Hiromi Mizunaga

Geographical variation in the early regeneration process of Siebold's Beech (Fagus crenata BLUME) in Japan

The causes and timing of seed death in early regeneration process of Siebolds beech (Fagus crenata Blume) was studied at 15 sites along a snowfall gradient in Japan, in order to clarify why the seedling density of the species has geographic difference remarkably. Seed production did not significantly differ along the snowfall gradient. Pre-dispersal seed mortality by insect damage was higher at sites with light snowfall than at sites with heavy snowfall, but this only seemed to be a minor factor influencing the population. A large proportion of the viable nuts that fall in autumn ware killed in winter before germination. Winter mortality was much higher at sites with thin snow cover than that at sites with thick snow cover, and this factor was strongly correlated with the geographic variation of seedling regeneration probability. There was little seed mortality by winter desiccation. The main factor contributing to the geographic difference seemed to be a seed predation by rodents in winter. Deep snow cover may reduce the success of rodents finding seeds in winter. Thus the observed relationship between snowpack depth and early mortality may be due to an indirect effect through the process of seed predation.p>

Feasibility of silviculture for complex stand structures: designing stand structures for sustainability and multiple objectives

The concepts of ‘from homogeneity to heterogeneity’, ‘from simplicity to complexity’, and ‘from an agricultural system to a natural disturbance-based system’ are widely recognized in alternative silviculture. Stand structure is closely related to microclimate, cycling of materials, quality and quantity of wildlife habitat, and other ecological functions. Therefore, stand structure determines the sustainability and resilience of forest ecosystems. Most forest services, such as timber production, wildlife conservation, maintenance of aesthetics, and hydrological values, are stand structure dependent. These services are influenced by the manipulation of stand structure. Silviculture that maintains complex stand structure and continuous crown cover over time is termed multi-aged forestry (O’Hara 1996), close-to-nature forestry (Mlinsek 1996) or continuous-cover forestry (Garfitt 1995). This type of silviculture is being widely advocated to meet changing social demands, from economic profit to environmental services. Integrating complexity into silviculture prescription is therefore believed to improve the resilience and adaptability of managed forests (Puettmann et al. 2008). Achieving a silvicultural system for complex stand structures requires close, diligent control of overstory stock and canopy coverage to ensure successful seedling regeneration and growth. Therefore, a more complex silvicultural system is generally more expensive and labour intensive, or requires more advanced techniques. How can we feasibly build up forest ecosystems with complex stand structures from both the ecological and economic points of view? To help solve this question, we organized the Sixth Workshop of the Uneven-Aged Silviculture Group (IUFRO) in Shizuoka from 24 to 27 October 2008. The workshop was entitled ‘Feasibility of silviculture for complex stand structures, designing stand structures for sustainability and multiple objectives’. Ten papers presented at this workshop are included in this special issue, which we believe will promote future studies and practices for sustainable forest management. Studies on long-term dynamics of stand structures in uneven-aged stands provide us with a feasible basis for integrating complexity into silviculture. Three papers included in this issue show the result of stand structure dynamics in the long term after operations. Lähde et al. (2010) compare stand volume increments over 17 years among three alternative unevenand even-sized management approaches. Klopcic and Boncina (2010) show a difference in growth pattern in long-term growth of silver fir– European beech in single-selection forests in Slovenia. Deal et al. (2010) report on growth 50 years after partial harvesting of western hemlock–Sitka spruce stands in southeast Alaska and compare this with newly regenerating stands following clear-cutting, and uncut old-growth stands. Mimicking natural disturbance systems is recognized as an efficient silviculture approach for complex stand structures. Information on the response of stand structure to natural disturbance will provide tools and models for manipulating uneven-aged managed stands. We include here four examples of how information on natural H. Mizunaga (&) Faculty of Agriculture, Shizuoka University, Ohya 836, Suruga, Shizuoka 422-8529, Japan e-mail: mizunaga@agr.shizuoka.ac.jp

Soil Microbial Activities in Beech Forests Under Natural Incubation Conditions as Affected by Global Warming

Abstract Microbial activity in soil is known to be controlled by various factors. However, the operating mechanisms have not yet been clearly identified, particularly under climate change conditions, although they are crucial for understanding carbon dynamics in terrestrial ecosystems. In this study, a natural incubation experiment was carried out using intact soil cores transferred from high altitude (1 500 m) to low (900 m) altitude to mimic climate change scenarios in a typical cold-temperate mountainous area in Japan. Soil microbial activities, indicated by substrate-induced respiration (SIR) and metabolic quotient ( q CO 2 ), together with soil physical-chemical properties (abiotic factors) and soil functional enzyme and microbial properties (biotic factors), were investigated throughout the growing season in 2013. Results of principal component analysis (PCA) indicated that soil microbial biomass carbon (MBC) and β-glucosidase activity were the most important factors characterizing the responses of soil microbes to global warming. Although there was a statistical difference of 2.82 °C between the two altitudes, such variations in soil physical-chemical properties did not show any remarkable effect on soil microbial activities, suggesting that they might indirectly impact carbon dynamics through biotic factors such as soil functional enzymes. It was also found that the biotic factors mainly controlled soil microbial activities at elevated temperature, which might trigger the inner soil dynamics to respond to the changing environment. Future studies should hence take more biotic variables into account for accurately projecting the responses of soil metabolic activities to climate change.

Effects of components of the leaf area distribution on drag relations for Cryptomeria japonica and Chamaecyparis obtusa

The objectives of this study were to clarify the effects of components of the leaf area distribution on the drag coefficient of crowns and streamlining (e.g., leaf area index; LAI, outline of the crown shape, and clumpiness) and to contribute to the accumulation of data on drag relations by quantifying data for Chamaecyparis obtusa and Cryptomeria japonica. We conducted drag experiments while simultaneously capturing dynamic crown images for 28 Ch. obtusa crowns and 13 Cr. japonica crowns to analyze the relationships between the leaf area distribution components and drag coefficient or streamlining. The static drag coefficient increased with the LAI for Ch. obtusa and with decreasing clumpiness for Cr. japonica. The reduction rate of the static drag coefficient decreased with increasing clumpiness for Ch. obtusa and with a combination of increasing LAI and decreasing clumpiness for Cr. japonica. The reduction rate of the static drag coefficient had a clear relationship with the decreasing rate of the dynamic crown projected area of obstacles (foliage elements, branches, and stems) calculated from captured video images under windy conditions for Cr. japonica, while Ch. obtusa did not show clear relationship between them. The drag coefficients assuming non-porous crown; Cmax estimated by simple model combining LAI and clumpiness were approximately 1.0 in Ch. obtusa and 0.5 in Cr. japonica and were equivalent to the dynamic drag coefficients from video image under windy condition. The combination of LAI and clumpiness provided simple estimation for drag relations and enable to link crown structure to wind damage easier.

Is Foliage Within Crowns of Cryptomeria japonica More Heterogeneous and Clumpy With Age

Foliage clumping structure is important for forest ecological functions but has not yet been quantitatively analyzed. We examined how foliage clustering within crowns of Cryptomeria japonica changed with age. We sampled 10 trees from four monospecific stands with different ages from 20- to 88-years-old, and measured foliage mass density in cubic cells. Three indices of foliage clumpiness—coefficient of variance, Morans I for aggregation of foliage density, and cluster fragmentation—correlated with the proportion of foliage gaps. As trees aged, foliage distributed more heterogeneously and clusters fragmented. Clumping in old crowns improves light interception under direct light conditions.