Heterobasidion on True Fir in the Sierra Nevada

Description

Root disease permanent plots: Heterobasidion true fir in the Sierra Nevada

Introduction:

The purpose of this project was to re-measure plots tracking the development and spread of root diseases in California forests.  Specifically, this study examined tree mortality centers associated with annosus root disease of true firs (Abies spp.) caused by Heterobasidion occidentale in mixed-conifer and pure-fir stands of Northern California. Data from re-measurements can be used to determine the long-term impacts of this pathogen in these stands and provide data to aid in root disease model development.

Annosus root disease is common in mixed conifer and true fir stands throughout California.  This disease often produces a recognizable pattern of mortality: an enlarging areas of dead and dying trees which occupies a site for many years (often >50).

In 1973 and 1974, Forest Pest Management personnel (USDA Forest Service Region 5) established monitoring plots to examine tree mortality throughout California forests, as part of the Pest Damage Inventory following the severe drought of the early 1970’s.  Study locations were initially located using aerial photographs; plots were then established and ground data on causes of mortality collected.  During 1980-81, 142 of these plots, in mixed-conifer and fir-dominated stands on the El Dorado and Stanislaus National Forests, were revisited and surveyed for root disease.  The presence of annosus root disease was determined by inspecting dead trees and stumps for conks and typical decay and by felling recently dead trees (and one randomly-selected living tree per plot) for sampling by incubation of a stump-top disc, for identification of the distinctive conidia produced by Heterobasidion spp. Based on these surveys, 81 mortality centers associated with annosus root disease were identified.  Plots were established around the initial point of infection for these centers.  In these plots, all living, standing dead, and fallen dead trees and stumps greater than 10.16cm (4in) diameter at breast height (dbh) were mapped, as were all trees extending 25 feet beyond mortality center boundaries.   Mapped tree characteristics recorded included: dbh, height, species, crown class, crown ratio, and all damages and diseases.  Stand basal area was also determined.  Plots were re-visited again in 1986 and 1989, and 65 of the plots were visited again in 1995-96 (fewer were visited due to limited funding).  In 2004, twenty-six of the plots were revisited (attrition due to fires, logging, and statistical decisions reduced the available pool of plots, and funding required a further reduction).  During all re-surveys, mortality since the last survey was recorded, tree data were updated, and mortality center maps were enlarged as necessary to maintain a 25 foot boundary of living trees around mortality center boundaries.  Additionally, GPS data and ground photos were collected in 2004 to expedite future visits.  Overall, this study provides data for determining root disease development and impact over a 30-year time period.

Results:

Levels of mortality and rates of enlargement were determined for the period of 1973-1989. Fir mortality observed at the average annosus gap in 1973 was 3.2 trees (>10.16cm (4in) dbh).  During the 16-year study period this total increased to 6.4 trees.  Thus, firs died at a rate of 1 every 5 years. Mortality occurred unevenly along the boundaries of the expanding centers and rarely extended beyond 8-10 meters from the 1973-74 mortality center boundaries. Mean gap area had increased by 52% (67m² to 102m²) from 1973 to 1989. The majority of gaps tended to be quite small: 49 had not reached 100m² by 1989, but 32 of the gaps were larger than 100m² by 1989.  Annosus-associated gaps enlarged at a mean rate of 2.2m²/yr (mean radial enlargement of 0.07m/yr).  Forty-eight percent of annosus gaps exhibited chronic mortality, with a radial enlargement rate slightly higher at 0.12m/yr.

Data analyses on the two later visits (1995-96 and 2004) have not been completed. Observations give preliminary indications that tree mortality and gap enlargement rates have slowed subsequent to the 1973-89 period.

The data collected for this study in 2004 are available in electronic format; all earlier data is currently only available in hard-copy form (housed at UC Davis).

For more information regarding the design and early finings of this project, please see (Slaughter and Parmeter Jr. 1989) (below).

Slaughter, G. W.; J. R. Parmeter Jr., 1989: Annosus Root Disease in True Firs in Northern and Central California National Forests.  Presented at: Symposium on Research and Management of Annosus Root Disease in Western North America, April 18-21, 1989, Monterey, California. USDA Forest Service General Technical Report; PSW-116.  Pgs. 70-77.