Vol. 32 – 2006 - Ecologia Mediterranea

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MOHAMED TARHOUNI, AZAIEZ OULED BELGACEM, BELGACEM HENCHI, MOHAMED NEFFATI 42 distances is explained by the fact that while in the grazed woodlands the cover of perennial plant patches remains low for a considerable distance from water (5-8 km), in grasslands, like in our case, plant cover reaches its expected maximum within 2 km from water (Ludwig et al. 2001). Two perpendicular measuring tapes, 20 m of length each, were installed at each sampling point. Eight 20meter transects by distance and 32 20-meter transects by well were sampled and monitored during the spring (rainy season) and fall (dry season) 2004 using the point intercept method as define by Daget & Poissonnet (1971) and Floret (1988). A fine pin was descended to the ground every 20 cm along the tape. Each of the 100 hits per tape was recorded according to the plant species and type of ground touched. The specific frequency of presence (SFP) is the number of hits of the specific species: SFPi = (ni /N) * 100 with ni : the number of hits of species i and N: the total number of hits (100 hits in our case). The Grime adaptive strategies were determined according to Jauffret (2001), Jauffret & Visser (2003). Plant species and their nomenclature are identified with flora books (Cuenod et al. 1954; Quezel & Santa 1962, 1963; Ozenda 1977; Pottier-Alapetite 1979, 1981). We ran one-way ANOVA on two separate models: one testing the effects of season on plant types and one testing the effects of distance on plant types (SPSS Inc 2002). The various plant types were treated as categorical explanatory variables. When significant, ANOVA were followed by Fisher LSD Posthoc tests. The Multivariate General Linear Model Test was used to show the crossed effect of season and distance on plant strategies. Results The cover of chamaephytes, hemicryptophytes and therophytes increase in the spring (rainy season) compared to the fall (dry season) (Figure 2). This is significant at well 3 for chamaephytes, at wells 3 and 2 for hemicryptophytes and at wells 1, 2 and 3 for therophytes (Table 1). During the dry season, when animals frequent wells one day every three days and induce the destruction of vegetation cover, the flora is mainly composed of hemicryptophytes at wells 2 and 3. Both chamaephyte and hemicryptophyte covers increase significantly with increasing distance from the watering point at wells 1 and 2, particularly between 250 m and 500 m from the wells (Table 1; Figure 3). Therophytes are not significantly influenced by distance from watering points. The cover of hemicryptophyte plants was the highest (24%) in the spring far from well 2 while it was the lowest close to this well in both the rainy and the dry season (Table 1; Figure 4). Contrarily the cover of therophyte plants was the highest (28%) in the spring close to well 3 while it was the lowest far from this well. During the dry season the cover of therophyte plants is null (Table 1; Figure 5). Figure 2 – Percent cover of plants classified with Raunkiaer biologic spectrum depending on the season. See Table 1 for ANOVA results. Values are means ±IC. a/b indicate differences for Therophyte plants; 1/2 indicate differences for Hemicryptophyte plants and α/β for chamaephyte plants. Plant cover (%) 40 35 30 25 20 15 10 5 0 Fall String Fall b 1 a a a Ch H Th Ch H Th Ch H Th Ch H Th Ch H Th Ch H Th String Fall String Well 1 Well 2 Well 3 b ecologia mediterranea – Vol. 32 – 2006 β 2 b
ecologia mediterranea – Vol. 32 – 2006 A preliminary overview of the effects of seasonal drought and animal pressure around watering points on plant species using adaptative strategy analyses in the Tunisian arid zone Table 1 – Results of one way ANOVA of the effects of seasonal drought and distance from water and their interaction carried with General Linear Model on Raunkiaer biologic spectrum, Noy-Meir types and Grime types. CH: Chamaephyte; H: Hemicryptophyte; TH: Therophyte; AA: Arido-Active; AP: Arido-Passive; C: Competitive; R: Ruderal; S: Stress tolerant. p
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Résumés de thèses Catherine BRET
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Résumés de thèses construit une
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Résumés de thèses Vincent OLLIVI
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Résumés de thèses Marnyye VELASQ
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Résumés de thèses Lure, les for
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Vol. 32 – 2006 - Ecologia Mediterranea

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