EcoService Models Library (ESML)
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Further explanation of top-level variable categories in the Variable Classification Hierarchy
View the Variable Classification Hierarchy (XLSX)The following table provides detailed information used in assigning categories to variables in ESML.
Category Name |
Description |
Examples |
Discussion |
Category 1. Policy Regarding Use or Management of Ecosystem Resources |
Variables that represent policies or prescriptions regarding either ecosystem resources or human actions related to the environment. |
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Category 1 comprises variables representing policies, prescriptions, regulations, requirements, designations, targets, recommendations, etc., whether new, existing or projected. This includes zonings, easements, conservation area designations, etc. The crucial difference between Category 1 and Categories 2 - 7 is that Categories 2 - 7 deal with descriptions of environmental or social traits observed or estimated to exist (or, for future scenarios, projected to exist), whereas Category 1 deals with prescriptions -- goals or designations -- for what may or should exist from a policy perspective. Land-based examples of Category 1 could include designation of biodiversity reserves (which define a protection level, and may or may not correspond to an actual biodiverse condition), or the recommended width of a riparian buffer (as opposed to an observed width). Water-based examples could include policy-based targets for water withdrawals or releases of water in rivers or reservoirs, or allowed releases of chemicals to waters (e.g., permit limits or Total Maximum Daily Loads). Future projections that are not policy-based generally should be treated as descriptive, using Categories 2 - 7, rather than prescriptive, using Category 1. |
Category 2. Land Surface (or Water Body Bed) Cover, Use or Substrate |
Land cover (e.g., vegetation type, water body type), other basic features of the landscape (soils, topography, bathymetry), and or use, and most geographic boundaries. |
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Variables describing basic features of the landscape (or the bed of a water body), such as vegetative cover type, substrate type, and/or type of human use, are categorized as Category 2. Category 2 variables are those that classify dominant characteristics of vegetation, substrate or human use. Broad-scale ecological classifications (e.g., ecoregions) are also Category 2. Category 2 variables describing landscape characteristics thus tend to be categorical variables; those that are cardinal are generally limited to those that describe areas, positions, elevations and distances to other features. In general, cardinal variables that describe the characteristics of soils, fauna or vegetation are classified as Category 5. These include cardinal measures related to soil composition, soil water-holding characteristics, or vegetative canopy structure /closure. Classifications derived from more detailed or specialized observation, sampling or mensuration, or requiring ecologically-informed analysis (e.g., habitat suitability for given taxa, or landscape ecological variables) also should be treated as Category 5.
Variables that describe geographic boundaries are usually Category 2. These include biophysical demarcations (watershed, floodplain or geographic feature boundaries, broad-scale ecological classifications such as ecoregions) and geopolitical boundaries, which are all categorized as Category 2. Exceptions, treated as Category 1, are those boundaries that represent an environmental policy demarcation more than a biophysical distinction; examples include zoning, conservation easements or ecological reserves. The latter are treated as Category 1 unless they clearly serve as a proxy for an actual (and not merely intended) physical/feature boundary, such as a distinct land cover. |
Category 3. Demographic Data |
Information about human populations, such as age, gender, income, residence, education level, etc. |
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Most variables describing the traits of human populations are categorized as Category 3. Land use/land-cover (LULC) classifications dealing with human characteristics (e.g., high, medium and low housing density) form an exception; LULC information should be classed as Category 2. However, with that one exception, Category 2 is limited to characteristics of the landscape, and any information on human populations and their characteristics is listed as Category 3. |
Category 4. Human-Produced Stressor or Enhancer of Ecosystem Goods and Services Production |
Human-produced influences or agents that may affect the potential for ecosystem structures or processes to produce services – negatively, in the case of stressors, positively for enhancers – and any human created feature that is more fine scale than the LULC class (e.g. roads, bridges). |
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Human-produced stressors classified as Category 4 are those physical, chemical or biological agents or influences caused by humans that may have adverse effects on ecosystem structures and processes and are not well described using other Categories. Similarly, human-produced enhancers are influences or agents that have positive effects on ecosystem structures and processes.
To avoid overlap with other Categories, Category 4 designation should be used sparingly. That is, if "habitat destruction" can be described as a change in LULC class, it should be classified as Category 2; and changes in ecological structure or function should be described as Category 5, even if they result from habitat destruction or restoration and regardless of their effect on species. Stressor examples include pollutant loads, water withdrawals, proximity to disturbance, impacts/disturbance related to harvest of ecosystem components (though not the harvested goods themselves), and introductions of invasive species. Variables describing impact-specific characteristics of stressors – e.g., the toxicity of a polluting chemical – are also classified as Category 4. However, variables describing the removal of stressors by ecosystems are classified as Category 5. Variables describing harvest activities or quantities as indications of human use or benefit are Category 6 if non-monetary, or 7 if monetary. Variables specific to human management actions – e.g., the spatial extent of a management action such as controlled burning or the placement of non-natural structures such as nesting boxes – are more adequately described by Category 4 than Category 5. Note, however, that management policies, which relate to prescribed as opposed to observed actions, are listed at Category 1. Ecological responses to management, however, would be described using Categories 2 (for land cover changes) or 5 (for ecological structure or process changes). Although wildland fires occur naturally, human interaction with wild lands has dramatically affected fuel levels and ignition sources; therefore, all wildland fire is classed as Category 4 (whereas fuel characteristics are generally Category 5). Although phosphorus, nitrogen and sediment are naturally occurring, due to the prevalence of pollution by excess quantities and the disruption of their normal cycling, we have treated variables specific to P, reactive N and sediment loadings to the environment as well as their concentrations in air and water as Category 4. Similarly, carbon concentrations in air, and releases to air, are treated as Category 4. Ecological processes specific to C, N or P sequestration or removal from these media are treated as Category 5. However, resulting changes in pollutant loadings or levels Occurrences in biological materials, or in media other than those specified above, are placed in Category 5. C-, N- or P-related variables explicitly associated with human actions are exceptions to this rule; variables such as "carbon in harvested biomass" or "percentage of soil carbon pool disturbed," are treated as Category 4. When "water quality" is used as a variable without reference to a particular stressor, or when it refers to use suitability (e.g., for bathing), it is classed as Category 5. We have elected to treat any human-created feature of the landscape that is more fine scale than LULC class, e.g. roads, bridges or docks, as Category 4 since they often appear in models as ecological stressors. However, impervious surfaces, though a human-produced stressor, are treated as a land cover/land-use feature and therefore, like other urban land use categories, are classed as Category 2. Human artifacts such as roads or bridges that are incidental to the presence of the environment and not specifically for the purpose of accessing environmental resources are included at Category 4; artifacts specific to human access (e.g., boat docks, hiking trails) are included in Category 6. |
Category 5. Ecosystem Attributes and Potential Supply of Ecosystem Services |
Attributes of ecological structure or process, including both Intermediate and Final Ecosystem Goods or Services |
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Some conceptualizations of ecosystem service production have attempted to distinguish structure and process. However, ecological structural variables and process variables are difficult to distinguish in practice; furthermore, although structures are sometimes seen as determining processes the reverse may also be true. Therefore, variables related to structure and process are combined in Category 5; moreover, ecological "process" is here meant to encompass ecological "function" (i.e., these terms also are not distinguished in this scheme).
Ecosystem processes are generally understood as flows or other changes in materials occurring over time. Example process variables include those associated with pollutant attenuation, changes in carbon storage and changes in biota (e.g., production, recruitment). Variables classified as ecosystem structure or process variables (Category 5) may be related to land cover variables (Category 2) but are distinguished from the former in either of two ways. First, they may provide greater detail than is available in typical land cover data sets. Biological community structure may include presence/absence, abundance or diversity of biota observed at various levels of scale or organization. Physical/chemical aspects of structure may include substrate variables, stream channel geometry or measures of vegetation structure such as canopy closure or leaf area index. Second, Category 5 variables may entail an ecologically-informed interpretation of land cover variables (e.g., landscape-ecological variables such as indices of fragmentation, identification of habitat corridors or determinations of habitat suitability). Meteorological data (e.g., temperature, rainfall, humidity) are also considered Category 5 because (a) they are strongly influenced by local ecology and (b) unlike LULC or elevation data they generally have to be locally and repeatedly measured. Certain ecosystem structural or process attributes can be defined as intermediate or final ecosystem services, to the extent that they contribute (indirectly or directly) to human well-being. Because their ability to do so is context-dependent, it is difficult to classify individual model variables according to whether or not they correspond to ecosystem services. Therefore, all ecosystem service variables are lumped with ecosystem structure/process variables in Category 5, even if they are explicitly identified as ecosystem services. Natural landscape features that are defined in terms of their direct value to humans (e.g., "Routes of geological interest," "climbing sites," "nature-based recreation sites") should be included at Category 5. With regard to human interaction with nature, the distinction between Categories 5 & 6 corresponds to the difference between supply and demand. Indicators of human demand or use are classified as Category 6. Category 5 variables have the potential to supply something of value and sometimes are defined in that vein (e.g., "Aesthetic quality of the landscape"). However, supply entails only the potential for benefit, and the existence of human access to an ecosystem good or service, absent an indication of demand, does not in itself indicate use or enjoyment. The supply of flood regulation services to residences in a floodplain does not imply a benefit without an indication that the area is marginally prone to flooding. On the other hand, indicators of investment in access (e.g., number of boat docks) that clearly indicate human use may be classified as Category 6. |
Category 6. Non-monetary Indicators of Human Demand, Use or Benefit of Ecosystem Services |
Non-monetary variables related to human demand, use, enjoyment or benefit – including health benefits; excluding land uses covered by Category 2. |
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Social benefit indicators reflect social welfare by determining quantity of service use, human preferences for the service, and/or scarcity/substitutability or services. All non-economic indicators of human demand or use/benefit/preference are classified as Category 6 regardless of whether the demand or use results from ecosystem service changes. Examples of demand may include size of human population demonstrably vulnerable to loss of a particular service; examples of use may include: non-monetary indicators of fish, crop or timber harvest yields; user-days at a recreational site; measures of health risk related to nature-based recreational opportunities; and indicators for hospital admissions related to air quality. Social benefit indicators may also relate to appreciation of ecosystem services (e.g., satisfaction related to the current or future existence of an ecological feature) independent of use. Note, however, that monetary values associated with any of these indicators would be classified as Category 7.
Broad land use classifications covered by Category 2 are excluded here, but more specific indicators of use (e.g., housing starts, recreational visits, harvest amounts). |
Category 7. Monetary Values |
Any quantity expressed in monetary terms (including, e.g., benefits, prices, costs). |
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Category 7 includes measures of economic value (i.e., consumer or producer surplus), or reasonable proxies thereof. Value may be that of ecosystem services or that of other inputs or outputs relevant to the EM (e.g., land or commodity prices). When valuing ecosystem services, it should be noted that true social welfare measures reflect supply and demand, including both vulnerability to service loss and the ability to adapt to and substitute for losses in ecosystem services. Value may include use or non-use values. |
Non-classified variables | Variables that contribute little further understanding of what kinds of environmental information are being used by an EM |
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The purpose of variable classification is to enable ESML users to understand what kinds of information are being used by an EM, without relying on variable nomenclature used by the modeler. Certain types of variables are included in ESML because they are important to model functioning yet are excluded from classification because they convey little additional information about the aspects of ecosystems, environmental management or human well-being that the model addresses. These include conversion factors, certain coefficients, and weighting factors, and spatial grid or polygon identification codes. Expressions of time also are non-classified, except when they are specific to events that should be classified (e.g., time of timber harvest). Statistically derived coefficients that modify other variables already identified (e.g., "Coefficient on depth x bed slope") typically are non-classified, whereas coefficients that convey more specific information, may have a recognized name, and may be obtainable from literature sources (e.g., "Zhang coefficient;" "Plant evapotranspiration coefficient," "In-stream nitrogen attenuation coefficient") should be classified according to the type of information they convey. |