Type 5 Streams and Small Wetlands Literature Review

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Characterization of Information Sources - An Emphasis on Documenting the Basis of Statements

In this literature review, statements were gathered from relevant sources regarding the protection needed for type 5 streams and small wetlands in the Pacific Northwest. Each article in this review was placed into one of the three following categories based on the means by which information was gathered: factual observations, case study, and experimental study.

Reviewing the available research on small streams and wetlands revealed the necessity for making the distinction between different experimental designs. By making such a distinction, DNR aims to prevent the error of interpreting the results of a study showing causal relationship in a specific region as a factual statement to be used in making HCP Adaptive Management policies. The reader is cautioned that this classification is not intended as a qualitative assessment; each grouping should be considered as a separate entity. One design is not necessarily better than another; each plays an important role in reaching an accurate and scientifically based conclusion. Refer to table 1 for a summary of the classification system used in this literature review.

The following provides a description of each category.

Factual Observation

The first category refers to reseach studies that create a hypothesis based on FACTUAL OBSERVATION . In this type of study, the scientist can determine that a change did indeed occur, but cannot determine what specifically caused the change. The scientist may make an educated guess based on past or present knowledge of the situation and may hypothesize a possible causal relationship for further study. For example, a scientist can count the amount of amphibians in the first and second years following a clear-cut harvest and compare the results. From this study one might infer that clear-cutting reduces amphibian abundance. However, the study cannot show definitively that clear-cutting decreased the amount of amphibians, since the study lacks a replicated sampling design and an unharvested control for comparison.

Case Study

The second category, CASE STUDY, refers to research studies that reveal patterns or trends and can be used as a baseline to monitor changes over time. As with factual observations, a case study lacks both a replicated study design and an untreated control. However, a case study does examine before and after effects. For example, a study of the relationships between clear-cutting and amphibians may examine the number of amphibians before clear-cutting and then again after clear-cutting. From this study, one cannot conclude that clear-cutting in and of itself decreases amphibian abundance since there may be a hidden cause that was not noticed. This type of study can reveal a particular pattern of response useful for further study.

Experimental Study

The third category, EXPERIMENTAL STUDY, referes to research studies that incorporate pre- and post-treatment monitoring, an untreated control, and a replicated sampling design. This type of study is designed to eliminate hidden factors through the use of replicated sampling. Not only are a number of sites tested, but they are tested in multiple eco-regions. While this study can develop conclusions, it is more often used to refine and validate factual observations and case study conclusions. Through the use of statistical analysis, an experimental study can determine cause-and-effect relationships.

Table 1. Classification Criteria.

  Quantitative Use of Untreated Controls Replication Statistical Analysis Before / After Comparison Geographic Scope
Observational (x)   (x)     x
Case Study x   (x) (x) x x
Experimental x x x x x x

Key: Blank = N/A, (x) = conditional, x = required


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