Study of gray mangrove (Avicennia marina) afforestation for greeningof desert coasts: Adequate ground level and interval for plantation ofgray mangrove seeds in the intertidal zone

摘要

The adequate ground level for planting of seeds of the gray mangrove, Avicennia marina (Forsk.) Vierh, in the intertidal zone is an important factor for successful afforestation of desert coasts. Seeds germinated at all levels in the intertidal zone except near the high tide line, and all seedlings grew steadily during the first year. However, most of the seedlings that had become established at the low and high tide levels died during the second year, and only trees that grew at the mid-tidal level with a mean tidal difference of 30.6-63% of the mean survived. For three years thereafter, there was no further mortality at this level. Therefore, the appropriate ground level for plantation of seeds is the area with a mean tidal difference of 30.6-41.4%. The increased seawater salinity under the soil at the level with a mean tidal difference of 43.2-63% probably inhibited trees from growing smoothly. Although more than 90% of seeds germinated during the 8-year afforestation project, a large number of seedlings were killed during the second year due to deposition of seaweed and flotsam. High-density planting of seedlings (at a 25-cm interval) could increase their survival under this type of pressure, because a dense patch of seedlings has more resistance to covering with seaweed and flotsam than a single seedling.