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Amphibians as indicators of wetland habitat conservation under variable retention harvesting
Wind, Elke
Small wetland habitats are numerically abundant across the landscape (e.g., see Wind 2003), and play an important role in maintaining connectivity among populations of wetland biota (Gibbs 2000). Species dependent upon moist environments use depressions, seeps, and small wetlands and streams as stepping stones to facilitate their movements throughout the landscape. Models from eastern North America suggest that all wetlands greater than 0.4 ha in size need protection in order to retain minimal wetland densities required to sustain wetland fauna such as amphibians which are dependent upon these habitats for breeding, cover, foraging, and hydration (Gibbs 2000). However, wetland legislation in North America is based on areal extent even though studies have not shown a relationship between wetland size and amphibian species richness (Snodgrass et al. 2000). For example, in BC isolated wetlands less 0.50 ha are not afforded riparian protection in the Forest and Range Practices Act (BCMFR 2004). The majority of amphibian species within BC are aquatic breeding, utilizing a variety of lentic water bodies including small wetlands and ponds that dry regularly (e.g., seasonal or semi-permanent). These latter habitats contain conditions conducive to improved larval development and overall fitness such as reduced predation and increased water temperatures (Alford 1999, Ultsch et al. 1999). However, under natural climatic conditions these habitats are unpredictable and larval survival rates fluctuate extensively from year to year. The success of aquatic-breeding amphibian populations is dependent upon the interactions that exist among ponds with various hydroperiods across the landscape (e.g., migrations between ponds). This ?boom or bust? life cycle is a natural strategy that helps maintain healthy amphibian populations. The greatest concern associated with forest harvesting and small wetland habitats is that they may act as population sinks for amphibian species. Amphibians may be attracted to breeding in ponds in newly harvested blocks due to increased solar radiation and the potential for greater productivity. Larvae and/or newly metamorphosed juveniles emerging from ponds at the hottest, driest time of the year may be negatively affected by forest harvesting, resulting in reduced overall abundance. One of the greatest factors that may be altered by forest harvesting that affects in-pond amphibian survival rates is hydroperiod, a variable that is highly dynamic and intimately related to local and climatic conditions. Concern for small vernal pools has increased in the United States, especially in the east (see e.g., Lawrence et al. 1998), but has lagged behind in most western states and provinces (except California). To my knowledge, no studies have investigated the role or importance of small wetlands or the effects of timber harvesting on these habitats within the Pacific Northwest. In 2003, we initiated a pre- and post-harvest experiment at three study sites with 70+ small wetland habitats less than 1 ha in size in the Nanaimo River Watershed to investigate the effects of forest harvesting on the hydroperiod and presence of breeding amphibians. Pacific Treefrogs, Red-legged Frogs, and Long-toed Salamanders occur in numerous ponds within the three study sites, including many relatively small ponds (e.g., 0.003 ha). To date, the results from this study confirm that all three pond-breeding amphibian species continue to reproduce in ponds within cutover areas initially after harvesting and that at least two of the species appear to exploit previously unoccupied ponds due to changes in the habitat characteristics (e.g., decreased canopy cover). In addition, the results have demonstrated that small ponds in the area have longer hydroperiods initially after harvesting due to a combination of increased water depths and slower drying rates. Initial habitat analyses indicate that canopy cover may be a major factor in breeding pond sel ...
Report Number
Final Technical Report
Wetland Assessment Field Card

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