Tamm Review: Reforestation for resilience in dry western U.S. forests

Authors: NORTH, MALCOLM - Us Forest Service (FS); GREENE, DAVID - University Of California; STEVEN, JENS - University Of California; COPPOLETTA, MICHELLE - Us Forest Service (FS); KNAPP, ERIC - Us Forest Service (FS); LATIMER, ANDREW - University Of California; RESTAINO, CHRISTINA - University Of California; TOPKINS, RYAN - Us Forest Service (FS); WELCH, KEVIN - University Of California; YORK, ROB - University Of California; YOUNG, DEREK - University Of California; AXELSON, JODI - University Of California; BUCKLEY, TOM - University Of California; ESTES, BECKY - Us Forest Service (FS); HAGER, RACHEL - Utah State University; LONG, JONAHTHON - Us Forest Service (FS); MEYER, MACR - Us Forest Service (FS); Ostoja, Steven; SAFFORD, HUGH - Us Forest Service (FS); SHIVE, KRISTEN - University Of California; TUBBESING, CARMEN - University Of California; WALSH, DANA - Us Forest Service (FS); WERNER, CHHAYA - University Of California; WYRSCH, PETER - University Of California

Submitted to: Forest Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2018
Publication Date: 9/21/2018
Citation: North, M.A., Greene, D.M., Steven, J.T., Coppoletta, M.W., Knapp, E.J., Latimer, A.J., Restaino, C., Topkins, R.D., Welch, K., York, R.K., Young, D., Axelson, J., Buckley, T.J., Estes, B., Hager, R., Long, J.W., Meyer, M.D., Ostoja, S.M., Safford, H.D., Shive, K.L., Tubbesing, C.L., Walsh, D., Werner, C.M., Wyrsch, P.M. 2018. Tamm Review: Reforestation for resilience in dry western U.S. forests. Forest Ecology and Management. 432:209-224. https://doi.org/10.1016/j.foreco.2018.09.007.
DOI: https://doi.org/10.1016/j.foreco.2018.09.007

Interpretive Summary: In the past several decades we have seen a sharp increase in large, high severity wildfires and other climatically linked disturbances like prolonged drought and forest pest outbreak events. This has resulted in large areas of forests being killed that require active reforestation efforts to restore these disturbed systems to promote forest recovery. In this paper we argue that traditional ‘plantation’ style reforestation is not a sustainable option for tomorrows forest that require increased resilience to endure increased climatic related pressures in the years to come. As such we promote reforestation where heterogeneity in forest structure results. We suggest that areas on the margins of the disturbed site be managed for natural regeneration where there is suitable nearby seed availability. In the second zone we suggest planting a combination of clustered and regularly spaced seedlings that varies in terms of microsite water availability in accessible areas; and a final zone defined by remote, steep terrain that limits reforestation efforts to the establishment of founder stands. We also suggest that early prescribed fire be included to build up resilience in the young establishing stands.

Technical Abstract: The increasing frequency and severity of fire and drought events have negatively impacted the capacity and success of reforestation efforts in many dry, western forests. Challenges to reforestation include the size, cost, and safety concerns of replanting large areas with standing dead trees, and high seedling and sapling mortality rates due to water stress, competing vegetation, and repeat fires that burn young stands. Standard reforestation practices have emphasized establishing dense conifer cover with gridded planting, followed by practices such as shrub control and pre-commercial thinning. Resources for such intensive management are increasingly limited, reducing the capacity for young plantations to develop early resilience to fire, drought, and bark beetle stress. This paper summarizes recent research on the conditions under which current standard reforestation practices are no longer tenable, and makes recommendations on how these practices might be modified to improve their success. In particular we examine where and when plantations with regular tree spacing elevate the risk of future mortality, and how planting density, spatial arrangement, and species composition might be modified to increase seedling and sapling survival through recurring drought and fire events. Within large areas of contiguous mortality, we suggest a “three zone” approach to reforestation following a major disturbance that includes working with natural recruitment within a peripheral zone near live tree seed sources; in a second zone, beyond effective seed dispersal range, planting a combination of clustered and regularly spaced seedlings that varies with microsite water availability in accessible areas; and a final zone defined by remote, steep terrain that limits reforestation efforts to the establishment of founder stands. We also emphasize the early use of prescribed fire to build resilience in developing stands subject to increasingly common wildfires and drought events. Finally, we highlight limits to our current understanding of how young stands may respond and develop under these proposed planting and silvicultural practices, and identify areas where new research is needed to refine them.