By: William E. Schlosser, Ph.D.
Date: November 2020
West of the Cascade Mountain range in Washington state, the subject species is Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco)). Douglas-fir var. menziesii, is found in forestlands of Vancouver Island, British Columbia, Canada, and within coastal British Columbia, Canada, and in adjacent forestlands within coastal ecosystems in Washington, Oregon, and California.
Along the Cascade mountain crest and eastward, the species transitions to (P. menziesii var. glauca (Beissn.) Franco)). This transition extends northward into interior British Columbia, Canada, to maintain the var. glauca specie characteristics in interior and intermountain areas through eastern Washington, Idaho, Montana, Wyoming, Colorado, and even as far south as Mexico.
Douglas-fir specialization finds this species filling the niche of plant competition where Douglas-fir is an initial sprouting species, competing for sunlight against all other trees: it is a competitor for height supremacy where photosynthetic energy is captured. When needed, Douglas-fir seedlings will sprout in partial shade, but only when the site is warm and dry, and the early arrivals provide some moisture retention and insolation against direct solar radiation. Ultimately, this species will survive so it can thrive for centuries on the stump.
Mostly, Douglas-fir regeneration is opportunistic to find niches where it can become established. It is a K species, with long life spans, resilient to low intensity wildfires, and it stands stable against high windstorms. These varieties come from the same original sources, but in today’s biome representatives evolved with the Cascade mountain range serving as a barrier to genetic material intermixing. Look at the range where the Columbia River cuts through the mountain range to see how eastern Cascade Mountain ecosystems support Douglas-fir as far east as Yakima. Which variety are these trees?
Douglas-fir pictured at Kamiak Butte
Competitive Market Products
Although Douglas-fir var. glauca logs are exchanged in competitive log marketplaces, the price is not treated on par with Douglas-fir var. menziesii prices witnessed on the west coast. Arbitrage pricing is not supported between these markets because of commodity characteristic differences and state laws preventing comingling of the specie varieties when scaling or milling into lumber (NLRAG, 2011).
Why these differences?
Consider biomes between western Washington and eastern Washington. Lands bordering the Pacific Ocean to the west are significantly influenced by climate with high amounts of precipitation and warm temperatures rising above 4⁰ Centigrade (40⁰ Fahrenheit) early in spring months. East of the Cascade Range, located on the leeward side of the mountains, the rain shadow effect delivers less precipitation and temperatures normally pass the 4⁰/40⁰ benchmark later in spring months. In the summer, temperatures climb higher in these interior regions when precipitation is less than what the west-side varieties experience.
Elevations are generally higher in these eastward regions while soils and nutrients dissolve for plants is significantly different. Competition between cohort species in each region faces striking differences. On the east side of the Cascade Mountains, ponderosa pine (Pinus Ponderosa) and western larch (Larix occidentalis) are site competitors with Douglas-fir. Ponderosa pine fills the niche to populate the hottest and driest forestland sites, such as the south facing aspect of Kamiak Butte. As the sites receive less direct solar radiation (Photosynthetically Active Radiation – PAR), Douglas-fir trees can thrive.
Western larch seedlings need marginally more available moisture than ponderosa pine and need to be the first seedlings to sprout in direct sunlight. While Douglas-fir seedings can tolerate some shade when germinating as seeds, western larch cannot. They need to be the first species entering the site. With this favorable first adopter modus, western larch will seek dominance in the overstory of all growing plants. This is where western larch and Douglas-fir trees compete in the overstory to be the most successful tree capturing photosynthetically active solar radiation.
By U.S. Geological Survey – Digital representation of “Atlas of United States Trees” by Elbert L. Little, Jr. , Public Domain, https://commons.wikimedia.org/w/index.php?curid=10258966
United States of America