Population structure and spatial patterns of major trees in a subalpine old-growth coniferous forest, central Japan

Abstract

We investigated the population structure and spatial pattern of major trees in a subalpine old-growth coniferous forest stand in the Ontake Forest Reserve of central Japan to examine the coexistence strategies of different species. We mapped all stems ≥5 cm in diameter at breast height (dbh) on a 2 ha plot. The stand contained nine woody plant species and 1508 living stems with a combined basal area of 55.6 m 2 ha −1. The four major species were divided into two groups based on density and size/age structure. Group A ( Abies mariesii and Abies veitchii) had a lower maximum age and higher density than group B, as well as reverse J- or L-shaped dbh distribution of live stems. Species in group B ( Picea jezoensis var. hondoensis and Tsuga diversifolia) had very few stems in the understory, higher maximum ages than group A, and bell-shaped dbh distributions. Group B species may compensate for having fewer stems in the understory by having a longer lifespan, while species in group A may compensate for lower longevity by having numerous young stems in the understory. Canopy and understory stems of the four major coniferous species were patchily distributed throughout the plot. The distribution of canopy stems of species in group B was negatively associated with that of group A, but positively associated with understory stems in their own group. Similarly, the distribution of canopy stems of species in group A was negatively associated with that of understory stems of group B species. These results suggest species differences in favourable canopy and forest floor condition. Differences in life history strategies and site preferences may explain the coexistence of these species.