Summary In two adjacent wet grasslands, a Cirsio‐Molinietum and a Senecioni‐Brometum, in the Netherlands, above‐ground phytomass, leaf area index (LAI), and canopy structure were measured at peak flowering season, during three consecutive years. Microclimate profiles in the canopies were measured. The Cirsio‐Molinietum produced a smaller phytomass with a larger LAI than the Senecioni‐Brometum, and the stem/leaf ratios were different too. Relative distribution of phytomass and leaf area in the canopies were remarkably constant during the three years and independent of total values. Differences in canopy structure including differences in vertical arrangement of phytomass and leaf area, leaf angles and leaf sizes result in differences in light interception patterns, air temperatures and saturation deficits within the canopies, and in soil temperatures. These differences are interpreted in terms of relative growth rates of the constituent species and photosynthetic performances of the vegetation types.

Various types of grasslands in the Netherlands were catagorized by their structure: phytomass and leaf area were measured in arbitrarily chosen vegetation layers with width intervals of 2.5, 5, 10 or 20 cm, depending on the height of the sward. Data were standardized for fixed width of layers (layer width set), and for equal numbers of layers of varying width (layer number set). Data were clustered by Ward's method as well as ordinated by Principal Components Analysis (PCA). The duster method revealed 6 groups; those of the layer number sets could be contrasted in their vertical built-up of leaf area index (LAI) -and phytomass profiles and could be characterized ecologically. The ordinations confirmed the findings of the cluster analyses. In our data grassland structure varied mainly along a gradient from constant and sufficient to strongly varying soil water supply during the growing season, and a gradient in soil nutrients from rich to poor. Sites with constant water supply appeared more often nutrient-rich and those with a varying water supply more often poor in nutrients.

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