In the research areas, natural vegetation is hardly seen, but crops, artificial vegetation and secondary vegetation.

研究区的天然植被已不多见，主要是栽培作物，人工植被和次生植被。

According to the interference that the man has done to the nature, the ecological water requirement consists of the water requirements for platted vegetation system and for the natural vegetation system.

按照人类对自然的干预程度,生态需水又可分为农田生态系统下的人工植被需水和自然生态系统下的天然植被需水。

Meanwhile, means and technology of acquiring resource is more and more efficient from survival natural vegetation by humankind. So the maintaining and recovering ability of the biodiversity of the world is dramatically declining.

同时，人类从残存自然植被中获得资源的手段和技术越来越有效，使得地球上的生物多样性维持、恢复能力大为下降。

Compared with the soil microbial biomass and number in steady natural vegetation fixed sand dune these different artificial vegetation fixed dunes have not reached the level of stability.

在不同年代人工植被固沙区结皮中,微生物生物量和数量与相对稳定的自然植被固沙区相比,仍未达到稳定状态。