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Creating More Resilient Through Active Manag ement

espite their stately nature and presumable permanence on the , forests are actually Dalways in a state of fux. Growing and dying, one species succeeding another, with the occasional disturbance, such as a wildfre or insect infestation, to wipe the slate clean and allow the process to start anew. And beyond these successional dynamics, forests change in structure, composition and ecological function over longer times as naturally vary.

ealthy forests typically are able to accommodate Summary Hthe minor, as well as the occasionally abrupt Drought, combined with higher temperatures, and more severe, disturbance and over time adapt is contributing to “megadisturbances” that to naturally changing climates in diverse ways. threaten western forests and require a Ecologists ascribe this ability as “resilience.” However, new approach to management. Malcolm North, Connie Millar and Jessica when the magnitude of the disturbance, the frequency Wright, researchers with the U.S. of the occurrence, pace of change, or a number of Service’s Pacific Southwest Research other extraneous factors make it difcult for a forest Station, have examined how changing to adapt, then can change quite drastically. conditions will likely transform the forests of the future and make Connie Millar and Malcolm North, researchers with recommendations on how to achieve the U.S. Forest Service’s Pacifc Southwest Research resiliency. Station, have been studying how disturbances and Reduced density and diversification of climatic conditions have shaped Californian and species has shown promise in creating Great Basin forest ecosystems from both a historical resistance to traditional and new threats. and pre-historical perspective. Teir research is More detailed recommendations by North giving land managers insights on how to successfully call for mimicking the effects of naturally occurring and regular . Southern-facin g shift forest structure and species composition to slopes benefit from wider spacing of larger create that are better able to survive trees. Cool, moist areas that experience le ss today’s disturbances, as well as weather tomorrow’s intensity can support denser growth. uncertainties. Managing individual stands for ladder fuels must be combined with regional approach es How Much Stress Can a Forest Take? that include varying stand density and the Te evolving understanding of forest dynamics has presence of open spaces. led to greater recognition that fres, insects and diseases are essential parts of a normal, functioning

Forest Pacific Southwest March 2018 D Service Research Station 2 | Creating More Resilient Forests Through Active Management and are, in fact, also increase water loss through stressors, can drive abrupt tree necessary for forest health. evaporation, as well as reduce mortality, according to Millar. snowpacks, which play a vital She and her co-author predict And while drought, too, has role in storing water that sustains that some forests will continue always existed as part of the landscapes through drier . to rebound from these stresses. cyclical nature of weather Over the long term, however, patterns, researchers have dubbed Millar, a senior research most temperate forests are likely the new combination of heat ecologist, co-authored a research to adjust and adapt Te efects and drought “global change paper in 2015 titled “Temperate will range from minor changes droughts” or “hotter droughts.” Forest Health in an Era of in forest density, age and species Tis new breed of hotter drought Emerging Megadisturbances.” composition, to more signifcant intensifes stress on trees, making In it, she discusses how much changes that include major them more vulnerable to other disturbance a forest can tolerate, transformations to factors, such as insects and what the long-term efects might types that can better survive diseases. Higher temperatures be, and how to minimize losses. in the new environmental conditions. “Megadisturbances,” defned in this case as the combination As land managers try to cope, of extreme drought and other Millar describes a typical cycle where foresters frst try to

t...... ,. r...... *.,... , . ,.• , ..... ,.,r 'f! lntemwd" • """""' • Smollfa • • • • ~ S"'10a< Small Pirie -- Hardwood Forest Service, Pacifc Southwest Research Station | 3 maintain tracts that refect the current norm. Tis can lead to some success, but if changes in climate and stressors are part of a longer-term trend, the forests will ultimately be rendered unstable and not adapted to current conditions. Once a threshold is exceeded, substantial mortality can occur and recovery can be slow or a new forest type can take hold.

“We have to understand that historic conditions may not be appropriate now as a guide,” Millar said. “If we want to use Researchers at the Pacifc a general technical report historic conditions as a guide, we Southwest Research Station authored by Malcolm North must fnd a time in the past that are conducting studies in the and his colleagues at the Pacifc is most like where we’re headed Stanislaus-Tuolumne, Sagehen Southwest Research Station, in the future.” and Teakettle Experimental ofers solid guidelines. Forests to better understand Millar’s work in paleoecology, “Simply restoring the forests to a feld of study that examines how to create a forest structure that can be sustained over time, their previous conditions is not ecological shifts across millennia, is resilient to disturbances, and the right approach,” said North, recommends management supports wildlife and recreation. a research forest ecologist. “Given practices that infuence the the reality of a changing climate transition to a more resilient While those fndings are not yet and recurring drought, we need forest. Resource managers must published, one thing is becoming a new management strategy, anticipate the evolution of the clear: Land managers need to be one that goes beyond short- forest and even facilitate it by ready to evolve their approach term fuel treatment objectives taking measures to reduce the to maintenance and and incorporates long-term probability of sudden die-back, for in response to ecological restoration and example, by forests to emerging conditions. improvement. We are conducting reduce competition for resources. Active Forest research now that will better Te goal is a more gradual Management Required inform those strategies and transition. Tis sort of managed practices.” change prevents the total collapse For foresters who are ready of the ecosystem and builds the to proactively manage for the Reforestation approaches where evolved forest back up to a point changing climate, “An Ecosystem new trees are planted close where the forest, albeit changed, Management Strategy for together with future plans for continues to fourish. Sierran Mixed Conifer Forests,” thinning, while once the norm, 4 | Creating More Resilient Forests Through Active Management

technical report provides a basic framework, not a one-size-fts-all •1-11_. ,T-"'-- ... ~ ,+--~MN solution. Foresters who choose ' '"'"'"' ....,.,.. •- to implement North and his colleagues’ recommendations must do so based on their unique, local circumstances, Rojas said. For example, sometimes there is a tension between creating forest tracts that can survive drought, fre and pests, and maintaining a habitat suitable for important species, like the spotted owl or fsher, Relative Moisture which require more density. wn Other factors afect the success of implementation of the recommendations within the may not always be the most Similarly, because insect and report, Rojas noted. For example, efective or expedient method, disease populations tend to the quality of the soil, elevation according to North. target one type or species of tree, of the forest, size of the trees diversity will also help reduce the and the localized intensity of the Instead, North asserts that possibility of one insect or disease drought all come into play. complexity – or heterogeneity killing all the trees in a region. – is the forest’s friend and ally, Moving Trees Uphill improving trees’ ability to Ramiro Rojas, a deputy regional If forests are going to be respond to stress and support silviculturist with the Forest replanted, which species and wildlife. Complexity includes Service’s Pacifc Southwest which seed sources make the varying stand density, including Region, has seen North’s most sense under projected openings of various sizes, a mix recommendations put into climate scenarios? Jessica Wright, of tree sizes and ages, and the practice and reports good results. a research geneticist with the presence of shrubs and . “Where we are able to reduce research station, is studying Given enough space, sunlight, density and create heterogeneity, whether shifting to trees from nutrients and water, trees have those stands seem to have far warmer climates leads to greater the capacity to grow and thrive. more survivors, both large and survivorship in the face of Tey become stressed when small trees,” Rojas said. “Where stressors. lacking any of these elements, there’s more density, they don’t “Te traditional approach was which make them more do as well.” to plant seeds from the same susceptible to attack by insects Rojas emphasized that the Pacifc seed zone when replanting,” and diseases, as well as drought Southwest Research Station’s Wright said. “But now it is or wildfre. previously mentioned general being considered appropriate Forest Service, Pacifc Southwest Research Station | 5 to move seeds uphill 500 feet to compensate for the warmer temperatures we are seeing.”

Wright pointed to an online resource called the Seedlot Selection Tool (https:// seedlotselectiontool.org/sst/) for help in replanting that is suited for changes in climate.

Te Seedlot Selection Tool is a collaboration between the U.S. Forest Service, Oregon State University and the Conservation Biology Institute. It is a web- based mapping application designed to help natural resource managers match seedlots with planting sites based on climatic information. It allows the Mimicking Nature — The Role of Fire user to control many input North and his co-authors recommend creating landscape diversity parameters, such as selecting in the by mimicking the forest conditions that would particular climate variables (i.e., be the result of regular, natural fires. temperature and ), Following this model, cool or moist areas, where historically fire and scenarios. would have burned less frequently or at lower severity, would Te generated maps include the have higher density and greater canopy cover. In contrast, upper, seed zones, allowing the user southern-facing slopes, which receive more sunlight, would have low densities of large fire-resistant trees. to compare the results of the tool with traditional planting When planting trees, then, North’s research suggests introducing a diverse mix of trees planted at varying densities, based on their approaches. position on a slope, or the steepness of the slope, as well as the “We just planted more than availability of water. 1,000 pine trees as part of a For individual groupings of trees, known as stands, vertical diversity post-wildfre reforestation project can be achieved by organizing groups of trees based on their using trees from warmer and canopy height, or strata, according to North. For example, a group of intermediate-sized trees that could serve as ladder fuels might drier locations,” Wright said. be thinned or removed if they are growing under taller trees. The “We are monitoring to see how same-size trees in a discrete group, however, might be left alone if they are perform. Te idea is the group does not present a ladder fuel for taller trees. to answer the question: Do This strategy would produce within-stand vertical differentiation, as these trees from warmer places well as discrete tree clusters, which would contribute to horizontal perform better here in this time heterogeneity. of changing climate?” 6 | Creating More Resilient Forests Through Active Management

Te results from this study will be compared to the predictions made by the Seedlot Selection Key Findings Tool to determine how well it predicted plant • The emergence of “hotter droughts” are creating performance, and particularly which climate previously unseen conditions that are likely to variables were most closely associated with plant change forests as we know them in the Sierra survivorship. Nevada. • Hotter droughts, combined with other Conclusion: The Time to Act disturbances, can cause abrupt tree mortality. Is Now Some forests can recover, but other regions Te current environmental conditions and could transition to a landscape with far fewer trees, unless steps are taken to intervene. projections that call for higher temperatures, drought and related disturbances will require a • Historical norms may no longer serve as a guide more active and thoughtful approach to forest for coping with tree mortality, and foresters must find ways to manage for new climate projections. management if we are to adequately maintain the resources forests provide. Monitoring and • Managing the transition of forests to new norms ongoing research will continue to shed light can prevent a total collapse of an ecosystem. on the efectiveness and best applications of • Mimicking the role of fire in shaping forests can these eforts, but the important thing is to start create a more resilient ecosystem. implementing the most promising of those practices now. Land Management Implications • Trying to maintain current forest structures may “Tere has to be a sense of urgency,” Rojas said. be futile in the face of long-term climate changes “We cannot lose hundreds of thousands of acres and the related stressors of insects, drought and of forest every decade.” diseases. What’s Next? • Shaping forests that are best suited to survive means anticipating what climate change will Malcolm North and several of his colleagues bring. at the Pacifc Southwest Research Station are • The Pacific Southwest Research Station’s currently examining how extensive tree mortality general technical report “An Ecosystem from a decade-long drought in might Management Strategy for Sierran Mixed Conifer afect wildfre and the future development of the Forests” (GTR-220) provides guidelines on forest as it responds to and re-establishes in areas how to structure forests to create resiliency, but where most of the large overstory trees have died. individual conditions must be taken into account. Studies suggest that managed fre is probably • The Seedlot Selection Tool (https:// the best, most economical means of thinning seedlotselectiontool.org/sst/), used in and restoring forests over the large expanses of conjunction with current seed zones, can help in afected forests, but such broad use isn’t always selecting trees for replanting that are suited for feasible. North is working with scientists and projected changes in climate. land managers to address fre implementation issues, such as air quality, liability, risk aversion and cost. Forest Service, Pacifc Southwest Research Station | 7

For Further Reading Scientist Profiles • North, M.; Managing Sierra Nevada Malcolm North is a research Forests, 2012, Gen. Tech. Rep. PSW- forest ecologist with the GTR-237. U.S. Department of Agriculture, U.S. Forest Service’s Pacific Forest Service, Pacific Southwest Southwest Research Station. Research Station His work includes research • North, M.; Lydersen, J.; Knapp, E.; Collins, examining different management B.; 2013. Quantifying spatial patterns of practices and the effect of tree groups and gaps in mixed-conifer forest structure, composition and function. His lab forests: Reference conditions and long- focuses on forest and fire ecology of Sierra Nevada term changes following fire suppression mixed-conifer forest. He has worked at several and logging, Forest Ecology and experimental forests, examining new silvicultural Management, 304: 370-382 practices and their ability to increase forest resilience to fire and drought. • North, M.; Stine, P.; O’Hara, K.; Zielinski, W.; Stephens, S. 2009. An Ecosystem Connie Millar is a senior Management Strategy for Sierran Mixed research ecologist with the Conifer Forests, Gen. Tech. Rep. PSW- U.S. Forest Service’s Pacific GTR-220. U.S. Department of Agriculture, Southwest Research Station. Forest Service, Pacific Southwest Her research team focuses on Research Station the role of historic and ongoing • Millar, C; Stephenson, N. 2015. Temperate

climate change in high-elevation Forest Health in an Era of Emerging forest ecosystems, including the Eastern Sierra Megadisturbance, Science, 304: 823-826. Nevada. She is also involved in the integration of science with policy, and is particularly interested • Achieving Long-Term Forest Health and in interpreting and communicating the current Resilience in California, http://www. research on climate change and its ecological fire.ca.gov/treetaskforce/downloads/ effects in conservation and restoration. FHRWG%20White%20Paper.pdf

Web Resources • Stanislaus-Tuolumne Experimental Forest https://www.fs.fed.us/psw/ef/stanislaus_ Jessica Wright is a research tuolumne/ geneticist with the U.S. Forest Service’s Pacific Southwest Learn more about the Pacific

Research Station. She uses Southwest Research Station at genetic tools to understand https://www.fs.fed.us/psw or population responses to threats scan the QR code to the left with including climate change, your smart device. pathogens and stress in forest ecosystems. Her current research intends to understand the genetics underlying tree responses to climate and how populations might be impacted by a changing

climate. USDA is an equal opportunity provider, employer and lender. 8 | Creating More Resilient Forests Through Active Management