3. Is fire bad?

The number of large and severe wildfires in the United States has more than doubled in the past decade, even while there has been a decline in all fires over the past three millennia, and passive and active suppression of fire during the last two centuries. In the U.S., the Forest Service and Interior Department spent about $1.7 billion last year fighting fires, a $500 million increase over the previous year and double the average amount spent a decade ago. What is causing this increase in such destructive fires? What are the long-term effects on ecosystems and climate?  Can and should we do anything about it?  Is fire bad?

 

Fire at night

Fire at night. Photo provided by Jennifer Balch

 

A trio of pyrogeographers at Penn State— Jennifer Balch, Alan Taylor, and Erica Smithwick—and their students are conducting research on fire and landscapes and ecosystems to find some answers to the dilemma of how humans can more effectively manage our complex relationship with fire.


Briefly describe your areas of focus and interest in comparison with each other.

JKB: My research explores the diversity and distribution of fire, and consequent ecosystem response to shifting fire regimes. My work aims to address the following major unsolved questions: What is fire’s role in the Earth system, and particularly the climate system? How are fire regimes altered by invasive species? How is the unprecedented increase in human-initiated fires altering tropical forest dynamics?

EAHS: I am interested in fire patterns at ecosystem to landscape scales and how fire modifies biogeochemistry, particularly carbon and nutrient cycles in forested systems.  I use observational, laboratory, and ecosystem modeling approaches to understand how past fire influences current patterns in ecosystem function (everything from microbes to landscape carbon budgets) and predict these effects into the future under climate change. Like Jennifer, I am interested in the conditions that produce novel fire patterns.  In addition, I am interested in contextualizing these patterns based on the work that Alan does, as well as thinking about how multiple disturbances (for example, bark beetles and fire) interact and whether we are able to capture those dynamics in models.

AT: My fire research is focused on the spatial and temporal controls of fire regimes, particularly the influence of fuels and vegetation, land use and climate variation. In comparison to Erica and Jennifer, I tend to use a more historical approach that often involves techniques such as tree ring or charcoal analysis to capture variability in fire regimes over periods of centuries to millennia. I am also interested in how knowledge of vegetation structure, fire behavior and spatial controls on fire regimes can be used to assist managers in designing effective landscape strategies to reduce fire risk and fire hazard in landscapes prone to severe fire.

What is your assessment of the current fire regime in the western United States? 

AT: There is high fire hazard in lower-elevation forests that once burned frequently but are now more dense because of fire suppression. This means these forests are likely to burn at high severity. High-severity burns can result in long-term vegetation shifts from trees to shrubs in some areas. I expect a bad fire season in California this summer because of severe drought, as well as in the southwest which has been under an extended drought. Under severe drought most forests have the potential to burn—even those at higher elevation—in fact, extreme drought conditions are about the only time high-elevation forests in the western U.S. will burn.

EAHS:  The current fire regime in the western U.S. is very severe; the fires are much more extreme than in the past due to a combination of fire suppression and severe climate conditions.  Some places, like Yellowstone, are adapted to severe, stand-replacing fires (when the trees are killed), but have mechanisms in place for rapid recovery, and so fire suppression has had a minimal effects. This is very different than many places in the U.S. however, where frequent fires were more common historically but fire suppression has drastically modified fuel loads. Our models project that the climate conditions that produce these fires are likely to be more common in the future.  Our results suggest these novel fire-climate relationships could have significant consequences for vegetation in the region.

JKB: Increased spring and summer temperatures and an earlier spring snowmelt in the western U.S. have led to increased frequency of large wildfires and longer wildfire seasons. Current fire patterns look like they’re departing from historical patterns. And this appears to be a global syndrome. Large wildfires may be a warning sign that something bigger is happening. Changing fire regimes may be a global phenomenon, not isolated disasters

Is there a positive feedback loop between severe fire and climate change?

AT: There could be in some parts of the western U.S. I am familiar with. In these places, if warming and drying promote more severe forest fires, forest will be replaced by shrublands. When shrublands burn they tend to be replaced by shrubs again. If this kind of vegetation switching occurs over wide areas, it can influence the ability of vegetation to sequester carbon taken up from the atmosphere—hence the feedback. There is emerging evidence of this kind of vegetation switching in recent severe fires in California and Oregon.

EAHS:  Severe fire that deviates from historical patterns could lead to net carbon losses to the atmosphere, which could have a positive feedback because enhanced carbon in the atmosphere will lead to warmer temperatures that promote more fire.  The largest changes will be if forest vegetation cannot recover from fire and instead is replaced by lower-carbon-storing shrublands and grasslands. While the carbon cost of this transition would be high, ultimately these systems would produce fire cycles that are less severe due to lower fuel loads, which could ultimately be a negative feedback.  Although each shrubland fire would release less carbon to the atmosphere, the total carbon lost caused by the forest to shrubland transition is more important in terms of net carbon stocks.

JKB: A positive feedback between climate change and biomass burning is plausible given the direct impact of fire on biogeochemical cycles, particularly carbon fluxes.  Nonetheless, it is widely assumed that, at the global scale, long-term (i.e. decadal to longer) effects of fire on carbon fluxes are largely cancelled by vegetation regrowth following fire. However, with rapidly changing climates and large social and industrial changes, this assumption may be increasingly (and dangerously) wrong. We can look at past climate and relationships with charcoal deposits to reconstruct climate-fire interaction. In a study of North America, charcoal data show that climate plays a substantial role in determining the major levels of fire activity.

What is the role of natural fire in the ecosystem and how is it different from human-caused fire?

EAHS:  The entire study of pyrogeography is trying to address this by recognizing that fire is uniquely adapted to its environment (fuels, climate) and to unravel how the patterns in fire are caused by shifting human use of the landscape versus changes in these other factors.  We know people have used fire for over 300,000 years and that it is fundamental to maintaining many systems in the natural state that we recognize for them (e.g., savannas).  In the absence of fire, these systems would fundamentally change.  But, it’s important to recognize that there is a gradient in the degree to which humans have modified ignitions as well as the degree to which this modification deviates from the natural fire cycle.  In other words, the impacts of human fire modifications is different in different places. 

JKB: Humans and their ancestors are unique in being a fire-making species, but natural (i.e. independent of humans) fires have an ancient, geological history on Earth. Natural fires have influenced biological evolution and global biogeochemical cycles for several hundred million years, making fire integral to the functioning of some biomes. Globally, debate continues about the impact on ecosystems of prehistoric human-set fires, with views ranging from catastrophic to negligible. Understanding of the diversity of human fire regimes on Earth in the past, present, and future remains rudimentary. It remains uncertain how humans have caused a departure from natural background levels that vary with climate change. Available evidence shows that modern humans can increase or decrease background levels of natural fire activity by clearing forests, promoting grazing, dispersing plants, altering ignition patterns and actively suppressing fires, thereby causing substantial ecosystem changes and loss of biodiversity.

AT: Geography really matters in answering this question. People have greatly increased ignitions above background levels for their particular purposes. For example, evidence of natural fire before the Polynesians arrived to New Zealand is scant. Upon arrival, they used fire extensively to clear forests and maintain the types of vegetation they wanted. The human-caused fires were clearly different than the relatively infrequent background fires that occurred in this environment. On the other hand, in highly fire-prone dry pine in the West, lightning ignitions are so abundant and fires spread so easily that it is difficult to distinguish ignitions that would be from lightning or people in the historical record.

In your most recent research, what findings have surprised you the most?

JKB: We provided a first estimate of fire’s contribution to the climate system. Surprisingly, fire influences the majority of the components that change global mean temperature. But more importantly, this review is a consensus view of the importance of fire in the Earth system by some of the world’s experts.

EAHS: We really thought, after decades of field and modeling work in Yellowstone, that it was resilient to severe fire.  It seems like the vegetation is adapted to it, and that it has successfully withstood severe fire through the Quaternary.  We also have documented that the system is able to recover all its nitrogen and carbon before the next fire cycle.  However, projections of future fire portend a very different story—that fire cycles could be ten times more frequent (going from 300- to 30-year fire cycles in some places).  While we hope our model predictions bound the upper levels for expected change, it is clear that changes in fire regime are more likely than not to affect vegetation in the region.  To say that Yellowstone is not a resilient landscape is quite surprising, and not a result we expected.
 
AT: Two things come to mind. First, the importance of temperature in driving variability of long-term fire activity. Our multi-century tree ring records of fire activity in the Sierra Nevada and other parts of the West show that fire activity increases when it is warm and decreases when it is cool. This pattern even holds during the last 100 years when fires were being suppressed. This clearly points to more fire under global warming. Second, the importance of the physical template, or terrain, in influencing vegetation patterns, and spatial patterns of fire severity and fire effects. Terrain effects tend to promote patterns of fire severity that are repeated in space over periods of at least centuries. This has important implications for biodiversity and how pyro-diversity may beget biodiversity across landscapes.

What research-based practices for preventing or responding to severe wildfires can forest managers adopt now?

EAHS: Certainly efforts should be in place to prioritize fire protection around important structures and places, and efforts need to be increased to educate people on firewise activity (reducing fuel loads around homes in fire-prone areas, for example).  In addition, models can be used to prioritize those areas that are most vulnerable to shifts in fire and climate.  In some areas, fuel reductions may not be a good way to manage the landscape if fires are driven more by climate than fuel; in other areas, some fuel reduction treatments may be appropriate. Finally, managers should consider what a resilient landscape should look like in the future and expect that that landscape may be a dynamic one and include different patterns and processes than today.  Easing ecosystems through dramatic transitions may be a more efficient path than preventing the changes that are surely coming.

AT: We know a lot about how to manipulate vegetation to alter fire behavior. Managers are using this knowledge mainly in areas where there are high values at risk and where there is a hazard of high-severity fire. Areas of focus for these treatments are usually around communities that border or are surrounded by highly flammable vegetation. These treatments will work, but one of the challenges is that they have to be maintained to continue to be effective. These treatments have a natural lifespan because vegetation grows back. A one-shot approach does not get you very far, and managers are having to grapple with the increased emphasis to treat more area and keep up with what they have already done. The spatial scale of the fuel-fire hazard problem is enormous—even geologic, making progress difficult.

What are the most pressing research questions that need to be investigated and answered?

EAHS:  How multiple disturbances interact over time and space. We need to develop observational studies and models to explore how these processes interacted in the past, how they are patterned now, and how they are likely to interact in the future. Tipping points in landscape function are likely to be a product of these interactions rather than a result of a single disturbance event. We also need to understand how spatial tools such as remote sensing can be used to quantify these patterns at regional to global scales and to integrate them into global scale models that include feedbacks from terrestrial systems to the atmosphere.

JKB: We need to turn our attention to the effects of altered fire regimes in the Earth system. This requires better understanding of the diversity of human fire use, especially possible positive and negative feedbacks across a range of scales. This demands integrative, multidisciplinary perspectives on landscape fire, its ecological effects and relationships with human societies, spanning geographic scales from the local to the global, whilst retaining an ecological and evolutionary frame of reference. Comparative studies of past and current human influences on fire regimes amongst biomes are required to identify excursions from the historical range of variability, a key step in identifying locally sustainable and unsustainable human–fire relationships. An understanding of different cultural traditions and political (local to global) influences in the management of fire is essential for evaluating the costs and benefits of contrasting fire regimes within individual landscapes and biomes.

AT: There are several. From the standpoint of dealing with the fire problem, optimal landscape strategies need to be designed that significantly reduce fire behavior across landscapes. We need to understand how variation in treatment type, treatment area, and spatial arrangement would affect fire behavior over large areas. This is an inherently geographical problem which needs focused work so that prescribed fires or wildfires can be used over wide areas to do the things we want them to be doing. We also need fundamental research on people’s attitudes about fire, how they develop, and how they could be changed if fire is going to be widely used as a tool to reduce fire hazard and manage natural resources.