Density‐dependence and co‐existence of conifer and broad‐leaved trees in a Japanese northern mixed forest

Abstract

Abstract. The growth and survival of coniferous trees (particularly Abies sachalinensis) and broad‐leaved trees (particularly Quercus crispula) were followed over a 15‐yr period in a 15.5‐ha area in a northern mixed forest in Japan, and the coexistence of the two groups was simulated by a density‐dependent projection matrix model. The density‐dependent model assumes that the density effect of mother trees due to one‐sided competition for light on smaller‐sized tree regulates the demographic functions. The mother tree densities of conifers and broad‐leaved trees have stronger negative effects on the recruitment and survival of seedlings of their own group than of the other group. These results support the idea of reciprocal replacement for conifer and broad‐leaved trees. Simulations using the density‐dependent model showed that the two groups will co‐exist within a particular range of recruitment rates. However, the density of both groups did not affect the growth rate of any tree, and equilibrium DBH‐distributions from density‐dependent matrices were quite different from present distributions both for conifers and broad‐leaved trees. On the other hand, equilibrium DBH‐distributions of conifer and broad‐leaved trees from density‐independent matrices were quite distinct from each other, reflecting different survivorship curves of the two dominants. These results suggest that density‐dependent processes are not so important for shaping population structures in this northern mixed forest.