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Landscape patterns of pre-logging forest conditions in western Oregon

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Abstract

Using historical maps and tools provided by GJS, the spatial patterns of pre-logging forest conditions were quantified for three landscapes in western Oregon. The spatial coincidence between forest patches and topographic features was determined for slope gradient, aspect, elevation, and distance from streams. Pre-logging and current forest compositions were compared. The pre-logging landscape was dominated by old growth conifer with less than 10% consisting of early seral disturbance patches. Fire patches differed in size and shape between the Oregon Coast Range and the Oregon Cascade Range provinces. The size and variability of fire patches was larger in the Cascades, with shorter mean distances between fire patches and smaller perimeter to area ratios compared to fire patches in the Coast Range. Mean fire return intervals ranged from 170 to 292 years for the Oregon Coast Range. The most frequent patch size, regardless of patch type and study area, ranged from 100 to 999 ha. Forest patch types varied predictably by topographic feature for instance: fewer fire patches occurred on cool, moist aspects while more occurred on hot, dry, aspects. More burn area and less old growth conifer than expected occurred within 4000 m of major rivers. Late seral forest cover has declined dramatically across all three landscapes since 1933.

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