 5) taking a watershed scale approach to restoration efforts. Future revegetation efforts should take account of these and other lessons already learned. When employed in combination with monitoring, this will lead to an adaptive management approach that increases the potential success of future revegetation efforts