Keeping up with the landscapes: promoting resilience in dynamic social-ecological systems

Guest Editorial, part of a special feature on The Many Facets of Forest Resilience in the Lake Tahoe Basin

INTRODUCTION

Forest managers working in seasonally dry, fire-adapted forests have long contended with fire as a process (e.g., Show and Kotok 1923). Communities and governments continue to work toward reducing the occurrence and impacts of extreme wildfire events; however, there is a cost to constraining processes that are inherent to an ecosystem. For example, the long-standing reliance on fire suppression as a management strategy has engendered large areas of overly dense forests that are more vulnerable to drought, intense wildfire behavior, high tree mortality, and harm to human communities. Climate change is supercharging the situation through increased temperatures and extended and/or intensified droughts; accelerating tree mortality from drought, insect, and disease stresses; increasing prevalence of high-severity fire; and reducing essential water yields from watersheds (e.g., Allen et al. 2010, Bentz et al. 2010, Crockett and Westerling 2017, Coop et al. 2020, Halofsky et al. 2020).

Across the United States and dry forest regions worldwide, an increasingly common objective of forest management is to enhance resilience (e.g., Thompson et al. 2009, U.S. Forest Service [USFS] 2016, Environmental Protection Agency 2021, Intergovernmental Panel on Climate Change [IPCC] 2022), although in application resilience is often left undefined by forest managers, or its definition varies widely among applications depending on the constitution of a given project. Social-ecological resilience has become a pre-eminent framework for natural resources management (e.g., Long et al. 2014, Folke et al. 2021), especially because it embraces the concept of humans as part of ecosystems and the need for humans to continually adapt to ever changing environments. In social-ecological systems, resilience can be defined as the degree to which a system is capable of self-organization, learning, and adaptation, reflected in its ability to deal with disturbance and change while continuing to adapt and develop and change (Walker et al. 2004, Sterk et al. 2017, Cumming and Peterson 2017). In forested landscapes, this translates to the ability of ecological and social systems to persist, cope with, and adapt to the inherent primary disturbances, such as wildfire and drought, as well as more novel disturbances, such as more frequent threats of flooding, impacts from surges of human disturbance in response to extreme heat, and the economic impacts of changes in the availability of natural resources.

There are multiple perspectives on how best to conceptualize and quantify resilience in social-ecological systems (Allen et al. 2019). In our studies, we regarded resilience as an emergent property of sustaining characteristic systems and interactions, including the character of and response to disturbances, as per Cutter et al. (2008): “...inherent conditions that allow the system to absorb impacts and cope with an event, as well as post-event, adaptive processes that facilitate the ability of the social system to re-organize, change, and learn in response to a threat.” However, specific applications require additional declarations. Is resilience achieved when ecological, social, and economic systems are mutually supportive (e.g., the metaphor of a three-legged stool or “triple-bottom line”; Young 1997, Winter et al. 2014, Cumming and Peterson 2017)? Or is a more explicitly hierarchical framing important, with ecological systems being the foundation upon which economic and social systems depend (Dawe and Ryan 2003, Barnard and Elliott 2015)? In social-ecological systems, where social-ecological interactions are considered native to the system, is the requirement of human input to maintain an ecological system a sufficient measure of resilience, or rather is resilience a function of the sustainability and self-reinforcing nature of the interaction? In reality, all of these lenses on the concept of resilience reflect relevant aspects of social and ecological interaction and interdependence that directly affect the ability of a system to be resilient to disturbance and change.

In the evaluation and management of complex adaptive social-ecological systems across large forested landscapes over the next several decades, the question, “resilience of what to what” (Carpenter et al. 2001) is challenging to answer. Interpreting conditions in terms of resilience is a common and heralded practice (Holling and Meffe 1996). Managers in the Lake Tahoe West Restoration Partnership (https://www.nationalforests.org/regional-programs/california-program/laketahoewest) adopted a philosophy of resilience based on the premise of identifying conditions that were most likely to confer resilience to future disturbances, and thereby result in a high likelihood that the existing social-ecological system (its processes, functions, and benefits) would persist over time (i.e., not experience an undesirable state change). This is consistent with and exemplifies the “golden rule for ecosystem management,” put forward by Holling and Meffe (1996) as a robust resilience practice. Our science team worked directly with managers on gaining a better understanding of how major components of the Lake Tahoe basin social-ecological system that are directly affected by the primary forest disturbances (fire, beetles, and management) and their interactions combined with climate change are likely to be affected over the next century. Specifically, we evaluated the degree to which different types and amounts of management investment were likely to affect conditions across multiple ecological and social features in the social-ecological system across the basin and the implications for resilience.

THE PROJECT APPROACH

As detailed in this Special Feature, our science team worked with resource managers and stakeholders over a two-year period in support of the Lake Tahoe West Restoration Partnership, to define conditions resilient to the host of primary disturbances across the 88,000-ha basin expected over the next 80 years. Managers are pressed to scale up planning and implementation from more traditional scales of stands and small landscape units (e.g., Underwood et al. 2010) to large watersheds that encompass 100,000 ha or more to better match the scale at which landscape dynamics are operating and can be addressed. The spatial scale of the Lake Tahoe basin comports well with the scale of landscape analysis that managers are moving toward: large enough to take landscape dynamics into account, but at a scale for which data on resource conditions and thresholds are detailed and accurate enough to develop specific, near-term management treatment plans.

Lake Tahoe managers acknowledged that, lacking additional management investments, the following outcomes were increasing in likelihood: the potential for undesirable state change was increasing over time as a result of changing climates, the capacity of management investments to alter those trajectories was increasingly uncertain, and management needed to be thoughtfully designed with the specific intention of enhancing resilience rather than simply maintaining current conditions. Managers applied the concept of maintaining a “safe operating space” (i.e., condition domains) within which the risk of a state change is less likely (Rockström et al. 2009), by identifying metrics for primary resource areas (e.g., forests, meadows, riparian areas, wildland-urban interface areas, overall biodiversity, water quality) and thresholds beyond which state change was likely and undesirable.

As such, managers and stakeholder groups applied a broad interpretation of social-ecological resilience, under which a need for continual human inputs did not necessarily indicate a lack of resilience. Managers viewed human inputs, such as fire suppression, thinning treatments, and intentional ignitions, as an integral part of the social-ecological system that exists across forested landscapes in the basin. The idea of continual human inputs being integral to the ecosystems at Lake Tahoe is supported by centuries of Indigenous stewardship, including seasonal settlement, burning, and harvesting, prior to Euro-American colonization (Elliott-Fisk et al. 1996). In turn, our science team evaluated the character of those inputs and their anticipated outcomes over the next century as measures of resilience, including their efficacy in maintaining and adapting characteristic components and functions, and their sustainability. Investments with a high return on investment (ROI) were generally interpreted as enhancing resilience, with ROI indicated by environmental quality, conservation of biodiversity, and reduced risk of extreme losses and triage responses that carry high costs and inequitable burdens (Holling and Meffe 1996, Twidwell et al. 2019).

We collaborated with managers to first develop target conditions across multiple social-ecological features (as addressed in the individual papers in the Special Feature) that reflect domains of resilience and associated thresholds, which were adopted and documented in the Lake Tahoe West Landscape Resilience Assessment (Gross et al., unpublished manuscript). Our science team supported managers in drawing from and interpreting peer-reviewed literature to identify conditions (domains and thresholds) likely to be resilient to future non-management disturbances across a wide array of ecological and social resources, deriving these interpretations from a variety of historical and contemporary sources. In many cases, thresholds were based on historical conditions that were resilient to disturbances characteristic of the Holocene (e.g., lower tree densities and frequent fires resulting in low-severity fire regimes that perpetuated open forest structure and a frequent, moderate-severity fire cycle); for some values, comparable forest ecosystems with restored fire regimes were derived (Gross et al., unpublished manuscript). In others, the thresholds were based on socially derived conditions, such as metric tons of fine sediment and daily smoke emissions, which relate to regulatory thresholds set to protect ecological and human health. The analyses also considered measures of social tolerance, such as number of days of burning, financial costs of treatments, and staffing requirements, which are inherently adaptable constraints but are nevertheless meaningful metrics for evaluating social resilience.

The science team then worked with managers to develop management scenarios that represented an array of forest treatments expected to be likely to occur and/or to be effective in improving prospects for social-ecological system resilience in the future to achieve resource objectives, which were then projected over an 80-year period to evaluate long-term outcomes. The management scenarios represented a variety of treatment approaches, including hand and mechanical thinning, wildfire suppression, prescribed burns, and lightning-ignited wildfires. Finally, we used a dynamic landscape modeling framework that represents forest succession and fire dynamics in response to the primary disturbances pressing on forests across the Lake Tahoe basin. Primary disturbances expected to affect this landscape over the 21st century that were subsequently modeled included fire, beetles, drought, climate change, and management. The 80-year temporal span encompasses multiple natural fire and insect outbreak cycles, maturation of conifer forest, credible limits of climate projections, and impacts on future human generations. Previous research as part of the Lake Tahoe West project found that treatments, both intentional fire and thinning, can moderate effects of fires and drought for 10–20 years (Low et al. 2021), which matches the predominant fire cycle at lower elevations throughout the basin; consequently, the 80-year span of our team’s modeling was sufficient to reflect the influence of human management on natural disturbance cycles.

The LANDIS-II model at the core of much of the analysis provides for interactions between climate, fire, and insect mortality in a coupled systems approach. It included important feedbacks, such as self-limiting effects of fire and harvest on each other, as well as climate effects on wildfire and ability to use prescribed fire. We used the model results to speak directly to the effects on forest dynamics, fire dynamics, and associated forest outcomes (structure, composition, carbon; see Maxwell et al. 2022a,b). We then layered on additional statistical and simulation modeling frameworks to evaluate changes and outcomes for wildlife habitat, water, air quality, and economics (see White et al. 2022, Slauson et al. 2022, Dobre et al. 2022, Long et al. 2022, Evans et al. 2022, and Holland et al. 2022, respectively). Our modeling did not delve into questions related to the effects of different combinations or sequences of treatments. We acknowledge that treatment combinations can have different levels of effectiveness on target objectives (e.g., reduced risk of high-severity fire; Fulé et al. 2001); however, our objectives were to evaluate a commonly applied set of management treatments to determine how resource responses, costs, and benefits co-varied across a wide array of social-ecological outcomes. We then built a decision support model to evaluate the degree to which each management scenario met the priorities and expectations of stakeholders based on their ranking of priority outcomes relative to the composite of costs and benefits associated with each scenario (see Abelson et al. 2021, 2022). The results of these various modeling efforts were incorporated into a strategic plan for enhancing social-ecological resilience that was developed by the managers and served as the blueprint for project design, implementation, and monitoring.

As an introduction to this Special Feature, we delve into some key themes that emerged over the course of the research and the human dimensions that shaped the approach and outcome of the research, and thereby generated insights into the experience of co-producing science to manage for the resilience of social-ecological systems.

DISTURBANCE IS DISTURBING, BUT NECESSARY

Different priorities for ecological and social systems

A core tension in the interactions between ecological and social systems concerns the role of disturbance. Over a century ago, as a response to extreme fire events, national forest managers in the United States adopted a goal of extinguishing all wildfires as soon as possible following their detection (Loveridge 1944). However, contemporary ecologists and managers recognize the positive and necessary function of fire and other disturbances in maintaining ecosystem services, including biodiversity and regulation of nutrient and water flows (e.g., Pausas and Keeley 2019). Forest management itself is a form of disturbance, and in ecological forestry (Batavia and Nelson 2016) the mechanical removal and manipulation of trees and other woody material in dry forest ecosystems are intended to function as a form of alternative disturbance in lieu of natural disturbances, such as wildfire and beetles.

In fire-adapted systems, low- to moderate-intensity fires are within the capacity of a forest system to absorb and recover from, and fires strengthen the capacity of a system to withstand more impactful perturbations without inducing a state change (i.e., ecological resilience; Mitchell et al. 2023). In contrast, social resilience is commonly cast as the ability to limit losses associated with disruptions or to recover quickly and fully from them (e.g., disaster recovery; Buikstra et al. 2010, Bollettino et al. 2017). In the context of a social-ecological system, however, the resilience of both ecological and social elements is often strengthened by maintaining a regime of lower-impact disturbances, in terms of both creating more opportunities for adaptive management (Temperli et al. 2012) and increasing resilience to higher-impact disturbances, thereby becoming less vulnerable to state change (Johnstone et al. 2016, Hessburg et al. 2019, Franco-Gaviria et al. 2022).

The tension between social and ecological systems in framing the role and impact of disturbance tends to result in management strategies that are dominated by actions aimed at maintaining existing conditions (a protection strategy) through mechanical treatments and prescribed fire. This is particularly true in the Lake Tahoe basin, where maintaining the clarity and ecological integrity of Lake Tahoe is of paramount importance to the resilience of the lake to future disturbances. For example, increases in fine sediments and nutrients reduce clarity, which in turn has substantial ecological and social consequences: eutrophication alters the aquatic food web structure of the lake, making it more susceptible to trophic simplification and collapse as water temperatures rise in response to climate change (e.g., Chandra et al. 2005, Noble et al. 2023); in addition, the ecological integrity and beauty of the lake are essential features supporting a robust resource-based economy that in turn motivates and sustains substantial conservation investments. By extension, maintaining and improving the resilience of upland forested ecosystems are integral to the well-being of Lake Tahoe and the surrounding communities, similarly based on ecological and social processes that intricately link the fate of aquatic and terrestrial ecosystems across the basin. To gain a more holistic understanding of potential management outcomes, the studies in this Special Feature evaluated the expected outcomes of status quo management approaches compared to more intensive and extensive management approaches and their concomitant risks.

Finding common ground in a shifting sea of disturbances

The science team’s findings indicated that status quo management will be less effective at protecting and improving desired outcomes than more active management approaches, primarily because of climate change. Specifically, management strategies that were more closely aligned with historical fire frequency (e.g., Steel et al. 2015) were most successful in moving conditions closer to resilient conditions/domains (see Maxwell et al. 2022a), but fell short of reaching outcomes with the highest potential for resilience (based on domains and thresholds derived from historical and contemporary references) across the social-ecological spectrum (see Abelson et al. 2022). A greater alignment with historical fire frequency reduced the risk of high-severity fire and reduced tree mortality to sustainable levels (see Maxwell et al. 2022a), bolstered biodiversity (see White et al. 2022) compared to status quo management, and reduced the potential for loss of infrastructure and associated social impacts (see Evans et al. 2022). These findings are consistent with the principle that redesigning disturbance regimes is a critical part of enhancing ecological resilience (Franklin et al. 2002, North and Keeton 2008).

Nevertheless, key metrics associated with social-ecological resilience still declined across all management scenarios, although less for scenarios that had more active management. Maxwell et al. (2022b, this Special Feature) found that climate change will increase wildfires and insect disturbances, and Abelson et al. (2022, this Special Feature) reported that many important social and ecological values would deteriorate as a result, with limited prospect for recovery given climate change. These findings are consistent with recent publications stating that the “warming climate and other factors are rapidly constraining our options” (Safford et al. 2022), and that “active management will be required under future predicted fire regimes to conserve and create fire resilient old forest” (Ager et al. 2022).

The social and economic benefits of management were primarily in the form of avoided risk of future losses. Both lower and higher frequency of management approaches contained risks, but similar to observed ecological outcomes, the risks associated with more active management were estimated to be lower in the long term. For example, more active management scenarios had lower net risk to infrastructure from fire (see Evans et al. 2022), lower associated economic costs (see Holland et al. 2022), and lower air quality risks to human health (see Long et al. 2022), all of which aligned well with stakeholder values (see Abelson et al. 2022). The resulting challenge for management is that more active management requires a greater financial investment and, according to the modeling, risks greater near-term impacts, including reduced habitat quality for some wildlife species associated with mature forest (see Slauson et al. 2022), short-term reductions in air quality (see Long et al. 2022) and water quality (see Dobre et al. 2022), and greater potential for fire to get out of control, in order to avoid even greater impacts from more intense future fire behavior expected to occur without management intervention.

Understandably, managers may be attracted to approaches that gradually restore historically based reference conditions while minimizing near-term costs and risks, as opposed to advancing more extensive changes that hold the promise of greater resilience to future climates and disturbance regimes but which disrupt the conditions to which people have become accustomed. The alternative of choosing more active management approaches consisting of low to moderate disturbances across large portions of landscapes also holds challenges in terms of greater perceived risk and logistical complexities associated with accelerated treatments. For example, local communities would be challenged to tolerate longer periods of low-level smoke; to support systems to effectively use intentional, frequent fire; to develop processing capacity to utilize residual biomass rather than leaving it to be burned in the forest; and to accept the uncertainty associated with greater reliance on fire (see Long et al. 2022). It seems likely that a shift in culture (e.g., transformative adaptation; Fedele et al. 2019) will be necessary for managers, leaders, and communities to effectively manage systems beyond the status quo toward resilience-centric constructs that directly inform and shape management.

WHEN TREATMENT TYPE MATTERS

Maxwell et al. (2022a,b, this Special Feature) found that treatment type (thinning versus burning) may not be as critical as the extent of the landscape being treated in improving overall system resilience to fire, beetles, climate, and drought (based on moving system metrics toward conditions considered within a safe operating space within a resilient domain), relative to the current status of the landscape, but different treatments did affect individual resource objectives differently. A recent study from the same region similarly found that both “fire and active management have similar landscape outcomes for some but not all restoration objectives” (Ager et al. 2022). So when and how does treatment type matter?

Results from this Special Feature suggest that overall, increasing the use of prescribed burning met a greater breadth of objectives and outcomes than mechanical thinning (see Maxwell et al. 2022, Slauson et al. 2022, White et al. 2022). Mechanical thinning also generated multiple benefits (see Dobre et al. 2022, Holland et al. 2022), as others have found in the Lake Tahoe basin (e.g., Krogh et al. 2020), and showed greater benefits for biodiversity conservation and carbon storage compared to prescribed fire. Nonetheless, prescribed fire outpaced mechanical treatments in terms of yielding overall benefits in moving the landscape toward more resilient conditions (see Abelson et al. 2022). Prescribed fire promoted a more favorable fire regime by reducing fuels and high-severity fires and increasing low-severity fires, which in turn promoted a wide range of other desired outcomes (e.g., reduced risk to human communities, increased carbon retention, reduced emissions). These forecasts are consistent with recent research published by others indicating that restoration of fire is the most efficient means of promoting forest resilience (North et al. 2014, 2021) and securing carbon stored in large trees (Hurteau et al. 2019).

Importantly, increased use of prescribed fire is also expected to enhance values of Indigenous peoples in the basin, which is vital to the Washoe Tribe, for whom the Lake Tahoe basin is the center of their ancestral homeland. Abelson et al. (2022, this Special Feature) represented these values as a series of “cultural resource quality” metrics, including extensive low-intensity fire and management that favored aspen, quail, and deer (as indicators of herbaceous and deciduous vegetation communities) to represent the important role of fire in promoting plant species and characteristics needed for traditional cultural practices (Lake and Long 2014).

Mechanical thinning and prescribed fire also have different implementation challenges, and across much of the western United States, implementation challenges are considered a primary limiting factor in increasing the pace and scale of treatment. Predominant implementation challenges include infrastructure and workforce capacity (e.g., Fargione et al. 2021, Yung et al. 2022), operational constraints (e.g., Lydersen et al. 2019), and unintended social-ecological impacts (see Dobre et al. 2022). Many of these challenges are consistent across types of treatments; here, we focus on implementation challenges that are unique to each of the two most common treatments applied to existing forests: thinning and prescribed fire. For example, prescribed fire is commonly the only feasible treatment for steeper (> 35%) slopes that are often dominated by shrubs and poorly suited for timber harvest (North et al. 2015, Lydersen et al. 2019); however, use of fire control can also be challenging in these conditions. Although such areas are difficult to manage, they are nevertheless critical for achieving objectives of moderating wildfire disturbances (Coen et al. 2018). Holland et al. (2022, this Special Feature) demonstrated that prescribed fire is considered generally less expensive than thinning, as others have noted in other similar landscapes (North et al. 2012; but see Hartsough et al. 2008). Yet, prescribed fire cost estimates are commonly based only on staffing required to attend to a low-intensity fire, as opposed to a fire that may require a stronger fire response capacity (Quinn-Davidson and Varner 2012), particularly in more challenging topographic locations. The unique limitations, benefits, and costs of the various treatment methods are explored in more detail below.

Mechanical treatment is limited by operability and material disposal

Analyses of treatment constraints in the region have shown that mechanical treatments alone are insufficient to reduce the risk of wildfire impacts to forest ecosystems (North et al. 2015). Although various harvest technologies, including cable and helicopter-based yarding systems, can enable removal treatments on steeper areas, distance from roads and limitations on equipment use in wilderness and other roadless areas limit the ability to reduce forest biomass without using fire. Holland et al. (2022, this Special Feature) note that a second limitation of mechanical treatments is the lack of industry capacity to process woody biomass generated by treatments. As a consequence, woody material is disposed on site through piling and burning, lopping and scattering, chipping, or mastication, which can increase surface woody fuels and associated fire risk for some period of time (Safford et al. 2009). Further, pile burning typically faces similar constraints as prescribed fire (see below), resulting in a substantial backlog of wood piles that can fuel intense fires (e.g., Safford et al. 2009).

Prescribed fire is limited by air quality, water quality, and risk tolerance

Despite the efficacy of fire as a management tool, debate about the merits and perils of fire as a primary management tool persist for several reasons. The primary, long-standing limitations associated with prescribed fire include: (1) smoke emission impacts on air quality and the associated limited periods of time (“burn windows”) when conditions are acceptable for burning to be initiated (Biswell 1999, Striplin et al. 2020, and see Long et al. 2022); (2) short-term impacts on water quality from sediment and nutrients, which, although far lower than from wildfire (see Dobre et al. 2022), are cause for concern given the objective of maintaining pristine water quality in Lake Tahoe (Grismer 2013); and (3) the risk that the prescribed fires will escape and threaten forests and human communities and infrastructure (Biswell 1999, Ryan et al. 2013). As the interface and intermix of wildlands and urban and exurban infrastructure increases, the potential impacts to human well-being (e.g., reduced air quality, infrastructure damage and loss from fire, economic impacts) also increase. Emissions from fires that burn infrastructure (e.g., the Camp Fire of 2018) can pose greater risks to human health than pure forest fires because they release toxic pollutants, including heavy metals and phthalates (Willson et al. 2021, Boaggio et al. 2022). The intentional use of fire, despite its many benefits and advantages, is likely to continue to be constrained, as wildland fires and associated smoke exposure increase, and changes in climate constrain the opportunity to burn within traditional burn windows.

The relevance of financial costs vacillates in its importance in the face of climate crises

Effective solutions that reduce the threat of climate change to ecosystem services and values are of paramount importance, and although cost efficiency is important, evidence suggests that the initial cost of treatments is becoming less important than expected short- and long-term benefits (Stephens et al. 2016). The role of treatment costs in decision making can vary across landscapes and over time in relation to values at risk, ranging from a barrier (insufficient funding to pay contractors to conduct treatments), a driver (limited funding influencing what areas get treated and how), or simply a consideration (alternative management options with cost as one of several factors considered). The influence of climate is likely to outpace all but the most strategic and active management approaches in determining the fate of future forests (see Maxwell et al. 2022a) and their ecosystem services (see Abelson et al. 2022). When large, high-severity wildfires and other severe disturbances occur, they highlight the strong linkage between wildland ecosystems and human societies, which ideally fosters learning and bolsters efforts to invest in proactive management and updating policies (Spies et al. 2014, Mockrin et al. 2018).

Hence, the cost of individual treatment types may become less relevant as the consequences of ineffective action on social and ecological systems become more apparent and impactful, which highlights the need and value of systemic social-ecological investments. For example, the immediate cost of implementing prescribed fire as a management tool is typically less expensive than conducting mechanical treatments over the same area, and both are cheaper per unit area than wildfire suppression; our team found that those relationships held up when evaluated over the long term, as well (see Evans et al. 2022, Holland et al. 2022). However, one of the primary concerns for relying heavily on prescribed fire is the risk of unintended consequences, including escaped burns (e.g., Quinn-Davidson and Varner 2012, Marks-Block and Tripp 2021). These limitations are being mitigated in some cases through institutional collaborations to make dedicated staffing and equipment available during prime prescribed burn times (Marks-Block and Tripp 2021), which increases the level of investment required to rely on prescribed fire as a management tool. Mitigating the risk of fire use to within socially acceptable levels is a form of transformative adaptation (Kates et al. 2012, Fedele et al. 2019) that is likely to require institutional change, with substantial social engagement and financial investment that could easily exceed that of mechanical treatment in order to be an enduring solution.

DUCK, DUCK, CARBON?

Regardless of the treatment method used to manage forests, be it thinning or burning, a range of benefits are likely to result, such as water yields, biodiversity, forest health, fire dynamics, and public safety (Abelson et al. 2022, this Special Feature). The notable exception is carbon sequestration from forested landscapes. The prevailing evidence suggests that as climate changes, dry forests, including those in the Sierra Nevada, are likely to become net sources of carbon release into the atmosphere as opposed to sequestering carbon from it (e.g., Liang et al. 2017). Increasing or even maintaining current carbon stores may not be feasible over the next century, given that the future resilience of forest carbon is highly uncertain (Pugh et al. 2020, Cabon et al. 2022). Multiple natural processes affect carbon accumulation in dry forest ecosystems, which are being altered by climate change: (1) tree growth rates, (2) tree mortality rates from fire and beetles, (3) tree regeneration success, and (4) woody biomass (living and dead) consumption by fire. More intensive forest management can reduce beetle and fire mortality, but the resulting balance sheet in terms of carbon benefits is less clear, particularly when larger diameter trees are removed. Generally carbon recovery and net benefits associated with management treatments depend on the characteristics of the landscape, vegetation composition and structure, vulnerability to fire, and treatment parameters (e.g., Mitchell et al. 2009, Campbell et al. 2012, Wiechmann et al. 2015).

Indeed, in the Lake Tahoe basin our science team found net increases in carbon storage over the next century. Maxwell et al. (2022b, this issue) observed that carbon accumulated in Lake Tahoe West landscape in every management scenario, including the suppression-only scenario, consistent with Loudermilk et al. (2013), but more slowly in more intensive management scenarios. Maxwell et al. (2022b, this Special Feature) found that carbon declined in proportion to the intensity of the treatment, particularly in the short term (5–10 years following treatment), and that even in the case where management was minimal and wildfires were more prevalent, carbon storage increased more than under more active management. These results seemingly run counter to the argument that the “avoided cost” of losses from wildfire (e.g., Cathcart et al. 2010) are greater than the near-term reductions resulting from management. We attribute this largely to the physiographic characteristics of the basin. The west side of the Lake Tahoe basin is relatively mesic compared to the rest of the basin and much of the Sierra Nevada region. Many of the higher elevation zones across the Sierra Nevada typically have persistent winter snowpack and higher precipitation compared to lower elevations on the western and eastern flanks of the range. They are also still recovering from intensive logging in the 19th and 20th centuries (Loudermilk et al. 2013). We expect that these results are more accurate when assessing the relative carbon sequestration among management scenarios, and likely represent an optimistic scenario for mesic forest net carbon sequestration over the next several decades.

Perhaps most importantly, maintaining carbon in the form of existing dense forests runs counter to promoting overall system resilience for a variety of reasons. Even though the second growth forests of Lake Tahoe are continuing to recover from historic harvesting (Loudermilk et al. 2013), the promotion of large trees combined with an overall reduction in forest biomass may be the more feasible goal. Historical levels of carbon were likely much lower than in present-day fire-suppressed forests, as much as 2.5 times lower in a study of an old-growth forest by Harris et al. (2019). In a study within the Lake Tahoe basin, Taylor (2007) found that contemporary Jeffrey pine–white fir forests had on average five‐fold more trees and nearly two‐fold more basal area than forests prior to Euro-American colonization. This coincides with recent findings in California that active interventions, including greater use of fire, are needed to bring biomass levels to lower, more sustainable levels (Knight et al. 2022) and to reduce dead forest biomass (surface fuels) and tree density (ladder fuels) to avoid more extreme fires (Stephens et al. 2022). Because the more active management scenarios modeled by our science team reduced tree density and fuels toward historical levels, they also resulted in both a near-term and long-term reduction in carbon storage compared to contemporary “business as usual” management. Realigning forest conditions to reduce extreme forest mortality and risks to infrastructure can be accomplished, with varying trade-offs among co-benefits (e.g., biodiversity conservation), although potential carbon storage may be diminished, depending substantially on the realized climate future.

THE UNGAINLY NATURE OF CO-PRODUCING SCIENCE TO MANAGE UNCERTAINTY

The Lake Tahoe basin is a prime example of a high-value social-ecological landscape, with leaders and constituents expecting the best-of-the-best in all efforts to conserve and restore environmental quality and enhance the resilience of the Lake Tahoe basin social-ecological system. The availability of a robust scientific foundation to inform and guide policy and management is inherent in these expectations. The science and management communities regularly work closely together to identify important information gaps and generate an actionable understanding of the status of environmental quality, where it is vulnerable, and how it can be improved (e.g., Hymanson et al. 2010). There is also a keen appreciation for the interdependence of environmental quality and social, cultural, and economic well-being of the basin and the surrounding region.

The Lake Tahoe West project, as with a growing number of large landscape restoration projects, engaged scientists to work directly with managers to develop an actionable scientific foundation to support a restoration strategy that could serve as a model for the future. Our science team contained a diversity of expertise across the social-ecological spectrum and was tasked with building a better understanding of the efficacy of different management strategies in accomplishing short- and long-term objectives set by managers, given an uncertain future climate. Managers were particularly keen on understanding how climate change was likely to affect the efficacy of proposed management strategies, and how to design management to improve environmental quality while reducing risks and providing benefits to communities and stakeholders. By considering climate change, the effects of the most prevalent disturbances (namely wildfire, drought, and beetle-related mortality), and alternative management regimes, they were able to project the response of many different facets of the social-ecological system in the Lake Tahoe basin to these perturbations individually and in composite over multiple decades, rather than being limited to measures of vulnerability as an indicator of potential resilience. We highlight some emerging themes from our experience of leading the co-production of science—in short, it is partnership that requires cooperation, patience, and skill, with the pay-off of science-based decision processes and outcomes that would not be otherwise possible.

Climate change is eroding established contexts for defining resilient conditions and affecting confidence in the outcome of management

The concepts “historic range of variability” and “natural range of variability” have been valuable touchstones for managers to derive quantitative targets for desired conditions (e.g., Safford and Stevens 2017, Meyer and North 2019, Meyer et al. 2023). However, the changing climate is eroding the assumption that pre-1850 structure and composition will be resilient to future environmental conditions as disturbance regimes morph under a changing climate (Ravenscroft et al. 2010, Maxwell et al. 2022a, this issue; Hill et al. 2023). Consequently, scientists and managers are now working to develop future-oriented resilience targets, and new tools for projecting forest resilience (Lucash et al. 2017, Meyer et al. 2021). Nevertheless, it can be challenging for managers if models of future conditions run contrary to currently held expectations as to what a resilient future landscape is likely to entail—a phenomenon termed “future shock” (Toffler 1970, Kimmins 2002). Furthermore, models may lead people to give too much weight to the attributes of a system that are most conducive to modeling while ignoring attributes that are important but difficult to represent, such as human adaptation through land use policies and practices (Kline et al. 2017). A result could be that managers might be pressured to advance plans that satisfy concerns of diverse stakeholder and management communities, even though they may not sufficiently account for anticipated future impacts.

Technological advances and the field of decision support are pushing management culture and stress-testing science-management partnerships

Research and development in government, academia, and the private sector are rapidly producing new, increasingly sophisticated analytical approaches and tools that are being applied by scientists across landscapes to inform management (e.g., Abelson et al. 2021). There is a clear and acknowledged need for more and better information to provide a scientifically sound underpinning to management decisions, but management agencies are often not sufficiently staffed to receive all the data and tools being delivered by scientists. The need for management to be informed by scientifically robust information is high, but a gap often exists as a function of two cultural factors: (1) neither scientist nor managers have a clear mandate to apply new tools (i.e., “turn the crank”); thus, there can be a gap between development and application; and (2) management’s enthusiasm for decision support tools may be dampened by the potential to over-prescribe solutions, and because scientific information is just one factor taken into consideration in management decisions. The result can be that, despite good intentions by scientists and managers, relevant information and innovative, science-based tools and solutions are underutilized.

The value of co-production is attractive but requires precious time

Co-producing science is the practice of increasing interaction between scientists and managers in the process of conducting research, with the goal of enhancing the impact of knowledge development (Jasanoff 2004, Arnott et al. 2020). Indeed, co-production commonly bears fruit in terms of more relevant and applicable results (e.g., Cash et al. 2003). The challenge is that co-production can be very time consuming (Lemos et al. 2018). As with any collaboration among diverse stakeholders, it takes time to build trust, establish realistic and workable operating principles, meet frequently to discuss and navigate each step of the analysis process, and ultimately reach some degree of consensus on how to interpret results and their implications for management. For this project, members of the science team met with managers multiple times per week for over two years, in addition to meetings among science team members. Functionally, co-production expands the science team to include non-scientist members, but all the same norms still apply to generating, interpreting, and delivering science.

Over the course of the work conducted by our team and the collective co-production experiences of the co-authors, we found that working directly with managers is essential to tailoring investigations, analyses, and products to best meet the needs of managers; however, it comes with a cost. The outcomes (costs and benefits) of our co-production experiences can be summarized in four main themes: (1) participating scientists and managers gain a much greater understanding of and appreciation for what is required to do the other’s job; (2) the participants are impacted by the additional time required to accomplish the work (managers and scientists spending time explaining their methods and decision-making processes to each other, as well as awaiting feedback from the multiple project partners); (3) more protracted timelines for providing scientific products can impact management schedules, resulting in delayed planning objectives, or decisions proceeding without scientific input; and (4) results that are contrary to expected outcomes or the status quo perceptions within the management community create uncertainty that can make it challenging to incorporate findings into near-term decisions (Briley et al. 2015, Newton and Elliott 2016). In the latter two circumstances, the result is that scientific findings and products may not be immediately useful to management, despite significant investments by scientists and managers in co-production. Nonetheless, these investments and challenges ultimately strengthen the science-management partnership, and through the push and pull of co-production, forge a more relevant and applicable scientific foundation that informs and supports management and enhances the ability of management to operate effectively in an environment of increasing uncertainty.

The co-production of science is a marriage, not a date

Scientists are famous for ending every report and publication with the statement that more research is needed—and it is. Understandably, managers have pressing needs and want quick, reliable, and definitive answers. Projects and partnerships like Lake Tahoe West are not one-off, stand-alone projects in the bigger scheme of managing the Lake Tahoe basin for long-term resilience. Rather, they are essentially one pearl in a string of complementary investments over time, each building on the last, learning from the past, and pushing to new levels of understanding and partnership about this high-value social-ecological system and how environmental dynamics are shaping and changing its landscapes and communities over time. For example, the first comprehensive social-ecological assessment was conducted across the Lake Tahoe basin in the late 1990s (Murphy and Knopp 2000a,b), and that work identified a wide array of important information gaps (Hymanson et al. 2010). Subsequently, all levels of government and non-governmental organizations operating in the basin have helped form and support some form of formal science advisory function for over the past two decades. For example, the extant Tahoe Bi-State Science Council established by the Governors of California and Nevada exists to help direct, prioritize, accomplish, and deliver research that is relevant and applicable to managing to achieve and conserve environmental quality in the basin (e.g., Knopp et al. 2016).

CONCLUSION

Interdisciplinary research to improve our understanding of social-ecological systems, such as the coordinated suite of studies in this Special Feature, allows scientists, managers, and stakeholders to consider many facets of social-ecological resilience and to productively address the challenges of a changing climate. In the case of Lake Tahoe, President Clinton and Vice-President Gore visited the Lake Tahoe basin over two decades ago and launched the Lake Tahoe Restoration Act with an emphasis on science-based environmental improvement, setting the stage for actionable science and its application by managers toward greater resilience. The science-management partnership that ensued made possible many studies, including those presented in this Special Feature, which greatly improved our understanding of what the future may hold in this complex system. Our team’s results illustrate that models and scientific information are crucially important, and yet they can only provide part of the answer for how to enhance the resilience of complex, adaptive social-ecological systems.

A reasonable objective for science-management partnerships is not to fully account for the complexity of social-ecological systems, but rather to provide a sound basis for experimentation and adaptation. The degree of investment in the science-management partnership for Lake Tahoe West is not realistic for every 100,000-ha landscape, but it is also not necessary. Adaptation across social-ecological systems requires flexibility and resilience at all levels of our social systems (individuals, teams, institutions, and communities) in order to ask and answer meaningful and important questions, be realistic and explicit about what we do not know, recognize the vulnerabilities that those gaps present to decision making, and take every opportunity to learn more together. Further, as the quality and availability of remotely sensed and modeled data on natural resources and their linkages with social elements of systems is rapidly improving, the ability and ease of assessing conditions and evaluating management options is dramatically increasing, making it possible to conduct more in-depth analyses for less money and time across exponentially larger landscapes (e.g., Manley et al. 2023). Scientists and managers continue to collaborate on the next chapter of challenges in Lake Tahoe, including the joint development of climate adaptation strategies, updating desired conditions, and revamping environmental performance measures, all of which are designed to help managers and policy makers more effectively establish desired outcomes, make management investments, measure progress, and ideally thrive despite considerable uncertainty in the face of change.

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