28949 – Seasonal Effects of Prescribed Fire on Ponderosa Pine

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

Seasonal Effects of Prescribed Fire on Ponderosa Pine


Report Number: 28949

Permit Number: unknown

Date Received: Jul 30, 2004

Reporting Year: 2004

Principal Investigator: Dr James Agee, College of Forest Resources, University of Washington, Seattle, WA

Park-assigned Study Id. # unknown

Permit Expiration Date: Jul 30, 2005

Permit Start Date: Jul 30, 2005

Study Starting Date: Jun 15, 2001

Study Ending Date: Sep 30, 2004

Study Status: Completed

Activity Type: Research

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

Objectives: The objectives of this study were to quantify the effects of spring versus fall burning on standard fire response variables such as fuel consumption and forest structure, and also to quantify the effects of such fires on vigor and mortality of large ponderosa pine, the most important structural element in these mixed conifer forests.

Findings and Status:  Study results at this time reflect the effects of burning up to one year after treatment. Since fire effects appear to persist for several years after burning, the current analysis should not be considered final, but simply represents a report on the initial fire effects.

Fire behavior and fuel

Spring burns affected between 19 and 57% of the area of various units, with a mean value of 37%. Fire behavior was generally of low intensity. Fall burns were lit on October 9th and 10th, 2002. Compared with spring burns, fire behavior was more intense during the fall burns, and covered 64-86% of units. Dead woody fuel weights between treatment groups (spring burning, fall burning, controls) were similar, averaging 151 Mg/ha. On average, we measured a fuel reduction of 27.0 Mg/ha following spring burning, a reduction of 72.8 Mg/ha following fall burning, and an increase of 16.8 Mg/ha in controls (the latter is interpreted as measurement error, primarily in litter and duff biomass).

Forest structure

Burning significantly increased crown height, by an average of 0.8 m in spring burn units and 2.7 m in fall burn units. Only fall burns had a significant effect on canopy closure, where an average decrease of 2.1% in canopy closure was measured. Before burning, no ponderosa pine seedlings were present in any plots. One season after treatment, one spring burn unit and 3 fall burn units had new ponderosa pine seedlings, while there were still none in any control units.

Ponderosa pine population

A total of 1725 large pines were identified, tagged and measured for DBH and crown vigor class. Average diameter was 94.4 cm, and size-classes were normally distributed, reflecting an almost complete lack of recruitment of younger trees. One year after the burning treatments, 54 ponderosa pines (3.1%) had died. Ultimate causes of mortality include fire alone (19 trees), insects alone (5 trees), fire and insects (26 trees), and windthrow or other causes (4 trees). Logistic regression modeling on the pine population revealed that overall, mortality was higher in burn units than controls, and higher in fall burns than spring burns. In addition, mortality increased with decreasing crown vigor: the combination of fall burning and very low crown vigor was particularly lethal, killing over 20% of the trees in that group.

Ponderosa pine bark beetle resistance

Previous studies have shown that oleoresin exudation flow volume (OEF) and exudation pressure (OEP) can be indicative of a trees resistance to bark beetle attacks. After burning, resin measurements were successfully taken in 2002 (twice in spring burn units, once in fall burn units), and again in 2003 (twice in both spring and fall burn units). Immediately after burning (July 2002 for spring burns, October 2002 for fall burns), OEP and OEF were not significantly different between burn units and controls. However, at other measurement times, resin pressure and flow were higher on trees in burned units than in controls. Values were not always statistically different between treatment groups, however, or between trees in spring burn and fall burn units. Nevertheless, a clear pattern emerged that resin volume and pressure were higher in burned trees than in unburned (control) trees in the immediate months following treatment. This most likely reflects the effects of physical injury from the fires on the trees? boles, as wounding has been documented to cause increased resin production in a number of pine species.
Overall, fall burns were more effective at meeting the burning objectives with respect to changes in fuel loads, forest structure, and promoting ponderosa pine regeneration. However, fall burns did result in considerably higher mortality of large pines, apparently both from immediate fire effects as well as from bark beetle attacks in the months following the burns.

For this study, were one or more specimens collected and removed from the park but not destroyed during analyses? No

Funding provided this reporting year by NPS: 0

Funding provided this reporting year by other sources: 40000

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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