Old-growth Douglas-fir and ponderosa pine, South Umpqua River headwaters, Douglas County, Oregon, April 19, 2010. Photo by B. Zybach.
Recent discussion on this blog has centered around the desirability of managing forest trees on the basis of their diameter, their age, or their basal area for a given location. Some of that discussion has included age classes of 150 and 300 years as points of departure. This photograph illustrates some of these concerns and was first published in an article on forest restoration I wrote last year and also posted to this blog: https://forestpolicypub.com/2012/04/04/8829/
This is a typical stand of trees in the upper South Umpqua River basin that I documented in a 2010 research study of 125,000 acres of forestland, mostly contained in the Umpqua National Forest. Our research focus was to determine forest conditions for the area for the ca. 1800 time period that preceded white contact in the basin. The larger old-growth trees are estimated to be more than 300 years of age, and the younger invasive conifers are in two basic age groups: the 30-inch to 40-inch second-growth trees are less than 150 years old, and the smaller understory and roadside poles are probably 20 to 40 years of age.
In 2009 there were two sizable stand-replacement crown fires in the study area: the Boze and the Rainbow fires, totaling about 15,000 acres between them. Prior to these two events, there was no evidence of any other crown fires of this magnitude at any other time since 1800; i.e., these types of fires were unprecedented during historical time. Other large-scale wildfires in the area, such as the 2002 Tiller Complex, were noticeably spotty and only crowned in certain locations — mostly younger plantations in that instance.
Several thousands of acres of this type of condition were found and documented in the study area. The old-growth stem count was about 5-15 trees per acre, while the invasives (I know Sharon doesn’t like this word, but I don’t know what else to call them in instances such as this) totaled about 100 stems or more an acre. These trees are having two deleterious effects on the old-growth that are being “preserved” for wildlife habitat (which was notably more present, diverse, and abundant in the remaining Indian prairies and meadows): 1) they were competing directly with the older trees for sunlight, water, and nutrients; and 2) they were making crown fires such as the Rainbow and Boze now possible. Either way, they pose a very powerful threat to the remaining old-growth in the landscape.
The decision to passively manage these trees has resulted in an increasing threat to the health and survival of the old-growth for the reasons just stated. Suddenly opening them up from competition increases the risk of windthrow due to lower stabilizing branches having been shaded out long ago. Many of the remaining old-growth have become top-heavy as a result. However, based on my observations of the past 50 years, if the competing vegetation were removed, the large majority of the remaining trees would survive and benefit almost immediately (“about 5 years”) by the removal of competition — and at a potentially good profit, with numerous rural jobs, useful products, and greatly improved wildlife habitat for many other wildlife species, including understory shrubs and forbs, ungulates, carnivores, birds, and insect pollinators.
To try and use an homogenized diameter screen or age limit in managing this stand would be a waste of time. I think the same is true for a basal area approach. Common sense states the obvious: use it or lose it. If some animal species prefer this type of situation, then they will have to contend with a diminishing resource because of the problems just stated. My thought is to actually preserve, via active management, as many of the remaining precontact trees and stands as possible.
Those are my experiences and opinions, though, and there has been little scientific research in regards to these situations. Other thoughts?