Douglas Fir. Stephen F. Arno

with the dry conditions where I typically saw ponderosa pine in the Rocky Mountains. Well-drained, rocky soils left behind by receding glaciers likely accounted for the pine’s occurrence in this unexpected place. Ironically, coastal Douglas-fir encroachment under the remnant Fort Lewis ponderosa pine presented a tiny, more advanced example of the region-wide phenomenon slowly unfolding in the dry interior West, where inland Douglas-fir had just begun to invade and crowd out the historically dominant ponderosa pine.

      I spent the next nearly two years at Fort Ord along the central California coast, often traveling to Yosemite National Park for weekend hikes. It was in Yosemite that I observed Douglas-fir’s superior ability to thrive and grow large on what John Muir termed “earthquake talus,” slopes of large, nonstationary rocks at the base of cliffs. Although Yosemite marks the southernmost occurrence of coastal Douglas-fir in the Sierra, I saw occasional firs of surprising girth (5 feet in diameter and larger) on the Mist Trail, below Liberty Cap, and along the Panorama Trail.

      A 1971 trip to meet a friend in nearby San Francisco included a visit to Muir Woods National Monument and a surprise encounter with Douglas-fir. Muir Woods, located just a few miles north of San Francisco, is a several-hundred-acre enclave of redwoods up to 1100 years old that escaped the first wave of early logging. The monument also boasts a few impressive Douglas-firs, the largest being the massive 280-foot Kent Tree, named after a US Congressman who donated land for the preserve. Despite growing in a redwood sanctuary, the big Douglas-fir was Kent’s favorite tree, measuring more than 20 feet taller than the tallest redwood in the park.

      After completing military service in 1972, I worked out of a pickup camper as an itinerant research forester sampling regeneration in subalpine forests across the Mountain West. These sites ranged up to nearly 10,000 feet, which established the upper end of an astonishing elevational range for Douglas-firs when compared to the sea-level trees I had seen at Fort Lewis, and provided a real eyeopener for me.

      Following graduate school, I took my first full-time job with the US Forest Service Rocky Mountain Research Station in 1980. It was my dream job—travel the interior West and identify broadscale ecological problems on national forestlands from the Canadian line to southern Utah. Field evaluations on dozens of national forests revealed several extensive ecological concerns. One pervasive condition involved thickets, or a layer, of small inland Douglas-fir developing under an overstory of ponderosa pine, ultimately resulting in Douglas-fir dominance and increased threats to stand health and survival. Perhaps because the bottom-up transformation of ponderosa forests to Douglas-fir would take decades to play out, station personnel chose to focus on several other pressing ecological problems at the time.

      For this initial assignment, I traveled throughout a wide swath of the interior West, where I also observed Douglas-fir thriving in the dry, cold environments of “island” mountain ranges. Such ranges are typically separated from other mountain ranges and major forested areas by either semi-arid plains or high desert. I found that Douglas-fir often dominated these isolated, high-elevation mountains, where most of the forested zone was too cold for ponderosa pine and too dry for true firs, spruces, or aspen. On lower, less prominent islands, Douglas-fir often dominated at even the highest elevations.

      Years later while a forestry professor at the University of Montana, I combed the state’s island mountain ranges looking for suitable areas for a graduate student research project. Over previous decades I had hiked much of the Missouri River Breaks and similar topography along several smaller river systems in north-central and eastern Montana. On rare occasions, I found small individual Douglas-fir trees growing in unexpected places. Their presence on these harsh outlier sites was surprising—far beyond the known easternmost populations of Douglas-fir that grow in central Montana’s island mountain ranges. None of the few Douglas-firs I observed were anywhere close to maturity compared to nearby larger ponderosa pines, suggesting that fire kills the majority of these trees while they are still small and more vulnerable to fire than the pines. It also suggests that wind-driven fire rather than lack of water prevents these trees from developing to seed-bearing size. Though the casual observer could easily surmise that Douglas-fir is entirely absent from the eastern Montana landscape, time spent poking around these highly eroded river breaks and coulees may reveal a rare find—a small Douglas-fir growing in a moist microsite, perhaps fed by seepage from an underground spring, but likely surviving only until the next wildfire.

      Extensive traveling over the years further sparked my curiosity to visit some of the West’s little-known national forests and out-of-the-way national parks and monuments. One such trip included a stop at El Malpais National Monument in western New Mexico, where I was fascinated by the dwarf Douglas-firs clinging to life on nearly barren lava flows. Many of the stunted trees were centuries old but little more than head height. Recalling my earlier visit to Muir Woods, I was struck by the vast differences in growing conditions at El Malpais, yet Douglas-fir were able to grow to old age in both environments. And though both the massive Kent Tree and these elfin Douglas-firs were more than five hundred years old, the giant at Muir Woods was larger in diameter than some of the lava-flow trees were tall and had more than a thousand times the cubic volume. No other tree species on the planet displays such mind-bending contrasts in mature tree size. It is this extraordinary diversity that makes Douglas-fir such an intriguing species, richly deserving of deeper inquiry and broader exposure of its colorful history.

      Steve Arno’s deep ecological knowledge and experience with both varieties of Douglas-fir, coupled with our history of coauthoring two previous books, provided a strong incentive for me to join him in documenting the life story of this remarkable tree. Readers will find that Douglas-fir is indeed nature’s all-purpose tree. It has provided more wood than any other species for building the infrastructure of the American West; its exceptional genetic diversity allows it to have a wider geographic distribution than any other North American conifer; its unique and puzzling combination of characteristics prevented taxonomists from selecting an appropriate scientific name for 150 years; and its longevity and distinct annual rings have allowed scientists to estimate relationships between growth and precipitation extending back more than two thousand years. Finally, before the largest individuals were removed in the early days of logging, historical reports offer substantial anecdotal evidence that coastal Douglas-fir may have been the tallest trees in the world—taller even than redwoods.

       CHAPTER 1

       Unlocking Douglas-Fir’s Secrets

      Douglas-fir is an enigma. Its mix of distinctive structural features and physiological attributes produces a tree that is puzzling, exceptional, and in ways a marvel of nature. World class in height, geographic distribution, and wood quality, and unique in architecture and genetic composition, Douglas-fir also acquires nitrogen in novel ways, and at times even irrigates itself. Though this tree has long played an integral role in the lives of humans and animals, many of its secrets are only now being understood through modern science.

      Two geographic varieties are recognized, though they exhibit only subtle physical differences. The taller, faster-growing of the two varieties, coastal Douglas-fir (Pseudotsuga menziesii variety menziesii), occupies the Cascades, Sierra Nevada, and the British Columbia Coast Range, and extends westward to the Pacific shore. Regions to the east are inhabited by the typically shorter inland, or Rocky Mountain, Douglas-fir (P. menziesii var. glauca), which grows slower and is more cold-tolerant. There are, of course, exceptions. Some habitats within the coastal distribution—such as bedrock sites in the droughty San Juan Islands—support short, limby coastal Douglas-firs, while inland Douglas-firs in moist, wind-sheltered canyons and ravines often grow straight and very tall with little taper.

      Because of its much greater size and hence commercial value, the preponderance of scientific inquiry has focused on the coastal rather than inland variety of Douglas-fir. The descriptions, taxonomic difficulties, potential maximum sizes, and water and nitrogen relationships presented here pertain to coastal Douglas-fir unless otherwise noted.

      The tree’s botanical identity confounded