The earth's landscapes are being increasingly impacted by the activities of man. Unfortunately, we do not have a full understanding of the consequences of these disturbances on the earth's productive capacity. This problem was addressed by a group of French and U.S. ecologists who are specialists at levels of integration extending from genetics to the biosphere at a meeting at Stanford, California, sponsored by the National Science Foundation and the Centre National de la Recherche Scientifique. With a few important exceptions it was found at this meeting that most man-induced disturbances of ecosystems can be viewed as large scale patterns of disturbances that have occurred, generally on a small scale, in ecosystems through evolutionary time. Man has induced dramatic large-scale changes in the environment which must be viewed at the biosphere level. Acid deposition and CO increase are two 2 examples of the consequences of man's increased utilization of fossil fuels. It is a matter of considerable concern that we cannot yet fully predict the ecological consequences of these environmental changes. Such problems must be addressed at the international level, yet substantive mechanisms to do this are not available."

Our knowledge of the functional characteristics of the plants of mediterranean-cl imate regions has increased greatly in the past decade. In recent times the possibility of large-scale util ization of biomass for energy from these regions has been proposed. In order to assess the feasibil ity of these proposals we must consider the productive structure of these plant communities and how they vary through time and space. This symposium was an attempt to examine our recently acquired basic knowledge of the environmental I imitations on the productivity of Mediterranean plant communities in relation to the consequences of the possible util ization of these communities for energy and chemicals. Specifically in this book we examine the mechanisms by which plants of mediterranean-cl imate regions maintain their productive capacity under the prevail ing conditions of summer draught and winter cold. We consider the characteristics of leaves, their history, morphology and plasticity. Evergreen sclerophyll leaves are common to the dominant plants of all mediterranean-cl imate regions and thus they have significance in terms of enhancing carbon gain and water-use efficiency as well as ensuring survival under the prevail ing cl imatic conditions.

This book contains the results of a Symposium on the physiological ecology of plants of the lowland wet tropics held in Mexico in June 1983 organized by the Instituto de Biologla of the National University of M"exico (U. N . A. M. ), and sponsored by UNAM, CONACYT, NSF and UNESCO (CIET). A workshop portion of the Symposium was held at the tropical research station at Los Tuxtlas, Veracruz. This Symposium originated in response to the increasing interest in the physiological ecology of tropical plants, because of the potential. of this field to provide a basic understanding of functioning of tropical plant communities. The study of physiological ecology of tropical plants has been delayed in some cases by the lack of conceptual framework, but also by the absence of appropriate instrumentation and techniques with which to conduct precise measurements under high temperature, high humidity field conditions. Hypotheses and concepts of the physiological ecology of tropical plants have been based mainly on observational data and the analysis of growth forms and leaf anatomf. The early work of A. F. W. Schimper and o. Stocker in Asia, and the extensive surveys made by H. Walter on the osmotic potentials of plants in the tropics and subtropics, constituted, until relatively recently, the only available information on the water and carbon relations of tropical plants.

Physiological plant ecology is primarily concerned with the function and performance of plants in their environment. Within this broad focus, attempts are made on one hand to understand the underlying physiological, biochemical and molecular attributes of plants with respect to performance under the constraints imposed by the environment. On the other hand physiological ecology is also concerned with a more synthetic view which attempts to under stand the distribution and success of plants measured in terms of the factors that promote long-term survival and reproduction in the environment. These concerns are not mutually exclusive but rather represent a continuum of research approaches. Osmond et al. (1980) have elegantly pointed this out in a space-time scale showing that the concerns of physiological ecology range from biochemical and organelle-scale events with time constants of a second or minutes to succession and evolutionary-scale events involving communities and ecosystems and thousands, if not millions, of years. The focus of physiological ecology is typically at the single leaf or root system level extending up to the whole plant. The time scale is on the order of minutes to a year. The activities of individual physiological ecologists extend in one direction or the other, but few if any are directly concerned with the whole space-time scale. In their work, however, they must be cognizant both of the underlying mechanisms as well as the consequences to ecological and evolutionary processes."

Physiological plant ecology is primarily concerned with the function and performance of plants in their environment. Within this broad focus, attempts are made on one hand to understand the underlying physiological, biochemical and molecular attributes of plants with respect to performance under the constraints imposed by the environment. On the other hand physiological ecology is also concerned with a more synthetic view which attempts to under stand the distribution and success of plants measured in terms of the factors that promote long-term survival and reproduction in the environment. These concerns are not mutually exclusive but rather represent a continuum of research approaches. Osmond et al. (1980) have elegantly pointed this out in a space-time scale showing that the concerns of physiological ecology range from biochemical and organelle-scale events with time constants of a second or minutes to succession and evolutionary-scale events involving communities and ecosystems and thousands, if not millions, of years. The focus of physiological ecology is typically at the single leaf or root system level extending up to the whole plant. The time scale is on the order of minutes to a year. The activities of individual physiological ecologists extend in one direction or the other, but few if any are directly concerned with the whole space-time scale. In their work, however, they must be cognizant both of the underlying mechanisms as well as the consequences to ecological and evolutionary processes."

The chapters in this volume are based on a opportumtles for studying the links between symposium, "California grasslands: structure abiotic and biotic components. and productivity," supported by the National The contributions in this volume illustrate Science Foundation. The primary objective of the links between population-level processes this symposium was to integrate the current and system-level phenomena in a well-studied understanding of controls on ecosystem struc community. Unfortunately, some areas of cur ture and function with the approaches of popu rent research (e.g., nutrient cycling) are under lation biology. The annual grasslands are represented in this volume. For other topics eminently suitable for experimental and manip (particularly the role of invertebrate con sumers), the lack of data from the annual grass ulative studies of ecosystem processes. The short lives and small stature of the component land brought a broader grassland perspective. plant species make experimental work far more Together, however, the contributions illustrate practical than in forests or even in perennial the importance of different ecological ap dominated prairies. The system's small-scale proaches in studying the controls on structure patchiness, and the obvious importance of and function of a complex system. the region's mediterranean climate in the life cycle of the annual vegetation, afford many L.F. Huenneke and H.A. Mooney Huenneke, L.F. and Mooney, H. (eds) Grassland Structure and Function: California Annual Grassland."

Our knowledge of the functional characteristics of the plants of mediterranean-cl imate regions has increased greatly in the past decade. In recent times the possibility of large-scale util ization of biomass for energy from these regions has been proposed. In order to assess the feasibil ity of these proposals we must consider the productive structure of these plant communities and how they vary through time and space. This symposium was an attempt to examine our recently acquired basic knowledge of the environmental I imitations on the productivity of Mediterranean plant communities in relation to the consequences of the possible util ization of these communities for energy and chemicals. Specifically in this book we examine the mechanisms by which plants of mediterranean-cl imate regions maintain their productive capacity under the prevail ing conditions of summer draught and winter cold. We consider the characteristics of leaves, their history, morphology and plasticity. Evergreen sclerophyll leaves are common to the dominant plants of all mediterranean-cl imate regions and thus they have significance in terms of enhancing carbon gain and water-use efficiency as well as ensuring survival under the prevail ing cl imatic conditions.