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From open to closed canopy: A century of change in Douglas-fir forest, Orcas Island, Washington

Northwest Science

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Abstract

During the past century, forest structure on south-facing slopes of Mount Constitution, Orcas Island, Washington, has changed from open-grown Douglas-fir (Pseudotsuga menziesii) mixed with prairie to primarily closed canopy forest. Density of open-grown Douglas-fir was approximately 7 stems/ha in the 19th century, while current density of trees in closed-canopy mature forest is 426 stems/ha. Trees occur at intermediate densities in areas of transition from savanna-like stands to closed canopy. Analysis of fire scars indicates that at least seven fires have occurred on Mount Constitution since 1736, but only one fire has occurred since 1893, which suggests that the recent increase in stem density has been caused primarily by fire exclusion. The high stem densities currently found in this landscape put the relict (120-350+ years old) Douglas-fir at risk from contemporary fires, which would likely be high-intensity crown fires. Given the transition of forests on Orcas Island during the 20th century to closed canopy structure, undisturbed open-grown coniferous forest is now extremely rare in the San Juan Islands.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
From open to closed canopy: A century of change in Douglas-fir forest, Orcas Island, Washington
Series title:
Northwest Science
Volume
75
Issue:
3
Year Published:
2001
Language:
English
Contributing office(s):
Forest and Rangeland Ecosystem Science Center
Description:
p. 262-269
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Northwest Science
First page:
262
Last page:
269
Number of Pages:
8