Trendy セミナー   2009-06-30 (火) 15:00--18:45   北大・大学院地球環境 農学部会議室

自然撹乱体制を尊重した森林生態系管理

Trendy seminar & 北方森林研究集会 (合同企画)
(*普段と開催時間・場所が異なりますのでご注意下さい)

横国大の森章さんをお招きし、 自然撹乱体制を尊重した森林生態系管理 についてお話して頂きます。

また、スウェーデンとアメリカからも研究者3名をお招きする 「北方森林研究集会」を同時開催します。

タイトル: 『自然撹乱体制を尊重した森林生態系管理』

講演者: 森 章(横浜国立大学環境情報研究院)

要旨: 撹乱体制の定量化は,生態系管理において重要な項目のひとつである。特に,森林は多くの景観の主要要素である。ゆえに,森林の撹乱体制を尊重することで,生態系や景観全体での構造・機能・動態を包括的かつ健全に維持できるような森林管理を行うことができると考えられている。そして,その結果として,生態系に内包される遺伝子・種・個体群・群集,さらには地域景観に至る,各レベルでの生物多様性の維持に大きく貢献し得ると考えられている。本発表では,カナダ・ブリティッシュコロンビア州のいくつかの森林景観を例として,それぞれの地域の気候条件に応じた特有の自然撹乱体制を定量化し尊重することが,森林生態系管理の上でどのように重要視されているのかについて概説する。

ブリティッシュコロンビア州内には,1)低頻度で起こる大規模な火事撹乱が規定する森林景観,2)高頻度・低強度の林床火事により維持されてきた内陸の乾燥林,3)小規模なギャップ形成が主要撹乱要因として卓越する太平洋岸温帯雨林など,様々な撹乱体制によりその動態や構造が規定されている多様な森林生態系が存在する。しかしながら,過去の数世紀の間,各地域特有の撹乱体制を尊重しなかったがために,多くの森林が本来あるべき姿から変えられてしまったと考えられている。例えば,内陸地域のロッキー山脈の山岳林では,大規模な山火事が自然撹乱として卓越する。しかし,大規模な火事はしばしば"災害"として捉えられ,20世紀の後半まで人為抑制の対象となってきた。そして,その結果,火事に依存した生物相を衰退させてしまったと考えられている。さらに,現在,燃えずに残ってしまった森林が広範囲に蓄積しているために,過度の火災の危険性が危惧する声も聞こえる。実際に,この20年の間の温暖化・乾燥化傾向が相まって,北部ロッキー山脈の多くの山岳林では,破壊的規模の火事が頻発し始めている。現在,このような状況にあるために,森林で本来起こりえる自然撹乱体制の時空間的規模の定量化が急務となっている。これにより,1)予想を超える規模の撹乱が起こった際に,自然撹乱であるかどうかを見極めること,2)自然に起こり得る範囲を逸脱した撹乱の発生を避けること,3)撹乱体制の時空間的規模が本来の範囲から逸脱してしまった生態系を回復させること,が可能になる。森林生態系の健全な管理のために,自然撹乱体制を定量化し,尊重することが必要である。

Conservation of biodiversity in Swedish forests - an example of a multi-scaled model

Professor Lena Gustafsson, Swedish University of Agricultural Sciences, Box 7044, SE-750 07 Uppsala. lena.gustafsson@ekol.slu.se

Sweden is the 4th largest country in Europe by area and about 2/3 of the land area (28 million ha) is covered with forests. Forestry is highly mechanized and clear-cutting is the prevailing harvesting method, applied on 90% of the productive forestland. The forest industry is one of Sweden's most important export businesses.

Since the 1970s a multi-scaled conservation model has been applied, implying that trees are saved at different scale levels, from single 'eternity' trees and small tree groups at the stand level, small valuable areas (key habitats, mean size 5 ha) at the medium level, to establishment of large nature reserves at the highest level. Ecological theory supports this model, and the incorporation of biodiversity concern into production forests represents a form of ecosystem approach. Today more than 70% of the Swedish forestland is certified according to the systems FSC or PEFC.

There are three biogeographical zones: the boreal, the hemi-boreal and the temperate. In total there are about 50 000 plant and animal species of which about half are found in forests, and a number of these are declining due to impact from modern forestry, with about 2 000 being red-listed. Habitat alteration including large decreases in natural forest characteristics and lack of natural disturbances like fires are main causes for species declines. Conservation biology research has increased rapidly during the last 15 years in the Nordic countries. Examples of important directions are dead wood ecology and metapopulation modeling. Future research challenges include links between nature conservation and ecosystem services, and development and evaluation of conservation models to adapt to climate change. New forestry methods like plantation of exotic tree species, intense use of fertilizers, and whole-tree harvest will cause increased pressure on biodiversity.

Managing forests for timber and biodiversity at the same time - challenges and experiences from Sweden

Dr. Karin Perhans, Swedish University of Agricultural Sciences, Box 7044, SE-750 07 Uppsala. karin.perhans@ekol.slu.se

The largest part of forest biodiversity is not found within protected areas, but in the managed forest landscape. Focus on conservation measures in managed forests has therefore increased, both in Sweden and elsewhere. By dividing the responsibility for biodiversity conservation between the state (protected areas) and the private forest owners (managed forests), the forest owner's interest in, and awareness of, conservation issues can also hopefully be increased.

Biodiversity can be promoted at different stages in forest management practices, from preparation for planting to final harvest of trees, but research is struggling with many questions on how to make conservation measures as effective as possible. Important questions that are now in focus for research include: How many trees must be left on a clearcut to benefit forest birds and beetles? Can retained tree groups on clearcuts function as "life-boats" for bryophytes, lichens and spiders until the surrounding forest grows back? Is it possible to create more dead wood on clearcuts and in forests to benefit dead-wood-dependent species, and how should this dead wood be created? How much do conservation measures cost for forest owners and which measures are the most cost-effective?

The presentation will start with an overview of how conservation aspects are taken into account in forest management practices in Sweden. After this, important questions and knowledge gaps on the effectiveness of conservation measures will be identified. Finally, a number of interesting research projects that try to answer these questions will be described and discussed.

Forest Management Strategies to Enhance Biodiversiy and Increase Stand Structural Complexity in Temperate Rainforests of Alaska

Robert L. Deal, USDA Forest Service, Pacific Northwest Research Station, Portland, OR, USA

Temperate rainforests of southeast Alaska have relatively simple species composition but complex structures with high diversity of tree ages, sizes and forest canopy levels, and an abundant understory plant community. Wildlife and fisheries resources also play an important role in the ecological functioning of forest and aquatic systems. Clearcutting has greatly altered these forest ecosystems with significant decreases in structural diversity of forest stands and greatly reduced wildlife habitat. This research synthesizes information on management options to increase diversity of stand structures and their associated effects on biodiversity. Historical partial cutting in old-growth forests maintains the original diversity of overstory stand structure and understory plant communities. However, another problem is how to manage young-growth forests created following clearcutting. Thinning and pruning of these stands have limited value for maintenance of understory plants.

Another approach is the use of red alder intermingled with the regenerating conifer forests. Research has shown that red alder clearly benefits understory plants, and provides forage for deer and small mammals. Results also show a clear linkage with improved invertebrate diversity in aquatic systems. A combination of light partial cutting in older forests along with inclusion of red alder in conifer-dominated forests could provide the greatest amount of diversity and maintain the complex stand structures that are an important component of these forest ecosystems.

(このセミナーは、平成21年度 北海道大学GCOE (人材育成プログラム(e)海外研究者招聘および(g)人材育成自由企画B) (url) との共催です)

Trendy Seminar http://hosho.ees.hokudai.ac.jp/~trendy/2009/
世話役:宮田理恵
email:miyamiya@||@ees.hokudai.ac.jp
Phone:011-706-2267
Facsimile:011-706-4954
北海道大学大学院環境科学院 植物生態学