Virginia H. Dale

Climate Change and Forest Disturbances

tudies of the effects of climate change on forestshave focused on the ability of species to tolerate tem-perature and moisture changes and to disperse,but they haveignored the effects of disturbances caused by climate change(e.g.,Ojima et al.1991).Yet modeling studies indicate the im-portance of climate effects on disturbance regimes (He et al.1999). Local, regional, and global changes in temperatureand precipitation can influence the occurrence, timing, fre-quency,duration,extent,and intensity of disturbances (Baker1995, Turner et al. 1998). Because trees can survive fromdecades to centuries and take years to become established,climate-change impacts are expressed in forests, in part,through alterations in disturbance regimes (Franklin et al.1992, Dale et al. 2000).Disturbances,both human-induced and natural,shape for-est systems by influencing their composition,structure,andfunctional processes.Indeed,the forests of the United Statesare molded by their land-use and disturbance history.Withinthe United States,natural disturbances having the greatest ef-fects on forests include fire,drought,introduced species,in-sect and pathogen outbreaks, hurricanes, windstorms, icestorms, and landslides (Figure 1). Each disturbance affectsforests differently. Some cause large-scale tree mortality,whereas others affect community structure and organizationwithout causing massive mortality (e.g., ground fires). For-est disturbances influence how much carbon is stored intrees or dead wood. All these natural disturbances interactwith human-induced effects on the environment,such as airpollution and land-use change resulting from resource ex-traction, agriculture, urban and suburban expansion, andrecreation.Some disturbances can be functions of both nat-ural and human conditions (e.g., forest fire ignition andspread) (Figure 2).

Indices of landscape pattern

Landscape ecology deals with the patterning of ecosystems in space. Methods are needed to quantify aspects of spatial pattern that can be correlated with ecological processes. The present paper develops three indices of pattern derived from information theory and fractal geometry. Using digitized maps, the indices are calculated for 94 quadrangles covering most of the eastern United States. The indices are shown to be reasonably independent of each other and to capture major features of landscape pattern. One of the indices, the fractal dimension, is shown to be correlated with the degree of human manipulation of the landscape.

CHALLENGES IN THE DEVELOPMENT AND USE OF ECOLOGICAL INDICATORS

Ecological indicators can be used to assess the condition of the environment, to provide an early warning signal of changes in the environment, or to diagnose the cause of an environmental problem. Ideally the suite of indicators should represent key information about structure, function, and composition of the ecological system. Three concerns hamper the use of ecological indicators as a resource management tool. (1) Monitoring programs often depend on a small number of indicators and fail to consider the full complexity of the ecological system. (2) Choice of ecological indicators is confounded in management programs that have vague long-term goals and objectives. (3) Management and monitoring programs often lack scientific rigor because of their failure to use a defined protocol for identifying ecological indicators. Thus, ecological indicators need to capture the complexities of the ecosystem yet remain simple enough to be easily and routinely monitored. Ecological indicators should meet the following criteria: be easily measured, be sensitive to stresses on the system, respond to stress in a predictable manner, be anticipatory, predict changes that can be averted by management actions, be integrative, have a known response to disturbances, anthropogenic stresses, and changes over time, and have low variability in response. The challenge is to derive a manageable set of indicators that together meet these criteria. Published by Elsevier Science Ltd.

Ecological Principles and Guidelines for Managing the Use of Land

Decision-making levels in the United States and examples of their land-use management powers, both regulatory and nonregulatory (Dale et al, 2000, Reproduced with permission of Ecological Society of America, Redraivn by Travis Witt, 2014).

Sustainable Biofuels Redux

Science-based policy is essential for guiding an environmentally sustainable approach to cellulosic biofuels.

Global Change in Forests: Responses of Species, Communities, and Biomes

G change is often perceived as human-induced modifications in climate. Indeed, human activities have undeniably altered the atmosphere, and probably the climate as well (Watson et al. 1998). At the same time, most of the world’s forests have also been extensively modified by human use of the land (Houghton 1994). Thus, climate and land use are two prongs of human-induced global change. The effect of these forces on forests is mediated by the organisms within forests. Consideration of climate, land use, and biological diversity is key to understanding forest response to global change. Biological diversity refers to the variety of life at organizational levels from genotypes through biomes (Franklin 1993). The responses of ecological systems to global change reflect the organisms that are within them. While ecologists have sometimes not seen the forest for the trees, so to speak, it is also true that forests cannot be understood without knowledge of the trees and other component species. It is the responses of individual organisms that begin the cascade of ecological processes that are manifest as changes in system properties, some of which feed back to influence climate and land use (Figure 1). Beyond its role in ecosystems, biodiversity is invaluable to humans for foods, medicines, genetic information, recreation, and spiritual renewal (Pimentel et al. 1997). Thus, global changes that affect the distribution and abundance of organisms will affect future human well-being and land use, as well as, possibly, the climate. This article serves as a primer on forest biodiversity as a key component of global change. We first synthesize current knowledge of interactions among climate, land use, and biodiversity. We then summarize the results of new analyses on the potential effects of human-induced climate change on forest biodiversity. Our models project how possible future climates may modify the distributions of environments required by various species, communities, and biomes. Current knowledge, models, and funding did not allow these analyses to examine the population processes (e.g., dispersal, regeneration) that would mediate the responses of organisms to environmental change. It was also not possible to model the important effects of land use, natural disturbance, and other factors on the response of biodiversity to climate change. Despite these limitations, the analyses discussed herein are among the most comprehensive projections of climate change effects on forest biodiversity yet conducted. We conclude with discussions of limitations, research needs, and strategies for coping with potential future global change.

THE RELATIONSHIP BETWEEN LAND-USE CHANGE AND CLIMATE CHANGE

Land-use change is related to climate change as both a causal factor and a major way in which the effects of climate change are expressed. As a causal factor, land use influences the flux of mass and energy, and as land-cover patterns change, these fluxes are altered. Projected climate alterations will produce changes in land-cover patterns at a variety of temporal and spatial scales, although human uses of the land are expected to override many effects. A review of the literature dealing with the relationship between land-use change and climate change clearly shows that (1) in recent centuries land-use change has had much greater effects on ecological variables than has climate change; (2) the vast majority of land-use changes have little to do with climate change or even climate; and (3) humans will change land use, and especially land management, to adjust to climate change and these adaptations will have some ecological effects. Therefore, an understanding of the nonclimatic causes of land-use change ...

Predicting across scales: Theory development and testing

Landscape ecologists deal with processes that occur at a variety of temporal and spatial scales. The ability to make predictions at more than one level of resolution requires identification of the processes of interest and parameters that affect this process at different scales, the development of rules to translate information across scales, and the ability to test these predictions at the relevant spatial and temporal scales. This paper synthesizes discussions from a workshop on ‘Predicting Across Scales: Theory Development and Testing’ that was held to discuss current research on scaling and to identify key research issues.

Predicting the spread of disturbance across heterogeneous landscapes

The expected pattern of disturbance propagation across a landscape was studied by using simple landscape models derived from percolation theory. The spread of disturbance was simulated as a function of the proportion of the landscape occupied by the disturbance-prone habitat and the frequency (probability of initiation) and intensity (probability of spread) of the habitat-specific disturbance. Disturbance effects were estimated from the proportion of habitat affected by the disturbance and changes in landscape structure (i.e., spatial patterns). Landscape structure was measured by the number of habitat clusters, the size and shape of the largest cluster, and the amount of edge in the landscape. Susceptible habitats that occupied less than 50% of the landscape were sensitive to disturbance frequency but showed little response to changes in disturbance intensity. Susceptible habitat that occupied more than 60% of the landscape were sensitive to disturbance intensity and less sensitive to disturbance frequency. These dominant habitats were also very easily fragmented by disturbances of moderate intensity and low frequency. Implications of these results for the management of disturbance-prone landscapes are discussed. The propagation of disturbance in heterogeneous landscapes depends on the structure of the landscape as well as the disturbance intensity and frequency.

Comparing Large, Infrequent Disturbances: What Have We Learned?

The importance of natural disturbances in shapinglandscapes and influencing ecosystems is now wellrecognized in ecology. Disturbances span a broadrange of sizes and frequencies, and while under-standing of relatively small disturbances has in-creased rapidly, the ecological effects of disturbanceevents that are large in spatial extent and infrequentin occurrence are not well understood. Examples ofthese large and infrequent disturbances includevolcanic eruptions, big fires, and extreme floods orstorms. Whether large, infrequent disturbances arequalitatively different from small frequent distur-bances remains an unresolved issue in ecology, inpart, because of a paucity of long-term data on theeffects of broad-scale disturbances. The intensivepostdisturbance research focused on several largenatural disturbances (for example, the 1988 Yellow-stone fires, Hurricane Hugo in 1989, the eruption ofMount St. Helens in 1980, and the 1993 floods inthe Midwest) provides an opportunity to developcomparisons across these unusual events. The fol-lowing set of articles begins to synthesize what isknown about the ecological implications of