Fire Enhances Whitebark Pine Seedling Establishment, Survival, and Growth

Judy L Perkins

doi:10.4996/fireecology.1102084

Abstract

AbstractPeriodic fire is thought to improve whitebark pine (Pinus albicaulis Engelm.) regeneration by reducing competition and creating openings, but the mechanisms by which fire affects seedling establishment are poorly understood. I compared seedling vegetation production in adjacent sites, one last burned in 1880 and the other in 1988, to test the hypothesis that recent fire increases whitebark pine seedling growth. I experimentally tested effects of fire on seedling recruitment and growth by planting seeds in prescribed burned and nearby unburned sites. Experimental results showed nearly three times greater seed germination and seedling survival in recently prescribed burn plots. Seedling vegetation production in the 1880 and 1988 burn sites were measured using stem diameter and number of new needle bundles. Stem diameter was approximately 26 % greater after the more recent fire in the 1988 burn site, and new needle bundle production was approximately 40 % greater in this site relative to seedlings in the adjacent site that was last burned in 1880. Seedling growth, measured as both above- and belowground biomass, was approximately 57 % greater in a recently prescribed burn site relative to growth in an adjacent site that was unburned since 1910. Higher growth rates after prescribed fire corresponded with greater soil NO3− and soil-available P concentrations relative to unburned controls. However, high N concentrations in leaves of seedlings in unburned plots indicated that whitebark pine seedlings were not N-limited. Higher P, increased light availability, and earlier snowmelt after fire may be important factors in general postfire success of whitebark pine.

Highlights

Fire has shaped the structure and composition of forests throughout the northern Rocky Mountains (Habeck and Mutch 1973, Arno 1980, Agee 1993)
Comparing presettlement fire intervals with those since implementation of fire suppression policies, Brown et al (1994) found 2.4 times greater area burned in whitebark pine forests prior to fire suppression implementation in the Selway-Bitterroot Wilderness, Montana, USA
Seedling emergence from planted seeds at Beaver Ridge was much greater in the 1999 prescribed burn than in unburned forest, as was seedling survival, supporting the hypothesis that whitebark pine seedling recruitment is improved by fire

Summary

Introduction

Fire has shaped the structure and composition of forests throughout the northern Rocky Mountains (Habeck and Mutch 1973, Arno 1980, Agee 1993). A fire history study by Murray et al (1998), in subalpine forests of the West Big Hole Range spur of the Bitterroot Mountains, found increasing fire rotation intervals and fire severity in the post-settlement period, but with differences between east-side and west-side forests. Another fire history study in the Selway-Bitterroot Wilderness subalpine forests found an average presettlement fire return interval of 139 to 341 years (Kipfmueller 2003, Brunelle et al 2005)

Methods

Results

Conclusion