Individual growing conditions that affect diameter increment of tree saplings after selection harvesting in a mixed forest in northern Japan

We analyzed temporal patterns in diameter growth of saplings following selection harvesting in an uneven-aged mixed stand dominated by Abies sachalinensis, Acer mono, Quercus crispula, and Betula ermanii in Hokkaido, northern Japan. We examined interspecific differences in growth responses to local growing conditions including harvesting intensity, crowding, stem size, and past duration of the small growth period. Consistent with expectations based on shade tolerance of the species, the age at which the individual reached a diameter at breast height of 12.5 cm was highest for A. sachalinensis and lowest for B. ermanii. The interspecific growth differences between saplings that had or had not experienced local harvesting increased gradually for A. sachalinensis and B. ermanii, but peaked at around 4-6 years after harvesting for Q. crispula. Generalized linear mixed model analysis clearly suggested that individual growth conditions required to enhance diameter growth of saplings differed considerably among species. For Q. crispula and B. ermanii, local harvesting intensity was most strongly and positively associated with diameter growth rate, whereas for A. sachalinensis and A. mono, stem size had the strongest negative effect. Abies sachalinensis saplings responded more to surrounding harvesting when they were relatively small, whereas A. mono showed a weak opposite response. The duration of the small growth period before harvesting had negative effect for A. sachalinensis, but not for the other species. Our study indicated that the influence of selection harvesting on growth of shade-tolerant species depends upon pre- and post-harvest growing conditions

Changes in carbon stock following soil scarification of non-wooded stands in Hokkaido, northern Japan

To restore nonwooded stands dominated by dwarf bamboo species (Sasa kurilensis or S. senanensis) into forests, mechanical soil scarification has been applied in northern Japan since the 1960s. The treatment is followed both by natural regeneration and artificial planting. In this study, we quantified the total carbon stock (plants plus 0.3 m depth of soil) of these stands over 35-year age-sequences. The natural regeneration stands were gradually dominated by Betula ermanii. The carbon stock increased linearly to 215.1 ± 35.2 Mg C ha^[-1] for a 37-year-old stand formerly dominated by S. kurilensis, and 181.1 ± 29.8 Mg C ha^[-1] for 34-year-old stand formerly dominated by S. senanensis. The latter was similar to that of a Picea glehnii plantation, formerly dominated by S. senanensis, with comparable stand age (160.3 ± 6.7 Mg C ha^[-1] for 35-year-old stands). Although the carbon stock in plants quickly offset the untreated level, that in the soil remained depressed even in the older stands. This resulted in small differences in carbon stock of these stands with untreated dwarf bamboo stands. We conclude that natural regeneration following scarification could be a prime option for carbon sink management in the region. However, we should take a long rotation period (i.e. > 50-year) to ensure a carbon sink state. A potential of further improvements of the practice, including that reduce intensity of soil disturbance, was presented

Twenty years of community dynamics in a mixed conifer : broadleaved forest under a selection system in northern Japan

Single-tree selection has been employed widely in northern Japanese mixed forests, but management-induced changes in forests are not well understood. This study examined demographic parameters of major tree species during a 20-year study of a 68 ha stand in which single-tree selection has been conducted since 1971. Results showed that growth and survival of conifers (mostly Abies sachalinensis (Fr. Schm.) Masters) was the most strongly positively affected by the treatment. Nevertheless, recruitment of conifers was not sufficiently improved, suggesting their decreased dominance over the longer term. Instead, shade-intolerant broad-leaved species (mainly Betula ermanii Cham.) will gradually increase because of their higher recruitment rates after the treatment. Shade-tolerant broad-leaved species (mainly Acer mono Maxim. and Tilia japonica (Miq.) Simonkai) appeared to experience the most distinct negative effects, especially on survival. These trends differed markedly from those reported in previous papers concerning partial harvesting systems, which predicted an increase in dominance of shade-tolerant species. The results shown here should be generalized carefully because we have investigated only one stand without repetition of the control area. Nevertheless, trends described in this large-scale, long-term study could provide a basis for simulating stand dynamics. We discussed possible reasons for the observed patterns and provided implications for sustainable management in the region

Data from: A novel growth model evaluating age-size effect on long-term trends in tree growth.

1.One of the major problems in understanding growth trends in long-lived trees is the difficulty of separately quantifying the effects of tree size and age. Careful statistical control of the axiomatic age×size covariation is therefore required to identify long-term trends in tree growth and their drivers, and to predict forests’ responses to environmental changes reliably. 2.To address this issue, we present a novel tree growth model: a ‘two-dimensional lognormal growth model’. This is an extension of the one-dimensional lognormal growth model, in which tree growth is modelled primarily as a function of size. Our model assesses the trend in tree growth over time by explicitly partitioning the effects of age and size, controlling the covariation. The model is then extended to incorporate the effects of neighbourhood crowding and individual tree variation. 3.To demonstrate our model, we apply it to long-term monitoring data from a mature (104-year- old) plantation of Japanese cedar. Thinning operations of various intensities have been applied to this plantation, and the diameter of each individual tree has been measured repeatedly. 4.We observed a pronounced age-related decline in diameter growth. However, at each age, greater tree size was associated with a higher growth rate. The growth-size curve predicted from the model became flatter with tree age, and the curve's peak shifted rightwards as tree age increased. The model reveals that the sensitivity of a target tree to neighbourhood crowding depends strongly on neighbours’ size, and also provides an estimate of among-tree variation in growth performance. 5.Although the relationships between growth, size and age in long-lived trees are very complex, our growth model supports the conclusion that it is possible to predict long-term trends in tree growth reliably with respect to both age and size. In addition, the model's flexibility will facilitate more robust testing of species-specific responses to long-term environmental changes

Tree diameter growth data of Japanse cedar

The individual tree growth was monitored for a long-term in a mature plantation of Japanese cedar