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Biomass production and transpiration efficiencies of eucalypts in the Negev Desert
Forest Ecology and Management, 31 (1990) 81-90 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
81
Biomass Production and Transpiration Efficiencies of Eucalypts in the N e g e v Desert STANLEY R. HERWITZ1 and YITZCHAK GUTTERMAN 2 1Graduate School of Geography, Clark University, Worcester, MA 01610 (U.S.A.) 2Unit for Ecophysiology and Introduction of Desert Plants, Blaustein Institute [or Desert Research, Sede Boqer 84990 (Israel) (Accepted 20 December 1988)
ABSTRACT Herwitz, S.R. and Gutterman, Y., 1990 Biomass production and transpiration efficiencies of eucalypts in the Negev Desert. For. Ecol. Manage., 31: 81-90. The above-ground productivity and summer water-use patterns of five species of Western- and central-Australian eucalypts were examined in irrigated plantations in the northern Negev Desert of Israel. Biomass production was evaluated by whole-tree harvesting. Leaf transpiration rates were measured using a steady-state porometer. Eucalyptus salubris was considered the most efficient in its water use because it had the highest productivity (1169 kg ha -1 year -1) and the lowest transpiration rates. Eucalyptus torquata was only slightly less efficient than E. salubris. Eucalyptus woodwardii was comparable in terms of productivity but it transpired at much higher rates. Eucalyptus socialis and E. grossa were the least efficient in their water use because of their significantly lower productivity ( < 660 kg ha- ~year- ~). Of these five species, E. salubris and E. torquata appear to have the most potential for afforestation under conditions comparable to the northern Negev, where the potential evaporation rate is 2140 mm year -1, the soil is a calcareous loam, the mean annual rainfall is about 100 ram, and trickle irrigation provides a supplement of 150 mm year -~.
INTRODUCTION E u c a l y p t s are widely p l a n t e d in d r y l a n d e n v i r o n m e n t s b e c a u s e of t h e i r r a p i d g r o w t h r a t e s a n d t h e i r ability to w i t h s t a n d d r o u g h t s t r e s s ( P r y o r , 1976; J a c o b s , 1981; S a n d e l l et al., 1986; C h a m s h a m a a n d H a l l , 1987). T h e i n t r o d u c t i o n of e u c a l y p t s h a s b e e n criticized b e c a u s e o f t h e i r p u r p o r t e d a d v e r s e effects o n soils, a n d b e c a u s e t h e y are c o n s i d e r e d t h i r s t y t r e e s w h i c h are u n e c o n o m i c a l in t h e i r use of w a t e r r e s o u r c e s ( S h i v a a n d B a n d y o p a d h y a y , 1983; Joyce, 1988). T h e r e are, however, m o r e t h a n 500 species of E u c a l y p t u s ( B r o o k e r a n d Kleinig, 1983), a n d it is unlikely t h a t t h e s e g e n e r a l i z a t i o n s are applicable to all e u c a l y p t s ( P o o r e a n d Fries, 1985; Calder, 1986). M o s t o f t h e species of E u c a l y p t u s p l a n t e d in
0378-1127/90/$03.50
© 1990 Elsevier Science Publishers B.V.
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S.Z. HERWITZ AND Y. GUTTERMAN
dryland environments outside of Australia are adapted to rainfall conditions of more than 400 mm year- 1 (Jacobs, 1981). Our study was concerned with possible differences in the water-use efficiencies of slower-growing but more drought-resistant species of Eucalyptus adapted to mean annual rainfall totals of less than 300 mm. Pallardy (1981) has reviewed the abundant evidence for genotypic differences in the water relations of closely related woody plants (e.g., conspecifics as well as congeners). Tree species that effectively regulate their stomata and efficiently use water for the production of biomass would be most desirable for dryland afforestation, particularly if the trees have the benefit of irrigation during dry periods (Armitage, 1985 ). Significant differences in the control of water loss from different species of eucalypts have been previously documented in potted seedlings (Quraishi and Kramer, 1970; Gindel, 1971 ), and in experimental and natural stands in Western Australia (Greenwood and Beresford, 1979; Colquhoun et al., 1984). This paper reports on growth trials of five species of Western and central Australia eucalypts that were planted in the northern Negev Desert of Israel where they were exposed to identical environmental conditions and trickleirrigation treatments. The five species were E. grossa F. Muell. ex Benth., E. salubris F. Muell., E. socialis F. Muell. ex Miq., E. torquata Luehm., and E. woodwardii Maiden. The objective of our study was to provide information on above-ground productivity and transpiration, which could assist in the selection of suitable species for planting in arid environments. The null hypothesis was that the transpiration efficiencies of the five selected species were not significantly different. MATERIALS AND METHODS
Four of the five species, E. grossa, E. salubris, E. torquata and E. woodwardii, occur east of Perth in the southern part of Western Australia (Chippendale, 1973; Keighery et al., 1980) where the mean annual rainfall is about 250 mm and the mean annual maximum daily temperature is 25 °C (Hall et al., 1981 ). Eucalyptus socialis is a more widely distributed species, occurring from New South Wales to Western Australia (Mitchell, 1980). The seed provenance of E. socialis used in our study was central Australia near Alice Springs. Seeds of the five species were collected in their native habitats and germinated under greenhouse conditions at the Fohs Botanical Garden in Sede Boqer in the northern Negev Desert (30°53'N, 34°46'E, 480 m above sea level), where the mean annual rainfall is 105 mm, the mean annual maximum daily temperature is 24.7 ° C, and the potential evaporation rate is 2140 mm year-1 (Zangvil and Druian, 1983). Seedlings representing each species were planted roughly one year after germination in two experimental field plots on loessial plain deposits in the Botanical Garden. Eleven individuals of each species (ex-
BIOMASS PRODUCTION AND TRANSPIRATION EFFICIENCIES OF EUCALYPTS
83
cept E. socialis which was represented by ten) were planted in plot 1 in the northern part of the Garden, and two individuals of each species were planted in plot 2 in the southern part. The average spacing between trees was 2 m, equivalent to a density of 2500 trees h a - 1. The loessial soil of the northern Negev is a calcareous fine-grained sandy loam with a relatively low soluble-salt content in the upper layers (BidnerBarhava and Ramati, 1967; Evenari et al., 1968; Dan et al., 1973; Yaalon and Dan, 1974). The trickle-irrigation system in the two plots consisted of one emitter at the base of each tree, which supplied water at a rate of 6 + 2 1 h - 1. During the July/August study period, the mean frequency of irrigation was once every 10 days and the mean duration of each irrigation day was 2.9 h, resulting in inputs of 17 + 6 1 tree- 1. The annual irrigation input amounted to about 600 1 tree- 1 year- 1. Assuming a plantation density of 2500 trees h a - 1, this input would be equivalent to 150 m m year- 1. Above-ground biomass production was assessed by harvesting the trees in plot I during the summer of 1986, 20 months after planting. Heights and stem diameters were measured at the time of the harvest. The vegetative matter was oven-dried at 80 ° C for 48 h prior to weighing. The proportion of above-ground biomass allocated to leaf (including petioles), branch, and stem tissue was determined for each tree. Since litterfall and herbivory were negligible during the 20-month trial period, the annual above-ground productivity of each species was evaluated on the basis of the harvested biomass. Extrapolating to a stand density of 2500 trees h a - 1, the above-ground productivity was expressed in kg h a - 1 year- 1. The leaf area of each tree was computed from its leaf biomass using mean surface-area:dry-weight ratios determined for each species. Interspecific differences were tested using the Kruskal-Wallis one-way analysis of variance by ranks (Siegel, 1956). The water-use patterns of the five species were examined in plot 2, where the trees were the same age and approximately the same size as the harvested trees in plot 1, having been exposed to the same environmental conditions and irrigation treatments, and it was assumed that their transpiration rates were representative of each species. Stomatal resistances and leaf transpiration rates were measured using a LI-1600 steady-state porometer (LI-COR Inc., Lincoln, Nebraska). The measured transpiration rates were corrected for differences in the aerodynamic leaf boundary-layer resistance in the sampling cuvette as compared with the open environment (Herwitz et al., 1988a). The corrections were made on the basis of the known boundary-layer resistance of a leaf in the LI-1600, the mean leaf width of each species, and the windspeed at the time of the porometer measurement (Goudriaan, 1977; Herwitz et al., 1988b). Since all five species are amphistomatous, the porometer measurements were made on both the adaxial and abaxial leaf surfaces. The sampling routine during the 2-month study period consisted of hourly measurements made on four
84
S.Z. HERWITZ AND Y. GUTTERMAN
leaves of each species (two leaves from each of the two trees) on the different days after irrigation (I1 to/lo, where In is the number of days after irrigation). The daily courses of transpiration were obtained by plotting the hourly means as a function of time of day. The transpiration data after/4 were aggregated to give 2-day mean values for/5 and Is,/7 and Is, and/9 and Ilo because these days were less-intensively sampled. Planimetric integration of the areas under the courses of transpiration gave the daily rates of water loss per unit leaf area. Transpiration efficiencies were assessed by considering the above-ground productivity of the five species in relation to their summer transpiration rates. The dry summer months of July through August represent the period of the highest evaporative demand in the Negev, with Class-A pan evaporation rates averaging 9 mm day- ~ (Zangvil and Druian, 1983 ). We assumed that the transpiration values were representative of the relative degree of stomatal control exhibited by each species under the irrigated trial conditions. The integrated daily transpiration rates from 11 to Ilo were summed to give the average rate of water loss for each irrigation cycle (i.e., the 10-day period between irrigation days ). Those species with relatively high rates of biomass production and low transpiration values were considered to have the higher transpiration efficiencies. RESULTS
Biomass production On the basis of all the harvested trees, the mean standing biomass of each tree was 666 g. The mean values for each species ranged from 371 (E. grossa ) to 855 g tree-1 ( E. salubris ) , with E. saIubris, E. torquata and E. woodwardii the most productive species. Each of these species produced > 1.6 X more aboveground biomass per tree than E. socialis and > 2 X more than E. grossa. The mean annual above-ground productivity based on all harvested trees was equivalent to 910 kg ha-1 year-1. For E. salubris the mean productivity was equivalent to 1169 kg h a - 1year- 1 (Table 1 ), production of leaf tissue was equivalent to 725 kg ha-1 year-1, and of woody tissue, to 444 kg ha-~ year-1. Although E. woodwardii produced less total above-ground biomass, it had the highest rate of woody biomass production (485 kg h a - 1 year- ~). The Kruskal-Wallis test indicated that the five species were significantly different in their heights (P < 0.001 ), stem diameters ( P < 0.05), and aboveground biomass (P<0.001). The species also were significantly different in both the absolute quantities and the relative proportions of biomass allocated to stem, branch and leaf tissue (Fig. 1 ). Eucalyptus woodwardii allocated the highest proportion of its above-ground biomass (43%) to woody tissue; E. sal-
85
BIOMASS P R O D U C T I O N A N D TRANSPIRATION EFFICIENCIES OF EUCALYPTS TABLE
I
Mean ( -+SE) dimensions and above-ground productivityof the trialspecies
Height(cm) Stem diameter (cm) ~ Number ofleaves tree -1 Leaf-area: mass ratio (cm 2 g - 1) Leaf area (m2 t r e e - l ) b Productivity (kg ha- 1 year - 1) Stem
E. grossa
E. salubris
E. socialis
67 -+6 1.6+_0.2 198 + _ 5 7 25.8 0.7+_0.2
125 -+7 2.3+_0.2 2020 +_401 40.7 2.2+0.4
80 -+5 109 -+6 1.7+_0.1 2.3+_0.2 1012 +_121 1287 +_168 29.3 36.8 1.0+_0.1 1.9+_0.2
70 +_18 194 79 +_29 250 359 +_102 725 508 +_149 1169
Branch Leaf
Total
+_33 +_66 +_145 -+240
81 117 454 652
E. torquata
+_10 +_15 -+55 +_78
167 217 690 1074
+_27 +_26 +_90 +141
E. woodwardii 169 +14 2.2+_0.2 298 +_55 28.0 1.3+_0.2 336 149 643 1128
+_64 +_33 +_120 +_213
"Measured 3 cm above ground surface. bOne-sided leaf surface area. Stem
Branches
i
i
i
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Leaves
i
q
u
n
i
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.................................................
E. s a l u b r i s
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....... •
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E grossa
E torquata
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80
Aboveground biomass (%)
Fig. 1. Mean proportions of above-ground biomass allocated t o s t e m , branch and leaf tissue.
ubris and E. torquata allocated 38% and 36%, respectively, to woody biomass. The species which allocated the lowest proportion of its biomass to woody tissue (29%) and the highest proportion to leaf tissue (71%) was E. grossa. Transpiration Figure 2 shows the daily courses of transpiration of the five species on/i when the summer soil-moisture conditions were highest. All of the species had peak mean hourly transpiration rates > 2 pg c m -2 s -]. The species with the highest peak hourly rate on/i was E. woodwardii (5.06 #g c m -2 s -] ), followed by E. grossa and E. torquata, with E. salubris and g. socialis the lowest. Oscil-
lations in stomatal resistance, been previously noted in eucalypts (Teoh and Palmer, 1971 ), were evident through the afternoon hours. But in general, the daily course under the well-watered conditions of I~ and/2 showed a rapid increase through the early morning hours followed by a late-morning or earlyafternoon peak rate. Transpiration ceased in the early evening when the pho-
86
s.z. HERWITZAND Y. GUTTERMAN i
i
5
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~2
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-
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8
12
16
20
Time of day (h)
Fig. 2. Courses of leaf transpiration of the five species on 11.
TABLE 2
Integrated leaf transpiration rates on selected days after irrigation (I.) and for the entire 10-day period between irrigation days Transpiration (mg cm -2 day -1) I1
/2
/5
Transpiration (mg cm -2 cycle- 1)a 11o
/~-1o E. E. E. E. E.
grossa salubris socialis torquata woodwardii
95 70 53 89 126
59 40 26 39 65
28 20 36 25 34
26 19 36 29 31
379 276 381 351 482
aCycle refers to the 10-day period between irrigation days.
tosynthetically active radiation was < 20 Hmol m - 2 s - 1. The daily courses be came increasingly flattened, with peak transpiration rates occurring earlier in the morning on successive days after irrigation. Relationships between measured rates and leaf water-potentials were discussed by Herwitz et al. (1988b). Table 2 shows the integrated daily transpiration rates on/1, I2, I5 and 11o, and the sum for the entire 10-day period 11-11o. The transpiration rates of E. grossa, E. salubris, E. torquata and E. woodwardii decreased dramatically from 11 to I4, reaching a more asymptotic decrease from 14 to Ilo. Eucalyptus socialis maintained much more constant transpiration rates through the 10-day period after irrigation. On 11, the integrated daily transpiration rates ranged from 53 mg cm -2 day -1 for E. socialis to 126 for E. woodwardii (Table 2). By 11o, the transpiration rates of all the species except E. socialis were < 33% of the rates on 11. The transpiration losses over the first 2 days after irrigation (I1 and I2)
t~IOMASSPRODUCTION AND TRANSPIRATION EFFICIENCIES OF EUCALYPTS
87
ranged from only 21% (E. socialis) to as much as 41% (E. grossa) of the total loss at the end of the 10-day period. The sum of the integrated daily transpiration losses ranged from 276 mg cm -2 cycle -1 for E. salubris to 482 for E. woodwardii (Table 2). The other three species transpired at rates ranging only from 351 to 381 mg cm -2 cycle- 1
Transpiration efficiency The relationship between above-ground productivity and the integrated summer-transpiration values provided a useful index of transpiration efficiency. This relationship indicated that E. salubris was the most efficient species (Fig. 3A ). Eucalyptus salubris transpired at the lowest rates and produced the greatest amount of biomass, with E. torquata only slightly less efficient. Eucalyptus woodwardii produced comparable amounts of biomass but transpired at higher rates, whereas E. socialis and E. grossa transpired at lower rates than E. woodwardii but produced significantly less biomass. It is not known to what extent the transpiration rates per unit leaf area were affected by differences in whole-tree leaf area. The results shown in Fig. 3 are supported by Gindel's (1971) finding that the transpiration rates of some other dryland species of Eucalyptus were not significantly affected by differences in leaf area. However, to illustrate the differences in whole-tree leaf area among the five species in our study, the transpiration values were normalized on the basis of the mean whole-tree leaf area of each species. Figure 3B shows the normalized transpiration values (mg cm -2 cycle-1) per m 2 of whole-tree leaf area. Some slight differences in the relative positions of the data points are evident; E. grossa and E. socialis are more clearly the least efficient of the spei
{
E. salubris
1200
i
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E. woodwardii
'L
®
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( ~ E woodwardii
®
E. torquata
1000 ~
I
E, salubns
E. torquata
g >, >
800
® E.sooia,s
"o
£
a_
® E. sociahs
6O£
A
( ~ E. grossa
E. grossa(~
B 400 200
I 300
I 4o0
Transpiration (mg
I 5o0
cm2 cycle 1)
I 100
1 2o0
I 3oo
I 4oo
I 50o
600
Normalized (mg cm 2 cycle.1 m ~)
Fig. 3. T h e relationship between aboveground productivity a n d the integrated summer-transpiration rates as an index of t r a n s p i r a t i o n efficiency. (A) Before, a n d ( B ) after normalization of the t r a n s p i r a t i o n data.
88
S.Z. HERWITZ AND Y. GUTTERMAN
cies examined because they produced the least amount ofbiomass and, for their given whole-tree leaf areas, they transpired at the highest rates. DISCUSSION Afforestation in dryland environments is a land-use activity that is likely to continue at an increasing rate over the next several decades (Armitage, 1985; Salem and Palmberg, 1985). Some workers have noted that multipurpose indigenous tree species may meet the needs of the local human populations in developing countries better than exotic species (Allen, 1986; De Troyer, 1986). However, the advantages of indigenous species may not necessarily include rapid growth and high transpiration efficiencies. Where rapid growth is a high priority, exotic species such as eucalypts probably will continue to be selected (Jacobs, 1981; Burley, 1982). Several studies recently have reported on the performances of exotic tree species in various geographic localities including India (Calder, 1986; Nimbkar et al., 1986), Tanzania (Allen, 1986; Chamshama and Hall, 1987), Somalia (Zollner, 1986), and Nigeria (Buckley, 1988). Among the most commonly introduced and studied dryland eucalypts are the species E. camaldulensis and E. tereticornis (Jacobs, 1981 ). Our study represented a consideration of some lesser-known eucalypt species. On the basis of our above-ground productivity and transpiration data, we reject the null hypothesis of no significant differences in the transpiration efficiencies of the five selected species. Of the species examined, E. salubris and E. torquata appear to have the greatest potential for afforestation under conditions comparable to the northern Negev, where the potential evaporation rate is 2140 mm year-1, the soil is a calcareous loam, the mean annual rainfall is about 100 mm, and a trickle irrigation system provides an additional 150 mm year-1. These two species made the most efficient use of the available water resources. Eucalyptus woodwardii, which allocated the highest proportion of its biomass to woody tissue, was found to be more productive than E. torquata, but it was less economical in its water use. Eucalyptus socialis and E. grossa were the least efficient in their water use because of their significantly lower productivity. Booth et al. (1988) have discussed the importance of defining the ecological niches of exotics in their native habitats to assist in the selection of appropriate species for introduction. The interspeciflc differences in water-use efficiency found in our study presumably correspond to ecophysiological characteristics which have adaptive value under natural conditions in Australia. These characteristics persist when the species are introduced as exotics. In the case of E. salubris and E. torquata, their high transpiration efficiencies in the Negev may reflect their adaptation to the Goldfields region of Western Australia near Coolgardie, where these two species are sympatric (Keighery et al., 1980).
BIOMASSPRODUCTIONANDTRANSPIRATIONEFFICIENCIESOF EUCALYPTS
89
In a study of the growth performances of selected eucalypts and other dryland tree species in Central Australia, Sandell et al. (1986) concluded that, with the judicious selection of species and provenances, tree productivity could be enhanced. Our comparative study in the Negev evaluated the performance of species on the basis of their relative transpiration efficiencies. We conclude that comparative studies of the kind reported here may assist in the selection of species which will make the most efficient use of the available water resources while satisfying the demand for tree production in arid environments. ACKNOWLEDGEMENTS
We thank Shmoulek Hadjes, Yochai Samish, and Shlomo Feingold for their help in the field, and Ian Brooker and John Zwar for providing useful information on the eucalypts of western and central Australia. We also acknowledge the logistical support provided by the Unit for the Ecophysiology and Introduction of Desert Plants at the Blaustein Institute for Desert Research. This study was supported by grants from Clark University and the Blaustein International Center. REFERENCES Allen, J.C., 1986. Soil properties and fast-growing tree species in Tanzania. For. Ecol. Manage., 16: 127-147. Armitage, F.B., 1985. Irrigated Forestry in Arid and Semi-Arid Lands: A Synthesis. International Development Research Centre, Ottawa, 160 pp. Bidner-Barhava, N. and Ramati, B., 1967. The tolerance of some species of Eucalyptus, Pinus and other forest trees to soil salinity and low soil moisture in the Negev. Israel J. Agric. Res., 17: 65-76. Booth, T.H., Nix, H.A., Hutchinson, M.F. and Jovanovic, T., 1988. Niche analysis and tree species introduction. Forest Ecol. Manage., 23: 47-59. Brooker, M.I.H. and Kleinig, D.A., 1983. Field Guide to Eucalypts. Vol. 1, South-Eastern Australia. Inkata Press, Melbourne, 288 pp. Buckley, G.P., 1988. Soil factors influencing yields of Eucalyptus camaldulensis on former tinmining land in the Jos Plateau region, Nigeria. For. Ecol. Manage., 23: 1-17. Burley, J., 1982. Obstacles to tree planting in arid and semi-arid lands: comparative case studies from India and Kenya. United Nations University, Tokyo, 52 pp. Calder, I.R., 1986. Water use of eucalypts - a review with special reference to South India. Agric. Water Manage., 11: 333-342. Chamshama, S.A.O. and Hall, J.B., 1987. Effects of site preparation and fertilizer application at planting on Eucalyptus tereticornis at Morogoro, Tanzania. For. Ecol. Manage., 18: 103-112. Chippendale, G.M., 1973. Eucalypts of the Western Australian goldfields (and the adjacent wheatbelt). Department of Primary Industry, Forestry and Timber Bureau/Australian Government Publishing Service, Canberra. Colquhoun, I.J., Ridge, R.W., Bell, D.T., Loneragan, W.A. and Kuo, J., 1984. Comparative studies in selected species of Eucalyptus used in rehabilitation of the northern jarrah forest, Western Australia. I. Patterns of xylem pressure potential and diffusive resistance of leaves. Aust. J. Bot., 32: 367-373. Dan, J., Moshe, R. and Alperovitch, N., 1973. The soils of Sede Zin. Israel J. Earth Sci., 22: 211227.
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De Troyer, C., 1986. Desertification control in the Sudanian and Sahelian zones of West Africa Better management of the renewable resource base. For. Ecol. Manage., 16: 233-241. Evenari, M., Shanan, L. and Tadmor, N.H., 1968. Runoff farming in the desert. I. Experimental layout. Agron. J., 60: 29-32. Gindel, I., 1971. Transpiration in three Eucalyptus species as a function of solar energy, soil moisture and leaf area. Physiol. Plant., 24: 143-149. Goudriaan, J., 1977. Crop micrometeorology: A simulation study. Centre for Agricultural Publishing and Documentation, Wageningen, The Netherlands. Greenwood, E.A.N. and Beresford, J.D., 1979. Evaporation from vegetation in landscapes developing secondary salinity using the ventilated-chamber technique: I. Comparative transpiration from juvenile Eucalyptus above saline groundwater seeps. J. Hydrol., 42: 369-382. Hall, N., Wainwright, R.W. and Wolf, L.J., 1981. Summary of meteorological data in Australia. CSIRO For. Res. Div. Rep., No. 6. Herwitz, S.R., Yair, A. and Shachak, M., 1988a. Water use patterns of introduced carob trees (Ceratonia siliqua L.) on rocky hillslopes in the Negev Desert. J. Arid Environ., 14: 83-92. Herwitz, S.R., Gutterman, Y. and Srinivasan, R., 1988b. Comparative transpiration of irrigated juvenile eucalypts in the Negev Desert. Irrig. Sci., 9: 233-247. Jacobs, M.R., 1981. Eucalypts for Planting. FAO, Rome, Forestry Series No. 11,677 pp. Joyce, C., 1988. The tree that caused a riot. New Sci., 117: 54-59. Keighery, G.J., Goff, J. and Marchant, N.G., 1980. Notes on the biology and phytogeography of Western Australian plants. Parts 9-10: Eucalyptus species (Myrtaceae). Kings Park and Botanic Garden, Perth, Australia. Mitchell, A.S., 1980. Eucalypts of Central Australia. Conservation Commission of the Northern Territory, Alice Springs, Tech. Bull. No. 3. Nimbkar, B.V., Nimbkar, N. and Zende, N., 1986. Desertification of Western Maharashtra: Causes and possible solutions. I. Comparative growth of eight tree species. For. Ecol. Manage., 16: 243-251. Pallardy, S.G., 1981. Closely related woody plants. In: T.T. Kozlowski (Editor), Water Deficits and Plant Growth. Academic Press, New York, pp. 511-548. Poore, M.E.D. and Fries, C., 1985. The ecological effects of eucalyptus. FAO, Rome, For. Pap. 59, 87 pp. Pryor, L.D., 1976. The Biology of Eucalypts. Studies in Biology No. 61. Institute of Biology/ Edward Arnold, London, 82 pp. Quraishi, M.A. and Kramer, P.J., 1970. Water stress in three species of Eucalyptus. For. Sci., 16: 74-78. Salem, B.B. and Palmberg, C., 1985. Place and role of trees and shrubs in dry areas. In: G.E. Wickens, J.R. Goodin and D.V. Field (Editors), Plants for Arid Lands. Allen and Unwin, London, pp. 93-102. Sandell, P., Kube, P. and Chuk, M., 1986. Dryland tree establishment in Central Australia. For. Ecol. Manage., 16: 411-422. Shiva, V. and Bandyopadhyay, J., 1983. Eucalyptus - a disastrous tree for India. Ecologist, 13: 184-187. Siegel, S., 1956. Nonparametric Statistics for the Behavioral Sciences. McGraw-Hill, New York. Teoh, C.T. and Palmer, J.H., 1971. Nonsynchronized oscillations in stomatal resistance among sclerophylls of Eucalyptus umbra. Plant Physiol., 47:409-411. Yaalon, D.H. and Dan, J., 1974. Accumulation and distribution of loess-derived deposits in the semi-desert and desert fringe areas of Israel. Z. Geomorphol. Suppl., 20:91-105. Zangvil, A. and Druian, P., 1983. Meteorological data for Sede Boqer. Blaustein Institute for Desert Research, Sede Boqer, Israel, Desert Meteorol. Pap. Ser. A, No. 8. Zollner, D., 1986. Sand dune stabilization in central Somalia. For. Ecol. Manage., 16: 223-232.
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Biomass Production and Transpiration Efficiencies of Eucalypts in the N e g e v Desert STANLEY R. HERWITZ1 and YITZCHAK GUTTERMAN 2 1Graduate School of Geography, Clark University, Worcester, MA 01610 (U.S.A.) 2Unit for Ecophysiology and Introduction of Desert Plants, Blaustein Institute [or Desert Research, Sede Boqer 84990 (Israel) (Accepted 20 December 1988)
ABSTRACT Herwitz, S.R. and Gutterman, Y., 1990 Biomass production and transpiration efficiencies of eucalypts in the Negev Desert. For. Ecol. Manage., 31: 81-90. The above-ground productivity and summer water-use patterns of five species of Western- and central-Australian eucalypts were examined in irrigated plantations in the northern Negev Desert of Israel. Biomass production was evaluated by whole-tree harvesting. Leaf transpiration rates were measured using a steady-state porometer. Eucalyptus salubris was considered the most efficient in its water use because it had the highest productivity (1169 kg ha -1 year -1) and the lowest transpiration rates. Eucalyptus torquata was only slightly less efficient than E. salubris. Eucalyptus woodwardii was comparable in terms of productivity but it transpired at much higher rates. Eucalyptus socialis and E. grossa were the least efficient in their water use because of their significantly lower productivity ( < 660 kg ha- ~year- ~). Of these five species, E. salubris and E. torquata appear to have the most potential for afforestation under conditions comparable to the northern Negev, where the potential evaporation rate is 2140 mm year -1, the soil is a calcareous loam, the mean annual rainfall is about 100 ram, and trickle irrigation provides a supplement of 150 mm year -~.
INTRODUCTION E u c a l y p t s are widely p l a n t e d in d r y l a n d e n v i r o n m e n t s b e c a u s e of t h e i r r a p i d g r o w t h r a t e s a n d t h e i r ability to w i t h s t a n d d r o u g h t s t r e s s ( P r y o r , 1976; J a c o b s , 1981; S a n d e l l et al., 1986; C h a m s h a m a a n d H a l l , 1987). T h e i n t r o d u c t i o n of e u c a l y p t s h a s b e e n criticized b e c a u s e o f t h e i r p u r p o r t e d a d v e r s e effects o n soils, a n d b e c a u s e t h e y are c o n s i d e r e d t h i r s t y t r e e s w h i c h are u n e c o n o m i c a l in t h e i r use of w a t e r r e s o u r c e s ( S h i v a a n d B a n d y o p a d h y a y , 1983; Joyce, 1988). T h e r e are, however, m o r e t h a n 500 species of E u c a l y p t u s ( B r o o k e r a n d Kleinig, 1983), a n d it is unlikely t h a t t h e s e g e n e r a l i z a t i o n s are applicable to all e u c a l y p t s ( P o o r e a n d Fries, 1985; Calder, 1986). M o s t o f t h e species of E u c a l y p t u s p l a n t e d in
0378-1127/90/$03.50
© 1990 Elsevier Science Publishers B.V.
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S.Z. HERWITZ AND Y. GUTTERMAN
dryland environments outside of Australia are adapted to rainfall conditions of more than 400 mm year- 1 (Jacobs, 1981). Our study was concerned with possible differences in the water-use efficiencies of slower-growing but more drought-resistant species of Eucalyptus adapted to mean annual rainfall totals of less than 300 mm. Pallardy (1981) has reviewed the abundant evidence for genotypic differences in the water relations of closely related woody plants (e.g., conspecifics as well as congeners). Tree species that effectively regulate their stomata and efficiently use water for the production of biomass would be most desirable for dryland afforestation, particularly if the trees have the benefit of irrigation during dry periods (Armitage, 1985 ). Significant differences in the control of water loss from different species of eucalypts have been previously documented in potted seedlings (Quraishi and Kramer, 1970; Gindel, 1971 ), and in experimental and natural stands in Western Australia (Greenwood and Beresford, 1979; Colquhoun et al., 1984). This paper reports on growth trials of five species of Western and central Australia eucalypts that were planted in the northern Negev Desert of Israel where they were exposed to identical environmental conditions and trickleirrigation treatments. The five species were E. grossa F. Muell. ex Benth., E. salubris F. Muell., E. socialis F. Muell. ex Miq., E. torquata Luehm., and E. woodwardii Maiden. The objective of our study was to provide information on above-ground productivity and transpiration, which could assist in the selection of suitable species for planting in arid environments. The null hypothesis was that the transpiration efficiencies of the five selected species were not significantly different. MATERIALS AND METHODS
Four of the five species, E. grossa, E. salubris, E. torquata and E. woodwardii, occur east of Perth in the southern part of Western Australia (Chippendale, 1973; Keighery et al., 1980) where the mean annual rainfall is about 250 mm and the mean annual maximum daily temperature is 25 °C (Hall et al., 1981 ). Eucalyptus socialis is a more widely distributed species, occurring from New South Wales to Western Australia (Mitchell, 1980). The seed provenance of E. socialis used in our study was central Australia near Alice Springs. Seeds of the five species were collected in their native habitats and germinated under greenhouse conditions at the Fohs Botanical Garden in Sede Boqer in the northern Negev Desert (30°53'N, 34°46'E, 480 m above sea level), where the mean annual rainfall is 105 mm, the mean annual maximum daily temperature is 24.7 ° C, and the potential evaporation rate is 2140 mm year-1 (Zangvil and Druian, 1983). Seedlings representing each species were planted roughly one year after germination in two experimental field plots on loessial plain deposits in the Botanical Garden. Eleven individuals of each species (ex-
BIOMASS PRODUCTION AND TRANSPIRATION EFFICIENCIES OF EUCALYPTS
83
cept E. socialis which was represented by ten) were planted in plot 1 in the northern part of the Garden, and two individuals of each species were planted in plot 2 in the southern part. The average spacing between trees was 2 m, equivalent to a density of 2500 trees h a - 1. The loessial soil of the northern Negev is a calcareous fine-grained sandy loam with a relatively low soluble-salt content in the upper layers (BidnerBarhava and Ramati, 1967; Evenari et al., 1968; Dan et al., 1973; Yaalon and Dan, 1974). The trickle-irrigation system in the two plots consisted of one emitter at the base of each tree, which supplied water at a rate of 6 + 2 1 h - 1. During the July/August study period, the mean frequency of irrigation was once every 10 days and the mean duration of each irrigation day was 2.9 h, resulting in inputs of 17 + 6 1 tree- 1. The annual irrigation input amounted to about 600 1 tree- 1 year- 1. Assuming a plantation density of 2500 trees h a - 1, this input would be equivalent to 150 m m year- 1. Above-ground biomass production was assessed by harvesting the trees in plot I during the summer of 1986, 20 months after planting. Heights and stem diameters were measured at the time of the harvest. The vegetative matter was oven-dried at 80 ° C for 48 h prior to weighing. The proportion of above-ground biomass allocated to leaf (including petioles), branch, and stem tissue was determined for each tree. Since litterfall and herbivory were negligible during the 20-month trial period, the annual above-ground productivity of each species was evaluated on the basis of the harvested biomass. Extrapolating to a stand density of 2500 trees h a - 1, the above-ground productivity was expressed in kg h a - 1 year- 1. The leaf area of each tree was computed from its leaf biomass using mean surface-area:dry-weight ratios determined for each species. Interspecific differences were tested using the Kruskal-Wallis one-way analysis of variance by ranks (Siegel, 1956). The water-use patterns of the five species were examined in plot 2, where the trees were the same age and approximately the same size as the harvested trees in plot 1, having been exposed to the same environmental conditions and irrigation treatments, and it was assumed that their transpiration rates were representative of each species. Stomatal resistances and leaf transpiration rates were measured using a LI-1600 steady-state porometer (LI-COR Inc., Lincoln, Nebraska). The measured transpiration rates were corrected for differences in the aerodynamic leaf boundary-layer resistance in the sampling cuvette as compared with the open environment (Herwitz et al., 1988a). The corrections were made on the basis of the known boundary-layer resistance of a leaf in the LI-1600, the mean leaf width of each species, and the windspeed at the time of the porometer measurement (Goudriaan, 1977; Herwitz et al., 1988b). Since all five species are amphistomatous, the porometer measurements were made on both the adaxial and abaxial leaf surfaces. The sampling routine during the 2-month study period consisted of hourly measurements made on four
84
S.Z. HERWITZ AND Y. GUTTERMAN
leaves of each species (two leaves from each of the two trees) on the different days after irrigation (I1 to/lo, where In is the number of days after irrigation). The daily courses of transpiration were obtained by plotting the hourly means as a function of time of day. The transpiration data after/4 were aggregated to give 2-day mean values for/5 and Is,/7 and Is, and/9 and Ilo because these days were less-intensively sampled. Planimetric integration of the areas under the courses of transpiration gave the daily rates of water loss per unit leaf area. Transpiration efficiencies were assessed by considering the above-ground productivity of the five species in relation to their summer transpiration rates. The dry summer months of July through August represent the period of the highest evaporative demand in the Negev, with Class-A pan evaporation rates averaging 9 mm day- ~ (Zangvil and Druian, 1983 ). We assumed that the transpiration values were representative of the relative degree of stomatal control exhibited by each species under the irrigated trial conditions. The integrated daily transpiration rates from 11 to Ilo were summed to give the average rate of water loss for each irrigation cycle (i.e., the 10-day period between irrigation days ). Those species with relatively high rates of biomass production and low transpiration values were considered to have the higher transpiration efficiencies. RESULTS
Biomass production On the basis of all the harvested trees, the mean standing biomass of each tree was 666 g. The mean values for each species ranged from 371 (E. grossa ) to 855 g tree-1 ( E. salubris ) , with E. saIubris, E. torquata and E. woodwardii the most productive species. Each of these species produced > 1.6 X more aboveground biomass per tree than E. socialis and > 2 X more than E. grossa. The mean annual above-ground productivity based on all harvested trees was equivalent to 910 kg ha-1 year-1. For E. salubris the mean productivity was equivalent to 1169 kg h a - 1year- 1 (Table 1 ), production of leaf tissue was equivalent to 725 kg ha-1 year-1, and of woody tissue, to 444 kg ha-~ year-1. Although E. woodwardii produced less total above-ground biomass, it had the highest rate of woody biomass production (485 kg h a - 1 year- ~). The Kruskal-Wallis test indicated that the five species were significantly different in their heights (P < 0.001 ), stem diameters ( P < 0.05), and aboveground biomass (P<0.001). The species also were significantly different in both the absolute quantities and the relative proportions of biomass allocated to stem, branch and leaf tissue (Fig. 1 ). Eucalyptus woodwardii allocated the highest proportion of its above-ground biomass (43%) to woody tissue; E. sal-
85
BIOMASS P R O D U C T I O N A N D TRANSPIRATION EFFICIENCIES OF EUCALYPTS TABLE
I
Mean ( -+SE) dimensions and above-ground productivityof the trialspecies
Height(cm) Stem diameter (cm) ~ Number ofleaves tree -1 Leaf-area: mass ratio (cm 2 g - 1) Leaf area (m2 t r e e - l ) b Productivity (kg ha- 1 year - 1) Stem
E. grossa
E. salubris
E. socialis
67 -+6 1.6+_0.2 198 + _ 5 7 25.8 0.7+_0.2
125 -+7 2.3+_0.2 2020 +_401 40.7 2.2+0.4
80 -+5 109 -+6 1.7+_0.1 2.3+_0.2 1012 +_121 1287 +_168 29.3 36.8 1.0+_0.1 1.9+_0.2
70 +_18 194 79 +_29 250 359 +_102 725 508 +_149 1169
Branch Leaf
Total
+_33 +_66 +_145 -+240
81 117 454 652
E. torquata
+_10 +_15 -+55 +_78
167 217 690 1074
+_27 +_26 +_90 +141
E. woodwardii 169 +14 2.2+_0.2 298 +_55 28.0 1.3+_0.2 336 149 643 1128
+_64 +_33 +_120 +_213
"Measured 3 cm above ground surface. bOne-sided leaf surface area. Stem
Branches
i
i
i
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Leaves
i
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i
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E torquata
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80
Aboveground biomass (%)
Fig. 1. Mean proportions of above-ground biomass allocated t o s t e m , branch and leaf tissue.
ubris and E. torquata allocated 38% and 36%, respectively, to woody biomass. The species which allocated the lowest proportion of its biomass to woody tissue (29%) and the highest proportion to leaf tissue (71%) was E. grossa. Transpiration Figure 2 shows the daily courses of transpiration of the five species on/i when the summer soil-moisture conditions were highest. All of the species had peak mean hourly transpiration rates > 2 pg c m -2 s -]. The species with the highest peak hourly rate on/i was E. woodwardii (5.06 #g c m -2 s -] ), followed by E. grossa and E. torquata, with E. salubris and g. socialis the lowest. Oscil-
lations in stomatal resistance, been previously noted in eucalypts (Teoh and Palmer, 1971 ), were evident through the afternoon hours. But in general, the daily course under the well-watered conditions of I~ and/2 showed a rapid increase through the early morning hours followed by a late-morning or earlyafternoon peak rate. Transpiration ceased in the early evening when the pho-
86
s.z. HERWITZAND Y. GUTTERMAN i
i
5
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-
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8
12
16
20
Time of day (h)
Fig. 2. Courses of leaf transpiration of the five species on 11.
TABLE 2
Integrated leaf transpiration rates on selected days after irrigation (I.) and for the entire 10-day period between irrigation days Transpiration (mg cm -2 day -1) I1
/2
/5
Transpiration (mg cm -2 cycle- 1)a 11o
/~-1o E. E. E. E. E.
grossa salubris socialis torquata woodwardii
95 70 53 89 126
59 40 26 39 65
28 20 36 25 34
26 19 36 29 31
379 276 381 351 482
aCycle refers to the 10-day period between irrigation days.
tosynthetically active radiation was < 20 Hmol m - 2 s - 1. The daily courses be came increasingly flattened, with peak transpiration rates occurring earlier in the morning on successive days after irrigation. Relationships between measured rates and leaf water-potentials were discussed by Herwitz et al. (1988b). Table 2 shows the integrated daily transpiration rates on/1, I2, I5 and 11o, and the sum for the entire 10-day period 11-11o. The transpiration rates of E. grossa, E. salubris, E. torquata and E. woodwardii decreased dramatically from 11 to I4, reaching a more asymptotic decrease from 14 to Ilo. Eucalyptus socialis maintained much more constant transpiration rates through the 10-day period after irrigation. On 11, the integrated daily transpiration rates ranged from 53 mg cm -2 day -1 for E. socialis to 126 for E. woodwardii (Table 2). By 11o, the transpiration rates of all the species except E. socialis were < 33% of the rates on 11. The transpiration losses over the first 2 days after irrigation (I1 and I2)
t~IOMASSPRODUCTION AND TRANSPIRATION EFFICIENCIES OF EUCALYPTS
87
ranged from only 21% (E. socialis) to as much as 41% (E. grossa) of the total loss at the end of the 10-day period. The sum of the integrated daily transpiration losses ranged from 276 mg cm -2 cycle -1 for E. salubris to 482 for E. woodwardii (Table 2). The other three species transpired at rates ranging only from 351 to 381 mg cm -2 cycle- 1
Transpiration efficiency The relationship between above-ground productivity and the integrated summer-transpiration values provided a useful index of transpiration efficiency. This relationship indicated that E. salubris was the most efficient species (Fig. 3A ). Eucalyptus salubris transpired at the lowest rates and produced the greatest amount of biomass, with E. torquata only slightly less efficient. Eucalyptus woodwardii produced comparable amounts of biomass but transpired at higher rates, whereas E. socialis and E. grossa transpired at lower rates than E. woodwardii but produced significantly less biomass. It is not known to what extent the transpiration rates per unit leaf area were affected by differences in whole-tree leaf area. The results shown in Fig. 3 are supported by Gindel's (1971) finding that the transpiration rates of some other dryland species of Eucalyptus were not significantly affected by differences in leaf area. However, to illustrate the differences in whole-tree leaf area among the five species in our study, the transpiration values were normalized on the basis of the mean whole-tree leaf area of each species. Figure 3B shows the normalized transpiration values (mg cm -2 cycle-1) per m 2 of whole-tree leaf area. Some slight differences in the relative positions of the data points are evident; E. grossa and E. socialis are more clearly the least efficient of the spei
{
E. salubris
1200
i
®
E. woodwardii
'L
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I
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( ~ E woodwardii
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1000 ~
I
E, salubns
E. torquata
g >, >
800
® E.sooia,s
"o
£
a_
® E. sociahs
6O£
A
( ~ E. grossa
E. grossa(~
B 400 200
I 300
I 4o0
Transpiration (mg
I 5o0
cm2 cycle 1)
I 100
1 2o0
I 3oo
I 4oo
I 50o
600
Normalized (mg cm 2 cycle.1 m ~)
Fig. 3. T h e relationship between aboveground productivity a n d the integrated summer-transpiration rates as an index of t r a n s p i r a t i o n efficiency. (A) Before, a n d ( B ) after normalization of the t r a n s p i r a t i o n data.
88
S.Z. HERWITZ AND Y. GUTTERMAN
cies examined because they produced the least amount ofbiomass and, for their given whole-tree leaf areas, they transpired at the highest rates. DISCUSSION Afforestation in dryland environments is a land-use activity that is likely to continue at an increasing rate over the next several decades (Armitage, 1985; Salem and Palmberg, 1985). Some workers have noted that multipurpose indigenous tree species may meet the needs of the local human populations in developing countries better than exotic species (Allen, 1986; De Troyer, 1986). However, the advantages of indigenous species may not necessarily include rapid growth and high transpiration efficiencies. Where rapid growth is a high priority, exotic species such as eucalypts probably will continue to be selected (Jacobs, 1981; Burley, 1982). Several studies recently have reported on the performances of exotic tree species in various geographic localities including India (Calder, 1986; Nimbkar et al., 1986), Tanzania (Allen, 1986; Chamshama and Hall, 1987), Somalia (Zollner, 1986), and Nigeria (Buckley, 1988). Among the most commonly introduced and studied dryland eucalypts are the species E. camaldulensis and E. tereticornis (Jacobs, 1981 ). Our study represented a consideration of some lesser-known eucalypt species. On the basis of our above-ground productivity and transpiration data, we reject the null hypothesis of no significant differences in the transpiration efficiencies of the five selected species. Of the species examined, E. salubris and E. torquata appear to have the greatest potential for afforestation under conditions comparable to the northern Negev, where the potential evaporation rate is 2140 mm year-1, the soil is a calcareous loam, the mean annual rainfall is about 100 mm, and a trickle irrigation system provides an additional 150 mm year-1. These two species made the most efficient use of the available water resources. Eucalyptus woodwardii, which allocated the highest proportion of its biomass to woody tissue, was found to be more productive than E. torquata, but it was less economical in its water use. Eucalyptus socialis and E. grossa were the least efficient in their water use because of their significantly lower productivity. Booth et al. (1988) have discussed the importance of defining the ecological niches of exotics in their native habitats to assist in the selection of appropriate species for introduction. The interspeciflc differences in water-use efficiency found in our study presumably correspond to ecophysiological characteristics which have adaptive value under natural conditions in Australia. These characteristics persist when the species are introduced as exotics. In the case of E. salubris and E. torquata, their high transpiration efficiencies in the Negev may reflect their adaptation to the Goldfields region of Western Australia near Coolgardie, where these two species are sympatric (Keighery et al., 1980).
BIOMASSPRODUCTIONANDTRANSPIRATIONEFFICIENCIESOF EUCALYPTS
89
In a study of the growth performances of selected eucalypts and other dryland tree species in Central Australia, Sandell et al. (1986) concluded that, with the judicious selection of species and provenances, tree productivity could be enhanced. Our comparative study in the Negev evaluated the performance of species on the basis of their relative transpiration efficiencies. We conclude that comparative studies of the kind reported here may assist in the selection of species which will make the most efficient use of the available water resources while satisfying the demand for tree production in arid environments. ACKNOWLEDGEMENTS
We thank Shmoulek Hadjes, Yochai Samish, and Shlomo Feingold for their help in the field, and Ian Brooker and John Zwar for providing useful information on the eucalypts of western and central Australia. We also acknowledge the logistical support provided by the Unit for the Ecophysiology and Introduction of Desert Plants at the Blaustein Institute for Desert Research. This study was supported by grants from Clark University and the Blaustein International Center. REFERENCES Allen, J.C., 1986. Soil properties and fast-growing tree species in Tanzania. For. Ecol. Manage., 16: 127-147. Armitage, F.B., 1985. Irrigated Forestry in Arid and Semi-Arid Lands: A Synthesis. International Development Research Centre, Ottawa, 160 pp. Bidner-Barhava, N. and Ramati, B., 1967. The tolerance of some species of Eucalyptus, Pinus and other forest trees to soil salinity and low soil moisture in the Negev. Israel J. Agric. Res., 17: 65-76. Booth, T.H., Nix, H.A., Hutchinson, M.F. and Jovanovic, T., 1988. Niche analysis and tree species introduction. Forest Ecol. Manage., 23: 47-59. Brooker, M.I.H. and Kleinig, D.A., 1983. Field Guide to Eucalypts. Vol. 1, South-Eastern Australia. Inkata Press, Melbourne, 288 pp. Buckley, G.P., 1988. Soil factors influencing yields of Eucalyptus camaldulensis on former tinmining land in the Jos Plateau region, Nigeria. For. Ecol. Manage., 23: 1-17. Burley, J., 1982. Obstacles to tree planting in arid and semi-arid lands: comparative case studies from India and Kenya. United Nations University, Tokyo, 52 pp. Calder, I.R., 1986. Water use of eucalypts - a review with special reference to South India. Agric. Water Manage., 11: 333-342. Chamshama, S.A.O. and Hall, J.B., 1987. Effects of site preparation and fertilizer application at planting on Eucalyptus tereticornis at Morogoro, Tanzania. For. Ecol. Manage., 18: 103-112. Chippendale, G.M., 1973. Eucalypts of the Western Australian goldfields (and the adjacent wheatbelt). Department of Primary Industry, Forestry and Timber Bureau/Australian Government Publishing Service, Canberra. Colquhoun, I.J., Ridge, R.W., Bell, D.T., Loneragan, W.A. and Kuo, J., 1984. Comparative studies in selected species of Eucalyptus used in rehabilitation of the northern jarrah forest, Western Australia. I. Patterns of xylem pressure potential and diffusive resistance of leaves. Aust. J. Bot., 32: 367-373. Dan, J., Moshe, R. and Alperovitch, N., 1973. The soils of Sede Zin. Israel J. Earth Sci., 22: 211227.
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De Troyer, C., 1986. Desertification control in the Sudanian and Sahelian zones of West Africa Better management of the renewable resource base. For. Ecol. Manage., 16: 233-241. Evenari, M., Shanan, L. and Tadmor, N.H., 1968. Runoff farming in the desert. I. Experimental layout. Agron. J., 60: 29-32. Gindel, I., 1971. Transpiration in three Eucalyptus species as a function of solar energy, soil moisture and leaf area. Physiol. Plant., 24: 143-149. Goudriaan, J., 1977. Crop micrometeorology: A simulation study. Centre for Agricultural Publishing and Documentation, Wageningen, The Netherlands. Greenwood, E.A.N. and Beresford, J.D., 1979. Evaporation from vegetation in landscapes developing secondary salinity using the ventilated-chamber technique: I. Comparative transpiration from juvenile Eucalyptus above saline groundwater seeps. J. Hydrol., 42: 369-382. Hall, N., Wainwright, R.W. and Wolf, L.J., 1981. Summary of meteorological data in Australia. CSIRO For. Res. Div. Rep., No. 6. Herwitz, S.R., Yair, A. and Shachak, M., 1988a. Water use patterns of introduced carob trees (Ceratonia siliqua L.) on rocky hillslopes in the Negev Desert. J. Arid Environ., 14: 83-92. Herwitz, S.R., Gutterman, Y. and Srinivasan, R., 1988b. Comparative transpiration of irrigated juvenile eucalypts in the Negev Desert. Irrig. Sci., 9: 233-247. Jacobs, M.R., 1981. Eucalypts for Planting. FAO, Rome, Forestry Series No. 11,677 pp. Joyce, C., 1988. The tree that caused a riot. New Sci., 117: 54-59. Keighery, G.J., Goff, J. and Marchant, N.G., 1980. Notes on the biology and phytogeography of Western Australian plants. Parts 9-10: Eucalyptus species (Myrtaceae). Kings Park and Botanic Garden, Perth, Australia. Mitchell, A.S., 1980. Eucalypts of Central Australia. Conservation Commission of the Northern Territory, Alice Springs, Tech. Bull. No. 3. Nimbkar, B.V., Nimbkar, N. and Zende, N., 1986. Desertification of Western Maharashtra: Causes and possible solutions. I. Comparative growth of eight tree species. For. Ecol. Manage., 16: 243-251. Pallardy, S.G., 1981. Closely related woody plants. In: T.T. Kozlowski (Editor), Water Deficits and Plant Growth. Academic Press, New York, pp. 511-548. Poore, M.E.D. and Fries, C., 1985. The ecological effects of eucalyptus. FAO, Rome, For. Pap. 59, 87 pp. Pryor, L.D., 1976. The Biology of Eucalypts. Studies in Biology No. 61. Institute of Biology/ Edward Arnold, London, 82 pp. Quraishi, M.A. and Kramer, P.J., 1970. Water stress in three species of Eucalyptus. For. Sci., 16: 74-78. Salem, B.B. and Palmberg, C., 1985. Place and role of trees and shrubs in dry areas. In: G.E. Wickens, J.R. Goodin and D.V. Field (Editors), Plants for Arid Lands. Allen and Unwin, London, pp. 93-102. Sandell, P., Kube, P. and Chuk, M., 1986. Dryland tree establishment in Central Australia. For. Ecol. Manage., 16: 411-422. Shiva, V. and Bandyopadhyay, J., 1983. Eucalyptus - a disastrous tree for India. Ecologist, 13: 184-187. Siegel, S., 1956. Nonparametric Statistics for the Behavioral Sciences. McGraw-Hill, New York. Teoh, C.T. and Palmer, J.H., 1971. Nonsynchronized oscillations in stomatal resistance among sclerophylls of Eucalyptus umbra. Plant Physiol., 47:409-411. Yaalon, D.H. and Dan, J., 1974. Accumulation and distribution of loess-derived deposits in the semi-desert and desert fringe areas of Israel. Z. Geomorphol. Suppl., 20:91-105. Zangvil, A. and Druian, P., 1983. Meteorological data for Sede Boqer. Blaustein Institute for Desert Research, Sede Boqer, Israel, Desert Meteorol. Pap. Ser. A, No. 8. Zollner, D., 1986. Sand dune stabilization in central Somalia. For. Ecol. Manage., 16: 223-232.