Abstract
Cambium injury is an important factor in post-fire tree survival. Measurements that quantify the degree of bark charring on tree stems after fire are often used as surrogates for direct cambium injury because they are relatively easy to assign and are non-destructive. However, bark char codes based on these measurements have been inadequately tested to determine how well they relate to live or dead cambium. Methods for assessing cambium injury through direct sampling have also been questioned as a potential factor for increasing tree mortality. In this study we used data collected from 11 wildfires and 6 prescribed fires in California, Idaho, Montana, and Wyoming to develop a relationship between bark char codes and cambium status for 14 coniferous species. Burned trees were assessed at groundline for bark char severity on each bole quadrant and then sampled at the center of each quadrant to determine cambium status (live or dead). We found that the moderate and deep bark char codes were strongly associated with dead cambium for thin-bark species: lodgepole pine (Pinus contorta), whitebark pine (P. albicaulis), western white pine (P. monticola), western redcedar (Thuja plicata), Engelmann spruce (Picea engelmannii), western hemlock (Tsuga heterophylla), and subalpine fir (Abies lasiocarpa). However, bark char codes were somewhat inaccurate in predicting cambium status of the thicker-bark species of white fir (Abies concolor), incense cedar (Calocedrus decurrens), ponderosa pine (Pinus ponderosa), Jeffrey pine (P. jeffreyi), Douglas-fir (Pseudotsuga menziesii), western larch (Larix occidentalis), and sugar pine (P. lambertiana). We also evaluated the effect of direct cambium sampling on ponderosa pine tree mortality in eastern Montana. Mortality rates were equivalent for eastern Montana ponderosa pines with and without cambium sampling. Our results support using bark char codes as surrogates for cambium sampling in tree species with thin bark, but bark char codes for thick-bark species, especially the moderate char code, are often not accurate fire-injury variables, as they do not correlate well with cambium status.
Highlights
A tree’s ability to survive after fire largely depends on the level of injury sustained to the crown, bole, and roots (Ryan 1982, Filip et al 2007)
Ryan (1982) first developed categories of bark char severity to indicate stem injury resulting from fire, but he cautioned that these codes should only be used in conjunction with direct cambium sampling
While these studies reported that various measures of bark char were statistically significant variables for predicting delayed tree mortality, it is unknown how well bark char relates to cambium injury for many species (Fowler and Sieg 2004)
Summary
We collected fire-injury data from mixedseverity burned areas in 11 wildfires and 6 prescribed fires in California, Idaho, Montana, and Wyoming within one year of the fires (Table 1). All fires except the Power, Oops, Canyon Creek, Slowey, Air Patrol, Brewer, and Early Bird fires (Table 2) have been reported elsewhere and will not be described here. The Power Fire began approximately 44 km east of Pioneer, California, in Amador County, and burned areas of private timberlands and the Eldorado National Forest, including a small portion of the Mokelumne Wilderness. It was primarily a moderate surface fire with some pockets of individual tree torching. The Early Bird, Air Patrol, and Brewer Fires in eastern Montana were ignited by lightning. The Slowey Fire was a prescribed burn set to reduce fuel hazards and restore wildlife
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