the mystery of the spiny astragalus populations on marseilles coastline and frioul archipelago :...
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The mystery of the spiny Astragalus populations on Marseilles coastline
and Frioul archipelago : dead or alive ?
• Amm Annabelle1, Boissy Marie-Line1, Brest Sébastien1, Di Liello Marion1 & Dumas Pierre-Jean1
• Affre Laurence2, Baumel Alex2, Roche Philip2, Tatoni Thierry2 & Torre Franck2
• Delauge Julie3 & Patrick Vidal3.
1 Student of the Master of Environnemental Sciences, University Aix Marseille III2 Institut Méditerranéen d'Ecologie et de Paléoécologie, UMR CNRS 6116, University Aix-Marseille III, IMEP - Bat. Villemin, Europole de l'Arbois, BP80 - 13545 Aix en Provence Cedex 04. Email : [email protected] CEEP-Parc Maritime des Îles du Frioul, Sémaphore de Pomègues, Le Frioul, 13001 Marseille. Email : [email protected]
Astragalus tragacantha L. (Fabaceae) develops as small, round, compact and spiny shrubs, living in small and rare populations along coastline of Portugal, Spain, France, Corsica, Sardinia or Tunisia. In France, the species is listed in the red book of the French threatened flora and appears in the annex 1 of the national list of protection. One station (Aude) has been lost, and the others situated in the Bouches du Rhone and Var departments are exposed to numerous disturbances.
The south border of Marseilles and the Frioul archipelago shelter the biggest French populations. But they are impacted directly or indirectly by human activity. Disturbances are numerous : urbanization, waste of building industry, polluted sea sprays, human treading and overabundance of seagulls.
This poster introduce a projet intending to assess the viability of Astragalus populations.
First demographic investigations are based on population census lead by CEEP and IMEP. Population parameters were recorded exhaustively or by sampling : number of plants, size, ratio of dead part, and reproductive sucess.
The first important feature of the results concerning the population demographic of Astragalus tragacantha on Pomègues island shows a dramatic lack of juveniles (small plants) associated
with a high proportion of adults affected by leaves and branches mortality that could be caused by polluted sea sprays.
A second important feature concerns a high reproductive effort (flower production) of Astragalus tragacantha which is counterbalanced by a moderate reproductive success (fruit
production), the impact of parasitized fruits, and, particularly, a very low seed production by fruit. However estimate of seed production at a coarse scale shows an important potential for
natality, but in 2005 no seedlings were observed on both islands and continent.
As population dynamics of A. tragacantha are not know, two hypothesis must be tested :
"ALIVE" : reproduction is naturally rare and the aging of populations should not be considered as an alert.
OR
"DEAD" : reproduction is inhibited or prevented by one or a set of abiotic and biotic factors associated with disturbances, in such case extinction is possible.
Further investigations should be based on reproduction biology, demographic monitoring, dendroecology, soil ecology and populations genetics for foresee optimal
management alternatives, if necessary. .
Effects of polluted sea sprays ? Most individuals show dead parts !
Flowers of A. tragacantha, Frioul 2005
Census on Pomègues islandCensus on the continent
Wastes, roads, examples of disturbance at the core of the distribution area
Sizes structure and proportions of dead parts of Astragalus population in the non disturbed location (32 plants).
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Size categories (cm)
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Sizes % of dead part > 20% % of dead part < 20%
Sizes structure and proportions of dead parts of Astragalus population in the disturbed location (44 plants)
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Sizes % of dead part > 20% % of dead part < 20%
Sizes structure and proportions of dead parts of Astragalus population in a continental location (38 plants).
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Size categories (cm)
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Sizes % of dead part > 20% % of dead part < 20%
Exhaustif census on Pomègues island Station impacted by sea sprays, Pomègues island
Sampling census on the continent, Escalette station
Station non-impacted by sea sprays, Pomègues island
Sizes structure and proportions of dead parts of Astragalus population on Pomègue Island (1626 plants).
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Per
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Sizes % of dead part > 20% % of dead part < 20%
1626 individuals alive on Pomègues island
Reproduction effort on Pomègues island, approximately: 8,7 .106 Flowers.
Proportion of flowers fertilized : 43.5 % (sampling on 40 individuals)
Ripe fruits : 73.7 %Parasited fruits : 7 % Aborted fruits : 19.2 %
Number of ripe fruits : 2,8 .106
Mean number of seed per fruits : 2.17 (sampling on 30 individuals,
2369 fruits monitored)
Potential for natality, approximately : 6 .106 seeds for 2005
331 flowered branches per individual (sampling on 40 individuals)16 flowers per flowered branch (sampling on 40 individuals)
Distribution of A. tragacantha around Marseilles
Results
Frioul
Marseilles
Pomègues
Ratonneau
Demographic census Reproduction effort and success