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Le projet majeur africain de la Grande Muraille Verte

 | 
Abdoulaye Dia
, 
Robin Duponnois

Partie I. Espèces végétales de la Grande Muraille Verte

Pruning of Acacia salicina trees irrigated with runoff water in arid zones

Jhonathan E. Ephrath, Kebba N. Sonko e Pedro R. Berliner

Abstract

In arid and semi arid lands, forest and agricultural productions are declining due to water scarcity and drought. The objective of this study was to determine the effects of shoot pruning at different heights of acacia salicina lindl, grown in the Israeli Negev Desert and irrigated with runoff water. The specific objectives of this study were to examine the most appropriate pruning height, growth rate and biomass production, water use efficiency of A. salicina shrubs irrigated with floodwater and the water uptake rate and soil water content change at the different pruning height treatments. The trees were planted in 1993 in a 0.5 ha plot at a design of 1m between trees within the rows and 4 m between rows (1,250 trees ha-1). The trees were pruned at a height of 0.5m, 1.0m and 2.0m above soil surface and were compared to non-pruned trees (NP treatment, served as control treatment). Measurements of trunk diameter at a height of 0,3 m above soil surface, re-growth of new branches and soil water uptake by trees, using a neutron moisture gauge that has been previously calibrated in the field), were take every two weeks. Three pruning were carried out during the two years of the experiment. The first pruning was at the beginning of the experiment in March 2003, the second one in December 2003 and the third one in October 2004. Biomass measurements were taken after the second and the third pruning. A non-destructive biomass evaluation was carried out to the NP treatment by using a linear regression of cross Sectional Area (CSA) of trunk versus biomass yield developed from an adjacent plot of A. salicina of the same age. The results of the experiment indicate that more biomass was obtained from the 2,0 m pruning treatment followed by the 1,0 m. Water Use Efficiency had the same pattern. Under the condition of this experiment, the most appropriate pruning height for A salicina trees irrigated with floodwater is 2, 0 m.

Testo integrale

Introduction

1Among the main leading causes of desertification in arid and semiarid zones of underprivileged countries in the world are deforestation and overgrazing (Middleton and Thomas, 1997; Eggleton, 2002; Cline-Cole et al., 1990). As a result, short-rotation plantations of fast growing, multi-purpose nitrogen-fixing trees or shrubs, based on local water resources, may offer a solution to these problems and alleviate pressure on the local vegetation. The use of water for agricultural production in water scarce regions requires innovative and sustainable research and appropriate transfer techniques. In arid lands, uses of appropriate technologies that are economically viable and socially acceptable are areas of priority for the developing agricultural (Pereira 2002). Worldwide, dryland agriculture is generally rain-fed. Because of low precipitation, special farming techniques and well-adapted crops are needed to ensure successful and sustainable agriculture. Runoff generated during rainfall events flows by gravitation into the lower parts of the landscape and is retained in wall plots. In these plots, crops are planted and have an adequate water supply. Rainfall is characterized as short and intense rainstorms, which produce large amounts of water that are lost as runoff water. Furthermore, the crusted nature of most arid and semiarid soil limits its water infiltration capacity and increase runoff, exacerbating the scarcity of available soil water. The collection of runoff water in an infiltration basin is, however, a proven viable approach to produce food, fodder and firewood in arid and semiarid areas.

2The growth of a tree is enhanced by the supply of assimilates. Trees having larger leaf mass fractions (leaf mass/total plant mass) can produce more assimilates per unit plant mass and invest proportionately more assimilates to growth (Zeng, 2003; Poorter, 1998).

3Tree pruning is a common management practice in agroforestry for mulching, fuel wood, fodder and reducing competition between the annuals and perennial crops (Peter and Lehmann, 2000). The harvest of woody products often involves in partial or complete removal of canopy on a regular basis. The amount, frequency and quality of water supplied to the plant may significantly affect the regrowth and functioning of shoots and roots.

4Pruning effectively reduces root development and decrease potential below-ground competition with intercropped plants (Peter and Lehmann, 2000). The reduction in roots also increases the danger of nutrients losses by leaching of mobile nutrients (Peter and Lehmann, 2000).

5Tree pruning strongly decrease the root length density by lowering the supply of assimilates from the leaves and retranslocating sugar to above-ground organs. Therefore, pruning the above-ground biomass is an effective way of controlling below –ground growth. The lower root abundance and the laterally restricted root system after pruning decrease below-ground competition and result to positive crop yields in an intercropping system (Peter and Lehmann, 2000).

6Droppelmann et al. (2000) stated in their study that tree pruning decreased water uptake compared to non-pruned. They also stated that after complete pruning, a large fraction of the whole active sapwood area of the trunk turns prematurely into heartwood and, replacement sapwood is formed in order to support the newly formed branches and leaves. Pruned trees spent a larger portion of their photosynthates on leaf growth than on biomass accumulation in the trunk (Droppelmann at al., 2000).

7There are two factors that may affect the rate of biomass accumulation after cutting over a given period: the technique used for the tree harvesting (e.g. Lopping, pruning, pollarding or coppicing) and the timing of harvesting (i.e. cutting intervals) (Droppelmann at al., 2000).

8Pruning changes the structure of tree crowns dramatically. The study of Zeng (2003) on pruning of a one year old Pinus massoniana trees gave interesting results: the Above Ground Leaf Mass Fraction (AGLMF) of twice-pruned P. massoniana trees one year after pruning was higher than the AGLMF of trees that were pruned once a year. The conclusion of that study revealed that pruned trees are able to adjust biomass partitioning within their shoot and recuperate their AGLMF quickly. This reaction would be beneficial to the re-growth and recovery of the pruned trees following pruning. In plants, early stage of shoot elongation is typical for the new leaves to receive photosynthates from storage tissues in the previous year’s growth of the tree (old leaves). However, as the season of the growth progresses, the maturing leaves become more self-sufficient, and become the source of carbohydrate to the tissue (Lanner, 2002).

9In arid and semi-arid regions of the world, there is a wide range of indigenous water harvesting (WH) techniques used. The two major types of WH systems utilize direct and the indirect methods. The direct WH system store runoff water in the soil profile of the planted area while the indirect WH system use tanks or reservoirs to collect runoff, which is applied, to the planted area with some form of irrigation system (Ojasivi, 1999).

10Flooding affects soils by altering soil structure, depleting O2, inducing anaerobic decomposition of organic matter, and, reducing iron and manganese (Prinz, 2001). In some cases, flooding increases stem thickness through the growth of bark tissue (Kozlowski, 1997). Flood tolerant varies greatly among plant species, genotypes and rootstocks, and is influenced by plant age, time and duration of flooding, condition of the floodwater and the site characteristics (Kozlowski, 1997).

11The main objective of this study was to determine the effects of different pruning heights of Acacia salicina trees irrigated by runoff in an arid zone on growth, development and water use. More specifically, the objectives of the study presented here were (1) To determine the optimal height of pruning of fast growing trees (A. salicina) subjected to flood conditions and their rate of re-growth for maximum yield; (2) to determine the growth rate and biomass accumulation of A. salicina in terms of trunk diameter increment for four pruning treatments; (3) to determine yield (leaves and wood) of A. salicina trees as affected by irrigation from floods generated by runoff for all pruning treatments and (4) to monitor soil water uptake by the trees at the different pruning treatments.

Material and Methods

12The experiment was carried out at the highlands of Israeli Negev Desert (31°08’N, 34°53’E;) at the runoff experimental farm located in Wadi Mashash. The site is at an elevation of about 400 m above sea level (m.a.s.l.).

13The Climate in Wadi Mashash is classified as arid with a P/PET (ratio of precipitation over potential evaporation) of 0.04-0.05. The mean annual precipitation in the site of the experiment is 115 mm, most of which occurs between October and April. Maximal daily temperature is about 33°C during July and August, and minimal temperature is close to 5.0°C during January. The annual evaporation from a class A Pan is between 2500 to 3000 mm per year.

14The rainy season of 2003-04, began in October 2003 and ended in March 2004 with a total of 81.2 mm. During the period of this experiment, two flood events occurred, one in December 2003 and one in February 2004.

15The soils in Wadi Mashash are characterized by two meters deep loessial deposit with a high water holding capacity (17% v/v). The profile is relatively homogenous with occasional thin layers of fine gravel or course sand starting at one meter depth. In deeper layers, more gravel is found with lime and flint stones (Lovenstein, 1993). The topsoil is slightly sandy loam with an average of 24% clay, 22% silt and 55% sand. The soil bulk density is 1.45 g/cm3. On average, this soil has an infiltration rate within the non-crusted upper layer close to 11 mm/hr. The soil type in the experimental site is mainly sandy clay loam and forms surface crust under the impact of raindrops conductive to runoff production (Eggleton, 2002).

16The area of the experimental plot was 0.5 ha. It was planted with Acacia salicina in 1993. The plot, surrounded by walls from three sides formed a leveled water catchment basin.

17At the end of the winter of 2002-2003 (February 2003), soil samples from two representative points in the basin were taken at 30 cm increment up to the depth of 210 cm with a soil auger and oven dried for determining initial soil moisture content.

18Acacia salicina Lindl. belongs to the family Fabaceae. It is indigenous to mainland Australia. A. salicina is an evergreen fast growing tree, which attains a height of about 15 m, with a spreading crown of 4 m and a recorded trunk diameter of over a meter. The stem is erect and suckering, with a rounded crown and branches weeping almost to the ground. A. salicina plants were propagated from seeds and planted out in the field in 1994. At the beginning of the experiment in March 2003, the height of the trees ranged between 5-8 m with a crown width of 2-4 m with dropping crowns close to the ground. The diameter of tree trunks ranged between 11 cm to 70 cm. About 10% the trees were branched about 1.0 m above ground level.

19Four pruning treatments were carried out (Table 1). Each treatment was replicated three times. Three prunings were carried out throughout the experiment. First pruning was done in early March 2003 and re-growth count was carried out from May 22 until July 13, 2003. The second pruning was done in December 2003. Since right after the pruning a flood event occurred, the counting of re-growth (new branches) was carried out from April 3 to June 13, 2004. Third pruning was made at the end of the experiment in September 2004. The time period between the first and second pruning will be termed hereafter “First re-growth period “ and the period between the second and third pruning termed accordingly “: Second re-growth period”.

20Soil moisture was estimated using a neutron probe. The neutron probe was fieldcalibrated against volumetric water content measurements. Separate calibration equations were developed for the top 0.15 m and the deeper soil layers. Two aluminum access tubes were installed to a depth of 6m in each plot with a distance of 0.5 m and 2.0 m from two selected trees respectively. Soil moisture was determined at 0.15 m intervals down to the depth of 1.2 m and at intervals of 0.30 m increments thereafter down to the depth of approximately 6 m.

Results

Biomass production

21Figures 1 and 2 shows the re-growth of new branches of the three pruning treatments (0.5 m, 1.0 m and 2.0 m) for the first and second re-growth periods respectively.

22In both growing periods, the 2.0 m pruning treatment produced the highest number of branches followed by 1.0 m and 0.5 m pruning treatments respectively. A significant difference (Turkey HSD comparison test, alpha = 0.05) in the number of new branches was found between all three pruning treatments with the exception of day 52 after pruning of the first re-growth period for which no significant differences between the 1.0 m and 0.5 m was found. Results of the experiment in the second re-growth period indicate that there were more new branches from the 2.0 m pruning treatment followed by 1.0 m and 0.5 m treatments. There was a significant difference (Turkey HSD comparison test, alpha = 0.05) between all the three treatments. The number of new branches in the second re-growth period was smaller when compared to the first re-growth period.

Figure 1

Figure 1

Number of new branches during the first re-growth period. Bars denote one standard deviation.

Figure 2

Figure 2

Number of new branches during the second re-growth period. Bars denote one standard deviation.

23Tree trunk cross-sectional area increment for the four pruning treatments is presented in Figures 3 and 4. In both years, the largest increment was measured in the NP treatment and was significantly higher (Turkey HSD comparison test, α = 0.05) than that of the other three pruning treatments. No significant differences in the trunk increments werefound among the remaining the pruned treatments. Comparing the increment of the trunk in the two growing seasons of the experiment showed a significant difference in the trunk cross sectional increment during the second year when compared with the first year in all pruning treatments.

Figure 3

Figure 3

Trunk cross-sectional area increment of A. salicina during the first re-growth period. Bars denote one standard deviation.

Figure 4

Figure 4

Trunk cross-sectional area increment of A. salicina during the second re-growth period. Bars denote one standard deviation.

24The second and third pruning events were carried out at the end of each of the re-growth periods. The fresh biomass (leaves, branches and twigs) was weighted directly in the field. A sub-sample of branches and leaves were than oven dried in the laboratory at a temperature of 65°C for two weeks and was used to estimate the total dry weight (Figures 5 and 6).

25In both years, the 2.0 m pruning treatment gained the highest dry biomass both in leaves and twigs with branches. In the first year, there was a significant difference between the leaf dry weight of the 2 m pruning treatment and the 1 and 0.5 m pruning treatments. No significant difference was found between the 1.0 m and 2.0 m pruning treatments in the total biomass but a significant difference was found between the two treatments for leaf biomass. A significant difference (Turkey HSD comparison test, α = 0.05) was found between the 2.0 m and 0.5 m for both branches and leaves. No significant differences were found between the 1.0 and 0.5m pruning treatments. The final pruning of the trees of this experiment was conducted from September 26 to October 3, 2004. The result on biomass production for second re-growth period is presented in Figure 3. Leaves dry biomass of the 2.0 m treatment was significantly higher (Turkey HSD comparison test, α = 0.05) than that of the 1.0 and 0.5 m pruning treatment.

Figure 5

Figure 5

Leaves, branches with twigs and total dry biomass (destructively sampled) produced during the first re-growth period. Bars denote one standard deviation.

Figure 6

Figure 6

Leaves, branches with twigs and total dry biomass (destructively sampled) produced during the second re-growth period. Bars denote one standard deviation.

WATER UPTAKE

26The precipitation in Wadi Mashash experimental farm during the winter of 2002-3 and 2003-4 is presented in Figure 7.

27The total soil water content was computed to a depth of 4.2 m. The changes in the total water content during the first re-growth period showed relatively little change and are presented in Figures 8 and 9.

Figure 7

Figure 7

Monthly rainfall (mm) recorded in Wadi Mashash Experimental farm during the winter of 2002-03 and 2003-2004

Figure 8

Figure 8

Total soil water content to a depth of 4.2 m during the first re-growth period. Bars denote one standard deviation.

28For all the pruning treatments, water in the soil profile was higher at the beginning of the experiment in July and declined gradually until the end of October 2003. The highest amount of water was found in the 2.0 m followed by 1.0 m, 0.5 m and lowest in NP treatments. There was a significant difference (Turkey HSD comparison test, α = 0.05) between NP and 1.0 m and 2.0 m pruning treatments. There was no significant difference (Turkey HSD comparison test, α = 0.05) between NP and 0.5 m pruning treatment. The 1.0 m and 2.0 m pruning treatments were not significantly different. The 0.5 m pruning treatment was significantly different to 2.0 m.

29Water in the soil profile for second re-growth period (June –September 2004), is presented in Figure 9. Since two flood events occurred during the winter of 2003/4, the amount of water in the soil in the second re-growth period was higher than that of the first year. In all the pruned treatments soil water content decreased at a constant rate throughout the second re-growth period of the experiment. The rate of decrease in soil water content in the NP treatment changed in the middle of July and it became more moderate. A significant difference (Turkey HSD comparison test, α = 0.05) in soil water content was found between the NP treatment and the 1 and 2 m pruning treatments.

Figure 9

Figure 9

Total soil water content to a depth of 4.2 m during the second re-growth period Bars denote one standard deviation.

Soil Water-uptake

30Water uptake during the last five months of the first re-growth period is presented in Figure 10. The highest soil water uptake was found in 2.0 m treatment and the lowest in 0.5 m. treatment.

Figure 10

Figure 10

Water uptake to a depth of 4.2 m during the last five months of the first re-growth period. Bars denote standard deviation.

Figure11

Figure11

Water uptake to a depth of 4.2 m during the last four months of the second re-growth period Bars denote one standard deviation.

31A significant difference at the 5% level (Turkey HSD comparison test) was found between the 2.0 m treatment and the other pruning treatments. No significant difference in water uptake was found between the NP, 0.5 m and 1.0 m treatments.

32Water uptake during the second re-growth period (June – September 2004) is presented on Figure 11. The 1.0 and 2.0 m pruning treatments had no significant different in their water uptake. Water uptake in these two treatments was significantly higher (Turkey HSD comparison test, α = 0.05) when compared to the 0.5 m and the NP treatment. No significant difference was found between the NP and 0.5 m

Water Use Efficiency (CSA Measured Biomass from Trunk)

33WUE changed according to the different pruning heights (Figure 12). The lowest WUE in the first year was measured in the 2.0 m pruning treatment. The highest one was found in the 0.5 m pruning treatment. A significant difference (Turkey HSD comparison test, α = 0.05) was found only between the 2.0 m pruning and the other pruning treatments.

34WUE during the second re-growth period are presented in Figure 13. Low WUE values were measured for the 1.0 and 2.0 m pruning treatments. Unlike the first year, the NP treatments had the highest WUE values. Those values were significantly higher (Turkey HSD comparison test, α = 0.05) than those of the 1.0 m and 2.0 m pruning treatments but were not significantly different than those of the 0.5 m pruning treatment.

Figure 12

Figure 12

WUE (kg/mm/ 4 m2) for the last five months of the first re-growth period. Bars denote one standard deviation.

Figure 13

Figure 13

WUE (kg/mm/ 4 m2) for the last four months of the second re-growth period. Bars denote one standard deviation.

Conclusion

35The result of this experiment was based purely on data collected on the field at Wadi Mashash. It is worth noting that even though trees of the same age for these pruning treatments were selected, there were a few big trees that were problematic in the analysis.

Re-growth

36Re-growth of the various parts of the trees were according to the pruning height: The best growth was of the 2.0 m pruning and as the pruning height decreased, the new re-growth decreased as well (Figures 1 and 2).

Water in Soil Profile

37Water use efficiency during the first year, which can be characterized as dry year (Figure 8, July to November) was the highest in treatment 0.5 m. During the second re-growth period, which was characterized with high soil water content for a longer period of time (Figure 9), the highest WUE was found in treatment 2.0 m. In relation to these results, pruning height should be done according to the amount of water available in the soil profile.

Water Use Efficiency

38In this experiment, the best pruning height for trees was 2.0 m, followed by 1.0 m and 0.5 m, for the period after the floods (February to September 2004). This is based on the fact that higher pruning height treatments produced more biomass and having almost the same WUE (Figure 17) than lower pruning height (Figure 12 and 13).

Pruning and Biomass Production

39The best height to prune based on biomass yields (leaves and wood) in this experiment after the flood were 2.0 m, 1.0 m and 0.5 m respectively (Figs 3-6) Additional water increased the biomass of the treatments in order of their pruning heights from high to low. However, more water is needed to produce more biomass relative to the heights of pruning mentioned above. Therefore, in water scarce regions, one has to be mindful of pruning height against water use in terms of yield production because the trees pruned at higher heights in our experiment used more water. The results of this pruning experiment on height and water use was important because it determined the level of water uptake and the biomass produced by the trees. The results on biomass production in this experiment also supported the work report by Droppleman (2000) that as trees take more water as they produced more biomass.

Bibliografia

Cline-Cole, R., J.A. Falola, H.A.C Main, M.J. Mortimore, J.E. Nichol and F.D.O’Reilly, 1990. Wood Fuel in Kano, United Nations University Press, Tokyo, Japan. 124 p.

Droppelmann, K.J., Lehmann, J., Ephrath, J.E., and Berliner, P.R., 2000. Water Use Efficiency and Uptake Pattern in a Runoff Agroforestry System in an Arid Environment. Agrofor Syst 49: 223-243

Eggleton, M. D., 2002. The Effect of Water Quality, Irrigation Frequency and Runoff Flooding on Shoot and Root Development of Pollarded Acacia salicina Shrubs in an Arid Environment. M.Sc. Thesis, Albert Katz International School of Desert Studies, Ben Gurion University, Israel, pp. 1-97.

Kozlowski, T.T., 1997. Responses of Woody Plants to Flooding and Salinity. Tree Physiology Monograph No.1-Heron Publishing Victoria, Canada, pp 1-29.

Lanner, R. M., 2002. Why do Trees Live so Long: Ageing Research Reviews, 1: 653-671.

Middleton, N. and D. Thomas (eds.), 1997. World Atlas of Desertification. Second Edition. United Nations Environment Programme, Arnold Publishers, U.K., 181 p.

Ojasivi, P.R., R.K. Goyal., J.P. Gupta., 1999. The Micro-catchment Water Harvesting Technique for the Plantation of jujube (Ziziphus mauritiana) in an Agroforestry System under Arid Condition: Agricultural Water Management 41: 139-147.

Pereira, L. S., Oweis., T., Zairi, A., 2002. Irrigation Management under Water Scarcity: Agricultural Water Management, 57: 175-206

Peter, I., and Lehmann, J., 2000. Pruning Effects on Root Distribution and Nutrient Dynamics in an Acacia Hedgerow Planting in Northern Kenya. Agrofor Syst 50: 59-75.

Poorter, L., 1998. Seedling growth of Bolivian Rain Forest Tree Species in Relation to Light and Water Availability. PhD Thesis. Utrecht University, Utrecht.

Zang, B., (2003). Aboveground Biomass Partitioning and Leaf Development of Chinese Subtropical Trees following pruning: Forest Ecology and Management 173: 135-144.

Indice delle illustrazioni

Titolo Figure 1
Legenda Number of new branches during the first re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-1.jpg
File image/jpeg, 124k
Titolo Figure 2
Legenda Number of new branches during the second re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-2.jpg
File image/jpeg, 136k
Titolo Figure 3
Legenda Trunk cross-sectional area increment of A. salicina during the first re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-3.jpg
File image/jpeg, 104k
Titolo Figure 4
Legenda Trunk cross-sectional area increment of A. salicina during the second re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-4.jpg
File image/jpeg, 104k
Titolo Figure 5
Legenda Leaves, branches with twigs and total dry biomass (destructively sampled) produced during the first re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-5.jpg
File image/jpeg, 112k
Titolo Figure 6
Legenda Leaves, branches with twigs and total dry biomass (destructively sampled) produced during the second re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-6.jpg
File image/jpeg, 124k
Titolo Figure 7
Legenda Monthly rainfall (mm) recorded in Wadi Mashash Experimental farm during the winter of 2002-03 and 2003-2004
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-7.jpg
File image/jpeg, 60k
Titolo Figure 8
Legenda Total soil water content to a depth of 4.2 m during the first re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-8.jpg
File image/jpeg, 164k
Titolo Figure 9
Legenda Total soil water content to a depth of 4.2 m during the second re-growth period Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-9.jpg
File image/jpeg, 172k
Titolo Figure 10
Legenda Water uptake to a depth of 4.2 m during the last five months of the first re-growth period. Bars denote standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-10.jpg
File image/jpeg, 92k
Titolo Figure11
Legenda Water uptake to a depth of 4.2 m during the last four months of the second re-growth period Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-11.jpg
File image/jpeg, 120k
Titolo Figure 12
Legenda WUE (kg/mm/ 4 m2) for the last five months of the first re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-12.jpg
File image/jpeg, 88k
Titolo Figure 13
Legenda WUE (kg/mm/ 4 m2) for the last four months of the second re-growth period. Bars denote one standard deviation.
URL http://books.openedition.org/irdeditions/docannexe/image/2117/img-13.jpg
File image/jpeg, 87k

Autori

Wyler Department of Dryland Agriculture, French Associates Institute for Agriculture and Biotechnology of Drylands, Blaustein Institutes for Desert Research,
Ben-Gurion University of the Negev Sede Boqer Campus Sede Boqer 84990 Israel
yoni@bgu.ac.il

Albert Katz International School for Desert Studies, Blaustein Institutes for Desert Research,
Ben-Gurion University of the Negev Sede Boqer Campus Sede Boqer 84990
Department of Forestry, Gambia

Wyler Department of Dryland Agriculture, French Associates Institute for Agriculture and Biotechnology of Drylands, Blaustein Institutes for Desert Research,
Ben-Gurion University of the Negev Sede Boqer Campus Sede Boqer 84990, Israel

© IRD Éditions, 2010

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