Chaparral and coastal sage scrub habitats in southern California support biologically diverse plant and animal communities. However, native plant and animal species within these shrubland systems are increasingly exposed to human-caused wildfires and an expansion of the human–wildland interface. Few data exist to evaluate the effects of fire and anthropogenic pressures on plant and animal communities found in these environments. This is particularly true for carnivore communities. To address this knowledge gap, we collected detection–non-detection data with motion-sensor cameras and track plots to measure carnivore occupancy patterns following a large, human-caused wildfire (1134 km2) in eastern San Diego County, California, USA, in 2003. Our focal species set included coyote (Canis latrans), gray fox (Urocyon cinereoargenteus), bobcat (Lynx rufus) and striped skunk (Mephitis mephitis). We evaluated the influence on species occupancies of the burned environment (burn edge, burn interior and unburned areas), proximity of rural homes, distance to riparian area and elevation. Gray fox occupancies were the highest overall, followed by striped skunk, coyote and bobcat. The three species considered as habitat and foraging generalists (gray fox, coyote, striped skunk) were common in all conditions. Occupancy patterns were consistent through time for all species except coyote, whose occupancies increased through time. In addition, environmental and anthropogenic variables had weak effects on all four species, and these responses were species-specific. Our results helped to describe a carnivore community exposed to frequent fire and rural human residences, and provide baseline data to inform fire management policy and wildlife management strategies in similar fire-prone ecosystems.
The impacts of escalating wildfire in many regions — the lives and homes lost, the expense of suppression and the damage to ecosystem services — necessitate a more sustainable coexistence with wildfire. Climate change and continued development on fire-prone landscapes will only compound current problems. Emerging strategies for managing ecosystems and mitigating risks to human communities provide some hope, although greater recognition of their inherent variation and links is crucial. Without a more integrated framework, fire will never operate as a natural ecosystem process, and the impact on society will continue to grow. A more coordinated approach to risk management and land-use planning in these coupled systems is needed.
Wildfires can pose a significant risk to people and property. Billions of dollars are spent investing in fire management actions in an attempt to reduce the risk of loss. One of the key areas where money is spent is through fuel treatment – either fuel reduction (prescribed fire) or fuel removal (fuel breaks). Individual treatments can influence fire size and the maximum distance travelled from the ignition and presumably risk, but few studies have examined the landscape level effectiveness of these treatments. Here we use a Bayesian Network model to examine the relative influence of the built and natural environment, weather, fuel and fuel treatments in determining the risk posed from wildfire to the wildland-urban interface. Fire size and distance travelled was influenced most strongly by weather, with exposure to fires most sensitive to changes in the built environment and fire parameters. Natural environment variables and fuel load all had minor influences on fire size, distance travelled and exposure of assets. These results suggest that management of fuels provided minimal reductions in risk to assets and adequate planning of the changes in the built environment to cope with the expansion of human populations is going to be vital for managing risk from fire under future climates.
Aim: Conservation efforts in Mediterranean-climate regions are complicated by species’ variability in response to multiple threats. Functional type classifications incorporating life history traits with disturbance response strategies provide a framework for predicting groups of species’ response to fire, but it is unclear whether these classifications will be useful when species are exposed to multiple threats or differ in spatial context. We evaluate whether species of the same fire-response functional type exhibit similar responses to disturbance relative to, and in combination with, climate and land-use change and whether the dominant threat depends on spatial context.
Location: Mediterranean southern California.
Methods: We developed species distribution models under current and future climate conditions for two fire-obligate seeding native shrub species that differ in geographical location and area of occupancy. Dynamic habitat maps representing alternative scenarios of climate change and urban growth were coupled with population models and simulated stochastic fire regimes.
Results: The disturbance that defines their classification, fire, is projected to be the most serious threat to both species when fire frequency is high. At longer fire return intervals, however, the projected ranking of threats differed between the species, and spatial context played an important role in defining vulnerability.
Main conclusions: Considering ongoing increases in fire frequency in Mediterranean-climate regions worldwide, functional type classification based on disturbance response may continue to provide a useful framework for biodiversity conservation efforts, but spatial context should also be accounted for. It may be most useful to consider the distribution of vulnerable species with regard to urban development patterns, areas of ‘high-velocity’ climate shifts, and places where altered fire regimes are likely to interact with other threats.
As a clear consensus is emerging that habitat for many species will dramatically reduce or shift with climate change, attention is turning to adaptation strategies to address these impacts. Assisted colonization is one such strategy that has been predominantly discussed in terms of the costs of introducing potential competitors into new communities and the benefits of reducing extinction risk. However, the success or failure of assisted colonization will depend on a range of population-level factors that have not yet been quantitatively evaluated – the quality of the recipient habitat, the number and life stages of translocated individuals, the establishment of translocated individuals in their new habitat and whether the recipient habitat is subject to ongoing threats all will play an important role in population persistence. In this article, we do not take one side or the other in the debate over whether assisted colonization is worthwhile. Rather, we focus on the likelihood that assisted colonization will promote population persistence in the face of climate-induced distribution changes and altered fire regimes for a rare endemic species. We link a population model with species distribution models to investigate expected changes in populations with climate change, the impact of altered fire regimes on population persistence and how much assisted colonization is necessary to minimize risk of decline in populations of Tecate cypress, a rare endemic tree in the California Floristic Province, a biodiversity hotspot. We show that assisted colonization may be a risk-minimizing adaptation strategy when there are large source populations that are declining dramatically due to habitat contractions, multiple nearby sites predicted to contain suitable habitat, minimal natural dispersal, high rates of establishment of translocated populations and the absence of nonclimatic threats such as altered disturbance regimes. However, when serious ongoing threats exist, assisted colonization is ineffective.
Increasing numbers of homes are being destroyed by wildfire in the wildland-urban interface. With projections of climate change and housing growth potentially exacerbating the threat of wildfire to homes and property, effective fire-risk reduction alternatives are needed as part of a comprehensive fire management plan. Land use planning represents a shift in traditional thinking from trying to eliminate wildfires, or even increasing resilience to them, toward avoiding exposure to them through the informed placement of new residential structures. For land use planning to be effective, it needs to be based on solid understanding of where and how to locate and arrange new homes. We simulated three scenarios of future residential development and projected landscape-level wildfire risk to residential structures in a rapidly urbanizing, fire-prone region in southern California. We based all future development on an econometric subdivision model, but we varied the emphasis of subdivision decision-making based on three broad and common growth types: infill, expansion, and leapfrog. Simulation results showed that decision-making based on these growth types, when applied locally for subdivision of individual parcels, produced substantial landscape-level differences in pattern, location, and extent of development. These differences in development, in turn, affected the area and proportion of structures at risk from burning in wildfires. Scenarios with lower housing density and larger numbers of small, isolated clusters of development, i.e., resulting from leapfrog development, were generally predicted to have the highest predicted fire risk to the largest proportion of structures in the study area, and infill development was predicted to have the lowest risk. These results suggest that land use planning should be considered an important component to fire risk management and that consistently applied policies based on residential pattern may provide substantial benefits for future risk reduction.
Large shifts in species ranges have been predicted under future climate scenarios based primarily on niche-based species distribution models. However, the mechanisms that would cause such shifts are uncertain. Natural and anthropogenic fires have shaped the distributions of many plant species, but their effects have seldom been included in future projections of species ranges. Here, we examine how the combination of climate and fire influence historical and future distributions of the ponderosa pine–prairie ecotone at the edge of the Black Hills in South Dakota, USA, as simulated by MC1, a dynamic global vegetation model that includes the effects of fire, climate, and atmospheric CO2 concentration on vegetation dynamics. For this purpose, we parameterized MC1 for ponderosa pine in the Black Hills, designating the revised model as MC1-WCNP. Results show that fire frequency, as affected by humidity and temperature, is central to the simulation of historical prairies in the warmer lowlands versus woodlands in the cooler, moister highlands. Based on three downscaled general circulation model climate projections for the 21st century, we simulate greater frequencies of natural fire throughout the area due to substantial warming and, for two of the climate projections, lower relative humidity. However, established ponderosa pine forests are relatively fire resistant, and areas that were initially wooded remained so over the 21st century for most of our future climate x fire management scenarios. This result contrasts with projections for ponderosa pine based on climatic niches, which suggest that its suitable habitat in the Black Hills will be greatly diminished by the middle of the 21st century. We hypothesize that the differences between the future predictions from these two approaches are due in part to the inclusion of fire effects in MC1, and we highlight the importance of accounting for fire as managed by humans in assessing both historical species distributions and future climate change effects.
Chapter 5. “The 2003 and 2007 Wildfires in Southern California” in Natural Disasters and Adaptation to Climate Change
Introduction
Although many residents of southern California have long recognised that wildfires in the region are an ongoing, constant risk to lives and property, the enormity of the regional fire hazard caught the world’s attention during the southern California firestorms of 2003 (Figure 5.1). Beginning on 21 October, a series of fourteen wildfires broke out across the five-county region under severe Santa Ana winds, and within two weeks, more than 300,000 ha had burned (Keeley et al., 2004). The event was one of the costliest in the state’s history, with more than 3,600 homes damaged or destroyed and twenty-four fatalities. Suppression costs for the 12,000 firefighters have been estimated at US$120 million, and the total response and damage cost has been estimated at more than US$3 billion (COES, 2004).
Just four years later, almost to the day, this event was repeated. Beginning on 22 October 2007, thirteen wildfires broke out across the same region, and under similar Santa Ana winds, consuming more than 175,000 ha, destroying more than 3,300 structures and killing seven people (Keeley et al., 2009). The 2003 and the 2007 wildfires were remarkably similar in their causes, impacts and the human responses they elicited. Particularly alarming is the observation that these fire events are not new to the region, as large fire events have occurred historically.
Most species face multiple anthropogenic disruptions. Few studies have quantified the cumulative influence of multiple threats on species of conservation concern, and far fewer have quantified the potential relative value of multiple conservation interventions in light of these threats. We linked spatial distribution and population viability models to explore conservation interventions under projected climate change, urbanization, and changes in fire regime on a long-lived obligate seeding plant species sensitive to high fire frequencies, a dominant plant functional type in many fire-prone ecosystems, including the biodiversity hotspots of Mediterranean-type ecosystems. First, we investigated the relative risk of population decline for plant populations in landscapes with and without land protection under an existing habitat conservation plan. Second, we modeled the effectiveness of relocating both seedlings and seeds from a large patch with predicted declines in habitat area to 2 unoccupied recipient patches with increasing habitat area under 2 projected climate change scenarios. Finally, we modeled 8 fire return intervals (FRIs) approximating the outcomes of different management strategies that effectively control fire frequency. Invariably, long-lived obligate seeding populations remained viable only when FRIs were maintained at or above a minimum level. Land conservation and seedling relocation efforts lessened the impact of climate change and land-use change on obligate seeding populations to differing degrees depending on the climate change scenario, but neither of these efforts was as generally effective as frequent translocation of seeds. While none of the modeled strategies fully compensated for the effects of land-use and climate change, an integrative approach managing multiple threats may diminish population declines for species in complex landscapes. Conservation plans designed to mitigate the impacts of a single threat are likely to fail if additional threats are ignored.
Chaparral shrublands in southern California, US, exhibit significant biodiversity but are prone to large,intense wildfires. Debate exists regarding fuel reduction to prevent such fires in wildland areas, but the effects of these fires on fauna are not well understood. We studied whether fire severity and distance from unburned fire perimeter influenced recovery of the small-mammal community from 13 to 39 months after the large (1134.2 km2) Cedar fire in San Diego County. In general, neither factor influenced small-mammal recovery. However, vegetation characteristics, distance to riparian habitat and the prevalence of rocky substrate affected recovery in species-specific patterns. This indicates the effects of fire severity and immigration from outside the fire perimeter, if they occur, do so within 1 year, whereas longerterm recovery is largely driven by previously known relationships between small mammals and habitat structure. Our results, when combined with results from other studies in southern California, suggest where human lives or infrastructure are not at risk, efforts to preserve chaparral biodiversity should focus on maintaining the native plant community. Doing so may require novel management strategies in the face of an increasing human population, ignition sources and the spread of invasive exotic plants.