USDA "5:::7iii5 United States Department of Agriculture Creating More Resilient FORESTS Through Active Manag ement espite their stately nature and presumable permanence on the landscape, 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 climates 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 silviculture management. Malcolm North, Connie Millar and Jessica when the magnitude of the disturbance, the frequency Wright, researchers with the U.S. Forest 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 ecosystems can change quite drastically. climate 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 fires. Southern-facin g shift forest structure and species composition to slopes benefit from wider spacing of larger create landscapes that are better able to survive trees. Cool, moist areas that experience le ss today’s disturbances, as well as weather tomorrow’s fire 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 ecosystem 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 seasons. 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 vegetation 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 woodland maintenance and and incorporates long-term probability of sudden die-back, for reforestation in response to ecological restoration and habitat example, by thinning 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 Soil 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 meadows. “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