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Investigator’s Annual Reports (IAR’s) for Crater Lake National Park

The role of western dwarf mistletoe in fire susceptibility and behavior in mature ponderosa pine stands

Report Number: 32134

Reporting Year: 2004

Permit Number: CRLA-2002-SCI-0008

Principal Investigator: Sharon Stanton, Department of Geography, Portland State University, Portland, OR

Date Received: Mar 31, 2005

Additional investigator(s): Ms Sharon Stanton

Park-assigned Study Id. # CRLA-02028

Permit Expiration Date: Sep 30, 2005

Permit Start Date: Jul 18, 2002

Study Starting Date: Jul 18, 2002

Study Ending Date: Sep 30, 2005

Study Status: Continuing

Activity Type: Research

Subject/Discipline: Fire (Behavior, Ecology, Effects)

Objectives: This research focuses on the fire ecology of old-growth ponderosa pine forests (Pinus ponderosa) infested with parasitic dwarf mistletoe (Arceuthobium campylopodum). Few studies have examined the impacts of dwarf mistletoe on the structure and function of ponderosa pine forests, and the relationships between dwarf mistletoe and disturbance, especially fire, are poorly documented. The objective of this research is to increase our knowledge of the complex ecological relationships among dwarf mistletoe, host tree growth, and fire dynamics.

Primary hypotheses the study will address include:

1. Dwarf mistletoe increases surface fuel composition in ponderosa pine stands.
2. Prescribed fire behavior differs according to dwarf mistletoe infestation level.
3. Infected trees are more susceptible to post-fire mortality than healthy trees.

The dwarf mistletoes are a group of flowering plants that evolved in the Old World as obligate parasites on a wide range of conifers. A common host reaction to infection by dwarf mistletoe is the formation of “witches’ brooms.” Dormant buds activate, resulting in masses of host twigs growing in a dense pattern of abnormal branching. Broomed branches tend to show reduced cone and seed production, greater biomass, and fewer needles. Dwarf mistletoe alters crown structure in ponderosa pine, leading to several possible implications in terms of wildfire behavior and susceptibility. There is a need for baseline information on the ecological role of mistletoe, especially regarding its inclusion in fire hazard management decisions. Increasing use of prescribed fire as a restoration tool requires that we understand how mistletoe alters fire behavior. It may be necessary to treat infested stands differently when attempting to mimic natural disturbances such as fire.

Findings and Status:  Live and dead fuel compositions were inventoried in 14 plots and at the base of 41 mature ponderosa pine trees representing a range of mistletoe infection and brooming levels. Fuel inventories were completed in the summer of 2003, prior to prescribed burning in fall 2003, and again in the spring of 2004. The results presented below include only plot-level analyses of dead fuels. These results are preliminary and should not be considered final or complete. Further analyses at both the tree and plot level will be completed in 2005.

There was no significant difference in fuel biomass between infested and healthy plots, neither prior to nor following prescribed burning. Changes in fuel composition as a result of prescribed burning did differ among infection levels.

Prescribed burns were generally successful at reducing dead fuel on the forest floor, especially fine fuels (1-hour and 10-hour classifications). Fine fuels were reduced by at least one-half in twelve of fourteen plots. Healthy plots experienced a 61% reduction in fuels on average, compared to only 46% for infested plots. Larger fuels (100 and 1000-hour) increased in half of the study plots following prescribed burning. An increase in coarse woody debris resulted from several trees falling over following intense basal damage. Increases in large fuels did not differ significantly between plots with or without mistletoe. Large, rotten logs were significantly reduced in the healthy plots, despite these plots burning at lower temperatures.

Prescribed burns significantly reduced litter and duff biomass (p<0.05). Litter was reduced by more than two-thirds on all but one plot. Duff was reduced by more than one-half in all healthy plots. Changes in duff biomass were not significant for infested plots alone (p>0.1); large amounts of duff were consumed in some of the infested plots, but other plots with mistletoe experienced almost no change in duff biomass during prescribed burns.

Ordination (redundancy analysis) of biomass of litter, duff, and total coarse woody fuels with respect to stand characteristics reveal weak correlations between mistletoe abundance and fuel biomass. Variation in fuel distribution is more strongly influenced by basal area and density of ponderosa pine and white fir than by mistletoe infection.

For this study, were one or more specimens collected and removed from the park but not destroyed during analyses? Yes

Funding provided this reporting year by NPS: 0

Funding provided this reporting year by other sources: 0

Full name of college or university:  n/a

Annual funding provided by NPS to university or college this reporting year: 0

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