Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Wildland Resources

Committee Chair(s)

R. Justin DeRose


R. Justin DeRose


Eugene W. Schupp


John D. Shaw


Spruce-fir forest type covers nearly 10 million acres of forested land in the interior west, but there is a lack of research defining how these forests grow for future planning. Stand density index (SDI) represents the average tree size and number of trees in a stand multiplied. Each species has specific maximum number the growing space can handle known as ‘fully stocked’. If the stand is fully stocked, it must wait until trees die for individuals to grow. Spruce and fir have similar maximum stocking values, and similar growth characteristics, allowing them to be plotted together. Using current forest data, tree size and number can be fit to complex equations that tell us relative density of the stand, average stand height, and estimated wood volume. A graph with tree number on the x-axis and average size on the y-axis, that can also include height and volume lines, is called a density management diagram (DMD). Using a local height reference, the stand age and rotation time can be estimated. Large areas of spruce forest are dying because of spruce beetle populations which have been associated with larger average tree size and higher density. If a stand grows to a big enough average size, or has enough trunk surface area, it is more likely to increase growth of large beetle populations. Previously defined risks of beetle attack were plotted on a graph of average tree size by tree density, and scores were calculated for each zone of the diagram. Zones were plotted on the DMD so forest managers can see both beetle risk and stand growth at the same time. Forest managers can plan forest growth, and how they would select and remove trees to reduce the potential risk to beetle infestation. Using a DMD, a forest manager could plot multiple stands to compare hazard ratings and prioritize treatments. The forest manager could mitigate a contiguous high-risk stand by thinning corridors of low-risk to divide the larger area and reduce probability of spread. A forest manager could also predict future stand development and plan thinning treatments to prevent increasing beetle risk.