Vegetation succession of the medium and low mountainous areas along the subtropics of the upper Yangtze River in recent 500 years

Abstract

In this paper,the author holds that the sub-tropical medium and low mountainous areas,at an altitude of 3000-1500m above the sea level along the upper reaches of the Yangtze River were mainly covered with arbors mixed with meadow landscape 500 years ago,rather than meadow and shrub-grass-based landscape today.Since man mostly live on flat grounds,platforms and hilly regions at an altitude below 1500 m,human activities have little impact on the mountainous areas over 1500 m.In short,along the upper reaches of the Yangtze River,wetland and grass-slope zone in the low hills with 1500-3000 m above the sea level,which was described statically by modern geologists,was actually mixed coniferous and deciduous forests dominated by abies and picea 500 years ago.The main reasons for the change are land cultivation,commercial logging and timber gathering for the imperial palaces in recent 500 years.The ecological environment thus cannot be completely restored,either by artificial or natural reconstruction. Timber gathering for the imperial palaces and commercial logging had a great impact on the forest of medium and low mountains along the upper reaches of the Yangtze River.Phoebe and China Fir chopping greatly affected the canopy density of the forest in particular,but it exerted no introgression to the forest resources.Land cultivation,especially the stable farming activities which had dug a large amount of roots,made it impossible for the recovery of the forest resources.So far we have not found out the causes of the vegetation alteration,of which how much was caused by the climate change,so further study is needed.