Density Management and Riparian Buffer Study
Investigation of aquatic-dependent vertebrates within
and along headwater streams in managed forests of
western Oregon.
Research Description:
The Density Management and Riparian Buffer Study of Western Oregon is the only experimental study of the combined effects of alternative forest thinning designs and riparian buffer widths in the U.S. northwest. Several coordinated projects are investigating the utility of thinning young managed forest stands with stream buffers for: 1) acceleration of late-successional forest structure; 2) sustained wood production; 3) carbon sequestration; and 4) retention of aquatic conservation strategy objectives, including stream habitats for sensitive aquatic species. In particular, my pretreatment analyses have advanced the characterization of headwater stream systems and aquatic vertebrate fauna, I am monitoring these stream reaches in years 1, 2, 5, and 10 post-treatment to examine the effects of thinning and stream buffers on a variety of aquatic habitat attributes and species, and I am currently investigating the effects of a second-entry thinning with our original riparian buffers. New directions are examining the interaction of climate change and the thinning-and-buffer treatments on headwater forest resources.
Key Findings:
Figure 1
Headwater Stream Habitats
Spatially-intermittent streams are the most frequent stream reach type in our sample. These small streams are only a meter or two in width and have discontinuous surface flow during both the spring rainy season and the summer dry season. Intermittent streams and their streamside riparian zones are not well understood, and our studies are advancing knowledge of their ecology and management in managed forests. In addition, we are finding an abundance of down wood within our stream channels, and we are tracking down-wood patterns 10-years post-thinning and after a 2nd entry of thinning. Our case study analyses have documented more down wood near headwater streams than upslope.
Figure 1. Headwater stream in western Oregon. Photo by L. Ellenburg, USFS.
Amphibians: Headwater ‘Funnels’
Figure 3
Figure 2
We have found 13 species of amphibians and 3 fish taxa occurring within and along headwater streams, although some species are only rarely detected. These species are ordered into different assemblages that are spatially segregated by habitat type: perennial streams are dominated by fishes and coastal giant salamanders; intermittent streams are dominated by torrent salamanders, which are Oregon sensitive species; Dunn’s and western red-backed salamanders dominate stream banks; and a terrestrial salamander assemblage occurs upslope, associated with habitat features such as down wood and coarse substrates. Amphibians are most abundant within 2 m of streams, suggesting that headwater riparian zones are spatially compressed. A case study revealed relatively restricted movements of salamanders in uplands, and more frequent movements of animals along streamside zones. Headwater riparian zones appear to ‘funnel’ animals along narrow near-stream corridors.
Figure 2. Headwater drainage with pie charts showing species assemblages. Graphic by K. Ronnenberg.
Figure 3. Southern torrent salamander, Rhyacotriton variegatus. Photo by W. P. Leonard.
Figure 4
Thinning: A Benign Disturbance
Thinning from 200-350 trees per acre (tpa; ~500-850 trees per hectare [tph]) to 80 tpa (~200 tph) appears to be a relatively benign disturbance relative to headwater aquatic-vertebrate assemblages and stream habitats. Amphibians have persisted at sites after thinning-with-buffers, and to date, reduced abundances have been observed in only a few instances for some upland salamanders. Site-specific effects of thinning in uplands appear to be affected by current conditions, with adverse effects of thinning apparently being mitigated by the abundance of large down wood within stands, a ‘legacy’ from the initial clearcut logging that occurred over 60 years ago at some of our study sites, and the occurrence of coarse substrates.
Figure 4. Upland thinning treatment, Green Peak study site. Photo by P. Anderson, USFS.
Figure 5
Headwater Connectivity: Up and Over
Our headwater studies and the thinning and buffer designs that we are examining have application to management of headwater connectivity areas. Amphibians occurring within and along headwater streams have terrestrial dispersal life stages, with over-ridge dispersal needed to maintain gene flow among sub-populations in adjacent drainages. Headwater linkage area designs that extend riparian buffers and connect them up and over ridgelines to neighboring drainages may reduce fragmentation of these habitats and populations in managed forests. ‘Chains’ of connectivity can be envisioned with riparian and overland links. Green tree retention in these linkage areas and down wood placement with log orientation from ridgelines toward headwater streams may aid overland dispersal of low-mobility species, including amphibians and a variety of other ground-dwelling taxonomic groups (mollusks, lichens, bryophytes, fungi, small mammals). Although retained stands may anchor habitats in headwater linkage areas, our thinning designs with leave islands and down wood management might be considered as an effective management alternative for overland chains.
Figure 5. Linkage area designs between headwater streams, using down wood and green tree retention.
Graphic by K. Ronnenberg.
Short Summaries
Headwater stream flow and climate variation: reduced surface stream flow in warm, dry years, with further reductions projected in the future (Olson and Burton 2019)
Water temperatures at a case study site: variable stream temperatures with site conditions but lack of treatment effects (Leach et al. 2017)
Down Wood Spatial and Temporal Patterns in Headwater Streams: most instream down wood comes from trees within 15 m of stream (Burton et al. 2016)
Utility of Cover Boards to Assess Plethodontid Ecology in Headwater Drainages: most salamander movements were within 15-m of streams (Olson and Kluber 2014)
5-year and 10-year post-treatment effects of buffers and thinning on stream fauna: reduced Dunn’s salamander densities along streams with narrow buffers (Olson, Leirness et al. 2014)
Initial effects of a 2nd thinning with buffers: reduced Dunn’s and torrent salamanders with the narrowest buffers (Olson and Burton 2014)
Upland thinning affects riparian tree growth: tree-growth edge effect into no-entry buffer (Ruzicka et al. 2014, Ruzicka et al. 2017)
Upland vegetation: carbon and biodiversity tradeoffs (Burton et al. 2013)
Coming Soon
5-year post-treatment effects of 2nd thinning with buffers: increased abundance of torrent salamanders, giant salamanders and sculpins with a one site-potential tree-height buffer (Olson and Ares, submitted)
10- to 12-year data collection of post-treatment effects of 2nd thinning with buffer is ongoing
Selected Publications:
Burton, J.I., D.H. Olson, and K.J. Puettmann. 2016. Effects of riparian buffer width on down wood loading in headwater streams after repeated forest thinning. Forest Ecology and Management 372: 247–257.
Burton, J.I., A. Ares, D.H. Olson, and K.J. Puettmann. 2013. Management trade-off between aboveground carbon storage and understory plant species richness in temperate forests. Ecological Applications 23(6): 1297-1310.
Emel, S.L., D.H. Olson, L.L. Knowles, and A. Storfer. 2019. Comparative landscape genetics of two endemic torrent salamander species, Rhyacotriton kezeri and R. variegatus: implications for forest management and species conservation Conservation Genetics 20: 801-815. https://doi.org/10.1007/s10592-019-01172-6
Kluber, M.R., D.H. Olson, and K.J. Puettmann. 2009. Thermal profiles of downed wood under different forest management regimes in the Oregon Coast Range and their potential impact on plethodontid salamander habitat. Northwest Science 83:25-34.
Kluber, M.R., D.H. Olson, and K.J. Puettmann. 2008. Amphibian distributions in riparian and upslope areas and their habitat associations on managed forest landscapes of the Oregon Coast Range. Forest Ecology and Management 256:529-535.
Leach, J.A., D.H. Olson, P.D. Anderson, and B.N.I. Eskelson. 2017. Spatial and seasonal variability of forested headwater stream temperatures in western Oregon, USA. Aquatic Sciences 79: 291-307. doi:10.1007/s00027-016-0497-9. Supplemental material.
Olson, D.H. 2013. Riparian buffers and thinning in headwater drainages in western Oregon: Effects on amphibians. 2013. In: Anderson, P.D. and K.L. Ronnenberg, eds. Density management in the 21st century: west side story. General Technical Report PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 148-162. Link to the full GTR at http://www.fs.fed.us/pnw/pubs/pnw_gtr880.pdf
Olson, D.H., and A. Ares. 2022. Riparian buffer effects on headwater-stream vertebrates and habitats five years after a second upland forest thinning in western Oregon, USA. Forest Ecology and Management 509:120067.Link to article in Treesearch.
Olson, D.H. and K.M. Burnett. 2013. Geometry of forest landscape connectivity: Pathways for persistence. In: Anderson, P.D. and K.L. Ronnenberg, eds. Density management in the 21st century: west side story. General Technical Report PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 220-238. Link to the full GTR at http://www.fs.fed.us/pnw/pubs/pnw_gtr880.pdf
Olson, D.H. and K.M. Burnett. 2009. Design and management of linkage areas across headwater drainages to conserve biodiversity in forest ecosystems. Forest Ecology and Management 259S:S117-S126.
Olson, D.H., and J.I. Burton. 2020. Climate associations with headwater streamflow in managed forests over 16 years and projections of future dry headwater stream channels. Pp. 161-188 in G. Sun, K. Bishop, S. Ferraz, and J. Jones (Eds.), Managing Forests and Water for People under a Changing Environment, Open Access, MDPI Books, Basel, Switzerland; SBN 978-3-03928-823-6 (Pbk); ISBN 978-3-03928-824-3 (PDF); https://doi.org/10.3390/books978-3-03928-824-3 (registering DOI); https://www.mdpi.com/books/pdfview/book/2270; Accessed 15 May 2020.
Olson, D.H., and J.I. Burton. 2019. Climate associations with headwater streamflow in managed forests over 16 years and projections of future dry headwater stream channels. Forests 10: 968; https://doi.org/10.3390/f10110968; 28 p
Olson, D.H. and J.I. Burton. 2014. Near-term effects of repeated thinning with riparian buffers on headwater stream vertebrates and habitats in Oregon, USA. Forests 5: 2703-2729. doi:10.3390/f5112703
Olson, D.H., and M.R. Kluber. 2014. Plethodontid salamander distributions in managed forest headwaters in western Oregon. Herpetological Conservation and Biology 9(1): 76-96.
Olson, D.H., and R. Mazza. 2015. Heed the head: buffer benefits along headwater streams. Science Findings 178.
Olson, D.H., J.B. Leirness, P.G. Cunningham, and E.A. Steel. 2014. Riparian buffers and forest thinning: Effects on headwater vertebrates 10 years after thinning. Forest Ecology and Management 321: 81-93.
Olson, D.H., S.S. Chan, and C.R. Thompson. 2002. Riparian buffers and thinning designs in western Oregon headwaters accomplish multiple resource objectives. Pp. 81-91 in: Johnson, A.C., R.W. Haynes, and R.A Monserud (eds.). Congruent Management of Multiple Resources: Proceedings from the Wood Compatibility Workshop; December 5-7, 2001, Skamania Lodge, Stevenson, WA. Gen. Tech. Rep. PNW-GTR-563. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station.
Roon, D.A., J.B. Dunham, J.R. Bellmore, D.H. Olson, and B.C. Harvey. 2022. Influence of riparian thinning on trophic pathways supporting stream food webs in forested watersheds. Ecosphere 13(9):e4219. Doi: 10.1002/ecs2.4219. Link to journal: https://doi.org/10.1002/ecs2.4219 Link to paper on Treesearch: https://www.fs.usda.gov/research/treesearch/65429
Rundio, D.E. and D.H. Olson. 2007. Influence of headwater site conditions and riparian buffers on terrestrial salamander response to forest thinning. Forest Science 53(2):320-330.
Rundio, D.E., and D.H. Olson. 2003. Antipredator defenses of larval Pacific giant salamander (Dicamptodon tenebrosus) against cutthroat trout (Oncorhynchus clarki). Copeia 2003(2): 392-397.
Rundio, D.E., and D.H. Olson. 2001. Palatability of Southern Torrent Salamander (Rhyacotriton variegatus) larvae to Pacific Giant Salamander (Dicamptodon tenebrosus) larvae. Journal of Herpetology 35(1): 133-136.
Rundio, D.H., G. Weaver. 2007.
Ruzicka, K.J., Jr., K.J. Puettmann, and D.H. Olson. 2014. Management of riparian buffers: upslope thinning with downslope impacts. Forest Science 60(5): 881-892. http://dx.doi.org/10.5849/forsci.13-107
Ruzicka, K.J. Jr., D.H. Olson, K.J. Puettmann. 2013. The intertwining paths of the Density Management and Riparian Buffer Study and the Northwest Forest Plan. In: Anderson, P.D. and K.L. Ronnenberg, eds. Density management in the 21st century: west side story. General Technical Report PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 10-21. Link to the full GTR at http://www.fs.fed.us/pnw/pubs/pnw_gtr880.pdf
Rykken, J.J, A.R. Moldenke, and D.H. Olson. 2007. Headwater riparian forest-floor invertebrate communities associated with alternative forest management practices. Ecological Applications 17(4):1168-1183.
Sheridan, C.D., and D.H. Olson. 2003. Amphibian assemblages in zero-order basins in the Oregon Coast Range. Canadian Journal of Forest Research 33: 1452-1477.