Holter Ridge Thinning Study, Redwood National Park: Preliminary Results of a Twenty-five Year Retrospective

Redwood National Park is comprised of large areas of overstocked stands resulting from harvest of the old-growth stands in the late 1940s to the 1970s. The Holter Ridge Thinning Study was initiated in 1978 to address this problem and examine the effects that thinning to varying spacing would have on forest development. Densities following thinning in 1979 ranged from 150 to 790 stems/acre with the controls ranging from 1170 to 3410 stems/acre. Mortality from 1979 to 2003 showed a positive relationship to the number of stems/acre post thinning. The number of redwood sprouts was positively related to the number of redwoods thinned. The percent cover of herbaceous and shrub species showed a negative exponential response to stand density while the change in percent cover from 1984 to 2003 for the shrubs also had a negative response to stand density. Stand structure differed between the control plots and the thinned plots. The control plots showed no stratification of the canopy, but the thinned groups showed stratification into an upper-canopy composed of redwood and Douglas-fir and a lower-canopy of redwood and tanoak. After twenty-five years the thinned stands show the initial signs of a mature forest while the controls still exhibit intense competition.