Ecological Indicators for the Nation (2000) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-17
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Although no current indicators of environmental conditions or trends have the stature of the most influential economic indicators, some environmental indicators, such as global mean temperature, sea surface temperatures, and atmospheric carbon dioxide concentrations, are attracting considerable attention. Developing indicators of comparable power for ecological processes will help focus appropriate attention on ecological conditions, providing clues that could help guide significant and informed policy choices.
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This report concentrates on ecological indicators; this was the charge to the committee and an area in which better indicators are urgently needed. Our report does not cover other important types of environmental indicators, such as physical and chemical indicators of climate change, ozone depletion, acid precipitation, or air and water quality, although those indicators are no less important than the ones to which we give our primary attention here.
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Is it based on well-established scientific principles? The conceptual model provides the rationale for the indicator, suggests how it should be computed, and enables us to understand the features of the indicator and how they change.
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Most ecological indicators depend on data gathered by means of long-term monitoring. The challenge is deciding which rates of change to watch, and to determine which of the changes observed represent significant departures from expected natural variability.
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In general, the minimum number of physical samples saved should ensure the ability to recalibrate the entire data set, should that become necessary because of changes in sampling or analytical technologies. The costs of preserving physical samples in forms that do not decay or otherwise change must be weighed against the opportunity cost of not being able to recalibrate a data set with improved or modified measurement techniques.
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THE COMMITTEE'S CONCEPTUAL MODEL FOR CHOOSING INDICATORS To guide its selection of ecological indicators, the committee used the above criteria and a conceptual model of the factors that most strongly influence ecosystem functioning, described in Chapter 2. The goods and
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THE RECOMMENDED INDICATORS Based on consideration of the desirable characteristics of indicators, the sources of data that underlie them, the models that support them, the criteria summarized above, and the conceptual model we used, the committee recommends the following national ecological indicators in three categories: · As indicators of the extent and status of the nation's ecosystems, the committee recommends land cover and land use. · As indicators of the nation's ecological capital, the committee recommends total species diversity, native species diversity, nutrient runoff, and soil organic matter.
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and unmanaged ecosystems; the indicators of nutrientuse efficiency and overall nutrient balance are specific to agricultural ecosystems. Indicators of Ecosystem Extent and Status The largest ecological changes caused by humans result from land use.
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The essential capital includes physical components such as soil condition, as well as the species that drive and maintain ecosystem processes. Therefore the committee recommends indicators of species diversity, soil condition, and nutrient runoff.
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It thus allows one to compare the species richness in various land cover types as well as the effects on species richness of various natural environmental and human-caused changes. The second indicator, native species diversity, reflects human impact on the land.
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The committee recommends an indicator of nutrient runoff, which measures the loss of essential nutrients from the soil and is related to soil erosion, because excess nutrients, especially nitrogen and phosphorus, reduce water clarity, increase nuisance algal blooms, and increase the incidence of hypoxia (low oxygen) in waters.
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High stream oxygen indicates much photosynthetic activity and the likelihood of high nutrient concentrations, algal blooms, and rapid growth of leafy aquatic plants. Low stream oxygen indicates higher respiration than photosynthesis and the likelihood of organic enrichment from wastewater or high plant production upstream.
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Nonetheless, full development and implementation of the indicators will be expensive and will take some time, especially for the recommended indicators of species diversity. For this reason, the committee recommends a sequential approach to the development and implementation of the indicators.
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These attributes support the continued provision of the following goods and services from forests: wood and wood products, opportunities for recreation, tourism, and aesthetic enjoyment, maintenance of wildlife resources, control of erosion and nutrient losses to surface waters, and mitigation of greenhouse-gas emissions. The most valuable indicators for forests are those that can provide early warning of adverse trends in productivity, species diversity, and structural diversity.
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The indicator of the independence of a local area is computed using the expected values of species diversity for a large area of the same vegetation type as the area under consideration. It provides an estimate of the number of sink species in the sample but it does not specify them.
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To evaluate the deficiency of diversity in an area, the raw value of species density in the area is decreased by subtracting exotic species that follow human settlement and tolerant natives that would thrive anywhere. The remaining native species density provides an estimate of the value of a site in supporting biological diversity.
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Research is especially needed on unusually sensitive species and processes, microbial communities, keystone species, and the temporal and spatial behavior of indicators and how their variability is influenced by underlying ecological interactions. For some recommended indicators, especially the ones that measure land cover, land use, and species diversity, further work is needed on how best to operationalize the indicators and to help identify future research plans.
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