Ecology and development of Douglas-fir seedlings and associated plant species in a Coast Range plantation

Abstract

On an average site in northern coastal California, a tanoak-mixed shrub community was given several treatments (manual release one, two, and three times; a combination chainsaw and cut surface chemical treatment; two foliar chemicals; and a tank mix of the two chemicals) to study its development over an 11-year period in both a broadcast-burned (untreated control) and released (treated) condition. The chemicals were 2,4-D, Garlon 3A, and Garlon 4, each applied two times. In addition to Douglas-fir, data are presented individually for the four most abundant and well distributed species (tanoak, hairy manzanita, huckleberries, and rhododendron), and for these plus two more of the tallest and most abundant (but poorly distributed) species (snowbrush, elderberry) combined. At the study's end in 1991, combined shrubs in the control had a mean density of 4,733 plants per acre, foliar cover of 16,800 ft2 per acre, and height of 9.5 feet. In contrast, combined shrubs in one of the most effective treatments for controlling them-2,4-D-had a mean density of 2,000 plants per acre, foliar cover of 2,600 ft2 per acre and height of 5.5 feet at the end of the study. Here, mean Douglas-fir diameter was 4.0 inches at 12 inches above mean ground line, height averaged 18.7 feet, and mean foliar cover was 34,800 ft2 per acre. The cost (including chemical) was $77 per acre. The biological and economical data in this paper provide the ecosystem manager, wildlife biologist, and fuels manager with knowledge on how to attain plant communities with different density and development potentials, and the cost of creating them.