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特集　―　森林攪乱研究へのアプローチ：変動性・森林の更新

種類：　特集／エディトリアル
Title： 　Approaches for forest disturbances studies: natural variability and tree regeneration
巻頁：　J For Res 16 (3): 153-154
題名：　森林攪乱研究へのアプローチ：変動性・森林の更新
著者：　Ahto Kangur，吉田俊也，久保田康裕，Marek Metslaid
所属：　Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Estonia
抄録：　持続可能な生態系管理のためには、生態系プロセスに関する十分な理解が欠かせない。従来の森林管理は、木材の生産のみを主眼としていた結果、生態系の持続性が保たれない事態を生じさせている。将来の管理方法を確立するためには、自然攪乱のレジームや、攪乱に対する生態系の反応などについて、さまざまなデザインや方法で研究を進めることが必要である。このような問題意識のもと、2009年9月、エストニアにおいて”Natural Disturbance Dynamics Analysis for Forest Ecosystem Management”ネットワーク（Nordic Forest Research Co-operation Committee）による 国際ワークショップが開催された。この特集では、そこで議論された中から、自然攪乱または人為攪乱に関連した11の研究を紹介する。

種類：　特集／総説
Title： 　The influence of storm-induced microsites to tree regeneration patterns in boreal and hemiboreal forest
巻頁：　J For Res 16 (3): 155-167
題名：　北方林域における樹木の更新に与える風倒起源のマイクロサイトの効果
著者：　Floortje Vodde，Kalev Jõgiste，久保田康裕，Timo Kuuluvainen，Kajar Köster，Aljona Lukjanova，Marek Metslaid，吉田俊也
所属：　Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Estonia
抄録：　北方林域を対象として、マイクロサイトや樹種の機能特性をとくに考慮した更新に関するレヴューを行った。風倒に起因するマイクロサイトの重要性は、一般に1)マイクロサイトの形状と分布、2)種子供給（林分履歴や、樹種ごとの種子散布能力、種子源の分布が影響）、3)気象・地位、4)残存木や植生の反応など複数の要因に依存していた。また、中・大規模の攪乱は資源量や生育条件を根本的に変化させるため、凍上、浸食、被食などの要因を介した影響も重要である。一般に遷移初期種は、中・大規模の攪乱で生じがちな、裸地を伴うマウンドのようなマイクロサイトで定着・成長する。一方、遷移後期種は、林床植生が繁茂する林床でセーフサイトとなりうる、林冠ギャップ周辺の倒木やマウンドに定着する。

種類：　特集／総説
Title：　Carbon dynamics of North American boreal forest after stand replacing wildfire and clearcut logging
巻頁：　J For Res 16 (3): 168-183
題名：　北アメリカの寒帯林における強度の山火事および皆伐後の炭素動態
著者：　Meelis Seedre，Bharat M. Shrestha，Han Y. H. Chen，Steve Colombo，Kalev Jõgiste
所属：　Faculty of Natural Resources Management, Lakehead University, Canada
抄録：　Boreal forest carbon (C) storage and sequestration is a critical element for global C management and is largely disturbance driven. The disturbance regime can be natural or anthropogenic with varying intensity and frequency that differ temporally and spatially the boreal forest. The objective of this review was to synthesize the literature on C dynamics of North American boreal forests after most common disturbances, stand replacing wildfire and clearcut logging. Forest ecosystem C is stored in four major pools: live biomass, dead biomass, organic soil horizons, and mineral soil. Carbon cycling among these pools is inter-related and largely determined by disturbance type and time since disturbance. Following a stand replacing disturbance, (1) live biomass increases rapidly leading to the maximal biomass stage, then stabilizes or slightly declines at old-growth or gap dynamics stage at which late-successional tree species dominate the stand; (2) dead woody material carbon generally follows a U-shaped pattern during succession; (3) forest floor carbon increases throughout stand development; and (4) mineral soil carbon appears to be more or less stable throughout stand development. Wildfire and harvesting differ in many ways, fire being more of a chemical and harvesting a mechanical disturbance. Fire consumes forest floor and small live vegetation and foliage, whereas logging removes large stems. Overall, the effects of the two disturbances on C dynamics in boreal forest are poorly understood. There is also a scarcity of literature dealing with C dynamics of plant coarse and fine roots, understory vegetation, small-sized and buried dead material, forest floor, and mineral soil.

種類：　特集／原著論文
Title： 　The ecology of tree regeneration in mature and old forests: combined knowledge for sustainable forest management
巻頁：　J For Res 16 (3): 184-193
題名：　壮齢林と老齢林における樹木更新の生態：持続可能な森林管理のための知識の統合
著者：　Jaan Liira，Toivo Sepp，Kaupo Kohv
所属：　Institute of Ecology and Earth Sciences, University of Tartu, Estonia
抄録：　We focused our attention on quantifying the factor complex of forest regeneration in 423 mature and old stands with contrasting environmental conditions. We recorded the microhabitat selection of tree recruits, the frequency of tree seedlings, and evaluated the drivers of sapling abundance and diversity. The majority of forest regeneration was established on undisturbed forest floor. Dead wood was a frequent substrate in spruce-(co)dominated forests. Seedling frequency within a stand was related to the site-type specific productivity gradient of stands–pine seedlings were common in low-productivity and spruce in high-productivity boreal forests. Seedlings of temperate broad-leaved trees dominated in productive boreonemoral forests, except for oak, which showed a uniform distribution of abundance in all forest site-types. Sapling abundance was dictated by forest site-type, and facilitated by stand diversity, variability in stand closure, lying dead wood, abundant moss, and a thick organic layer. Only in boreal forests was sapling abundance suppressed by the abundant spruce and younger trees. Upon considering the relationship between sapling abundance and species richness, sapling diversity was dependent on forest site-type, suppressed by stand density and dead wood (old gap) abundance, and facilitated by stand diversity. In addition, boreonemoral stands, competition from herbs, and facilitation by mosses occurred. The observed pattern of tree recruitment points to the importance of top-down effects of the overstory, competing or facilitating interactions with forest floor vegetation, and availability of regeneration microhabitats, which in complex make their ecology comparable with forest herbs. Natural forest regeneration can be enhanced if silvicultural methods support mixed stands and enhance field layer diversity. Oak can provide the universal tree species to improve stand structure over a wide range of habitats.

種類：　特集／原著論文
Title： 　Silviculture as a disturbance regime: the effects of clear-cutting, planting and thinning on polypore communities in mixed forests
巻頁：　J For Res 16 (3): 194-202
題名：　攪乱としての造林：混交林の皆伐，植林，間伐が多孔菌群集に及ぼす影響
著者：　Asko Lõhmus
所属：　Institute of Ecology and Earth Sciences, University of Tartu, Estonia
抄録： The structure of modern forest landscapes is profoundly affected by human-caused disturbances, particularly forest management; however, the effects and prospects of individual silvicultural techniques are insufficiently understood. This study distinguishes the effects of clear-cutting, planting and thinning on species richness and community composition of polypore fungi. In 2008-2009, 181 forest compartments (ranging from naturally regenerated deciduous stands to planted Picea abies stands and 0-137 years post clear-cutting) were explored in a hemiboreal landscape subjected to even-aged management. Altogether 104 polypore species were recorded. For species richness, time since clear-cutting was the most influential factor at both stand and landscape scales, followed by thinning. Clear-cuts had distinct polypore communities (including several red-listed species) whose species richness declined in time. Following 20 years post clear-cutting, species richness started to increase along different community-composition pathways determined by regeneration type. The communities developed after planting were moderately species rich at stand scale but homogeneous over larger areas. Thus, at landscape scale, mature unmanaged naturally regenerated stands hosted most species; thinning reduced species richness by approximately 15%, and among thinned stands, planted areas had a further 9-22% fewer species than naturally regenerated areas. In such variably managed landscape, silviculture appeared to create particularly distinct communities in young stands on nutrient-rich soils, which naturally provide polypores with a rich supply of small deciduous snags absent from stands artificially planted with P. abies and intensively thinned.

種類：　特集／原著論文
Title： 　Fine-scale heterogeneity in overstory composition contributes to heterogeneity of wildfire severity in southern boreal forest
巻頁：　J For Res 16 (3): 203-214
題名：　南部寒帯林の上層木構成における不均質性が山火事強度の違いに寄与する
著者：　Daren J. Carlson，Peter B. Reich，Lee E. Frelich
所属：　Department of Forest Resources, University of Minnesota, USA
抄録：　Wildfire can create a mosaic of impacts of varying severity across the landscape. Although widely recognized, this feature and its causes are little understood or studied in ecology. We studied a 1,200-ha wildfire in the southern boreal forest of the Boundary Waters Canoe Area Wilderness (BWCAW) in northeastern Minnesota, USA, using 275 ground plots (stand-scale) and 1:7,000 scale aerial photographs for the entire burned area (landscape-scale). Fire severity was markedly heterogeneous. Overall, 50% of the burn extent was classified as high burn severity, but patches burned this severely were on average less than 70 m from patches of low severity. As expected, lowlands had lower average fire severity than uplands, but several lowland areas burned, and some upland areas remained unburned. At the landscape scale, pre-fire vegetation type–itself heterogeneous–and patch size of less flammable cover types influenced fire severity. Crown fire severity in upland areas was lowest in pure aspen-birch and red/white pine stands and highest in jack pine and spruce-fir stands. At the stand-scale, slope position and the density of certain tree species at adjacent plots influenced fire severity. Improved understanding of the severity patterns created by wildfire can help to guide the management of spatial patterns of forested systems. Based on our study, a larger range in disturbance severity at scales of 0.1 to several ha and increasing the average size, and range of sizes, of residual patches would in aggregate better mimic natural disturbance than typical harvests.

種類：　特集／原著論文
Title： 　Tree mortality in a natural mixed forest affected by stand fragmentation and by a strong typhoon in northern Japan
巻頁：　J For Res 16 (3): 215-222
題名：　北海道の天然生混交林における樹木の死亡率に及ぼす林分孤立化と台風の影響
著者：　吉田俊也，野口麻穂子，植村滋，簗場聡，宮久史，日浦勉
所属：　北海道大学北方生物圏フィールド科学センター
抄録：　風倒は、多くの森林における主要な攪乱である。林分が孤立化すると、風への露出が高まるためその影響は増加すると考えられる。本研究では、北海道北部の針広混交林において、3つの孤立した林分サイズ（面積400m², 1600m², 6400m²）を試験的に設定して10年間にわたって動態を記述することにより、孤立林の林縁からの距離に伴う樹木個体の死亡のパターンを検討した。死亡率は小さい林分で高い傾向があったが、それは研究前半の期間でしか認められなかった。また、距離依存的な死亡の傾向も、優占種であるトドマツにおいて、やはり最初の5年間のみで顕著であった。一方、2004年9月の強い台風の影響があった後半の期間には、そのような傾向は認められず、樹木個体の死亡は林分内の各所で生じていた。これらの結果は、風倒の生じるパターンが風の強さによって異なることを示唆していた。林縁効果は、例外的な強風時には生じにくい、すなわち、林分孤立化の影響は比較的小規模な攪乱時にのみ重要となる可能性が示唆された。

種類：　特集／原著論文
Title： 　Ground vegetation under natural stress conditions in Scots pine forests on fixed sand dunes in southwest Estonia
巻頁：　J For Res 16 (3): 223-227
題名：　エストニア西南部の安定砂丘上のヨーロッパアカマツ林における自然ストレス条件下の地上植生
著者：　Mari Tilk，Malle Mandre，Jaan KLõšeiko，Priit Kõresaar
所属：　Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Estonia
抄録：　Ecosystems on dunes are influenced by critical environmental factors (mineral nutrients, water deficiency, etc.) considered decisive for their existence. The present paper is based on studies carried out on dunes on the coastal area of the Baltic Sea, southwest Estonia. The nature of forest ecosystems on dunes was studied from the aspects of chemical characteristics of soil, vascular plant species richness and diversity. Sampling sites on the dunes with different heights were selected in Cladina and in Vaccinium vitis-idaea site-type Scots pine forests. Vascular plant species richness and diversity were related to edaphic gradients. On the dune with a height of 32.1 m a.s.l., significant relationships were revealed between the number of species of ground vegetation, pH, volumetric water content in soil and the position of the sample plots. No relationships were revealed between the number of vascular plant species, soil pH, volumetric water content and mineral nutrients on the dune with a height of 9 m a.s.l. The most frequent and abundant plant species on the higher dune were Deschampsia flexuosa, Vaccinium vitis–idaea and V. myrtillus; the highest number of species were found at the bottom of the dune, while on the top only some xeromorphic species such as Festuca ovina, Sedum acre and Crepis tectorum occurred. On the lower dune, the most frequent were Vaccinium vitis–idaea, V. myrtillus and Melampyrum pratense, while V. uliginosum was found only on the bottom and slope and Empetrum nigrum on the top of the dune.

 

種類：　特集／原著論文
Title： 　Radial growth patterns of dominant trees in two old-growth forests in eastern Fennoscandia
巻頁：　J For Res 16 (3): 228-236
題名：　フェノスカンディア東部の老齢林における優勢木の直径成長パターン
著者：　Laura Niukkanen，Timo Kuuluvainen
所属：　Department of Forest Sciences, University of Helsinki, Finland
抄録：　We investigated the characteristics and variability of radial growth patterns and the occurrence of growth releases in dominant trees in two old-growth forests in eastern Finland, one dominated by Picea abies and the other by Pinus sylvestris. The dominant trees exhibited high variation in radial growth patterns suggesting that the trees had experienced very different growing conditions and competitive situations during their lifespans. Based on visual evaluation, five types of radial growth patterns were distinguished: descending, even, unimodal (one peak in the growth rate), bimodal (two peaks in the growth rate with an intermediate depression) and fuzzy (no clear pattern). One or more growth releases were detected in 18% of the sampled Picea and in 21% of the Pinus trees. In both the Picea– and the Pinus-dominated sites, the temporal distribution of growth releases was relatively even, except for a moderate peak in 1855-1860. This suggests that small-scale disturbances have been the predominant disturbance mode in both sites during the last 150 years. We conclude that the detected variability in radial growth patterns likely reflects the overall small-scale heterogeneity of structure and developmental processes that are typical of old-growth forests.

 

種類：　特集／原著論文
Title： 　Growth patterns from different forest generations of Scots pine in Estonia
巻頁：　J For Res 16 (3): 237-243
題名：　エストニアの異なる世代のヨーロッパアカマツ林の成長パターン
著者：　Sandra Metslaid，Allan Sims，Ahto Kangur，Maris Hordo，Kalev Jõgiste，Andres Kiviste，Pertti Hari
所属：　Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Estonia
抄録：　There is strong evidence that climate change alters tree growth in boreal forests. In Estonia, the analysis of ring measurements has been a common method to study growth changes. In this study, annual height growth data from dominant or co-dominant Scots pine (Pinus sylvestris L.) trees were used to develop a growth model for three forest generations. Stem analysis was applied and annual height growth was measured as the distance between whorls, as detected by branch knots of whorls on the split stem surface. Retrospective analysis of height growth produced comparative trends for three different age groups. Statistical analyses were used to estimate the impact of different factors on growth. Annual height growth was considered the best indicator for detecting possible trends in the growth potential of trees. Study results indicate that three generations (separated by time periods of 30-40 years) showed significant differences in growth patterns caused by shifts in climatic factors and management regimes (anthropogenic and natural disturbances).

種類：　特集／原著論文
Title： 　Forest land-use history affects the species composition and soil properties of old-aged hillock forests in Estonia
巻頁：　J For Res 16 (3): 244-252
題名：　エストニアにおける林地利用の履歴が堆積小丘上の老齢林の種構成と土壌形質に影響する
著者：　Jaanus Paal，Margit Turb，Tiina Köster，Elle Rajandu，Jaan Liira
所属：　Institute of Ecology and Earth Sciences, University of Tartu, Estonia
抄録：　Decisions regarding forest typology, management and protection are often based on the structures of present-day forests, ignoring their successional history. Forests growing on kames, eskers and various moraine hillocks common in regions with Holocene glaciation are good examples of this approach. In Estonia, these forests locally persist as fragments of continuous primary forest, but usually they are situated on former slash-and-burn areas (bushlands) or reforested agricultural land. Our aim was to elucidate the strength of the effect of long-term land-use history on the present-day vegetation compositions of mature hillock forests and their soil chemistry. It appeared that even the mature secondary hillock forests are still distinct from historically continuous stands in terms of species composition. We discovered connections between stand history and species content in hillock forests as well as transformed soil properties. The carbon and nitrogen contents in the humus horizons of secondary forests are lower while their carbon-nitrogen ratios are higher than in continuous forests. The relationship between vegetation and stand history is demonstrated by the higher proportions of anthropophytic and apophytic species in the herb layer of the secondary forests. The presence of species that are tolerant of anthropogenic impact on the secondary hillock forests floor can also be partly explained by the effect of different species in the tree and shrub layers, gaps in the tree canopy, and the boundary effect caused by the small areas of forest patches, neighboring grasslands or fields. The extinction debt in secondary communities should also be considered.

種類：　特集／原著論文
Title： 　Understory thinning reduces wood-production efficiency and tree species diversity in subtropical forest in southern Japan
巻頁：　J For Res 16 (3): 253-259
題名：　琉球島嶼の亜熱帯林における成長動態と林木種多様性を制御する下層除伐施業
著者：　藤井新次郎，久保田康裕
所属：　琉球大学理学部
抄録：　琉球島嶼の亜熱帯林における森林構造や林木種多様性に対する下層除伐の長期的なインパクトを、空間明示的な個体ベースモデルSEIB-DGVMのシミュレーションにより予測した。下層除伐の施業シナリオは、除伐サイクルと除伐対象サイズの組み合わせにより定義される。モデルシミュレーションの結果は、下層除伐が林冠木の成長に影響を与え、長期的には林分の地上部現存量を減少させることを明らかにした。小径木の頻繁な除伐は、下層種の再生を阻害し、林木種多様性を極端に減少させた。私たちの予測は、下層除伐が琉球島嶼の亜熱帯林の木材生産の経済効率と林木種多様性の回復に負の影響を及ぼすことを示唆した。これは、伝統的な里山施業と同じ効果を持つと期待されている下層除伐は、種多様性を維持する木材生産林を育てるという予想に反する結果である。