The cover of each species was recorded following the Sigmatic
Method [29]. This method assigns to the cover of each species a
value between þ (sparse and covering a small area) and 5 (covering
more than 75% of the area). These values are transformed into the
mean value of the Braun-Blanquet cover-abundance scale
(þ ¼ 0.01%; 1 ¼ 5%, 2 ¼ 17.5%, 3 ¼ 37.5%, 4 ¼ 62.5%, 5 ¼ 87.5%).
Plants were identified following local flora [30].
In order to analyse the differences in floristic composition of
each plot, non-metric multidimensional scaling (NMDS) using
BrayeCurtis dissimilarity distance was performed, which has been
proved to be the most suitable unconstrained ordination method in
community ecology [31]. Smooth surfaces of survey dates were
applied on the NMDS plot so as to find temporal differences in
floristic composition. In NMDS analysis, a biplot is obtained, where
graphic distance among surveys is function of the similarity in
floristic composition. Therefore, those surveys with similar floristic
composition will appear closer in the biplot.
Finally, to quantify the diversity variables, the richness (total
number of species by plot) and the Shannon Diversity Index
H0 ¼ PpiLnpi, where pi is de cover value of species I in the plot for
each plot on each month was calculated. Shannon diversity index is
sensible both to the number of species and to the relative coverabundance
of the species. Hence, this index gets higher values
when the richness of species increases and the relative abundance
of those species are more equitable. Statistical analyses were performed
using R [32].