Forest Investment Account (FIA) - Forest Science Program
FIA Project Y083027

    Amphibians as indicators of wetland habitat conservation under variable retention harvesting
Project lead: Beese, William J. (Western Forest Products Inc.)
Author: Wind, Elke
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
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 selection for Pacific Treefrogs, but less so for Red-legged Frogs and Long-toed Salamanders which are somewhat constrained by hydroperiod due to the longer duration of larval development within these two species. For these latter species, pond size may be important to ensure sufficient hydroperiods. During this and earlier work on amphibians in the area we recognized a number of issues in relation to the management of small ponds within harvested landscapes: 1) The majority of small ponds were left off cutblock maps initially, or were indicated as sensitive soils. the management of these ponds is greatly affected by forestry technicians that walk the area because most ponds <1 ha cannot be identified from air photos (Wind 2003); 2) Small ponds were lost due to road construction, infilling with logs and debris (e.g., purposefully for machine access, or incidentally during felling and hauling, etc.), or through the planting of water tolerant tree species (e.g., cedar); 3) Variable retention harvesting methods often anchored retention patches over small ponds, inadvertently providing riparian habitat; 4) Even small amounts of riparian retention helped to protect the quality of the in-pond habitat; and 5) Retention was based largely on pond size. From this, we determined that there was information that we could provide to forestry technicians that would help them allocate their limited retention resources in the most beneficial way for amphibians. Based on our observations and research results to date, the research question we have with regards to this FSP study is what factors influence where these pond-breeding amphibian species reproduce (i.e., what are the species-specific habitat requirements) and can this information be packaged in such a way so that foresters and technicians laying out cutblocks can identify and prioritize ponds for retention? The purpose of this study is to create a field-friendly information and assessment card for foresters and technicians that can be used when surveying and laying out cutblocks to help them identify potential amphibian breeding ponds that should be considered for retention. This will be accomplished by utilizing existing data sets (e.g., the Nanaimo Lakes study sites) and from the literature. The field card will be field tested by E. Wind and by volunteer foresters and technicians to ensure that it is effective (i.e., ponds with amphibians were allocated retention) before promotion and distribution to various forestry companies. Field testing will consist of repeat surveys of numerous forested ponds by an amphibian biologist to identify and confirm the amphibian species breeding there and site visits by forestry volunteers at different times within the season (i.e., with different amounts of water and vegetative growth), as well as single and repeat visits, to see whether those ponds that are allocated retention contain amphibian larva based on information gathered using the field card.
Related projects:  FSP_Y061027,  FSP_Y072027


Final Technical Report (0.9Mb)
Wetland Assessment Field Card (0.3Mb)

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Updated August 16, 2010 

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