This book is a printed edition of the Special Issue "Fire Regimes: Spatial and Temporal Variability and Their Effects on Forests" that was published in Forests

Both fire and climatic variability have monumental impacts on the dynamics of temperate ecosystems. These impacts can sometimes be extreme or devastating as seen in recent El Nino/La Nina cycles and in uncontrolled fire occurrences. This volume brings together research conducted in western North and South America, areas of a great deal of collaborative work on the influence of people and climate change on fire regimes. In order to give perspective to patterns of change over time, it emphasizes the integration of paleoecological studies with studies of modern ecosystems. Data from a range of spatial scales, from individual plants to communities and ecosystems to landscape and regional levels, are included. Contributions come from fire ecology, paleoecology, biogeography, paleoclimatology, landscape and ecosystem ecology, ecological modeling, forest management, plant community ecology and plant morphology. The book gives a synthetic overview of methods, data and simulation models for evaluating fire regime processes in forests, shrublands and woodlands and assembles case studies of fire, climate and land use histories. The unique approach of this book gives researchers the benefits of a north-south comparison as well as the integration of paleoecological histories, current ecosystem dynamics and modeling of future changes.

Fire regimes-that is, patterns of fire occurrence, size, uniformity, and severity-have been a major force shaping landscape patterns and influencing productivity throughout North America for thousands of years. Faunal communities have evolved in the context of particular fire regimes and show patterns of response to fire itself and to the changes in vegetation composition and structure that follow fire. Animals' immediate responses to fire are influenced by fire season, intensity, severity, rate of spread, uniformity, and size. Responses may include injury, mortality, immigration, or emigration. Animals with limited mobility, such as young, are more vulnerable to injury and mortality than mature animals. The habitat changes caused by fire influence faunal populations and communities much more profoundly than fire itself. Fires often cause a short-term increase in productivity, availability, or nutrient content of forage and browse. Fires generally favor raptors by reducing hiding cover and exposing prey. Small carnivores respond to fire effects on small mammal populations (either positive or negative). Large carnivores and omnivores are opportunistic species with large home ranges. Their populations change little in response to fire, but they tend to thrive in areas where their preferred prey is most plentiful-often in recent burns. In forests and woodlands, understory fires generally alter habitat structure less than mixed severity and stand-replacement fires, and their effects on animal populations are correspondingly less dramatic. Stand-replacing fires reduce habitat quality for species that require dense cover and improve it for species that prefer open sites. Population explosions of wood-boring insects, an important food source for insect predators and insect-eating birds, can be associated with fire-killed trees. Woodpecker populations generally increase after mixed-severity and stand-replacement fire if snags are available for nesting. Secondary cavity nesters, both birds and mammals, take advantage of the nest sites prepared by primary excavators. Many animal-fire studies depict a reorganization of animal communities in response to fire, with increases in some species accompanied by decreases in others. Like fire effects on populations, fire effects on communities are related to the amount of structural change in vegetation. Bird abundance and diversity are likely to be greatest early in succession. When shrub or tree canopy closure occurs, species that prefer open sites and habitat edges decline and species that prefer mature structures increase. Major changes to fire regimes alter landscape patterns, processes, and functional linkages. These changes can affect animal habitat and often produce major changes in the composition of faunal communities. In many Western ecosystems, landscape changes due to fire exclusion have changed fuel quantities and arrangement, increasing the likelihood of large or severe fires, or both. Where fire exclusion has changed species composition and fuel arrays over large areas, subsequent fires without prior fuel modification are unlikely to restore presettlement vegetation and habitat. In many desert and semi desert habitats where fire historically burned infrequently because of sparse fuels, invasion of weedy species has changed the vegetation so that burns occur much more frequently. Many animals in these ecosystems are poorly adapted to avoid fire or use resources in postfire communities. Collaboration among managers, researchers, and the public is needed to address tradeoffs in fire management, and fire management must be better integrated with overall land management objectives to address the potential interactions of fire with other disturbances such as grazing, flood, wind throw, and insect and fungus infestations.

This synthesis provides an ecological foundation for management of the diverse ecosystems and fire regimes of North America, based on scientific principles of fire interactions with vegetation, fuels, and biophysical processes. Although a large amount of scientific data on fire exists, most of those data have been collected at small spatial and temporal scales. Thus, it is challenging to develop consistent science-based plans for large spatial and temporal scales where most fire management and planning occur. Understanding the regional geographic context of fire regimes is critical for developing appropriate and sustainable management strategies and policy. The degree to which human intervention has modified fire frequency, intensity, and severity varies greatly among different ecosystems, and must be considered when planning to alter fuel loads or implement restorative treatments. Detailed discussion of six ecosystems--ponderosa pine forest (western North America), chaparral (California), boreal forest (Alaska and Canada), Great Basin sagebrush (intermountain West), pine and pine-hardwood forests (Southern Appalachian Mountains), and longleaf pine (Southeastern United States)-- illustrates the complexity of fire regimes and that fire management requires a clear regional focus that recognizes where conflicts might exist between fire hazard reduction and resource needs. In some systems, such as ponderosa pine, treatments are usually compatible with both fuel reduction and resource needs, whereas in others, such as chaparral, the potential exists for conflicts that need to be closely evaluated. Managing fire regimes in a changing climate and social environment requires a strong scientific basis for developing fire management and policy.

This state-of-knowledge review about the effects of fire on flora and fuels can assist land managers in planning for ecosystem management and fire management, and in their efforts to inform others about the ecological role of fire. Chapter 1 presents an overview and a classification of fire regimes that is used throughout the report. Chapter 2 summarizes knowledge of fire effects on individual plants, including susceptibility to mortality of aerial crowns, stems, and roots; vegetative regeneration; seedling establishment from on-site and off-site seed sources; seasonal influences such as carbohydrates and phenological stage; and factors affecting burn severity. Five chapters describe fire regime characteristics such as fire severity, fire frequency, and fire intensity, and postfire plant community responses for ecosystems throughout the United States and Canada. Typical fuel compositions, fuel loadings, and fire behavior are described for many vegetation types. Vegetation types including Forest-Range Environmental Study (FRES), Kuchler, and Society of American Foresters (SAF) types are classified as belonging to understory, mixed, or stand replacement fire severity regime types. The severity and frequency of fire are described for the pre-Euro-American settlement period and contrasted with current fire regimes. Historic fire frequencies ranged from a fire every 1 to 3 years in some grassland and pine types to a fire every 500 to 1,000 years in some coastal forest and northern hardwood types. In many vegetation types characterized by understory fire regimes, a considerable shift in fire frequency and fire severity occurred during the past century. Successional patterns and vegetation dynamics following disturbance by fire, and in some cases related grazing and silvicultural treatments, are described for major vegetation types. Management considerations are discussed, especially for the application of prescribed fire. A chapter on global climate change describes the complexity of a changing climate and possible influences on vegetation, fuels, and fire. The uncertainty of global climate change and its interactions with vegetation means expectations for fire management are general and tentative. Nonetheless, manipulation of wildlands and disturbance regimes may be necessary to ensure continual presence of some species. The last chapter takes a broader, more fundamental view of the ecological principles and shifting fire regimes described in the other chapters. The influences of fire regimes on biodiversity and fuel accumulation are discussed. Strategies and approaches for managing fire in an ecosystem context and sources of technical knowledge that can assist in the process are described. Research needs are broadly summarized.