Evolution of Forest Mensuration in the West
Where have we come? Where are we? Where to from here?
By James D. Arney, Ph.D.
This paper presents a chronology of the evolution of forest mensuration in the western States in the last half of the 20th century. The significant turning points were the result of a mixture of people, technology and changing direction of the forest industry. The intensity increased and evolved from general principles of forest management to site-specific prescriptions requiring precise timing of events.
The result of increased intensity of research and development in the last decades of the 20th century was an unexpected decline in long-term commitments to ongoing research in the 21st century. This paper brings together many of the factors contributing to this evolution in forest mensuration with a view to some possible future scenarios.
Somehow the forest industry has arrived in the 21st century with a multitude of questions about what kind of forest management to practice and what are the impacts of alternative forest management practices on society. The U.S. National Forests are now characterized as reservoirs of carbon, water, wildlife and spirit. These are popular characterizations and are commonly believed to be too complex to understand. It is also popular to believe that nature knows best and humans are not part of that universe. The USFS approach to forest management has evolved into a program of stabilizing all forests as broadly-spaced, residual old trees with a minimum of understory vegetation. The objective is low exposure to fire and insect attacks with little consideration about future growth capacity.
Where will this popular view lead forest tenure and management? More specifically, what analytical methods do we have available to us to evaluate the status of our forests and to forecast the alternative outcomes of different forest management strategies? Do we have tools, insights or results from the last fifty years of forestry research and development?
There are those who believe that all of these problems are new and that they require new approaches and skills. On that note, let’s remember that forest management practices have been researched, developed, exercised and taught in the West for well over fifty years. When a forester walks into a forest in 2009, what is observed now relative to what was observed in 1959 (fifty years ago)? What means are now available to that forester to assess the health and status of that forest? What other professional support (methods, tools, research and experience) is available to make those assessments?
It should become apparent in reading this article that there exists a wealth of research, tools, methods and practices that have been developed for assessing our forest resource. However, the current practice of our profession may be leading us to believe this background is not relevant. In addition, it is important to note that this review is not about any individual person or organization. It is simply a review of what has transpired in our recent past with a view of the future.
Where have we come?
Forest mensuration up to the early 1970’s
Let’s start with a foundation reference to the USDA Technical Bulletin No. 201 published in 1930 (revised 1949) by Richard E. McArdle and Walter H. Meyer. This Bulletin describes the “Yield of Douglas Fir in the Pacific Northwest” with tables and charts. These yields were for “normal” stands with variation due only to site and age. They did not reckon with variation in yield due to silvicultural treatment, species composition, stocking, defect or utilization practice. Site capacity was indexed on total height achieved at a stand age of 100 years.
Forest mensuration includes balancing and integrating technologies in inventory, yield forecasting and harvest scheduling. Each component is dependent on the evolution of technologies in the other components. This is a key factor to understanding mensuration.
During the 1950’s large tracts of forest ownership were cruised to obtain estimates of the standing volume in commercial timber species. Only trees greater than 11 inches were recorded. Western Hemlock, Red Alder and most secondary species were considered weeds regardless of size. Cruises were compiled on a 40-acre basis across each Section of a Township. Paper maps were then produced with color coding for different age, size and volume levels per acre.
These cruises were typically strip cruises one chain wide with breaks every five chains to constitute a plot. One transect was run for each 40-acre block with four transects per Section. This constituted a five percent cruise. Most commercial species larger than 8-inches in diameter were tallied by the 1960s.
In the late 1950’s and early 1960’s Bitterlich (1939) angle gauge became popular especially when Grosenbaugh (1952, 1958) expanded on this approach with labels of “Plot-less timber estimates” and “Point sampling”.
Forest harvest planning also began to take hold in the 1960’s. It was targeted on the “total” forest resource and the “proportion” of that resource that could be harvested annually without degradation. Little detail was known about the magnitude and character of the forest resource at that time. In addition, analytical tools to process forest inventories were not available or previously known. Harvest levels were computed from simple formulae, such as the Hanzlik formula, the Austrian formula and the Kemp formula.
“An important maxim of forestry is the management of forest lands for a continuous, controlled flow of timber. The key to achieving sustained yield is to establish a regulated forest with the proper distribution of stand age and size classes so that approximately equal periodic harvests of the desired size and quality are produced. Usually the forester is not so fortunate as to start management on a forest with a regular stand distribution. To achieve the desired distribution, he must often liquidate large tracts of old-growth virgin timber, reforest un-stocked and under-stocked lands, and thin or harvest stands of intermediate-age classes. These management operations transform or convert the irregular forest structure to the regulated one.” (Hennes, Irving & Navon, 1971)
These formulae were used to compute harvest levels from existing inventories with estimates of future volume coming from hand lookup of Bulletin #201 yield tables. The inventories were summarized into site classes and age classes to assign yields from the yield table. Total acres in each site-class by age-class cell were the most important factors affecting the calculation of the future harvest capacity over time. The classes were fixed while acres were shifted from one stratum to another as acres were harvested and grown to the next age class.
This yield table lookup helped clarify the observation by many foresters that the young forests which they were managing appeared to grow at rates different than the yield tables. In fact, it became readily apparent that thinning an over-dense stand would significantly improve its growth rates to achieve some target tree size. This prompted George Staebler and Dick Williamson (1954) to launch field trials to test various levels of thinning intensities and timings for their resulting impact on harvest age volumes. Others were also interested in these questions and yield potentials. This led Weyerhaeuser Company to hire George Staebler as their forestry research director. His mission was to lead broad investigations into the dynamics of young forests and their associated yield capacities under management. Staebler lead the development of the “Target Forest” silvicultural treatment regime. This regime concept later became the “High Yield Forest”; which was publically and robustly promoted by Weyerhaeuser over the next four decades.
It was in this same period of time that Jim Girard identified that these trees growing in various densities resulted in different taper and volume. He went on to develop a cruising technique wherein an additional diameter measurement at 16 or 32-foot height on the tree could provide a more precise estimate of standing volume. After cruising stands of all species over much of the Pacific and Inland Northwest, Jim Girard and Don Bruce (1963) produced a set of Form Class tables (16-foot and 32-foot) for estimating Scribner board foot volume given diameter at breast height, form class and tree height in numbers of logs. This approach was taken up almost immediately by almost all other company timber cruisers.
Meanwhile, Gerry Hoyer and Gene Little from the Washington Department of Natural Resources were recognizing the same variation in tree volume of cruised stands. Together with Ken Turnbull (then Instructor of Forest Mensuration at the University of Washington), they developed the Washington State Tarif Tables (1963). These tables accomplished the same result as Jim Girard’s form class tables with the additional ability to identify the volume of any tree in the stand by Dbh alone, once a Tarif number was assigned to the stand.
Interestingly, these two approaches could be applied to individual trees by assigning a form class or tarif number to each measured tree and then deriving the amount of volume by tree. Instead, most cruise compiling methods were set up to initially assign a single form class or tarif number to each stand, then derive volumes of all trees using the same index. This actually lost some of the potential precision that could have been gained using either of these approaches, but the computations by tree seemed too cumbersome. In fact, Don Bruce made the comment on the last page of their form class table handbook that it would be “easy to write a single equation giving the volume for trees of any height. Such an equation is cumbersome in use, and apparently of no practical value.”
Others like Lew Grosenbaugh (1954) began investigating tree taper and volume with the result that whole tree taper profiles became of significant interest. His research paper on height accumulation in steps of diameter instead of height provided Arney (1972) with the insight to apply a 4-power rifle scope to Bitterlich’s Spegiel Relaskop ( ) to measure upper stem taper profiles and volume. Later Walter Bitterlich produced a compact tele-releskop which he was not able to patent in the United States due to Arney’s previous work. This is the second example of many where different researchers were tackling the same problems (and opportunities) at the same time and then arriving at similar ends. The first example was form class tables and tarif tables.
The observation that stands could grow at a wide range of different rates became both an opportunity and a problem. The conventional lookup of yield capacity by site and age class in Bulletin #201 was not as definitive as previously expected. Both species composition and differences in silvicultural history of an existing stand were major reasons for departures from the USDA Bulletin #201 yield tables.
- Region wide expansion of research
The first was an aggressive and region-wide expansion of research by the U.S. Forest Service Pacific Northwest (PNW) Forest and Range Experiment Station into the long-term effects of initial tree spacing of new stands and thinning of existing stands. Experimental Forests were established opportunistically in various locations throughout Washington and Oregon. Research field trials were established in these Experimental Forests to evaluate growth and yield under varying levels and timing of silvicultural treatments. One cooperative study across many ownerships in the West was the Cooperative Levels-of-Growing Stock (LOGS) Study. These trials were established from Campbell River, British Columbia to Roseburg, Oregon on Federal, Provincial, State and private ownerships. Many USDA Research Papers and Research Notes have been generated from progress on these field trials.
- Establishment of a systematic grid of Continuous Forest Inventory (CFI)
The second development was establishment of a systematic grid of Continuous Forest Inventory (CFI) plots on many ownerships in the West. These permanent plots provided both a measure of standing volume and an estimate of current growth rates on each plot. This growth estimate included observations of individual species, size, density, and defect factors imbedded in the forecasted growth capacity. Owners of the mixed species forests of the Inland Northwest found this type of inventory to be much more useful for forest harvest planning than the standard lookup table approach popular in the Douglas-fir forests of Coastal British Columbia, Western Washington and Western Oregon. Many timber companies (e.g., Boise Cascade) and BIA Reservations found this CFI method to be very useful for establishing future harvest levels when combined with the Austrian formula. This approach is still the mandated method of harvest planning by the USDI Bureau of Indian Affairs in Portland, Oregon, for all Native American reservations under their administration.
The CFI database provided species composition, size and density for each permanent plot. The density of permanent plots across the ownership provided the number of acres which each permanent plot represented.
Permanent Plot Examples
- Non-Federal lands – Forest Survey 3.4-mile grid 7,398.4 acres/plot
- Federal Forest lands 1.7-mile grid 1,849.6 acres/plot
- Large Industrial Forest Ownership 0.25-mile grid 160.0 acres/plot
This CFI method is still in use in 2009 on a few ownerships, primarily native reservations managed by the USDI Bureau of Indian Affairs. It was also the foundation technology for the USDA Forest Survey across all non-federal lands in the United States. This later evolved into the USDA Forest Inventory and Assessment program with essentially the same technology base. The primary goal is past growth and current status of the forest.
Like Weyerhaeuser owners, others with large tracts (500,000 acres or more) realized that there was something to learn about silviculturally managing the dynamics of the young forest. Staffing of USFS Experiment Stations increased, field stations were established, the British Columbia Ministry of Forests established the Research Branch and Inventory Branch, the Canadian Forestry Service established the Pacific Forest Research Center in Victoria, and a number of private companies developed their own internal forestry research groups (MacMillan-Bloedel, Weyerhaeuser, Crown Zellerbach and Potlatch). Lots of good will and cooperation was exchanged in these years as demonstrated by Weyerhaeuser publishing the 50-year Douglas-fir Site Index report by King (1966). This report from a private company became the second (compared to Bulletin #201) most quoted forestry publication in the West. It also recognized that forest stands were likely to be harvested before reaching a total age of 100 years and a younger reference point was needed. By the mid 1970’s, Staebler had developed a leading forestry research team unparalleled anywhere in North America with nearly 100 professional forest scientists in silviculture, nursery practice, growth & yield, watershed, wildlife and genetic research programs. The organization became a reference point for intensive forest management.
 Submitted 2009-June-30, Final 2009-September-04. Senior Biometrician, Forest Biometrics Research Institute, Philomath, Oregon.