www.sciencemag.org **SCIENCE** VOL 342 4 OCTOBER 2013 

### 41 

# POLICY FORUM



# W ith projected climate change, we

expect to face much more forestfi re in the coming decades. Policymakers are challenged not to categorize all fires as destructive to ecosystems simply because they have long fl ame lengths and killmost of the trees within the fi re boundary. Ecological context matters: In some ecosystems,high-severity regimes are appropriate, but climate change may modify these fi re regimes and ecosystems as well. Some undesirable impacts may be avoided or reduced through global strategies, as well as distinct strategies based on a forest’s historical fi re regime. Fire regimes are commonly characterized by burn frequency and severity within a givenarea. Severity is often estimated as the proportion of overstory trees killed by fi re. In general, as frequency increases, fuels have less time to accumulate, reducing intensity and subsequent tree mortality. However, a great deal of variation occurs even within fi re regime types ( 1 ). The spatial scale and patchsize distribution of different severity classes are key in assessing whether fire regimes have changed over time and whether changes maintain or compromise forest ecosystems. Globally, fi re frequency and severity vary among forest types. Essentially all fi res have high-severity effects, where most of the trees are killed, at some spatial scale and patch

size. The critical issue is whether tree mortality patch sizes (and their temporal and spatial frequency) allow recovery of the same or similar vegetation types. If high-severity patch sizes are too large, microclimates andregeneration mechanisms (e.g., seed abundance and dispersal) can limit tree reestablishment (see the fi gure) . Large high-severity patches may produce vegetation typechanges, especially in forests adapted to frequent, low- to moderate-severity fi re regimes or in forests that lack in situ propagulesources. Introduced species, such as nonnative grasses, also may alter forest fi re regimes and lead to changes in vegetation type ( 2 ). Changing fi re severity is at the heart ofecological debates about historically highfrequency, low- to moderate-severity fire regimes, such as ponderosa pine (Pinus ponderosa ) and semiarid mixed-conifer forests.A central concern is whether high-severity patches in wildfi res are too large, which results in undesirable ecosystem changes (see the fi gure). Rising temperatures, related drought stresses, and increased fuel loads aredriving high-severity patches to extraordinary sizes in some areas ( 3 ).In contrast, forests adapted to low-frequency, high-severity regimes such as Rocky 

# Managing Forests and Fire in Changing Climates **LAND USE**

S. L. Stephens, 1 * J. K. Agee, 2 P. Z. Fulé, 3 M. P. North, 4 W. H. Romme, 5 T. W. Swetnam, 6
M. G. Turner 7 Policy focused on fi re suppression only delays

the inevitable.

*Corresponding author. E-mail: sstephens@berkeley.edu 1 University of California, Berkeley, CA 94720, USA. 2 University of Washington, Seattle, WA 98195, USA. 3 Northern Arizona University, Flagstaff, AZ 86011, USA. 4 U.S. Department of Agriculture Forest Service, Pacifi c Southwest Research Station, Davis, CA 95618, USA. 5 Colorado State University, Fort Collins, CO 80523, USA. 6 University of Arizona, Tucson, AZ 85721, USA. 7 University of Wisconsin, Madison, WI 53706, USA.

Prefire forest High postfire resilience Low postfire resilienceHigh-frequency, low-severity fireLow-frequency, high-severity fire

Historical forest fi re regimes. ( Top ) Mixed-conifer forest in northern Californiawith fuels accumulated from a century of fi re suppression (left), mature surviving and regenerating trees in an area that had been mechanically thinned to reduce fuels and residues either removed or burned (center, 10 years after the 2002 Cone Fire), and an adjacent untreated area lacking live seed trees, now dominated by shrubs (right, 10 years after the Cone Fire). ( Bottom ) Lodgepole pine forests in Greater Yellowstone (left) regenerated abundantly from the canopy seedbank after the stand-replacing 1988 Yellowstone Fires (center, 15 years postfi re), but regeneration was greatly reduced in forests of comparable age and serotiny after the 2000 Glade Fire, which was followed by summer drought 1 year after the burn (right, 10 years postfi re). Forests are within 4 km of each other

at each site.CREDIT: (TOP) MALCOLM NORTH; (BOTTOM) MONICA TURNER

P u b l i s h e d b

y A A A Son October 1, 2015www.sciencemag.orgDownloaded from4 OCTOBER 2013 VOL 342 **SCIENCE** www.sciencemag.org 

### 42 

## POLICY FORUM

Mountain lodgepole pine ( Pinus contorta

var. latifolia ) have evolved to regenerate after large, high-severity events. Seed banks storedin tree crowns survive even the highest-severity fi res and are released shortly after the fi re ends. If seeds germinate in open conditions conducive to relatively high growth rates, a

new forest can become established in a few decades (see the fi gure). Other species can regenerate a new crown from one burned by

fi re because of dormant buds.

Future Fire Under Changing Climates With projected climate warming ( 4 ), forests around the globe will likely undergo major landscape-scale vegetation changesin coming decades. In some areas, plant productivity may decline to a point where fi re will become less frequent ( 5 ). In more productive areas, fi re regimes may shift from being mostly climate-controlled (top-down) to mostly fuel-controlled (bottom-up) ( 6 ). In both cases, slow vegetation change may be abruptly accelerated by a change in fi re regime driven by novel climatic conditions. Increased frequency and size of large, severe forest fi res are expected in Australia, the Mediterranean Basin, Canada, Russia, and the United States ( 3

, 7

, 8 ). In the western United States, increased frequency and sizeof fi res is associated with increased temperatures, earlier spring snow melt, and longer fi re seasons ( 9 )—mechanisms that are applicable to other regions of the world. Trends and projections of climate and fi reresponses suggest that new strategies to mitigate and adapt to increased fi re are needed to sustain forest landscapes. Identifying and implementing appropriate responses will not be easy because the complexity of local-to-regional dynamics makes uniform,simple, or unchanging policy and management strategies ineffective ( 10 ). It is especially diffi cult to motivate social response to environmental transitions that unfold slowly

and are thus diffi cult to detect before it is too late ( 11 ). We suggest strategies for forests of all fi re regimes: Landowners should follow “Firewise” guidelines (

www.firewise.org/

) for houses and other infrastructure. Increased development in fi re-prone landscapes has increased suppression costs, exacerbated risk to human safety and infrastructure, and reduced management options. People living in these forests must be prepared rather than relying solely on fire departments. Someplaces may be so hazardous that building should be prevented, discouraged, or removed (e.g., by regulation or insurance and/or tax incentives). Fire managers should avoid trying to uniformly blacken wildfi re landscapes through burnout and mop-up operations, especially

in burn interiors. As wildfire sizes have grown in recent decades, direct attack has been replaced with indirect attack, where fi re lines are placed some distance from the active fi re front, and then the area between is intentionally burned, often with high-severityfi re, to reduce fuel and create a wider fi re barrier. Unburned or partially burned patches are critical refugia that aid postfi re recovery inforests of all fi re regimes and should be conserved whenever possible. Land managers could anticipate changes using models of species distribution and ecological processes and should consider using assisted migration ( 12). Dominant forest species may be unable to recover from fi res with large high-severity patches. Replacement ecosystems of shrublands or grasslands may provide some ecologicalbenefi ts, but they offer very different habitats for wildlife and have reduced carbon storage relative to native forests.We also suggest several distinct strategies based on a forest’s historical fi re regime.Mitigation in forests with historically highfrequency, low- to moderate-severity fire
regimes: (i) Restore resilient forest structure similar to historical patterns that survived during past high-fi re periods (and those anticipated in the future) (see the figure).

Fuel reduction and restoration treatmentscan increase resiliency by reducing density-dependent tree mortality ( 4 ) and excessive insect and/or disease problems and can increase spatial heterogeneity. (ii) Fund forest restoration. We know howto treat forests to reduce fi re hazards, with generally positive or neutral ecological effects, although impacts to wildlife with large home ranges have not been fully assessed ( 13 ). Public acceptance of these treatments is increasing ( 14 ); the barrier is cost. Treatment rates are far below what is needed for landscape resilience ( 15 ). Because the federal government has no jurisdiction in development policies in the privately owned urban-wildland interface, state and local jurisdictions could pay for fi re suppression in the interface. This would enable a signifi cant increase in criticalforest restoration funding and would probably reduce building in the interface. Adaptation in forests with historically low-frequency, high-severity fire regimes: (i) Expect changes in forest type and age across the landscape (see the fi gure). Some forest types will be relatively resilient to more frequent fi res, notably resprouting or seed-banking species. However, even these forests will likely exhibit substantial changes in landscape structure, such as shifts to a preponderance of young stands ( 16 ). (ii) Some forests will change to nonforest vegetation after fi re. Spruce-fi r ( Picea-Abies ) and interior Douglas fi r ( Pseudotsuga menziesii ) forests may exhibit large changes in structure and species composition becausethey lack persistent seed banks or sprouting capability. Some areas may even shift to a nonforest state, especially if trees cannot reestablish in a warmer, drier climate. Such changes will not necessarily be catastrophic (e.g., a shift to nonforest could potentially increase water yield) and could be expectedto reduce intensity of subsequent fi res. However, shifting from forest to nonforest would affect most ecosystem services. There areno clear guidelines for increasing the resilience of these forest types—unlike for forestsadapted to high-frequency, low- to moderateseverity fi re regimes—other than minimizing additional stresses from excessive grazing, recreation, and salvage logging. The annual cost of fire suppression is increasing and unsustainable; costs exceeded
$2 billion in the United States in 2012. Fire policy that focuses on suppression onlydelays the inevitable, promising more dangerous and destructive future forest fi res. In contrast, land management agencies could identify large fi resheds (20,000 to 50,000 ha) where, under specifi ed weather conditions, managed wildfi re and large prescribed fi re are allowed to burn, sometimes after strategic mechanical fuel treatments ( 15 ). Acknowledging diversity in fi re ecology among forest types and preparing forests and people for larger and more frequent fi res could help reduce detrimental consequences.

References
1. T. Schoennagel et al

., BioSci. 54 , 661 (2004).
2. J. K. Balch et al

., Glob. Change Biol. 19 , 173–183 (2013). 3. P. Attiwill, D. Binkley, For. Ecol. Manage. 294 , 1–3 (2013).

4. A. P. Williams et al

., Nat. Clim. Change 3 , 292–297 (2013).

5. M. A. Moritz et al

., Ecosphere 3 , art49 (2012).
6. J. S. Littell et al

., Ecol. Apps. 19 , 1003–1021 (2009).

7. M. Moriondo et al

., Clim. Res. 31 , 85–95 (2006). 8. M. Flannigan et al

., Glob. Change Biol. 15 , 549–560 (2009). 9. A. L. Westerling et al

., Science 313 , 940–943 (2006). 10. F. S. Chapin et al

., BioSci. 58 , 531 (2008). 11. T. P. Hughes et al

., Trends Ecol. Evol. 28 , 149–155 (2013).
12. L. R. Iverson, D. McKenzie, Landscape Ecol. 28 , 879–889 (2013). 13. S. L. Stephens et al

., BioSci 62 , 549–560 (2012). 14. S. M. McCaffrey, C. C. Olsen, “Research perspectives on the public and fi re management: A synthesis of current social science on eight essential questions” (Gen. Tech. Rep. NRS-104, U.S. Department of Agriculture Forest Service, Newtown Square, PA, 2012).

15. M. P. North et al

., J. For. 110 , 392–401 (2012). 16. A. L. Westerling et al

., Proc. Natl. Acad. Sci. U.S.A. 108

, 13165–13170 (2011).

10.1126/science.1240294

P u b l

i s h e d b

y A A A S