Biogeography in the Bitterroot

Studying forest types and structures along a mountain climate gradient

Lauren Kluemper and Leydon Thornton

On Friday October 5, the fieldtrip with Professor Andrew Larson took us out to study forest types and structures along a mountain climate gradient.  We made four stops moving from East to West over Lolo Pass along Highway 12.

Our first stop was Blue Mountain Trail Head, where the forest was sparse, dry, and mainly consisted of Ponderosa Pine.  The open canopy and limited water supply allowed for mainly grass species to grow on the forest floor, creating a beautiful savanna beneath our feet. We also kept our eye out for evidence of disturbances in each area, and at this particular sight it seemed that there had not been a fire or an insect infestation in a long time.

We continued up the pass to Lee Creek Campground, on the east side of the pass and already began to notice a dramatic change in the forest structures.  It was a mixed conifer forest predominately made of Lodgepole Pine and a nearly closed canopy (interspersed were Subalpine Fir, Douglas Fir, Engleman Spruce, and Larch).  Lodgepole pine was the dominant species because it can tolerate the shady environment of this area.  There was more diversity in the understory species because of the increase precipitation available at this higher elevation.

After having lunch at the top of Lolo Pass we ventured into the forest to be greeted by clumped Engleman Spruce, Subalpine Fir, and Whitebark Pine of similar ages.  This is a wetter environment in which the plants have had to adapt to a heavy snow load for half of each year.  Because of this the understory is diverse with species that have flexible branches so that they can bend without breaking in the winter.  There were huckleberry plants! But no huckleberries…

Our final stop was the coolest place ever. It was the Devoto Cedar Grove on the Westside of Lolo Pass near the headwaters of the Lochsa River.  The old growth forest consisted of Western Red Cedars and Grand Fir.  The luscious understory was full to the brim with moisture loving plants, like FERNS (“Oh, so pretty,” gasps Lauren), wild ginger, and other plants found in the Pacific North West.  Tip up mounds were a plenty, along with decayed trees and a seemingly healthy and diverse ecosystem.

We ended the field trip with a better understanding of the way ecosystems change over different elevations and climates.  We have bettered our skill of estimating the historical factors and climatic reasons of why forests can change dramatically even within a days drive.