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. RÉSUMÉNous avons étudié la santé forestière du sapin rouge (Abies magnifica) et comment elle se compare à celle des espèces qui lui sont communément associées, telles que le pin de Jeffrey (Pinus jeffreyi), le pin tordu (Pinus contorta) et le sapin du Colorado (Abies concolor), dans les forêts de haute montagne de la Californie. Nous avons évalué les taux de mortalité des arbres, les changements dans la densité des arbres morts récemment, et dans la quantité de dommages causés aux arbres vivants par les insectes et les maladies avec inventaires foresiers complets. Le taux de mortalité annuel était de 1,8% pour le sapin rouge, alors que les taux pour le pin de Jeffrey, le pin tordu et le sapin du Colorado étaient respectivement de 1,9, 1,1 et 3,0%. La proportion de sapins rouges morts récemment a augmenté avec le temps, suggérant une augmentation de la mortalité. Toutefois, les modèles de transition d'état suggèrent que la structure de population actuelle du sapin rouge est stable. Les stress dus au petit gui et à la sécheresse sont des variables prédictives significatives de mortalité du sapin rouge. Les arbres présentant des dommages substantiels avaient une plus forte probabilité de subir une mortalité en 5 ans. Notre résultats sont concordent avec ceux d'autres études, mais la période étudiée est trop courte pour permettre de tirer des conclusions au sujet de déclins à plus long terme. Les résultats suggèrent que le petit gui est le plus significatif parmi plusieurs facteurs biotiques impliqués dans les processus causant la mortalité du sapin rouge, tandis que l'âge des arbres et la proportion de vieilles forêts pourraient également influencer les taux de mortalité.

Susceptibility of red fir and white fir to fir dwarf mistletoe (Arceuthobium abietinum) in California

“…Death of the lower branches has been attributed to dwarf mistletoe infection alone, to infection of dwarf mistletoe-infected branches by a canker fungus (Cytospora abietis Saccardo) and/or to branch shading in dense, old-growth fir stands (Parmeter & Scharpf, 1989;Scharpf, 1969a;Scharpf & Bynum, 1975;Scharpf & Parmeter, 1976). Mortenson, Gray, and Shaw (2015) also observed high levels of branch dieback in RFDM-infected red firs and attributed the widespread branch mortality to Cytospora canker. Substantial death of fir dwarf mistletoe-infected branches infected with Cytospora canker resulting in reduced live crown ratios and tree vigour has also been reported for grand fir (Abies grandis [Douglas ex D. Don] Lindley) in Oregon (Filip, 1984).…”

“…The percentage of dead true firs was low in plots (<4%), but was much higher in transects: 12% for red fir and 10% for white fir. Mortenson et al, (2015) reported annual mortality rates in the SNM for red fir and white fir of 1.8% and 3.0%, respectively. These annual mortality rates were based on data from permanent plots, not temporary plots.…”

“…Mortenson et al, (2015) reported annual mortality rates in the SNM for red fir and white fir of 1.8% and 3.0%, respectively. Mortenson et al, (2015) reported annual mortality rates in the SNM for red fir and white fir of 1.8% and 3.0%, respectively.…”

“…Mortenson et al, (2015) reported annual mortality rates in the SNM for red fir and white fir of 1.8% and 3.0%, respectively. However, Mortenson et al, (2015) also reported RFDM was the most significant factor related to mortality and decline of red fir and that the basal area of recently dead red firs was positively correlated with dwarf mistletoe infection (DMR). Therefore, the amount of mortality observed in the dwarf mistletoe-infested stands sampled in this study cannot be directly compared with that reported by Mortenson et al, (2015).…”

“…particularly Heterobasidion root disease (Heterobasidion occidentaleGarbelloto & Otrosina)(Mortenson et al, 2015). However, dead red firs were not examined for evidence of root disease or insect attacks in this study.Fir dwarf mistletoe populations distributed in the Klamath-Siskiyou Mountains in northwestern California and southwestern Oregon have been classified as a different subspecies-A.…”