AGE AND GROWTH RATE ESTIMATION OF GREY MANGROVE AVICENNIA MARINA (FORSK.) VIERH FROM PAKISTAN

This study focused on the determination of age and radial growth in grey mangrove Avicennia marina (Forsk.) Vierh. The growth rate was measured by using two different methods. Firstly, the dendrometer technique was employed in which a dendrometer was fixed properly on the main tree trunk in order to determine the monthly radial growth; secondly, the manual measurements were taken from the healthy branches, the upper and the lower portions of the main trunk. The major purpose of this study was to evaluate the applicability of stem diameter change measurements in detecting the growth rate of the trees. In both the measurement techniques, the radial growth of main trunk as well as the branches significantly increased with the passage of time. The results of the dendrometer method showed the maximum growth rate (9.54 +/- 0.95cm) in the month of July, whereas it was minimum (0.58 +/- 0.058cm) in the month of October. It was found that the growth rate was higher in the upper branches, whilst it was lesser in the lower part of the main trunk. Age and the growth rate of Avicennia marina were estimated by applying the standard dendrochronological techniques, with dendrometer, manual measurement and cross-sectioning plants of the known ages. The maximum age of 32 +/- 1.42 years was recorded from the Port Qasim whereas the minimum (10 +/- 0.57 years) was recorded from the Korangi Crossing. The average growth rate ranged between 0.98 +/- 0.04 to 1.40 +/- 0.16 year/cm. Appearance and the successive development of cambium, characteristics of the initiation of growth rings were also investigated. Avicennia marina plants were grown by seeds in natural habitat as well as in the greenhouse. The cross sections were taken at the regular intervals to observe the appearance of growth rings. It was demonstrated that Avicennia marina has exhibited non-annual growth rings. It was concluded that the classical dendrochronological methods alone could not be applicable to this mangrove species.