Ecologia mediterranea 1999-25(2)

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Abd El-Ghani Soil variables affecting the vegetation ofinland western desert ofEgypt Station Mersa Matruh Siwa Dakhla Temperature (QC) Mean Min Mean Max 12.4 24.7 4.1 38.0 5.8 39.3 Relative Humidity (%) Mean Min Mean Max 51 67 42 61 19 42 Rainfall (mm annuar l ) 144.0 9.6 0.7 Evaporation (mm daft) 8.3 11.5 18.4 Table I. Climatic characteristics (average 1931-1978) of three stations distributed in the study area (after Zahran, 1972; Zahran & Willis, 1992) TWINSPAN group I 11 III IV V VI VII VIII Group size 7 16 45 19 5 23 24 5 Prosopis farcta (P fr) 121 2 1 Phoenix dactylifera (P df) 15 9 5 Calotropis procera (C pr) 1 12 1 Tamarix nilotica (T ni) 30 109 19 4 23 6 1 Stipagrostis plumosa (S pi) 2 6 3 6 I 9 Pulicaria incisa (P cr) 1 1 I 12 4 8 5 Heliotropium digynum (H dg) 5 I 7 3 2 4 Alhagi graecorum (A gr) 77 22 2 3 2 Citrullus colocynthis (C cl) 1 2 2 I Fagonia bruguieri (F br) 1 9 3 Zygophyllum album (Z al) 12 4 Traganum nudatum (T nd) 1 2 /mperata cylindrica (I cy) 5 1 Nitraria retusa (N rt) 11 1 Launaea nudicaulis (L nu) 5 2 Hyoscyamus muticus (H mu) 1 I Zygophyllum coccineum (Z co) 8 69 14 5 4 5 Salsola imbricata subsp. imbricata (S im) 18 62 10 Cornulaca monacantha (C mo) 1 15 142 5 Fagonia arabica (F ar) 1 I 71 5 6 1 Pulicaria crispa (P cr) 36 4 2 5 Monsonia nivea (M nv) 2 1 3 2 I Fagonia indica (F in) 4 Sarcocorniafruticosa (S fr) 1 Calligonum polygonoides subsp. comosum (Ccm) 1 3 1 Zilla spinosa subsp. spinosa (Z sp) 10 2 9 4 2 Acacia tortilis subsp. raddiana (A rd) 1 19 6 2 Astragalus trigonus (A tr) 3 2 3 2 2 Anabasis articulata (A ar) 3 13 14 1 15 Atriplex leucoclada (A lu) 109 4 2 Herniaria hemistemon (H he) I Deverra tortuosa (D tr) 14 39 86 Randonia africana (R af) 107 26 19 Carduncellus mareoticus (C mr) 2 14 Farsetia aegyptia (F ag) 3 1 Capparis spinosa var. aegyptia (C sp) 12 96 75 Zilla spinosa subsp. biparmata (Z bi) 3 7 33 Helianthemum lippii (H 1p) 1 1 6 Salsola villosa (S vr) 4 2 Ephedra alata (E a1) 3 Table 2. Species composition of the 144 stands in the two transects, arranged in order of occurrence in the eight TWINSPAN groups. Entries in bold are characteristic species in each group. Species abbreviations displayed in Figures 2, 3 and 5 are given between parentheses. 176 ecologia mediterranea 25 (2) - /999
Abd El-Ghani Soil variables affecting the vegetation ofinland western desert ofEgypt Soil variable TWINSPAN groups F- ratio P I 11 III IV V VI VII VIII EC (mS cm-I) 0.5±0.3 2.8±0.7 0.8±0.9 0.9±0.7 2.2±0.2 0.7±0.7 0.5±0.3 1.1±0.9 19.0 0.0001 pH 8.0±0.6 8.8±0.4 7.9±0.5 7.9±0.4 7.7±0.5 7.7±0.5 7.9±0.4 7.6±0.4 1.3 0.3 CaC0 3 (%) 9.6±2.6 11.3±4.9 15.0±5.8 13.5±5.3 21.0±8.1 14.8±6.0 15.1±5.5 19.1±3.8 4.6 0.0001 MC (%) 1.5±0.3 2.0±0.6 2.12±0.7 2.3±0.5 2.5±0.2 2.6±0.8 2.9±0.7 3.3±0.7 5.4 0.0001 OM(%) 1.5±0.2 0.3±0.4 0.21±0.3 0.2±0.3 0.1±0.1 0.1±0.1 O.I±O.I 0.1±0.06 29.5 0.0001 Sand (%) 93.5±1.0 93.3±1.8 94.5±4.1 92.4±2.0 91.2±0.9 91.5±1.0 88.4±16.9 90.4±0.9 12.5 0.0001 Silt + clay (%) 6.5±1.4 6.7±1.8 5.5±2.1 7.6±2.0 8.8±0.9 8.4±1.0 11.6±1.1 9.6±1.0 8.6 0.0001 Table 3. Mean values, standard deviation errors and ANOVA F values of the soil variables in the stands supporting the 8 vegetation groups obtained by TWINSPAN. EC =electric conductivity, CaC0 3 =calcium carbonate, MC =moisture content and OM = organic matter Eigenvalues DCA CCA Species-environment correlation coefficients DCA CCA 1 0.830 0.474 0.724 0_781 Axis 2 0.496 0.376 0.468 0.871 3 0.377 0.292 0.409 0.658 Table 4. Comparison of the results of ordination by DCA and CCA: eigenvalues and species-environment correlation coefficients for the first three axes are demonstrated Canonical coefficient Intra-set correlations Soil variables Axis I Axis 2 Axis 3 Axis I Axis 2 Axis 3 EC -0.48* 0.88* 0.01 -0.50 0.85 0.35 pH -0.13 -0.16* -0.10 -0.22 0.07 0.06 CaC03 -0.08 0.02 -0.21 0.06 -0.08 -0.37 MC 0.28* 0.09 0.10 0.49 -0.10 0.24 OM -0.33* -0.19* 0.88* -0.41 -0.28 0.85 Sand 0.12 -0.06 0.01 -0.09 -0.07 0.005 Silt + clay 0.53* 0.29* 0.25 0.67 0.53 0.27 Table 5. Canonical coefficients and the intra-set correlations of soil variables with the first three axes of CCA * = t-values > 2.3 (only indicative of coefficient strength) EC =electric conductivity, CaC03 =calcium carbonate, MC =moisture content and OM =organic matter The exploratory CCA was evaluated using the intraset correlations, since the canonical coefficients were unstable due to inclusion of highly correlated variables. Eight soil variables were included: electric conductivity, pH, CaC03 , soil moisture, organic matter, sand, silt and clay. The significance of differences between the different vegetation groups, as to their edaphic variables, was tested by ANOVA. CCA axes were evaluated statistically by means of a Monte ecologia mediterranea 25 (2) - 1999 Carlo permutation test (ter Braak, 1988). All the statistical techniques were according to student SYSTAT software (STUSTATW 5: Berk, 1994). RESULTS Sixty plant species related to 19 families of the angiosperms and one of the gymnosperms were recorded in this study. They constituted 40 perennial and 20 annual species: Cruciferae and Chenopodiaceae (13.3% 177
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