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Andropogonetum Hempsteadi: A Long Island Grassland Vegetation Type

Stanley A. Cain, Mary Nelson and Walter McLean
The American Midland Naturalist
Vol. 18, No. 3 (May, 1937), pp. 334-350
DOI: 10.2307/2420573
Stable URL: http://www.jstor.org/stable/2420573
Page Count: 17
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Andropogonetum Hempsteadi: A Long Island Grassland Vegetation Type
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Abstract

The composition and structure of the association, Andropogonetum Hempsteadi, was studied by plant sociological methods. At six different stations, series of 25 quadrats each 0.25 sq. m. were laid out and examined. On each quadrat the coverage class of each species was noted along with the total coverage in per cent for all species. From these data it was possible to determine the frequency and the average coverage for each species for each station and for the six stations collectively. The species lists for each station and for the whole were augmented by examination of the entire unsampled area for additional species. These additional species were all assumed to be, and apparently were, of low frequency and coverage. The size of the quadrat and the number of them to be used were determined by a preliminary study at one of the stations. By a study of comparative frequencies and the species-area curves obtained on a basis of 0.25, 0.5, and 1.0 sq. m. quadrats it became evident that the smallest size was adequate. Similarly, on a basis of sampling 50 quadrats it became apparent that 25 was a sufficiently large number of the 0.25 sq. m. quadrats. Since the practice was to take a random sample by widely and evenly spacing the 25 quadrats within the station, irrespective of the area of the station (in as much as it is more than the minimal area), it was felt that the method worked out at one station was suited to the others. This supposition was substantiated by the results, and since all stations were occupied by the same, relatively homogeneous association the method proved to be valid. The differences in area of the stands were relatively unimportant since all stands were much larger than the minimal area necessary for the association to develop its characteristic floristic assemblage and structure. It is nevertheless startling that such a small amount of sampling could produce such regular results, when the surveys of the individual stations are compared with each other. The total area of the 150 quadrats was only 0.006 per cent of the total area of the six stands examined. In one instance only 0.002 per cent of the stand was sampled (Mitchell Field). At the other extreme (Westbury) 0.06 per cent of the stand was sampled. Yet at each station our results were similar and sufficiently exact for sociological description and were similar to the results for the whole, synthesized from the six stations. This similarity points to two facts: first, the association is an homogeneous one and the six stations are all truly representative stands; second, the sampling technique was adequate for the type of description desired. We feel that a detailed description of vegetation, prepared by following such plant sociological methods, represents a great improvement over the more general types of description. Although this particular association is a relatively simple one, it would seem reasonable to assume that this method of work, the preliminary determination of quadrat size and number, would be applicable to other types of associations.

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