The importance of small fires for wildfire hazard in urbanized landscapes of the northeastern U.S.

Frequent, small wildfires can pose dangers to homes in the wildland–urban interface, but are not often included in wildfire hazard models. We assessed patterns of small wildfire occurrence probability in the Northeast region of the United States, focusing on (1) spatial and seasonal variations; (2) differences between small and large fires (size threshold of 4 ha); and (3) how predicted probabilities are influenced by inconsistent wildfire definitions in urbanised landscapes. We analysed fire incident report data from 2005 to 2017 to parameterise maximum entropy (MaxEnt) models based on land cover, topography, climatic water deficit, soil moisture and road density. Overall, wildfire occurrence was highest in areas with lower agricultural cover and with more low-density urban development (explaining 53.5 and 28.6% of variance, respectively, in our region-wide model), while larger fires were concentrated in areas with intermediate levels of development, higher climatic water deficit and more rugged topography. These patterns were largely consistent when we assessed models for individual states, but differences in wildfire reporting patterns led to differences in the effect of urban development on fire probability. Our results provide novel understanding of small wildfire patterns in the Northeast and demonstrate the need to more reliably quantify these hazards.

File: nrs_2021_carlson_001.pdf

Historical fire regimes of North American hemiboreal peatlands

Peatlands contain one-third to one-half of global soil carbon, and disturbances, specifically fire, directly influence these carbon stocks. Despite this, historical variability of peatland fire regimes is largely unknown. This gap in knowledge partly stems from reconstructions of peatland fire regimes with methods limited to evaluating infrequent, severe fire events and not capturing frequent, low-severity events. Furthermore, variability in fire regimes is likely higher in heterogenous landscapes like the hemiboreal subzone, the transition between boreal and temperate biomes, where peatlands are embedded in landscapes including forests with high proportions of fire-dependent species, such as red pine (Pinus resinosa), that are well adapted to frequent low-severity fires. Here, we sought to evaluate the role of low- and moderate-severity fires within hemiboreal peatlands in central North America to better understand historical variability in fire regimes. We reconstructed historical fire regimes using fine-scale (temporal and spatial) dendrochronology methods to estimate frequency of low- and moderateseverity fires, identify synchronous fire events among forested uplands within and surrounding individual peatlands as well as among sites, and assess fire-climate relationships. We collected 220 cross-sections or partialtree sections within three poor fen peatlands across the Great Lakes Region. Using standard dendrochronological techniques, we crossdated 129 samples, assigning dates to 414 fire scars (128 unique fire years) comprising a 500-year tree-ring record (1520–2019). Prior to the mid-1900s, fire events were frequent and widespread within peatlands we evaluated, with mean fire return intervals (MFRI) ranging from 7 to 31 years. Fire events were also synchronous among forested uplands within and surrounding peatlands. Fires predominantly occurred in the dormant and latewood (growing season) positions and during regionally dry conditions corresponding to mild and moderate drought (Palmer Drought Severity Index ≥ 􀀀 2.99) but interestingly not during regionally severe drought (Palmer Drought Severity Index ≤ 􀀀 3.00). While large-scale, high-severity fires are important to the ecology of peatlands and to changing climate-fire interactions, our results suggest that widespread low- to moderate-severity fires were historically frequent in hemiboreal peatlands and likely central to their development and maintenance. Evaluating whether peatlands will continue to be carbon sinks or become carbon sources due to climate change requires an understanding of the inherent variability in fire regimes, especially in hemiboreal systems.

File: 1-s2.0-S0378112721006514-main.pdf

Growth of the wildland-urban interface within and around U.S. National Forests and Grasslands, 1990-2010

The wildland-urban interface (WUI), where housing is in close proximity to or intermingled with wildland vegetation, is widespread throughout the United States, but it is unclear how this type of housing development affects public lands. We used a national dataset to examine WUI distribution and growth (1990–2010) in proximity to National Forests and created a typology to characterize each National Forest’s combination of WUI area and housing growth. We found that National Forests are hotspots for WUI growth, with a 38% increase in WUI area and 46% growth in WUI houses from 1990 to 2010, in excess of WUI growth for the conterminous U.S. Growth within National Forests was higher than the surrounding area. Diffuse intermix WUI, where houses are intermingled with wildland vegetation, is common within National Forests, but WUI houses around National Forests were primarily in denser interface WUI areas, which lack substantial wildland vegetation. WUI was more prevalent within and around National Forests in the East, while National Forests in the West experienced higher rates of WUI growth. National Forests with the most challenging WUI issues—extensive WUI area and rapid growth in intermix and interface—were found primarily in the South and interior West. Given the diversity of WUI landscapes, effectively responding to current and future WUI challenges will require both engagement with individual homeowners dispersed throughout National Forests, as well as increased emphasis on mitigating denser interface development around National Forests. At a time when wildfire risks are expected to intensify due to climate change, and 75% of privately owned land within and around National Forests is not yet WUI, understanding WUI growth patterns in proximity to public lands is vital for land management and human wellbeing.

File: 1-s2.0-S0169204621002462-main.pdf

Post-wildfire rebuilding and new development in California indicates minimal adaptation to fire risk

Every year, wildfires destroy thousands of buildings in the United States, especially in the rapidly growing wildland-urban interface, where homes and wildland vegetation meet or intermingle. After a wildfire there is a window of opportunity for residents and public agencies to re-shape patterns of development, and avoid development in locations that are inherently at higher risk of wildfire destruction. We examined 28 of the most destructive wildfires in California, the state where most buildings are destroyed by wildfires, to evaluate whether locations of rebuilt and newly constructed buildings were adaptive (i.e., if building occurred in lower risk areas). In total, these fires burned 7,075 buildings from 1970 to 2009. We found minimal evidence for adaptation both in the number and placement of buildings post-fire. Rebuilding was common: 58% of the destroyed buildings were rebuilt within three to six years, and 94% within thirteen to twenty-five years after the fire. Similarly, we found minimal trends toward lower risk areas in the placement of 2,793 rebuilt and 23,404 newly constructed buildings over the course of 13–25 yr. In fact, long-term data revealed that relative risk of new construction either did not change significantly over time or increased. A destructive wildfire could provide an opportunity to assess and change building practices, yet our results show that such change is largely not occurring. As wildfires increasingly threaten communities, this lack of change could result in growing rates of destruction and loss of life.

File: Kramer_etal_2021_LUP.pdf

Rethinking Peatland Fire: Detecting frequent fire in peatlands of the Great Lakes Region to support its ecological role in management and conservation

Peatland fires can be some of the most catastrophic and expensive fires globally, including in the Great Lakes Region where wildfires in the mid-2000s burned through tens of thousands of acres in Michigan peatlands, and in 1976, when the Seney Fire burned for months underground consuming peat. Deep burning peatland fires can lead to the conversion and the permanent loss of peatlands, which are important refugias for plant and animal species. Such fires, however, have been infrequent since European settlement, and are assumed to have occurred only every few centuries or millennia. We investigated fire in peatlands to determine if historically fire in peatlands was indeed infrequent and severe.

Map of three peatland sites sampled across the Great Lakes Region in Wisconsin and Michigan.

Between 2017 and 2019, we collected samples from 220 fire-scarred trees in three peatlands within the Hiawatha and Chequamegon-Nicolet National Forests in the Great Lakes Region. Our sites were poor fen peatlands intermixed with dry to dry-mesic northern forests. We identified 141 fire years from 1548 to 1955. Prior to 1955 fires were historically frequent across our peatland sites occurring on average every 7 to 34 years depending on the site sampled. By using fire-scarred tree samples to investigate historical fire, we could identify fires that were likely low- to moderate-severity because fire scars are indicative of more frequent, low-severity fire whereas high-severity fires would have consumed most trees rather than just scarring them. We did not detect any fires after 1955, corresponding to the period when fire suppression efforts of the United States Forest Service became increasingly effective.

Fire-scarred tree sample including fires in 1734, 1755, and 1792 and the corresponding position (dormant or latewood) of the fire scar in individual tree rings.

Historically, fire was frequent in the peatlands we investigated and our research warrants rethinking of the role of fire in these ecosystems. Such a rethinking could have major implications on how managers use prescribed fire and mitigate wildfire risk in peatlands. Fire suppression since the mid-1900s in Great Lakes’ peatlands likely has unintended consequences including the encroachment of undesirable vegetation into open bogs and fens that were historically maintained by frequent fires over hundreds of years. Furthermore, it is possible that by removing frequent fire from peatlands in the Great Lakes Region these systems could become more prone to more severe, catastrophic fires that burn deep consuming peat soils. A possible mechanism for such a shift may be encroaching vegetation drawing more water from peat soils making them more susceptible to burning under severe drought conditions. Repeated prescribed burning under the more moderate conditions (e.g., surface vegetation of the peatlands is dry, but the peat soils are inundated with water) could be one approach to prevent encroachment and maintaining low-severity fire regimes. Fire management in peatlands of the Great Lakes Region needs to include rethinking the role of fire, considering it not just as a threat but also as a potential tool.

Collaborators: Jed Meunier (Wisconsin DNR) and Eric Rebitzke (US Forest Service)

High wildfire damage in Interface communities in California

Globally, and in the US, wildfires pose increasing risk to people and their homes. Wildfire management
assumes that buildings burn primarily in the wildland–urban interface (WUI), where homes are either ignited directly
(especially in intermix WUI areas, where houses and wildland fuels intermingle), or via firebrands, the main threat to
buildings in the interface WUI (areas with minimal wildland fuel, yet close to dense wildland vegetation). However, even
urban areas can succumb to wildfires. We examined where wildfire damages occur among urban, rural and WUI (intermix
and interface) areas for approximately three decades in California (1985–2013). We found that interface WUI contained
50% of buildings destroyed by wildfire, whereas intermix WUI contained only 32%. The proportion of buildings destroyed
by fires among classes was similar, though highest in interface WUI areas (15.6%). Our results demonstrate that the
interface WUI is where most buildings were destroyed in California, despite less wildland fuel. Continued advancement of
models, mitigation and regulations tailored for the interface WUI, both for California and elsewhere, will complement the
prior focus on the intermix WUI.

File: Kramer_etal_IJWF_2019.pdf

Globally, and in the US, wildfires pose increasing risk to people and their homes. Wildfire management
assumes that buildings burn primarily in the wildland–urban interface (WUI), where homes are either ignited directly
(especially in intermix WUI areas, where houses and wildland fuels intermingle), or via firebrands, the main threat to
buildings in the interface WUI (areas with minimal wildland fuel, yet close to dense wildland vegetation). However, even
urban areas can succumb to wildfires. We examined where wildfire damages occur among urban, rural and WUI (intermix
and interface) areas for approximately three decades in California (1985–2013). We found that interface WUI contained
50% of buildings destroyed by wildfire, whereas intermix WUI contained only 32%. The proportion of buildings destroyed
by fires among classes was similar, though highest in interface WUI areas (15.6%). Our results demonstrate that the
interface WUI is where most buildings were destroyed in California, despite less wildland fuel. Continued advancement of
models, mitigation and regulations tailored for the interface WUI, both for California and elsewhere, will complement the
prior focus on the intermix WUI.

Future changes in wildfire potential, spring droughts, and false springs across Forest Service lands

Public lands provide many ecosystem services and support diverse plant and animal
communities. In order to provide these benefits in the future, land managers and policy
makers need information about future climate change and its potential effects. In particular,
weather extremes are key drivers of wildfires, droughts, and false springs, which in turn can
have large impacts on ecosystems. However, information on future changes in weather
extremes on public lands is lacking. Our goal was to compare historical (1950–2005) and projected
mid-century (2041–2070) changes in weather extremes (fire weather, spring droughts,
and false springs) on public lands. This case study looked at the lands managed by the U.S.
Forest Service across the conterminous United States including 501 ranger district units. We
analyzed downscaled projections of daily records from 19 Coupled Model Intercomparison
Project 5 General Circulation Models for two climate scenarios, with either medium-low or
high CO2 equivalent concentration (RCPs 4.5 and 8.5). For each ranger district, we estimated:
(1) fire potential, using the Keetch-Byram Drought Index; (2) frequency of spring
droughts, using the Standardized Precipitation Index; and (3) frequency of false springs, using
the extended Spring Indices. We found that future climates could substantially alter weather
conditions across Forest Service lands. Under the two climate scenarios, increases in wildfire
potential, spring droughts, and false springs were projected in 32–72%, 28–29%, and 13–16%
of all ranger districts, respectively. Moreover, a substantial number of ranger districts
(17–30%), especially in the Southwestern, Pacific Southwest, and Rocky Mountain regions,
were projected to see increases in more than one type of weather extreme, which may require
special management attention. We suggest that future changes in weather extremes could
threaten the ability of public lands to provide ecosystem services and ecological benefits to
society. Overall, our results highlight the value of spatially-explicit weather projections to
assess future changes in key weather extremes for land managers and policy makers.

File: Martinuzzi_et_al-2019-Ecological_Applications.pdf

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Where wildfires destroy buildings in the US relative to the wildland-urban interface and national fire outreach programs

Over the past 30 years, the cost of wildfire suppression and homes lost to wildfire in the U.S. have increased dramatically, driven in part by the expansion of the wildland-urban interface (WUI), where buildings and wildland vegetation meet. In response, the wildfire management community has devoted substantial effort to better understand where buildings and vegetation co-occur, and to establish outreach programs to reduce wildfire damage to homes. However, the extent to which the location of buildings affected by wildfire overlaps the WUI, and where and when outreach programs were established relative to wildfire, is unclear. We found that most threatened and destroyed buildings in the conterminous U.S. were within the WUI (59% and 69%, respectively), but this varied considerably among states. Fires with the greatest building loss were close to outreach programs (such as Firewise), but for 76% of destroyed buildings, the nearest outreach program was established post-wildfire. In these locations, as well as places new to the WUI or in areas where the fire regime is predicted to change, pre-emptive outreach could improve the likelihood of building survival and reduce the human and financial costs of structure loss.

File: Kramer2018_Fire_Buildings_IJWF.pdf

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Assessing wildfire exposure in the Wildland-Urban Interface area of the mountains of central Argentina

Wildfires are a major threat to people and property in Wildland Urban Interface (WUI) communities
worldwide, but while the patterns of the WUI in North America, Europe and Oceania have been studied
before, this is not the case in Latin America. Our goals were to a) map WUI areas in central Argentina, and
b) assess wildfire exposure for WUI communities in relation to historic fires, with special emphasis on
large fires and estimated burn probability based on an empirical model. We mapped the WUI in the
mountains of central Argentina (810,000 ha), after digitizing the location of 276,700 buildings and
deriving vegetation maps from satellite imagery. The areas where houses and wildland vegetation
intermingle were classified as Intermix WUI (housing density > 6.17 hu/km2 and wildland vegetation
cover > 50%), and the areas where wildland vegetation abuts settlements were classified as Interface
WUI (housing density > 6.17 hu/km2, wildland vegetation cover < 50%, but within 600 m of a vegetated patch larger than 5 km2). We generated burn probability maps based on historical fire data from 1999 to 2011; as well as from an empirical model of fire frequency. WUI areas occupied 15% of our study area and contained 144,000 buildings (52%). Most WUI area was Intermix WUI, but most WUI buildings were in the Interface WUI. Our findings suggest that central Argentina has a WUI fire problem. WUI areas included most of the buildings exposed to wildfires and most of the buildings located in areas of higher burn probability. Our findings can help focus fire management activities in areas of higher risk, and ultimately provide support for landscape management and planning aimed at reducing wildfire risk in WUI communities.

File: Arganaraz2017_WUI_Argentina_JEM.pdf

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