According to the different contribution of rare and common species in the total plant species diversity, it is important that diversity component of each analysis is done separately.
A recent paper in Ecography describes a nice quantitatie index to measure commonnes (and rarity). It allows stablishing an objective criterion to separate common and rare species and is based on the h index.
I think it may be useful in your case, the manuscript is:
Gabriel Arellano, Leslie Cayola, Isabel Loza, Vania Torrez and Manuel J. Macía. 2014
Commonness patterns and the size of the species pool along a tropical elevational gradient: insights using a new quantitative tool. Ecography 37
I think you just did not understand my question. I looking method for identify of rare and common species not analysis of them. i.e. common species is that plant species from the entire community that occurred in at least 25% of grassland.
The rarity of a taxon is assessed with reference to the area it occupies on the scale of a given territory.
A very rare species in an area should be considered, in fact, be threatened because the reduced number of stations which shelter is itself an element of insecurity and exposes more strongly to a
risk of extinction. However, the notion of scarcity is highly relative and depends strongly on the geographical area and. A species may be rare or very rare locally, but globally common. Conversely, some species have very limited areas worldwide, but are locally common.
The scarcity of taxa present throughout the territory of intervention can be assessed
from the calculation of the relative frequency within a standardized global mesh: mesh UTM (Universal Transverse Mercator).
The relative frequency of plants within the network maillespermet therefore allocate
taxa catalog into categories or classes of scarcity.
Bigot & Bodot (1973), distinguished four species groups according to their frequencies of occurrence:
1-very accidental species (Vac) have an occurrence of less than 10%;
2-accidental species (Acc) are those whose occurrence varies between 10 and 24%; 3-common species (Cmt) are present in 25-49% of records;
4- constant species (Cst) are present in 50% or more of the samples.
Ref:
Bigot L., Bodot P., 1973. Contribution à l’étude biocénotique de la garrigue à Quercus coccifera - Composition biotique du peuplement des invertébrés. Vie et Milieu. 23 (2) : 229-249.
Dear Reza, Based on quantitative survey you can determine the rare and common species in nature. this is straight forward method. the you obtained from the nature and plot it in bar graph. the bar will focus the rare and common species .