Forest Investment Account

Abstract of FIA Project 200123

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The effect of Armillaria root disease on stand productivity on growth and yield of second-growth stands in the ICH

Author(s): Cruickshank, Mike; Morrison, Duncan
Subject: British Columbia, Pathology
Series: Forest Investment Account (FIA) - Land Base Investment Program - Innovative


The belowground incidence of trees infected with Armillaria root disease (DRA) ranged from 23-33% in Douglas-fir plantations, and 80% in one mid-rotation stand. The increase in incidence of newly infected trees peaked about age 16-20, consistent with root closure in the stand. The fungus continues to infect both within and between roots as the trees age, but symptoms are also mostly not apparent because of building host resistance as the trees age. Juvenile trees with all root lesions contained (callused) increased with age from 18% to 38%. In mid-rotation trees, 52% of the trees had all lesions contained. There are still many trees with spreading lesions that probably represent new infections as the fungus repeatedly infects new areas (primarily with rhizomorphs) in the root system. Mortality is expected to stabilize somewhat between the ages of 30 and 60, but then is expected to increase after this time with mortality between 20 to 60% by age 100 due to the repeated root infections occurring belowground. These figures do not include in-growth that will occur in larger openings in the more severely affected stands, but growth is expected to be poor in light of the high inoculum left by the dead fir.
Trees that are able to contain the fungus completely and survive suffer growth losses of about 7-10% for the five juvenile and one mid-rotation stands. Stand losses are underestimated in older stands because the remaining healthy trees tend to be small and losses are calculated by the difference between healthy and infected tree growth. The healthy population is represented by smaller trees because their size reduces the probability of contact with the fungus.
Compensatory growth, where healthy trees have increased growth due to their proximity to infected neighbors, did not occur. Compensatory growth, if it did occur, would be short lived as the percentage of healthy trees in stands steadily diminishes to a low percentage by age 60. Healthy trees cannot be relied upon to compensate for growth losses in infected trees mostly because of the high incidence of infection as the stands age.
The disease affected the tree crown by limiting the amount of foliage on larger branches of diseased trees. The distribution of bole area increment was also altered by DRA; less wood was added between the base of the crown and the soil line. These factors will be introduced into the TASS growth and yield model in the future.
Operational adjustment factors (OAFs) were developed for TIPSY using the data for growth losses and mortality. The OAFs were created specifically for the disease and are not covered by other OAFs traditionally used (e.g., OAF1 and OAF2). The results suggest that Armillaria will have a significant impact on Douglas-fir plantations by age 100. These OAFs are intended to be temporary until more sophisticated models, such TASS, can be modified to simulate diseased stands accurately.
A step towards filling the knowledge gaps concerning how DRA affects growth and yield has been achieved by creating OAF factors for the disease in TIPSY. Knowledge gaps in this area have led to uncertainty surrounding stand tending and planting practices with Douglas-fir, which should be carefully considered in light of the results of this study. Unfortunately, most of the disease effects occur well after the free-growing assessment, resulting in overlooked impacts. The current work is a step towards rectifying this issue. Results indicate that planting monoculture Douglas-fir and then stand tending are not recommended unless inoculum removal is practiced. Planting conifer mixes of tolerant and susceptible species help to limit mortality (growth loss still occurs), and several resistant or tolerant conifer species produce high value timber. Study results show that DRA will affect the yield, size distribution, and species composition of Douglas-fir plantations. The potential effects of DRA should be considered whenever further silviculture treatments are contemplated or when new plantations are established. As well, the study will allow for the first time the benefits of treatment to be estimated in cost-benefit analyses, because it is now possible to estimate the volume impact of the disease.
Knowledge gaps still exist for impacts in other species, especially mixed stands. To fill these gaps, the basic biology and modeling infrastructure developed in our oldest plantations (Douglas-fir), could be adapted for mixed-species stands. To do this, a calibration of losses, not a total alteration of model or basic biology, is needed with limited additional sampling and funding. Knowledge on belowground incidence of infection in some other species already exists in the ICH, IDF, and ESSF.
Tech transfer included a teleconference for representatives of seven southern interior TSAs, the MoF, and collaborators in December. Questions were answered concerning the study and future funding options were explored. Project staff presented partial study results at a January workshop sponsored by the SIGY, and presented a poster on study results at SISCO in March. SIGY is sponsoring a summer workshop in summer 2003 about impacts and stumping of DRA. The OAF factors will be available for various levels of disease severity when the next version of TIPSY is released at:
Potential users include licensees, contractors, the MoF, and anyone wishing to account for impacts of the disease in their Douglas-fir plantations in TSR or for estimating the impact of treatments.

For further information, please contact Mike Cruickshank, Natural Resources Canada, Canadian Forest Service (

Updated September 08, 2005 

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