An Index for Establishing the Degree of Maturity in Plant Communities

The purpose of this paper is ta introduce an index which may be used as a datum of orientation in statistical studies of plant communities. In carrying out the investigations in a community we usually make the floristic list of the species present in a certain number of sample plots scattered over the ground under examination. This work, carried out on the spot, enables us to establish what species are present therein and calculate with sufficient accuracy what is the frequency percentage with which the single species appear. With these data we are in a positiQn to construct a table in which are listed the names of the species present in the community with their respective frequency percentages and to calculate the biological spectrum of the community on the basis of the different life forms to which the separate species belong. The table and the biological spectrum accompanied by other data collected on the site itselfj e.g. vitality, stratification, etc., allow us to give a sufficiently accurate description of the quantitative and qualitative characteristics of the community in question. However, in order to give a clearer picture of the vegetation, in addition to these data I thought it useful to introduce a new datum, which I have named 'maturity index'. The maturity index is the quotient of the total of the frequency percentages of all the species in the community-a total which Raunkiaer* calls 'points'-divided by the number of the species found on the station. This reflects the long-accepted notion that the higher the frequency percentage of each species and the smaller the number of sporadic species, the more mature the plant community. The calculation of the maturity index is very easy, since the points, as well as the number of the species, are not only easily calculable, but also indispensable for obtaining the biological, spectrum of the community in question. As an example of calculation of the maturity index I take the following communities (Table 1) studied by Raunkiaer and quoted on p. 339 of the collected papers of the author.t Calculating the maturity index for these communities and integrating the data already calculated by Raunkiaer, we obtain the spectrum given in Table 2. The maturity index, to the best of my knowledge, is now introduced for the first time into the statistical studies of vegetation. It affords us a datum of orientation for establishing the maturity of plant communities, which may be of some use in the study of -the development of the vegetation.