Effects of understory vegetation on the ecophysiological characteristics of an overstory pine, Pinus densiflora

The ecophysiological effects of understory vegetation on an overstory tree Pinus densiflora were examined in secondary pine forest stands, west Japan. Three pairs of pine forests were compared. Each pair contained an unmanaged stand and a managed stand in which the understory vegetation was clear cut. The two stands in each pair were adjacent to each other and had similar light conditions, ground matrix, precipitation and aerial conditions. Total fine root biomass in the soil surface layer was significantly larger in the unmanaged stands than in the managed stands because of the invasion of other understory trees. In the unmanaged stands, the maximum net photosynthesis (P_max) and stomatal conductance (gl_max) were smaller and δ¹³C values of needles were larger than those in the managed stands. These results suggested that water for pine needles was more restricted and water use efficiency (WUE) was higher in the unmanaged stand than in the managed stands. Nitrogen contents in the needles and photosynthetic nitrogen use efficiency (NUE) in the unmanaged stands were lower than those in the managed stands. There was no significant difference between the managed and the unmanaged stands in the emission of stress ethylene from needles. Our results showed that the understory vegetation which invaded during the process of secondary succession had negative physiological effects on the overstory pine needles through the competition of roots for water and nutrients. The traditional style of forest floor management in Japan had significant positive effects on the health condition of P. densiflora plantations.