毛乌素沙地油蒿群落的循环演替

CYCLIC SUCCESSION OF ARTEMISIA ORDOSICA KRASCH COMMUNITY IN THE MU US SANDY GRASSLAND

流动沙地→半流动沙地白沙蒿群落→半固定沙地油蒿＋白沙蒿群落＋固定沙地油蒿群落→固定沙地油蒿＋本氏针茅＋苔藓群落→地带性的本氏针茅草原及其迅速沙化的植被发展过程是毛乌素沙地植被自发演替的基本过程。油蒿具有耐沙埋、抗风蚀、耐旱、耐土壤贫瘠等特性，是该地区最主要的优良固沙植物和重要牧草。半固定、固定沙地油蒿群落在毛乌素沙地的生态环境保护和农牧业生产方面发挥着极其重要的作用，维持其稳定十分重要。然而，其沙化的现象在毛乌素沙地相当普遍地存在。沙化原因主要是因为过度放牧所致的逆行演替，但在个别地段则是群落演替循环中的一个过程。从沙地油蒿群落的循环演替与逆行演替的规律来看，适度的放牧是保持沙地油蒿群落稳定的关键，即一方面要限制过度放牧的情况发生，另一方面也不能完全封闭保护，使固定沙地油蒿群落向下一个演替阶段发展，导致油蒿群落的衰败。

This paper describes the role of Artemisia ordosica in the successional processes of drifting and fixed sanddune vegetation and its interaction with the process of desertification in the Mu Us sandy grassland. An autogenic successional pathway in vegetation of this region can be described which is associated with change from drifting to stablesand dunes and back: this proceeds from bare-sand dunes to A. sphaerocephala on semi-drift-sand dunes, then throughA. ordoslta + A. sphaerocephala on semi-fixed-sand dunes, and A. ordosica on fixed sand dunes, to a A. ordosica+Stipa bungeana + moss community on fixed-sand dunes which passes to a S. bungeana steppe which leads rapidly tothe ultimate desertification of the steppe to drift-sand. These processes compose a cycle of vegetation succession.The semi-shrub of A. ordosica tolerates the burying of sands, wlnd erosion, a dry climate and nutrient poor soil.It is a good fodder plant and is the most important plant in fixing sand dunes in the area. The communities it dominates play a very lmportant role in both protecting the soil against wind erosion and in agriculture and livestock husbandry. However, these communities frequently become desertified, and intensive grazing, leading to successionalretrogression, is a major factor in this process in many places. In other places, however, the desertification is part ofthe processes of the vegetation autogenic succession cycle. To maintain the stability of A. ordosica communities and toprotect the sand dunes from desertification, moderate grazing on fixed sand dunes is proposed as a management tool toarrest vegetation succession in this sere.