December 18, 2009
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Defects (or broken tops, reiterated tops, and cavities) are considered important habitat features in old-growth trees and snags. We know that marbled murrelets rely on large limbs to lay their eggs and raise their chicks. Suitable limbs come with age, and growth can be hastened when tops get broken off. Bats roost in "goose pens" or large hollows, guano littering the cavity floor. Wood rats also take shelter, constructing nests inside large basal hollows. Black bears have been known to take up residence in such trees. Snags are commonly thought to be important to wildlife for nesting, roosting, and foraging, and they are also utilized for courtship display, food caching, perches, and plucking posts. And, of course, downed logs provide a rich ecosystem of their own, one that changes depending on whether the trees fall vertically down slopes, horizontally across them, or they land in or across streams.
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Basal hollows or interior cavities are formed from a combination of fire and fungal activity. They are usually initiated when hot fires expose the heartwood. Subsequent fires along with fungi cause the core of the tree to decay and hollow out. The size and shape of these cavities vary, some reaching dozens of vertical feet within the interior of the tree, others providing mini-caverns with just a window to the outside. The common factor, however, is that all need fire to initiate the cavity-forming process.
Scientific studies show that the most common ignitions of coast redwood fires were from Native Americans, who burned areas to increase efficiency of food gathering, clear the way for travel, increase food production, and reduce acorn-eating insects. One additional possible motivation would have been to avoid bears or other large mammals hidden in the understory. Fires are commonly set in African landscapes for just this reason. Early ranchers, farmers, and loggers also burned vast tracts during the 19th and 20th centuries. Lightning fires are particularly rare in the coast redwood region due to topography and moisture content--relevant factors typically accompanying lightning strikes.
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Even with the spate of recent wildland fires in the Santa Cruz Mountains, burning more than 13,000 acres, cavity creation and retention seem to be at risk. In the Summit Fire (2008), at least one large old tree with a basal hollow was labeled a "killer tree" and felled. This stem stood alone upslope of a county road since slash burning in the area (maybe 100 years ago), sporting a large basal cavity on its upslope side. While the latest fire did minimal damage to the tree's integrity, it was suddenly seen as a threat to public safety and was killed, something fire was unable to do.
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Will we or won't we? Will human concerns continue to take precedence over retention and creation of bio-diverse ecosystems, or will we recognize that such complexity is for the good of us all.
Jodi Frediani became involved in forest and watershed protection in 1980 when 30 acres of old-growth redwoods were proposed for logging adjacent to her spring and fronting a half mile along Majors Creek in Santa Cruz County's Bonny Doon area. Through her efforts, that forest is now protected as state park land, and her spring continues to produce outstanding clean, clear water. Jodi has remained a strong voice for forest and watershed protection, focusing on timber harvest impacts, particularly those affecting old growth and riparian habitat. Jodi's column in FRN focuses on the effects of fire in forested ecosystems.
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TOC for Forest & River News, Winter 2009