Gap characteristics and gap regeneration in subalpine old‐growth coniferous forests, central Japan

Abstract

AbstractGap characteristics and gap regeneration were studied in three old‐growth stands of subalpine coniferous forests in the northern Yatsugatake and the northern Akaishi mountains, central Japan. With the results of the present study and those of a previous study conducted in another locality, general features of gap characteristics and gap regeneration behavior of major tree species in subalpine coniferous forests of central Japan were summarized and discussed. Of the total 237 gaps investigated in the 14.48 ha of forested area, the percentage gap area to surveyed area, gap density and mean gap size were 7.3%, 17.2 ha−1, and 43.3 m2, respectively. The gap size distributions were similar among stands and showed a strong positive skewness with a few large and many small gaps; gaps <40m2 were most frequent and those >200 m2 were rare. Gaps due to the death of multiple canopy trees comprised 44.7% of the total ones. Canopy trees died in various states; standing dead (42.6%) or trunk broken (43.7%) were common and uprooted (12.2%) was an uncommon type of death of canopy trees. These figures indicate that general features of gap characteristics in this forest type are the low proportion of gap area and the high proportions of small gap size and multiple‐tree gap formation. In general, shade‐tolerant Abies frequently, and Tsuga, infrequently, regenerate in gaps from advance regenerations recruited before gap formation, while Picea and shade‐intolerant Betula possibly regenerate in gaps from new individuals recruited after gap formation. Gap successors of conifers occurred in a wide range of gap size and did not show the clear preference to species specific gap size. In old‐growth stands without large‐scale disturbance (≥0.1 ha in area) of subalpine coniferous forests of central Japan, major tree species may coexist with their different gap‐regeneration behaviors and, probably, different life history traits.