Silvicultural Alternatives for Pacific Silver Fir Stands on the Yakama Reservation

Abstract

The Yakama Nation’s (YN) upper-elevation forestlands dominated by Abies amabilis (Pacific silver fir) and Tsuga mertensiana (Mountain hemlock) have tremendous natural and cultural resources that are valued by the YN. Unfortunately, these forest stands are experiencing high mortality rates due to insects and disease following extreme drought events. Increasing tree mortality rates in these upper-elevation forests have been predicted by climate models but field research to document the extent of tree mortality and changes in species composition has not been conducted in upper-elevation forests in eastern Washington State. The lack of research in these upper-elevation forests is not unexpected considering that low-to-mid elevation forests are actively managed because of their high economic importance. The upper-elevation forests need greater research and management attention because of the high mortality they are experiencing. These forests need to be managed to sustain the multiple resources for future generations. The objectives of this research were to: 1) Use the Continuous Forest Inventory (CFI) data and technology to verify the related forest health issues that are causative to the high mortality rates within the Pacific silver fir habitat type in the upper elevations of the Yakama Reservation; 2) Estimate the growth rates of all tree species found growing in the upper-elevation Pacific silver fir habitat type using the Yakama CFI database; 3) Assess the mortality rates of tree species in the upper-elevation Pacific silver fir habitat type using the CFI database; and 4) Assess which of three silvicultural treatments would re-establish healthy and productive forests at these upper elevations by using the CFI data in the Forest Vegetation Simulator (FVS) to project growth and yield. This research showed that the Pacific silver fir habitat type is experiencing higher rates of mortality compared to growth, i.e., a net loss of silver fir habitat. The 2005 mortality rate in these forests was 1.4% of stocking compared to a typical annual mortality rate of ~1% for these forests. Some tree species were more vulnerable to these changes in climate and secondary insect/pathogen attacks which have the potential to change the distribution of these tree species in these upper-elevation forests, i.e., whitebark pine (13.6% in 2005), lodgepole pine (5.2%), western white pine (3.8%), subalpine fir (3.5%), and Engelmann spruce (1.1%). Silvicultural alternatives are needed to improve the growth and health of the upper-elevation forestlands on the Yakama Reservation. This research suggests that it is not a viable option to not manage these forests. Simulations conducted during this study suggest that the diversity and wood quality would decrease if silvicultural practices were not implemented to restore these high-diversity forests. Furthermore, the YN cannot afford to lose the cultural resources and wildlife habitats that these forest stands provide.