Egypt. J. Bot., Vol. 52 (2), 199-212 (2012)

Growth Performance of Four Irrigated Plantations in Egypt

Emad Farahat1,* and Hans W. Linderholm2

1Botany and Microbiology Department, Faculty of Science, Helwan University, Cairo, Egypt

2 Regional Climate Group, Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden

HE objective of this study was to compare and evaluate the spatial variation in crown architecture

traits, related growth and foliar traits and their relation to height (H) for five tree species

(Eucalyptus camaldulensis Dehnh., Khaya senegalensis (Desr.) A. Juss., Dalbergia sissoo (Roxb.),

Cupressus sempervirens L. and Casuarina spp.), irrigated with wastewater and/or ground water in four

desert planted forests in northern Egypt. The studied traits were significantly different for each tree

species among sites. The positive correlation between H and crown architecture traits increased with

decreasing tree heights, and strongly correlated with crown length in all species. Crown diameter and

area, and Leaf mass per area (LMA) appear to be potential indicators for the plastic changes in growth

performance of the species and its adaptability to site conditions. Stem diameter (dbh)-H relationship

was nonlinear and highly significant for all tree species except Cupressus sempervirens and their best

correlations were obtained at small tree heights. Soil sand content was the main operating edaphic factor

and accounted for 40.8% of the species traits-environment relationship among the sites. The growth

performance of trees was not correlated only with tree age or water availability but also with other site

conditions and silviculture practices.

Keywords: Crown architecture, Size traits, LMA, Management, Planted forests, Egypt

Tree architecture is an important determinant of height extension, light capture, and mechanical stability of

trees, and it allows species to exploit the vertical height gradient in the forest canopy as well as the horizontal

light gradients at the forest floor (Poorter et al. 2006). The concept of plant architecture suggests that each plant

species has its own growth form (Bell 1984). Westoby and Wright (2006) stated that addressing the questions

of how and why plant traits and architectures vary among species and sites is the most important single step

towards understanding land-ecosystem properties in general. Inter-specific variation in height growth rates is

related to that in crown architectural traits (Takahashi & Rustandi 2006). Changes in crown morphology have

been shown to play an important role in the acclimatization capacity of species to different light environments,

and crown-morphological plasticity was found to be important to shade-tolerant trees (Canham 1988, 1989,

Beaudet & Messier 1998). Crown-architecture traits (crown area, diameter, length and shape) are important

factors affecting the light environment in forest canopies. The plasticity in crown traits under different stress

T

Corresponding author, Email: emad23_1999@yahoo.com

200 EMAD FARAHAT and HANS W. LINDERHOLM

and light conditions has been reported by many investigators of forest trees (e.g. Takahashi et al. 2005, Chmura

et al. 2007, 2009).

In general, the plasticity strategies for plants which are to successfully endure in arid regions have

been found to be associated with two main adaptive traits; minimizing water loss and maximizing water uptake.

Foliar traits, such as leaf mass per area (LMA ) and leaf area, are indicators for this strategy, either by

increasing LMA or reducing light absorbance through rolled leaves (Pena-Rojas et al. 2005, Stefanos et al.

2008). Higher LMA is a main adaptation to droughts, and is positively related to the photosynthetic tissue per

unit area and investment in structural tissues, allowing higher tolerance to unfavorable conditions (Marcoco et

al. 2000, Chen & Wang 2009). Differences in leaf morphology and physiology and changes in crown

architecture traits and LMA among tree species are common. These traits changes dramatically with growth

stage, tree height and/or susceptibility to drought stress and they are size-dependent in nature (Koch et al. 2004,

Poorter et al. 2006, Ryan et al. 2006, He et al. 2008, Tanaka-Oda et al. 2010). Leaf trait responses to

environmental conditions often differ among species (Bond 2000, Ryan et al. 2006) and can be used as

indicators of whole-organism physiology, such as drought tolerance and growth performance, under stressful

circumstances.

Crown architecture affects tree growth through control of leaf area and its display for effective light

capture and photosynthesis. So, it may important to quantify crown traits for effective use of intensive

silvicultural practices to improve tree growth in forest plantations (Chmura et al. 2007). It is also very relevant

in studies of the growth of stands due to the close correlation between crown size and stem diameter, and

density of trees in a stand (Hemery et al. 2005). Knowledge of the crown traits-tree size relationship of a

species can be applied to indicate the tolerance of a species to variations in stand density (Dawkins 1963), for

predicting basal areas, devising thinning regimes and, given the inclusion of height data, for developing stand

volume estimates. Our understanding to these relationships will assist in decision which tree can be selected in

a certain site exposed to a range of site conditions (e.g. wind speed) according to the crown parameters and to

inform the design of forest management prescriptions (Hemery et al. 2005, Thorpe et al. 2010).

The impacts of different silviculture practices e.g. thinning, repeated fertilization, control of competing

vegetation, plant density and irrigation method, on the growth and crown traits of the plants were studied by

many investigators (e.g. Chmura et al. 2007, Waterworth et al. 2007, Thorpe et al. 2010, Yanga et al. 2011) .

For instance, Stem growth of Pinus radiata (10-29 years old) responded markedly to irrigation, with a strong

interactive effect when combined with N fertilization. Moreover, irrigation increased growth in the larger trees

GROWTH PERFORMANCE OF FOUR… 201

proportionally more than the smaller trees, resulting in an increased diameter distribution compared with the

non-irrigated stands. Cessation of irrigation in combination with thinning after 5 years of treatment immediately

reduced annual basal area growth of Pinus radiata to levels similar to the control for at least 2 years

(Waterworth et al. 2007).

The establishment of planted forests in the world is expected to help in preventing desertification of

agricultural land, as well as providing increased wood supplies and reducing negative impacts of environmental

pollutions (FAO 2006). In Egypt, the establishment of planted forests is an ongoing annual activity by the

Ministry of State for Environmental Affairs to cope with an increase in wastewater production burden (about

2.4 billion m3year-1) (Egypt State of the Environment Report 2009). Considering the scale of recent

establishment of the planted forests, there is not enough literature on growth performance, biomass production,

economic products, efficiency of current silvicultural practices, wood diseases, shoot dieback and tree death.

The objective of this study was to compare and evaluate the spatial variation of tree crown architecture

traits, related growth and foliar traits and their relation to height (H) for five tree species (Eucalyptus

camaldulensis Dehnh., Khaya senegalensis (Desr.) A. Juss., Dalbergia sissoo (Roxb.), Cupressus sempervirens

L. and Casuarina spp.) growing in four desert planted forests in Egypt named: Sadat, Wadi El-Natrun,

Sarapium and El-Tur forest. We tried to answer the following questions: 1. Is there a spatial variation in growth

performances of the studied tree species in desert planted forests? 2. Are the variations in architectural traits

related to tree height? 3. What is the relation between height and diameter among species and sites? 4. Which

environmental variables have most influence on species performance?. This study will provide more

understanding for the performance of tree species in their habitats and help in improving species selection

techniques for successful planting in arid areas.

Methods

Study sites and tree species

This study was carried out in four desert planted forests (plantations) in Egypt. Two forests are located

in the Western Desert, and are commonly known as Sadat Forest (officially: Chinese-Egyptian Friendship

Young People Forest) and Wadi El-Natrun Forest (officially: Japanese Planted Forest). The third forest is

located in the Eastern Desert and is commonly known as “Sarapium Forest”. The fourth forest is “El-Tur”

which is located outside El-Tur City, South Sinai Governorate (Fig. 1). The trees planted in the forests are

irrigated with lightly treated sewage wastewater, except in Wadi El-Natrun, which is irrigated with

Egypt. J. Bot. 52 (2) (2012)

202 EMAD FARAHAT and HANS W. LINDERHOLM

Fig. 1. Location map showing the distribution of studied four planted forests in Egypt

groundwater. The quality of wastewater varied among the forests depending on the efficiency of treatment

method. The forested area ranges from 420 ha (Sarapium) to 63 ha (El-Tur forest). More details about irrigation

systems and their efficiency, and climate characteristics in the different study sites are shown in Table 1.

Silviculture practices include fertilization, tillage; control of competing understorey vegetation and pest control

are the most common practices in Sarapium forest only compared with other forests. In addition, not all of the

sampled tree species are cultivated in all sites, and they vary in age and density within and among forests

(Table 2). More canopy gaps were observed in El-Tur and Wadi El-Natrun forests for most tree species

compared with the other forest sites. The sampled tree species were: Eucalyptus camaldulensis Dehnh. (River

Red gum), Khaya senegalensis (Desr.) A. Juss. (Dry zone Mahogny), Dalbergia sissoo (Roxb.) (Sissoo),

Cupressus sempervirens (Italian cypress) and Casuarina spp. (Australian pine). All trees are cultivated as

single overstory species. The Casuarina spp. consisted of mixed populations, represented by 3 species (C.

GROWTH PERFORMANCE OF FOUR… 203

Table 1. General characteristics of the studied planted forest in Egypt

Parameter/Forest Sadat Sarapium Wadi El-Natrun

El-Tur

Area (ha) 210 420 63 84

Irrigation system Drip Drip Drip Flooding

Type of water Sewage Sewage Ground Sewage Efficiency of irrigation system

*Poor *Good Poor *Excellent

Air temperature, æC (Min.-Max.)

**15-27.2 13.9-28.7 15-27.2 17.2-29.7

Relative humidity % (Min.-Max.)

63-72 52-66 63-72 46-59

* Poor = the irrigation network is frequently blocked by water suspended solids and the trees are irrigated

irregularly, Good = the irrigation network is maintained and the trees are irrigated regularly in

considerable amounts, Excellent = large pipes are used for distributing the water of irrigation and trees are

flooded by water during irrigation

** The distance between Sadat and Wadi El-Natrun forest locations is ca. 38.3 km

Table 2. Age (yr.) and density (trees ha-1) of the sampled tree species in 2009 in the studied planted forests in Egypt

Tree species/Forest Sadat Sarapium Wadi El-Natrun El-Tur

Age Density Age Density Age Density Age Density

Eucalyptus camaldulensis Dehnh 9 1114 8 1005 11 900 13 750

Casuarina spp. 10 1213 6 1100 10 1100 13 850

Cupressus sempervirens L. 10 1213 6 825 10 857 - -

Khaya senegalensis(Desr.) A. Juss. 10 1020 8 1089 - - - -

Dalbergia sissoo(Roxb.) 10 716 6 957 - - - -

glauca Sieb., C. equisetifolia L., C. cunninghamiana Miq.) and one hybrid, cultivated irregularly in the stands.

Consequently, we dealt with Casuarina. spp. as one species in this study to avoid mis-identification during

sampling process.

Data collection

Sampling and data collection were conducted during the main growing season of the trees in 2010

(spring and summer). In all the four forests, and for each tree species, we conducted the measurements through

North-South transects (lengths ranging from 300 to 700 m). The number of transects was depending on the area

occupied by the tree species in each forest. The positions of transects were decided to represent all the apparent

variations in growth and height of trees. Twenty five trees were measured across their whole height range. The

Egypt. J. Bot. 52 (2) (2012)

204 EMAD FARAHAT and HANS W. LINDERHOLM

selected trees were healthy, upright standing, and had undamaged crowns and with no forks or obvious weak

vigor according to the criteria suggested by Poorter et al. (2006). Total height (H), crown length (CL), average

crown diameter (Cdia), projected crown area (Carea), and stem diameter at breast height (dbh at 1.3 m) were

measured in the field for each tree. Height and crown lengths were measured with a clinometer (model HEC-R,

Haglöf, Sweden), while the dbh was measured with a diameter tape. The base of the crown was defined as the

lowest leaf-bearing branch. At the end of the main growing season for all trees (in summer) and before leaf

senescence in autumn, the average crown diameter was calculated as the mean of two perpendicular diameter

measurements, one of which was the maximum crown diameter. The crown diameter was measured in north–

south and east–west directions, and for smaller trees in the direction of the longest width and perpendicular to

it. Crown area was calculated as an ellipse according to the shape of the trees, using the equation 0.25 d1d2, in

which d1and d2 are the two crown diameter measurements per tree, and crown length as the height of the tree

minus the height of the trunk beneath the lowest leaf-bearing branch (Beaudet & Messier 1998, Poorter et al.

2006). The crown shape (CS) of each tree was described as the ratio of crown length to mean crown diameter

(see Beaudet & Messier 1998).

Leaf mass per area (LMA) was calculated for each tree species (10 tree individuals, 10 fully expanded

leaves/ individual). The sampled leaves were collected during the main growing season for trees from all the

canopy directions at a height range 1.5-3.0 m above soil surface. In the case of Cupressus sempervirens, ten

small branches with their carrying scale-like green leaves were sampled for this analysis. The sampled leaves

were scanned, and then leaf area was measured from the scanned image. Measurements of leaf area was

performed, where the public domain ImagJ 1.44 image program (available on the internet at website:

http://imagej.nih.gov/ij/download.html) was used to estimate the fresh leaf area. The leaves were weighed after

oven-drying at 60 °C for at least 48 h. Petioles of leaves were excluded from the measurements of the leaf traits

(leaf area and leaf dry mass), because their function is the support of leaf blade. To determine the growth rate of

each tree per life time, as a function of both stem height (HGR) and dbh (DGR), we assumed that the initial

stem height and dbh for the trees at the time of transplanting was 0.4 m and 1.0 cm respectively, based on what

was reported by the workers in the forests (personal communications). These values were subtracted from each

tree height and dbh to calculate its growth rate per life time. We divided the tree height by its life time (i.e. age

in years) to obtain rough estimate for the growth rate of the trees in each forest.

Soil and water analysis

GROWTH PERFORMANCE OF FOUR… 205

Soil samples were collected from five locations in each forest, under the tree canopies, and each

location was represented with one composite sample (N=3). Soil samples were collected through soil profiles

including the topsoil layer at a depth of 0-50 cm. The samples were used as representative samples for each

forest. The soil samples were brought to the laboratory in plastic bags shortly after collection, spread over paper

sheets; air dried, passed through a 2 mm sieve to remove gravel and debris, and then packed in paper bags

ready for physical and chemical analysis. Soil texture was determined by a set of stainless steel test sieves

confirming to ASTM standards, whereby the percentage of clay, silt and sand were calculated. Soil extracts

were prepared to meet the requirements for different determinants, 1:5 (w: v) soil (g): distilled water (ml)

extract. This extract was used to measure soil conductivity (EC), pH, bicarbonates, calcium, magnesium,

sodium and potassium. The pH values of soil samples were determined using a glass electrode pH meter

(Model 9107 BN, ORION type). Salinity was evaluated by a conductivity meter (dS m-1). Bicarbonates were

estimated by titration against 0.01N HCl using methyl orange as indicators (Allen et al. 1989, Maff 1986).

Soluble soil cations (Ca, Mg, K and Na) were determined by atomic absorption spectrometer in the Central

Laboratory of Ein-Shams University, Egypt.

Water samples were collected in plastic bottles directly from the main pipe feeds in each forest and

brought to the laboratory shortly after collection. pH and EC were determined directly after collection, after

which the samples were kept at –4 °C for further analysis. Bicarbonates, calcium, magnesium, sodium and

potassium were estimated using the same methods as in the soil analysis.

Data analysis

To test the significance of the spatial variations in crown architecture, size and leaf traits, we compared

the obtained data for each tree species among the forests using the analysis of variance (ANOVA). The same

technique was applied on growth rates as functions of height and dbh. Pearson’s correlations coefficients were

calculated for the architecture traits of each tree species and height in all locations using STATISTICA 7.0

Software (StatSoft. Inc. 2004).

Analysis of allometry

To check the relationships between height and dbh, we first regressed height data against dbh, and

polynomial fitted second-order equations for each relationship were conducted using Microcal Origin 5.0

Software (Microcal Software Inc. 1997). Bivariate trait relationships were analyzed using Pearson’s

correlations on untransformed trait values. To assess multivariate trait associations among species, principal

Egypt. J. Bot. 52 (2) (2012)

206 EMAD FARAHAT and HANS W. LINDERHOLM

component analysis (PCA) was done on the grouped traits data of height and crown architecture for each

species in all sites, using PC-ORD v.3.0 (McCune & Mefford 1997).

Environmental variable-trait relationships

To check the relationship between the measured tree traits and environmental variables (soil and

water) for all species, canonical corresponding analysis (CCA) was used. All soil and water parameters were

included in this analysis and all the default settings for the CCA in the PC-ORD software were used (McCune

& Mefford 1997). To assess the importance of all environmental variables, the intra-set correlations from CCA

were used, where the significance of the correlations with the CCA axes was tested by calculating Pearson’s

correlation coefficients for the variable at p < 0.05.

Results

Spatial variations in crown architecture, foliar traits and growth rate of trees

The highest average values for size traits (H, dbh), Cdia and Carea of E. camaldulensis were obtained

in El-Tur forest, while most of the lowest values for the traits were found in either Sadat or Wadi El-Natrun

forests (Fig. 2). The highest values of dbh, LMA and crown shape for Cupressus sempervirens were found in

Wadi El-Natrun forest, while the values of the other traits were lower than that in Sadat and Sarapium forests.

The size traits and Carea growth of Dalbergia sissoo were greater in Sarapium forest compared to Sadat site. In

contrast LMA was greater at Sadat than Sarapium at which the species had its highest mean LMA value. The

growth performance of Khaya senegalensis was higher in Sarapium than Sadat forest for most traits with

significant differences in H values. Generally, E. camaldulensis and Casuarina spp. had significant Cdia, Carea

and dbh in El-Tur forest greater than other sites while all the species showed more H and dbh growth rates in

Sarapium forest.

Significance of the spatial variations in traits

The results of the one-way ANOVA tests showed that most of the measured traits were significantly different

(at p < 0.05) for individual tree species among the forests (Table 3). The stem H and dbh of a species generally

varied among the forests but the species maximum H did not necessary coincide with maximum dbh at the

same site, and this was independent of tree age. For instance, the highest dbh values of Casuarina spp. (at El-

Tur forest, flood irrigation, age >13 years) and C. sempervirens (at Wadi El-Natrun forest, drip irrigation, age

H10 years) did not coincide with the obtained highest stem H values for species (Table 3). Despite the age

difference between K. senegalensis plantations in Sadat and Sarapium forests (H 2 years), there was no

GROWTH PERFORMANCE OF FOUR… 207

significant difference in stem dbh values (at p < 0.05). It is appeared from the results of K. senegalensis that the

relationship between the two size traits was very weak for the species (r = 0.2).

Leaf mass per area (LMA) was significantly different at p < 0.05 for all species among forests, with

maximum values in Wadi El-Natrun forest (for E. camaldulensis and C. sempervirens) or Sadat forest (for D.

sissoo and

Fig. 2. Spatial variation of the architecture traits, size traits, foliar traits and growth rates for each tree species among forests. H = height, dbh = stem diameter at breast height, LMA = leaf mass per area, Cdia = crown diameter, Carea = crown area, CL = crown length, CS = crown shape, HGR = growth rate using stem height, DGR = growth rate using dbh data. Error bars represent the standard error of mean.

Egypt. J. Bot. 52 (2) (2012)

208 EMAD FARAHAT and HANS W. LINDERHOLM

Table 3. The results of One-Way ANOVA for the measured tree traits in different locations. * = significance at probability level < 0.05 or p < 0.01, **= significance at probability level < 0.0001. Within each row, mean values with the same letter do not differ significantly between treatments at p < 0.05.

Trait Species Sadat Sarapium Wadi El-Natrun El-Tur F

Height (m) E. camaldulensis 13.6a 14.6ab 12.6ac 17.3d 15.4**

Casuarina spp. 9.0a 13.5b 9.7ac 10.7c 25.5**

C. sempervirens 10.2a 10.0a 7.3b - 17.8**

D. sissoo 7.7a 10.1b - - 44.4**

K. senegalensis 5.5a 12.0b - - 115.3** dbh (cm) E. camaldulensis 17.7a 19.8ab 15.1ac 25.8d 17.3**

Casuarina spp. 10.2a 14.0b 13.8b 22.3d 41.3*

C. sempervirens 11.8a 12.9a 14.8b - 4.5*

D. sissoo 9.1a 12.9b - - 25.6**

K. senegalensis 11 10.8 - - 0.01 LMA (mg cm-2)

E. camaldulensis 11.1a 11.0a 18.1b 11.2a 10.2**

C. sempervirens 23.9a 21.6a 34.8b - 35.8**

D. sissoo 15.9a 11.0b - - 22.9**

K. senegalensis 8.5a 6.1b - - 7.5* Crown diameter (m) E. camaldulensis 3.2a 4.8b 3.9ab 7.2c 15.1**

Casuarina spp. 3.5a 3.8a 5.5b 5.6b 13.2**

C. sempervirens 1.9a 2.3a 1.2b - 8.7*

D. sissoo 4.4 5.1 - - 0.8

K. senegalensis 4.2 5.8 - - 3.2 Crown area (m2) E. camaldulensis 8.9a 18.8b 14.4a 43c 14.8**

Casuarina spp. 10.4a 12.0a 25.0b 25.0b 13.3**

C. sempervirens 2.9a 4.4a 1.3b - 7.8**

D. sissoo 17.0 22.3 - - 0.9

K. senegalensis 15.3 30.3 - - 3.3 Crown length (m) E. camaldulensis 10.9 a 3.1b 8.1c 5.3d 21.1**

Casuarina spp. 11.2 a 8.8ab 10.4a 1.3c 80.7**

C. sempervirens 8.7 8.1 7.9 - 0.5

D. sissoo 7.2 6.7 - - 0.5

K. senegalensis 4.5 a 8.0b - - 45.8** Crown shape E. camaldulensis 3.9 a 0.7b 2.3c 1.4d 17.1**

Casuarina spp. 3.3 a 2.4b 1.9c 1.3d 18.5**

C. sempervirens 5.0 a 4.0ab 7.7ac - 5.1**

D. sissoo 1.8 1.4 - - 2.9

K. senegalensis 1.1a 1.7b - - 4.0 Height growth rate (m yr-1)

E. camaldulensis 0.9a 1.6b 0.8ac 0.8c 92.8*

Casuarina spp. 0.9 a 2.2b 0.9ac 0.8ad 202.2**

C. sempervirens 1.0 a 1.6b 0.7c - 109.0*

D. sissoo 0.7 a 1.2b - - 134.2**

K. senegalensis 0.5 a 1.6b - - 159.8** dbh growth rate (cm yr-1)

E. camaldulensis 1.0 a 1.6b 1.3c 1.6bd 12.3** Casuarina spp. 0.9a 2.2b 1.3c 1.6d 47.8* C. sempervirens 1.1 a 2.0b 1.4c - 34.3** D. sissoo 0.8 a 1.5b - - 70.5**

K. senegalensis 1.0 a 1.4b - - 9.6*

GROWTH PERFORMANCE OF FOUR… 209

K. senegalensis). LMA value for C. sempervirens in Wadi El-Natrun forest was 2- to 3- fold higher than the

other tree species.

The variations in crown-architecture traits were more profound than the size and foliar traits.

Significant variations in Cdia and Carea were found for C. sempervirens, with the highest values obtained in El-

Tur forest for E. camaldulensis and Casuarina spp. and in Sarapium forest for the other species (Table 3). The

highest values for CL and CS were obtained in Sadat forest for all species except K. senegalensis and C.

sempervirens, while the spatial variations of these traits were highly significant (at p < 0.05) for E.

camaldulensis and Casuarina spp. and size-dependent more than that found for other tree species.

Height growth rate (HGR) and diameter growth rate (DGR) for each species were significantly different in all

forests (at p < 0.05). The highest growth rates for all species, irrespective of their ages, were found in Sarapium

forest (Table 3). Non-significant variations (at p < 0.05) in HGR and DGR around the mean value were

observed between species in the same forest (data not shown).

Traits associations

The relationship between H and dbh was highly significant, at p < 0.0001 or p < 0.01, for all species

except C. sempervirens (Fig. 3). The equations indicated a nonlinear relationship between both variables for all

species and among forests. The best values for the coefficient of determination (R2) between the two variables

were obtained for D. sissoo (R2 = 0.55) and E. camaldulensis (R2 = 0.37). Although K. senegalensis had more

or less equal mean values for size traits compared with D. sissoo, the coefficient of determination was very low

(R2 = 0.16) indicating a weak H-dbh relationship.

The correlation between H and crown traits (diameter, area and length) was often size-dependent; the positive

sign of the correlation coefficient (r) increased with decreasing tree heights (Fig. 4). The highly significant

positive correlations between H and crown traits were observed in the canopies of D. sissoo, while the lowest

correlations were found in E. camaldulensis canopies. Crown length was strongly correlated with height in all

species (r range: 0.36-0.96), while the correlation between height and crown shape was not significant for any

species (at p < 0.05). The correlation pattern between H and crown traits was similar for each species in all

forests, with non-significant variations (data not shown).

Egypt. J. Bot. 52 (2) (2012)

210 EMAD FARAHAT and HANS W. LINDERHOLM

Fig. 3. Polynomial regression for the stem height (log H) and diameter (log dbh) for tree species in all forests. R2 value is shown when the relation is significant at probability level, p < 0.0001 or p< 0.01.

Fig.4. Pearson’s correlation coefficients (r) between height and crown architecture traits of the sampled tree species (crown diameter = Cdia, crown area = Carea, crown length = CL and crown shape = CS). The trees are plotted on x-axis from shorter to taller species.

GROWTH PERFORMANCE OF FOUR… 211

The associations of architectural traits and height for all tree species in all locations were explored with

PCA (Table 4). The first PCA axis explained 50.6% of the variation in traits, and had high positive correlation

with Cdia (0.92) and Carea (0.89). In contrast, CS had high negative correlation with the first PCA axis (-0.82).

On the other hand, the second PCA axis explained 33.9% of the variation in architecture traits, with highly

negative correlation with height (-0.86) and CL (-0.73).

Table 4. Eigenvalues and Euclidean distance for the measured traits and its correlation to the first three axes of PCA analysis. The last two columns indicate the Pearson’s correlation between the traits and the first and second axes of PCA. Significant correlations are shown in bold.

PCA axis

PCA1 PCA2 1 2 3 Eigen-value 2.28 1.28 0.78 % of variance 52.60 30.04 8.96 Height (m) 0.20 -0.66 0.53 0.03 -0.82 Crown diameter (cm) 0.60 -0.09 -0.07 0.97 -0.11 Crown area (m2) 0.57 -0.11 -0.02 0.92 -0.14 Crown length (m) -0.18 -0.67 -0.71 -0.30 -0.82 Crown shape -0.48 -0.27 0.44 -0.78 -0.34

Soil and water characteristics and CCA correlations

The analysis of soil samples showed an increase in the soil salinity (expressed as EC) in both Wadi El-

Natrun and Sadat forests compared with the other forests (EC = 7.7 and 5.2, respectively) (Table 5). Likewise,

soil soluble Mg, K and Na cations were higher in these two forests than in El-Tur and Sarapium forests. On the

contrary, the highest values for Ca (1235.6 ppm) and Na (1377.7 ppm) were obtained in El-Tur and Wadi El-

Natrun forest, respectively. There were no distinct variations in the quality of water among the forests despite

the differences in the quality of treatments. The irrigation water in Wadi El-Natrun forest (ground water) only

differed from the others with its high EC (5.1 dSm-1) and Na concentration (130.2 ppm).

The canonical corresponding analysis for environmental variables (soil and water) and species

measured traits showed weak eigenvalues with the three canonical axes. The total variance in the species data

was 0.25, indicating a weak variability in the environmental data among forests (ter Braak 1990). The first

canonical axis explained 40.8% of the variance, while the second canonical axis explained only 5% of the

variance (Table 6). As expected from the total variance in species data, these results suggested a weak

association between measured traits and the environmental variables. CCA axis 1 was negatively correlated

with soil cations and water K and positively with soil sand (at p < 0.05). On the other hand, CCA axis 2

correlated positively with soil clay content, Mg, K, Na and water Mg and Na, and negatively with soil pH and

Ca in water and soil.

Egypt. J. Bot. 52 (2) (2012)

212 EMAD FARAHAT and HANS W. LINDERHOLM

Table 5. General soil and irrigation water characteristics of the studied planted forests. All the measured parameters are significantly different between forests at p < 0.05.

Parameter Sadat Sarapium Wadi El-Natrun

El-Tur

1-Soil: Physical properities

Soil type Sandy Sandy Sandy Calcareous

Soil particles (%)

Sand 79.4 85.0 80.1 80.3

Silt 10.1 11.5 11.3 16.5

Clay 10.5 4.6 8.6 4.1

pH(1:5) 7.8 7.6 7.9 8.1

EC (dSm-1) 5.2 2.1 7.7 4.5

Soluble Cations (ppm)

Ca 700.0 81.5 269.2 1235.6

Mg 165.4 77.2 132.7 46.1

K 330.7 138.9 212.6 121.8

Na 1332.2 234.3 1377.7 345.4

Soluble anions

HCO3 (ppm) 175.1 293.1 112.4 207.4

2- Water properities

pH 7.5 7.2 7.8 7.3

EC (dSm-1) 3.7 2.1 5.1 3.9

Ca

Ppm

128.3 151.4 44.8 191.6

Mg 36.3 38.6 14.9 17.5

K 23.4 17.9 4.9 14.0

Na 105.8 76.3 130.2 68.7

HCO3 110.1 85.1 154.9 120.3

Discussion

Intra- and inter-specific spatial heterogeneity of traits

The cultivated species in our study were worldwide and nationally tested for their drought resistance, salinity

and waterlogging tolerance (El-Lakany 1983, Aswathappa & Bachelard 1986, Van Der Moezel et al. 1988,

1989, Gilman & Watson 1993). The crown architecture, size and foliar traits revealed plastic changes among

forests. The growth performance of E. camaldulensis was more pronounced in El-Tur and Sarapium forest for

most measured traits. Meanwhile it had general poor performance in Wadi El-Natrun forest which could be

attributed to general poor silviculture operations and site conditions. On the other hand, the greater value of

LMA for C. sempervirens in Wadi El-Natrun forest, which is classified as a soil salinity tolerant species

GROWTH PERFORMANCE OF FOUR… 213

Table 6. Intra-set correlations (of ter Braak 1986) of the soil and water variables with the first three axis of the canonical correspondence analysis (CCA), together with eigenvalues and traits–environment correlation coefficients. * = significance at p < 0.05.

CCA axis

1 2 3

Eigen values 0.10 0.01 0.01

% of variance explained 40.8 5.0 2.4

Cumulative % of variance explained

40.8 45.8 48.2

Soil variables

Sand % 0.80* 0.30 0.032

Silt % 0.02 -1.00 -0.00

Clay % -0.62* 0.67* -0.40

pH -0.48 -0.68* -0.54

EC (dSm-1) -0.35 0.09 -0.93*

Ca (ppm) -0.75* -0.65* -0.60*

Mg -0.51* 0.79* -0.32

K -0.73* 0.66* -0.17

Na -0.52* 0.54* -0.65*

HCO3 0.45 -0.10 0.88*

Water variables

pH -0.22 0.32 -0.92*

EC (dSm-1) -0.37 -0.09 -0.90*

Ca (ppm) -0.17 -0.57* 0.80*

Mg -0.00 0.56* 0.80*

K -0.51* 0.29 0.80*

Na -0.16 0.58* -0.79*

HCO3 -0.16 -0.11 -0.97*

(Gilman & Watson 1993), might indicate its adaptability to the local site unfavorable conditions more

than other species.

The significant differences in tree species growth among forest reflect direct responses and plastic

changes in traits according to the prevailing conditions has previously been shown for trees in natural forests

(e.g. Pena-Rojas et al. 2005, Stefanos et al. 2008). It is revealed from the significant correlations between tree H

and dbh, that trees tend to invest more resources in radial growth than in height growth after certain age. This

was more pronounced in El-Tur and Wadi El-Natrun forests compared with Sadat and Sarapium forests. We

can attribute this growth pattern for the presence of considerable canopy gaps for most trees in these forests,

which enhance the plant to invest more resources in radial growth than vertical growth. Furthermore, flood

irrigation in El-Tur seems to be another enhancing factor assist in this growth pattern, while the availability of

water and waterborne-nutrients secure for the trees more resources to invest in horizontal growth (Waterworth

Egypt. J. Bot. 52 (2) (2012)

214 EMAD FARAHAT and HANS W. LINDERHOLM

et al. 2007). This uni-direction investment of resources was confirmed by H and dbh data of K. senegalensis.

Similar correlation patterns were reported by Poorter et al. (2006) for tropical trees, in which the tree first

grows mainly in height until it reaches its reproductive size (or the canopy); after which height growth levels

off and diameter expansion continues. This correlation pattern between H and dbh was expected to be clearer in

the planted forests due to absence of interspecific competitions and approximately fixed distance between trees

which minimize the intra-specific competition for light and resources.

In spite of the fact that we have no direct evidence, the differences in LMA among tree species are

more likely related to their susceptibility to unfavorable site conditions in Wadi El-Natrun and Sadat forests.

This may be supported by the obtained high EC in water and soil samples and the observed low frequency of

irrigation and poor silvicultural management practices in both sites. Increasing LMA is a known plastic strategy

for the species to minimize water loss in arid regions (Pena-Rojas et al. 2005, Stefanos et al. 2008), and it has

been shown to be a main adaptation to drought and related to photosynthetic tissue per unit area (Marcoco et al.

2000, Damoura et al. 2008, Chen & Wang 2009). For this clear plastic change in LMA among species, Tanaka-

Oda et al. (2010) proposed the likelihood of LMA to be new important criteria for plantation species selection

on the Loess Plateau, China.

Crown diameter and area increased with the height of trees, which increase the amount of

photosynthesizing leaf area and capturing of light (Givnish 1988, Beaudet & Messier 1998). Both crown area

and diameter increased more strongly with tree height than crown length and shape. These were the same

findings for tropical rain forest trees in Bolivia (Poorter et al. 2006) and many other tree communities (Parent &

Messier 1995, Chen et al. 1996). The crown length of the trees in planted forests may be subjected to artificial

partial pruning (e.g. Italian cypress) or natural peeling out and death for bark and lower branches as in Eucalypt

and Italian cypress. Crown shape is an important trait affecting the light environment in forest canopies

(Chmura et al. 2009). In this study, the changes in crown shape may be related to tree genetics, stem density

and age as the most likely factors affecting tree shape in planted forests as reported for natural forests (Ishii &

McDowell 2002).

The intra-specific differences in growth rate per life for tree H or dbh can be interpreted as a direct

response to the local environment and silviculture practices. However, although water is the main key limiting

factor for plants in the desert, the highest values for species growth rates was in Sarapium forest. In other

words, the other biotic (e.g. silviculture practices) and abiotic factors (e.g. soil fertility) beside water are key

factors which determine the growth of tree species in desert plantations. To confirm this hypothesis, a study on

GROWTH PERFORMANCE OF FOUR… 215

the biomass production in drip- and flood irrigated forests should be carried out for the same tree (s) species.

The observed non-significant growth rate differences between tree species in the same forest cannot be

understood as an equal performance for these species or the environmental conditions are even for all tree

canopies. This simply could be ascribed to the changes in species growth with age and according to growth

stage; which differ inherently between species (Sillett 2010).

H-dbh and crown architecture association

Non-linear relationships between tree H and dbh has previously been reported for natural forest trees,

where tree height increases steeply with dbh, and starts to cease when species attain their maximal height and

start to reproduce (Thomas 1996, Poorter et al. 2006). In our study, the more correlated H-dbh relation for D.

sissoo compared with other small species (e.g. K. senegalensis) or large species (e.g. E. camaldulensis) may be

due to that Sissoo trees start to reproduce at small dbh. This may foster the species to invest more resources in

dbh growth rather than height, to cope with reproductive needs and carry the developing crown. Moreover, this

could be a strategy for the woody vegetation in hyper-arid lands to provide safe sights for their self regeneration

(Shaltout & Mady 1993). On the contrary, D. sissoo individuals grow in five natural habitats in Nile Delta,

Egypt; tend to expand vertically rather than horizontally when growing in dense populations (Shaltout et al.

2010). The observed negative correlation between crown length and diameter at small heights in this study

agrees with the finding of Beaudet and Messier (1988) and Poorter et al. (2006). The impact of site and height

size did not have any effect on the crown shape of the species which let us to claim that this trait is more

species specific and may be related to other factors (e.g. age and density) more than the other crown traits. This

is in agreement with the findings of Chmura et al. (2009) for young stands of loblolly pine (Pinus taeda L.) in

the southeastern US.

The PCA1 was highly correlated with light capture traits of the species (Carea and Cdia) while the

PCA2 was high negatively correlated with the stature of the species (H and CL). Meanwhile, crown shape was

negatively correlated with both PCA axes. This seems logic and accepted correlation pattern in presence of very

weak or absent competition among a tree species, where the tree individuals are almost equally spaced and

watered. This suggests that a tree invests more in building a robust and extended crown to maximize their

capture for light while the need for tall stature is not necessary, which is similar to trees growing in open

canopies (Gasser et al. 2006, Poorter et al. 2006). Crown diameter was found to be the best predictor for the dry

weight of the total aboveground parts and leaves of D. sissoo in Nile Delta, Egypt (Shaltout et al. 2010)

Egypt. J. Bot. 52 (2) (2012)

216 EMAD FARAHAT and HANS W. LINDERHOLM

The weak species-environment relationship and presence of high correlation with soil sand content

could be explained by the fact that in drip irrigated soil, the root system concentrates in the wetted zone

developed in the irrigated side of the tree (Sokalska et al. 2009); by presence of more sand content, the root

system will grow more downwardly to reach the permanent water table. In contrast, in case of flood irrigation,

sand help in more growth and aeration around the root system which finally help the tree to grow normally. In

addition, the long root system assists in stability of trees and provides more resistance against the prevailing

wind in our deserts (Sterken 2005).

Management implications

Results from this study improve our knowledge and provide new tools for understanding growth

performance of tree species in planted forests in arid lands. This information can be used to inform the design

of forest management prescriptions. Detailed understanding for the growth performance of crown traits and its

relationship with tree height in different desert regions and at different ages assists in decisions on spacing

when planning the spacing of single and mixed tree stands. Moreover, it may help in deciding which tree can be

selected in a certain site exposed to a range of environmental conditions according to the crown parameters.

Our results improve knowledge about spatial variations in crown architecture of the tree species which may

lead to improved forest productivity overall. The importance of silviculture management practices are

becoming commonplace, but the contribution of these practices in the overall growth of species in desert

plantations should be understandable for the managers in artificial plantations.

Conclusion

In conclusion, the ecological performance of tree species was significantly different between forests.

E. camaldulensis had their best growth in El-Tur and Sarapium forest with general poor performance in Wadi

El-Natrun forest. The greater value of LMA for C. sempervirens in Wadi El-Natrun forest compared to other

species might indicate its adaptability to the poor local site conditions more than other species which in

consistent with many reported results . The highest H and dbh growth rates for the tree species in Sarapium

forest revealed that growth of trees in desert plantations not correlated only with tree age or water availability

but also with site conditions and silviculture practices. The non-linear relationship between H and dbh in our

planted forests coincides with that reported for natural forests which may indicate that this is genetically and

environmentally controlled performance. The investment of small trees to more resources in building strong

stem diameters more than tall stems at certain moment in lifecycle was a strategy for the tree species in the

desert plantations. The crown diameter and crown area, as a reflector to light capturing capacity, were much

GROWTH PERFORMANCE OF FOUR… 217

stronger predictors for change in growth performance of the tree species and were more size-dependent (Poorter

et al. 2006); which confirmed by PCA. Crown shape was the least important architecture trait and has no direct

positive correlation with height. The growth of trees was not only affected by the availability of water or the

type of irrigation, but also with many other environmental factors. Soil sand content was the main

environmental factor correlated with variations in species traits among forests as shown by CCA. Our results

are important in management and planning of future man-made forests.

Acknowledgments

This work was supported by the Swedish Research Council; and Swedish International Development

Cooperation Agency SIDA [grant no. 2008-6087]; and partial funding was provided for the first author by

Helwan University. The authors wish to express their thanks to The Ministry of Agriculture and Reclaimed

Lands, Egypt and Dr Saed Khalifa, the Director of Central Administration for Afforestation and Environment

Protection, for their facilities and permit access to the locations of present study.

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