鹤山马占相思生态系统在重建过程中对立地水热因子的调节作用

THE REGULATION ON WATER AND HEAT FACTORS DURING THE RESTORATION PROCESS OF AN ACACIA MANGIUM PLANTATION

分析南亚热带鹤山人工马占相思 (Acaciamangium)生态系统水热的连续观测资料 ,采用时空互代的方法 ,并与邻近的退化草坡、裸地相比较 ,得到如下一些主要结果 :1)本区域年内降水分配不均 ,而热量输入却相对均匀 ,存在湿季水土流失和干季水分亏匮的可能性。 2 ) 7龄后的马占相思林分反射率明显小于裸地与草坡 ,为该系统提高生产力和生物量累积提供了前提条件。 3)马占相思生态系统对立地气温、地温的调节集中表现在缩小其变化振幅 ,使得林地的气温、地温变化有其自身的规律 ,倾向于有益于生态系统发育方面的变化。 4)干季时 ,林地内的大气相对湿度明显高于裸地 ,而蒸散力又明显低于裸地的自由水面蒸发 ,使系统摆脱了干旱的威胁 ,对植被恢复和系统健康发育起到了重要作用。 5 )植被恢复过程中 ,系统的蒸散量呈增加趋势 ,总径流呈减小趋势 ,但减小的是雨季可能造成灾害的地表径流量 ,产水量的主体地下径流量仍然是增加的 ,林地的土壤水分较草坡地有所增加 ,变化幅度也较草坡地小 ,以上说明森林植被对系统水分的调节是明显的。

Previously, Heshan County, Guangdong province was covered with degraded grassland, bare land and other degraded plantation ecosystems due to the removal of natural vegetation. In recent years, vegetation rehabilitation has succeeded in this region by integration with intensive scientific studies and practices, which also resulted in a great progress in water and heat environments there. This experiment was carried out in Heshan hillyland interdisciplinary station (22°41′ N, 112°54′ E), a very good place for studies on the rehabilitation and reconstruction of degraded ecosystems in the northern subtropical zone. Based on long term field measurement data, this paper reported the development of water and heat factors during the restoration progress, started in degraded grassland and using Acacia mangium forest stands as the pioneer community. Interactions between hydro_thermal and forest and their temporal and spatial dynamics were analyzed. The monsoon climate brings abundant rainfall to the experimental area, but more than 85% of annual rainfall falls in the wet season (April to September). Owing to the uneven distribution of the monthly rainfall in a year but evenly distributed monthly rich solar radiation, the potential of soil erosion during the wet season and water deficit in the dry season is high. The high productivity potential can be anticipated in an ecosystem if it can reduce the water demand in the dry season and increase water storage in the wet season, such as is seen in Acacia mangium plantation. On the contrary, degraded ecosystems in this region do not have the ability to adjust, tend to be further degraded and are hard to restore. Reflectivity in restoration process for Acacia mangium plantation was much less than that of grassland or bare land, which decreased with tree growth before 11 years old and fluctuated between 6.7%_7.0% after 11 years old. The fluctuations of air temperature indexes in Acacia mangium plantation stand were less than those in bare land, for example, the fluctuation of the highest extreme monthly mean air temperature in bare land is 9.2 ℃, but only 5.0 ℃ in Acacia mangium plantation stand. The same pattern was seen with soil temperature. It benefited the rehabilitation and reconstruction of function and structure of the ecosystem. The relative humidity of Acacia mangium plantation was much higher than that of bare land in the dry season, but the potential evapotranspiration was opposite. This pattern greatly reduced the water demand and evapotranspiration in this plantation, and lessened its tension of water supply. Therefore, the growth of Acacia mangium plantation can sustain the dry season, which made the ecosystem rehabilitate smoothly. With the succession of Acacia mangium plantation, its evapotranspiration and groundwater increased but the total runoff was decreasing. At the same time, the soil moisture of Acacia mangium plantation became higher than that of grassland. Based on the above, it could be concluded that there was evidence of vegetation controlling the heat balance and the water distribution in an ecosystem. As a whole, the seasonal water consumption in Acacia mangium plantation became more reasonable and water and heat conditions were improved. The hydrological and thermal interactions of the ecosystem resulted in the maintenance of a healthy forest in a region where soil degradation, erosion and loss of fertility have often followed the removal of natural vegetation.