Vegetation structure in relation to micro-landform in Tiantong National Forest Park, Zhejiang, China

The relationship between plants and conditions is one of the most essential characters of plant communities. The landform of a hilly area usually consists of various micro-landform units. The heterogeneous habitats created by spatial arrangement of those units may support richer species and more communities. Landforms are assumed to be one of the most principal and determinant factors affecting the vegetation pattern within a climatic region. In humid hilly regions, the habitats are influenced by water erosion, which varies in frequency and extent. Tiantong National Park (29°48'N, 121°47'E), a representative hilly and lower mountainous area with well-protected vegetation in East Zhejiang, was selected to study the relationship between micro-landforms and vegetation structure. Seven micro-landform units, i.e., crest slope (CS), upper sideslope (US), head hollow (HH), lower sideslope (LS), foot slope (FS), flood terrace (FT) and river bed (RB), were identified. They could be classified into two parts based on the similarity of species composition, namely upper hillslope (UHA) (including CS, US and HH) and lower hillslope (LHA) (including LS, FS, FT and RB). The result was coincident with that divided by erosion line. Based on the distribution patterns between the UHA and LHA, the species were classified into three groups. Group A was mostly or strictly confined to UHA, group B was confined to LHA, and group C was associated statistically with neither part. Evergreen species of Fagaceae, Theaceae, Symplocaceae and Aquifoliaceae were the main components of the vegetation developed in UHA, while deciduous species of Juglandaceae, Ulmaceae, Anacardiaceae and evergreen species of Lauraceae were the main components of vegetation developed in LHA. Though the densities were lower than those in UHA, the vertical structure of the forest stands on the micro-landform units in LHA was more complex. The existence of emergent layer composed by species of Juglandaceae, Ulmaceae and Anacardiaceae was the most remarkable feature of the forest stands in LHA. However, among the micro-landforms in UHA, vegetation on two micro-landforms, i.e., crest slope and head hollow, lack obvious tree layer. Above results indicated that the erosion front is an important reference in demarcating different habitats within the hilly regions. The UHA and LHA demarcated by the erosion line were functional areas for assessing species composition and stand structure.