Restoring a wetland complex for amphibian populations, south Okanagan Valley, British Columbia, Canada (2003 to 2014)
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Date
2015-10-05
Authors
Ashpole, Sara
Journal Title
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Publisher
University of Waterloo
Abstract
The arid south Okanagan Valley is a highly anthropogenic landscape experiencing intense development pressure from agriculture and urban expansion. Ecologically, wetland and riparian habitat loss now exceeds 84% of what existed since the 1800s. Based on these conditions, I tested whether species richness, distribution, and relative density of native herpetofauna among 108 wetlands surveyed during 2003 to 2006 would show significant differences among sites as defined by their land-use characteristics. I identified seven land-use stressors: water withdrawal or discharge; infilling or shoreline modification; burn pile / garbage dumping; non-native invasive species; agricultural input (e.g. pesticides, herbicides); nutrient input (unrestricted livestock, turf fertilization); and artificially constructed sites. At least one of the seven identified land-use stressors was present at 88% of sites and 74% of sites experienced nutrient inputs. The highest overall frequency of stressors occurred at agricultural sites. And yet, these agricultural sites breeding habitat value with the highest species richness of native herpetofauna and some of the highest observed densities of species early life stages. Despite repeat surveying, more than two-thirds of sites had less than two herpetofaunal species detected annually. In response to the apparent ecological degradation based on field observations, a collaborative stakeholder approach was initiated to increase the quantity and quality of lowland wetland habitat. The approach used was landscape ecological restoration, i.e. reconnecting known amphibian-breeding sites with constructed and/or enhanced small ponds. The prior herpetofauna monitoring data (2003 to 2006) determined both ecological and management based strategic locations: 1) proximity to known herpetofaunal breeding locations, 2) distance to adjacent water bodies, 3) distance to roadways, 4) historic wetland infilling, or 5) partnership with local conservation authorities. Habitat enhancement outcomes initiated as part of my research (Ntotal = 21 sites) included 10 newly constructed ponds, enhancement of 8 re-contoured ponds after historic infilling, and invasive non-native predatory species removal at 3 sites (2006 to 2011). Project ponds were monitored annually (2007 to 2014) for all life stages of herpetofauna. Over this eight year period, metamorphic success for the Great Basin spadefoot (Spea intermontana) (13 sites) and the pacific chorus frog (Pseudacris regilla) (N = 7 sites) populations has been observed. Enhancement and construction of ponds in the lower valley roughly doubled the number of available discrete breeding ponds within the study area from 13 to 31 ponds and through voluntary stewardship engaged landowners. Whether enhancement and construction of ponds have aided species recovery is unclear, because it can take multiple species generations and habitat protection to establish whether there has been a permanent ecological restoration; however the data on colonization provides early supporting evidence that some species are recovering. The project results support a “build it and they will come” action; this approach likely works because there was severe decline in available breeding habitat, hence any improvement tends to provide an initial increase in some widely distributed populations of herpetofauna. Nonetheless, the ongoing lack of critical upland habitat needed by amphibian species poses a significant threat to species movement and long-term population success. Planning and management challenges remain, namely enforcement of wetland protection measures and moving beyond like-minded collaborations and towards targeted stewardship of less motivated persons.
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Keywords
anthropogenic stressors, constructed wetlands, amphibian diversity, ecological planning and management, agroecosystems, restoration ecology