Aboveground biomass and structural characteristics of poisonous Pieris japonica shrub stands dominating under deer pressure

Abstract

ABSTRACT Canopy tree seedlings rarely grow in regions with overabundant deer in Japan, whereas Pieris japonica, a shrub species that is unpalatable to deer, has been expanding its habitat and occasionally forms dense pure stands in disturbed locations. Although this species could be the key to understanding vegetation structure and function under intense deer pressure, little information is available regarding the structural and functional aspects of P. japonica stands. Here, we examined aboveground mass (M A) and several structural parameters for 13 P. japonica stands of various developmental stages (3–64 years old as estimated from the number of growth rings of component plants); the stand M A and leaf area were estimated by developing relevant allometric equations for individual plants. The M A of P. japonica stands (≤50 Mg ha−1) were less than a fifth of that recorded for neighboring forests consisting of deciduous broad-leaved trees and conifers. Leaf area index (≤4.9 m2 m−2) and basal stem area (≤62 m2 ha−1, determined at 5 cm from the ground) of the stands reached the level comparable to tree forests, whereas canopy height (≤4.4 m) was much shorter and plant density (≥7,300 stems ha−1) was fairly high compared with those of average tree forests in neighboring regions. The stand structure lacked thick and long boles, resulting in low biomass accumulation in P. japonica stands. Thus, one possible consequence of the long-lasting deer pressure is the reduction of the carbon sequestration capacity to a fraction of that of the present forests.