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Grasses are one of the most abundant floras on all continents except Antarctica. Their divergence is estimated to have taken place 200 million years ago. Humans have intentionally and unintentionally introduced these species to North America through travel and trade. On the North American plains, prairies, grasslands, and meadows at least 11% of grasses are non-native. North America is considered a hotspot for many of grasses, which threatens all of the endangered native grass species and potentially threatens other grass species. Conservation tactics and management policies can help prevent invasive species from taking over and driving native North American plants to extinction. ==Attributes== Non-native grasses are classified as invasive if they have the following three attributes: # The grass must have a pathway to be delivered to a new location, e.g. boat, shoe, animal, vehicle, feed, contaminated seed, etc. # It is able to tolerate its new environment long enough to establish and reproduce. # It is able to co-exist with native plants. Invasive grasses can outcompete native plants species by manipulating environmental conditions through either chemicals or other physiological factors. These factors give an upper hand, which will allow the invader to outcompete the native plants. For example, a study conducted in the Mojave desert of California by Smith ''et al.'' in 2006, found that invasive grass species increase in areas with higher concentrations of carbon dioxide (CO2), especially in arid conditions which make up 20% of Earth’s terrestrial surface area. Therefore, the annual invasive grasses will outcompete the natives because they use CO2 to their advantage. 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「Invasive grasses of North America」の詳細全文を読む スポンサード リンク
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