STUDY AREA DESCRIPTION
The study area along the lower south
facing slopes of the Pend-d’Oreille River is part of a rare ecosystem
in Canada. There are only about 50,000 ha of this ecosystem known
to exist in Canada and most of it is situated in the Pend-d’Oreille
river valley. In the language of the BC Biogeoclimatic Ecosystem
Classification; this unique ecosystem is known as the "very
dry warm interior cedar-hemlock subzone" or, in short acronym
format, the "ICHxw".
For detailed information on this
classification system and the characteristics of the ICHxw, see
Braumandl and Curran (1992). A very detailed report on the soil
and vegetation resources has been prepared by Vold et al.
(1980). The following synopsis of the physical and biological environment
has been lifted from these sources.
The valley is located in the southern
portion of the Selkirk Range of the Columbia Mountains, just SE
of the city of Trail. Readers who are totally unfamiliar with the
geography of SE British Columbia might want to know that the study
area is immediately north of the NE corner of Washington State or
might prefer to know that the valley is immediately north of the
49th parallel and runs from 117 degrees 17 minutes to
38 minutes. The ICHxw is present from mid slope to valley floors
with an elevation range of 450 to 1100 metres. Climate is characterized
by very hot, dry summers and very mild winters with very light snowfall.
Monthly mean maximum temperatures during July and August range from
25 to 30 degrees Celsius, depending on elevation. Freeze free duration
is in the range of 113 to 147 days and growing season varies from
185 to 236 days, depending on elevation.
The study area has an interesting
foundation of volcanic, sedimentary and intrusive rocks overlain
by a variety of colluvial, morainal, glaciolacustrine and aeolian
deposits. Soils are predominantly orthic eutric brunisols with lesser
amounts of orthic dystric brunisol and chernozem. We non-pedologists
commonly refer to these soils as "brown dirt".
These variable environmental conditions,
coupled with a natural disturbance regime characterized by frequent
wildfires means there is little in the way of climax forest vegetation
here. This is very good for butterflies ! Douglas fir is the dominant
tree species. Ponderosa pine and western larch are also common.
Western red cedar, grand fir and some hemlock are found on more
mesic and wetter sites. Lodgepole pine and white pine are less common
seral species but pockets of aspen poplar, cottonwood and white
birch are also present. A vast array of shrubs, forbs and grasses
are present in response to environmental variables. Much of the
valley does have trees growing on it but there are both natural
and not-natural habitats which have few or no trees. These areas
are especially important as butterfly habitat. A significant number
of rare plants have been reported from this area also.
is a satellite image of the study area and shows the specific locations
where butterflies were observed and sampled.