Document: PHI-3-68-3

Cambial heat resistance in understory trees in Californian mixed conifer forests .

VAN MANTGEM, P.* ^1,2 and M.W.SCHWARTZ ²

USGS Western Regional Research Center, Sequoia and Kings Canyon Field Station, Three Rivers, CA, USA ¹
University of California, Davis, CA, USA ²

Abstract:
An essential component to models of forest response to fire is an assessment of fire-caused cambial damage. Cambial heat resistance has been traditionally measured in large-sized overstory trees with thick bark, although juvenile trees have thinner bark and therefore more sensitive to fire. We undertook this study to determine if current models of heat transfer are applicable to small-sized trees. We performed this work on four common species in mixed conifer forests of the Sierra Nevada Mountains, California; white fir (Abies concolor), incense cedar (Calocedrus decurrens), ponderosa pine (Pinus ponderosa) and douglas fir (Pseudotsuga menziesii). We found the allometric relationship between bole diameter and bark thickness for each species to be strongly linear (p<0.01), even for very small sized trees (5 cm dbh). White fir had significantly thinner bark (p<0.05) across the range of measured tree sizes than any of the other species. Our findings from experimental fire resistance trials are in agreement with current models in so far as bark thickness alone is the crucial determinant of cambial heat resistance. However, between species differences are large and best explained in terms of species specific differences in bark moisture and density. Experimental trials also demonstrate that small-sized trees are more resistant to heating than is expected from existing models. Differences between observed and expected rates of cambial heating are explained by differences in bark anatomy between large and small sized trees.

Keywords: fire, forest structure, disturbance

This abstract is being presented at: 1:30 PM in session:
Oral Session #35: Fire Ecology.