A forest health inventory assessment of red fir (Abies magnifica) in upper montane California

Abstract

We investigated the forest health of red fir (Abies magnifica) and how it compared with commonly-associated species Jeffrey pine (Pinus jeffreyi), lodgepole pine (Pinus contorta) and white fir (Abies concolor) in the upper montane forests of California. We evaluated tree mortality rates, changes in the density of recently-dead trees and the amount of insect and disease damage on live trees from comprehensive forest inventories. The annual mortality rate for red fir was 1.8%, while the rates for Jeffrey pine, lodgepole pine and white fir were 1.9, 1.1 and 3.0%, respectively. The proportion of recently-dead red fir trees increased over time, suggesting an increase in mortality; however, stage-transition models suggested the current population structure of red fir is stable. Dwarf mistletoe and drought-stressed sites were significant predictors of red fir mortality. Trees with substantial damage had a higher probability of experiencing mortality in five years. Our results are consistent with others, but the timeframe is too short to make conclusions about long-term declines. Our results suggest that the most significant of multiple biotic factors involved in red fir mortality processes is dwarf mistletoe, while tree age and the proportion of forest in old-growth may also influence mortality rates.