Relationships between Abundance of Cascade Torrent Salamanders and Forest Age

Abstract

To determine how abundance of stream-breeding Cascade torrent salamanders (Rhyacotriton cascadae) changes in response to forest harvest and subsequent regeneration, we surveyed first-order streams in forest stands 0-94 years old on industrial timberlands in the Cascade Mountains of southern Washington, USA, during the summers of 1998 and 1999. Regression tree analysis grouped captures into forest age classes that corresponded to broad successional stages of regenerating forests in this region. Captures were highest in 25- to 60-year-old forests, lowest in 0- to 24-year-old forests, and intermediate in forests ≥61 years. Although a second regression tree grouped captures based on stream temperature, temperatures did not differ among the forest age classes identified. The results suggest that despite the presence of assumed suitable stream conditions, torrent salamander populations are found at low levels in streams surrounded by young forests, but reach high levels by mid-rotation. These patterns may relate to successional changes in tree species composition and varying levels of riparian cover.