Vol. 32 – 2006 - Ecologia Mediterranea
Vol. 32 – 2006 - Ecologia Mediterranea
Vol. 32 – 2006 - Ecologia Mediterranea
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from watering points. One third (1/3) of<br />
Tunisian flora is composed by arido-active<br />
species (chamaephytes and perennial grasses)<br />
versus 2/3 of arido-passive species (essentially<br />
annual plants) (Jauffret 2001). The<br />
ephemeral characters of arido-passive species<br />
and persistent characters of arido-active<br />
species represent the two major strategies to<br />
support the dry season by therophytes and<br />
chamaephytes respectively (Evenari et al.<br />
1975). Our results indicate that the aridoactive<br />
species are more affected by the degradation<br />
degree than by climatic drought. The<br />
arido-passive species avoid dry periods by<br />
various dormancy shapes and mark the sites<br />
with very advanced degradation (Glatzle<br />
1985). Hence, flora seems to be more adapted<br />
to abiotic conditions than the disturbance<br />
degree. We show that arido-passive plants are<br />
not affected by disturbance degree around<br />
wells. This is can be explained probably by<br />
two reasons: (i) degradation around watering<br />
points is very advanced and the floristic<br />
cortege becomes homogeneous (Tarhouni et<br />
al. <strong>2006</strong>) and (ii) animal activity around<br />
watering points contributes in seed dissemination,<br />
provoke the extinction of more competent<br />
species and encourage annuals development.<br />
The plant species in Tunisian arid zones, in<br />
spite of some recent studies (Jauffret 2001;<br />
Jauffret & Visser 2003), are not yet classified<br />
following their adaptative strategies sensu<br />
Grime. The majority of the arid zone plant<br />
species, that occupy very drastic sites, are<br />
stress tolerant. In their study, Madon &<br />
Médail (1997) showed that annuals in<br />
<strong>Mediterranea</strong>n grasslands are often S strategies<br />
but Jauffret (2001) concludes that annuals<br />
are only RS and never S strategies. These<br />
stress-tolerant and ruderal taxa (RS) are more<br />
adapted to climatic stress and human disturbances<br />
(Grime 1977). According to disturbance<br />
degree, plant species can develop different<br />
adaptative strategies. For example at<br />
intermediate disturbance the competitive<br />
plants (C) can survive, while at sufficiently<br />
high level of disturbance only fugitive species<br />
(annual) can survive (RS) (Jauffret & Visser<br />
2003; Sagar et al. 2003). In our previous<br />
study, Tarhouni et al. (2007), we show the<br />
dominance of RS-species in the more disturbed<br />
sites (close to watering points), CRSand<br />
CS-species at medium disturbance and<br />
CS- and S-species in lower disturbance sites<br />
(further from water).<br />
ecologia mediterranea <strong>–</strong> <strong>Vol</strong>. <strong>32</strong> <strong>–</strong> <strong>2006</strong><br />
A preliminary overview of the effects of seasonal drought and animal pressure around watering points<br />
on plant species using adaptative strategy analyses in the Tunisian arid zone<br />
The present results constitute valid hypotheses<br />
for future work which must study more<br />
wells on skeletal soils and more wells on<br />
sandy soils with more measured distances.<br />
The period of exploitation as well as the variation<br />
of geomorphologic substratum and the<br />
technical aspects of the water point (depth,<br />
daily water yield, water salt content, equipment,<br />
location, etc.) can play a determinant<br />
role in the vegetation repartition. The characteristics<br />
particular to each well can be considered<br />
as the key determinants of the animalload<br />
(number of animals) in each site<br />
(Thebaut & Batterbury 2001).<br />
Conclusion<br />
In southern Tunisia, and especially in its<br />
hyperarid part, the floristic cortege is submitted<br />
to several constraints in relation with the<br />
edapho-climatic conditions and human disturbance.<br />
These combined factors lead to<br />
increase the degradation of plant communities.<br />
Such degradation cause changes in the<br />
physiognomy and structure of vegetation<br />
cover especially in sites submitted to a strong<br />
animal pressure like watering points. The<br />
main results of this study show that the covers<br />
of plant types are lower during the fall.<br />
Some plant types are altered by the grazing<br />
gradient around watering points but some others<br />
are more affected by the seasonal drought<br />
than the animal activity. This is explained by<br />
the strong animal stamping which is amplified<br />
by climatic and edaphic drought. During<br />
the rainy season, animal activity around<br />
watering points is reduced or null. Hence vegetation<br />
surrounding wells benefits from a temporary<br />
break. The strong contribution of<br />
annual plants to vegetation cover around wells<br />
can play a beneficial role by fixing the soil<br />
particles and improving its fertility.<br />
References<br />
Aronson J. & Le Floc’h E., 1996. Vital landscape attributes:<br />
Missing tools for restoration ecology. Restoration<br />
Ecology, 4 (4): 377-387.<br />
Aronson J., Le Floc’h E., Gondard H. & Romane F.,<br />
2002. Environmental management in <strong>Mediterranea</strong>n<br />
region: references and linked indicators to plant biodiversity.<br />
Revue d’écologie (Terre et Vie) Suppl. 9:<br />
225-240.<br />
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