A Forest Management Success Story
By David Suddjian
Even a beginning student of natural history soon learns that snags – standing dead trees – have great value for birds. Locally, they are required by various woodpeckers, chickadees, titmice, nuthatches, some swallows, bluebirds, owls and some others. They are important nest and roost sites, and favored foraging sites for many species. A snag often provides for these basic life history needs for many years after the death of the tree, and may be used by a variety of species as long as it stands. It seems odd to say it, but when I visit forests my assessment of their quality for birds is always linked to the amount of death and decay. A healthy forest habitat offers many snags and downed logs, in addition to the live trees. I suspect this is not news for most readers.
The Santa Cruz Mountains are largely forested, but only small areas have escaped major changes from human land use. Forests managed for timber production, and forests around homes, tend to be poor in snags, especially those formed by the death of large, tall trees. Past forest management has reduced their natural recruitment, and actively removed snags for safety and to reduce fire hazard. However, as awareness of the value of snags for wildlife has increased, land managers have begun to seek to retain snag resources and occasionally to even create them.
Such was the case with a 50-acre timber harvest conducted at Long Ridge in the Soquel Demonstration State Forest (SDSF) in 1995. Forest manager (and Santa Cruz Bird Club member) Thom Sutfin decided to create snags from 10 large Douglas-fir trees. These trees, 34-50 inches in diameter at breast height, were to be killed by topping them at heights of 65-80 feet, and removing the live branches. I began a bird study the season before the logging to assess its effects on breeding bird populations. But I must admit, snag-lover though I am, that I had mixed feelings about those 10 firs. They were already important for birds. Large firs provide great foraging habitat for various insect and seed-eating birds, and are favored by several of our forest breeders, and they are relatively uncommon in the much of the forest of SDSF. Still, the snag creation program went forward as planned in summer 1995.
One thing was sure: it would take years for the 10 fir trees to decay sufficiently to attract foraging and cavity-nesting birds. How long that would be was unknown. I conducted breeding bird surveys subsequent to the logging in 1996, 1998 and 2001, one, three and six years after the harvest. I kept an eye on those snags.
In 1996 there was no outward evidence of decay in any of the trees, and I never saw any birds use the trees. In 1998 some decay was evident on half of the trees, as conks (Fomitopsis) and bracket fungus (Trichaptum) began to appear on the boles. But, there was no evidence of bird use during my visits. All that changed by 2001.
By this year all the trees had conks (numerous on most trees) and bracket fungus was growing on seven of 10. There was also evidence of the presence of carpenter ants and wood-boring beetles on all 10 trees. And presto, all ten trees had evidence of use by cavity-nesting birds! The evidence was impressive.
Eight trees had a total of 15 woodpecker holes. Four trees had a total of seven holes made by Pygmy Nuthatch. Altogether, nine trees had holes made by either woodpeckers or the nuthatch, and the only tree without completed holes had numerous incomplete holes. Most exciting, Pileated Woodpecker, a newcomer in the Soquel watershed, had been foraging on at least six trees. I was amazed to find 10 active nests of six species in the new snags: two Acorn Woodpecker nests, two Hairy Woodpecker nests, three Pygmy Nuthatch nests, and (best of all!) nests of Western Screech-Owl, Northern Pygmy-Owl and Northern Saw-whet Owl. The little owls were all using holes made previously by woodpeckers.
Clearly these large snags were a welcome resource for the birds of SDSF. Prior to their creation there were only two large conifer snags in the 50-acre harvest area, although snag resource needs were met to some degree by smaller hardwood snags. But even those were not numerous. Bird populations have changed accordingly. Acorn Woodpeckers, absent on the 1995 pre-harvest surveys, occurred at 67% of the survey stations in 2001 and have become the most numerous woodpecker in the study area. Hairy Woodpeckers occurred at 40% more stations by 2001 and numbers increased by 60%. Northern Flickers went from nearly absent in 1995 to being present at 50% of the stations in 2001. Pileated Woodpecker, although not nesting in the study area, was seen at two stations for the first time in 2001. Pygmy Nuthatch occurred at twice as many survey stations by 2001 and their numbers had doubled. I didn’t monitor the owls in previous years, so I cannot assess any changes for them, but I was most impressed to find three species nesting in the snags this year. Some of these population changes are probably not due entirely to the new snags, but all the cavities, active nests and foraging evidence certainly suggest the snag management program played a big role.