Fire Regimes Spatial And Temporal Variability And Their Effects On Forests

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.

Ecologists continue to debate the role of fire in forests of the southern Appalachian Mountains. How does climate influence fire in these humid, temperate forests? Did fire regimes change during the transition from Native American settlement to Euro-American settlement? Are fire regime changes resulting in broad vegetation changes in the forests of eastern North America? I used several approaches to address these questions. First, I used digitized fire perimeter maps from Great Smoky Mountains National Park and Shenandoah National Park for 1930-2009 to characterize spatial and temporal patterns of wildfire by aspect, elevation, and landform. Results demonstrate that fuel moisture is a primary control, with fire occurring most frequently during dry years, in dry regions, and at dry topographic positions. Climate also modifies topographic control, with weaker topographic patterns under drier conditions. Second, I used dendroecological methods to reconstruct historical fire frequency in yellow pine (Pinus, subgenus Diploxylon Koehne) stands at three field sites in the southern Appalachian Mountains. The fire history reconstructions extend from 1700 to 2009, with composite fire return intervals ranging from 2-4 years prior to the fire protection period. The two longest reconstructions record frequent fire during periods of Native American land use. Except for the recent fire protection period, temporal changes in land use did not have a significant impact on fire frequency and there was little discernible influence of climate on past fire occurrence. Third, I sampled vegetation composition in four different stand types along a topographic moisture gradient, including mesic cove, sub-mesic white pine (Pinus strobus L.) hardwood, sub-xeric oak (Quercus L.), and xeric pine forests in an unlogged watershed with a reconstructed fire history. Stand age structures demonstrate changes in establishment following fire exclusion in xeric pine stands, sub-xeric oak stands, and sub-mesic white pine-hardwood stands. Fire-tolerant yellow pines and oaks are being replaced by shade-tolerant, fire sensitive species such as red maple (Acer rubrum L.) and hemlock (Tsuga canadensis L. Carr.). Classification analysis and ordination of species composition in different age classes suggest a trend of successional convergence in the absence of fire with a shift from four to two forest communities. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148082

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.

Fire is a natural component of most ecosystems, and it has effects on vegetation, soil, water, atmospheric composition, and human well-being. Despite increasing interest in interdisciplinary approaches to analyzing global fire activity and the growing body of wildfire research, there are still many gaps and uncertainties in our knowledge. Some come from the lack of understanding of the complex relationships between fire and climate, which is additionally entangled by the strong influence of human activity. This dissertation evaluates the role of environmental context in determining the spatial patterns of fire activity on a large scale. First, the fire-climate relationship was analyzed in terms of the most studied and understood fire metric - the amount of burned area - which was shown to have changed significantly in the last two decades. Most of the recent changes were attributed to the decrease in fire activity in Africa, where the amount of burned area declined by 18.5% between 2002 and 2016. Although humans have a long history of modifying fire activity in Africa, climate factors directly related to biomass productivity and aridity explained about 70% of the changes in burned area in natural land covers, providing evidence that increased terrestrial moisture during 2002-2016 facilitated declines in fire activity in Africa. These results illustrate the strong influence of climate on fire activity and in particular proxy for fuel productivity and fuel dryness. Based on these findings, a framework was proposed for defining and classifying fire regimes (a range of characteristics that describe the fire events in the space-time window). This framework was based on the assumption that fuel productivity and desiccation are the two fundamental processes that limit fire activity, and their combination sets important boundary conditions for key fire regime metrics on a large scale. By testing this approach in Africa and Australia, it was evident that while the amount of rainfall is an important driver of fire through controlling fuel productivity, a variation of rainfall within and between years drives fuel dryness and fire activity especially in Australia, a continent with a strong precipitation gradient. Additionally, among continents, fire metrics vary substantially even within the same biome. These results informed an additional global analysis, where 26 distinct fire regions were identified, not including areas where fire activity is highly modified by human activity. This approach did not only discriminate between regions with significantly different fire activity across a number of biomes but also identified how fire attributes vary under different conditions and what factors constrain modern fire regimes. These findings should help to improve our understanding of fire complexity and its interaction and feedbacks with climate which is essential to assess the potential effect of global climate change on fire regimes.

What is a natural forest disturbance? How well do we understand natural forest disturbances and how might we emulate them in forest management? What role does emulation play in forest management? Representing a range of geographic perspectives from across Canada and the United States, this book looks at the escalating public debate on the viability of natural disturbance emulation for sustaining forest landscapes from the perspective of policymakers, forestry professionals, academics, and conservationists. This book provides a scientific foundation for justifying the use of and a solid framework for examining the ambiguities inherent in emulating natural forest landscape disturbance. It acknowledges the divergent expectations that practitioners face and offers a balanced view of the promises and challenges associated with applying this emerging forest management paradigm. The first section examines foundational concepts, addressing questions of what emulation involves and what ecological reasoning substantiates it. These include a broad overview, a detailed review of emerging forest management paradigms and their global context, and an examination of the ecological premise for emulating natural disturbance. This section also explores the current understanding of natural disturbance regimes, including the two most prevalent in North America: fire and insects. The second section uses case studies from a wide geographical range to address the characterization of natural disturbances and the development of applied templates for their emulation through forest management. The emphasis on fire regimes in this section reflects the greater focus that has traditionally been placed on understanding and managing fire, compared with other forms of disturbance, and utilizes several viewpoints to address the lessons learned from historical disturbance patterns. Reflecting on current thinking in the field, immediate challenges, and potential directions, the final section moves deeper into the issues of practical applications by exploring the expectations for and feasibility of emulating natural disturbance through forest management.