Presenter/s: Deanna (Dede) Olson
Symposium Session: 2024 - 11 Restoring Habitat for Overlooked Aquatic Organisms
Topics covered: amphibians
ABSTRACT
Moist coniferous forest ecosystems in the US Pacific Northwest are managed for multiple aims including wood production, restoration and conservation of late-successional and old-growth (LSOG) forest species and habitats, and mitigations to reduce adverse effects of natural disturbances. Management approaches for aquatic-riparian ecosystems within these forests have focused on retention of water quality and quantity while maintaining habitats for aquatic species. Headwater basins in these forests are a transitional zone between uppermost fish distributions and reaches dominated by stream-associated amphibians. The Density Management and Riparian Buffer Study of Western Oregon is a Before/After/Control/Impact experiment characterizing headwater aquatic-vertebrate assemblages and habitats in managed forests and assessing effects on them of alternative streamside buffer widths with upland thinning for forest restoration. After 30 years of implementation, results provide insights for application of riparian buffer widths for system restoration, conservation, and risk mitigation.
We examined aquatic-vertebrate densities and habitats at 43 stream reaches across 8 study sites with data from pretreatment surveys and surveys in years 1, 2, 5, and 10 after a first thinning treatment, followed by years 1, 5, and 11-12 after a second thinning treatment, along with unthinned controls. Streamside buffer-width treatments included the one site-potential tree-height buffer of the federal Northwest Forest Plan (~70 m; 1-tree), and two narrower buffers – a streamside retention buffer (6 m) and a variable-width buffer (minimum width 15 m). Composite animal and habitat characterization separated two unique headwater ecosystems within these forests: distinct low- and high-flow systems and associated fauna which may warrant discrete management consideration for conservation. No significant buffer-width effects on were detected overall, yet selected sites showed increased coastal giant salamander densities and down wood inputs in reaches with 1-tree buffers. With the value of 1-tree buffers apparent in some cases for both LSOG animals and habitats, a mixed-width buffer approach warrants consideration in heterogeneous headwater ecosystems for both restoration and conservation aims, and as a trade-off with both episodic winter-storm treefall events and summer-wildfire risk, as increased down wood in 1-tree buffers was tied to a single-year winter storm event over the 30-year study and is a fuels consideration for subsequent summer fire risk.