Edge Effects and the Effective Size of Old-Growth Coast Redwood Preserves
Dr. William Russell, Dr. Joe McBride, and Ky Carnell have found that old-growth coast redwood forest reserves with areas larger in proportion to the length of their perimeters suffer fewer negative effects from exposed edges.
With less than 5% of the pre-settlement range of old-growth redwoods still standing, ecologists and forest managers have to worry about encroachments from the outside on relatively small patches of forest. Before European settlers arrived, coastal redwood forests stood as large continuous tracts of very tall trees where the inner trees and their ecosystems were sheltered by outer ones. Now, smaller old-growth reserves with more vulnerable perimeters are in danger of excessive wear and tear from exposure to heavy winds, exotic plant and animal species invasions, and distorted levels of solar radiation. An especially serious problem is what ecologists call windthrow—whipping winds toppling ancient old-growth trees. Two solutions to this problem, the researchers of this study report, include making reserves bigger and surrounding them by buffer zones, bands of mature second-growth trees that serve as copper does around a garden plant, to mitigate the encroachment of unwanted outside invaders.
Russell, McBride, and Carnell investigated how past clear-cut harvests around old-growth stands in Redwood National Park have affected important characteristics of the forest, including the amount of solar radiation and the diversity of plant and animal species. Unlike past studies on edge effects in which researchers have considered only one variable, Russell and his co-workers measured fourteen. All of the variables showed improved ecological conditions as one travels further from the edge and closer to the core of the forest. They found, for example, a higher diversity of plant species and fewer red alder trees, which are rare in undisturbed redwood forests, closer to the core.
These results are a good indication that smaller forests and forests with thinner buffers suffer more negative edge effects. The researchers suggest buffers as wide as three times the height of trees at the center of the reserve (i.e. 300 ft). This study is a crucial addition to the information forest managers have to draw from when making management decisions in or near old-growth reserves.
–The researchers’ report was published in the USDA Forest Service Proceedings RMRS-P-15-VOL-3, 2000 under the title “Edge Effects and the Effective Size of Old-Growth Coast Redwood Preserves”