Abstract: The present research studied the ecological factors affecting Salix distribution in Egypt. Two species of Salix were recorded, S. tetrasperma (only male) and S. mucronata (both sexes). They were recorded at River Nile canal system and in the Eastern Oasis. Female S. mucronata was recorded in the all studied habitats, where the male of same species was recorded only in Fayoum Region. Salix tetrasperma neither recorded in Upper Egypt nor Eastern Oasis. Elevation from water surface, soil texture, soil salinity and temperature were the most effective factors affecting the distribution of Salix sp.
INTRODUCTION
Salicaceae comprises two main genera, Salix (willows) and Populus (poplars). It exhibits many characteristics that allow it to grow in habitats subjected to flooding and disturbance through erosion and deposition of sediments (Karrenberg et al., 2002).
Salix is a colonizing floodplain genus characterized by vigorous growth rate and production of a massive root system that can rapidly stabilize stream bank sediments (Grissinger and Bowie, 1984; Hupp, 1992; Van Splunder et al., 1996; Shields et al., 1995; Anonymous, 2005). It also occurs in ditches and on the edges of swamps, lakeshores and other wetland habitats. It is ideal for stream bank restoration because of its easily propagation from cutting, quickly growth and providing rapid soil stabilization (Bentrup and Hoag, 1998; Cronk and Fennessy, 2001). Willow (Salix) has been cultivated for an agricultural crop to many purpose, sucfh as for bioenergy (Perttu, 1998), making baskets, made a tea from the bark and some medical uses (Foster and Duke, 1990).
Several environmental factors such as soil moisture and soil texture have been identified as being critical in determining survival and performance of planted willow cutting (Pezeshki et al., 1998; Schaff et al., 2003). Water table decline and the associated water stress have been also, cited as one of the most common causes of mortality in Salix species in the field (Mahoney and Rood, 1992; Karrenberg et al., 2002). Inadequate soil moisture leading to plant desiccation was reported as one of the causes of first year mortality of willow cutting planted in riparian habitats (Shields et al., 1998; Karrenberg et al., 2002). Such unrooted cutting are especially vulnerable to low soil moisture conditions early in the growing season due to transpiration water losses until root systems, with their vascular tissues have developed (Grange and Loach, 1983; Ikeda and Suzaki, 1986).
Genus Salix L. in Egypt represented by two wild species, Salix tetrasperma Roxb. and Salix safsaf Trautv. (latter treated as Salix mucronata Thunb.); as recoreded by Tackholm (1956, 1974) and Boulos (1999). These species, in addition to its medicinal values, attained a special historic and ethnic importance in Egypt. Salix species are distributed in Nile and Faiyum Regions, in addition to Mediterranean coastal strip. Earlier study recorded the presence of both species in western desert Oases (Bolous, 1999). In Egypt, Salix sp. are used frequently as a restoration species, while other Salix sp. are widely used elsewhere (Svejcar et al., 1992; Hoag, 1993, 1995; Anonymous, 2005). Salix tetrasperma and S. mucronata, as many other Salix sp., regenerate from root and shoot fragments and is often planted along stream banks as dormant, unrooted cutting (Bentrup and Hoag, 1998; Cronk and Fennessy, 2001).
Egypt is an arid country which depends almost entirely on the River Nile for its water supply; agriculture is almost totally dependent on this source. It is estimated that the Nile provides 95% of the country’s fresh renewable water supply. There is no any earlier study on factors affecting distribution of Salix in Egypt. The present study deals with environmental factors affecting the distribution of Salix sp. in Egypt.
MATERIALS AND METHODS
Field trips were carried out during the study years 2005-2008. Fifteen trips were carried out covering the River Nile and its water canal system from Upper Egypt (Aswan) to lower (Alexandria) and Baharia Oasis.
Soil sampling and analysis: For each habitat three soil samples were collected from profiles of 10-50 cm depth under Salix sp. These samples were then pooled together to form one composite sample, air-dried and thoroughly mixed. Thirty composite samples were obtained representing all Salix habitats. Textures were determined by the hydrometer method, providing quantitative data on the percentage of sand, silt and clay. The concentration of soil minerals Na+, K+, Fe3+, Ca2+ and Mg2+ in soil were determined using a Perkin 403 atomic absorption spectrophotometer (Perkin-Elmer Corp, Norwalk, Conn., USA) according to Analytical Methods for Atomic Absorption Spectrophotometry, Levinson (1983). Chlorides were quantified by titrating 5 mL of the 1 : 5 soil/distilled water extract against 0.01 N silver nitrate solution using potassium chromate (1%) as indicator. Bicarbonates was determined by titrating 5 mL of the 1.5 soil/distilled water extract against 0.01 N HCl using phenolphthalein and methyl orange as indicators (Jackson, 1962). pH and conductivity of the soil samples were determined in saturated soil paste extract by pH and conductivity meters, respectively. Temperature measurements were obtained from the Egyptian Meteorological Station. The percentage of organic carbon in the soil was determined by Walkely and Black’s rapid titration method according to Ryan et al. (1996).
Statistical anlysis: Pearson correlation coefficient has been calculated to find out the correlations between Salix sp. and soil parameters.
RESULTS
The extensive survey in the present study reported two Salix species, S. tetrasperma and S. mucronata (male of the former species and the two sexes of the other one) (Table 1, Fig. 1). Salix species were recorded, in canal banks, ditches, on the edges of swamps and lakeshores, a habitats characterized by high moist content.
Table 2 shows that soil analysis where Salix found
characterized by electric conductivity (as a salinity indicator) ranging from
0.4 to 2.9 mS cm-1, slightly alkaline (with mean pH 7.4). Salix
sp. reported in varied soil textures but mainly occurred in a medium soil
texture, loamy sandy soil. Female S. mucronata reported in different
canal banks all over the country, where the male was recorded only in Fayium
Region.
| Fig. 1: | Distribution of Salix sp. in Egypt |
| Table 1: | Distribution of Salix sp. in different parts of Egypt |
| +: Present, -: Absent | |
| Table 2: | Elevation from water surface and soil parameters of different parts of Egypt |
| *: No. of analyzed soil samples; ** Mean±SE | |
| Table 3: | Some soil characters of habitats where Salix sp. recorded |
| *: Mean±SE | |
The male S. tetraspermata neither recorded in Upper Egypt nor in Baharia Oasis. It appeared from Beni Suef governorate downward to Alexandria.
With regard to elemental analysis, S. mucronata prefers soil with high content of organic matter, Na and Fe than S. tetrasperma (Table 3). While, S. tetrasperma was recorded in soil with high concentration from Mg and Ca (ranged from 90 to 1850 mg kg-1 soil and from 365 to 900 mg kg-1 soil, respectively), compared with S. mucronata existed in soil with low concentration of these elements (from 37.8 to 858 mg kg-1 soil of magnesium and from 118.4 to 810 mg kg-1 soil of calcium) (Table 3).
Temperature recorded a decrease with the direction downward reaching the minimum
at Alexandria (Fig. 2). pearson correlations analysis (Table
4) showed a significant positive correlation of S. mucronata with
organic matter content and significant negative correlation of S. tetrasperma
with both soil salinity and sodium content.
| Table 4: | Pearson correlations between Salix sp. and some soil parameters |
| Fig. 2: | Average monthely temperaturs recorded in Salix habitats |
All species showed a significant negative correlation with elevation from water surface.
DISCUSSION
In the present study Salix sp. were recorded only on River Nile water systems and besides wells in Baharia Oasis. The earlier finding because of Salix roots prefer growing in the saturated groundwater zone and will rapidly elongate to maintain contact with free water (Amlin and Rood, 2002). Moisture content and soil texture are the most important factors affecting Salix growth (Hansen and Phipps, 1983; Phipps et al., 1983; Woods and Cooper, 2005). Both fine and coarse soil texture components contributed to lower survival rate. Moderate soil texture allowing for an aerated soil condition that also maintained some water-holding capacity. In contrast, fine-textured sediments led to poor plant performance due to compaction and the associated low aeration. Sandy soils, on the other hand, have larger pore spaces but lower water-holding capacity, increasing the risk for periodic drought stress for plants on stream banks. Many studies documented the importance of rapid root growth for the survival and growth of Salix trees (Mahoney and Rood, 1992; Segelquist et al., 1993; Van Splunder et al., 1996; Kranjcec et al., 1998; Scott et al., 1999; Horton and Clark, 2001; Amlin and Rood, 2002). The absence of S. tetrasperma from Upper Egypt may be due to high temperature. Lammeranner et al. (2005) proved the suitability of S. tetrasperma for winter plantation at low temperature. Its absence from Oases can be explained according to its intolerant to salinity. Jackson et al. (1990) reported the intolerance of S. gooddingii to soil salinity.
The significant negative correlation between Salix and elvation from water surface because Salix species are relatively shallow-rooted, drought-intolerant tree species. (Horton and Clark, 2001; Glenn and Nagler, 2005), they prefer low elevation from water surface. Fine roots of these trees are concentrated in the capillary fringe, just above the water table; they are sensitive to fluctuation in water table depth, particularly on coarse soil with a narrow capillary fringe. The occurrence of S. tetrasperma and both male and female S. mucronata in Fayoum due to presence of low elevation from water surface. Fayoum is the largest Oases in Egypt, situated 90 km south-west of Cairo, 75 km from Giza Pyramids. It considers a natural depression in the desert, linked to the River Nile by a branch called Bahr Yosuf and characterized by high quantity of water with nearly permanent full canal banks.
CONCLUSION
It is advisable to cultivate Salix sp. By cutting in a saturated soil or at canal banks with low elvation from water surface.