Initiating Climate Adaptation in a Western Larch Forest

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For. Sci. 65(4):528–536 APPLIED RESEARCH doi:10.1093/forsci/fxz024 Published by Oxford University Press on behalf of the Society of American Foresters 2019. This work is written by (a) US Government employee(s) and is in the public domain in the US.

silviculture

Justin S. Crotteau, Elaine Kennedy Sutherland, Theresa B. Jain, David K. Wright , Melissa M. Jenkins, Christopher R. Keyes, and Linda M. Nagel

Western larch forests are iconic in the interior northwest, and here we document the preemptive steps that scientists and managers are taking to steward these forests into the future. Changing climate is forecast to have acute and chronic impacts on growth and disturbance in western larch forests. A group of scientists and managers in the northern Rocky Mountains have teamed up with the Adaptive Silviculture for Climate Change Network in an experiment to proactively manage forests for climate adaptation. The collaborative group developed a gradient of adaptation treatments (i.e., resistance, resilience, and transition) focused on climate change at Coram Experimental Forest and the Flathead National Forest. Treatments are scheduled, and monitoring will follow to fuel future research and to help guide regional managers who seek to learn from our treatments. We conclude with predictions of future dynamics in these stands and emphasize the value of landscape heterogeneity and the necessity of long-term monitoring for silvicultural experiments.

Keywords: Larix occidentalis, adaptive management, experimental silviculture, disturbance mitigation, Adaptive Silviculture for Climate Change

Western Larch Forests Extensive western larch forests in the northern Rocky Mountains The western larch (Larix occidentalis Nutt.) forest type (SAF provide many ecosystem benefits such as pleasing aesthetics, cul- Cover type 212; Eyre 1980) is a prominent icon in the interior tural significance, timber for local communities, habitat for wild- northwest, occupying 1.7 million acres (4.2 million hectares) in life, recreation opportunities, and clean water. great swaths of cool and moist, midelevation sites (Oswalt et al. Historically, western larch forests have been both resilient to and 2014). Western larch is a long-lived, deciduous conifer that dependent on disturbances such as insect outbreaks and wildfire. dominates composition in this forest type, growing up to 200 feet Western larch is highly tolerant of associated pests and pathogens (61 m) tall, over 7 feet (2.1) in diameter at breast height, and over except when old or associated with western hemlock (Tsuga 900 years old (Schmidt and Shearer 1990). It is an early-seral spe- heterophylla [Raf] Sarg.) (Schmidt and Shearer 1990, Cooper et al. cies with rapid early height growth and is the most shade-intolerant 1991, Carlson et al. 1995), and it persists when more vulnerable of its many tree associates (Schmidt et al. 1976, Pfister et al. 1977, species succumb to agents such as bark beetles or fire. Wildfire is the Fiedler 1995), resulting in highly diverse forest compositions. most dominant disturbance agent in these forests, with fire regimes

Manuscript received July 27, 2018; accepted April 4, 2019; published online May 10, 2019. Affiliations: Justin S. Crotteau ([email protected]), USDA Forest Service, Pacific Northwest Research Station, Juneau, AK. Elaine Kennedy Sutherland ([email protected]), Sutherland USDA Forest Service, Rocky Mountain Research Station, Missoula, MT. Theresa B. Jain ([email protected]), USDA Forest Service, Rocky Mountain Research Station, Moscow, ID. David K. Wright ([email protected]), USDA Forest Service, Rocky Mountain Research Station, Missoula, MT. Melissa M. Jenkins ([email protected]), USDA Forest Service, Flathead National Forest, Kalispell, MT. Christopher R. Keyes ([email protected]), University of Montana, WA Franke College of Forestry and Conservation, Missoula, MT. Linda M. Nagel (linda. [email protected]), Colorado State University, Warner College of Natural Resources, Fort Collins, CO. Acknowledgments: We gratefully acknowledge those who made this study installation possible, including funding by USDA Forest Service Region One’s Resource Inventory and Monitoring Board, Barry Bollenbacher, retired regional silviculturist who inspired the project, and Renate Bush (Region One Inventory and Analysis) who assisted in developing the monitoring design. The Northern Institute of Applied Climate Science is a key partner in the Adaptive Silviculture for Climate Change (ASCC) Network and helped facilitate the Kalispell, MT workshop. We thank Molly Roske (former ASCC Network Coordinator) for shepherding the project during the workshop and treatment developed phase. Employees of the Flathead National Forest have been critical to this effort, including Amanda Rollwage who found and laid out the study areas; Karl Anderson who led the stand exam crews that installed the plots and performed much of the pretreatment monitoring; Sarah Canepa, Eric Trimble, and Michele Draggoo who were instrumental in leading the NEPA process; and Hungry Horse District Ranger Rob Davies who has been in every way supportive of these efforts.

528 Forest Science • August 2019 varying from low- to moderate- and mixed-severity (Arno 2000). and Neuenschwander 1993, Keane et al. 2018). Further, climate Western larch has a high resistance to fire because of its thick basal will indirectly affect these forests through interaction with distur- bark, high live crowns, and deep roots (Brown and Davis 1973, bance regimes (Dale et al. 2001). If warmer, drier futures promote Arno and Fischer 1995, Hood and Lutes 2017); this high tolerance larger and more severe wildfires, they will increase overstory mor- historically enabled it to thrive with frequent, low-severity fire in tality and potentially limit regeneration (e.g., Haffey et al. 2018). low topographic positions and near cultural centers with anthro- Dwarf mistletoe infestation increases western larch water use (Sala pogenic ignitions. Moderate- and mixed-severity fires occur where et al. 2001); with increased evapotranspiration, infested trees will fire is infrequent and fuels build up, with subsequently higher fire grow even more slowly and be at greater risk of mortality. Thus, a severities (Barrett et al. 1991). Western larch is resilient to fire- changing climate threatens to alter long-term persistence of western caused injuries, rapidly enclosing cambial injuries and forming larch by reducing growth rates, increasing the potential for injury scars (Smith et al. 2016); if buds are not killed, western larch is also and mortality from fire, pest, and pathogens, and decreasing regen- able to quickly rebuild scorched crowns because of its deciduous eration success. habit (Smith and Fischer 1997). When fire kills trees and exposes mineral soil, western larch again demonstrates resilience because ASCC in Western Larch it regenerates well from prolifically produced, lightweight, wind- Proactive forest management can provide a solution to hedge po- blown seed (Schmidt and Shearer 1990). tential climate-related decline in these forests. In fact, federal land Western larch is predominantly located in the northern Rocky managers are mandated to consider the effects of changing climate Mountains and southern British Columbia, a region at the inter- on forest ecosystems (USDA Forest Service 2012) and encouraged section of wet, maritime air from the Pacific Ocean and cooler, to maintain ecosystem integrity into the future. However, many drier air from Canada. This confluence of air masses generates most land managers do not have the tools or precedent knowledge to ac- precipitation in the winter, whereas summers are typically dry. tively steward forests toward adaptation (Janowiak et al. 2014), and There is a gradient of decreasing precipitation from west to east past management tools may need adjustment for future application resulting in relatively moister and cooler site types to the west (e.g., (Kubiske et al. 2018). Adaptation-oriented science-management Idaho) and drier and warmer site types to the east (e.g., western partnerships have been making headway in knowledge exchange Montana). Over the historical period of record (1895–2012), mean over the past decade (e.g., Halofsky and Peterson 2016, Swanston monthly minima have increased 3.0° F (1.7° C) and mean monthly et al. 2016), and such partnerships have been galvanized as an of- maxima by 0.6° F (0.3° C). Future climate projections have been ficial vehicle of the Forest Service’s shared stewardship strategy specifically developed for the geographic range of western larch in (USDA Forest Service 2018). the northern Rocky Mountains (Joyce et al. 2018, and citations The ASCC project is an experimental effort to cooperatively de- therein). Temperatures are warming and predicted to increase for all velop silvicultural strategies that mitigate the negative effects of fu- seasons by 5–10° F (2.8–5.6° C) by 2100. Precipitation is projected ture climate on the goods and services expected from forests across a to slightly increase in the winter and spring, and decrease in the network of sites (Nagel et al. 2017). The project brings together re- summer, exaggerating summer drought. Most precipitation histor- gional stakeholders, managers, and scientists in a workshop format ically fell as snow, but more is now falling as rain, decreasing the to create locally relevant forest treatments with four approaches to storage capacity of mountain snowpack. Snowmelt and runoff are climate adaptation: no action (allow forests to respond to climate starting earlier in the spring, resulting in earlier and longer growing change without direct management intervention), resistance (main- seasons, as well as earlier and longer wildfire seasons. tain relatively unchanged conditions over time), resilience (allow Looking to the future, western larch forests are expected to be one of the northern Rocky Mountains’ most vulnerable forest types to this warming and drying climate (Bollenbacher et al. 2014, Management and Policy Implications Keane et al. 2018). In some aggressively warming climate scenarios, it is even projected to be extirpated from the United States, re- Many western regions are expecting warming futures, but direct and indirect maining solely in Canada (Rehfeldt and Jaquish 2010). In their climate effects on forests are uncertain. Defensible stewardship of western physiologically based species distribution modeling, Rehfeldt and larch forests in the northern Rocky Mountains includes actively diversifying Jaquish (2010) projected a much narrower bioclimatic range for these forests to hedge against future climatic conditions and associated western larch than its associates, particularly with respect to impor- disturbances. As part of the ASCC network, we have established an opera- tant interacting variables like summer dryness, winter temperature, tional framework for implementing strategies to mitigate climate change in growing season precipitation, and degree days greater than 41° F (5° western larch forests. We anticipate this precedent will provide the tools for C). Under these climate change scenarios, larch forest community future scientists and forest managers to cooperatively meet the demands dynamics are likely to change. of future forests. Although still in its infancy, this study’s future results will Changing climate poses both direct and indirect effects on demonstrate the utility of unique silvicultural techniques for increasing forest western larch (Halofsky et al. 2018). Warmer climate with more adaptation to novel environments. We corroborate that management and re- sporadic or less frequent precipitation may have direct negative search partnerships are mutually edifying, and enable the coproduction of effects on mature tree growth if warmer temperatures do not coin- creative, adaptive management while maintaining scientific rigor. Finally, cide with precipitation. Snow-free cold snaps and summer droughts monitoring approaches that conform to management analysis and reporting may affect larch population dynamics more negatively by killing needs are extremely useful and beneficial for managers, making partnership susceptible cones, seedlings, and saplings, especially in the warmer with research immediately advantageous. and drier parts of the range (Schmidt and Shearer 1990, Oswald

Forest Science • August 2019 529 some change in current conditions, but encourage an eventual re- experimental design: four replicates of each treatment with a total turn to reference conditions after disturbance), and transition (ac- of 16 experimental units, each between 25 and 50 acres (10.1 and tively facilitate change to encourage adaptive responses). For each 20.2 hectares) in area (Figure 2). Currently, treatment boundaries of the three active treatments, project participants establish desired are delimited, pretreatment data have been collected, and trees are future conditions, management objectives that are met by those marked for harvest. Units are expected to be harvested in 2019, conditions, and specific silvicultural tactics to achieve the broader then planted with over 50,000 seedlings in 2020. objectives of each adaptation approach (i.e., resistance, resilience, Initial conditions at these sites (elevation: 3,800–4,300 ft and transition). All ASCC network sites have committed to im- [1,158–1,311 m]) consist of even-aged western larch-mixed co- plementation and short- and long-term monitoring so the study nifer stands that regenerated after commercial harvests in the 1950s can effectively address a suite of overarching research questions, and 1960s, and were precommercially thinned in the 1970s and including: Will adaptation approaches and treatments work in a 1980s. Western larch comprises 72 percent of overstory basal area, real-world context to meet local management goals and objectives? and the balance is composed of six conifer and three hardwood See Nagel et al. (2017) for further research questions, goals, and species (Table 1; Abies lasiocarpa/Clintonia uniflora habitat type; expectations. Pfister et al. 1977). The average conditions across the treatment The western larch forest type is one of five forest types that cur- units are 260 trees ac–1 (642 trees ha–1) with 106 ft2 ac–1 (24.6 m2 rently make up the ASCC Network (www.adaptivesilviculture.org). ha–1) of basal area, with a mean overstory tree diameter (i.e., quad- Staff from the USDA Forest Service joined the national ASCC ratic mean) of 8.7 in (22.1 cm), and dominant/codominant height team to develop and establish treatments in northwest Montana’s of 62.4 ft (19.0 m). western larch forest. They strategically focused on second-growth Although definitive effects of future climate on western larch are forests because 62 percent of accessible western larch forests in unknown, our present opportunity is to proactively diversify stand Montana are young (i.e., less than 100 years old) second growth structure and composition to mitigate climate-driven threats to this that naturally regenerated following harvests from the 1950s to forest type. We hypothesize that decreasing stand density will (1) 1980s (Menlove et al. 2012). The team hosted a one-day profes- decrease tree competition for soil water and relieve water stress, so sional workshop in 2016 to inform a broad group of local land that tree growth rates are maintained or increased; (2) increase tree managers about regional climate change expectations (Bollenbacher ability to be resistant or resilient to insect and pathogen infestation, et al. 2014, Halofsky and Peterson 2016, Keane et al. 2018) and and reduce their spread; and (3) decrease fuel loading and interrupt walked them through a climate-adaptive decisionmaking frame- fuel continuity, reducing the potential for severe fire. work (Figure 1; Swanston et al. 2016). Following this workshop, The resistance treatment is designed to reduce the effects of fu- an expert panel of local managers and regional scientists gathered ture drought, fire, insects, and pathogens while maintaining an at Coram Experimental Forest to work through a facilitated process even-aged western larch stand (Table 2). Objectives included re- to codesign resistance, resilience, and transition treatments for a local, ducing moisture stress and forest fuels, promoting development of second-growth western larch forest. The team used the network large-diameter trees, and modifying overstory species composition.

Figure 1. An expert panel of Adaptive Silviculture for Climate Change (ASCC) national team leaders, US Forest Service Flathead National Forest managers and Rocky Mountain Research Station scientists, and University of Montana researchers, who convened in June 2016 at Coram Experimental Forest to discuss implementation of ASCC treatments given the complex social demands of western larch forests. Photo credit: Molly R. Roske, Colorado State University, Fort Collins, CO (Currently at Fundación Cordillera Tropical, Cuenca, Ecuador).

530 Forest Science • August 2019 Figure 2. Map of the study area. Experimental treatments are located on the Flathead National Forest and Coram Experimental Forest, Montana. Treatment units are evenly split across two blocks along Hungry Horse Reservoir (Lion Hill and Trout Lake), each having two replicates of each of the four treatment types.

Table 1. Initial overstory species composition at the northern Rocky These objectives will be achieved using commercial thinning from Mountains Adaptive Silviculture for Climate Change Study site. below to 70–85 ft2 ac–1(16.3–19.7 m2 ha–1) (Figure 3), which is approximately 35 percent of maximum stand density index and Latin name Common name Percentage of total stems the lower threshold for full site occupancy (Reineke 1933, sensu Abies grandis Grand fir 0.2 Long and Shaw 2005). The low residual densities are expected to Abies lasiocarpa Subalpine fir 6.7 Betula papyrifera Paper birch 4.9 reduce moisture stress and favor the retention of species that are Larix occidentalis Western larch 72.2 both shade-intolerant and fire-tolerant. The thinning prescription Pinus contorta Lodgepole pine 3.6 was specified on an average spacing basis (16–18 ft [4.9–5.5 m]); Picea engelmannii Engelmann spruce 2.5 Pinus monticola Western white pine 0.2 although the prescription stated that irregular spacing was both ac- Populus balsamifera Cottonwood 2.0 ceptable and necessary, no measures were taken to secure clumps Populus tremuloides Quaking aspen 0.3 or gaps. This strategy aligns with the conventional approach to Pseudotsuga menziesii Douglas-fir 7.4 western larch management, so one specific research question for

Forest Science • August 2019 531 Table 2. Desired future conditions, silvicultural objectives, and initial tactics for achieving treatments in the northern Rocky Mountains Adaptive Silviculture for Climate Change study.

Treatment Desired future condition Objectives Tactics Control (allow forests to • Naturally regenerated mixed- • Reserve stand as is for reference • No active management respond to climate change species, multiaged stand without direct management intervention) Resistance (maintain • Even-aged with composition • Maintain vigorous growing trees • Commercial thinning from below to 70–85 ft2 relatively unchanged dominated by western larch • Mitigate moisture stress ac–1 (16.3–19.7 m2 ha–1) conditions over time) and high canopy base heights • Reduce probability of crowning and • Mostly uniform spacing of residual trees with torching some hardwood clumps • Minimize future disturbance from insects • Favor WL and QA and diseases • Slash shrubs and saplings Resilience (allow some change • Multiaged with high structural • Maintain vigorous growing trees • Group selection with clumped reserves in current conditions, but and spatial heterogeneity, com- • Mitigate moisture stress (1/3 of stand) encourage an eventual return position dominated by western • Increase proportion of disturbance-adapted ○ Create 2–4 ac (0.8–1.6 hectares) openings to reference conditions after larch and western white pine species. ○ Leave 6–8 clumps per acre of 1–4 trees per disturbance) (disturbance- • Minimize future disturbance from insects clump, total 12–16 trees per ac (30–40 per adapted species) and disease hectare) • Increase age-class, spatial, and structural ○ Plant 300 seedlings per ac (741 per hectares) of heterogeneity to improve resilience to improved WL and WWP; WL from mid- and disturbances high-elevation seed zones • Thin from below in matrix (2/3 of stand) ○ Retain 75 ft2 ac–1 (17.4 m2 ha–1) in the matrix, mostly uniform spatial pattern • Favor retention of WWP, WL, QA • Slash shrubs and saplings, and minimize the abundance of shade-tolerant species by weeding Transition (actively facilitate • Two-aged with structural and • Increase proportion of disturbance-adapted • Irregular seed tree harvest with reserves change to encourage adaptive spatial heterogeneity, compo- species • Retain 16 trees per ac (40 per hectares) in at responses) sition dominated by western • Introduce drought-resistant, fire-resistant PP least 7 irregularly spaced clumps per ac (17 per larch, western white pine (both • Minimize disturbance from insects and hectares) of 1–5 trees disturbance- disease • Plant 300 seedlings per ac (741 per hectares) of adapted species), and pon- • Increase genetic diversity to allow for the improved WL, WWP, and PP; WL and PP from derosa pine (fire-tolerant and stand to adapt to a future environment mid- and high-elevation seed zones drought-tolerant species) • Promote a two-aged stand by inducing a • Favor retention of WWP, WL, QA second age-class of WL, WWP, PP, and • Slash shrubs and saplings and minimize the hardwoods (esp. QA) to enable the stand to abundance of shade-tolerant species by weeding adapt to a warmer and drier future

Note: PP, ponderosa pine; QA, quaking aspen; WL, western larch; WWP, western white pine. this treatment is: does this thinning effectively sustain western larch Douglas ex D. Don) stock that is resistant to white pine blister rust as the climate becomes warmer and drier? (Cronartium ribicola). Western white pine was selected because it The second treatment, resilience, is also designed to reduce the is an on-site, generalist, shade-intolerant species that is adapted to effects of drought, fire, and insects on the stand; beyond that, it is mixed-severity fire regimes, regenerating quickly after wildfire. Two designed to reduce the long-term impacts of future disturbances specific research questions for this treatment are: What role does and maintain western larch dominance while actively promoting forest spatial and compositional heterogeneity play in resilience fol- other future-adapted species (Table 2). The silvicultural objectives lowing disturbances? What tree species will survive and thrive as for this treatment include enhancing age-class, spatial, composi- the climate becomes warmer and drier under these stand structures? tional, and structural heterogeneity. Another objective is to hedge The transition treatment is meant to actively facilitate structural for the future by increasing genetic diversity and the proportion and, more notably, novel compositional changes to create stands of fire-adapted species that are considered to have broad environ- that reduce the immediate and long-term effects of drought, fire, mental tolerances (generalists). To accomplish this wide range of disease, and insect disturbances in a warmer, drier future (Table 2). objectives, the stand will be managed using a group selection with Of the three active treatments, we hypothesize this would be the a reserves system (Figure 3). At initial treatment, two-thirds of the most successful treatment if the climate rapidly changes to reflect stand will be commercially thinned from below to 70–85 ft2 ac–1 growing conditions currently present in warmer site types instead (16.3–19.7 m2 ha–1), similar to the resistance treatment. Scattered of the present cool site types. To actively adapt this ecosystem type throughout this matrix, 2–4-ac (4.9–9.9-hectare) groups will be toward a warmer and drier environment, the objectives are to en- harvested with clumped reserves left to maintain structure and hance age-class and structural heterogeneity, increase genetic diver- seed source, constituting a third of the stand area. Natural regen- sity, and bolster the proportion of species already present that are eration following the harvest will be supplemented with nursery- disturbance-adapted, and to supplement species composition with propagated 2-0 bare-root seedlings of western larch from both a fire-tolerant species that is more drought-tolerant than those cur- within and above the site’s seed source elevation zone. This treat- rently present. We chose to introduce ponderosa pine (Pinus pon- ment will also be planted with western white pine (Pinus monticola derosa Lawson & C. Lawson) to the sites; although not presently in

532 Forest Science • August 2019 Figure 3. Anticipated, simplified stem maps and canopy profiles following initial treatments at the Northern Rockies Adaptive Silviculture for Climate Change study site. Retained trees are represented in black, and cut trees or stumps represented in gold. The matrix of the resilience treatment (gray shading) will compose future group selection harvests. Western larch silhouette from http://tidcf.nrcan.gc.ca/ en/trees/factsheet/289. the treatment stands, ponderosa pine in northwest Montana exists likelihood of maintaining forested conditions under future climate on warmer, drier locations at both higher and lower elevations conditions and associated droughts and wildfires? than these sites (i.e., up to 5,300 ft [1,616 m]). Furthermore, ponderosa pine is more fire-tolerant than most associates at small stem Monitoring diameters and has an erect branching structure and self-pruning Regular measuring or monitoring is required to detect changes habit that is less conducive to crown fire than species such as in forest composition and structure over time. Per the standards Douglas-fir (Oliver and Ryker 1990), exhibiting a collective set of of the ASCC Network (see Table 2 in Nagel et al. 2017), all pre- growth attributes that may allow it to perform well under future treatment monitoring will be completed before expected harvests in climates. This treatment will be accomplished using an irregular 2019, and then in 2020 after seedlings are planted. Post-treatment seed tree with reserves silvicultural system (Figure 3). Clumped monitoring will take place (at minimum) 1 year and 5 years fol- seed trees will aid natural regeneration, which will be supplemented lowing harvest. In most research studies, the principal investigators with 2-0 artificial regeneration. Western larch and ponderosa pine design a monitoring plan based on the research needs unique to will be sourced from both within and above the site’s elevation the study. However, the resulting data are not necessarily useful zone, and western white pine will be rust-resistant. A sample of for National Forest System reporting practices because they do the planted trees will be tagged to follow their growth and survival not conform to their standards. In cooperation with the Forest over time. Questions associated with this treatment include: Will Service’s Region 1 and the Flathead National Forest, the replicate a future climate favor the growth and development of ponderosa stands were given working stand numbers, so information about pine, western white pine, or both? And, does this treatment’s forest them could be entered into official Forest Service databases. We structure and the assisted migration of ponderosa pine increase the developed a variant of the Region 1 Common Stand Exam (https://

Forest Science • August 2019 533 www.fs.fed.us/nrm/fsveg/, Region 1 User Guide Appendix) to use the context of traditional, even-aged management of western as a monitoring protocol. A Flathead National Forest stand exam larch. A followup thinning from below and subsequent broadcast crew installed plots and performed the pretreatment monitoring of burning is planned when the basal area exceeds 130 ft2 ac–1 (30.2 the overstories, entering data into dataloggers in the field. Because m2 ha–1) and quadratic mean diameter reaches approximately 14 of this cooperation, these data were automatically in the correct in. (35.6 cm). Although the current system includes maintaining format for storing data in the Forest Service’s FSVeg database and stocking within lower and upper timber-management thresholds, running the Forest Vegetation Simulator to simulate forest growth managers may elect to modify these plans if overstory survivorship (Dixon 2002). Research crews will finish the midstory and under- declines with drought or if fire hazard becomes high: silvicultural story vegetation and fuel-loading pretreatment data collections density reduction will be the primary means to aid overstory sur- using this protocol. In the future, both National Forest System vival. In the short-term, the resistance treatment will help these and research crews can use these stand exam protocols to continue stands endure summer droughts and intense fire, but if the western monitoring and to store the data in a consistent format. larch overstory does not tolerate future climate, biotic and abiotic stressors will cause high mortality and reduce seed production so Future Forest Dynamics and Management there may be no regeneration to replace the overstory. The ASCC project is still in its infancy. As we and Nagel et al. Theresilience treatment embraces a multiaged strategy to reduce (2017) have documented, the foundation has been laid for future the impacts of disturbance both now and in the future by stimu- research, but many of the most valuable findings are still decades lating natural regeneration with potentially better-adapted genetics away. Although some aspects will remain the same in years to come, and supplementing natural genetics with artificial regeneration. forests, forestry, and society are in a state of constant change, and Group selection regeneration harvests are planned to continue on we can only predict future outcomes based on current available a 30–50-year cutting cycle in a third of the stand at a time so that knowledge. We anticipate substantial change in forest structure as three primary age classes (i.e., excluding reserve trees) may be man- treated stands age, and an adaptive management framework will be aged for climate adaptation and merchantable timber production needed when those changes do not align with the management ap- in perpetuity. Planting will likewise follow future harvests, although proach (i.e., adaptation strategy) for each of the treatments. species and seed sources may change to better accommodate future We expect stand dynamics to vary by treatment in the years to climate, since this study seeks to follow an adaptive management come precisely because of the age-class, structural, and composi- framework. The matrix will be tended to ensure desired structures tional modifications that characterize each treatment. Management and species compositions develop, although these intermediate and vegetation dynamics will directly affect stand response to treatments would ideally be limited to cutting cycle years. Also, the the two abiotic disturbances that these treatments are specifically regenerated groups will likely need weeding to promote larch and designed to ameliorate: wildfire and drought (Figure 4). The re- white pine over lodgepole pine and subalpine fir regeneration. If the sistance treatment is designed to mitigate future disturbances in climate becomes warmer and wetter (as is possible in western parts

Figure 4. Anticipated stand resistance to fire and drought disturbances following treatments at Northern Rockies Adaptive Silviculture for Climate Change study site. In this conceptual figure, resistance is defined as the ability of a stand to maintain its overstory structure and composition (i.e., avoid significant overstory mortality) given a disturbance.

534 Forest Science • August 2019 of its range), we expect that desired western white pine and western Closing Notes larch would require release treatments to compete with the more One of the most valuable attributes of this project is the dem- shade-tolerant tree species. If the climate becomes warmer and onstration of silvicultural strategies along a continuum of treat- drier, we expect that western larch will be favored. However, this ment and adaptation intensity. Managers of western larch forests type of applied study that examines various climate-adapted silvi- can use these treatments as markers along the climate adaptation cultural treatments combined with long-term monitoring will allow continuum to develop a treatment that is appropriate for their managers and scientists to determine which species are best adapted context. Furthermore, managers can use this continuum of silvi- to future climate; by supplementing regeneration in these stands, cultural approaches to diversify forest landscapes and reduce the we are hedging for a future with at least one or two tree species and impacts of future disturbances beyond the stand scale. However, associated vegetation to adapt to the changing climate. Should a informed and defensible application of future findings will be wildfire occur, regeneration may slightly elevate the torching hazard limited by our ability to establish, maintain, and monitor these as it develops into ladder fuels near the residual overstory, but har- treatments in years to come. For example, long-term research from vest patterns will break up horizontal canopy continuity and reduce Coram Experimental Forest has been useful to local management the probability of stand-wide crowning, exhibiting a tradeoff be- because of the foresight, scientific rigor, and maintenance provided tween hazard to horizontal and vertical crown fire spread. The re- by past researchers (e.g., Jang et al. 2015, 2016, Schaedel et al. silience treatment has an especially high adaptive capacity to future 2017). Without proper resources and commitment to inventory climates because each cutting cycle will stimulate regeneration that and upkeep, we will be unable to realize the gamut of tradeoffs may be better suited to those conditions. Because this treatment’s associated with these treatments, and ill-equipped to steward our success is dependent on more frequent regeneration, adaptive man- forests into the future. Carrying the study into the future will be agement may take the form of additional measures to aid regener- challenging, but close cooperation among researchers and National ation establishment, or alternative genetics for larch and western Forest System partners will offer many avenues for success. In doing white pine to better suit future climate needs. so, the silvicultural treatments and monitoring protocols developed Whereas resistance and resilience treatments are intended to and used in this study position multiple parties to benefit and pro- adapt to climate change using species on site, the transition treat- vide compelling impetus to maintain this valuable research. ment introduces a drought-tolerant species commonly found at drier sites in the region: ponderosa pine. We hypothesize that Literature Cited ponderosa pine may be physiologically the best suited species to a future warmer, drier climate. Whereas some historical planting of Arno, S.F. 2000. Fire in western forest ecosystems. P. 97–159 in Wildland off-site ponderosa pine in Region 1 has led to low-quality timber fire in ecosystems: Effects of fire on flora, Brown, J.K., and J.K. Smith (eds.). USDA Forest Service Gen. Tech. Rep. RMRS-GTR-42, Rocky stands, experience from these relic pine plantations provides Mountain Research Station, Ogden, UT. guidance to evaluate the performance of the locally sourced, Arno, S.F., and W.C. Fischer. 1995. Larix occidentalis—Fire ecology improved ponderosa pine seedlings in this study. Yet, we will and fire management. P. 130–135 in Ecology and management of Larix also supplement western larch and ponderosa pine with western forests: A look ahead; Proceedings of an international symposium; 1992 white pine, a species with a broad environmental range. By ar- October 5–9; Whitefish, Montana, Schmidt, W.C., and K.J. McDonald tificially regenerating those three fire-adapted species, this treat- (eds.). USDA Forest Service Gen. Tech. Rep. INT-GTR-319, Rocky ment is providing the widest potential for stands to transition into Mountain Research Station, Ogden, UT. a range of potential future climates and associated fire regimes. Barrett, S.W., S.F. Arno, and C.H. Key. 1991. Fire regimes of western However, there will be periods of vulnerability to disturbance as larch–lodgepole pine forests in Glacier National Park, Montana. Can. these two-cohort stands develop. The current management plan J. For. Res. 21(12):1711–1720. aims to avert density-dependent mortality and reduce fire hazard Bollenbacher, B.L., R.T. Graham, and K.M. Reynolds. 2014. Regional forest landscape restoration priorities: Integrating historical by precommercial thinning of the new cohort at age 15. This will conditions and an uncertain future in the northern Rocky Mountains. be accompanied by pruning western white pines to reduce white J. For. 112(5):474–483. pine blister rust infection. As individuals in this cohort age and Brown, A.A., and K.P. 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