Showing papers in "Ecological Applications in 1991"

Northern Peatlands: Role in the Carbon Cycle and Probable Responses to Climatic Warming.

Abstract: Boreal and subarctic peatlands comprise a carbon pool of 455 Pg that has accumulated during the postglacial period at an average net rate of 0.096 Pg/yr (1 Pg = 1015g). Using Clymo's (1984) model, the current rate is estimated at 0.076 Pg/yr. Longterm drainage of these peatlands is estimated to be causing the oxidation to CO2 of a little more than 0.0085 Pg/yr, with conbustion of fuel peat adding °0.026 Pg/yr. Emissions of CH4 are estimated to release ° 0.046 Pg of carbon annually. Uncertainties beset estimates of both stocks and fluxes, particularly with regard to Soviet peatlands. The influence of water table alterations upon fluxes of both CO2 and CH4 is in great need of investigation over a wide range of peatland environments, especially in regions where permafrost melting, thermokarst erosion, and the development of thaw lakes are likely results of climatic warming. The role of fire in the carbon cycle of peatlands also deserves increased attention. Finally, satellite—monitoring of the abundance of open water in the peatlands of the West Siberian Plain and the Hudson/James Bay Lowland is suggested as a likely method of detecting early effects of climatic warming upon boreal and subarctic peatlands.

Biological Integrity: A Long-Neglected Aspect of Water Resource Management

Abstract: Water of sufficient quality and quantity is critical to all life. Increasing human population and growth of technology require human society to devote more and more attention to protection of adequate supplies of water. Although perception of biological degradation stimulated current state and federal legislation on the quality of water resources, that biological focus was lost in the search for easily measured physical and chemical surrogates. The "fishable and swimmable" goal of the Water Pollution Control Act of 1972 (PL 92-500) and its charge to "restore and maintain" biotic integrity illustrate that law's biological underpinning. Further, the need for operational definitions of terms like "biological integrity" and "unreasonable degradation" and for ecologically sound tools to measure divergence from societal goals have increased interest in biological monitoring. Assessment of water resource quality by sampling biological communities in the field (ambient biological monitoring) is a promising approach that requires expanded use of ecological expertise. One such approach, the Index of Biotic Integrity (IBI), provides a broadly based, multiparameter tool for the assessment of biotic integrity in running waters. IBI based on fish community attributes has now been applied widely in North America. The success of IBI has stimulated the development of similar approaches using other aquatic taxa. Expanded use of ecological expertise in ambient biological monitoring is essential to the protection of water resources. Ecologists have the expertise to contribute significantly to those programs.

Effects of Climate Change on Plant Respiration

Abstract: Plant respiration is a large, environmentally sensitive component of the ecosystem carbon balance, and net ecosystem carbon flux will change as the balance between photosynthesis and respiration changes. Partitioning respiration into the functional components of construction, maintenance, and ion uptake will aid the estimation of plant respiration for ecosystems. Maintenance respiration is the component most sensitive to changes in temperature, CO2 , protein concentration and turnover, water stress, and atmospheric pollutants. For a wide variety of plant tissues, maintenance respiration, corrected for temperature, appears to be linearly related to Kjeldahl nitrogen content of live tissue. Total and maintenance respiration may decline under CO2 enrichment, but the mechanism, independence from changes in protein content, and acclimation are unknown. Response of respiration to temperature can be modelled as a Q10 relationship, if corrections for bias arising from daily and annual temperature amplitude are applied. Occurrence and control of the cyanide-resistant respiratory pathway and acclimation of respiration rates to different climates are poorly understood, but may substantially affect the reliability of model estimates of plant respiration.

Potential Net Primary Productivity in South America: Application of a Global Model

Abstract: We use a mechanistically based ecosystem simulation model to describe and analyze the spatial and temporal patterns of terrestrial net primary productivity (NPP) in South America. The Terrestrial Ecosystem Model (TEM) is designed to predict major carbon and nitrogen fluxes and pool sizes in terrestrial ecosystems at continental to global scales. Information from intensively studies field sites is used in combination with continental-scale information on climate, soils, and vegetation to estimate NPP in each of 5888 non-wetland, 0.5° latitude °0.5° longitude grid cells in South America, at monthly time steps. Preliminary analyses are presented for the scenario of natural vegetation throughout the continent, as a prelude to evaluating human impacts on terrestrial NPP. The potential annual NPP of South America is estimated to be 12.5 Pg/yr of carbon (26.3 Pg/yr of organic matter) in a non-wetland area of 17.0 ° 106 km2 . More than 50% of this production occurs in the tropical and subtropical evergreen forest region. Six independent model runs, each based on an independently derived set of model parameters, generated mean annual NPP estimates for the tropical evergreen forest region ranging from 900 to 1510 g°m-2 °yr-1 of carbon, with an overall mean of 1170 g°m-2 °yr-1 . Coefficients of variation in estimated annual NPP averaged 20% for any specific location in the evergreen forests, which is probably within the confidence limits of extant NPP measurements. Predicted rates of mean annual NPP in other types of vegetation ranged from 95 g°m-2 °yr-1 in arid shrublands to 930 g°m@ ?yr-1 in savannas, and were within the ranges measured in empirical studies. The spatial distribution of predicted NPP was directly compared with estimates made using the Miami mode of Lieth (1975). Overall, TEM predictions were °10% lower than those of the Miami model, but the two models agreed closely on the spatial patterns of NPP in south America. Unlike previous models, however, TEM estimates NPP monthly, allowing for the evaluation of seasonal phenomena. This is an important step toward integration of ecosystem models with remotely sensed information, global climate models, and atmospheric transport models, all of which are evaluated at comparable spatial and temporal scales. Seasonal patterns of NPP in South America are correlated with moisture availability in most vegetation types, but are strongly influenced by seasonal differences in cloudiness in the tropical evergreen forests. On an annual basis, moisture availability was the factor that was correlated most strongly with annual NPP in South America, but differences were again observed among vegetation types. These results allow for the investigation and analysis of climatic controls over NPP at continental scales, within and among vegetation types, and within years. Further model validation is needed. Nevertheless, the ability to investigate NPP-environment interactions with a high spatial and temporal resolution at continental scales should prove useful if not essential for rigorous analysis of the potential effects of global climate changes on terrestrial ecosystems.

The effects of climate change on decomposition processes in grassland and coniferous forests

Abstract: Current models of climate change predict a reduction of area covered by northern coniferous forests and tundra, and an increase in grasslands. These scenarios also indicate a northerly shift in agricultural regions, bringing virgin soils under cultivation. The direct effects of man on tundra, boreal forest, and temperate grassland ecosystems are likely to result in less carbon mobilization from soils and vegetation than from tropical forests. However, as a consequence of climate change, carbon mineralization rates from arctic and sub-arctic soils could be very rapid under warmer and drier conditions because of low stabilization of soil organic matter (SOM) and enhanced microbial responses to small changes in soil moisture and temperature. Predicting the response of these systems to climate change is complicated where the edaphic environment regulating SOM dynamics is not a direct function of macroclimatic conditions. Grasslands contain a greater proportion of highly stabilized SOM than coniferous forests, distributed over greater depth in the soil profile, which is less susceptible to changes in mineralization rates. It is concluded that short-term responses of soil processes to climate change are more predictable in well-drained grassland and forest soils than in waterlogged soils of the tundra and boreal region. Over longer periods of time, however, plant species and soil types will alter in response to new temperature and moisture regimes above- and belowground interacting with the effects of carbon enrichment and changes in nutrient availability. The dynamics of these plant-soil interactions and the future status of soils in different life zones as sources or sinks of carbon is poorly understood. More data are also needed on the distribution of waterlogged forest soils in the boreal zone and responses to warming, which include the production of methane as well as CO2 . The primary recommendation for future research is for integrated studies on plant and soil processes.

Carbon Fluxes in Plant-Soil Systems at Elevated Atmospheric CO2 Levels.

Abstract: The flow of carbon from photosynthesizing tissues of higher plants, through the roots and into the soil is one of the key processes in terrestrial ecosystems. An increased level of CO2 in the atmosphere will likely result in an increased input of organic carbon into the soil due to the expected increase in primary production. Whether this will lead to accumulation of greater amounts of organic carbon in soil depends on the flow of carbon through the plant into the soil and its subsequent transfor- mation in the soil by microorganisms. In this paper the major controls of carbon trans- location via roots into the soil as well as the subsequent microbial turnover of root-derived carbon are reviewed. We discuss possible consequences of an increased CO2 level in the atmosphere on these processes.

Current Velocity and Its Effect on Aquatic Macrophytes in Flowing Waters.

Abstract: Current velocity significantly affected the biomass and shoot density of aquatic macrophytes in two slow-flowing rivers in western Canada. Studies of aquatic macrophyte communities at three sites on the Bow River, Alberta, Canada, between 1982 and 1985 showed that biomass decreased with increasing current velocity within the weed bed over the range 0.01-1 m/s; at current speeds in excess of 1 m/s, aquatic macrophytes were rare. Transplant experiments in which Potamogeton pectinatus was grown in pails containing three sediments differing in texture at three sites with different current velocities also demonstrated that biomass and shoot density were affected by both the direct effects of current velocity on plant shoots and its indirect effects on sediment nutrient concentrations. These results indicate that current velocity is an important factor regulating aquatic mac- rophyte biomass in flowing waters and suggest that even a relatively modest increase in current velocity within weed beds reduces the abundance of submerged aquatic plants.

The Influence of Plant Nutrition on Biomass Allocation.

Abstract: The influence of nutrition on the allocation of dry matter is investigated using data from previously published experiments with forest tree species (Betula pendula Roth., Picea abies (L.) Karst., Pinus contorta Dougl., and Pinus silvestris L.) where the nutnent status of the plants was maintained constant over a considerable period of time and biomass increase (steady-state nutrition and growth). We demonstrated that the al- location patterns of a plant species under limiting nutrient conditions and at optimum can be derived from parameters that have been used to characterize relationships between nutrient status, nutrient uptake, and growth of the species. The properties of the plant that control biomass allocation are discussed on the basis of these findings.

State‐of‐the‐Art of Models of Production‐Decomposition Linkages in Conifer and Grassland Ecosystems

Abstract: We review the state-of-the-art of models of forests and grasslands that could be used to predict the impact of a future climate change arising from increased atmospheric carbon dioxide concentration. Four levels of resolution are recognized: physiologically based models, population models, ecosystem models, and regional or global models. At the physiological level a number of important processes can be described in great detail, but these models often treat inadequately interactions with nutrient cycles, which operate on longer time scales. Population and ecosystem models can, on the other hand, encapsulate relationships between the plants and the soil system, but at the expense of requiring more ad ho formulations of processes. At the regional and global scale we have so far only steady-state models, which cannot be used to predict transients caused by climate change. However, our conclusion is that, in spite of the gaps in knowledge, there are several models based on dominant processes that are well enough understood for the predictions of those models to be taken seriously.

Factors controlling nitrogen cycling and nitrogen saturation in northern temperate forest ecosystems

Abstract: An analysis of the factors controlling rates of nitrogen cycling in northern temperate forest ecosystems is presented based on a quantitative analysis of an extensive data set for forests in Wisconsin and Massachusetts as those data are synthesized in a computer model (VEGIE) of organic matter and nutrient dynamics. The model is of the "lumped-parameter," nutrient-flux-density type, dealing with major components of forest ecosystems rather than stems or species. It deals explicitly with the interactions among light, water, and nutrient availability in determining transient and equilibrium rates of primary production and nutrient cycling. Data are presented for parameterizing the plant component of the system at either the species or community level. A major conclusion is that the ultimate control on equilibrium nitrogen-cycling rates resides not within the nitrogen cycle itself (for example in litter quality or net primary production [NPP] allocation patterns) but rather in ratios of resource-use efficiency by vegetation as compared with the ratios of resource availability. Litter quality and allocation patterns, along with rates of N deposition, do affect the rate at which a system approaches the equilibrium cycling rate. The model is used to explain observed variation in nitrogen-cycling rates among forest types, and to predict the timing and occurrence of "nitrogen saturation" (N availability in excess of biotic demand) as a function of nitrogen deposition rates and harvesting.

Tropical Soil Fertility Changes Under Monocultures and Successional Communities of Different Structure

Abstract: For 5 yr we monitored the fertility of a volcanic-ash derived Inceptisol at a site in the humid tropics of Costa Rica. After forest felling and burning, we established four treatments in a randomized block design with six blocks: a sequence of monocultures (two crops of maize [Zea mays] followed by cassava [Manihot esculenta], then the tree species Cordia alliodora), successional vegetation, a mimic of successional vegetation that was physiognomically similar to the model but shared no species with it, and a species-enriched version of successional vegetation. In addition, one plot was maintained free of vegetation. Species-rich successional vegetation was effective at maintaining soil fertility, although we observed general trends of soil-nutrient decline beneath all treatments, presumably because of plant uptake. It proved possible to imitate the fertility-maintaining characteristics of successional vegetation by creating an equally species-rich community of different floristic composition, but the maintenance of fertility was not enhanced by further species enrichment. Successive peaks of nitrate-nitrogen in soil solution, extractable phosphorus, and extractable potassium occurred during the 1st yr, perhaps driven by an early increment of organic matter from postburn debris and roots. Organic matter, total nitrogen, and extractable sulfur were remarkably stable during the 5-yr period. Depletions of cations, decreases in effective cation exchange capacity (CECe ), and increases in acid saturation were related to treatment in the following order: bare soil > monocultures > the three diverse, successional communities. In the bare-soil plot, fertility decreased dramatically: there was a net loss of exchangeable cations and inorganic nitrogen, the phosphorus-fixation capacity increased, and acid saturation reached a potentially toxic 86%. At the start of the study, three of the blocks had soil with lower pH, lower CECe , and higher acid saturation. During the study this less fertile soil lost proportionally more cations and increased more in acid saturation and phosphorus-fixation capacity. The less fertile soil under monocultures proved exceptionally vulnerable to loss of fertility; after 5 yr under monocultures, for example, acid saturation reached 38% in the more fertile soil and 75% in the less fertile soil. In the species-rich communities, however, changes in soil fertility were far less marked.

Successful Biological Control of Ragwort, Senecio Jacobaea, by Introduced Insects in Oregon

Abstract: The purpose of our study was to estimate the variability in a biological control process on a regional scale, identify its causes, and quantitatively evaluate overall control success. We present evidence of the success of biological control of Senecio jacobaea (ragwort) in western Oregon following introduction of three natural enemies. First, observations from a single site showed that ragwort declined to <1% of its former abundance and has been replaced by a plant community composed predominantly of introduced perennial grasses. Second, a perturbation experiment showed that introduced insects, within one ragwort generation, can depress the density, biomass, and reproduction of ragwort to <1% of populations protected from natural enemies. Third, a 12-yr survey of 42 ragwort populations showed that strong and persistent depression of ragwort recurred at many sites and at different times. Three features of this case history may be useful in the development of ecological theory as an explanation and guide for biological control: (1) the impact of the natural enemies depends on the distribution of individual sizes and ages in the ragwort population; (2) the long-term dynamics of ragwort may be influenced by the presence of large persistent seed bank which is invulnerable to the natural enemies; and (3) the success of biological control of ragwort in western Oregon appears to be independent of variation in environmental conditions. Combining local, short-term experiments and regional long-term observations is a powerful method for demonstrating successful biological control.

Inputs of Sediment and Carbon to an Estuarine Ecosystem: Influence of Land Use.

Abstract: Estuaries and coastal marine ecosystems receive large inputs of nutrients, organic carbon, and sediments from non-point-source runoff from terrestrial ecosystems. In the tidal, freshwater Hudson River estuary, such inputs are the major sources of organic carbon, driving ecosystem metabolism, and thus strongly influencing dissolved oxygen concentrations. We used a watershed simulation model (GWLF) to examine the controls on inputs of organic carbon and sediment to this estuary. The model provides estimates of water discharge, sediment inputs, and organic carbon inputs that agree reasonably well with independent estimates of these fluxes. Even though the watershed for the Hudson River estuary is dominated by forests, the model predicts that both sediment and organic carbon inputs come overwhelmingly from urban and suburban areas and from agricultural fields. Thus changes in land use within the Hudson River basin may be expected to alter inputs to the estuary, thereby altering its metabolism. Precipitation is important in controlling carbon fluxes to the estuary, and so climate change can be expected to alter estuarine metabolism. However, the day-to-day and seasonal patterns of precipitation appear more important than annual mean precipitation in con- trolling organic carbon fluxes.

The large marine ecosystem concept: research and management strategy for living marine resources'

Abstract: The principles adopted by coastal nations under the terms of the United Nations Convention for the Law of the Sea (UNCLOS) have been interpreted as supportive of the management of living marine resources from an ecosystems perspective. Large marine ecosystems (LMEs) are described as regional units for the conservation and management of living marine resources in accordance with the legal mandates of UNCLOS. The principal forces driving large—scale changes in living marine resources vary among LMEs. Progress in the research and management of living marine resources and their biomass yields can be enhanced by comparing the multiple stable states among LMEs with regard to the causes of stress or perturbation on the system and the feedback of the system to stress. Ecological considerations that are presently shaping the management of biomass yields in several LMEs in the Pacific, Atlantic, and Southern Oceans are discussed. See full-text article at JSTOR

Nitrogen Assessments in a Constructed and a Natural Salt Marsh of San Diego Bay.

Abstract: Soil nitrogen pools were lower in a 4-yr-old constructed salt marsh than in an adjacent natural marsh of San Diego Bay. Aboveground biomass and foliar nitrogen content of Spartina foliosa were both lower for the constructed marsh. Soil organic carbon, which was highly positively correlated with total nitrogen, was also lower in the constructed marsh. Rates of nitrogen fixation were higher for the natural marsh in surface soils (1 cm depth) but not in the rhizosphere (10 cm depth). Experimental additions of organic matter increased rates of nitrogen fixation substantially for both the constructed and natural marsh soils, with glucose stimulating greater increases than Spartina foliosa detritus (roots and rhizomes). In comparison with natural marshes studied elsewhere, the San Diego Bay sites have low nitrogen pools and little soil organic carbon. Nitrogen mineralization rates (in situ incubations) were high in both marshes studied. The low nitrogen pools reflect low tidal import and infrequent streamflow influxes and, possibly, high nitrogen demands of vegetation stressed by hypersaline soils.

Functional Responses of Riparian Vegetation to Streamflow Diversion in the Eastern Sierra Nevada

Abstract: Partial streamflow diversion due to the siting of hydroelectric generating plants may increase the incidence and degree of water stress in riparian vegetation. This study, conducted on Bishop Creek in the eastern Sierra Nevada (California), compared the water relations of riparian vegetation on paired undiverted (natural flow) and diverted (low flow) reaches. Riparian plants on diverted reaches had reduced stomatal conductance and water potential compared to plants on undiverted reaches in a dry year, but not in a high-runoff year. Juvenile plants on diverted reaches had reduced stomatal conductance and lower midday water potentials relative to surrounding mature trees, a trend that was not observed on undiverted reaches. Predawn water potentials were uniformly high in all species and sites, but low midday water potentials (-1.2 to -1.5 MPa) were observed for most species on diverted reaches. Plants on diverted reaches possessed significantly smaller, thicker leaves and a reduced total leaf area relative to trees on streamside reaches. Reduced community leaf area and effective stomatal control of water loss may allow riparian corridors on diverted reaches to retain their canopies in low-runoff years. However, a long-term consequence of streamflow diversion may be selective mortality of juvenile plants because of the elimination of floods and high flows.

Ecological Risk Assessment at The Regional Scale

Abstract: Ecological risk assessments are used by policymakers and regulatory agencies for balancing and comparing ecological risks associated with environmental hazards. An approach for regional-scale ecological risk assessment is described and demonstrated by modeling environmental risks associated with elevated ozone in a forested region. The demonstration illustrates (1) how a regional-scale risk assessment might be done, (2) the importance of spatial characteristics in considering regional-scale risk, and (3) the necessity of considering terrestrial and aquatic linkages. Generic problems often encountered when doing regional assessments, the foremost of which is the frequent lack of region-specific information and spatial data, are also highlighted. In the demonstration, two levels of elevated ozone and five different at-risk regional features are considered (forest cover, forest edge, forest interior, landscape pattern, and lake water quality). The mechanism for impacts on these features is ozone-induced stress in coniferous trees, patches of which can then be killed by bark beetle attacks. A stochastic spatial model of land-cover change is developed to evaluate the risks or probabilities of significant changes in the selected ecological features as a consequence of these ozone-triggered beetle attacks. Risk to regional water quality of lakes is evaluated by linking the land-cover output from the spatial stochastic model to an empirical water-quality model that is sensitive to land-cover changes within a lake's wa- tershed. The risk analysis shows that those environmental features that are sensitive to the location of coniferous forest (such as forest edge) are at risk of a significant change due to ozone-induced conifer mortality even though overall coniferous forest cover is only slightly affected. The analysis also suggests a high probability of changes in regional water quality of lakes as a consequence of location-specific forest-cover change.

Regulation of Zooplankton Community Structure of an Acidified Lake by Chaoborus

Abstract: To test the hypothesis that the structure of zooplankton communities of acidified, fish-free lakes can be regulated by predation from larval Chaoborus, the rates of production of the principal prey species of Chaoborus in Swan Lake, a small, fish-less, acid lake near Sudbury, Canada, were compared with their estimated rates of consumption by Chaoborus. The production of Bosmina longirostris, the major crustacean zooplankter in the lake, rarely exceeded its apparent rate of loss to Chaoborus. In contrast, the production rate of Keratella taurocephala, the dominant rotifer in Chaoborus diets, virtually always exceeded the rate at which it was consumed. The unusually small contribution of Crustacea to total zooplankton biomass in the lake could be attributed to predation by Chaoborus. While Chaoborus can regulate zooplankton community structure in acidified, fish-free lakes, the frequency of occurrence of such control remains uncertain.

Primary Production in Grasslands and Coniferous Forests with Climate Change: An Overview

Abstract: In energy terms primary production is the driving step of the global carbon cycle. To predict the interaction of ecosystems with the "greenhoude" effect, it is necessary to understand how primary production, consumption, and decomposition will respond to climate change. Most estimates of primary production have been made by extrapolation from measured standing crops. For grasslands we show this approach to be seriously in error. Even where detailed studies of turnover and belowground production have been undertaken, errors are invariably high, severely limiting the value of models based on correlation of climate with measured production. Detailed information is available on the responses of individual plant processes to individual climatic variables at the leaf, plant, and stand level, giving potential for a more mechanistic approach in modelling. This approach is limited by lack of information on multivariate interactions and on some key physiological processes, and by uncertainties in scaling up to populations and communities. Despite this, some important insights to possible community responses, particularly those of C3 and C4 types, may be gained from knowledge of responses at the plant level and below. This review outlines the expected character of climate change in grasslands and coniferous forests. Knowledge of the responses of different physiological processes underlying production to individual aspects of climate change is considered, and its implications for higher levels of organization are discussed. Although feasible, mechanistic models of production compound the errors associated with individual process responses with uncertainties surrounding interaction and scaling up, and result in very large errors in any prediction of response to climate change. We conclude that there is insufficient information to predict accurately the response of primary production to climate change. The key processes for which information is inadequate and the parameters that have meaning at different scales need to be identified. Of particular promise is the approach of predicting production from light interception and conversion efficiency.

Human Disturbance of an Avian Scavenging Guild

Abstract: In order to investigate the effects of human activities on relationships within foraging guilds, we examined inacanus dynamics of eagles, crows, and gulls scavenging on spawned salmon in the Pacific Northwest. We examined several hypotheses that postulate the asymmetric foraging relationships of the three guild members and that reveal the influence of competition and facilitation in these relationships. Spatial and temporal patterns of resource use by the three primary guild members varied with the presence and absence of human activity at experimental feeding stations. At control (undisturbed) stations, eagles preferred to feed >100 m from vegetative cover, whereas gulls fed <50 m from cover. At experimental (disturbed) stations, eagles rarely fed, and feeding activity by gulls increased at both near and far stations. Crows often fed on alternate food sources in fields adjacent to the river, especially when salmon carcasses were scarce, whereas eagles and gulls rarely did so. We also examined if and how the behavior of single guild members changes in the presence or absence of other guild members. In the absence of eagles, gulls and crows preferred stations far from cover, numbers of both increased at feeding stations, birds were distributed nearer to carcasses, and they fed more. We emphasize that guild theory lends important insights to our understanding of the effects of human disturbance on wildlife communities.

The Role of Ecology in Biological Conservation.

Abstract: The emerging science of conservation biology represents an intersection of elements of ecology, genetics, biogeography, and many traditional applied disciplines such as wildlife management and forestry. Its major concern is providing a valid scientific basis for actions that will slow or stop the accelerating loss of biological diversity worldwide. Ecology's major contributions to conservation biology so far include the equilibrium theory of island biogeography and the theoretical relationship between population size and persistence time. In the future ecologists can contribute their skills to conservation biology in numerous ways; I suggest three in particular. These are investigating the autecology and natural history of rare species, testing hypotheses concerning population viability with carefully designed laboratory and field experiments, and working to establish and implement a national policy for the protection of biological diversity on United States public lands.

Habitat-Specific Resilience of the Invasive Shrub Amur Honeysuckle (Lonicera Maackii) During Repeated Clipping

Abstract: In the development of novel strategies for control of invasive plant species, researchers might first consider plant performance throughout a range of habitats and then concentrate management activities in habitats where plants are least resilient. We determined the relative resilience of forest- and open-grown populations of the invasive shrub Lonicera maackii (Caprifoliaceae) growing in northern Kentucky. Resilience was assessed by imposing a clipping regime (once each year from 1986 to 1989) during which shrub resprouting abilities were measured. Habitat-specific population regeneration from seeds in the seed bank was also measured. Forest-grown L. maackii shrub were less resilient than open-grown shrubs when stressed by repeated clipping, due presumably to exhaustion of stored reserves in shrub bases. This suggests that forests are secondary habitats for L. maackii. However, resprouting potential and seed production in forests appear sufficient to regenerate populations after most common disturbances. The ability to modify sprouting patterns while maintaining resprounting ability and some seed production over a wide range of habitats is an important adaptation of this invasive shrub. Management suggestions for shrub eradication are provided.

Biological response to climate change: an agenda for research'

Abstract: Our knowledge of the structure and functioning of terrestrial ecosystems on a global scale is not developed to a sufficient degree to understand-much less predict-the consequences of climate change either on the systems themselves or on subsequent atmospheric interactions. In many regards we have lagged behind the atmospheric scientists, and to a certain degree the oceanographers, in establishing a global understanding of the dynamics of our respective systems. This is due in part to the inherently greater complexity of biotic systems, but also to the lack of appropriate tools to measure regional biotic processes. These tools are now becoming available and with them a better understanding of terrestrial and atmospheric interactions. Even as these capabilities become a reality we must be realistic in recognizing that we have so far to go along the road to understanding that useful predictive capacity may elude us for a long time to come. What we need to do is act on the recommendations that have been emerging over the past few years and develop a global program to document more precisely the distribution, structure, and quantity of the earth's biotic systems, their principal functional properties, and-most difficult of all-their changing nature. In order to do this we will have to: (1) perfect some of the emerging new tools for assessing these properties, (2) fill some of the gaps in our knowledge about the relevant processes, and (3) establish an international network of long-term observations and large-scale ecosystem manipulations. We have been aware of these needs and shortcomings for some time and we must move from plans to concerted international action.

Critical issues for understanding global change effects on terrestrial ecosystems

Abstract: Marked alterations in the Earth's environment have already been observed, and these presage even greater changes as the impact of human (i.e., land use and industrial) activities increases. Direct and indirect feedbacks link terrestrial ecosystems with global change, and include interactions affecting fluxes of water, energy, nutrients, and "greenhouse" gases and affecting ecosystem structure and composition. Community development can affect ecosystem dynamics by altering resource partitioning among biotic components and through changes in structural characteristics, thereby affecting feedbacks to global change. The response of terrestrial ecosystems to the climate—weather system is dependent on the spatial scale of the interactions between these systems and the temporal scale that links the various components. The International Geosphere—Biosphere Programme (IGBP), which was initiated by the International Council of Scientific Unions (ICSU) in 1986, has undertaken to develop a research plan to address a predictive understanding of how terrestrial ecosystem will be impacted by global changes in the environment and the potential feedbacks. The IGBP science plan, which incorporates established Core Projects and activities related to research on terrestrial ecosystem linkages to global change, includes the International Global Atmospheric Chemistry Project (IGAC); the Biospheric Aspects of the Hydrological Cycle (BAHC); the Global Change and Terrestrial Ecosystems (GCTE); Global Analysis, Integration, and Modelling (GAIM); IGBP Data and Information System (DIS); and IGBP Regional Research Centers (RRC). The coupling of research and policy communities for the purpose of developing mechanisms to adapt to these impending changes urgently needs to be established.

Fish and Fisheries Ecology.

Abstract: My paper on fish and fisheries ecology is offered to demonstrate a rich blending of applied and fundamental ecology, achieved by the intersections among fishery science, ichthyology, and ecology. The example, while specific, parallels practices and opportunities available in other areas of applied ecology. The emergence of fish and fisheries ecology as a discipline is evidence by such recent textbooks as Fisheries ecology by Pitcher and Hart (1982) and Ecology of teleost fishes by Wootton (1990). The ecology relevant to fish and fisheries includes not only marine and freshwater ecology, oceanography, and limnology, but also terrestrial study. Early work in fish and fisheries ecology came from Stephen A. Forbes > 100 yr ago in his books On some interactions of organisms (Forbes 1880) and The lake as a microcosm (Forbes 1887). These constitute one of the earliest conceptualizations of an ecosystem. By 1932 E. S. Russell concluded that fishery research was a study in marine ecology. I give examples of applications from six different categories of ecology. (1) Physiological ecology: The F. E. J. Fry school of fish physiology developed the concepts of temperature as a lethal, controlling and directive factor. More than 40 yr later, this knowledge is being combined with G. E. Hutchinson's concept of an n-dimensional niche to analyze potential influences of global climate warming on fishes. (2) Behavioral ecology: A. D. Hasler and students formulated and tested the hypothesis of olfactory imprinting as the mechanism by which Pacific salmon "home" to their natal spawning streams. Applications to reestablish salmon runs are as important to Hasler as the original scientific discovery; this is evident in his proposed "Salmon for Peace" for the river bounding USSR and China. (3) Population ecology: The realization that reproductive success of fishes depends more on larval mortality than on egg production emerged from the ideas of J. Hjort (1914). To this day inconsistencies between recruitment and reproductive stock size impart uncertainty into fishery management, while the search for explanatory mechanisms attracts the curious mind. (4) Community ecology: Species interactions are the grist of community ecology; predation and fishing are a natural for comparative study and application. Also, consumption by fish can control the dynamics of planktonic and benthic animal/plant communities; thus, apparent water quality of lakes depends on the consumer community as well as on nutrient inputs. (5) Ecosystem ecology: D. S. Rawson grouped external, abiotic influences on lakes into climatic, edaphic, and morphometric factors. The morphoedaphic index (Ryder 1965) predicts fish yields from this base, providing fish managers with a useful approximation and ecologists with a conceptual base for synthesis of production processes. (6) Landscape ecology: Regional ecology often incorporates land-water boundaries into the way ecological systems work. Application of island biogeography to lakes, as islands, has allowed predictions of fish assemblages for use by managers. Also, the extent and connectedness of lake and ocean "landscapes" offer insight into contrasts between marine and freshwater fishery research and management. In conclusion, the ecotone between academic and applied ecology seems an ideal place from which to advance both applied ecology and ecology in general.

Individual-Based Model for Growth of Young-of-the-Year Walleye: A Piece of the Recruitment Puzzle

Abstract: Young-of-the-year (YOY) walleye (Stizostedion vitreum vitreum) growth is a vital step in walleye recruitment. An individual-based model (IBM) was developed to describe the growth of YOY walleye in Oneida Lake (New York, USA) and Lake Mendota (Wisconsin, USA). In Oneida Lake the only prey species included in the model was yellow perch (Perca flavescens), whereas both yellow perch and bluegill (Lepomis macrochirus) were prey species in the model for Lake Mendota. IBM predictions for length frequencies of the YOY walleye population at the end of the growing season showed good agreement with observed length frequencies. A theoretical relationship was derived between the encounter rate, @l, used in the IBM and the half-saturation constant, k, used in a type II functional response model. Estimates of k from the two models showed good agreement, thus corroborating the value of ° chosen for the IBM application to Oneida Lake. The mean length of the YOY walleye cohort and the percentage of larger (@> 175 mm in total length) walleyes in the cohort at the end of the growing season were most sensitive to gross growth efficiency, bioenergetics parameters for maximum daily consumption by walleyes, and the ratio of prey length to predator length at which the prey is susceptible to predation. In Lake Mendota the vulnerability of bluegills to predation by YOY walleyes was especially important in determining the growth of walleyes during their first growing season. The IBM approach was valuable for modeling those stages of life history in which characteristics of the individual were critical in determining recruitment.

Ecosystem Modeling with Lisrel: A New Approach for Measuring Direct and Indirect Effects.

Abstract: Evaluating the effects of toxicants in ecosystems is difficult despite numerous attempts to develop field and laboratory tests. The problem appears to be the lack of an analytical methodology capable of taking advantage of the available experimental designs. Therefore, we propose a technique for modeling ecosystems-linear structural modeling with LISREL. LISREL is a path analytic technique that is more flexible than classical path analysis. Modeling with LISREL involves placing ecosystem structure and function into a framework of concepts and indicator variables. Concepts are theoretical constructs that are placed into a cause-and-effect network to reflect true ecosystem structure. Concepts are @indicated" by indicator variables; these are the measured variables in the ecosystem. LISREL incorporates measurement error into the modeling process by establishing a portion of the variance of each indicator variable as measurement error. The framework of concepts and indicators in a cause-and-effect network becomes a hypothesis that is tested using LISREL. LISREL also provides a determination of the total, direct, and indirect effects of the variables on each other. A measure of ecosystem stability is provided as part of the modeling process.

Herbivory by Canada Geese: Diet Selection and Effect on Lawns.

Abstract: Flocks of free-ranging Canada Geese (Branta canadensis) often are consid- ered nuisances when they graze on lawns because they litter the sites with fecal material, and their grazing often is perceived to be detrimental to the turf. I tested whether goose grazing had changed the composition of grass species at 20 sites in Connecticut where geese were considered nuisances. At these sites Kentucky bluegrass (Poa pratensis) was less prevalent in areas grazed heavily by geese than in areas of the same lawn that received light grazing. At six sites where up to several hundred geese wait daily for food handouts, 46% of the ground was devoid of vegetation except for a moss. I examined the palatability of different grass species to Canada Geese by giving captive birds the opportunity to feed in plots of five cool-season turf-grass species. The birds spent more time feeding in plots of Kentucky bluegrass and less time feeding in plots of tall fescue (Festuca arundinaceae cv. K-3 1) than would have been expected if the geese were grazing among plots at random. Time spent grazing in plots of colonial bentgrass (Agrostis tenuis cv. Highland), perennial ryegrass (Lolium perenne), and red fescue (F. rubra) did not differ from the expected. Feeding preferences for grass species were negatively correlated with the ash content of the leaves and with the amount of force required to sever a specific leaf mass. Captive Canada Geese would not feed on common periwinkle ( Vinca minor), Japanese pachysandra (Pachy- sandra terminalis), or English ivy (Hedera helix). These results suggest that Canada Goose numbers can be reduced at sites where they are foraging on turf if lawns are replaced by an unpalatable ground cover, or, to a lesser extent, with a tough-leaf grass species such as tall fescue.

Mowing and Fertilization Effect on Productivity and Spectral Reflectance in Bromus Inermis Plots.

Abstract: Experiments were conducted to examine the potential role of grazing on ecosystem-level parameters as part of the NASA-sponsored First ISLSCP (International Satellite Land Surface Climatology Programme) Field Experiment (FIFE) conducted at Konza Prairie Research Natural Area in 1987. Here we report results of one experiment conducted in a field consisting primarily of Bromus inermis, a cool season C3 grass. The experiment involved four simulated grazing components (unmowed control, 20-, 10-, and 5-cm mowing heights) and fertilization (untreated control and ammonium nitrate appli- cation). The plots were mowed to ground level and raked in April, following which they were mowed seven times during the growing season from May to October. Biomass pro- duction, N production, and spectral reflectance data were collected with a hand-held ra- diometer throughout the growing season, with standing crop estimates taken at two periods (7 August (day 219) and 27 October (day 300)) to correlate with the remote sensing in- formation base. Standing crop values of mowed plots were as much as 67-70% lower than controls, but they produced significantly larger amounts of both biomass and total N. Maximum season- long production values in the mowed plots were -43% above controls, with major differ- ences developing as a result of fertilization. Fertilized plots produced 67% more foliage than unfertilized plots. Our data show over-compensatory growth as a result ofthe simulated grazing treatments. Indexes (NDVI (normalized difference vegetation index) and greenness) derived from the reflectance data were poorly correlated with biomass. The correlation of NDVI with N content of the canopy foliage was somewhat stronger, particularly if stratified by mowing class. NDVI was a better predictor of vegetation status than the greenness indexes, but in plots simulating heavily grazed areas where leafy vegetation was sparse and soil became more visible from above the canopy its utility decreased significantly.

Modifying Scent‐Marking Behavior to Reduce Woodchuck Damage to Fruit Trees

Abstract: Woodchucks (Marmota monax) damage fruit trees by gnawing on main stems during scent marking, a behavior unrelated to feeding. I tested whether damage could be reduced by providing alternative sites for scent marking or by applying predator odor to trees. Nearly all hardwood stakes supplied as alternative sites for scent marking were used, and the elapsed time from activation of a burrow until onset of damage to an adjacent tree was significantly greater for sites with stakes. However, the mean level of damage to trees was not significantly reduced. Impregnating hardwood stakes with sodium chloride increased their use as gnawing sites relative to untreated stakes, presumably due to dietary sodium deficits incurred by woodchucks during spring. Use of NaCl-treated stakes did not reduce damage to adjacent trees, however. Application of a predator odor, bobcat urine, as a topical spray reduced mean levels of gnawing by 98.3% relative to untreated trees, and placement of bobcat urine in capillary tubes at the bases of trees also resulted in significant reductions in damage over a 3-mo period.