64 THE STUDY OF PLANT COMMUNITIES ■ Chapter IV 



Qualitative Characters.— These characters, which include socia- 

 bility, vitality, stratification, and periodicity, are mostly not de- 

 rived from quadrat studies but from observation of, and wide ex- 

 perience with, the community. They describe the plan and organ- 

 ization of its components, which have been evaluated previously 

 in terms of measurements and counts. When the quantitative an- 

 alysis has been fairly complete, especially including density or 

 cover in conjunction with frequency, and when strata have been 

 analyzed separately, the qualitative characters are already largely 

 included in the quantitative picture. 



Sociability .—This character evaluates the degree that individuals 

 of a species are grouped or how they are distributed in a stand. It 

 has also been expressed as gregariousness or dispersion. Each of the 

 various scales used to indicate degree of sociability include expres- 

 sions which range from plants occurring singly, as one extreme, 

 through intermediate conditions (patches, colonies, or groups), to 

 large colonies, mats, or pure stands at the opposite extreme. 



The sociability of a species is not a constant, for it is determined 

 by the habitat and the resulting competition of the species with 

 which it is associated. Since habitat conditions are not constant and 

 since communities change, especially in plant succession, the so- 

 ciability of a species, even in the same locality, may change con- 

 siderably. 



Dispersion is a statistical expression that has been applied to 

 sociability. If dispersion is normal, it implies a randomized distri- 

 bution such as might be expected by chance. In hyperdispersion 

 there is irregular distribution, which results in crowded individ- 

 uals in some areas and their complete absence from others. Hypo- 

 dispersion means that the arrangement is more regular than would 

 be expected by chance, as, for instance, the plants in a cornfield. 

 All of these conditions are recognizable in natural communities 

 and, when density-frequency values have been determined, are 

 noticeable in the data. 



Vitality.— Not all species found in a given stand need belong to 

 the community. Unless the plants are reproducing, they are not 

 completely adapted to the conditions and may disappear entirely. 

 Even species constantly present in a community mav be derived 

 from seeds produced elsewhere and transported by wind or some 



