Environmental Monitoring

Environmental Monitoring

Issues of space and time will in part determine the type of study design that is possible. For example, studies of large geographic areas may preclude replication, suggesting before-after-control-impact paired (BACI-P) study. Similarly, long response times may suggest retrospective analysis of past actions to provide a preliminary assessment of the impact of a proposed action.

Issues of space

Five kinds of spatial effects can influence the design of a study as well as the
interpretation of its results:

  1. What is the influence of on-site management activities on off-site conditions? That is, local management may influence remote conditions, both directly and indirectly.
  2. What is the relative influence of off-site management activities on on-site (desired) conditions? On-site conditions can be influenced by other offsite activities
  3. To what degree do local management activities influence the on-site (desired) conditions? That is, to what extent do background noise and other environmental factors affect on-site conditions? Local management may influence only a portion of the total variation in local conditions.
  4. What is the relative influence of conditions and activities from different spatial scales, particularly the effects on local stand-level conditions from broader landscape-level factors? That is, desired conditions and management actions are best addressed at appropriate scales of geography.
  5. What are the cumulative effects of stand-level treatments as they spread across the landscape? For example, wind fetch and thus wind speed may increase as clearcuts become wider with sequential, adjacent cuts. Thus, the windthrow hazard in one cutblock may increase as adjacent areas are cut, and the windthrow hazard in those cutblocks cannot simply be extrapolated from the hazard measured in a single cutblock surrounded by trees.

For each of these five kinds of spatial effects, adaptive management monitoring studies would be designed and implemented differently. Where this is not possible, spatial influences should at least be acknowledged as potential sources of variation and included in the analysis.

Issues of time

Answering questions about time effects can help distinguish true cause from non-
causal correlation, and treatment effects from natural variation. Three typical time
scale issues follow:

  1. What are the response times of variables? For some variables, response may be apparent in a relatively short period of time; others may respond more slowly.
  2. What are the lag times of variables? Some variables may not immediately respond to a treatment or may depend greatly on site history. This lack of short- term response should not lead one to conclude that management actions (in this example, the reduction or removal of granary trees) have no effect. Sometimes these lags in response result when conditions from prior time periods overwhelm or influence responses from current actions. Thus short-term changes in a response variable may reflect both the management action and past site history. Some time-lag effects can be quite variable and manifest as nonmonotonic (up and down) trends over the long term.
  3. What are the cumulative effects of a variable over time? Some variables do not make a mark except over time or until a particular threshold has been exceeded. An example is the adverse effect of certain pesticides on wildlife reproduction. The detrimental effect may not be apparent until the pesticide concentrations reach a particular level of toxicity.

The design of adaptive management studies and selection of analysis methods are guided in part by these considerations of space and time. For example, replication is one major consideration in designing studies. Given a large geographic area, as tends to be the focus in ecosystem management, or a rare condition, such as a threatened species population, are spatial replicates possible? That is, can landscapes or threatened populations be replicated at all, or inadequate numbers? Other kinds of studies (e.g., analytical surveys, expert testimony) might help in assessing the impact of the treatments, although they do not allow strong inference about cause. Similarly, long response times and time lags make temporal replication difficult. Retrospective studies provide one alternative for gaining insight into the long-term effects of management actions. In cases where either spatial or temporal replication is severely limited, a higher probability of Type 1 and Type II errors might need to be tolerated. In some cases, a powerful adaptive management study may be possible but managers, decision-makers, industries, or other interested bodies may not be willing to bear the cost, duration, and tight controls on management activities. The consequences of not using an optimum study must be explicitly considered and understood by all.


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