东北半干旱地区防护林网的农业生态效应估价

Evaluation of the Agroecological Effects of Shelterbelt Network in Northeast Semi-arid Regions.

一、问题的提出半干旱地区防护林的建设,一个很重要的意义就是改变该地区的恶劣生态环境。过去关于防护林带的气候效应研究,多数只是用某一风向风速情况下,林带不同树高倍数处单项气象因子与旷野的比较。缺乏较长时间的对整个网内全方位综合气候效益场的分析和林网在农业生态建设中的科学估价。实际上林网对网内任意部位农作物的气候效应,不仅在风向上是全方位的。

The ecological effects of shelterbelt network result from its integrated affections on variousmeteorological factors.In semi-arid regions,it can be expressed by evaporation power:Ec=1/2[1.6(10T/I)~a+1.05(e_a-ed)(1+0.5u)].The calculated regression equation is:Ec=246.52-12.17e+0.58t+6.58u.Because of the shelter effect,the monthly field evaporation in grow-ing season can be reduced by 30—32.5mm maximumly,just equal to having another heavyrainfall compared with open areas.The average monthly reduction is 13.8mm,it's equal tohaving a middle rainfall in sheltered farmland.The best benefited area oceupies two third ofthe total area in networks.The non-or little benefited area occupies only 4—5%.It de-pends on tree height of shelterbelt and size of network,which can be regulated by rationaldesigning.