Plethodon vandykei

Plethodon vandykei and P. idahoensis formerly were regarded as conspecific (as. P. vandykei). Nussbaum et al. (1983) concluded that idahoensis is not distinct even as a subspecies. However, recent studies indicate that the two disjunct taxa are not conspecific. Howard et al. (1993) examined genetic variation and recommended that idahoensis be regarded as a distinct species; further, they noted some differentiation between coastal and Cascade populations in Washington and recommended further study of morphological differentiation. Results of a morphometric analysis led Wilson and Larsen (1999) to support recognition of P. vandykei and P. idahoensis as distinct species. These authors also detected significant differentiation between coastal and Cascade populations.

Fewer than 100 isolated populations occur in three regions in Washington; populations are generally small and isolated, fewer than 25% are believed to have high viability. Populations are believed to be roughly stable, but surveys are lacking. This species is threatened by timber management practices, road building, and climate change.

This species occurs in three disjunct areas in western Washington: the Willapa Hills, Olympic Peninsula, and the southern Washington Cascade mountains. Populations are separated by glacial and alluvial deposits that may limit the regional distribution (Wilson et al. 1995). Generally occurs in small isolated populations (Olson and Crisafulli 2014). Olson and Crisafulli (2014) estimated range extent at 15,078 sq km, but acknowledge that additional undiscovered sites may exist. Note that their estimate of range extent excludes areas outside the three occupied population areas. The estimated range encompassed by all three population areas (convex hull) is 33,939 sq km.

418 locality records (Olson and Crisafulli 2014), but it is not clear how these may translate to occurrences. Some of the locality records are in close proximity to each other, suggesting the number of unique sites may be lower. These locality records are spread across all three regions (Willapa Hills, South Cascades, Olympic Peninsula). They are distributed across 81 6th-field watersheds (Olson and Crisafulli 2014), and this may be a more accurate estimate of number of occurrences. Average size of 6th field watersheds in western Washington is approximately 104 sq km. Wilson et al. (1995) reported about 80 subpopulations, but it is not known how many persist.

The primary threats to this species include activities that alter habitat, microhabitat, and microclimate conditions (Olson and Crisafulli 2014). The most significant threats are timber harvest (particularly clear cutting) and climate change (Case 2014, Olson and Crisafulli 2014, Washington Department of Fish and Wildlife 2022). Timber harvest damages microhabitat and can alter moisture regimes (Olson and Crisafulli 2014). Clear-cutting has the potential to eliminate populations in areas where woody debris is the primary source of surface shelter and nesting sites (Wilson et al. 1995). One study in the Olympic Mountains found P. vandykei absent in logged areas (Raphael et al. 2002). Rock removal and mining alter hydrologic regimes and microhabitats (Olson and Crisafulli 2014).

Climate change is likely to result in reduced water flows and increased temperatures, negatively impacting this species (Olson and Crisafulli 2014). Washington Department of Fish and Wildlife (2022) identifies this species as highly sensitive to climate change with moderate confidence. The species is relatively sedentary, with narrow ecological tolerance that limit its ability to survive in or colonize disturbed habitats. Thus, climate change is likely to negatively impact this species (Washington Department of Fish and Wildlife 2022). Because populations are typically small, individual populations are vulnerable to stochastic events.

Fire frequency and intensity are expected to increase in this species' range. Large fires may result in increased landslides, damaging habitat (Olson and Crisafulli 2014).

Road construction and culvert installation damages microhabitats and alters moisture regimes (Olson and Crisafulli 2014). Recreational activities can compact soil, remove woody debris, and otherwise alter habitat (Olson and Crisafulli 2014). Chytrid fungus may be a threat to P. vandykei (Olson and Crisafulli 2014), but effects have not been studied.