Alison Cariveau, Avian Ecologist, Alison.Cariveau@gmail.com
David Pavlacky, Biometrician, Rocky Mountain Bird Observatory, david.pavlacky@rmbo.org
Rocky Mountain Bird Observatory, P.O. Box 1232, 14500 Lark Bunting Lane, Brighton, CO 80603, www.rmbo.org
Greenline Editor’s Note: The complete Assessment and Conservation of Playas in Eastern Colorado report and the Colorado Playas Map Viewer are available at www.rmbo.org under Publications – Reports – Research Reports. We have reproduced Tables 1, 5, and 12 here as examples of the information provided in the complete report.
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This is the Final Report for the project entitled Survey and Assessment of Playa Wetlands in Eastern Colorado, funded by the United States Environmental Protection Agency (EPA), with matching funds provided by the Colorado Division of Wildlife (CDOW). Earlier phases of the project were supported by a United States Fish and Wildlife Service (USFWS) Neotropical Migratory Bird Conservation Act grant, a CDOW State Wildlife Grant, and a Playa Lakes Joint Venture (PLJV) Conoco-Phillips Research Grant.
Playas are shallow, depressional wetlands fed exclusively by rainfall and runoff, and are found throughout much of the Great Plains. These wetlands are vital to biodiversity in this ecoregion, but are threatened by agriculture and development. While attention has been focused on playas in other regions, such as the High Plains of Texas (Haukos and Smith 2003), prior to this study, playa wetlands in Colorado were relatively unknown. This study provides basic playa distribution and ecological information to facilitate conservation efforts of playas in eastern Colorado.
A fundamental goal of this project was to provide conservation practitioners with information important to playa conservation in eastern Colorado. We conducted analyses that translated playa attributes of conservation importance into spatially explicit maps. These data layers may be used by partners to guide conservation efforts and identify particular regions of the study area best suited for accomplishing specific conservation goals. In addition, we synthesized the findings of this project into a set of conservation recommendations.
Our random sample of playas within the study area provided the first empirical estimate of playa density and abundance within the BCR 18 of Colorado. Including all sizes of playas, our model estimated a range of approximately 14,000 – 23,000 playas within the study area. These numbers are two to three times the number occurring within the GIS database, and far exceed previous estimates of playa numbers in this region. Therefore, continued work to locate additional playas is warranted. We suggest that using aerial photography such as the NAIP may be an effective way to identify potential playa locations. In addition, private landowners are an excellent source of knowledge about the locations and histories of playas in eastern Colorado.
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In this study, we documented within Colorado playas 245 species of plants including 85 wetland species, 148 species of birds including 27 Colorado Species of Greatest Conservation Need, as well as other species of wildlife including black-tailed jack rabbit (Lepus californicus), coyote (Canis latrans), horned lizards (Phrynosoma spp.), spadefoot toad (Spea hammondii), Woodhouse’s toad (Bufo woodhousii), lesser earless lizard (Holbrookia maculate), snakes, damselflies, butterflies, and clams. We also documented vegetation and soils on playa restoration projects.
Our analyses indicated that several characteristics of playas are related to plant distribution and use by birds. Plant species richness was higher in playas within grasslands than playas within cropland. Landbirds were also more abundant in grassland playas than in farmed playas. Grassland playas are also valuable because they are not at direct risk for filling in due to sedimentation, and the native vegetation surrounding them facilitates inundation by sheet flows during heavy rainfall events. We also found the abundance of landbirds, shorebirds, and waterfowl responded positively to playa area. Shorebird and waterfowl abundance also increased with the percent of playa cover in the surrounding landscape. Furthermore, smaller playas are much more common than larger ones, so prioritizing the conservation of larger playas may be an effective conservation strategy.
Our work also highlights conservation opportunities for playas in eastern Colorado. We found evidence for greater shorebird numbers in playas without hydrologic modifications. Therefore, pit removal and other hydrologic restorations may provide shallow water foraging habitats for migrating shorebirds. These projects are also relatively affordable, and, when done with the development of alternative water sources, provide landowners with more reliable, cleaner alternative for watering their livestock. In addition, farmed playas present conservation opportunities because retiring and buffering farmed playas is an effective way to reduce the likelihood they will fill in by sedimentation. We are encouraged to see the numbers of such projects on the rise both here in Colorado as well as in other states within the range of playas. Care should be taken when selecting buffer plantings to ensure that the vegetation stature is appropriate for the site and does not impede natural flows of water to the playas.
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Here we summarize our accomplishments according to the four primary objectives set forth in our EPA grant, Survey and Assessment of Playa Wetlands in Eastern Colorado:
Objective 1.A. Verify the location and condition of at least 1,000 playas. We collected location and field condition information for 1,087 playas. 657 of these were predicted by the GIS database and 430 were newly discovered in the field by RMBO staff. All of these playas are portrayed in the GIS dataset provided to EPA as “Verified.” These playas are found in 27 counties of eastern Colorado, throughout the entirety of the study area. Our playa confirmation analysis indicated the Soils Survey Geographic Database (SSURGO; 77%) data source was more accurate than the LANDSAT satellite imagery (55%) and National Hydrography Dataset (34%) data sources. Within the SSURGO data, the confirmatation rate of the Apishapa soil series was greater than the intermittent water and playa types. As an indication of playa condition, we recorded information about anthropogenic disturbances including farming, hydrologic alterations including excavation, and hydrologic impacts of roads. We found that 29% were tilled, 45% were grazed, and 25% had no agricultural use reported. We detected hydrologic modifications including pits, berms, levees, wells, or constricted inlets or outlets at 13% of the playas surveyed. In addition, 15% of the playas were directly impacted by roads: 9% split into two sides and 6% bordered on one side by the road. Looking across all forms of conditional information, 34% could be classified as in high condition, with the rest in categories of moderately to severely impacted. The estimated mean density of playas was 0.46 playas/mi2 and the average playa size was 6.68 ac. We projected the number of playas in Colorado to be 14,597 – 22,623, with 8,357 – 14,922 playas greater than 1 acre in size.
Objective 1.B. Document the surrounding landuse, playa alterations, surface hydrology, wildlife habitat quality, bird use, hydroperiod, and soils of at least 60 playas. Surrounding landuse, surface hydrology, wildlife habitat condition, bird use, and the presence of hydrologic alterations were recorded at all 1,087 playas visited. Fifty-two percent of playas were found in grassland, 28% were in cropland, 4% were in the USDA Conservation Reserve Program, and the rest were surrounded by multiple land uses. Playas were dry on nearly half of the surveys. During fall 2006, the observed hydroperiod ranged from 32 to 41 days, including playas that remained wet until the end of the fall migration season. The mean vegetation cover of the sampled playas was 50% with an average plant height of 26 cm. We documented 48,830 bird detections for 148 species using the playas. We sampled soils at 21 playas in the first year of work, indicating clay soils present in all playas and sedimentation, indicated by non-clay soils on top of the clay layer, at one playa. We did not continue sampling soils because of the limited amount of variation observed in our initial sample and time needed for other aspects of the project.
Objective 2. Implement playa conservation programs through cooperative efforts with other non-profit and government agencies and evaluate the effectiveness of various restoration techniques as they relate to hydrology, runoff, sedimentation, wetland quality, and wildlife use. RMBO delivered 19 playa conservation projects protecting or enhancing 1,039 playa acres, in partnership with the USFWS Partners for Wildlife, the Colorado Division of Wildlife, Playa Lakes Joint Venture, USDA Natural Resources Conservation Service, and National Fish and Wildlife Foundation. The conservation practices applied were fencing with grazing management, removal of pits, and development of alternate water sources for livestock. We visited each of the playas in this program as well as suitable controls annually to track changes in vegetation composition. Because of the short duration of this study, dominant drought conditions, and time constraints imposed by the multiple objectives of this project, we did not directly observe impacts of restoration on hydrology, runoff, sedimentation, wetland quality, or wildlife use. However, we relate vegetative conditions to these parameters and synthesize what has been found by other researchers on these topics. We found that restored playas did not differ from control playas in terms of percent cover of bare ground or grass, but that forbs were more prevalent in restored playas. We will further investigate the response of birds and vegetation to levels of human disturbance in the Floristic Quality and Assessment Project to be completed in 2009.
Objective 3. Create a comprehensive database integrating remotely-sensed data layers with site visit information and develop a spatial model identifying playas with the high conservation potential that are useful for prioritizing playa wetland conservation in eastern Colorado. Based on the July 2008 meeting with conservation partners, we determined that because stakeholders have different conservation priorities they require different inputs to meet their conservation goals. For instance, a land trust organization such as The Nature Conservancy may prioritize large tracts of native shortgrass prairie with relatively undisturbed playas for conservation, while an NRCS soils conservationist may prioritize farmed playas within their county for restoration. Therefore, we provided important data layers (playa locations, sizes, densities, human impacts) that can be tailored to the specific conservation goals of various stakholders. We presented these data layers, along with a set of conservation recommendations, in two formats. First, we posted an interactive, non-technical pdf document on-line to increase public awareness about playa wetlands, including their values, threats, and conservation opportunities. This document contained most of the map figures from this report and will be posted to the RMBO website (www.rmbo.org) in January 2009. The second way we disseminated the data is in an ESRI ArcGIS 9.x geodatabase, which provided the relevant datasets to conservation partners for use in their own GIS planning environments.
Objective 4. Generate a report that includes a summary of the data, results from the site assessments, recommendations for playa conservation and restoration techniques, and a model depicting playas of the highest conservation value. This report, the pdf product for the public posted to the web, the geodatabase dispersed on CD, and a scientific manuscript (to be submitted to Wetlands) together fulfill this objective.