|
The Pacific temperate rainforests ecoregion of North America is the largest temperate rain forest ecoregion on the planet as defined by the World Wildlife Fund (other definitions exist). The Pacific temperate rain forests lie along the western side of the Pacific Coast Ranges along the Pacific Northwest Coast of North America from the Prince William Sound in Alaska through the British Columbia Coast to Northern California, and are part of the Nearctic ecozone, as also defined by the World Wildlife Fund. The Pacific temperate rain forests are characterized by a high amount of rainfall, in some areas more than 300 cm (120 inches) per year and moderate temperatures in both the summer and winter months (between 10-24°C). This ecoregion is a subregion of the Cascadia bioregion. These rain forests occur in a number of ecoregions, which vary in their species composition, but are predominantly of conifers, sometimes with an understory of broadleaf trees, ferns and shrubs. In the WWF's system, sub-ecoregions of the Pacific Temperate Rain Forests Ecoregion are the Northern Pacific coastal forests, Haida Gwaii, British Columbia mainland coastal forests, Central Pacific coastal forests, Central and Southern Cascades forests, Klamath-Siskiyou forests, and Northern California coastal forests ecoregions. The forests in the north contain predominantly Sitka spruce and western hemlock, while those in the coastal forests are home as well to coast redwood (''Sequoia sempervirens''), coast Douglas-fir (''Pseudotsuga menziesii''), western redcedar and shore pine. Notably, the three tallest species of trees are found here. Dense growths of epiphytes and mosses cover the trees, and lush vegetation is present everywhere. Hardwood trees such as the bigleaf maple and the alder are also common, especially at lower elevations and along stream banks, and are vital to the ecosystem, in part because of their nitrogen fixing. ==History== About 200 million years ago (during the Triassic and Jurassic periods), the landscape was dominated by conifers, which were the most diverse group of trees and constituted the greatest majority of large trees. When flowering plants emerged (in the following Cretaceous period), they quickly prevailed, causing most conifers to become extinct, and those that survived to adapt to harsh conditions. Perhaps the most significant difference in this change is that the primitive conifers invested their energy in the basic food supply for every seed, with no certainty of fertilization; by contrast, flowering plants create the food supply for a seed only after it is triggered by fertilization. The Pacific temperate rain forest now remains the only region on Earth of noteworthy size and significance where, due to unique climatic conditions, the conifers flourish as they did before being displaced by flowering plants.〔Davis, Wade (2000). Rainforest: Ancient Realm of the Pacific Northwest. Chelsea Green Publishing Company. ISBN 1-890132-79-9.〕 The northern Pacific temperate rain forests are relatively young, emerging in the past few thousand years following the retreat of the ice sheets of the last ice age.〔Davis, Wade (2000). Rainforest: Ancient Realm of the Pacific Northwest. Chelsea Green Publishing Company. ISBN 1-890132-79-9.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pacific temperate rain forest (WWF ecoregion)」の詳細全文を読む スポンサード リンク
|