| Casuarina equisetifolia, introduced abroad into the southeastern coastal area since 1950s, has become the important species of coast protection forest, playing important role in defending wind and fixing sand, ameliorating environment, and offering timber. However, the long-term unreasonable management and the bad influences of nature factors led to single component and irrational structure of Casuarina equisetifolia forest belt, and result in aging early, stunting growing, and low-value and low-effectiveness in preventing, This exerts negative influences for the sustainable development of coastal protection forest system. Many researchers focus their studies on the rational structure and function of sustainable coastal protection forest of Casuarina equisetifolia, try to reveal the contributing factors to cause low-value and low-effective forest and probe into its mechanisms. All these studies put scientific basic for rational management for sustainable coastal protection forest of Casuarina equisetifolia, and meet the demand of the construction of coastal prevent system project.Water is the one of essential ecological factors in forest ecosystem. It also plays very important role in plant life activities. Water deficit is the main factor to restrict the crops and tree to give full play to its genetic potential, especially in dry and semidry area. In southeastern area, generally, the soil is eolian, porous and very bad capacity to keep water. In addition, the seasonal dry from October to the next March and a great quantity water consumption during tree developing result in that water become the restriction factor for Casuarina equisetifolia development. In view of shortage of studies on water ecology of Casuarina equisetifolia protection forest, this thesis carried out experiments on water ecology in young-aged Casuarina equisetifolia plantation, middle-aged Casuarina equisetifolia plantation from April 2001 to March 2002 at Chihu protection forest farm, Hui'an County, Fujian, Three standard plots were set up in the two typical stands and incontrol treatment (non-forest land) respectively. The three monitoring wells were dug in the three plots to survey the water ecological characteristics of Casuarina equisetifolia forest.1. In southeastern coastal area of Fujian, the annual rainfall is not even. The rainfall in 2001 is 748.8mm, 66.9% of the average. The rainfall during April to October is 640mm, accounting for 85.5% of the annual amount, and the amount of rainfall in other months is 108.8mm, accounting for 14.5% of the annual amount. The height growth and diameter (at breast height) growth in young-aged Casuarina equisetifolia plantation were positive relevant to the rainfall, its relevant coefficients were 0.94 and 0.95. Therefore, the rainfall was the restriction factor for Casuarina equisetifolia development.2. The seasonal dynamic of soil water in Casuarina equisetifolia plantation can be divided into five periods such as: accumulating period (from April to May), lowering period (from June to July), buffering period (from August to September), stable period (from October to the middle ten days of December), and recovery period (from the middle ten days of December to the next March). According to the rainfall rhythm and the seasonal dynamic of soil water, it is better time for forestation from the third days of March to May.3. The soil at experimental area belongs to eolian, porous and bad capacity to keep water. This kind of soil can add its water content rapidly during raining, and decrease its water content rapidly after rain. This change also displays on the vertical profile, the coefficient of variation for water content along 1 meter depth were over 0.45. Therefore, even in raining season, the soil water can not meet the tree demand effectivly. This is the essential reason that dry often happen in eolian.4. The soil water content is positive relative to meteorological factors, especially to relative humidity and precipitation. The rainfall and its rhythm directly influence the...
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