Coastal Disjunct

Glade Creek, Fred Rabe Photo Credit

In contrast to the ponderosa and lodgepole pine forests that dominate so much of the northern Rockies, the Clearwater Basin contains many vascular plant species similar to those in coastal temperate rainforests of Oregon and Washington. These species are known as coastal disjunct.

Temperate rainforests generally occur within 100-miles of the Pacific coast where moisture from offshore winds is trapped by mountains.

The interior “wetbelt” forests of the northern Rockies is the largest known interior rainforest in the world stretching over 30-million acres of land from central British Columbia south to the Clearwater.

The origin of coastal disjunct species in the Clearwater can be explained by the geological history of our region. The Bitterroot Mountains used to form the western edge of the continent, with moisture extending from the Pacific into the forests of Idaho. When the Cascade Mountains formed, however, they blocked the wet coastal winds from reaching the now interior forests. As a result, most of the inland temperate rainforests and many of their associated plant species disappeared, except for scattered sites in southern British Columbia, western Montana and northern Idaho. This helps explain the many endemic and genetically unique populations that have been documented in the Clearwater Basin.

Idaho has the largest and most unique interior rainforest in the world. While moist forests similar to the temperate rainforests of the Pacific Northwest coast were once common in our region, the forests of the upper Lochsa River and the N. Fork of the Clearwater River are among the few examples of these forest refugia that remain.

While driving along the Lochsa River, one may observe a seemingly endless dense, dark forest of Western redcedar and grand fir. If hiking the N. Fork Clearwater, one can observe thickets of red alder and maidenhair fern while boaters on the lower Selway may come across Pacific Dogwood.

A good example of a coastal disjunct community is the Lochsa Research Natural Area (RNA) established primarily to preserve examples of Pacific Coast vegetation types that occur over very limited sites in the state of Idaho.The RNA contains three different sizes of entrenched streams that feed the Lochsa River. Fourteen different coastal disjunct species occur in the RNA, most of which are riparian. The forest climax type of both streams is western hemlock overstory and ladyfern/ maidenhair understory. Red cedar is also a common overstory species. Such a plant assemblage indicates a warm, nutrient-rich site. Some additional coastal disjunct include Rocky Mountain Maple, buckthorn, Pacific Dogwood and red alder.

Aquarius Research Natural Area was established in 1991. It is two miles in length and includes the last free-flowing unroaded stretch of the N. Fork Clearwater River. The site is characterized by relatively warm temperatures, high precipitation and humidity. Such conditions mimic those on the west coast, what botanists term coastal disjunct habitat. The RNA is a microcosm of mostly the lower canyons of the North Fork, Selway, St. Joe and Coeur d’Alene Rivers that also contain an extraordinary assemblage of disjunct and endemic plant and animal taxa together with unique vegetation types. The RNA also contains unidentified species of earthworms, terrestrial beetles and contrasting macroinvertebrate communities from tributary streams on both sides of the North Fork. Such ecosystems occur nowhere else east of the Cascades.



Comments are closed.