             
 The LUHNA Book!
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Land Use History of North America: Clues from the Past About Our Future Environment Most of us realize that our lives are lived on a scale that is insignificant when compared to geological time. Continents break up and drift apart, mountains rise and are worn away by the elements, and all of human history is dwarfed by the vastness of earth's history. What many of us fail to realize is that, like the continents and the mountains, the Earth's living ecosystems are in constant change. While faster than the movement of continents, ecological change occurs at a pace that can be difficult to detect over the span of a human lifetime. Plant communities are constantly shifting in distribution and species composition -- much of what was a rich wetland when humans first crossed the Bering land bridge into North America is now desert, and large expanses of arid grassland seen by the pioneers during the United States' westward expansion has given way to shrubs and woodland. Many such changes in vegetation -- collectively referred to as land cover change -- have resulted from, or been intensified by human activities. From the spread of fire to the expansion of agriculture, humans have shaped the face of North America. Resource managers and scientists, working together, are coming to terms with land cover change and the dynamic view of ecosystems and ecological processes. We can no longer assume that the nature exists in a static, unchanging "natural" condition interrupted only by the work of humans. Instead, we must view nature as a dynamic system of which we are a part, recognizing that a variety of forces -- ranging from climatic change, to fire, to human land conversion -- are constantly interacting to determine the magnitude and direction of change. And we must accept responsibility for the fact that, in most places, our activities have become a dominant component of biological change. Understanding the relationship between human land use and land cover change, and assessing implications for the future, is the goal of a new national program: Land Use History of North America, or LUHNA. In the summer of 1995, the National Biological Service (now the Biological Resources Division of the U.S. Geological Survey) hosted a diverse group of scholars working on the issues of land use, land cover, and ecological change. Historians, geographers, ecologists, and sociologists met with scientists from NBS, the Park Service, NASA and other institutions to discuss how the work of the different agencies and academic subdisciplines might be brought together to provide an integrated perspective on land cover and land use history, from pre-European times to the present. The LUHNA project, now in a pilot phase, is exploring approaches for fostering this cross-disciplinary work and developing data products and analytical tools for researchers, resource managers, educators, and the general public. The first task is to develop a clearer understanding of the historic changes in the distributions of plants and animals and their relation to human-induced changes to the landscape. Much of the impact that people have had on the environment can be viewed as a series of unplanned experiments, with particular perturbations generating measurable responses, in the form of contractions in the ranges of some species and expansions in the ranges of others. Within the context of these temporal dynamics, species extinctions and the spread of non-indigenous species may be seen as the extreme cases, where biological elements are lost or introduced. These experiments have been run, and environmental scientists are assembling the data needed to assess the results. Among the efforts supported by LUHNA are pilot projects examining patterns of forest clearing and reforestation in New England, a comparison of the influences of natural fire and timber harvest in forest development in the Greater Yellowstone ecosystem, a multi-scale view of the vegetative change in the arid Southwest emphasizing fire history, and a continental perspective on the spread of exotic species. You can explore these and other projects by following various LUHNA Tracks, described below. Embracing the dynamic perspective of North American ecosystems has opened up a new understanding for many North Americans, and a new set of challenges for land and resource managers. For much of this century parks, wildlife refuges, and wilderness areas were viewed as inert relics of a natural state that had been lost over most of the continent. However, changes observed in these natural areas over just the past few decades plainly indicate that, like the rest of the landscape, the parks themselves are changing. Climatic variation, the dynamics of plant and animal populations, and the direct and indirect effects of humans are influencing the ecological character of pristine and altered lands, alike. In such a dynamic world, what is the role of the resource manager? Managing parks and wildlands for what is believed to be a "natural" condition has become a vague, unsatisfying goal. Increasingly, scientists and managers are trying to understand the effects of management options in the context of the background rates of change -- often referred to as the natural range of variation or NRV -- of ecological systems. And again, they are turning to our parks and wilderness areas, this time not as specimens of "natural" conditions but as living laboratories, where ecological processes are operating with minimal interference from humans. A complementary approach for understanding NRV is to look back in time and study the rates and magnitude of change that occurred before humans came to dominate most terrestrial ecosystems. In some cases, what seem to be profound and lasting human impacts may appear insignificant when viewed in the context of the system's natural range of variation. In other cases -- such as the removal of old-growth forests and the draw-down of freshwater aquifers -- consideration of NRV confirms that change is occurring at a rate that is unprecedented in the recent history of the planet. Recognizing the difference is a new and critical challenge for environmental scientists. BRD and its LUHNA collaborators are working to bring this hard-won understanding to the management of natural resources.
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