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 49^th 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.

Figure 1 is a satellite image of the study area and shows the specific locations where butterflies were observed and sampled.