Plant functional groups in a heterogeneous environment

Abstract

Species membership of plant functional groups and the relationship to soil variables were studied in two paddocks with long‐term differentiated management in New Zealand hill country. The microrelief of the paddocks contained three slope classes (low, medium, and high) with contrasting soil variables. Soil variables (unsaturated hydraulic conductivity, bulk density, volumetric soil moisture, total soil porosity, field volumetric soil moisture, soil compression, soil rebound, and air permeability), botanical composition and herbage mass accumulation were determined. Analysis of variance, cluster analysis, simple correlation analysis and canonical variate analysis were performed on the data. Seven functional plant groups were determined. High fertility grasses and Lolium perenne were strongly affected by changes in the level of soil variables. Low fertility species appeared to be affected indirectly by soil variables, as they were poor competitors when availability of soil resources was high. Some species (e.g., Agrostis capillaris) were indifferent to changes in the levels of available resources due to soil characteristics. Species and functional groups colonised the evaluated sites according to the soil resources. Species and functional groups were shown to have the capability to respond positively to soil resources, adjusting their growth according to the varying circumstances. The relationship between plant functional groups and field condition, a grazing management concept that measures the deviation from some ideal ecological state, was also examined. Results suggested that field condition and plant functional groups are complementary concepts in grassland dynamic analyses.