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