Ecological Monitoring

In the sense used here, environmental monitoring is an activity that involves repeated measurements of inorganic, ecological, social, and/or economic variables. This is done with a view to detecting important changes over time, and to predicting future change. Within this larger context, ecological monitoring deals with changes in the structure and functioning of ecosystems.

Monitoring investigates scientific questions that are rather uncomplicated, involving simple changes over time. However, the success of monitoring depends on: (1) the astute choice of a few, appropriate indicators to measure over time, from a diverse array of potential indicators, and (2) successful data collection, which can be expensive and difficult, and requires longer-term commitments because important changes may not detectable by short-term studies.

It is important to understand that monitoring programs must be integrated with research, which examines relatively complex questions about the causes and consequences of important environmental and ecological changes that may be detected during monitoring. The ultimate goals of an integrated program of ecological monitoring and research are to: (1) detect or forecast changes, and (2) determine the causes and implications of those changes.

Monitoring involves the repeated measurement of indicators, which are relatively simple measurements related to more complex aspects of environmental quality. Changes in indicators are determined through comparison with their historical values, or with a reference or control situation. Often, monitoring may detect changes in indicators, but the causes of those changes may not be understood because the base of environmental and ecological knowledge is incomplete. To discover the causes of those changes, research has to be undertaken.

For example, monitoring of forests might detect a widespread decline of some species of tree, or of an entire forest community. In many cases the causes of obvious forest declines are not known, but they are suspected to be somehow related to environmental stressors, such as air pollution, insect damage, climate change, or forestry. These possibilities must be investigated by carefully designed research programs. The ecological damages associated with forest declines are very complex, and are related, for example, to changes in: productivity, amounts of living and dead biomass, age-class structure of trees and other species, nutrient cycling, soil erosion, and biodiversity values. However, in an ecological monitoring program designed to study forest health, only a few well-chosen indicators would be measured. A sensible indicator of changes in the forest as an economic resource might be the productivity of trees, while a species of mammal or bird with specific habitat needs could be used as an indicator of the ecological integrity of mature or older-growth forests.

Indicators can be classified according to a simple model of stressor-exposure-response:

1. Stressors are the causes of environmental and ecological changes, and are associated with physical, chemical, and biological threats to environmental quality. Stressors and their indicators are often related to human activities, for example, emissions of sulfur dioxide and other air pollutants, concentrations of secondary pollutants such as ozone, the use of pesticides and other toxic substances, or occurrences of disturbances associated with construction, forestry, or agriculture. Natural stressors include wildfires, hurricanes, volcanic eruptions, and climate change.
2. Exposure indicators are relevant to changes in the intensity of stressors, or to doses accumulated over time. Exposure indicators might only measure the presence of a stressor, or they might be quantitative and reflect the actual intensity or extent of stressors. For example, appropriate exposure indicators of ozone in air might be the concentration of that toxic gas, while disturbance could be indicated by the annual extent of habitat change caused by forest fires, agriculture, clear-cutting, or urbanization.
3. Response indicators reflect ecological changes that are caused by exposure to stressors. Response indicators can include changes in the health of organisms, populations, communities, or ecoscapes (landscapes and seascapes).

Indicators can also take the form of composite indices, which integrate complex information. Such indices are often used in finance and economics, for example, stock-market indices such as the Dow-Jones, and consumer price indices. For reporting to the public, it is desirable to have composite indices of environmental quality, because complex changes would be presented in a simple manner. However, the design of composite indices of environmental quality or ecological integrity are controversial, because of difficulties in selecting component variables and weighing their relative importance. This is different from composite economic indicators, in which all variables are measured in a common currency, such as dollars.