Condition of live fire-scarred ponderosa pine twenty-one years after removing partial cross-sections
Ponderosa pine is widely distributed in fire-dependent ecosystems across western North America. Some individuals of this long-lived species have survived repeated wounding by frequent, low-severity fires and have a cavity surrounded by fire scars, termed a catface. Our understanding of the historical role of surface fires in ponderosa pine ecosystems is based on the records of fire preserved in these catfaces. This record has been extracted from many dead ponderosa pine trees, but it has also been extracted from thousands of live trees across the western U.S. by removing a partial cross section from one or both sides of the catface with a chain saw. Concern over the effects of removing partial cross sections may limit live-tree sampling and consequently restrict the development of science-based management. Casual observation indicates that sampling wounds generally do not kill trees. However, the effect on tree mortality of removing fire-scarred partial cross sections is poorly quantified. Over the past twenty years, we have been monitoring mortality rates for ponderosa pine trees in the Blue Mountains of northeastern Oregon since we removed a fire-scarred partial cross-section from them. We originally surveyed 138 trees that were alive when we sampled them in 1994-1995 and 387 similarly sized, unsampled living neighbor trees of the same species. The annual mortality rate for sectioned trees from 1994-1995 to 2015 was 2.4% compared to 1.8% for the neighbor trees.
However, many of the trees that died between 2000 and 2005 were likely killed by two prescribed fires. Excluding all trees in the plots burned by these fires regardless of whether they died or not, fire-scar sampling did not have a significant effect on tree mortality during the first two decades after sampling; the annual mortality rate for sectioned trees was 1.6% compared to 1.3% for neighbor trees. We suggest that sampling live, fire-scarred ponderosa pine trees remains an important and generally non-lethal method of obtaining information about historical fires that can supplement the information obtained from dead fire-scarred trees.