Written by experts in wildlife biology, ecosystem science, landscape ecology, and forest science, the book shows not only that many things changed after the fires (for ecological components of the system are interactive) but also that some things did not change. The largest effects of the fires were felt at the smallest scales, and the long-term devastation predicted did not come to pass. The resilience of this naturally functioning ecosystem to these huge fires has important lessons for heavily managed regions.
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About the Author
Linda L. Wallace is Samuel Roberts Noble Presidential Professor and professor of botany at the University of Oklahoma.
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After the Fires
The Ecology of Change in Yellowstone National Park
Yale University Press
Copyright © 2004 Yale University
All right reserved.
The Fires of 1988: A Chronology and Invitation to Research
Linda L. Wallace, Francis J. Singer, and Paul Schullery
The goal of this volume is to take a comprehensive look at the large-scale fires of 1988 that swept through the Greater Yellowstone Ecosystem(GYE), most notably in Yellow stone National Park (YNP). We will not examine the political ramifications of the fires, but rather will look at the fires as they affected the geology, ecology, and structure of this system. Research work is continuing as this volume is being written and printed. However, the work presented represents a little more than one decade of research by scientists from across the United States in a number of different disciplines. Although many of these individuals have published results of studies in separate papers, this volume gives us an opportunity to synthesize these results and compare findings in a cohesive and comprehensive manner.
The goals of this introduction are twofold. First we will briefly describe the chronology of the 1988 fires and discuss what areas were burned and the extent of fire in those regions. Second, we will set the stage for the research work and describe the different ecological scales that the different research projects represent.
GENERAL DESCRIPTION OF THE GREATER YELLOWSTONE ECOSYSTEM
The GYE is centered on YNP, a truly unique volcanic landscape. The original goals of Yellow stone, founded in 1872, were top reserve unique thermal features, including geysers, hot springs, and thermal pools. Later, it became obvious that one of the other key factors attracting visitors to YNP was the wildlife. In 1883, wildlife was protected from hunting in the park and became a major management focus as well. As our knowledge of ecosystem science expanded, management's concerns expanded to include the habitat of important wildlife species and the health of forage species, trees, and soils. Fishing and aquatic systems management gradually joined traditional wildlife management as important focuses of administrative action. By 1910, U.S. Army administrators were beginning to think of protecting native fish species from further nonnative fish introductions. Increased attention to aquatic systems followed the creation of the National Park Service in 1916, though intensive manipulation of many park fisheries continued until midcentury (Varley and Schullery 1998).
Yellowstone National Park can be divided into two major areas, the northern range and the subalpine plateau (Fig. 1.1). The northern range is deeply dissected low to midelevation (2400-2800 m) sagebrush grasslands (55 percent grasslands) and forests and acts as the winter range to populations of elk (17,000-23,000) and bison (500-2000) (Houston 1982). Soils are andesetic in origin and are hence fairly nutrient rich. The subalpine plateau is mid- to high elevation and is largely forested with smaller grassland openings (less than 5 percent grasslands). However, some important grassland areas such as Hayden Valley and Pelican Valley also occur here. The largest thermal areas are found here as well. Soils are rhyolitic in origin and are fairly nutrient poor. This region is typically the summer home for very large populations of elk and bison. In excess of 32,000 elk from eight different herds migrate each summer to the park's central plateau (Singer and Mack 1999). Many fewer individuals overwinter on the plateau because of deep snow and frigid temperatures. Some notable exceptions are animals overwintering in the thermal basins as well as a small bison herd that persists in the deep snows of Pelican Valley (Meagher 1973, Singer 1991).
AN ABBREVIATED HISTORY OF THE 1988 FIRES
The fires of 1988 resulted from a combination of drought, above-average temperatures, and numerous dry thunderstorms with lightning strikes and high winds. This meteorological combination, considered to be a 300-400-year event, resulted in the burning of 1,405,775 ha in the GYE (Despain and others 1989, Schullery 1989). About one-third of the 590,000 ha summer range for elk and bison burned, and 22 percent of the 134,000 ha winter range for the northern Yellowstone elk and bison herd burned in this series of fires. The meteorology of 1988 should not be viewed in isolation, however. Prior to the drought of the summer of 1988, the GYE had experienced dry winter and spring conditions in both 1986 and 1987. This helped set the stage for the extremely low fuel moistures that subsequently occurred by July 1988. Fuel moisture levels were only 2-3 percent (Schullery 1989), lower than values found in household furnishings!
High temperatures further exacerbated the low precipitation in 1988. June and July averages were 8.6 and 2.7ºC above normal, respectively. Fire starts were frequent during July-September because a series of abnormally dry cold fronts passed through the park, igniting fires but bringing almost no rain. Winds during the passage of these fronts were as high as 64-96 km [hr.sup.-1] (Schullery 1989). This resulted in fires spotting 2 km ahead of fire fronts with fires moving as fast as 3 km [hr.sup.-1]. Fire fronts advanced as much as 8-16 km per day (Schullery 1989).
In 1971, the National Park Service (NPS) instituted a policy in which backcountry and high-elevation fires would not be suppressed if they were of lightning origin and did not threaten critical structures, habitat, or human life. This had resulted in 235 fires burning only 13,823 ha during this entire time, with the largest fire burning only 2,995 ha (Schullery 1989). During 1988, a number of fires were allowed to burn within the park until July 21, when park staff was convinced that fire conditions were too extreme to allow further burning. All existing and new fires were suppressed after this date, but firefighting efforts had little influence. An enormous firefighting presence was in the park, involving firefighters from the NPS, the Forest Service, and the military. On the evening of September 14, 1988, approximately 1 cm of snow fell, effectively extinguishing the fires of 1988. Fire crews remained in the park doing mop-up work and later worked on revegetation of fire lines.
Given the scale of the fires, scientists felt that this represented an Unprecedented opportunity for fire research. In October of 1988, the authors of the chapters in this volume gathered at the University of Wyoming Research Ranch in Grand Tet on National Park and began planning coherent research projects. This volume represents our synthesis of these widely varying research efforts.
RESEARCH QUESTIONS AND SCALES
The volume is divided into four sections: Historical and Geological Perspective, Effects on Individuals and Species, Effects on Aquatic Systems, and Terrestrial Ecosystem and Landscape Perspective, plus an Epilogue. Using this rubric, we can first examine the historical context of fire in this ecosystem using two different geological tools, charcoal found in lake sediment cores (Chapter 2) and dated debris-flow layers (Chapter 3). Further, both of these techniques can tell us about how this ecosystem responds to fire via difference vegetation structure and debris-flow movement of nutrients from terrestrial to aquatic habitats. Further, both chapters point out the importance of differences in regional climate in the park relative to fire events.
One of the biggest concerns of the public during and after the fires of 1988 was how individual plants and animals fared. Thinking hierarchically (Ahl and Allen 1996), we know that the patterns seen at the community and ecosystem levels are the result of mechanistic responses at the individual and population levels. Therefore, it is important to know how forest trees (Chapter 4) and grassland species (Chapter 5) responded. Some of the greatest public concern was for large animals, particularly elk. Elk mortality and population responses after the fires took some surprising turns (Chapter 6).
Although responses in aquatic systems can readily fit into the hierarchies above, We chose to separate aquatic systems into a special section for several reasons. First, the effects of fire on aquatic species are primarily indirect, with only a few areas subject to direct heating from flames (Chapter 7). The real so is a great deal of public interest, particularly by sportsmen, in how the fisheries of the GYE were affected by the fires. Because the effects of the fires on aquatic systems are indirect, it is important to understand streams and rivers from an ecosystem perspective and to see how changes in streamside cover, stream flow characteristics, and streambed morphology can influence species composition and survival after fires (Chapter 8). Further, basic changes in community structure and food webs in streams present a unique challenge to life not seen in terrestrial environments (Chapter 9). Finally, public interest in how fires affect water availability and quality downstream from burned watersheds is quite high in the arid West (Chapter 10).
In order to make adequate predictions of what life will be like in the GYE after the fires of 1988, it is imperative that we look at past fires and see how community and ecosystem parameters responded to those (Chapter 11). Also, it is important that we look at all components of the ecosystem, including those which are less "glamorous" but highly essential in terms of nutrient retention and release. Again, in the arid West, coarse woody debris is important as a nutrient sponge as well as being potential fuel for future fires (Chapter 12). In the brief time between the 1988 fires and the present, plant communities have already established and have grown. The GYE is an extremely heterogeneous environment. Are there rules governing how these communities respond in the different growth environments of the GYE (Chapter 14)? Plant communities provide essential habitat for the megaherbivores (elk and bison) of the GYE as well. Although we know numbers and how the populations of these animals have changed since the fires, it is difficult to determine the mechanisms behind these changes. Using simulation models and comparing their results with reality can yield important insights as to the mechanisms governing ungulate response to fire (Chapter 13).
Given the vast amount of research effort and thought that these fifteen chapters represent, we now have the opportunity to synthesize these results into a more cohesive picture of how cold, arid montane systems respond to large-scale fires. Research efforts covered nearly the entirety of the GYE (Fig. 1.2), which enables us to be more confident in our understanding of whole-system responses. Several fire seasons since 1988 have captured both public and political attention because of the scale and intensity of the fires that burned large areas of the West. What can we tell them from the Yellowstone experience? How are the ecosystems of these areas going to respond? How are the members of those ecosystems going to respond? It is important that we understand both the mechanisms and scales of system response to fire (Chapter 15) in order to effectively analyze what our policy response to fire has been in the past and might be in the future.
Postglacial Fire, Vegetation, and Climate History of the Yellowstone-Lamar and Central Plateau Provinces, Yellowstone National Park
Sarah H. Millspaugh, Cathy Whitlock, and Patrick J. Bartlein
The fires of 1988 were unique in the history of Yellowstone National Park (YNP), because during that summer a relatively small number of fires occurred over an enormous region (Schullery 1989). Previous fires in YNP were confined to particular regions and comparatively small sizes (Chapters 4, 14). Although the 1988 event has been considered unprecedented on short time scales, knowledge of fire history is required to evaluate its uniqueness over longer periods. In particular, the 1988 fires raise important questions about the natural range of variability of large fires: What is the long-term frequency of fires in different parts of Yellowstone National Park, and how often and under what conditions is fire occurrence synchronized across regions? How have fire regimes responded to different climate and vegetation conditions in the past, and what do past fire-climate interactions suggest about future fire regimes given the nature of projected changes in regional climate? These questions can be answered only by looking at the prehistoric fire record.
The Yellowstone climate at present is characterized by two geographically delineated precipitation regimes (Despain 1987, Whitlock and Bartlein 1993). These regimes are a local manifestation of large-scale climate features that determine the seasonal pattern of precipitation in the western United States (Tang and Reiter 1984, Mock 1996). One regime receives a significant amount of precipitation in summer as a result of summer storms generated by the onshore flow of moisture from the Gulf of California and Gulf of Mexico into the southwestern United States, the Great Plains, and the southern Rocky Mountains. This type of monsoonal circulation extends to the northern part of YNP and the eastern Snake River Plain, where convectional precipitation occurs along orographic barriers. The other regime, with relatively dry summers, occurs in areas under the influence of the northeastern Pacific subtropical high-pressure system and accounts for summer aridity in the Pacific Northwest, the western Snake River Plain, and central and southern YNP. In both regions precipitation in winter is generated by individual mountain ranges intercepting storm systems moving inland from the Pacific Ocean.
Paleoenvironmental data from the northern and central Rocky Mountains suggest that the contrast between summer-wet and summer-dry precipitation regimes was greater during periods of higher-than-present insolation (Whitlock and Bartlein 1993, Whitlock and others 1995, Fall and others 1995). In this chapter, we examine the influence of such climate changes on the Holocene fire and vegetation history of two geovegetation provinces of YNP that are influenced by different precipitation regimes at present (see Despain 1990 for a description of YNP geovegetation provinces). The environmental history, which is obtained from an analysis of charcoal and pollen in radiocarbon-dated lake-sediment cores at two sites, reveals the long-term interactions among fire, climate, and vegetation within YNP over the past ca. 15,000 cal years.
Slough Creek Lake (Lat. 44º57' N, Long. 110º21'W, elevation 1884 m) is located in the Yellowstone-Lamar Province and lies in a kettle-hole depression in a broad valley that is underlain by andesitic volcaniclastic rocks and carbonate rocks and shale. Most of the soils derive from glacial till deposited during the Pinedale Glaciation (Pierce 1979). The Yellowstone-Lamar Province receives precipitation in spring and summer, as well as during winter (Despain 1987, Whitlock and Bartlein 1993). The late spring and summer precipitation maximum (May-June) is produced by a combination of isolated upper-level low-pressure systems and convection from increased land surface temperatures (Mock 1996). In July, surface warming causes moist air from the Gulf of California to flow northward into the interior of the continent along the western edge of an upper-level subtropical ridge (Higgins and others 1997). Climate records from the Lamar Ranger Station near Slough Creek Lake indicate a mean January temperature of -25ºC and an average July temperature of 15.3ºC from 1948 to 1972. Average annual precipitation from 1948 to 1972 was 36 cm (Dirks and Martner 1982). The Pseudotsuga parkland surrounding Slough Creek Lake is maintained by low-intensity surface fires that are generally lethal to under-story vegetation but do not kill the mature trees. Dendrochronological records suggest that fires prior to about 1890 occurred every twenty to fifty years in the Pseudotsuga parkland (Houston 1973, Barrett 1994). Between about 1850 and present day, there were only a few small fires (Houston 1973), with the exception of 1988, when 34 percent of the Slough Creek Lake catchment burned.
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