Optimal Leaf Phenology and Photosynthetic Capacity of Herbs Dependent on the Genet Density of Herbs in Their Habitat

The optimal leaf phenology and photosynthetic capacity of herbs were studied in relation to the genet density of herbs in their habitat. It was assumed that each herb maximizes its net photosynthates of the year in a seasonable environment, in which the light condition changes due to the leafiness of canopy trees, and other environmental factors also change seasonally. It was also assumed that stem height increases with the genet density. It was shown that short herbs in a habitat of low genet density emerge early and shed late because of the small height cost. Tall herbs in a habitat of high genet density emerge late and shed early because of the large height cost. Then the short herbs photosynthesize for a long period without shading by the canopy trees, and have a high photosynthetic capacity, which is efficient in sunny conditions. The tall herbs photosynthesize for most of the period of shading by the canopy trees, and have a low photosynthetic capacity, which is efficient in shady conditions. The short herbs become vernal (or autumnal) if their photosynthetic rate decreases largely when the canopy trees have leaves.