The Relevé Survey Method

How Center for
Urban Habitats Determines a Name for a Plant Community

Before one can assign a name to a habitat, one must understand first what the dominant plants and features are in that habitat. The name of a habitat is something that reflects a great number of combined details. In the end the name most often conveys the so-called indicator species in each layer of a forest, wetland, savanna, prairie, barren, or other habitat type. These are the species that are typical of the ecosystem, and frequently dominant. An example of a plant community title is, “Acer rubrum – Fraxinus (pennsylvanica, americana) / Lindera benzoin / Symplocarpus foetidus Forest”. This is a typical vegatative assemblage in a wetland known as a Piedmont Basic Seepage Swamp. The characteristic indicator species in the habitat are red maple, ash, spicebush, and skunk cabbage. But, classification and naming goes way beyond that. Other important indicator characteristics, such as physiographic shape, soils, and geology, must be considered. While there are many ways to figure these things out, the type of data collection survey we use is called a Relevé.

A Relevé method
is one of many ways to classify Native Plant Communities. The procedure was
developed by plant ecologist,
Josias Braun-Blanquet, in the early part of the 20th century,
and continues to this day to be one of the more comprehensive approaches recognized in
the field. A Relevé procedure
results in an exhaustive description of a given unique
ecological community. It relies upon intense data collection, within a plot of
sufficient size, to accurately represent the community being classified. During a Relevé, within
a landscape being studied, each unique habitat or plant community receives its
own sample plot.

The Relevé approach
focuses on the habitat’s vegetation content and structure, as well as a number
of physical factors such as geology, topography, soil drainage, soil chemistry.
The approach operates under the premise that all layers of the forest, from the
upper canopy to the forest floor, contribute to describing the plant
communities’ relationships to the land and to one another. Certain species of
flora have unique growing requirements, and thus they serve as “indicator
species” for hypothesizing about plant community types. When several of these
occur together, the confidence level increases. For this reason, indicator
species are important for classification and for naming the plant communities.
They are among the primary influencing factors when determining where and how
many plots should be executed on a given tract of land.

The Relevé
method is widely employed in the United States by natural heritage programs.

Influenced greatly by the Virginia Natural Heritage Division’s natural
plant community classification methodology, Center for Urban Habitats has created
an adapted form of the
Relevé for
its ecosystem surveys. We’ve done this for many reasons:
  • We feel that a Relevé procedure is the most practical,
    holistic, and multidisciplinary framework for quantifying a given plant
    community on the Virginia landscape.
  • Relevé methodology may be employed on a variety of scales, and with different resolutions, making it ideal for accommodating varied project budget limitations
  • It covers all important factors that
    determine where a plant grows and why. 
  • It allows one to compare across an existing
    hierarchical classification scheme to see larger landscape patterns and
    variations. 
  • We are able to align our species cover class data with already
    classified and named plant communities in order to determine names for those we
    observe. 
  • The detailed information that results creates a data base that informs Center for Urban Habitat’s ecosystem-modeled landscape designs.
  • Finally, we try to adopt as many metrics currently used by the
    majority of individuals and institutions in the field of population ecology so
    that our data may be useful beyond the confines of the individual project.

In addition to Plants: In addition to the intensive plant assessment of the Relevé, CUH adds fungi and fauna by
enlisting specialized teams that visit the site at advantageous times. This
approach provides a more complete illustration of the ecosystem and all
of its living parts, and occasionally produces animal species that are
indicators for ecosystem health and quality. Animals are on the move, and thus
they also provide information about relationships between systems across the
landscape.