In class on Wednesday we learned about the difference between physiography and topography, being the regional surface features and the configuration of landforms respectively. We discussed orographic lift, or the movement of air masses from low to high elevations as they move across rising terrain. The orographic lift results in diabatic heating and/or cooling as the pressure changes due to physiography. Adiabatic heating and/or cooling is the stationary affect of local topographic features, for example the slope of terrain affects moisture levels and the aspect, or relation of the slope relative to the sun, affects light exposure. This frosty Friday morning we set our for our second Conservation Ecology field trip with Andrew Larson. Our goal for the day was to observe species distribution on Route 12 relative to the physiography and topography of the areas.
After our essential coffee stop at Safeway we headed to Blue Mountain on the southern end of Missoula. The hillside was a dry grassland and Ponderosa Pine forest. That location receives approximately 13 inches of precipitation annually, with the hottest months being May and June. The Ponderosa Pine is a drought resistant species capable of thriving in those conditions. Approximately 20 to 30 years ago there was a low intensity ground fire indicated by fire scars on the older trees and the mineral soil layer. The new established younger cohort appeared to be about that age as well. We observed how aspect can affect the diameter and shape of the Ponderosa Pine. The diameter was smaller and self pruning indicated a more dense packed stand in the north facing arroyo. Also in the arroyo we found more bio diversity in tree species which included Douglas Fir, and Western Larch, and had taller grasses and shrubs. We also learned about the history of fire suppression and livestock grazing in the Western United States. With increased fire suppression the amount of course woody debris is higher making fires burn hotter and longer. In some cases the high intensity fires are more likely to be a stand replacing event even for fire resistant species like the Ponderosa Pine. On Blue Mountain we witnessed the spread of the Ponderosa onto formerly grazed grassland, as indicated by younger trees further out.
Our next stop was the Lee Creek Campground. Lee Creek had a notably higher species diversity consisting of larch, Engelmann spruce, grand fir, subalpine fir, Douglass fir, lodgepole pine, and ponderosa pine. There were few ponderosas because of the moisture content. While this was partially due to the fact that this area receives much higher annual rainfall than Blue Mountain, the species diversity can also be attributed to a change in soil composition. The campsite is located on the Idaho Batholith, which is primarily composed of well-drained granitic rock. The mixed-severity fire regime of the area also has an impact on the number and types of species at the site.
One interesting species we observed at Lee Creek was dwarf mistletoe (Arceuthobium). Arceuthobium is a parasitic species that attaches itself to its host by sending tendrils into the branches to tap into the hosts supply of nutrients and water. It reproduces by explosively discharging its seeds (up to 11 meters at 65mph!) which have a sticky residue that will attach to nearby trees. Because of its highly developed reproductive process Dwarf mistletoe is closely tied into a healthy fire regime. Fire suppression will create dense stands of Douglass fir, so it is much easier for Dwarf Mistletoe to spread from tree to tree with its large “blast range.” Luckily, we only saw a handful of infected trees, which was most likely a result of fire being involved in the site’s history in the recent past. Though the witches broom growths caused by the mistletoe are important habitat for birds and insects and small mammals, and a significant disturbance feature of a forest. Often in forests managed for timber harvests the mistletoe is exterminated because it kills otherwise healthy trees that could harvested.
We made our next stop was Lolo Pass where we all made sure to set our watches to the Pacific Time Zone to limit confusion. There was a similar composition of species in the forest there, but NO ponderosas were present because the yearly precipitation is too high, about 50-60 inches annually. The subalpine fir and Engelman spruce had pronounced spire-like crowns from the heavy snowfall at the pass. While the trees were of a relatively old age, we decided it couldn’t be considered old growth because the canopy was relatively even and there were not enough snags augmenting the structural complexity of the area. Because this spot receives so much precipitation, there was almost no difference caused by the aspects of slopes in the site. We saw some Brown Felt Fungus, or Snow Mold which develops in heavy snow.
Our final stop was in DeVoto Memorial Cedar Grove named for Bernard DeVoto a conservationist and historian. This site was where he edited the Lewis and Clark Journals. This area of Idaho hosts the largest trees in the state. The western red cedar can live up to 3,000 years. After lunch the group was sleepy and Andrew Larson seemed to be near his lecture limit so our discussion was brief. Besides the obvious western red cedars there were pacific yew, engelmann spruce, doug fir, western larch, and a few noted ponderosa pines in a prominent south facing aspect, and grand fir was a dominant species. This site was also noted for the shade tolerant and moisture loving understory. Despite the obvious presence of moisture at this site there was also evidence of fire disturbance in the past shown by fire scars on the older cedars.
As a conclusion to the trip we made one final stop where Colt Killed Creek becomes the Lochsa river. We spread out into the woods to search for chanterelle mushrooms before heading back to Montana.