The Palouse Bioregion: A Historical Perspective
Prior to European settlement, amphibian habitat in the Palouse bioregion
was most likely provided by perennial and intermittent streams and wet
meadows. The introduction of agriculture dramatically changed the
nature of the riparian areas. Since 1900, 94% of the grasslands and
97% of the wetlands in the Palouse bioregion have been converted to
crop, hay or pasture. Wetlands were drained to make room for crops, and
rapid surface run-off from farmlands converted many perennial streams to
intermittent streams. In the latter part of the 20th century, artificial
ponds were created to provide watering holes for livestock, rural fish
ponds, and suburban landscape ponds (Black et al. 1997).
The impacts of these changes on amphibians is significant. While the
addition of ponds has possibly increased the overall habitat for
amphibians, these permanent ponds also provide habitat for bullfrogs
and fish, which are detrimental to native amphibian populations. In the
absence of permanent ponds, native amphibians, which lay their eggs in
early spring, have the advantage: their larvae metamorphose and return
to the forests before the ponds dry up. Bullfrogs, which spend two
years as tadpoles before metamorphosing, and fish, cannot survive in
the ephemeral ponds that previously characterized the Palouse, but
thrive in artificial ponds (Nussbaum 1983).
Another change to the Palouse ecosystem has been the loss of forested
land. It is possible that forest and shrub lands provide essential
overwintering habitat for amphibians, and are equally important for
amphibians as are riparian zones . Of the Palouse land covered by
forest in 1900, 37% has been converted to agriculture or urban
areas. Shrub lands which dotted the Palouse prior to European
settlement have been all but eliminated by agriculture (Black 1997).
The connectivity of habitat by forest and shrub lands has been shown to
be an essential element in sustaining some amphibian populations
(Wederkinch 1988; Laan and Verboon 1900; Monello 1988).
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