The Species-Area Curve

Abstract

Jaccard (1912), one of first who studied scientifically species-area relationships, did not confine his observations to a single type of community. The areas with which he dealt were occupied by several different plant communities. His work was fruitful and plant sociologists very soon were studying effect of size of stand on number of to be found within community. This led to concept of minimal area, the smallest area which can contain an adequate representation of an (BraunBlanquet, 1932, p. 52). The question is immediately raised: What constitutes an adequate representation of an association? When is a stand (an association individual) to be considered adequate and when is it inadequate, or fragmentary? The answer varies somewhat with different schools of plant sociology, i.e. it depends upon those aspects of community composition and structure which are emphasized. Minima of space and number of are certainly requirements which must be assigned to an says Braun-Blanquet. Not only a minimum number of but combination of must occur on area in question for stand to be considered a minimal area. This characteristic combination of species would mean, for some plant sociologists, (1) coverage of dominant species; for others (2) homogeneity of structure as shown by constant species, described in terms of presence, constance, and/or frequence; or (3) presence of characteristic species, i.e. those of high fidelity. It is apparent, also, that minimal area will vary greatly for different communities. It is equally obvious that this minimal area, which is said to be one of characteristics of an association, can be determined only by empirical methods. No concept of minimal area would appear to be certain if based on only one or a few stands of association. In other words, one must know association well in order to know what is characteristic combination of species. In practice, one may assume fairly that a certain stand is representative of association if it is extensive relative to apparent complexity of composition and structure of community. The species-area curve was quickly recognized as an important tool in community description and was used as a guide in determination of minimal area of a community. In its original form it was constructed as follows: number of found in an association individual (stand) is plotted on y-axis coordinate with area of stand which is plotted on x-axis. In this manner, when several association individuals of various sizes have been examined, it is found that species-area points define a curve. This curve rises rapidly from intersection of y and x