Sustainability of High-Value Timber Species in Mixed Conifer–Broadleaf Forest Managed under Selection System in Northern Japan

Kyaw Thu Moe,Toshiaki Owari

doi:10.3390/f11050484

Abstract

Understanding the sustainability of high-value timber species in managed forests provides useful information for the management of these species in the long-run. Using nearly 50 years of census data in long-term permanent plots, we investigated the sustainability of three high-value timber species—monarch birch (Betula maximowicziana Regel), castor aralia (Kalopanax septemlobus (Thunb.) Koidz), and Japanese oak (Quercus crispula Blume)—in cool-temperate mixed forest under a selection system in northern Japan. We used stocking, demographic parameters, and species proportions of these species as measures of sustainability. Results showed that the tree density and basal area of the three high-value timber species increased during the study period. Moreover, the basal area increment of these species showed an increasing trend across census periods. However, while no significant differences in the tree mortality of these species were observed, the numbers of in-growth fluctuated across census periods. Increasing trends in species proportions of monarch birch and Japanese oak were observed. Even though there were some fluctuations across census periods, especially in smaller diameter classes, diameter distribution curves of high-value timber species followed a reversed J-shaped pattern. The results revealed that the sustainability measures of high-value timber species can be achieved in forest stands managed under single-tree selection system. In addition, the results also indicated the changing structure and composition of the forest stand. The stocking and basal area increment of conifers decreased while those of broadleaves increased. The proportion of conifers decreased to 33.01% in 2008–2016 from 48.35% in 1968–1978. The results of this study would be useful for adapting silvicultural practices and harvesting practices as well as for simulating various silvicultural and management options for high-value timber species.

Highlights

In uneven-aged mixed conifer–broadleaf forests in northern Japan, monarch birch (Betula maximowicziana Regel), castor aralia (Kalopanax septemlobus (Thunb.) Koidz), and Japanese oak (Quercus crispula Blume) are important producers of high commercial value timber, which is used in the veneer and furniture industries
In order to assess the sustainability of high-value timber species, we considered the stocking and demographic characteristics, and species proportion, as suggested by O’Hara et al [8]
Significant differences in the proportion of Japanese oak were observed (p < 0.001), while no significant differences were observed for monarch birch (p < 0.22) or castor aralia (p < 0.31) across census periods

Summary

Introduction

In uneven-aged mixed conifer–broadleaf forests in northern Japan, monarch birch (Betula maximowicziana Regel), castor aralia (Kalopanax septemlobus (Thunb.) Koidz), and Japanese oak (Quercus crispula Blume) are important producers of high commercial value timber, which is used in the veneer and furniture industries. The supply of high-quality timber from these tree species is exclusively dependent on the cutting of large trees within the mixed forests. Understanding the sustainability of these species will facilitate forest management, conservation, and the simulation of various silvicultural practices. The achievement of sustainability from the use of various forest management practices is a central precept of forestry and is central to all silvicultural systems [8]. Uneven-aged forest management or selection system has gained growing interest in many parts of the world due to its stability in forest stand structures [9,10,11,12], and there has been increasing criticism for even-aged forestry, wherein the whole forest area is clear-cut and regenerated artificially. Sustainable forest management (SFM) has been encouraged as a guiding principle in forest management [13]

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Discussion

Conclusion