Old- Growth Classification

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Most of the remaining 14,623 acres of old-growth forest in the Cedar River Municipal Watershed are 200 to 300 years old and occur at higher elevations (>2,500 feet) on steeper slopes in the upper watershed. Yet, there are also stands with trees as old as 800 years that occur in the upper elevation valleys. As a result, there is considerable variability in the characteristics and structural complexity of the remaining old-growth forest in the municipal watershed.

As part of the Habitat Conservation Plan, scientists at Seattle Public Utilities (SPU) have conducted studies to classify the remaining old-growth forest in terms of structural variation, particularly for purposes of determining habitat value for old-growth dependent wildlife species.

A study in 2007 focused on identifying potential habitat for northern spotted owl and marbled murrelet. From this study, 36% of remaining old-growth was classified as suitable for northern spotted owl nesting and the other 64% suitable for foraging. There were no old-growth areas found to have high suitability for marbled murrelet nesting, but 58 % of the remaining old-growth had medium and 38% had low suitability for nesting.

Another study in 2012 examined the range of variation in structural attributes measured on the ground and from remotely-sensed LiDAR data. We found that most old growth is generally less well-developed structurally than typical Douglas-fir old growth in the western Cascades. This is to be expected since most of the old growth is in higher elevation areas within the Pacific silver fir zone. However, there were some old-growth forests that are comparable to the structurally most developed Douglas-fir dominated old-growth stands in the western Cascades. There was no apparent watershed-scale pattern of structural complexity in old growth. Rather, different levels of structural complexity occur in mosaics in most old-growth patches, indicating that the old-growth habitat is variable even at small scales.

Reports and Publications

Kane, V.R., R.J. McGaughey, J.D. Bakker, R.F. Gersonde, L.A. Lutz, and J.F. Franklin. 2010a. Comparison between field and LiDAR-based measures of stand structural complexity. Canadian Journal of Forest Research 40: 761-773.

Kane, V.R., J.D. Bakker, R.J. McGaughey, L.A. Lutz, R.F. Gersonde, and J.F. Franklin. 2010b. Examining conifer canopy structural complexity across forest ages and elevations with LiDAR data. Canadian Journal of Forest Research 40: 774-787.

Kane, V.R., R.F. Gersonde, L.A. Lutz, R.J. McGaughey, J.D. Bakker, and J.F. Franklin. 2011. Patch dynamics and the development of structural and spatial heterogeneity in Pacific Northwest Forests. Canadian Journal of Forest Research 41: 2276-2291.