Revue internationale d'écologie méditerranéenne International ...

140
◆ M. A. SHEIKH, M. E. MADY & K. H. SHALTOUT
INTRODUCTION
Special interest in the down-stream part of Wadi Gaza
arose from several view points: (i) it is a RAMSAR site
with great international importance for migratory as
well as resident birds; (ii) its phytogeographical location,
straddles the boundaries of Saharo-Arabian and Irano-
Turanian flora in the south and the Mediterranean flora
in the north; and (iii) it is considered the only wetland
site with unique habitats in Gaza Strip. Few floristic and
vegetation studies are available on Gaza Strip; among
them is that of Boulos (1959). Danin (1983) gave a
short account on the plant communities of Gaza Strip
in his study of the desert vegetation of Israel and Sinai.
After the initiation of the National Palestinian Authority,
some recent studies have been carried out such as that
of Mady (2001a) and Mady et al. (2002) on the flora of
the coastal sand dunes of Gaza Strip.
The present study aims at analyzing the vegetation
of the down-stream part of wadi Gaza, by how do the
biotic and abiotic features of the environment shape the
distribution and structure of the plant communities. It
provides also a general description of the floristic and
ecological features of the different habitats in the study
area which is considered one of the most diverse sites in
Gaza Strip, presumably due to the greater amounts of
run-off water collecting in it.
Study site
The term ‘wadi’ designates a dried water course in the
desert. It has the features of a natural drainage system
evolved under less arid conditions. The wadi comprises a
main channel and a number of tributaries which receive
runoff water from the branched affluents (Batanouny,
1973). Wadi Gaza has a length of about 150 km and a
width ranging between 150 and 500 m. It flows from the
Hebron mountains in the south, passing the Negev plateau
and crosses the middle part of the Gaza strip for a distance
of 8 km where its mouth ends in the Mediterranean Sea. It
is the unique source of surface water in Gaza strip (Mady,
2001b) (fig. 1). Its drainage system constitutes one main
tributary which is connected to many subsidiary ones
and can be compared to the classical drainage lines of
other arid and semiarid regions. Near the Mediterranean
coast, its mouth has been closed by soil embankment;
so, a pond of free water has been established. The study
area was located in the down-stream part of wadi Gaza
(about 8 km in length) where the following habitats are
distinguished: terrace, slope and bed of the main channel;
bank and water edge of the mouth pond; sand sheets and
sand dunes that surrounded the mouth pond. The wadi
bed of the main channel is composed of a variety of rocks
and fine texture soil. However, the alluvial deposits of the
wadi itself are mainly composed of gravel and alluvium
mixed with drifted sand.
The mean air temperature of Gaza strip varies
between 16.3 ºC (with mean minimum of 10.0 ºC and
mean maximum of 23.8 ºC) at Gaza in the north, and
20.2 ºC (with mean minimum of 14.5 ºC and mean
maximum of 25.8 ºC) at Rafah in the south. In general,
January is the coldest month of the year with a minimum
temperature of 9.7 ºC, while July and August are the hottest
with a minimum of 22.5 ºC. The minimum relative
humidity was 67 % during November, while the maximum
was 75 % during July-August period. The effective
rainy period is January (113 mm), with total amount
(340 mm) per year.
METHODS
Forty-one stands representing the different habitats of
wadi Gaza were selected systematically in stratified way
to represent seven types of habitat in the study area: 10
stands on the terrace (T), 7 stands on the slope (O) and
13 stands in the bed (B) of the main channel; 6 stands on
the bank (L) and 2 stands at the water edge (W) of the
mouth pond; 2 stands on sand sheets (S) and one stand
on sand dunes (D) that surrounded the mouth pond.
The size of the stand ranges from 1500-2000 m 2 at least
and the number of stands per habitat varied (between 2
and 13 stands) depending on the habitat heterogeneity. In
each stand, all plant species were recorded and identified
according to Zohary (1966, 1972) and Feinbrun-Dothan
(1978, 1986). Life forms (following Raunkiaer, 1937)
and chorotypes following Zohary (1966, 1972) and
Feinbrun-Dothan (1978, 1986) were recorded. Cover
values of all species were estimated using the line intercept
method (Canfield, 1941). Three soil samples, down
to 50 cm depth (most of the plant roots and available
nutrients are abundant in this depth), were collected from
each stand and mixed as a composite sample; air dried
and analyzed for soil texture using Bouycqos hydrometer
method (Allen et al., 1974). Calcium carbonate and bicarbonate
were estimated by titration method, pH on the soil
water extract by pH meter with KCl electrode, electric
conductivity (EC) by conductivity meter and chloride
by titration method, nitrate (NO 3) was estimated using
ecologia mediterranea, tome 29, fascicule 2, 2003