Ecological Amplitude: A story of climax

Original Publication DATE: 7/15/2011

Box Camp Mountain | Marble Mountain Wilderness

Ecological amplitude is the range of habitats, often dependent on and defined by elevation, within which a certain species has the ability to survive. In the Klamath Mountains there are two species of pines that define the highest elevations–growing at or near the summits of peaks from ~7500′ to 9000′ (The Klamath Mountains get no higher). Foxtail pine (Pinus balfouriana) and whitebark pine (Pinus albicaulis) inhabit our sky islands where they are the crowning jewels of this coniferous wonderland.

Jeffrey Kane ponders the approach to Box Camp Mountain from the Pacific Crest Trail.

Box Camp Mountain is interesting for several reasons. The first is that its summit is only 7,267′ yet both species of said pines live in this fringe habitat. This is generally on south-facing slopes where lack of competition from firs and hemlocks (which thrive on north-facing slopes) is minimal. When approaching the summit I began to doubt the reports of these pines being here; but in the last few hundred feet they began to appear. Throughout Holocene warming, these two species (and others) have slowly been retreating up  regional mountains. Now, after thousands of years, they have reached their ecological climax on Box Camp–there is no more up on which to grow. This mountain holds the most formidably presumptive story I have attempted to read in a high elevation Klamath landscape–and what I read does not appears to have a happy ending.

Where are the Klamath Sky Islands? Look at the ranges of these pines to see.

Foxtail Pine (Pinus balfouriana)

Growing on the uppermost ridgelines as well as along southeast slopes, I estimated the population to be ~200 trees on Box Camp. Trees are of various age classes and recruitment appears suffice. Overall the population appeared to be doing well. The striking issue was the trees killed by bark beetles–about 15 in all. This concentrated mortality is rare in the foxtail populations across the Klamath Mountains–clearly this issue is worth watching into the future.

Windswept foxtail pines dot the ridge of Box Camp Mountain.
Trees whose decline was accelerated by  a mountain pine beetle (Dendroctonus ponderosae) infestation.

Jeffrey points out out the MPB galleries on a dead foxtail pine.

whitebark pine (Pinus albicaulis)

Small population in fringe habitat = ecological outlier. There are fewer than 40 living trees on Box Camp–almost exclusively on the south and southwest slopes. The population has historically been larger as seen by the skeletons that remain of the once living–we estimated the mortality at 50%. This means that even at the turn of the century, before rapid climate change, there were only ~100 trees in this location. As you will see in the pictures that follow, many of the dead trees appear to have died long ago (<50 years) while others have died recently. The recent deaths are identified by the remaining fine branch tips as well as bark on branches and trunks. We believe that all the dead trees were put ‘over the edge’ by bark beetles but they were already stressed. My hypothesis is that due to the exposed nature of the south-facing forest edge where they grew (and some still grow), they suffered from early season water loss enhanced by climatic change–ultimately the habitat is drying out earlier and earlier each year. As net photosynthesis decreased with water loss the trees fell out of balance, bark beetles moved in, and life was lost.
Whitebark pine skeleton forests.
Beetle galleries.
We will be back to read the story again.

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