The climatic differences experienced in the three sites we visited were the primary determinants of the species that we found. While there were some species that we saw in all three locations, others were specific to one or two of the sites. The relative abundance of the species that were found ubiquitously (e.g., Douglas-fir, western hemlock, red alder) varied across the sites. In addition, we saw that the species composition also varied within a site. There were smaller-scale landscape features (e.g., aspect, topographic position, soils) that interacted with climate variables (e.g., precipitation, temperature) to alter the soil moisture regime and nutrient levels, creating a heterogeneous growth environment where certain species with certain environmental tolerance limits and competitive ability could survive best. This resulted in the diverse types and patterns of vegetation that we observed within each site.

Tree species that we encountered at each field trip site:

Each site is linked below:

Lake Tradition
Asahel Curtis
North Fork of the Teanaway

Lake Tradition

Forests here were dominated by Douglas-fir (Pseudotsuga menziesii) with some western redcedar (Thuja plicata) and western hemlock (Tsuga heterophylla).

Drier forest along upper trail (Douglas-fir, western hemlock, salal). Salal (Gaultheria shallon) is a shrub that typically grows on drier sites.

Semi-moist forest (Douglas-fir, western hemlock, sword fern) along mid to lower trail. Sword fern (Polystichum munitum) is a typical understory herb of moister sites.

Moist forest along lower trail (Douglas-fir, sitka spruce). Sitka spruce (Picea sitchensis) is normally a coastal species, found on moist, but well-drained sites.

Very wet forest at slope base (red alder, western redcedar). Red alder (Alnus rubra) and western redcedar are most often found on wet to moist sites, with alder preferring streambanks and flood plains and redcedar preferring seepage and alluvial sites.

Asahel Curtis

Forests here were also dominated by Douglas-fir with some western hemlock and western redcedar. However, the wetter sites had a larger true fir component than seen at Lake Tradition.

Lower, very moist forest near Snoqualmie Pass, close to the peak of increased precipitation due to the adiabatic cooling of air masses moving up and over the Cascades. This stand had many large diameter Douglas-fir, as well as smaller western hemlock and western redcedar.

Alpental experiences slightly more precipitation and is much cooler. We saw a new species, silver fir (Abies amabilis), as well as some mountain hemlock (Tsuga mertensiana) and subalpine fir (Abies lasiocarpa) in cooler drainages.

Western hemlock is dominant at this second growth site. This site has a lower understory cover and a higher amount of coarse woody debris than a site of simliar age and disturbance history at Lake Tradition. This could be because of the relatively steep slope and less infusion of light, especially at oblique angles.

At this old growth site, we could see the difference in growth habits of shade intolerant (Douglas-fir) and shade tolerate species (silver fir, western hemlock). Silver fir (behind the large Douglas-fir) has a shorter crown and western hemlock (on the right) tends to retain its lower branches. This diversity in vertical structure is most visible in these older stands.

In late successional (old-growth) forests, decaying logs often provide prime germination sites for vegetation. Western hemlock in particular seems to prefer to grow on these nurse logs. The distribution and placing of nurse logs in part determine the exact site where certain trees will be located.

North Fork of the Teanaway

There is an incredible species diverstiy in this general area. The most prevalent species were Douglas-fir, ponderosa pine, silver fir, and increasing subalpine fir and mountain hemlock at higher elevations. This species diversity is likely a result of differences in growth environment resulting from small changes in elevation, aspect, and moisture regime. These differences are greater here than in the other two sites as a result of steeper slopes and location just on the eastern side of the Cascades--so precipitation is not uniformly high, but it is not as consistently dry as in lower elevation east side forests. In addition, by encompassing river valleys as well higher elevations, this site captures some of the species that are best adapted to grow in colder locations with shorter growing seasons. In short there is somewhat of a convergence of typical westside and eastside tree species (e.g, pacific yew and mountain hemlock vs. western larch and ponderosa pine).

Western larch (Larix occidentalis)	Ponderosa pine (Pinus ponderosa)	Engelmann spruce (Picea engelmannii-in background)
These common eastside species are found here growing along a river valley. These are species that we didn't encounter in either Lake Tradition or Asahel Curtis.

The back-right of this forest shows a more historically typical lower eastside forest of sparsely spaced, larger diameter ponderosa pine (Pinus ponderosa) with a grassy understory. Fire suppression has largely replaced this forest structure with higher density, mixed species stands, simlar in outward appearance to the stand of trees on the left of this photo. This illustrates that disturbance regimes and management practices (along with climate and topography) have a substantial influence on forest structure and species composition.

This gnarled ponderosa pine is growing on low nutrient serpentine soils (left). These soils have limited the species composition of this immediate area, as many species cannot tolerate their various growth inhibiting characteristics (low moisture holding capacity, high Mg:Ca, low levels of nitrogen, phosphorous, and sometimes molybdenum, high levels of slightly toxic metals including cobalt, cromium, iron, and nickel). Species that are able to tolerate these inhibiting factors will be able to grow with minimum interspecific competition. The small scale interspersion of serpentine soils with other soils creates a distinct pattern of vegetation distribution across the landscape (right).

Snow is a prominent climatic factor that affects species composition and growth. Species that grow in areas that receive substantial amounts of snowfall must be adapted to colder soils, long periods of coverage of some or most of their foliage, and shorter growing seasons. The species that can do this are often not very prominent in low snowfall areas, as they are not able to compete with species that have not invested into developing a tolerance for snow. These species, all of which are found in this general area, include mountain hemlock (Tsuga mertensiana, more common on the westside), subalpine fir (Abies lasiocarpa), lodgepole pine (Pinus contorta), and whitebark pine (Pinus albicaulis).