Karst mountains are, typically, ecologically fragile. The soil is shallow and discontinuous, with a heavy clay texture. Moisture conent is low and a C horizon is generally lacking. The result is poor stability, with slow soil formation often leading to a state of negative growth and eventual lack of renewability. This occurs especially during use of the land for arable agriculture, and its sunsequent restoration with secondary vegetation Most previous res-earch has focussed on the physical and chemical properties of the soil, micro-organisms, and hydrology, with little work on palynology or vegetational history.
In the present study, we investigated Mt. Jigongshan, Beibei District, Chongqing City, using Platycladus orientalis communities of different ages to reconstruct the succession back to forest. Typical plots were chosen to analyse the vegetation at each stage. The original Zonal vegetation of the area was subtropical broadleaved forest, but this is now all removed. In its place are secondary forest trees such as Platycladus orientalis, Trachycarpus fortunei etc., and understorey shrubs such as Pyracantha fortuneara, Coriaria sinica and Mysine africana. The herb layer is of Imperata cylindrica etc. The farming was of two to three crops per year, of wheat, corn and sweet potato. The typical time sequence is slope farmland--1year abandoned farmland-bush grassland-15year scattered woodland-25year woodland. The vegetation and the pollen/spore content of the surface soil was recorded in each of these five types.
Results: (1) 46 pollen/spore taxa were recorded, with herbs and ferns dominant (58%-96%), then trees (mainly Cedrus deodara and Pinus massoniana) with 3%-21%, and then shrub pollen with only 1%-9%. (2) The abundance of the pollen types is not clearly related to the recovery stage. (3) The list of taxa at each site is, however, indicative of the vegetation. It is therefore concluded that palynology can indicate the stages of recovery in the natural environment of the study area.