Populations of the yellow cedar, a

Populations of the yellow cedar, a species of tree that is common in northwestern North America, have been steadily declining for more than a century now, since about 1880. Scientists have advanced several hypotheses to explain this decline.
One hypothesis is that the yellow cedar decline may be caused by insect parasites, specifically the cedar bark beetle. This beetle is known to attack cedar trees; the beetle larvae eat the wood. There have been recorded instances of sustained beetle attacks overwhelming and killing yellow cedars, so this insect is a good candidate for the cause of the tree’s decline.
A second hypothesis attributes the decline to brown bears. Bears sometimes claw at the cedars in order to eat the tree bark, which has a high sugar content. In fact, the cedar bark can contain as much sugar as the wild berries that are a staple of the bears’ diet. Although the bears’ clawing is unlikely to destroy trees by itself, their aggressive feeding habits may critically weaken enough trees to be responsible for the decline.
The third hypothesis states that gradual changes of climate may be to blame. Over the last hundred years, the patterns of seasonal as well as day-to-day temperatures have changed in northwestern North America. These changes have affected the root systems of the yellow cedar trees: the fine surface roots now start growing in the late winter rather than in the early spring. The change in the timing of root growth may have significant consequences. Growing roots are sensitive and are therefore likely to suffer damage from partial freezing on cold winter nights. This frozen root damage may be capable of undermining the health of the whole tree, eventually killing it.

結果 (中文) 1:

黄雪松，树是共同在北美西北部，一个物种的种群已日渐减少，现在，一个多世纪约 1880 年以来。科学家们已经提出几个假说来解释这种下降趋势。一种假设是黄杉数量下降可能引起昆虫寄生虫，专门雪松树皮甲虫。这种甲虫是已知的攻击雪松树木;甲虫幼虫吃木头。已记录的事例中的持续的甲虫攻击压倒性的和黄杉，所以这种昆虫是树的衰落原因的合适人选。第二种假说属性下降到棕色的熊。熊有时爪在香柏树，吃树皮，具有很高的糖分。事实上，雪松树皮可以包含尽可能多的糖，作为是熊的饮食主食的野果。虽然熊抓不太可能破坏树木本身，他们咄咄逼人的摄食习性批判性可能会削弱足够的树木要负责下降。第三个假说逐渐变化的气候可能是罪魁祸首。过去一百多年来，季节性以及日常温度的模式已经在北美西北部。这些变化影响根系的黄雪松 ︰ 精细表面根现在开始生长在冬末，而不在初春的早晨。根的生长时间的变化可能会造成严重后果。长根很敏感，因此容易遭受部分冻结在寒冷的冬夜。这种冷冻的根损害也许能够破坏整个树，最终杀死它的健康。

結果 (中文) 3:

美国西北部的一种树木，是一种常见的黄色雪松，其种类在一个多世纪以来一直在稳步下降，因为大约1880。科学家们已经提出了一些假说来解释这种下降。一个假设是，黄雪松下降可能是由昆虫寄生虫引起的，特别是雪松树皮甲虫。这种甲虫被称为攻击雪松，甲虫幼虫吃木头。有持续的甲虫攻击绝杀黄雪松记录的例子，所以这种昆虫是对树的下降的原因的很好的候选人。另一个假设属性的下降到棕色的熊。熊爪，有时在雪松吃树皮，具有很高的糖含量。事实上，雪松树皮可以含有大量的糖作为野生浆果，这是一种主食的熊的饮食。虽然熊爪是不可能摧毁的树木，他们积极的喂养习惯可能会严重削弱足够的树负责下降。这第三个假说认为，气候的逐渐变化可能会责怪。在过去的一百年里，在西北美国，季节性和日常的温度变化都发生了变化。这些变化已经影响到了黄雪松的根系统：表层的细面现在开始生长在晚冬而不是在早春。在时间的变化，根系生长可能会产生重大的后果。生长的根是敏感的，因此可能会受到损害，部分冻结在寒冷的冬季夜晚。这种冰冻的根损坏可能会破坏整个树的健康，最终杀死它。