Mortenson, L.A.; Gray, A.N.; and Shaw, D.C. 2015. A forest health inventory assessment of red fir ( Abies magnifica) in upper montane California. Écoscience. Early View: 1-12.

Abies magnifica. By Brian Bollman, Flickr.

DOI: 10.1080/11956860.2015.1047142.

Red fir ( Abies magnifica) is a high-elevation conifer that generally grows in mixed-species stands between 1,400 and 2,700 m. In California, red fir grows in the Sierra Nevada, the Klamath Mountains, parts of the Coast Range, and southern Cascades. Over the past several years, increasing and higher-than-expected red fir mortality has been observed in the central Sierra Nevada. In this study, Mortenson and others compared red fir, Jeffrey pine ( Pinus jeffreyi), lodgepole pine ( Pinus contorta), and white fir ( Abies concolor) health in upper montane California forests using Forest Inventory Analysis data. Based on stage transition models, the authors found that the red fir population structure is stable. The annual mortality rate for red fir was 1.8%, compared to 1.9% for Jeffrey pine, 1.1% for lodgepole pine, and 3.0% for white fir. Dwarf mistletoe infection and droughty sites were associated with red-fir mortality. However, red fir tree age and proportion of forest in old-growth were also higher, which may influence mortality.

Environmental conditions may be conducive for WPBR infection this year on Ribes and non-Ribes hosts in regions of California that received summer rains.

 

California has the greatest diversity of white pines in North America, with 6 of the 10 species distributed across the State's coastal and interior forests. All species are host to the non-native pathogen Cronartium ribicola, cause of white pine blister rust (WPBR). C. ribicola is a heteroecious rust that must infect both white pines and Ribes (currants) or non-Ribes alternate hosts to complete its life cycle. Ribes occur in a wide range of habitats, from riparian sites to mixed-conifer forests to dry, open, exposed slopes, with an elevational range of 900 - 3,700 m. Most Ribes species are susceptible to WPBR, but vary in their susceptibility. The 2 known non-Ribes alternate hosts, Castilleja and Pedicularis, are common forbs throughout California.

Infected Ribes with uredospores, Lake Tahoe Basin. By P. E. Maloney.

 

During the spring, aeciospores from perennial cankers on infected pine boles and branches are dispersed to infect leaves of the alternate hosts (mainly Ribes). Aeciospores have long-distance dispersal capabilities and can sometimes travel as far as 1,000 km or more. During the summer months, uredospores on infected Ribes leaves reinfect Ribes. This cycle repeats throughout the growing season. In late summer and early fall, lesions, or pustules, on Ribes leaves give rise to short-lived basidiospores that are locally dispersed, traveling <2 km to infect white pine. For infection to occur on both hosts, C. ribicola requires relative humidity (>90%) and temperatures of 2-18 degrees C.

 

Favorable conditions must exist (weather, microclimate, spatial connectivity between aecial and telial hosts, host phenology, and the environment) for infection to occur. WPBR wave years in California's Mediterranean climate (particularly western slope Sierra Nevada lower-elevation forests) typically occur every 7 - 14 years. In high-elevation forests, wave years may be more infrequent (25 - 40 years). When in the field, turn over alternate host leaves to look for signs of infection. If WPBR symptoms are found, email Patricia Maloney the infected alternate host location and species as well as a photo of the symptoms.  For more information, see  White Pine Blister Rust in California.