Climate Change, Forests, Fire, Water, and Fish: a Synthesis for Land and Fire Managers

Climate Change, Forests, Fire, Water, and Fish: A Synthesis for Land and Fire Managers Charles H. Luce, Penelope Morgan, Kathleen A. Dwire, Daniel J. Isaak, Bruce E. Rieman, and Zachary Holden Introduction As the climate changes in the western United States streams are warming, low flows in summer are declining, and winter floods are occurring more often in places where snowmelt is the main source of water (Stewart et al., 2005; Hamlet and Lettenmaier, 2007a; Luce and Holden, 2009; Isaak et al., 2010). Some of the changes have been subtle, others more noticeable, and they are expected to shift distributions of fishes (Rieman et al., 2007; Wenger et al., 2011a; Wenger et al., 2011b). At the same time, the terrestrial ecosystems surrounding the mountain streams of the west are changing in response to the same climatic signals. Drier years and drier summers have often led to more large fires, many of which are more severe (Dillon et al., 2011). Further, fire regimes are shifting, with fires becoming more frequent in some places and less frequent in others, and potential conversion of forests to shrubs in some places (Pierce et al., 2004; Breshears et al., 2005; Westerling et al., 2006; Morgan et al., 2008; Westerling et al., 2011). Fires have long been prevalent in western mountain landscapes. Many, but not all, ecosystems benefit from the biomass consumption, cycling of nutrients, rejuvenation of vegetation, and changing vegetation composition and structure after fires (Agee, 1993). Indeed many species and ecological communities in the western U.S. depend on fire in some form. Some benefit from frequent fires that consume small amounts of fuel, while others, seemingly paradoxically, thrive as a result of infrequent but severe fires that consume most of the available fuel in their path. Thus, fire itself has been long recognized as a considerable influence, apart from any consideration of a changing climate, on forest and stream ecosystems (e.g. Bisson et al., 2003; Shakesby and Doerr, 2006; Hessburg et al., 2007). The number of large fires has increased in recent decades, and future annual area burned is likely to increase further with concurrent concerns over costs of fire management and threats to safety of people and property (NWCG [National Wildfire Coordinating Group], 2009; Spracklen et al., 2009; Littell et al., 2010). Although not all environments are equally prone to 1 fire, and humans have been very effective at detecting and suppressing the majority of fires when they are small (Stephens and Ruth, 2005), forest fires will continue to occur. Global, national and regional trends of increasing number of large fires in recent decades are likely to continue with implications for both terrestrial and aquatic systems. Fire and related disturbances will be an agent of climate change in shifting forest ecosystems (Dale et al., 2001; Jentsch et al., 2007; Turner, 2010). Tree mortality can be caused directly by climate, or it may be induced by fire that is in turn responding to climate. Sometimes, the loss of the current forest canopy can pave the way for new species and even life forms (e.g. shrubs and grasses). Thus, climate change and climate variability have both direct and indirect implications for fish, streams, and aquatic ecosystems. Fire may become a critical point in the progression of individual forest stands or streams, where ecosystems may either gradually shift in response to climate change punctuated by fire and recovery (Figure 1a), much like they always have, or where ecosystems are relatively non-responsive to climate between events which provide the catalyst to adjust to new climate conditions (Figure 1b). This new transitioning role of fire as “coup de grace” will pose new challenges for land managers who are well versed in the cyclic dynamics of forests. Of course, this simple model must be thought of in different terms in the context of changing disturbance frequency and severity as well. Providing sustained ecosystem services through seemingly unpredictable change-points may represent a primary challenge for managers. 2 a b Ecological Departure Environmental Change Figure 1: Conceptual roles for disturbance in a changing climate. Disturbance could continue to operate much as it always has, with unique disturbance/recovery patterns, or it could become the catalyst that allows ecosystems to shift in response to climate. While natural systems have evolved adaptations to the kinds of disturbances provided by fire, plant and animal populations may not be resilient to fires when fire regimes change, or when the landscape context of those fires changes. Large trees that survived many surface fires in the past may die in high severity fires, and regeneration of new trees may fail if fire recurs before young trees grow to fire-resistant size. Where serotinous cones have aided rapid post- fire regeneration, such regeneration will be less successful if fires recur before trees are old enough to produce abundant cones. For species relying on recolonization through dispersal from unburned refugia, very large, severe fires may present too great a barrier. Trees may not regenerate successfully following high severity fires at lower timberline if the post-fire environment is less conducive than in the past or if invasive plants pose severe competition. An 3 awareness of how the chain of consequences from climate change interacts with natural adaptations will be critical to forming solutions that maintain valued ecosystem components and processes into the future. Within the pantheon of adaptation and mitigation concepts and approaches, two terms, resistance and resilience, stand out as critical ideas (e.g. Holling, 1973; Waide, 1988; Millar et al., 2007 and see Text Box). Resistance is the ability of an ecosystem to experience stressors but not change. For example old ponderosa pine and Douglas-fir trees with thick bark are very resistant to surface fires. Engineers describe resilience as the ability to return to a given state despite sometimes formidable changes. Ecologists, sociologists, and psychologists share a more generalized definition of resilience as the capacity to absorb and weather change in a way that both combines and transcends the engineering concepts. Nonetheless, the engineering- oriented metaphor highlights the point that if climate changes, there seems to be a difficulty in applying either concept, as resistance must eventually be overcome, and it’s difficult to “bounce back” if the driving pressures are maintained if not growing. The concept of facilitated change fills in this difficult space. For example, while thinning might be seen as a resistance step for fire in one context, it can also serve to help forests cope with a changed water balance in a more predictable manner than without treatment. Preparation in many forms contributing to both resilience and resistance will be important, as will appropriate responses during and after major disturbances. No longer will simple protective responses to events suffice, nor even simple protective preparations. A set of strategic measures encompassing whole landscape perspectives using combinations of protective, monitoring, and corrective approaches will be necessary to manage a dynamic system suffused with uncertainty from both chance events and incomplete understanding. There will be tradeoffs between current and future risks. Management actions taken in the present will, with certainty, pose some risk, especially in the short term. The question is whether the imposed risks outweigh potential future risks. Even if they do, there are questions about scaling imposed risks, like how much at once and how much do we leave to chance in the short to medium term. While none of these questions have universal answers, there are contexts that support one approach versus others, and attentive managers teamed with researchers can learn how to describe the tradeoffs rationally. Key Debates With respect to forests, critical issues revolve around fire and fuels management including mechanical fuel reduction, intentional fire treatments, and natural fire treatments. Each comes with attendant risks, such as fires with unintentionally high severity or size, long duration and severity of smoke exposure from fires, potential for increase in invasive species, and impacts of roads where they are needed to facilitate management. There are costs and benefits with 4 these actions, just as there are costs and benefits to no action. Decisions about where to prioritize work are a critical piece of the decision-making process. These decisions are made most frequently in the contexts of human habitation and threats to forests from fire, insects and disease. These decisions are sometimes difficult (and constrained) without considering the riparian and aquatic components of the ecosystem. Within riparian zones, most treatment options, including no action, have consequences for unique plant communities and adjacent streams. Considering aquatic communities brings in a range of other issues for water and aquatic management, some of which compete, or seem to compete, with decision space for forest management. Roads, which provide important access for silvicultural treatments and fire response now form a threat not just to native vegetation, but also to stream communities, intensifying the tradeoffs. Reframing the decision goals to optimize both aquatic and terrestrial conditions, can reveal opportunities in place of tradeoffs, particularly in previously managed areas with an existing

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