The effect of different cutting intensities of mangrove grey trees (Avicennia marina (Forssk.) Vierh.) on the reproduction and the growth of stand

Mangroves are one of the most important and effective cover of mandabi ecosystems, which are evergreen and resistant to salinity and grow in the coastal areas of tropical and subtropical regions, so that they can adapt to the conditions like high salinity, wind, anaerobic soil environment and tides with high height. Despite the many environmental services, these forests are considered as threatened ecosystems in tropical and subtropical regions, which are very vulnerable to human activities and climate changes and are exposed to a threat. During the recent centuries, the destruction of mangrove habitats as a result of coastal development, pollution, aquaculture, logging and exploitation and fuel supply has been done more intensively and has led to a drastic reduction in the area of the mangrove ecosystem. One of the most important human threats in the mangrove forests of Hormozgan province is especially the cutting of mangroves by local people in order to raise livestock. The percentage of importance of cutting in Hormozgan is much higher than other threats, so the purpose of this research is to investigate the effect of different intensities of cutting on the reproductive and growth characteristics of forest stand.

The location of the project was (an area 180 meters long along the coast and the length of the mangrove forest, along the highest and lowest tide levels). This design was carried out in a completely randomized design with 4 treatments and 10 replications in plots 40 meters long and 25 meters wide along the slope of coastal lands. In each plot along its diameter, 10 mangrove trees whose crown diameter was more than 2 meters were selected and cutting treatments with percentages (zero, 10, 20 and 30%) were implemented on the sample trees (40 sample trees). It is worth mentioning that the diameter at a height of 30 cm and the height of the sample trees, the reproduction status around the sample trees, the diameter and height of the surrounding trees, the sample trees before cutting and 5 years after cutting were measured and it was compared using one-way analysis of variance.

The results showed that the height and diameter growth rate of the sample trees was the highest in the control treatment with values of 0.45 meters and 2.37 centimeters, and significantly more than the 20% treatment (0.23 meters and 0.94 cm) and 30% treatment (0.17 meters and 0.52 cm). Also, the reproduction rate around the sample trees was significantly reduced by cutting. The reproduction rate was the highest in the control treatment with 0.093 seedlings per square meter, while the lowest value (0.031 seedlings per square meter) was observed in the 30% cutting treatment. It is worth mentioning that 10, 20 and 30% cutting was observed in the control treatments, respectively, with the number of 0, 3, 5 and 8 diebacked seedlings≤ 5 cm, during 5 years. In examining the effect of cutting on the growth of trees around the sample tree, no significant effect was observed.

Overall, the results of this research showed that grey mangrove trees are very sensitive to human intervention and cutting and react strongly. This reaction was shown in the field of the habitat in the form of a decrease in vegetative characteristics and seedling production around the cut trees.