Daniel B. Botkin

Forecasting the Effects of Global Warming on Biodiversity

ABSTRACT The demand for accurate forecasting of the effects of global warming on biodiversity is growing, but current methods for forecasting have limitations. In this article, we compare and discuss the different uses of four forecasting methods: (1) models that consider species individually, (2) niche-theory models that group species by habitat (more specifically, by environmental conditions under which a species can persist or does persist), (3) general circulation models and coupled ocean–atmosphere–biosphere models, and (4) species–area curve models that consider all species or large aggregates of species. After outlining the different uses and limitations of these methods, we make eight primary suggestions for improving forecasts. We find that greater use of the fossil record and of modern genetic studies would improve forecasting methods. We note a Quaternary conundrum: While current empirical and theoretical ecological results suggest that many species could be at risk from global warming, during the recent ice ages surprisingly few species became extinct. The potential resolution of this conundrum gives insights into the requirements for more accurate and reliable forecasting. Our eight suggestions also point to constructive synergies in the solution to the different problems.

Large-Scale Patterns of Forest Succession as Determined by Remote Sensing

The spatial pattern of and the transition rates between forest ecological states were inferred for °260 000 pixel—sized (3600 m2) landscape units using stallite remote sensing. Transition rates were estimated from 1973 to 1983 Landsat images of the study area, classified into ecological states associated with forest succession. The effects of classification error on transition rate estimates were modeled and error adjustments made. Classification of the 1973 and 1983 Landsat images of the 900 km2 study region required a relatively small set of ground—observed and photo—interpreted plots in 1983, with a total area of just 1.62 km2. An innovative technique for correcting multiyear Landsat images for between—image differences in atmospheric effects and sensor calibration, permitted classification of the 1973 Landsat image using 1983 ground observations. Given current Landsat data, and ground observations in one year, this technique would permit monitoring of forest succession and dynamics for nearly a 20—yr period. Results of applying these techniques to a forest ecosystem showed that during the 10—yr observation period it was patchy and dynamic. For both a wilderness and a nonwilderness area in the study region, sizeable values of transition rates were observed and over half of the landscape units were observed to change state: however, a Markov analysis, using the observed transition probabilities, suggests that at the regional level neither the wilderness nor the nonwilderness areal proportions of ecological states are undergoing rapid change.

Sensitivity of cool-temperate forests and their fossil pollen record to rapid temperature change

Abstract Simulations of cool-temperate forest growth in response to climatic change using the JABOWA computer model show that a decrease of 600 growing degree-days (equivalent to a 2°C decrease in mean annual temperature) causes red spruce ( Picea rubens ) to replace sugar maple ( Acer saccharum ) as the dominant tree. These changes are delayed 100–200 yr after the climatic cooling, producing gradual forest changes in response to abrupt temperature changes, and reducing the amplitude of response to brief climatic events. Soils and disturbances affect the speed and magnitude of forest response. The delayed responses are caused by the difference in sensitivity of adult trees and younger stages. The length of the delay depends on the life history characteristics of the dominant species. Delayed responses imply that fossil pollen deposits, even if they faithfully record the abundances of trees in forests, may not be able to resolve climatic changes within 100–200 yr, or to record very brief climatic events. This explains why pollen deposits do not as yet show responses to climatic changes during the past 100 yr. Only the Little Ice Age, which lasted several centuries, caused sufficient forest change to be recorded in fossil pollen, and only at certain sites.

Cities as environments

In starting a new journal about urban ecosystems, it is useful to review some of the dominant themes that have run through recent and historic discussions of cities as environments. Although concern with urban environmental issues may seem to be new, because of the great amount of attention paid during the past several decades to the negative aspects of urban environments – air, water, and soil pollution – there is a long history of thought, writing, and design about cities as environments, extending back throughout most of western history. This long history has modern relevance, but is more often ignored than used. This paper briefly reviews some central aspects of the major ideas about city planning and design, relates these to modern urban dilemmas and contemporary ecological knowledge, and proposes a new synthesis of classical and contemporary ideas. The issues are general, relating to cities around the world, but when examples are given in this paper, the focus is on cities in the United States, because of space limitations and because of an emphasis on the thoughts of Frederic Law Olmsted, the great American planner. In reviewing discussions of urban environments, we make five major points:

Ten Suggestions to Strengthen the Science of Ecology

Abstract There are few well-documented, general ecological principles that can be applied to pressing environmental issues. When they discuss them at all, ecologists often disagree about the relative importance of different aspects of the sciences original and still important issues. It may be that the sum of ecological science is not open to universal statements because of the wide range of organizational, spatial, and temporal phenomena, as well as the sheer number of possible interactions. We believe, however, that the search for general principles has been inadequate to establish the extent to which generalities are possible. We suggest that ecologists may need to reconsider how we view our science. This article lists 10 suggestions for ecology, recognizing the many impediments to finding generalizations in this field, imposed in part by the complexity of the subject and in part by limits to funding for the study of ecology.

MORTALITY RATES AND SURVIVAL OF BIRDS

Birds have been assumed to have a constant adult mortality rate in which a constant fraction of a cohort dies in each age interval. Average annual mortality rates reported for many species would result in exceedingly long potential life spans, and it seems more reasonable to assume that avian mortality is age dependent. Data on the mortality and survivorship of several species of birds are analyzed and alternative models of age-dependent mortality are discussed.

Studying the Earth's Vegetation from Space

Understanding the effects of modern technological civilization on the biosphere requires greatly improved global estimates of the spatial distribution and temporal dynamics of major types of terrestrial vegetation, as well as information on biomass, productivity, and exchange of energy and chemical elements between the vegetation and the atmosphere, oceans, and soils. Past estimates of these vegetation characteristics have been, by necessity, based on extremely limited data; they have been little more than expert testimony of knowledgeable ecologists and biogeographers. Advances during the past decade in satellite remote sensing technology and computer processing, however, have made accurate, repeatable measurements of these characteristics possible. Remote sensing is the study of objects and phenomena from a great distance by systems that are not in contact with the object or phenomenon being investigated. A number of factors have contributed to the development of remote sensing as we know it today; these include the invention and development of multispectral scanners producing digital information, advances in computer processing and its applications to remote sensing, the development of stable highaltitude aircraft and satellites to carry the sensors, and scientific interest in using these tools. The technological advances in remote sensing have largely developed to satisfy needs for specific information for specific applications; interest among scientists in using remote sensing for basic research has arisen secondarily.

Forest response to climatic change : effects of parameter estimation and choice of weather patterns on the reliability of projections

Computer projections suggest that forests may respond dramatically and rapidly to global warming, with significant and readily observable changes in forests of mid-latitudes occurring by the turn of the century or shortly thereafter. These results raise the question: how reliable are the projections? Sensitivity analyses reported in this paper suggest that projections of forest response to global warming will be generally insensitive to errors of 10% in parameter estimation. Even where projections are sensitive quantitatively, they are not changed in timing. Projections are insensitive to the choice of baseline weather records, unless the warmest or coldest decades of the 20th century are used as baselines.

Kirtland's Warbler Habitats: A Possible Early Indicator of Climatic Warming

Abstract If the projections of global climate models are correct, jack pine Pinus banksiana forests in central Michigan, managed as the primary nesting habitat for the endangered species Kirtlands warbler Dendroica kirtlandii , will soon be growing at a significantly slower rate than they have in the recent past. As a result, these forests may become unsuitable as habitat for the warbler within 30–60 years. This projection is based on results from a global climate model applied to a forest growth model. The robustness of these predictions is discussed. Measurement of tree growth in these forests could provide some of the earliest evidence of biological effects of climatic warming due to an increase in greenhouse gases in the atmosphere.

Biomass Dynamics in a Moose Population

From a simple model, we have calculated with a digital computer the standing crop, the gains in weight (secondary production), and the transfer of biomass by death (potential food for predators) on a monthly basis for all age and sex categories of the Isle Royale moose, a population unhunted by man and in equilibrium with its predator, the timber wolf. These estimates provide a more accurate and detailed picture than available before of biomass dynamics in a wild ungulate population. For this single—prey—single—predator system, results demonstrate that the accumulation of biomass in the prey population permits a steady flow of food to the predator, although production of food for the prey (woody and aquatic vegetation) is seasonally highly cyclic. The storage of biomass is examined in terms of the year classes of moose. Further uses of the model are discussed. See full-text article at JSTOR