元江干热河谷山地五百年来植被变迁探讨

元江河谷是云南省最干热地区之一,在海拔800—900米以下的山地上广泛分布着稀树灌草丛。根据《元江府志》(1714年编纂)、《元江州志》(1826年编纂)、《元江志稿》(1922年编篡)及对现存植被的考察,本文探讨了元江干热河谷山地五百年来植被的变迁。 元江县森林复盖率的减少与人口的增加有密切关系,十七世纪中期以前,森林复盖率在75％以上,十八、十九世纪时为70％左右,1958年为61.5％,1975年为27.3％,至1982年则为19.3％。研究表明,在十九世纪以前,这个地区分布的主要植被是热带季雨林,甚而热带季节雨林,以后热带稀树灌草丛则迅速发展。植被的历史变化与土壤流失密切相关。植物群落的演变是由以乔木树种为优势演变为以灌木种类为优势,再演变为以多年生草木植物为优势,而最后则成为裸地。本文也讨论了这个地区植被恢复的方法。

AN APPROACH TO THE VEGETATIONAL CHANGES FROM YUANJIANG DRY-HOT VALLEY OF YUNNAN IN THE LAST 500 YEARS

Yuanjiang valley is one of the most dry-hot areas in Yunnan Province. Savanna is distributed in mountains under the altitute of 800-900 meter widely.According to the Local Records of Yuanjiang County Printed in 1714, 1826 and 1922, and through our exploring to present-day vegetation, the authors give a brief view of vegetational change in Yuanjiang dry-hot mountains in the last 500 years.The paper presents that the forest cover degrees in the county were declined by increasing human population, it shows a progressive change from 75 percent in the county before the midle of 17th centry, then around 70 percent during the 18th and 19th Gentries, then 61.5 percent in 1958, then 27.3 percent in 1975 and finally 19.3 percent in 1982. The study shows that the main plant communities in the mountains were tropical monsoon forests even seasonal rainforest before later of the 19th centry, then the savanna was spreaded quickly. The changes in vegetation during the historic period is linked with soil erosion. The dynamics of plant successions show a progressive change from communities dominated by trees, then by perennial herbs, finally changing to bare land. The methods of vegetational recovery for the area are discussed in the paper as well.