BC’s Inland Rainforest – Conservation and Community

Conference Proceedings


Ecology, biogeography, and conservation of Inland Temperate Rainforests of the Pacific Northwest of North America: A comprehensive, international perspective


James Bergdahl +

The objective of this review is to provide a summary of the salient aspects of why we feel any comprehensive ecological definition and assessment of the geographic extent of the Inland Temperate Rainforest (ITR) region of the Pacific Northwest of North America should span the trans-boundary/international (Canada-USA) region between ~44-54o N Lat.

General location and forest types

This region runs northwesterly from the west slope of the Bitterroot Range of central Idaho (Salmon Mtns.) to the north end of the Columbia Range (Cariboo Mtns.) of east-central British Columbia (~1100 km, or ~450 mi), including parts of northeast Washington and northwest Montana. About half of this distance is in British Columbia and the half in the United States. The region spans large parts of the upper Columbia and upper Fraser rivers.

One should keep in mind that this region defines the extent of the geographic range where ITR may develop given adequate soils, moisture, temperature, aspect, slope, source populations, time and other factors. The dynamics of physical (e.g. fire, industrial logging) and biological disturbance (e.g. root fungi, bark beetles, other herbivores) also influence the age and structure of ITR in individual watersheds.

The topography is extremely mountainous, and includes many very large rivers, extensive forests, large expanses of alpine parkland and tundra, many glaciers and ice fields. Wet forest habitats in this region in British Columbia (BC) are typically described as various types of interior cedar-hemlock (ICH) at low elevations and Englemann spruce-subalpine fir (ESSF) at high elevations (Krajina 1965; Pojar et al. 1987). In USA they are referred to as moist to very moist types of Thuja plicata, Tsuga heterophylla and spruce forest but these are essentially the same or very similar to BC’s ICH and ESSF forest types. Maps of BC’s biogeoclimatic zones are readily available and are widely used by the general public. No comparable region-wide forest-type maps are easily available in the US. In contrast, mapping of ecoregions is much more advanced in USA (e.g. Omernik 2002; www.epa.gov/wed/pages/ecoregions), and as with forest types, comparable maps do not exist for Canada so another major map discontinuity follows the International border (Bergdahl 2000). The ITR in the USA occuries various subzones of the Northern Rockies (Selirk Mtns., Coeur d’Alene Metasedimentary, St. Joe Schnist-Gneiss, Clearwater Mtns. and Breaks, Purcell-Cabinet-North Bitterroot Mtns)., and Idaho Batholith (Lochsa-Selway-Clearwater Canyons, Lochsa Uplands, Glaciated Bitterroot Mtns. & Canyons, and possibly the Southern Forested Mtns.) ecoregions (Omernik 2002).

ESSF forests within the Interior Welt Belt are often referred to as “snowforest” because most precipitation falls as snow, which accumulate to >7m deep by April. Some of the western red cedar stands in the ITR region may be much older than their oldest trees, which have been documented to be almost 4000 yrs old. (Parker & Johnson 1994). Many of the old-growth stands of giant cedar-hemlock occur wet in valley bottoms and toes slopes that have consistently escaped large forest fires (Habeck 1973), which are frequent in the region.

In BC most of the ITR is Crown Land managed by a number of agencies of the Province if British Columbia. In the USA, most of the ITR is owned and managed by privately-owned timber companies or the federal US Forest Service. In the Slocan Valley watershed of southeast BC (~340000 ha), Hammond et al. (1996) estimate no more than 16% of the land base is suitable for sustainable commercial logging (stable & moderately stable terrain), but only 7% is suitable if incompatible competing uses are accounted for (e.g. tourism, community water sources, etc.)

1) Coarse-scale biological indicators: This region defines the Interior Wet Belt forest zone first suggested by Daubenmire (1952). Hudson Bay Company records from the Payette River area of the Salmon Mtns. of central Idaho show the historical distribution of mountain caribou (Rangifer tarandus) roughly coincides with the Interior Wet Belt. A number of more recent authors have referred to this region as the Interior Temperate Rainforest, in part to differentiate it from Coastal Temperate Rainforest to the west along the coast. Daubenmire’s recognition of an Interior Wet Belt was based on the fact that a number of primarily coastal, common tree and shrub species are found in the region. Some of these species are widespread in the ITR. The mountaineer Fred Butters (1914) published the first floristic studies of the Selkirk Mtns. clearly documenting the phenomena (~18% of the flora are coastal species). Because of the ecological diversity of these many plants species, we feel they should be used as primary indictors of the extent of ITR, and possibly some its subregions.

Common coastal trees in ITR:

Grand fir (Abies grandis)

Western white pine (Pinus monticola)

Western hemlock (Tsuga heterophylla)

Mountain hemlock (Tsuga mertensiana)

Western redcedar (Thuja plicata)

Yellow cedar (Chamaecyparis nootkatensis)

Pacific yew (Taxus brevifolia)

Pacific dogwood (Cornus nutallii)

Common coastal shrubs in ITR:

Cascara (Rhamnus purshiana)

Ocean spray (Holodiscus discolor)

Red huckleberry (Vaccinium parvifolium)

Oregon grape (Berberis nervosa)

Tea-berry salal (Gaultheria ovatifolia)

Devil’s club (Oplopanax horridum)

Oregon boxwood (Pachistima myrsinites)

The list of primarily coastal ferns, grasses and forb species in the ITR is long. Schofield (1992) and Goward & Sprible (2005) provide reference to many moss and lichen species respectively in British Columbia that are found in both coastal and “interior humid” forests. Many of these species also have ranges in the interior that appear to coincide very closely to the greater ITR region. Many animal species may also be suitable coarse-scale indicators, such as mountain caribou (Rangifer tarandus), as noted above

2) Latitudinal zonation of ITR: If the ITR ecoregion corresponds approximately to the trans-boundary Interior Wet Belt, it is reasonable to assume this large area may be subdivided into a number of sub-regions (zones) based on ecological characteristics much like Ecotrust (Kellogg et al. 1995) has done for the Coastal Temperate Rainforest (CTR). This trans-boundary analysis is complicated by the fact that information on relevant physical and biological geographic features is not consistent across the International border – Ecotrust relied on different sources of data for the various jurisdictions within their study area. Vegetation classification schemes frequently use vegetation structure to define regions, but frequently climatic variables are used in addition to floristics. Ecotrust used Alaback’s (1991,1995) definition of 4 subregions of Coastal Temperate Rainforest, based on temperature and precipitation, to map so-called subpolar, perhumid, seasonal and redwood zones. Any naturalist familiar with the full extent of CTR recognizes the reality of these forest types. For instance, recent studies of the arboreal, epiphtye communities associated with the canopies of CTR differ significantly between the subzones.

We feel studies of ITR would greatly benefit by formal recognition of similar latitudinal zonation within the region, although we do not necessarily think that the same criteria and thresholds used for the CTR may apply. For instance, in a comparison if coastal and interior rainforest Green et al. (1992) identify the following major differences: 1) the climate of the ITR is transitional from maritime to continental, 2) an older land surface with complex geologic history and soil development, 3) drier conditions with more frequent drought and forest fires, 4) regular occurrence of non-stand replacement fires, 5) stressed sites with more significant insect and pathogen influences, and 6) in the context of historical biogeography, a very different complex of plants and animal. Furthermore, coastal vs. interior rainforest tree species may be represented by genetically-distinct interior ecotypes with different environmental tolerances.

It is logical to assume that the northern and southern extremes of ITR may be as different as California’s redwood stands and Alaska’s subpolar rainforest - those familiar with the full extent of the ITR will probably agree. Kalela (1960), Hamet-Ahti et al. (1968) and Tuhkanen (1984) should also be consulted to help identify suitable criteria and thresholds. As on the coast (e.g. Chetco R., Queen Charlotte Strait, and Yakutat Bay), some natural geographic features may help define boundaries between the ITR zones, such as the upper Duncan, in BC, and Clark Fork, St. Joe, and Clearwater rivers in Idaho. Given the extreme topographic diversity in the ITR, vertical (elevational) zonation of the forest types will most likely complicate any clear latitudinal delineation of subzones. Unfortunately, during the heyday of mining in the early 1900s, huge forest fires destroyed much of the old-growth forest in the central and southern Selkirk Mtns. on either side of the International border - consequently our understanding of the nature of its original ITR is compromised. Clearly though, there are still vast tracts of old-growth ITR in the upper St. Joe and Clearwater river basin further south in Idaho, where the precipitation is very high, terrain is rugged, and road densities are relatively low.

3) Biological indicators of subzones: Recently Goward & Spribille (2005) have argued that the distribution of “oceanic” macrolichen species suggests the geographic extent of ITR should be limited to the northernmost forest ecotypes of the Interior Wet Belt between ~50-54o N Lat. in BC. Even Parks Canada now claims the world’s only ITR is found exclusively in British Columbia, and similar statements have been made by most non-profit conservation groups active in BC. We see no reason why oceanic macrolichens should be considered better indicators of ITR than any other taxa with coastal disjuncts. Specific taxa, such as oceanic macrolichens or species endemic to the ITR region, should be employed primarily to help delineate subregions, not the ITR as a whole. If any specific group of plants or animals are used one should be certain that their power-of-dispersal and major historical factors do not restrict their current distribution across the Interior Wet Belt. Also, extremely specialized autecological requirements should not grossly limit distribution of indicator species. These criteria may disqualify macrolichens for use in comprehensive delineation of the full extent if ITR. For instance, historical factors such as the availability of a dispersal corridor from the coast up the Skeena or Fraser rivers to the north end of the ITR may be primarily responsible for the latitudinal gradient in the number of coastal macrolichen species, not primarily climatic factors. Incomplete or unequal sampling effort across a study area may also contribute to a perception of a biogeographic gradient, a problem that confounds many biogeographic studies. For instance, lichenologists are still finding many new species records in British Columbia (Goward et al. 1996).

In fact, Alaback et al. (2000) have already documented ITR in the Clearwater River basin of central Idaho, where very wet storms coming off the Pacific funnel up the lower Columbia River gorge and dump vast quantities of rain and snow on the western, windward slopes of the Bitterroot Mtns. The interior cedar-hemlock forests of central Idaho were documented by Leiberg (1900) more than a century ago, and more recently by Parker (1986) and Lichthardt (1999). Parker (1986) estimates some of the giant western red cedars in Idaho approach 4000 yrs. old. If we use research on coastal rainforest as an example (e.g. the seasonal and redwood subzones), the fact that Idaho’s ICH & ESSF forests may experience a distinct summer-dry period should not disqualify them from interior rainforest status per se. There is no significant decrease in yearly precipitation between the northern and southern sub-regions of the greater ITR.

4) Historical Biogeography of ITR: Over many years of study we have found that some of the most interesting aspects of the ecology, biogeography, and conservation of ITR are as follows:

  1. Today’s inland temperate rainforests of the Pacific Northwest are remnants of ancient, montane, conifer forest types (communities of species) that replaced subtropical broadleaf forests in the Miocene (~10-15 million yrs ago) in response to the uplift of the Rocky Mountains, and at one time had a much larger geographic distribution (Axelrod 1964; Miller 1977; Leopold & Denton 1985; Ruddiman & Kutzbach 1991). The extent of these forests contracted as the climate became colder and drier, and many associated species appear to have gone extinct or were extirpated in North America.

  2. During the Pleistocene’s glacial maxima (as recently as 15000 yr BP) the southern interior region of British Columbia was more or less completely covered by the Cordilleran Ice Sheet reaching in places ~8,000 ft. deep. Although there is some evidence for the existence of ice-free glacial refugia during the maximum glaciation it is unlikely that any of them were capable of supporting interior temperate rainforest. Consequently, species characteristic of ITR in British Columbia have had to re-colonize the Columbia Mtns. from either south of the Ice Sheet in the United States or from refugia along the coast. Although large locally produced glaciers at one time occupied north and central Idaho, these were confined primarily to the western flanks of the largest mountain ranges (Omernik 2002).

  3. Only species with high to modest powers-of-dispersal have had enough time to re-colonize the ITR in British Columbia.

  4. The southern-most edge of the Cordillerean Ice Sheet was approximately the latitude of the Clark Fork region of northern Idaho. Immediately south of this in central Idaho climatic conditions must have been able to support Interior Cedar Hemlock forests. Since ITR has continuously occupied central Idaho since its inception in the Miocene, the opportunities for the evolution of taxa endemic to southern parts of the ITR has been many orders of magnitude greater than further north in British Columbia. Many of these species have very low powers-of-dispersal or require unique ITR habitats not found outside the immediate region.

  5. Consequently, the wet forest habitats in central Idaho support an extremely rich flora and fauna currently found only in habitats at the southern-most extent of the ITR. Many of these endemic species are very rare and many are still being discovered. For instance, among the ~700 species of carabid-beetles (Coleoptera, Carabidae) known from the Pacific Northwest, we have documented a diverse fauna of flightless species endemic to Idaho in lineages1 that probably evolved in Arcto-Tertiary forests. Many of these have not dispersed north into regions of northern Idaho that were covered by ice during the Pleistocene.

In summary, the ITR was “made” millions of years ago over a wide swath of land that would ultimately become, in part, the current, trans-boundary, ITR region. More recently, in the Pleistocene, the ITR in British Columbia was completely destroyed by massive glaciers. As these Ice Age glaciers retreated over the last ~14000 yrs, the ITR north of ~48oN has had to be reconstructed by dispersal of plants and animals over great distances. Many temperate rainforest species on the coast or in Idaho have been unable to re-colonize various sectors of the ITR due to limited powers-of-dispersal, the absence of suitable dispersal corridors, or simply not enough time. Significant Ice Age legacies in modern species distributions have recently been documented in North America (Montoya et al. 2007) and in Europe (Svenning & Skov 2005, 2007a, 2007b; Veken et al. 2007). Whereas Pleistocene glaciers caused the complete elimination of BC’s interior temperate rainforests, south of the Cordilleran Ice Sheet, locally produced glaciers on the western slopes of the Bitterroot Mtns. may have led to long-term fragmentation of conifer forests, providing opportunities for the creation of new genetic varieties in rapidly evolving species.

5) International conservation significance: Of the 116 generally recognized ecoregions in America north of Mexico, the ITR has the highest number of endemic plants in Canada and highest conifer species richness in North America, in addition to very high topographic diversity supporting huge rivers and glaciers. Surprisingly, despite large-scale and widespread negative environmental impacts by the commercial logging industry, the World Wildlife Fund ranked the region of only modest conservation concern in North America (WWF 1997). The region once had outstanding runs of Pacific salmon, steelhead, and bull trout that were keystone species in inland temperate rainforest ecosystems including a diverse suite of endangered carnivorous mammals. The ITR region is also now the focus of one of Canada’s largest conservation planning process for a threatened species - the mountain caribou – the most endangered mammal species in the United States.

In 2001, using information provided by BC Conservation Data Centre’s website for the Arrow, Clearwater, Columbia, Horsefly, Kootenay and Robson Forest districts, we determined there are 138 vascular plant and 43 vertebrate species listed as rare, threatened or endangered, plus 27 habitat types listed as rare, in BC’s ITR region (Bergdahl 2001). (Not all of these are forest-dependent species or forest habitats.) If we add to this list the numerous unique species and habitats associated with ITR found only in the United States, it should be very obvious that much work needs to be done towards a comprehensive understanding of the ecology, biogeography and conservation of our globally-significant interior temperate rainforests. Our efforts will undoubtedly be greatly enhanced if we join forces in a comprehensive, international outlook. There is little to be gained and much is to be lost in our understanding of ITR if special interests narrow its geographic extent, whether they are taxonomic specialists, government agencies, or conservation campaigns by non-profit environmental groups.

1 Some flightless, forest, ground-beetle species (Insecta: Coleoptera: Carabidae) endemic to southern parts of the ITR include species of Scaphinotus (Pseudonomaretus), Pterostichus (Pseudoferonina), Pterostichus (Hypherpes), Bembidion (Anillodes).

Contact Information


+ Conservation Biology Center, University of the Wilderness, 919 S. Adams St., Spokane, WA, USA, 99204. Email: jcbergdahl@gmail.com

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"Treebeard" (above) is portrayed courtesy of McBride artist Sheilagh Foster.

 
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