Have wet meadow restoration projects in the Southwestern U.S. been effective in restoring geomorphology, hydrology, soils, and plant species composition? (systematic review)
Wet meadows occur in numerous locations throughout the American Southwest, but in many cases have become heavily degraded. Among other things they have frequently been overgrazed and have had roads built through them, which have affected the hydrology of these wetland ecosystems.
Because of the important hydrologic and ecological functions they are believed to perform, there is currently significant interest in wet meadow restoration. Several restoration projects have been completed recently or are underway in the region, sometimes at considerable expense and with minimal monitoring. The objective of this review was to evaluate the effects of wet meadow restoration projects in the southwestern United States on geomorphology, hydrology, soils and plant species composition. A secondary objective was to determine the effects of wet meadow restoration projects on wildlife.
Electronic databases, internet search engines, websites and personal contacts were used to find articles of relevance to this review. Articles were filtered by title, abstract and full text. Summary information for each of the articles remaining after the filtering process was compiled and used to assess the quality of the evidence presented using two different approaches.
Our searches yielded 48 articles, of which 25 were published in peer-reviewed journals, 14 were monitoring or project reports, and 9 were published in conference proceedings or are unpublished theses or manuscripts.
A total of 26 operational-scale restoration projects were identified. A wide range of restoration techniques were employed, ranging from small-scale manipulations of stream channels (e.g., riffle structures) to large scale pond-and-plug projects. Other common restoration techniques included fencing to exclude livestock (and sometimes also native ungulates), other forms of grazing management, seeding, and transplanting seedlings.
Most of the articles reported that restoration was fully or partially effective, at least in the short-term. However, the relative lack of high quality quantitative data, and especially data extending more than two years after project implementation, greatly limits our ability to determine how effective restoration has truly been in practice.
While caution is warranted due to data quality limitations, progress has been made over the past 20 years in wet meadow restoration. In particular, important contributions have been made in restoring the highly degraded wet meadow systems that are characterized by deep, wide and relatively straight gullies. There is evidence, for example, that the pond-and-plug approach is an effective technique for restoring many aspects of these systems, albeit at the cost of creating new features (ponds) that are not necessarily natural features of wet meadows.
There is a need to allocate additional effort to project documentation, including better-designed and longer-lasting monitoring programs. One approach that might help is for practitioners to work with scientists from government agencies, local universities and colleges, and other organizations. When this type of collaboration has happened in the past it appears to have been effective. Many important lessons could have been learned, and mistakes avoided, if more effort had been put into documenting both successes and failures of past projects.
Systematic review, Wetland, Riparian, Biodiversity
High elevation streamside or spring-fed meadows occur in numerous locations throughout the American Southwest. They are often referred to as riparian meadows, montane (or high-elevation) riparian meadows, sedge meadows, or simply as “wet meadows,” which is the term we will use for this review. In the same high-elevation regions of the Southwest, wet meadows can occasionally be found in isolated depressions, such as along the fringes of ponds and lakes with no outlets.
Where wet meadows have not been excessively altered, sedges (Carex spp.), rushes (Juncus spp.), and spikerush (Eleocharis spp.) are common species (Patton and Judd 1970, Hendrickson and Minckley 1984, Muldavin et al. 2000). Willow (Salix) and alder (Alnus) species often occur in or adjacent to these meadows (Long 2000, 2002, Maschinski 2001, Medina and Steed 2002). High-elevation wet meadows frequently occur along a gradient that includes aquatic vegetation at the lower end and mesic meadows, dry meadows, and ponderosa pine (Pinus ponderosa) or mixed conifer forest at the upper end. These vegetation gradients are closely associated with differences in flooding, depth to water table, and soil characteristics (Judd 1972, Castelli et al. 2000, Dwire et al. 2006).
The extent of wet meadows in the American Southwest is unknown, but it is clear that they are relatively rare. Less than 1% of the landscape in the region is characterized as wetland (Dahl 1990), and wet meadows are just one of several wetland types that occur. The only estimate of the extent of wet meadows in the region that has been located to date is by Patton and Judd (1970), who reported that approximately 17,700 ha of wet meadows occur on national forests in Arizona and New Mexico; they also noted that many more wet meadows occur in areas adjacent to the national forests, such as on the Fort Apache Indian Reservation in eastern Arizona.
While relatively rare, wet meadows are believed to be of disproportionate value because of their use by wildlife and the range of other ecosystem services they provide. Elk and other ungulates, for example, have been shown to make extensive use of wet meadows as foraging sites (Patton and Judd 1972, Dodd et al. 2007). The high population of voles in some wet meadows is an important food source for Mexican spotted owls, a threatened species, where their home ranges encompass wet meadows (D. Fleishman, US Forest Service, personal communication). It is also likely that wet meadows perform many of the same ecosystem functions associated with other wetland types, such as water quality improvement, reduction of flood peaks, and carbon sequestration. In addition to their ecological values, wet meadows are known to be of significant cultural importance to some Native American tribes (Long 2002).
Despite their apparent value, wet meadows are one of the most heavily altered types of ecosystems in the American Southwest. Among other things, they have been used extensively for grazing livestock, have become the site of many small dams and stock tanks, have had roads built through them, and have experienced other types of hydrologic alterations, most notably the lowering of their water tables due to stream downcutting, surface water diversions, or groundwater withdrawal (Neary and Medina 1996, Gage and Cooper 2008). It is also possible that the extirpation of beaver in the Southwest led to profound changes in wet meadow environments by reducing flooding and potentially facilitating some of the stream downcutting that occurred in so many riparian areas (Parker et al. 1985, Weber 2005).
Because of their relative rarity and the important hydrologic and ecological functions they are believed to perform, there is currently a significant degree of interest in the restoration of wet meadows. Several restoration projects have been recently completed or are underway in the region (Long 2000, Medina and Long 2002, 2004, Anderson et al. 2003, Steed and DeWald 2003, Long et al. 2004, Mullen et al. 2006, Natural Channel Design, Inc. 2007), sometimes at considerable expense and with minimal monitoring. Before many new projects are initiated, it is important to review what has been done to date, as well as related hydrological and ecological research that has been published and that may help inform future restoration efforts.