Toshiya Yoshida

Silvicultural alternatives to conventional even-aged forest management - what limits global adoption?

BackgroundThe development of forestry as a scientific and management discipline over the last two centuries has mainly emphasized intensive management operations focused on increased commodity production, mostly wood. This “conventional” forest management approach has typically favored production of even-aged, single-species stands. While alternative management regimes have generally received less attention, this has been changing over the last three decades, especially in countries with developed economies. Reasons for this change include a combination of new information and concerns about the ecological consequences of intensive forestry practices and a willingness on the part of many forest owners and society to embrace a wider set of management objectives. Alternative silvicultural approaches are characterized by a set of fundamental principles, including avoidance of clearcutting, an emphasis on structural diversity and small-scale variability, deployment of mixed species with natural regeneration, and avoidance of intensive site-preparation methods.MethodsOur compilation of the authors’ experiences and perspectives from various parts of the world aims to initiate a larger discussion concerning the constraints to and the potential of adopting alternative silvicultural practices.ResultsThe results suggest that a wider adoption of alternative silvicultural practices is currently hindered by a suite of ecological, economic, logistical, informational, cultural, and historical constraints. Individual contexts display their own unique combinations and relative significance of these constraints, and accordingly, targeted efforts, such as regulations and incentives, may help to overcome specific challenges.ConclusionsIn a broader context, we propose that less emphases on strict applications of principles and on stand structures might provide additional flexibility and facilitate the adoption of alternative silvicultural regimes in a broader set of circumstances. At the same time, the acceptance of alternative silvicultural systems as the “preferred or default mode of management” will necessitate and benefit from the continued development of the scientific basis and valuation of a variety of ecosystem goods and services. This publication is aimed to further the discussion in this context.

The age of tropical rain-forest canopy species, Borneo ironwood ( Eusideroxylon zwageri ), determined by 14 C dating

Using 14 C dating, the life span and growth rate of Borneo ironwood ( Eusideroxylon zwageri , Lauraceae), which is a canopy tree species with extremely durable and decay-resistant wood distributed in tropical rain forests of South-East Asia, were studied. Timber segments collected from 15 logged stumps in Kubah National Park, Sarawak, Malaysia, were analysed by accelerator mass spectrometry and the obtained data were calibrated to determine the age of individuals. The 14 C dating turned out to be an effective method for estimating ages of long-lived trees, such as E. zwageri , in the aseasonal tropics because the estimated error was small compared with estimated age. We found that E. zwageri can live more than 1000 y and that the growth rate of this species was very slow, with a mean radial growth rate of 0·058 cm y -1 . The life span was much greater and the growth rate was much slower than those observed or estimated for trees of Dipterocarpaceae, the dominant family in this tropical forest. The long life span of this species may be caused by wood durability with a high specific gravity and abundant defensive compounds. Given equal carbon allocation, the high density and carbon-based defensive compounds may result in a reduced growth rate.

Variation in understory structure and plant species diversity influenced by silvicultural treatments among 21- to 26-year-old Picea glehnii plantations

We investigated effects of silvicultural treatments (planting and subsequent treatments) on understory structure and plant species diversity in managed Picea glehnii plantations (21–26 years old) in northern Japan. We evaluated the importance of each treatment (machinery site preparation, planting, weeding, and thinning) in 19 plantations, with considerable variation among treatments overall. The understory had 98 vascular plant species; the most dominant species was a dwarf bamboo Sasa senanensis, followed by tree species Abies sachalinensis and Betula ermanii. Multiple regression analyses showed that thinning negatively influenced plant species diversity. Planting density showed a strong positive correlation with density of seedlings (height <20 cm), but few independent variables were correlated with density of saplings (height ≥20 cm and diameter at breast height <1 cm). The negative effect of thinning and the positive effect of planting density seem to be related to the existence or reinitiation of dense cover of Sasa senanensis. We present possible mechanisms of response to treatments to generalize the results. We then suggest ways to improve current treatments to meet the goals of wood production and biodiversity conservation in the region.

Interspecific competition among three canopy-tree species in a mixed-species even-aged forest of central Japan.

Abstract We investigated causes and consequences of interspecific competition among canopy-tree species with different shade-tolerance. The shading effects caused by neighbors were determined for three tree species, shade-tolerant Fagus crenata, and intermediate tolerant Quercus crispula and Magnolia obovata, in six even-aged stands containing different proportions of each species. The competitive attributes (sensitivity to suppression and intensity of shading) varied considerably among species. Shade-tolerant F. crenata caused most intensive shading effects probably because of its deeper crown depth. Less-tolerant Q. crispula decreased its stem growth and crown depth markedly in association with the presence of shade-tolerant F. crenata. In contrast, F. crenata and M. obovata were less influenced by their neighbors; it may be due to its own higher shade-tolerance in the case of F. crenata and larger initial growth rates in M. obovata. We suppose that differences in initial species composition may lead a species to have different dominance in stand development. When shade-tolerant species are absent in mixture, less shade-tolerant species could maintain their dominance for a long period. In contrast, mixture with tolerant species would reduce the dominance of less-tolerant species, unless they had growth advantage in early stage in development.

The influence of storm-induced microsites to tree regeneration patterns in boreal and hemiboreal forest

We reviewed studies dealing with regeneration under variable conditions in boreal and hemiboreal forests as affected by different microsite types by tree species functional groups. Generally, the importance of storm-induced microsites for regeneration dynamics in boreal forests depends on several factors: (1) distribution and type of microsites (generated by storm characteristics and stand conditions); (2) viable seed supply (stand history, species dispersal traits and status of surviving trees) and their species’ life history strategy; (3) climatic and site conditions (pre-storm conditions and storm-induced changes); and (4) delayed storm effects, such as retarded falling of trees, favoured vegetation growth, etc. Studies acknowledging the significance of microsites were mostly related to intermediate or severe events, causing sufficient changes in resource levels and growth conditions, and influencing extrinsic factors such as frost heaving, erosion and browsing. Also, the dispersal traits of available tree species, including sprouting and response of surviving trees, such as canopy expansion, should be considered in evaluating microsite importance in individual cases. In intermediate to severe windstorm events, pioneer species are generally profiting most from the additional offer in microsites, requiring bare mineral soil and elevated locations for their establishment and growth. Under gap dynamics, shade-tolerant species benefit from dead wood and elevated locations as these offer safe sites in stands with abundant understorey vegetation.

The stand dynamics of a mixed coppice forest of shade-tolerant and intermediate species.

Abstract We investigated stand dynamics of a mixed coppice forest of shade-tolerant and intermediate species, Fagus crenata Bl. and Quercus crispula Bl., in five stands with canopy-stem densities from 420 to 1320 ha−1 (estimated stand age: 37–62 years). The mean basal area (BA), exposed-crown area (ECA) and crown depth (CD) per stem were significantly larger in F. crenata in the three lower density plots. Also Q. crispula had considerably less overtopped stems in the two lower density plots. The mean annual BA increments of the two species were similar in the earlier 20 years; however, in the most recent 5 years, F. crenata had a higher relative growth rate for basal area (RGRBA) than Q. crispula. The most critical variable of the RGRBA was the ECA for F. crenata and the relative height (RH) for Q. crispula. We predict that dominance of F. crenata will gradually increase over that of Q. crispula as stands mature. This seems to be caused by lower shade-tolerance despite the similar initial growth rates of Q. crispula compared with F. crenata.

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

Effects of crown release on basal area growth rates of some broad-leaved tree species with different shade-tolerance

We compare three or four years effects of crown release on stem growth rates among four deciduous broad-leaved tree species,Fagus crenata, Quercus crispula, Magnolia obovata andAcer mono, in an even-aged coppice forest, central Japan. The crown release significantly improved relative growth rates for basal-area (RGRBA) of the four species. However the effects of neighboring gap area (GAPA) on the RGRBA differed among the species. The effects were significant forQ. crispula andM. obovata, indicating that growth rates of these two species increase with intensity of the crown release. In contrast, the RGRBA ofF. crenata andA. mono were not correlated with the GAPA, suggesting that their growth rates are unrelated to the intensity. We considered that such differences among species were closely related to their photosynthetic characteristics of light use; less-tolerant species (Q. crispula andM. obovata) exhibit greater growth rates relative to the intensity of crown release than tolerant species (F. crenata andA. mono). Based on these results, we proposed implications for thinning practices in mixed forests of species with different shade-tolerance.

Stand structure and composition of a 60-year-old larch (Larix kaempferi) plantation with retained hardwoods

Tree retention is understood as a key practice in creating complexity, leading to heterogeneity in resources and habitats in managed stands. In this article, we clarify the long-term effects of tree retention on stand structure and tree-species composition in a 60-year-old Larix kaempferi plantation in central Japan. In our study plot (1.5 ha) there were 18 stems/ha of retained trees (determined by tree-ring analysis), mostly Quercus crispula. We conducted spatial analyses and tested the hypothesis that tree abundance, size structure, and species composition and diversity change with distance from the retained trees. Near the retained trees, L. kaempferi showed a reduction of 40%–60% in basal area, due presumably to the shading effect. In contrast, the nearby area showed greater species diversity in the canopy layer. The retained trees created patches of different species composition in the understory. The spatial gradient of shade and colonization opportunity provided by retained trees greatly affect the distribution of the colonized species, according to their shade tolerance and seed-dispersal ability, which resulted in the stand structure with a heterogeneous shrub-layer vegetation. Retention proved particularly important for the enhancement and long-term maintenance of structural and compositional complexity in L. kaempferi plantations.

An alternative management regime of selection cutting for sustaining stand structure of mixed forests of northern Japan: a simulation study

In uneven-aged conifer–broadleaved mixed forests in Hokkaido, northern Japan, single-tree selection cutting has been a common management practice since the early twentieth century. This practice is expected to produce timber without major changes in stand structure or tree species composition. The demographic response of forests to this practice has often been unexpected, and degradation of stand properties has been widely observed. We propose here a sustainable management regime of selection cutting, based on an individual-based forest dynamics simulation model, SORTIE-ND. Our simulations, based on demographic data from 15 long-term monitoring stands, suggest that selection cutting using a lower cutting intensity together with a longer rotation period and reduced removal of small trees and conifer species is more appropriate than traditional systems in terms of maintaining stand structure and tree species composition, as well as being profitable financially. Supplemental regeneration practices, which can counter accidental mortality incurred during harvesting operations, would also be necessary to ensure tree recruitment.