Name:  Mohamed El Sayed Abdel Fatah M. Elhag

Date of Birth: 10/8/1976                                                                                  

Nationality: Egyptian

Previous Degree: B.Sc. (Botany)

Registration Date: 17/2/2001

Awarding Date:

Supervision:                  -

1-     Prof. Ahmad K. Hegazy,

2-     Prof. Nadia El Sawaf,

Examiners:                    -

1-     Prof. Ahmad K. Hegazy,

2-     Prof. M. Ajmal Khan

3-     Prof. Ahmad El Khateeb,

Title of Thesis:

Population Demography and Dynamics of Acacia tortilis in South Sinai

Key words: Age classes, population dynamics, plant population, phenology, conservation and seed bank.

Summary:

Demography of Acacia tortilis (Forssk.) Hayne subspecies raddiana demonstrated that the estimated average age of the oldest individuals in the population reached 614 ± 91.7 years old. About 50 % of the trees have an age range from 5 to 50 years, while only 12.5% of the trees are of age less than 5 years.

During January the leaves cover about 44 % of the tree branches while the rest of the branches were naked. The maximum leaf cover occurred in February (56 %). The leaf senescence on the main branch increased till June reaching 64 %. The minimum leaf cover takes place in November (8 %) where the branches seem to be naked due to leaf senescence and shedding. During December, the leaf cover reached about 38 %.

A. tortilis flowered twice in the year; the first flowering event begins on old branches in late February and early March, while the second flowering event begins on the new branches in July.

Life table analysis and fecundity schedules showed that the flowers, seeds and seedlings are the shortest stages in the life span. The net reproductive rate was 0.281, the estimated intrinsic rate of increase reached -0.00337 per capita per year and the average generation time of the species attained about 380 years. Population demography, phenology and life table analyses draw the attention towards specific conservation considerations to manage the species populations in the protected and non-protected sites.

Seedlings of A. tortilis were raised in open greenhouse conditions under different water treatments equivalent to 100, 200, 400 and 800 mm equivalent rainfall. The highest relative growth rate reached 0.39 and 1.54 mg g^-1 day^-1 for the root and the shoot, respectively. The highest net assimilation rate exceeded 2 mg mm^-2   day^-1 at age of 45 days old seedlings and under all tested water treatments. The total resources allocated to roots and stems are around 50 % of the total phytomass which is equivalent to the amounts allocated to the leaves. The functional root-shoot ratios as

based on dry weight, length and volume varied with age and water treatment. The range of variation in root-shoot ratio ranged between 3.44 – 8.35 as based on dry weight, 3.64 – 9.92 when based on length, and 30.15 – 171.10 for the volume, with highest values attained in seedlings raised under water treatment equivalent to 200 mm rainfall.

Species composition changes with the variation of tree understory area. Seeds of protected A. tortilis understories are larger in number and more diverse than those of non-protected patches. The germinated seeds of Cleome droserifolia, Solenstemma arghel and Calotropis procera were found only under A (< 1 m³), C (10 – 50 m³) and D (50 – 100 m³) canopy classes respectively, while rest of the germinated seeds appeared under different understories classes . Seeds of Acacia tortilis and Fagonia mollios were found under class D (50 – 100 m³) and increased towards the largest crown size class F (< 200 m³). The germinated seeds of Senna italica and Zilla spinosa found under classes A and B respectively and decreased towards the larger understory area class D (50 – 100 m³).

The study demonstrated the need to take conservation measures to protect the species populations which are subject to human and climatic pressures.

 

 

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