Persistence, threats, pathogens, herbivores, interactions, fragmented, landscape, extinction, habitat, disturbance, restoration.

Providing a quantitative assessment of threatened plant populations, that holds for varying management scenarios, has become an essential part of conservation planning. Here, renowned plant ecologists provide information on: major threats to plants, when and where to conduct a plant viability assessment (PVA), what type of PVA to conduct, what alternative options to PVA are available, what information is required for which kind of viability assessment, what attributes of the population in question should be considered, and what the limits of the PVA would be. As such, this volume can be used as a training tool for the environmental manager or a teaching aid for reviewing the current state of knowledge on plant population viability.

Providing a quantitative assessment of threatened plant populations, that holds for varying management scenarios, has become an essential part of conservation planning. Here, renowned plant ecologists provide information on: major threats to plants, when and where to conduct a plant viability assessment (PVA), what type of PVA to conduct, what alternative options to PVA are available, what information is required for which kind of viability assessment, what attributes of the population in question should be considered, and what the limits of the PVA would be. As such, this volume can be used as a training tool for the environmental manager or a teaching aid for reviewing the current state of knowledge on plant population viability.

Many of the world's leading conservation and population biologists evaluate what has become a key tool in estimating extinction risk and evaluating potential recovery strategies - population viability analysis, or PVA.

From its inception, the U.S. Department of the Interior has been charged with a conflicting mission. One set of statutes demands that the department must develop America's lands, that it get our trees, water, oil, and minerals out into the marketplace. Yet an opposing set of laws orders us to conserve these same resources, to preserve them for the long term and to consider the noncommodity values of our public landscape. That dichotomy, between rapid exploitation and long-term protection, demands what I see as the most significant policy departure of my tenure in office: the use of science-interdisciplinary science-as the primary basis for land management decisions. For more than a century, that has not been the case. Instead, we have managed this dichotomy by compartmentalizing the American landscape. Congress and my predecessors handled resource conflicts by drawing enclosures: "We'll create a national park here," they said, "and we'll put a wildlife refuge over there." Simple enough, as far as protection goes. And outside those protected areas, the message was equally simplistic: "Y'all come and get it. Have at it." The nature and the pace of the resource extraction was not at issue; if you could find it, it was yours.

• • • John Harper • • • Nature conservation has changed from an idealistic philosophy to a serious technology. Ecology, the science that underpins the technol ogy of conservation, is still too immature to provide all the wisdom that it must. It is arguable that the desire to conserve nature will in itself force the discipline of ecology to identify fundamental prob lems in its scientific goals and methods. In return, ecologists may be able to offer some insights that make conservation more practicable (Harper 1987). The idea that nature (species or communities) is worth preserv ing rests on several fundamental arguments, particularly the argu ment of nostalgia and the argument of human benefit and need. Nostalgia, of course, is a powerful emotion. With some notable ex ceptions, there is usually a feeling of dismay at a change in the sta tus quo, whether it be the loss of a place in the country for walking or rambling, the loss of a painting or architectural monument, or that one will never again have the chance to see a particular species of bird or plant.

This technical reference applies to monitoring situations involving a single plant species, such as an indicator species, key species, or weed. It was originally developed for monitoring special status plants, which have some recognized status at the Federal, State, or agency level because of their rarity or vulnerability. Most examples and discussions in this technical reference focus on these special status species, but the methods described are also applicable to any single-species monitoring and even some community monitoring situations.We thus hope wildlife biologists, range conservationists, botanists, and ecologists will all find this technical reference helpful.