Revue internationale d'écologie méditerranéenne International ...

SAMI YOUSSEF, ERROL VELA, ALEX BAUMEL, THIERRY TATONI
Figure 1 –
Distribution of the
108 study stations,
white circles indicate
positions of one or
more close
occurrences of
Genista lobelii.
Note that the
highest altitudes,
around 1000 m a.s.l,
are encountered
within Sainte-
Victoire (VCT) and
Sainte-Baume
mountains (BM).
Genista lobelii
populations
indicated by
different codes
(AMR = Mont
Amarron;
BM = Sainte-Baume;
BSS = Gros Bessillon;
CM = Mont Caume;
CNL = Cap Canaille;
CRP = Carpiagne;
ETL = Chaîne de
l’Étoile;
FRN = Mont Faron;
GRL = Garlaban;
LB = Montagne de la
Loube; LMN = Mont
Puget; MRS = Mont
Marseilleveyre;
MZG = Mont
Mazaugues;
RNS = Rians;
TRT = Trets;
VCT = Sainte-
Victoire).
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field and divided in three classes (class 1
where surface area < 100 m 2 ; class 2 where
surface area was between 100 to 1000 m 2 ;
class 3 where surface area > 1000 m 2 ). The
species occurrences provide a nearly exhaustive
map of all G. lobelii stations in Basse
Provence. The estimate of occupied surface
was used an indicator of populations size
(Figure 1, Appendix 1). Floristic relevés
(108 in total) were carried out on 100 m 2 circular
areas, according to Gachet et al. (2005)
between April and June 2008. This period
allows the identification of a maximal number
of plant species. To characterize the vegetation
co-occuring with G. lobelii, each
species was assigned to a biological life form
(Raunkiaer 1934) following de Bolos & Vigo
(1984-2001), to a demographic modality of
the CSR model (Grime 1974) following Véla
(2002) and to a biogeographical distribution
following Pignatti (1982). For multivariate
analysis, rare species (frequency < 1%) were
removed. The data matrix was composed of
217 columns corresponding to species and
108 rows corresponding to stations. We consulted
geological map of BRGM to search for
eventual substrate diversity through the whole
distribution of G. lobelii.
Data analysis
All multivariate analyses were carried out
using R statistical software (R Development
Core Team 2006). The ordination of stations
according to their floristic similarity was done
by a Non-metric Multidimensional Scaling
(NMDS) using the “metaMDS” function of
VEGAN package. The analysis was based on
the Bray-Curtis dissimilarity index and the
number of random starts in search of stable
solution was set to 100. The Multiple
Response Permutation Procedure (MRPP)
was carried out to provide a test of a significant
difference between group’s dissimilari-
ecologia mediterranea – Vol. 36 (1) – 2010