Revue internationale d'écologie méditerranéenne International ...

148
◆ M. A. SHEIKH, M. E. MADY & K. H. SHALTOUT
VARIABLE
Community variables:
I II
Vegetation group
III IV V VI
Total mean ± SD F-value
Total cover 43.6 27.3 59.3 66.3 31.7 37.1 40.6±18 3.32**
Total number of species 8 11 23 22 29 34 21±9.8 --
Species richness (Spp/stand) 5.5 6.5 5.5 7.0 9.0 9.3 8.5±2.7 2.04
Species turnover 1.4 1.7 4.1 3.1 3.2 3.7 2.9±1.0 --
Shannon index 0.47 0.51 0.33 0.56 0.59 0.59 0.55±0.1 0.80
Simpson index
Soil variables:
0.49 0.49 0.60 0.46 0.47 0.38 0.46±0.1 0.67
Sand 98 77.6 96.0 87.0 67.8 85.6 79.6±13 2.06
Silt (%) 0.9 14.0 3.0 10.3 24.8 11.4 15.5±9.5 2.61
Clay 1.1 8.4 1.0 2.8 8.7 3.0 5.3±4.9 1.30
CaCO3 5.2 10.2 7.9 9.8 11.4 10.1 10.1±2.4 1.66
EC (m mhos/cm) 21.7 6.5 2.0 3.4 6.0 5.0 5.9±6.7 2.61*
pH 8.14 7.77 7.76 7.89 7.62 7.89 7.97±0.2 1.25
NO3 (mg/l) 301 609 229 141 548 837 533±523 0.85
Cl 168 51.0 25.5 22.7 37.6 27.9 39.4±50 2.96
HCO3 6.0 5.5 11.0 3.8 6.8 5.4 6.1±3.0 3.6**
Ca (meq/l) 452 75.5 27.0 31.0 64.3 46.7 71.8±132 4.25**
Na 1338 47.3 28.0 26.4 37.7 27.4 96.5±61 5.81***
K 13.2 1.4 2.8 1.7 1.7 1.4 2.3±3.7 5.09***
Table 4: Means of the community and soil variables of the six vegetation units identified in the down-stream part of wadi Gaza.
I. Arthrocnemum macrostachyum, II. Mesembryanthemum crystallinum, III. Tamarix nilotica – Arundo donax,
IV. Tamarix nilotica, V. Alhagi graecorum – Xanthium spinosum, VI. Centaurea ammocyanus – Atractylis carduus.
SD: standard deviation * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001, according to one-way ANOVA.
Step Variables Partial-R **2 Model-R **2 DCA AXIS 1
F-value r
1 HCO3 0.202 0.202 9.89** 0.45**
2 Simpson index 0.055 0.258 2.83 0.23
3 Species number 0.033 0.290 1.96 - 0.24
4 pH 0.027 0.318 1.44 - 0.06
5 Silt 0.058
DCA AXIS 2
0.375 3.25 0.26
1 CO30.232 0.232 11.80*** - 0.48***
2 K 0.076 0.307 4.14* 0.35*
3 Clay 0.065 0.373 3.89* - 0.11
4 Species number 0.066 0.440 4.25* - 0.26
5 NO30.017 0.457 1.12 - 0.22
6 Cl 0.015 0.473 1.01 0.37**
7 EC 0.128 0.601 10.67** 0.31*
8 Silt 0.015 0.617 1.31 - 0.34*
Table 5. Stepwise multiple regression (forward selection) of the DCA axes 1 and 2 on the soil and community variables.
* p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001. r = simple linear correlation coefficient.
ecologia mediterranea, tome 29, fascicule 2, 2003