當(dāng)原生植被被清除用于農(nóng)業(yè)或其他用途時(shí)人的行為ivities, habitats that were once continuous become divided into separate fragments. Habitat fragmentation has a number of effects. In a forest, the canopy (the uppermost layer of vegetation) buffers the microclimate of the forest floor, keeping the forest floor relatively cool, moist, and shaded during the day, and reducing air movement and trapping heat during the night. When a forest is cut so that separate smaller forests remain with cleared areas in between, these effects are reduced. s formerly forested areas become exposed to direct sunlight, the ground becomes much hotter during the day; without the canopy to reduce heat and moisture loss, formerly forested areas are also much colder at night and generally less humid. In the remaining forest fragments these effects are strongest at the fragment edge and decrease toward the interior. In studies of mazonian rainforest fragments, microclimate changes had strong effects up to 60 meters into the forest interior, and increased tree mortality could be detected within 100-300 meters of forest edges. Since species of plants and animals are often precisely adapted to temperature, humidity, and light levels, changes in these factors will eliminate many species from forest fragments. Shade-tolerant wildflower species of the temperate forest, late-successional tree species (those that dominate in mature forests) of the tropical fores t, and humidity-senility animals, like amphibians, often are rapidly eliminated by habitat fragmentation because of altered environmental conditions, leading to a shift in the species composition of the community.

???????由于缺乏其他植被的緩沖，當(dāng)太陽角度較低時(shí)，森林碎片邊緣可能具有非常高的白天溫度和非常冷的夜間溫度。然而，茂密的藤蔓和快速生長(zhǎng)的先鋒物種（第一個(gè)在受干擾的地區(qū)生長(zhǎng)）在森林邊緣生長(zhǎng)，以應(yīng)對(duì)這些變化的條件，并經(jīng)常形成阻礙，減少環(huán)境干擾對(duì)森林內(nèi)部的影響。片段。從這個(gè)意義上說，林緣在保存森林碎片組成方面起著重要作用，但在此過程中，林緣的物種組成發(fā)生了巨大變化，森林內(nèi)部物種所占面積急劇減少。隨著時(shí)間的推移，森林邊緣可能被與森林內(nèi)部不同的植物和動(dòng)物物種占據(jù)。如果森林恢復(fù)到清理區(qū)域，無論是通過次生林的自然生長(zhǎng)還是建立人工林，森林碎片可能會(huì)受到保護(hù)，不會(huì)發(fā)生變化。

???????Wind changes can have a significant effect in fragmented forest habitats. In an intact forest, wind velocity is substantially reduced by the tree canopies; the wind moves strongly over the forest but is reduced to a gentle breeze within the forest. When a habitat is fragmented, the wind is able to enter and move through the forest. The impact of wind will be greatest at the forest edge, which is subject to the full force of it, but the effects on air movement may be felt over a considerable distance as well, particularly in flat terrain. The increased wind and air turbulence directly damages vegetation, particularly at the forest edge. Trees that have grown up in the forest interior with minimal wind stress will have leaves and branches stripped off by the wind or may be blown down. Increased wind also leads to increased drying of the soil lower air humidity, and higher water loss from leaf surfaces. This increased water stress may kill many interior plant species and reduce the production of seeds. The overall result of wind effects may be to kill the trees along the forest edge,which will then be occupied by a new suite of species better adapted to the new conditions. Over time, with trees dying along the edge, the forest fragment will become smaller and might eventually cease to exist.

???????Increased wind, lower humidity, and higher temperatures make fires more likely, especially when wood has accumulated on the edge of the forest where trees have died or have been blown down by the wind. Fires may spread into habitat fragments from nearby agricultural fields that are being burned regularly, as in sugar-cane harvesting, or from the irregular activities of farmers practicing slash-and-burn agriculture.

1.When native vegetation is cleared for agriculture or other human activities, habitats that were once continuous become divided into separate fragments. Habitat fragmentation has a number of effects. In a forest, the canopy (the uppermost layer of vegetation) buffers the microclimate of the forest floor, keeping the forest floor relatively cool, moist, and shaded during the day, and reducing air movement and trapping heat during the night. When a forest is cut so that separate smaller forests remain with cleared areas in between, these effects are reduced. s formerly forested areas become exposed to direct sunlight, the ground becomes much hotter during the day; without the canopy to reduce heat and moisture loss, formerly forested areas are also much colder at night and generally less humid. In the remaining forest fragments these effects are strongest at the fragment edge and decrease toward the interior. In studies of mazonian rainforest fragments, microclimate changes had strong effects up to 60 meters into the forest interior, and increased tree mortality could be detected within 100-300 meters of forest edges. Since species of plants and animals are often precisely adapted to temperature, humidity, and light levels, changes in these factors will eliminate many species from forest fragments. Shade-tolerant wildflower species of the temperate forest, late-successional tree species (those that dominate in mature forests) of the tropical fores t, and humidity-senility animals, like amphibians, often are rapidly eliminated by habitat fragmentation because of altered environmental conditions, leading to a shift in the species composition of the community.