Age Structure and Population Dynamics of Moringa peregrina, an Economically Valuable Medicinal Plant

Egypt. J. Bot. 52, No. 2, pp. 499 - 519 (2012)

Age Structure and Population Dynamics of Moringa peregrina, an

Economically Valuable Medicinal Plant

M. S. Zaghloul*, A. A. Moustafa, and M. A. Dadamouny

Botany Department, Faculty of Science, Suez Canal University, 41522 Ismailia, Egypt.

EVERAL threats affect Moringa peregrina populations and lead to high

mortality, low recruitment, and poor survival rates. To conserve M. peregrina,

understanding the populations’ dynamics is fundamental. Four Wadis in Southern

Sinai, Egypt, representing the known local geographic distribution were surveyed

and selected for the study. Age of cross-cuts was identified and used to establish the

linear regression age-radius relationship. The estimated ages (based on their radii)

of sampled trees were used to determine the age distribution and construct a static

life table. The age structure of populations consisting of multiple cohorts was used

to estimate the survival patterns of the various age groups. Tree size distribution

and relation with age structure were studied also. The results showed that the

growth rings can be taken as regular time markers, and the tree size can be used to

expect the age class of the tree. The study revealed that M. peregrina grows very

slowly and that the estimated oldest tree is more than 380 years old. The age

structure results showed unhealthy shrinking populations with a sharp decline in the

last 20-40 years and high rate of mortality among the young and the old trees. The

study came out with a conclusion that unless conditions have been changed, these

populations will permanently disappear.

Keywords: age structure, life table, Moringa peregrina, population dynamics,

Southern Sinai, survivorship curve.

Abridged Title: Population dynamics of Moringa peregrina.

Moringa is the sole genus of Moringaceae, with thirteen species distributed throughout the

dry tropics of the world (Al-Kahtani and Abou-Arab, 1993). Moringa peregrina is one of the

most economically important medicinal plant species in Egyptian markets (Abd El-Wahab et

al., 2004). Its seeds are considered as a good source of oil (Migahid, 1978; Somali et al., 1984).

Local populations of M. peregrina are endangered due to over-cutting, and over-grazing whose

effects are magnified by the contemporary prevailing extreme of drought. So, failure of

regeneration and establishment of new individuals, as well as high mortality rate of the old

trees, was well recognized in recent decades. Since the healthiness of M. peregrina population

influence the function of the species in the ecosystem (Milton and Dean, 1995), any decline in

the number or the size of these populations may have serious reflections on wildlife in general.

Therefore, the conservation of M. peregrina tree has become very necessary.

Understanding the tree dynamics is fundamental to conserve it and enjoy the benefits of

sustainable management of its populations. Demographic studies have been shown to be useful

in understanding the regulation of population numbers (Silvertown, 1982). For the plant

populations with overlapping generations, mortality, survival and reproduction tend to vary with

age or size of the individual plants (Goldstein et al., 1985; Harper, 1983). Age dating enables

determination of the age class distribution of the population. And consequently, the dating of

successful regeneration events, which can then be related to record of climate and anthropogenic

practices, especially the climatic variations, soil properties, natural and human- induced

disturbance

S

* Corresponding author. E-mail: [email protected]

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Egypt. J. Bot. 52, No. 2 (2012)

disturbance, and biological interactions that determine the rates of establishment, growth, and

mortality of the different species in the community (Van Valen, 1975; Archer, 1994). Although

Hegazy et al. (2008) aimed to analyze age-specific survival, mortality and reproduction of M.

peregrina along its altitudinal range at Gebel Shayeb Al-Banat within the Red Sea coastal

mountains, there is no information on the age structure and dynamics of the Southern Sinai’s

populations. Therefore, the present study aimed to figure out the age and size structure of M.

peregrina populations in Southern Sinai, to build up a static life table for these populations, and

to discuss the conservational implications of the results.

Materials and Methods

Study area

The study area is located between 33o 30' to 34o 26' E, and 28o 23' to 28o 47' N (Figure 1). It

is described predominantly as smooth-faced granite outcrops forming mountains such as Gebel

Serbal, Gabel Catherine, and Gabel Mousa. The study area is part of the Southern Sinai’s

triangular mass of mountains which is composed of igneous and metamorphic rocks chiefly

granites. This mass of mountains is intensively rugged and dissected by a complicated system of

deep Wadis with different landforms and irregular topography (Moustafa, 1990; Said, 1990). It

has a wide range of altitudinal among other environmental gradients and it is characterized by a

long hot and rainless summer and mild winter (Migahid et al., 1959; Batanouny, 1981; Zohary,

1973; Issar and Gilad, 1982; Danin, 1983, 1986). While, it lies in the arid to extremely arid belt,

due to the high altitude. The mountainous area of Sinai receives amounts of precipitation

average to 44.9 mm (Abdel-Wahab, 2003, Dadamouny 2009). It is affected by the orographic

impact of the high mountains and the tropical influence along the Gulf of Suez and the Gulf of

Aqaba (Danin, 1986). The rainfall, which is characterized by extreme variability in both time

and space, is very low. Meanwhile, the topographic irregularities play a great role in the

collection and redistribution of the runoff water. Low areas as regards the local topography

receive much more resources than the measured rainfall (Ramadan, 1988). The orographic

precipitation felts on the summits, cliffs and gorges of the mountains and is then transposed to

the upstream tributaries of the Wadi system (Kassas and Girgis, 1970) which makes the Wadi

systems have exceptionally rich flora (Danin, 1986; Moustafa and Klopatek, 1995).

The study was carried out on forty-one populations (Figure 1) distributed within four Wadis;

Wadi Feiran, Wadi Agala, Wadi Zaghra, and Wadi Meir. Wadi Agala is a short (≈ 4 Km) and

narrow (≈ 40 m width) tributary of Wadi Feiran. Its surface consists of the rocky substrate near

the edges and gravel in the main water channel (Abdel-Hamid, 2009). W. Agala runs parallel to

W. Aliyat and drains into W. Feiran. M. peregrina in this Wadi is highly affected with over-

collection and over-grazing.

Wadi Feiran represents one of the longest Wadis in Southern Sinai. It is bounded by igneous

and metamorphic mountains with different varieties of dykes. Its principal tributaries include

Wadi El-Sheikh, W. Solaf, W. El-Akhdar, W. Nesrin, W. Tarr, W. Mekatab, and W. Alliat. The

vegetation cover throughout the Wadi ranges between 5 and 10%. The Wadi basin supports

vegetation consists of about 40 plant species and is dominated mainly by Acacia tortilis subsp.

raddiana (Dadamouny, 2009).

Wadi Zaghra is about 100 m width and 65 km long. Its surface is mainly covered by stones

and rocky substrates. Total plant cover ranges between 1-5% in the Wadi-bed while, at its

foothills, it reaches 5-10% where M. peregrina grows. The Wadi supports the following leading

associations; Haloxylon salicornicum, Solenostemma arghel, Moringa peregrina, Artemisia

judaica, Zygophyllum coccineum – Aerva javanica, Moringa peregrina – Acacia tortilis, Acacia

tortilis, and Retama raetam. The associated plants species recorded with M. peregrina in the

main.

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Fig. 1. Study area showing locations of Moringa peregrina studied populations.

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Egypt. J. Bot. 52, No. 2 (2012)

main Wadi are: Acacia tortilis at the foothills, Capparis spinosa on cliffs and Aerva javanica, Cleome

droserifolia, Ochradenus baccatus, Senna italica, and Crotalaria aegyptiaca (Abd El-Wahab et al., 2004).

Wadi Meir is about 140 m width and 30 Km long. Its surface is mainly covered by stones and

rocky substrates. The total plant cover ranges between 1-5% all over the Wadi and 20-30% at some

tributaries at the middle of the Wadi. This Wadi is richer in plant diversity than the other studied

Wadis and is characterized by 50 plant species including one endemic and 26 medicinal species. The

associated plants species recorded with M. peregrina in W. Meir include Hyoscyamus muticus,

Cleome droserifolia, Capparis sinaica, Capparis spinosa, Acacia tortilis, Acacia negavensis,

Ochradenus baccatus, Fagonia mollis, Retama raetam, Artemisia judaica, Pulicaria arabica,

Citrullus colocynthis and Cucumis prophetarum (Abd El-Wahab et al., 2004, Dadamouny, 2009).

Determination of age-radius relationship

Ninety-three cross-cut discs were collected from selected M. peregrina trees of unknown ages from

twenty-three populations at the four surveyed Wadis. Because of the importance of individual trees in

this arid region, already cut or dead trees or branches were only sampled (Zoltai, 1975; Stockes and

Smiley, 1968). In the laboratory, cross-cuts were further cut into thin sections and surfaced with

sandpaper from both sides for better resolution. The final polishing ensured that fine scratches could

not be confused with marginal parenchyma (Figure 2). The age of each sample was obtained directly

by counting the annual rings.

The data were treated as a linear regression relationship between the tree radius (excluding the bark

thickness) and the number of counted growth rings in the sampled ninety-three cross-cut sections. The

linear regression relationship between the tree radius and bark thickness in ninety-three cross-cut

sections was also determined. The radius was assessed as a mean of eight measurements of diameter.

Anderson-Darling test (Shapiro and Francia, 1972) was used to test significant departures from

normality in measured parameters; a number of rings, radius, and bark thickness. Simple Linear

Regression Analysis was applied to figure out the equation that controls the relationship between the

radius of cross-cut sections and the number of annual rings using Minitab 15 computer software

(MINITAB, 2007). The regression was forced to pass through the origin as a logic biological fact.

Population sampling and age dating

A population-based sampling concept was applied to cover the whole spectrum of demography and

age structure of M. peregrina community in Southern Sinai. Forty-one M. peregrina sites were

sampled; four sites from W. Agala, five from W. Feiran, six from W. Zaghra, and twenty-six from

W..Meir (Table 1). Four hundred and four trees were sampled (40 trees at W. Agala, 47 at W. Feiran,

82 at W. Zaghra, and 235 at W. Meir). The number of sampled trees in each population was up to 17

trees. The number of sampled trees depended on the actual population size.

Fig. 2. Cross-cut sections of sanded samples of Moringa peregrina

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Using the resultant age-radius relationship, the ages of the sampled four hundred and four trees

were then estimated based on their wood radii. There are, however, some serious limitations

associated with this approach. Because of the considerable uncertainties involved in determining the

age of individual trees, an unavoidable error is built into the age-radius model. So, the skewness from

the normality of the resultant age distribution was assessed by Anderson-Darling normality test to

figure out the magnitude of this error. Variation in estimated trees ages between the sampled three

Wadis was evaluated using one-way ANOVA. Tukey’s pairwise comparisons were done to

discriminate between different Wadis.

Measurements of size parameters

To study the tree size distribution and its relation with age structure of M. peregrina, vegetative

parameters (height, crown cover, trunk circumference at the ground level, and circumference/height

ratio) were measured or estimated for each tree following Zaghloul et al. (2008). Variation between

trees in the sampled three Wadis was evaluated using one way ANOVA. Tukey’s pairwise

comparisons were done to discriminate between different Wadis. The correlation between the height

and circumference/height ratio with the age of the tree was evaluated using Pearson linear correlation.

Simple linear regression equation that describes the relationship between the age and size was

developed. The regression was forced to go through the origin as a logic biological fact.

Age structure, size distribution, and life table

The estimated trees ages were used to determine the age distribution and construct a static life table

(Barbour et al., 1987). The age distribution of the studied populations was used as a predictive tool to

determine if the M. peregrina populations in Southern Sinai are growing or declining. The age

structure of populations consisted of multiple cohorts was used to estimate the survival patterns of the

various age groups in a static life table after Sharitz and McCormick (1973). In the static table, we had

to make two important assumptions: 1) the population has a stable age structure – that is, the

proportion of individuals in each age class does not change from generation to generation, and 2) the

population size is, or nearly, stationary.

Age specific mortality rate (qx = chance of death) was calculated as the percentage of the

population dying during a particular age class. Survivorship curve was produced by plotting the

survivorship lx at each age interval against time. The correlation between the different size parameters

(height, crown cover, and circumference/height) with the estimated age was evaluated used Pearson

linear correlation. Simple Linear Regression equation that describes the relationship between the age

and size was also developed. This regression also was forced to go through the origin as a logic

biological fact (Dadamouny, 2009).

Results

Age- and Bark-radius relationship

Table 1 shows the descriptive statistics for the tree age and size parameters (tree radius cm, bark

thickness cm, age in years, tree height m, crown area m2, circumference cm, and Circumference/

height ratio). It reveals also the significance of variation between the studied four wadis. The results of the

linear regression significantly (P = 0.000, r2 = 0.271, Figure 3) showed that relationship between the

tree radius (excluding the bark) and the number of counted growth rings in the cross sections is

governed by the equation:

No. of rings = 5.68 Radius (cm) - - - - - - - - - - - - - - - (1)

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TABLE 1. Summary table for the studied Moringa peregrina populations.

Location Site

no.

No. of

trees

Tree height (m)*** Crown cover area (m2)*** Circumference (cm)*** Circumference/ height ratio*

Min Max Mean StD Min Max Mean StD Min Max Mean StD Min Max Mean StD

W. Agala

1 11 3.50 8.20 5.96 1.59 2.40 19.23 9.98 5.25 31.66 112.00 48.95 22.60 0.05 0.15 0.08 0.04

2 7 3.20 6.20 4.39 1.13 1.77 11.94 6.87 4.59 27.00 67.00 43.43 16.84 0.04 0.2 0.11 0.06

3 6 3.00 7.30 4.80 1.97 2.40 14.18 8.56 4.61 25.00 65.00 40.87 13.68 0.05 0.12 0.09 0.02 4 16 1.70 12.00 5.31 2.83 0.57 32.15 12.66 8.94 30.00 242.00 96.59 63.27 0.09 0.3 0.19 0.07

Total 4 40 1.70 12.00 5.25 2.18 0.57 32.15 10.30 6.98 25.00 242.00 65.83 48.91 0.04 0.3 0.13 0.07

W. Feiran

5 4 3.80 6.20 4.75 1.03 8.81 14.85 11.93 3.03 38.50 63.00 48.50 11.71 0.08 0.12 0.10 0.02

6 14 2.30 10.50 4.77 2.66 0.31 42.99 8.96 12.52 27.00 149.00 65.57 42.17 0.08 0.29 0.14 0.06 7 7 2.00 8.00 5.56 2.17 1.65 34.19 17.92 11.76 31.00 97.00 64.07 26.49 0.08 0.18 0.12 0.04

8 15 1.80 11.40 6.25 3.09 1.13 40.13 11.52 10.88 26.00 145.00 56.47 34.02 0.05 0.17 0.10 0.04

9 7 1.70 5.20 3.19 1.19 0.64 27.79 6.40 9.59 19.00 46.00 25.57 9.75 0.04 0.12 0.09 0.03

Total 5 47 1.70 11.40 5.12 2.61 0.31 42.99 10.98 11.09 19.00 149.00 55.03 33.92 0.04 0.29 0.11 0.05

W. Zaghra

10 13 2.50 8.50 5.97 2.29 0.95 35.77 11.39 10.97 16.00 128.00 46.18 31.24 0.04 0.18 0.08 0.04

11 15 4.30 15.80 8.16 3.83 8.29 203.48 46.50 54.24 30.00 236.00 112.66 72.27 0.07 0.3 0.14 0.08

12 24 2.30 14.00 8.86 3.21 0.57 52.14 27.66 15.36 20.00 325.00 121.48 81.85 0.03 0.43 0.14 0.08 13 2 12.00 12.50 12.25 0.35 11.64 47.15 29.40 25.11 74.00 235.00 154.50 113.84 0.06 0.2 0.13 0.10

14 12 1.00 14.00 9.13 3.43 0.95 37.92 21.06 11.65 35.00 211.00 89.11 46.69 0.06 0.35 0.12 0.08

15 16 4.00 10.50 7.18 1.75 5.51 34.71 18.38 8.34 40.00 480.00 118.88 106.13 0.08 0.56 0.16 0.12

Total 6 82 1.00 15.80 8.07 3.17 0.57 203.48 25.79 27.58 16.00 480.00 103.49 79.20 0.03 0.56 0.13 0.09

W. Meir

16 12 3.50 14.50 9.50 3.50 2.40 50.87 23.19 17.21 42.00 134.00 85.53 28.65 0.06 0.17 0.10 0.03

17 9 2.50 15.50 8.89 4.63 2.69 53.43 25.06 17.04 37.00 140.50 88.43 34.08 0.07 0.2 0.12 0.05

18 10 3.00 14.50 8.15 4.31 2.69 116.36 28.56 36.84 42.00 190.00 92.78 44.43 0.09 0.16 0.12 0.02 19 5 1.90 12.50 6.38 4.22 0.64 39.02 17.98 17.51 35.00 113.00 62.60 32.68 0.06 0.18 0.12 0.05

20 14 1.50 15.00 5.45 3.52 1.33 25.95 10.10 8.59 40.00 161.50 81.29 37.94 0.06 0.31 0.17 0.06

21 7 6.00 17.00 11.07 4.33 11.64 107.46 48.21 33.06 38.50 325.00 148.43 91.74 0.06 0.25 0.14 0.07 22 3 2.00 8.00 5.83 3.33 3.30 18.47 11.87 7.78 58.50 88.50 69.67 16.40 0.07 0.31 0.17 0.13

23 6 3.00 16.00 9.30 6.12 1.28 105.63 53.16 53.42 37.00 138.00 89.17 38.27 0.08 0.21 0.12 0.06

24 16 3.00 10.50 5.97 2.23 1.33 25.50 10.70 7.74 41.33 184.00 99.54 48.91 0.08 0.33 0.17 0.07 25 14 2.00 15.50 6.31 4.05 0.79 64.29 16.24 17.98 32.00 137.00 67.46 36.20 0.08 0.17 0.12 0.03

26 6 2.60 14.00 7.55 4.16 2.14 30.66 14.12 10.11 51.00 160.33 98.47 39.56 0.11 0.2 0.14 0.04

27 8 2.50 16.00 10.94 4.72 3.63 87.37 22.17 27.77 43.00 158.50 86.75 42.40 0.05 0.17 0.09 0.04 28 15 1.50 11.80 5.23 3.28 1.13 39.02 9.71 9.75 40.00 170.00 71.07 34.41 0.05 0.27 0.16 0.05

29 2 2.60 10.00 6.30 5.23 5.94 20.02 12.98 9.96 57.00 103.50 80.25 32.88 0.1 0.22 0.16 0.08

30 9 3.50 16.30 8.32 4.48 2.27 36.30 16.90 9.86 52.50 146.00 87.17 32.36 0.09 0.19 0.12 0.04 31 5 4.70 14.80 9.58 3.64 9.34 47.15 28.63 15.32 72.00 270.00 147.90 84.75 0.06 0.26 0.16 0.09

32 6 4.70 9.50 7.37 1.98 8.55 20.42 13.22 4.97 72.50 217.00 130.00 52.53 0.11 0.23 0.18 0.05

33 12 1.80 8.50 5.82 2.46 1.54 30.66 11.60 8.56 54.00 217.00 112.75 48.16 0.14 0.3 0.21 0.06 34 8 2.00 12.50 7.18 3.90 1.59 42.41 16.57 15.95 48.00 302.50 165.04 95.64 0.15 0.38 0.23 0.07

35 10 3.00 10.50 6.00 2.25 3.30 37.92 12.48 10.11 43.00 307.50 90.48 78.52 0.09 0.29 0.14 0.06

36 9 2.80 9.60 5.93 2.20 1.65 20.82 10.72 6.43 43.00 308.50 99.59 84.15 0.09 0.32 0.15 0.07 37 17 3.00 12.50 6.33 2.17 2.40 39.57 13.04 8.57 43.00 219.00 80.83 40.30 0.08 0.18 0.13 0.03

38 12 2.30 9.50 5.09 2.25 2.69 21.64 10.11 7.04 40.00 179.50 78.13 47.68 0.11 0.25 0.15 0.04

39 7 4.00 7.00 5.64 1.11 5.51 14.18 10.14 2.64 37.00 77.00 53.86 13.04 0.07 0.12 0.10 0.02 40 10 5.50 14.50 8.98 3.07 5.94 47.15 21.17 13.55 42.50 149.50 82.60 37.38 0.06 0.19 0.10 0.04

41 3 4.50 7.00 6.00 1.32 12.88 37.37 23.69 12.49 79.00 138.00 102.33 31.37 0.12 0.31 0.19 0.11

Total 26 235 1.50 17.00 7.09 3.67 0.64 116.36 17.49 19.10 32.00 325.00 92.05 53.24 0.05 0.38 0.14 0.06

Pooled

population 41 404 1.00 17.00 6.88 3.47 0.31 203.48 17.70 20.19 16.00 480.00 87.47 59.19 0.03 0.56 0.13 0.07

Significance of variation between populations: * P ≤ 0.05, ** P ≤ 0.02, and *** P = 0.000

Continued

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TABLE 1. Continue.

Location Population no. Number of trees Radius (cm) Bark thickness (cm) Estimated age ***

Min Max Mean StD Min Max Mean StD Min Max Mean StD

W. Agala

1 11 5.04 17.83 7.79 3.60 0.61 2.16 0.94 0.44 25.17 89.04 38.92 17.97

2 7 4.30 10.67 6.92 2.68 0.52 1.29 0.84 0.32 21.47 53.27 34.53 13.39

3 6 3.98 10.35 6.51 2.18 0.48 1.25 0.79 0.26 19.88 51.68 32.49 10.88 4 16 4.78 38.54 15.38 10.07 0.58 4.66 1.86 1.22 23.85 192.39 76.79 50.30

Total 4 40 3.98 38.54 10.48 7.79 0.48 4.66 1.27 0.94 19.88 192.39 52.33 38.89

W. Feiran

5 4 6.13 10.03 7.72 1.86 0.74 1.21 0.93 0.23 30.61 50.09 38.56 9.31

6 14 4.30 23.73 10.44 6.71 0.52 2.87 1.26 0.81 21.47 118.46 52.13 33.52 7 7 4.94 15.45 10.20 4.22 0.60 1.87 1.23 0.51 24.65 77.12 50.94 21.06

8 15 4.14 23.09 8.99 5.42 0.50 2.79 1.09 0.66 20.67 115.28 44.89 27.05

9 7 3.03 7.32 4.07 1.55 0.37 0.89 0.49 0.19 15.11 36.57 20.33 7.75

Total 5 47 3.03 23.73 8.76 5.40 0.37 2.87 1.06 0.65 15.11 118.46 43.75 26.96

W. Zaghra

10 13 2.55 20.38 7.35 4.97 0.31 2.47 0.89 0.60 12.72 101.76 36.71 24.83

11 15 4.78 37.58 17.94 11.51 0.58 4.55 2.17 1.39 23.85 187.62 89.56 57.46

12 24 3.18 51.75 19.34 13.03 0.39 6.26 2.34 1.58 15.90 258.38 96.58 65.07 13 2 11.78 37.42 24.60 18.13 1.43 4.53 2.98 2.19 58.83 186.83 122.83 90.51

14 12 5.57 33.60 14.19 7.44 0.67 4.07 1.72 0.90 27.83 167.75 70.84 37.12

15 16 6.37 76.43 18.93 16.90 0.77 9.25 2.29 2.04 31.80 381.61 94.51 84.37

Total 6 82 2.55 76.43 16.48 12.61 0.31 9.25 1.99 1.53 12.72 381.61 82.27 62.96

W. Meir

16 12 6.69 21.34 13.62 4.56 0.81 2.58 1.65 0.55 33.39 106.53 68.00 22.78

17 9 5.89 22.37 14.08 5.43 0.71 2.71 1.70 0.66 29.42 111.70 70.30 27.10

18 10 6.69 30.25 14.77 7.07 0.81 3.66 1.79 0.86 33.39 151.05 73.76 35.32 19 5 5.57 17.99 9.97 5.20 0.67 2.18 1.21 0.63 27.83 89.84 49.77 25.99

20 14 6.37 25.72 12.94 6.04 0.77 3.11 1.57 0.73 31.80 128.40 64.62 30.16

21 7 6.13 51.75 23.64 14.61 0.74 6.26 2.86 1.77 30.61 258.38 118.00 72.93 22 3 9.32 14.09 11.09 2.61 1.13 1.71 1.34 0.32 46.51 70.36 55.39 13.04

23 6 5.89 21.97 14.20 6.09 0.71 2.66 1.72 0.74 29.42 109.71 70.89 30.43

24 16 6.58 29.30 15.85 7.79 0.80 3.55 1.92 0.94 32.86 146.28 79.14 38.88 25 14 5.10 21.82 10.74 5.76 0.62 2.64 1.30 0.70 25.44 108.92 53.64 28.78

26 6 8.12 25.53 15.68 6.30 0.98 3.09 1.90 0.76 40.55 127.47 78.29 31.45

27 8 6.85 25.24 13.81 6.75 0.83 3.05 1.67 0.82 34.19 126.01 68.97 33.71 28 15 6.37 27.07 11.32 5.48 0.77 3.28 1.37 0.66 31.80 135.15 56.50 27.36

29 2 9.08 16.48 16.48 5.24 1.10 1.99 1.99 0.63 45.32 82.28 82.28 26.14

30 9 8.36 23.25 13.88 5.15 1.01 2.81 1.68 0.62 41.74 116.07 69.30 25.73

31 5 11.46 42.99 23.55 13.50 1.39 5.20 2.85 1.63 57.24 214.66 117.58 67.38

32 6 11.54 34.55 20.70 8.36 1.40 4.18 2.50 1.01 57.64 172.52 103.35 41.76

33 12 8.60 34.55 17.95 7.67 1.04 4.18 2.17 0.93 42.93 172.52 89.64 38.29 34 8 7.64 48.17 26.28 15.23 0.92 5.83 3.18 1.84 38.16 240.49 131.21 76.03

35 10 6.85 48.96 14.41 12.50 0.83 5.92 1.74 1.51 34.19 244.47 71.94 62.42

36 9 6.85 49.12 15.86 13.40 0.83 5.94 1.92 1.62 34.19 245.26 79.18 66.90 37 17 6.85 34.87 12.87 6.42 0.83 4.22 1.56 0.78 34.19 174.11 64.26 32.04

38 12 6.37 28.58 12.44 7.59 0.77 3.46 1.51 0.92 31.80 142.71 62.11 37.90

39 7 5.89 12.26 8.58 2.08 0.71 1.48 1.04 0.25 29.42 61.22 42.82 10.37 40 10 6.77 23.81 13.15 5.95 0.82 2.88 1.59 0.72 33.79 118.86 65.67 29.71

41 3 12.58 21.97 16.30 5.00 1.52 2.66 1.97 0.60 62.81 109.71 81.36 24.94

Total 26 235 5.10 51.75 14.66 8.48 0.62 6.26 1.77 1.03 25.44 258.38 73.18 42.33

Pooled population 41 404 2.55 76.43 13.93 9.42 0.31 9.25 1.69 1.14 12.72 381.61 69.54 47.05

Significance of variation between populations: * P ≤ 0.05, ** P ≤ 0.02, and *** P = 0.000

506

AGE STRUCTURE AND POPULATION DYNAMICS OF MORINGA PEREGRINA

Egypt. J. Bot. 52, No. 2 (2012)

While the relationship between the bark thickness and radius is controlled by the significant (P =

0.000, r2 = 0.187, Figure 3) linear regression equation:

Bark thickness (cm) = 0.121 Radius (cm) - - - - - - - - - - - - - - - (2)

Meanwhile, the Anderson-Darling normality test showed that the measured parameters (number of

annual rings, radius, and bark thickness) are significantly deviated from normality (P = 0.030, <0.005,

and <0.005; consequently, Figure 4). Based on the regression equation, the estimated oldest M.

peregrina tree in studied populations is 382 years old (W. Zaghra), and the youngest tree is 12.7 years

old (W. Zaghra). The mean age of the trees in W. Zaghra (82.3 ± 63 years) is higher than in W. Meir

(69.5 ± 47.1 years), W. Agala (52.3 ± 38.9 years), and W. Fieran (43.8 ± 27 years) with an overall

mean of 69.5 ± 47.1 years (Table 1). The annual increment of tree radius has been estimated to be 1.76

mm.

Age dating and structure and life table

The age-radius regression equation was used to estimate the age of the sampled four hundred and

four trees. ANOVA revealed that there is an extremely significant variation (P = 0.000) in estimated

trees ages between the four Wadis. The estimated age distribution significantly departed from a

normal distribution (Figure 5). Anderson-Darling normality test showed that the skewness from

normality is associated with the extreme radii (lower than 7 cm and higher than 28 cm (Figure 6). This

trend means that estimated ages less than 40 years and more than 159 years have a higher degree of

uncertainty.

The age structure of M. peregrina populations (Table 2) showed that the majority (50.7%) of the

trees are 41-80 years old. It was also revealed that 50% of the trees in W. Agala, 40.4 % in W. Feiran,

76.8 % in W. Zaghra, 81.7% in W. Meir, and 72.8% for the pooled population are older than 40 years

(Table 2). New individuals established during the last 20 years are not exceeding 2.5% in W. Agala,

8.5% in W. Feiran, 7.3% in W. Zaghra, 2.7% in the overall population. In W. Meir, there are no new

individuals established at all during the last 20 years (Table 2) and only 18.3% of the population was

established in the last 20-40 years. It reflects the magnitude of stress that the populations faced. It

means that these populations are declining with almost no regeneration and most probably will face

extinction if not appropriate measurements are taken. Also, the age structure showed the unhealthy

status of M. peregrina populations due to the rapidly shrinking in both sides of the curve (Figure 5).

The shrinking phase started around 20 - 40 years ago with a sharp decline in the last 20 years. This

figure suggests that if the current situation remains unchanged, the populations of M. peregrina trees

will not persist, that the older trees are not being replaced by young trees.

Based on the static life table, the old M. peregrina trees (≥ 180 years in W. Agala, ≥ 100 years in

W. Feiran, ≥ 260 years in W. Zaghra, and ≥ 240 years in W. Meir) have a 100% chance of death (qx =

1.00) (Tables 3). These death-facing trees represent 5%, 6.4%, 1.2%, and 1.7% of populations at W.

Agala, W. Feiran, W. Zaghra, and W. Meir, respectively. Life table (Table 3) also showed that the

highest risk of death was recorded in trees older than 100 years old (represent 10%, 6.4%, 23.2%, and

20.9% of W. Agala, W. Feiran, W. Zaghra and W. Meir populations, respectively). The survivorship

curve (Figure 7) obtained from survivorship lx values showed that young and old individuals of M.

peregrina have higher rates of mortality. The value of lx was declined in three Wadis (Agala, Feiran,

and Zaghra) at the age class [21- 40] and the age class [41-60] in W. Meir.

Size distribution and its relation with age distribution

The size measurements of M. peregrina trees showed that the mean height is 6.9 m (± 3.5), the

mean crown cover area is 17.7 m2 (± 20.2), the mean circumference at ground level (CAG) is 87.5 cm

(± 59.2), and the mean circumference/height ratio is 0.13 (±0.07) (Table 1 and Figure 8). The highest

105

M. S. ZAGHLOUL et al.

Egypt. J. Bot. 52, No. 2 (2012)

Fig. 3. Regression curve and equation between the radius and (a) bark thickness (cm) and (b) number of annual

rings of sampled M. peregrina 93 cross-cuts.

Radius (cm)

Ba

rk t

hic

kn

ess (

cm

)

6543210

1.0

0.8

0.6

0.4

0.2

0.0

Line Fit Plot

Bark thickness = 0.121 * Radius (cm)

= 0.192 r

Radius (cm)

No

of

rin

gs

543210

35

30

25

20

15

10

5

0

Line Fit Plot

No of rings = 5.68 * Radius (cm)

= 0.272 r

(a)

(b)

508

AGE STRUCTURE AND POPULATION DYNAMICS OF MORINGA PEREGRINA

Egypt. J. Bot. 52, No. 2 (2012)

Fig. 4. Normality test for (a) radius, (b), bark thickness and (c) no. of rings in sampled M. peregrina 93 cross-

cuts.

Radius (cm)

Pe

rce

nt

654321

99.9

99

95

90

80

7060504030

20

10

5

1

0.1

Mean

0.030

3.614

StDev 0.7351

N 93

AD 0.833

P-Value

Probability Plot of RadiusNormal

No of rings

Pe

rce

nt

403530252015105

99.9

99

95

90

80

7060504030

20

10

5

1

0.1

Mean

<0.005

20.83

StDev 5.058

N 93

AD 1.154

P-Value

Probability Plot of RingsNormal

Bark thickness (cm)

Pe

rce

nt

1.251.000.750.500.250.00

99.9

99

95

90

80

7060504030

20

10

5

1

0.1

Mean

<0.005

0.4991

StDev 0.2026

N 93

AD 2.163

P-Value

Probability Plot of BarkNormal

(c)

(a)

(b)

105

M. S. ZAGHLOUL et al.

Egypt. J. Bot. 52, No. 2 (2012)

TABLE 2. Age structure of Moringa peregrina populations in Southern Sinai. Note, cumulative percent represents the percentage of individuals

with age more than the upper limit of the specified class.

Age W. Agala W. Feiran W. Zaghra W. Meir Pooled Populations

Class Freq. % Cum. % Freq. % Cum. % Freq. % Cum. % Freq. % Cum. % Freq. % Cum. %

[≤ 20] 1 2.5 39 97.5 4 8.5 43 91.5 6 7.3 76 92.7 0 0.0 235 100.0 11.0 2.7 393.0 97.3

[21-40] 19 47.5 20 50.0 24 51.1 19 40.4 13 15.9 63 76.8 43 18.3 192 81.7 99.0 24.5 294.0 72.8

[41-60] 10 25.0 10 25.0 9 19.1 10 21.3 16 19.5 47 57.3 71 30.2 121 51.5 106.0 26.2 188.0 46.5

[61-80] 4 10.0 6 15.0 5 10.6 5 10.6 16 19.5 31 37.8 42 17.9 79 33.6 67.0 16.6 121.0 30.0

[81-100] 2 5.0 4 10.0 2 4.3 3 6.4 12 14.6 19 23.2 30 12.8 49 20.9 46.0 11.4 75.0 18.6

[101-120] 2 5.0 2 5.0 3 6.4 0 0.0 5 6.1 14 17.1 24 10.2 25 10.6 34.0 8.4 41.0 10.1

[121-140] 0 0.0 2 5.0 0 0.0 0 0.0 2 2.4 12 14.6 9 3.8 16 6.8 11.0 2.7 30.0 7.4

[141-160] 0 0.0 2 5.0 0 0.0 0 0.0 1 1.2 11 13.4 4 1.7 12 5.1 5.0 1.2 25.0 6.2

[161-180] 0 0.0 2 5.0 0 0.0 0 0.0 5 6.1 6 7.3 6 2.6 6 2.6 11.0 2.7 14.0 3.5

[181-200] 2 5.0 0 0.0 0 0.0 0 0.0 3 3.7 3 3.7 0 0.0 6 2.6 5.0 1.2 9.0 2.2

[201-220] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 3 3.7 2 0.9 4 1.7 2.0 0.5 7.0 1.7

[221-240] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 3 3.7 0 0.0 4 1.7 0.0 0.0 7.0 1.7

[241-260] 0 0.0 0 0.0 0 0.0 0 0.0 2 2.4 1 1.2 4 1.7 0 0.0 6.0 1.5 1.0 0.2

[261-280] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 1.2 0 0.0 0 0.0 0.0 0.0 1.0 0.2

[281-300] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 1.2 0 0.0 0 0.0 0.0 0.0 1.0 0.2

[300-320] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 1.2 0 0.0 0 0.0 0.0 0.0 1.0 0.2

[321-340] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 1.2 0 0.0 0 0.0 0.0 0.0 1.0 0.2

[341-360] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 1.2 0 0.0 0 0.0 0.0 0.0 1.0 0.2

[361-380] 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 1 1.2 0 0.0 0 0.0 0.0 0.0 1.0 0.2

[>381] 0 0.0 0 0.0 0 0.0 0 0.0 1 1.2 0 0.0 0 0.0 0 0.0 1.0 0.2 0.0 0.0

510

AGE STRUCTURE AND POPULATION DYNAMICS OF MORINGA PEREGRINA

Egypt. J. Bot. 52, No. 2 (2012)

Fig. 5. Age structure of M. peregrina at the pooled population (a) and each studied Wadi separately

(b).

Fre

qu

en

cy

200

180

160

140

120

100806040200

20

15

10

5

0

120

100806040200

12

9

6

3

0

400

360

320

280

240

200

160

12080400

30

20

10

0

260

240

220

200

180

160

140

120

100806040200

60

45

30

15

0

W. Agala W. Feiran

W. Zaghra W. Meir

W. Agala

43.75

StDev 26.97

N 47

W. Zaghra

Mean 82.27

StDev 62.96

Mean

N 82

W. Meir

Mean 73.18

StDev 42.33

N 235

52.34

StDev 38.89

N 40

W. Feiran

Mean

Normal

Histogram of Ages by Wadi (2007)

W. Meir

W. Meir

Estimated Age (year)

Fre

qu

en

cy

400

380

360

340

320

300

280

260

240

220

200

180

160

140

120

100806040200

140

120

100

80

60

40

20

0

Mean 69.54

StDev 47.06

N 404

Normal

Histogram of Estimated Age (2007)(a)

(b)

155

M. S. ZAGHLOUL et al.

Egypt. J. Bot. 52, No. 2 (2012)

Fig. 6. Normality test of radii (a) and estimated age (b) in sampled M. peregrina trees.

Fig. 7. Survivorship curves of M. peregrina populations in Southern Sinai estimated in 2007.

Radius (R)

Pe

rce

nt

806040200

99.9

99

95

90

80

7060504030

20

10

5

1

0.1

Mean

<0.005

13.93

StDev 9.424

N 404

AD 18.023

P-Value

Probability Plot of Radius (R)Normal

(a)

Age (2007)

Pe

rce

nt

4003002001000-100

99.9

99

95

90

80

7060504030

20

10

5

1

0.1

Mean

<0.005

69.54

StDev 47.06

N 404

AD 18.025

P-Value

Probability Plot of Age (2007)Normal

(b)

512

AGE STRUCTURE AND POPULATION DYNAMICS OF MORINGA PEREGRINA

Egypt. J. Bot. 52, No. 2 (2012)

mean values of the tree height (8.1 m), crown cover area (25.8 m2), and circumference at

ground level (103.5 cm) were recorded in the trees of W. Zaghra populations. The shortest

tree (1 m) was recorded in W. Zaghra, while the tallest (17 m) in W. Meir. The smallest

crown cover (0.3 m2) was recorded in W. Feiran, while the largest (203.5 m2) in W. Zaghra.

The minimum (16 cm) and the maximum (480 cm) circumference were recorded in W.

Zaghra. ANOVA revealed that there is significant to highly significant variations in the

measured tree size parameters (height, crown cover area, trunk circumference, and

circumference/height ratio) between the four studied Wadis (Table 1). Tukey’s test couldn't

differentiate between size of trees at W. Zaghra and at W. Meir. The size structure of the

populations at the four Wadis showed that only 22.0% of the studied M. peregrina trees (2.5%

in W. Agala, 12.8% in W. Feiran, 7.3% in W. Zaghra, and 24.7% in W. Meir) are taller than 6

m. Meanwhile, only 8.4% (4.3% in W. Feiran, 15.9% in W. Zaghra, 8.1% in W. Meir, and

0.0% in W. Agala) of the trees have crown cover area more than 40 m2. These results reflect

the strength of the stress of over-grazing and over-cutting over the tree populations in the

study area where majority of the trees are small sized although they are old.

Based on the Pearson correlation coefficient, a highly significant (P = 0.000) positive

linear relationship was detected between tree size parameters (height, crown cover, and

circumference/height ratio) and estimated tree age. The output results of the linear regression

confirmed this strong relation and showed that either of size parameters can be used to infer

the age class of M. peregrina trees according to the following equations:

Age (years) = 9.66 height (m) - - - - - - - - - - - - - - - - - - - - - - (3)

Age (years) = 2.41 crown cover (m2) - - - - - - - - - - - - - - - - - (4)

Age (years) = 494 circumference/height ration - - - - - - - - - - - (5)

Discussion

To build up a long-term conservation plant, understanding of the structure and dynamics

of plant populations are required. The structure of a population of plants can be described in

terms of ages, sizes and forms of the individuals that compose it (Harper and White, 1974).

Age and size measurements are usually used to determine the age- or size-class distribution of

a tree population, from which inferences on the dynamics of that population can be drawn

(Fritts and Swetnam, 1989). The knowledge of age and growth rates of trees is necessary for

an understanding of tree recruitment patterns and woodland management (Suarez et al.,

2008). Tree growth rings are widely applied in ecological studies for determining tree ages,

investigating changes in growth rates and elucidating their causes (Fritts and Swetnam, 1989).

Besides being the most geographically wide-spread entity that can provide actual year-to-year

dating of current and prehistoric environmental changes (Jacoby and Wagner, 1993), annual

growth rings have been shown to be a reliable means of estimating tree age and growth rate in

temperate regions (Ogden, 1981; Schweingruber, 1988). However, few studies exist for arid

areas (e.g. Zaghloul et al., 2008).

To age date M. peregrina tree, we measured stem diameter in cross-cut samples,

regenerated a regression equation describing the relationship between age and diameter and

used this equation to estimate all tree ages. The obtained results of the linear regression

showed a highly significant relationship (P = 0.000, r2 = 0.27) between the tree radius

(excluding the bark) and the number of counted growth rings which means that the growth

rings can be taken as regular time markers and could be used for dating the trees. The results

suggested that M. peregrina trees in Southern Sinai grow very slowly, with an annual

increment of 1.76 mm, and their age range between 13 and 382 years with a mean of 69.5 ±

47 years. Problems associated with using stem diameter to predict age were discussed by

Ogden (1981); Norton and Ogden (1990), Wyant and Reid (1992). We had to assume that one

155

M. S. ZAGHLOUL et al.

Egypt. J. Bot. 52, No. 2 (2012)

TABLE 3. A static life table of Moringa peregrina populations in Southern Sinai. X = age entered by the time of census, Nx = number of individuals living in x age class, ax =

number of individuals that survive to age x, lx = proportion of original cohort surviving to age x, Lx = the average proportion alive at that age, Tx the total number of living

individuals at age class x and beyond, ex = the probability of living 'x' number of years beyond a given age, dx = number of individuals that die during intervals, and qx = proportion

of individuals entering age x that die during age x.

Age Wadi Agala Wadi Feiran Wadi Zaghra Wadi Meir Pooled Population

Class Nx ax lx Lx Tx ex dx qx Nx ax lx Lx Tx ex dx qx Nx ax lx Lx Tx ex dx qx Nx ax lx Lx Tx ex dx qx Nx ax lx Lx Tx ex dx qx

[≤ 20] 1 40 1.00 0.99 2.68 2.68 1 0.03 4 47 1.00 0.96 2.20 2.20 4 0.09 6 82 1.00 0.96 4.10 4.10 6 0.07 0 235 1.00 1.00 3.69 3.69 0 0.00 11 404 1.00 0.99 3.50 3.50 11 0.03

[21-40] 19 39 0.98 0.74 1.69 1.73 19 0.49 24 43 0.91 0.66 1.24 1.36 24 0.56 13 76 0.93 0.85 3.13 3.38 13 0.17 43 235 1.00 0.91 2.69 2.69 43 0.18 99 393 0.97 0.85 2.51 2.58 99 0.25

[41-60] 10 20 0.50 0.38 0.95 1.90 10 0.50 9 19 0.40 0.31 0.59 1.45 9 0.47 16 63 0.77 0.67 2.29 2.98 16 0.25 71 192 0.82 0.67 1.78 2.18 71 0.37 106 294 0.73 0.60 1.66 2.29 106 0.36

[61-80] 4 10 0.25 0.20 0.58 2.31 4 0.40 5 10 0.21 0.16 0.28 1.30 5 0.50 16 47 0.57 0.48 1.62 2.82 16 0.34 42 121 0.51 0.43 1.11 2.16 42 0.35 67 188 0.47 0.38 1.07 2.29 67 0.36

[81-100] 2 6 0.15 0.13 0.38 2.51 2 0.33 2 5 0.11 0.09 0.12 1.10 2 0.40 12 31 0.38 0.30 1.14 3.01 12 0.39 30 79 0.34 0.27 0.69 2.04 30 0.38 46 121 0.30 0.24 0.68 2.28 46 0.38

[101-120] 2 4 0.10 0.08 0.25 2.51 2 0.50 3 3 0.06 0.03 0.03 0.50 3 1.00 5 19 0.23 0.20 0.83 3.60 5 0.26 24 49 0.21 0.16 0.41 1.99 24 0.49 34 75 0.19 0.14 0.44 2.38 34 0.45

[121-140] 0 2 0.05 0.05 0.18 3.53 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 2 14 0.17 0.16 0.63 3.71 2 0.14 9 25 0.11 0.09 0.26 2.42 9 0.36 11 41 0.10 0.09 0.30 2.94 11 0.27

[141-160] 0 2 0.05 0.05 0.13 2.45 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 1 12 0.16 0.15 0.47 2.97 1 0.08 4 16 0.07 0.06 0.17 2.50 4 0.25 5 30 0.08 0.07 0.21 2.74 5 0.17

[161-180] 0 2 0.05 0.05 0.08 1.50 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 5 11 0.13 0.10 0.32 2.41 5 0.45 6 12 0.05 0.04 0.11 2.17 6 0.50 11 25 0.06 0.05 0.14 2.26 11 0.44

[181-200] 2 2 0.05 0.03 0.03 0.50 2 1.00 0 0 0.00 0.00 0.00 0.00 0 0.00 3 6 0.07 0.05 0.22 3.00 3 0.50 0 6 0.03 0.03 0.07 2.83 0 0.00 5 14 0.03 0.03 0.09 2.64 5 0.36

[201-220] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 3 0.04 0.04 0.16 0.00 0 0.00 2 6 0.03 0.02 0.05 1.83 2 0.00 2 9 0.02 0.02 0.06 2.83 2 0.00

[221-240] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 3 0.04 0.04 0.13 3.50 0 0.00 0 4 0.02 0.02 0.03 1.50 0 0.00 0 7 0.02 0.02 0.04 2.50 0 0.00

[241-260] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 2 3 0.04 0.02 0.09 2.50 2 0.00 4 4 0.02 0.01 0.01 0.50 4 1.00 6 7 0.02 0.01 0.03 1.50 6 0.00

[261-280] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.01 0.01 0.07 5.50 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.00 0.00 0.02 6.50 0 0.00

[281-300] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.01 0.01 0.05 4.50 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.00 0.00 0.01 5.50 0 0.00

[300-320] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.01 0.01 0.04 3.50 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.00 0.00 0.01 4.50 0 0.00

[321-340] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.01 0.01 0.03 2.50 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.00 0.00 0.01 3.50 0 0.00

[341-360] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.01 0.01 0.02 1.50 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.00 0.00 0.01 2.50 0 0.00

[361-380] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.01 0.01 0.01 0.50 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 0 1 0.00 0.00 0.00 1.50 0 0.00

[>381] 0 0 0.00 0.00 0.00 0.00 0 0.00 0 0 0.00 0.00 0.00 0.00 0 0.00 1 1 0.00 0.00 0.00 0.00 1 1.00 0 0 0.00 0.00 0.00 0.00 0 0.00 1 1 0.00 0.00 0.00 0.50 1 1.00

Total 40 47 82 235 404

514

AGE STRUCTURE AND POPULATION DYNAMICS OF MORINGA PEREGRINA

Egypt. J. Bot. 52, No. 2 (2012)

Fig. 8. Size structure of M. peregrina populations; (a) tree height, (b) crown cover, and (c)

circumference/height.

151

M. S. ZAGHLOUL et al.

Egypt. J. Bot. 52, No. 2 (2012)

growth ring can be equated with one year's growth. Angiosperms frequently produce

anomalous growth patterns and rings which are not necessarily annual. For example, a stress

period may occur during a growing season and cause more than one growth layer to form

within that year (Fritts and Swetnam, 1989). Alternatively, when conditions are extremely

limiting (which is the prevailing conditions in Southern Sinai), growth cannot occur and no

ring is produced (Steenkamp, 2000). Certain regions of the cambium may not divide at all

giving the appearance of a missing ring (Fahn, 1974; Fritts, 1976; Lilly, 1977; Walker et al.,

1986). As a result, there is a high probability that the estimated ages of the trees and

populations could be under-estimated.

The regeneration of M. peregrina tree in the area is severely limited. The age structure of

the studied M. peregrina populations confirmed the dominance of old individuals and showed

that only 2.7% of trees are ≤ 20 years old and 30% of the trees are older than 80 years old.

This type of age structure reflects the unhealthy shrinking status of populations in the study

area with sharp decline in the last 20-40 years. It also indicates that the major contribution to

the populations is made by the intermediate cohorts (20-80 years old). So, the first

conservation priority should be directed to these cohorts. Similar type of age structure was

obtained by Hegazy et al. (2008) for M. peregrina populations growing on Gebel Shayeb Al-

Banat within the Red Sea coastal mountains; nevertheless they recorded juveniles in all the

studied populations.

Although many of the individuals in populations may produce ripen viable seeds, no

individuals had been established for at least the last 20-40 years. These results was supported

by the results of static life table that revealed that trees ≥ 180 years old in W. Agala, ≥ 100

years in W. Feiran, ≥ 260 years in W. Zaghra, and ≥ 240 years in W. Meir have a 100%

chance of death (qx = 1.00). Also, the survivorship curve showed high rate of mortality among

the young and the old trees. It suggests that if the current situation remained unchanged, the

populations of M. peregrina trees will not persist, that the older trees are not being replaced

by the young trees. A very similar situation was revealed by Zaghloul et al. (2008) for Acacia

trees (Acacia tortilis subsp. raddiana) in the same study area (Southern Sinai). Any planned

conservation efforts should include restoration and rehabilitation programs aiming to

maximize the young ages to ensure a continuous and uninterrupted population dynamics

(Harper and White, 1974; Solbrig, 1980; Parish and Antos, 2004).

Since the fecundity and survival of plants are often much more closely related to size than

to age, it is necessary to study the size distribution (Harper, 1983; Caswell, 1986; Weiner,

1985; Shaltout and Ayyad, 1988). Some researchers (Werner and Caswell, 1977; Kirkpatrick,

1984; Caswell, 1986) argued that it is better to classify the life history of plants by size rather

than age that is the most widely used in classification of organisms. According to Emslie

(1991), it is necessary to study woody vegetation at a size classes. Plant size determines the

potential investment into reproductive structures and hence size classes are considered to be

better indicators of reproductive output than age classes (Werner and Caswell, 1977; Knowles

and Grant, 1983). Nevertheless, Grice et al. (1994) concluded that size is not a good indicator

of age and that it is unreliable to identify cohorts of the tree by examining size-class

frequency distribution. On the other hand, Ahmed et al. (2009), studying the relationship

between the ages and sizes of different mature stands of thirty nine gymnosperms based on

simple ring count and DBH measurements, showed that the largest tree is not necessarily the

oldest tree. However, in the present study, the Pearson correlation coefficient showed that

there is a highly significant positive linear relationship between the size and the estimated age

of M. peregrina tree. The correlation and linear regression analysis revealed that the size

(especially height and circumference/height ratio) can be used to expect the age class of M.

peregrina tree. Size could be used as indicator for age in other tree species (e.g. Niklas, 1997;

Sano, 1997; Stoneman et al., 1997; Suarez et al., 2008; Zaghloul et al., 2008).

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AGE STRUCTURE AND POPULATION DYNAMICS OF MORINGA PEREGRINA

Egypt. J. Bot. 52, No. 2 (2012)

Size differences may be return to the differences in growth rates, age differences, genetic

variation, heterogeneity of resources, nutrition, and competition (Weiner, 1985; Caswell,

1986). Daniels et al. (1995) indicated that the shape of age distribution of trees is affected by

number of factors like the variation in site characteristics, soil variations, degree of impact,

and climate changes that control the regeneration of the tree. In current study, ANOVA results

showed that there are highly significant variations (P ≤ 0.000) in the measured tree ages and

sizes (especially height, crown cover area, and trunk circumference) between the four studied

Wadis which may reflect different environmental factors and/or levels of human stress. As

most of the environmental factors are not different significantly between the studied Wadis

(Dadamouny, 2009), therefore, it seems that the variations in age and size distribution

between Wadis are most probably affected by anthropogenic effects (e.g. over-cutting,

grazing) which are more disturbing at W. Feiran and W. Agala than at W. Meir and than in

W. Zaghra.

Due to the shrinking status of M. peregrina populations in Southern Sinai, rapid

conservation efforts should be directed to minimize the exploitation of the species by local

people. In situ and ex situ conservation, restoration, and rehabilitation of M. peregrina

populations are strongly recommended. In general, magnified by the prevailing drought,

unmanaged human activities in the last twenty-five years have threatened rare species,

resulted in disappearance of pastoral plant species, and have caused an increased dominance

of unpalatable plant species in the area. The key to learning the status of a rare species of

special concern is to census the species and monitors its populations over time.

By repeating census for a population on a regular basis, changes in the population over

time can be determined accurately (Simberloff, 1988; Primack and Hall, 1992; Schemske et

al., 1994; Primack, 1998). Long-term census records can help to distinguish long-term

population trends of increase or decrease, possibly caused by human disturbance, from short-

term fluctuation caused by variations in weather or unpredictable natural events (Pechmann et

al., 1991; Primack, 1998). As the current study depended on static sampling, more accurate

modeling of the populations' structure would require data for growth and mortality over a

long time especially during the climatic extremes that probably have a major influence on

population structure for a number of years. Also, population viability analysis (PVA) is

urgently needed to identify the factors that are important in dynamics of M. peregrina

populations and management options precisely.

Acknowledgment

The authors are greatly thankful for Mr. Ayman Abd El-Hamid, the graduate student, for

his technical assistance. The authors' appreciation extends to the St. Catherine Protectorate

authorities for facilitating the field work.

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