Development of Tools to Age Grand Fir to Aid in Collaborative Restoration of Federal Lands in Eastern Oregon

Abstract

The USDA Forest Service is working closely with collaborative stakeholder groups to accelerate the pace and scale of restoration in fire-prone mixed conifer forests of eastern Oregon. Collaboratively planned restoration projects are typically designed to conserve older trees established before fire exclusion policies and other management practices began to alter forest landscapes beginning in the late 1800s. Tools exist for accurately estimating the age of common species including ponderosa pine, Douglas-fir, and western larch. There are no existing tools available for aging grand/white fir, although an important objective of many restoration projects in mixed conifer stands is to retain older grand/white fir while removing younger individuals that have infilled into stands in the absence of fire to enhance resilience of stands to future climate and disturbance regimes. This article describes the development of tools to age grand fir on the Malheur National Forest by taking simple field measurements of morphological characteristics. Bark fissure depth, height to live foliage, and diameter at breast height were the strongest noncorrelated tree morphological characteristics associated with tree age. Crown class had no predictive power for estimating tree age. A variety of methods are presented that can estimate the age of grand fir with reasonable accuracy and are appropriate for different management objectives. Additional field testing and continued experimentation with different tree aging methods within an adaptive management framework is recommended. Study Implications: Shade tolerant grand fir has expanded dramatically in mixed conifer stands of eastern Oregon in the absence of frequent fire. Collaboratively designed restoration projects in mixed conifer stands usually call for the removal of younger grand fir while maintaining older grand fir that contribute to stand- and landscape-scale biodiversity. It can be difficult to estimate the age of grand fir based on morphological clues because of highly variable growth forms in this species. However, several easy-to-use grand fir aging tools promise to facilitate restoration by making reasonably accurate estimates of tree age.