不同土地利用型态下潜在蒸散发量比较--以二次林生态系统与茶园生态系统为例

Comparison of latent evapotranspiration on the different land use type:a case study of second forest ecosystem and tea garden ecosystem

于栖兰山庄二次林与宜兰县大同乡之玉兰茶园内，以蒸发皿法量测与估算此二试验区之日潜在蒸散发量，了解在不同土地利用型态下，其日潜在蒸散发量的表现差异情况。研究结果发现，茶园生态系统之日潜在蒸散发量明显高于二次林生态系统之日潜在蒸散发量。究其原因为，茶园生态系统的经营型态属开放式经营型态，故整体茶园生态系统均匀曝晒于阳光下，因此接收足量之太阳辐射能，导致其日潜在蒸散发量较高。而栖兰山庄二次林生态系之表现情形则不尽相同，由于二次林生态系统内，其高、矮茎植物丛生，此差异性结构将产生互相遮阴现象，使得土壤之蒸发量与矮茎植物之蒸散量减少。此外，二次林生态系统的组成中亦多含深根性植物，其水土保持特性相对于茶园生态系统也有较佳的表现。研究中亦发现，在冬季时期，若将二次林生态系统开辟为茶园生态系统时，二次林生态系统每公顷土地之水分逸失量将增加100～150t。

This study is conducted in the second forest of Chi-Lan village and Yu-Lan tea garden of Ta-Tung country in Yi-Lan. We measured the latent evapotraspiration by evaporation disc method at the two study sites and tried to understand the difference of the evapotranspiration on the different land use type. We hope the results of this study can afford the reference for the concerned authorities and the land developer. The study results show that the latent evapotranspiration over the garden ecosystem is clearly higher than that in the second forest ecosystem. We think the reason is that the garden ecosystem is an open system and the whole open system is exposed to the sunshine so it can accept sufficient solar radiance and resultsd in the higher latent evapotranspiration. While the situation in the second forest ecosystem is quite different because the plants in it have different heights and cover each other, which results in receiving less solar radiance. Furthermore, there are many deep - root plants in the second forest ecosystem so the characteristics of soil and water conservation are relative better than the garden systems. The results also suggest that the loss of the water content in per hectare land will increase 100 - 150 tons when the second forest ecosystem is developed as the garden ecosystem in winter.