The Response Of Vegetation Community Structure To Environment Gradients In Yanhe River Basin

Plant community structure is spatial and temporal configuration status of all kinds of plants in community and relationships among different plants, between plant and environment. The structure, dynamics, classification and distribution patterns of plant community are controlled by specific environment conditions. The Studying of plant community structure and interaction between community structure and environment has significant implications for protecting the natural environment, maintaining ecological balance, restoring and improving the ecological environment of the Loess Plateau. Aiming to provide the support for vegetation restoration planning and decision making, this paper analyzed relationships of community structure, temperature, precipitation and topography, and exploring changes of community structure in response to environmental gradients based on the investigation of natural vegetation or stable secondary plant in Yanhe River Basin. The main results are as follows:(1)Based on the survey of plant community and environment factors of sampling sites, Canonical Correspondence Analysis was made to classify and rank plant communities in Yanhe River Basin, and to analyze interaction between plant community and environment factors, and explore main environment gradients influencing community structure. The environment factor which has greatest impact on axes 1 is annual precipitation, and the environment factors influencing axes2 follows the order: elevation, temperature and evaporation. The axes 1 illustrates a gradient from dry to wet while the axes 2 illustrates a gradient towards cold and dry. Canonical Correspondence Analysis indicates that plant community structure in Yanhe River Basin are mainly influenced by water and heat as well as topography which redistributes water and heat.(2)Changes in all species diversity along gradients of temperature, precipitation, altitude and different aspects were analyzed by using the method of direct gradient analysis. The result indicated that Shannon diversity index and species richness of shady slope was the highest, followed by semi-shady slope, semi-sunny slope and sunny slope, species richness increased with increasing temperature and precipitation, decreased with increasing elevation, shannon diversity has no obvious pattern along the precipitation gradient, but increased with temperature and elevation. The shannon diversity index and species richness of shrub increased with increasing precipitation, showed a unimodal pattern that first increased and then decreased along the gradient of temperature and elevation. The shannon diversity index and species richness of herbaceous decreased with increasing precipitation and temperature, and showed a pattern that first decreased and then increased along altitudinal gradient.(3)Plant height and biomass of the whole community and shrub layer increased with increasing precipitation and have significant positive correlation with precipitation, showed a unimodal pattern along gradient of temperature and elevation, followed the order among different aspects: shady slope>semi-shady slope>semi-sunny slope>sunny slope. Plant height and biomass of herb layer have no obvious pattern along the gradient of temperature, precipitation, elevation and aspect.(4)The proportion of phanerophytes increased with temperature and precipitation, peaked at the middle elevation, and was higher in semi-shady slope and semi-sunny slope; the proportion of hemicryptophyte has no significant changes along gradients of temperature, precipitation and elevation, and was highest in shady slope; the proportion of geophytes increased with decreasing temperature, increasing temperature and elevation, and was higher in shady slope and semi-shady slope; the proportion of chamaephytes has no significant changes along temperature gradient, increased with increasing altitudinal gradient, and higher in sunny slope and wet areas.( 5 ) The proportion of xerophyte, mesoxerophyte decreased with increasing precipitation, increased with increasing elevation; The proportion of mesoxerophyte, mesophyte increased with increasing precipitation and decreasing elevation. With the aspect changes from shady slope, semi-shady slope to semi-sunny slope, sunny slope, the proportion of xerophyte gradually decreased, and the proportion of mesophyte increased. The proportion of mesoxerophyte among different aspects has no significant difference.