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The effects of clear-cut timber harvest on the movement patterns of tailed frogs (Ascaphus truei) in southwestern British Columbia

University of British Columbia

Pitfall trap grids with drift fences were established in three mature forest stands (>81 years), and three clear-cut sites (<5 years) in the Chilliwack Valley of southwestern British Columbia during June to November 1998 and May 1999, to assess differences in tailed frog (Ascaphus truei) abundance and movement patterns. Frog abundance was similar in both habitat types, although immatures comprised 80% of captures in clear-cuts (CC) with bufferless streams, and 51% in mature stands (M). While significantly more adults and subadults were caught in M than CC, the number of immatures captured did not significantly differ between habitat types. However, captures of immatures and subadults did vary significantly between sites within habitat types. Direction of movement by frogs did not differ between habitat types. Capture distances from streamsides also did not differ significantly between habitats, although there were differences between sites within habitat type for immatures. There were more recaptures in M than CC (15% and 2%, respectively). Recaptures in CC were predominantly frogs that returned to traps immediately upon release; in M sites, more recaptures originated from other locations. There were no significant differences in weight (WT) or snout-to-vent length (SVL) between habitat types, although immature WT and SVL differed significantly between sites within habitat types. Similarly, tadpole WT, SVL and snout-to- tail length did not differ significantly between habitat types, while significant differences existed between sites for these measures. The presence of frogs at sites could be predicted from the occurrence of selected plant species and other habitat attributes. Pooled adult numbers were negatively correlated with clear-cut habitat variables (e.g., thimbleberry, willowherb thistle), and positively correlated with attributes of mature stands (e.g., leaf litter). Numbers of immatures were negatively correlated with attributes of mature stands (e.g., vine maple), and positively correlated with clear-cut habitat variables (e.g., foamflower). These findings suggest that there are age-specific impacts on tailed frogs in bufferless streams in clear-cuts relative to streams in mature forests. Additionally, variation among sites has a greater influence on immatures than habitat type, which may have long-term implications on population maintenance if survivorship to adulthood also significantly varies between sites. Thus blanket management procedures for tailed frogs (e.g., stream buffers proposed for larval habitat enhancement) will not necessarily be effective for all age classes or for all areas with the same macrohabitat (e.g., clear-cuts).

Thesis/Dissertation

application/pdf

2009-07-28

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http://hdl.handle.net/2429/11387

Forestry

University of British Columbia

UBCV

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