Ascent of the Oaks

オークの進化史 北半球を席巻したドングリの森

By Andrew L. Hipp /Paul S. Manos/Jeannine Cavender-Bares A. L. ヒップ /P. S. マノス/J. キャヴェンダ=ベアズ
English 日本語 日本語
If you were dropped into virtually any region of North America 56 million years ago, you probably would not recognize where you had landed. Back then, at the dawn of the Eocene epoch, the earth was warmer and wetter than it is today. A sea had just closed up in the middle of the Great Plains, and the Rocky Mountains had not yet attained their full height. The continent’s plant and animal communities were dramatically different. In the Canadian High Arctic, which today harbors relatively few tundra plant species, year-round temperatures above freezing nurtured a rich and diverse flora; Ellesmere Island in far northern Canada, across from the northwestern coast of Greenland, was home to alligators and giant tortoises. What is now the southeastern U.S. was dominated by tropical rain forest, complete with primates. The northeastern U.S., for its part, ranged from broad-leaved (as opposed to needle-leaved) evergreen forest to deciduous forests of ginkgo, viburnum, birch and elm, among other species. The deciduous broad-leaved forests that now cover 11 percent of North America north of Mexico were in their infancy. But that was about to change, with the spread and extraordinary diversification of what would eventually become some of the most ecologically and economically significant woody plants in the world: the acorn-bearing, wind-pollinated trees we call oaks.  もしも5600万年前の北アメリカのどこかに突然放り込まれたら,そこがどこか見当もつかないだろう。当時は始新世が始まったばかりで,地球は現在よりも暑くて湿度も高かった。海はグレートプレーンズの中ほどまで迫っており,ロッキー山脈はまだ現在の高さに達していなかった。
Over the course of some 56 million years, oaks, which all belong to the genus Quercus, evolved from a single undifferentiated population into the roughly 435 species found today on five continents, ranging from Canada to Colombia and from Norway to Borneo. Oaks are keystone species, foundational to the functioning of the forests they form across the Northern Hemisphere. They foster diversity of organisms across the tree of life, from fungi to wasps, birds and mammals. They help clean the air, sequestering carbon dioxide and absorbing atmospheric pollutants. And they have shaped human culture, feeding us with their acorns and providing wood to build our homes, furniture and ships. Indeed, oaks have proved so valuable to people that we have immortalized them in legends and myths for centuries.  コナラ属の木本植物であるオークは過去5600万年ほどの間に未分化の単一集団から約435の種に進化し,現在ではカナダからコロンビア,そしてノルウェーからボルネオまで,オーストラリアと南極を除く5つの大陸で見られる。オークは生態系に大きな影響を及ぼすキーストーン種であり,北半球各地の森林の機能的な基礎を形成している。オークの森は菌類からカリバチや鳥類,哺乳類まで生物全体の多様性を育み,二酸化炭素の固定や大気汚染物質の吸収を通して空気の浄化を助ける。オークはまた食料としてのドングリや,家や家具,船を作るための木材を提供し,人間の文化を形づくってきた。実際,オークが多くの伝説や神話に登場することからも人々にとって極めて重要だったことがわかる。
Oaks are especially prominent in the Americas. Approximately 60 percent of all Quercus species live here. This astounding variety, along with the fact that the oaks in this region account for more forest tree biomass than any other woody plant genus in North America and Mexico, makes them the single most important group of trees in the continent’s forests. To understand forests, then—their biodiversity, food webs and contributions to human well-being—one must understand how oaks came to rule them.  オークが特に目立つのがアメリカだ。コナラ属の種の約60%がここに生育している。この驚くべき多様性と,北米とメキシコの森林で最大のバイオマスを占めるのがコナラ属の樹木であるという事実から,オークは北米大陸の森林で最も重要な木だといえる。森林を理解するには,つまり森林の生物多様性と食物網,人類の幸福への貢献を理解するには,オークがどのように森を支配するようになったかをひもとかなければならない。