Effects of forest ages on spring soil moisture environment of eucalyptus plantations in the western part of Hainan Island

In recent years, there has been over two million hm² of Eucalyptus tress to be planted in Mainland China, and Hainan is one of the most important areas. Eucalyptus plantation yields substantial profits, while a series of relevant ecological problems have become topics of academic arguments. The annual rainfall is about 1000 mm in the west and southwest of Hainan, and the drought severity index is over 2. With the progressing of eucalyptus pulp plantation project, all trees are cleared at one time in 5 to 6 years, and multi-generation continuous planting rotations are exerting a significant impact on regional hydrology and soil ecology. Danzhou Forest Farm, lying in the west of Hainan, was chosen as the main study area to reveal the spatial and temporal characteristics of soil moisture and their relationship with ecological environment. Four fixed sample sites, adjacent to each other, consistent natural conditions, were set up in the Forest Farm. One is the palm trees, and others are eucalyptus plantations with different ages and continuous planting rotations. Through continuous field experimental study on soil moisture, the results showed that: 1) January - April for soil water consumption period, soil moisture decreased gradually, eucalyptus plantation soil moisture was obviously lower than that of coconut forests. 2) Soil water contents of surface, subsurface and deep layer were significantly different. Eucalyptus plantation´s surface soil moisture content was low, large variation; subsurface soil moisture was relatively stable, deep water content was larger, also more stable. 3) Multi-generation continuous planting rotations and forest age had obvious relationship with soil water content. The more rotation and the older the forest, the less soil water content was. The eucalyptus plantation, being cut in the past year, soil moisture was in the recovery phase, and its moisture content was higher. To realize the regional sustainable development, it becom- - es very necessary to take measures to improve the forest soil moisture environment.