Vegetation scientists study plant communities in order to identify their floristic composition, geographic and ecological distribution, dynamics, and environmental relationships. They classify vegetation in order to:
- reduce the plant community (vegetation) variation on the landscape into fewer classes or types;
- provide a set of 'natural' (or at least consistently defined) types that can be used for communication between various land managers and other classification users;
- develop interpretations for the types; and,
- use the classification and interpretations for land resource management, research, education and communication.
In classifying vegetation, a set of criteria is applied to the data to determine types. The criteria depend on the nature of the vegetation and the purpose for the classification. Criteria can include:
- species dominance, either of the overstory or of each structural layer
- floristic composition, either presence alone, or in conjunction with abundance
- combination of dominance or floristics with other factors, e.g., physiognomy/structure or environmental (habitat) features
- eco-regional zonation, as a 'higher-level' control on the resulting types.
Vegetation is not static, but changes over time in response to, and as a result of, stand altering disturbances.
Vegetation scientists can either classify existing vegetation, recognizing stages of successional development in the classification, or potential vegetation, i.e., the vegetation that would develop if succession was completed on the site, or both. Sites with similar climate and/or site characteristics should produce similar vegetation, as long as the time/disturbance factor is taken into consideration. Existing vegetation better describes the range of vegetation diversity on the landscape while potential vegetation is helpful for developing site classifications, or defining sites within a climatic region that have the potential to produce similar vegetation.
Whatever the objectives of the classification, data collected on sample plots are used to classify vegetation. The data are generally analyzed by both quantitative and qualitative methods. Quantitative methods are computerized algorithms that evaluate plot similarities and some methods can suggest a resulting classification. Qualitative methods use expert knowledge in combination with various plot summary techniques to evaluate the plot data. Usually, the most useful classification combines both these approaches, i.e., results from using several quantitative methods to show potential types and their relationships to each other are 'fine-tuned' using expert knowledge. The final classification is often summarized using a vegetation and environment data summary computer program.
Methods used within the CNVC are detailed in two documents:
Methodology for Development of Plant Associations for Forest Communities of the Canadian National Vegetation Classification
Methodology for Development of Plant Alliances for Forest Communities of the Canadian National Vegetation Classification.
These documents are under develpment.