黄杉是北美西北部多见的树木。来看本篇托福归纳写作优异作文练习题素材。托福代报名为我们带来托福归纳写作优异作文练习题：黄杉数量正在削减，托福代报名期望对我们托福备考有所协助。
托福归纳写作阅览资料： Populations of the yellow cedar, a speciesof tree that is common in northwestern North America, have been steadilydeclining for more than a century now, since about 1880. Scientists have advancedseveral hypotheses to explain this decline.
黄杉是北美西北部多见的树木。可是从1880年开端的一个多世纪以来，黄杉的数量在逐步削减。目前，科学家提出了几个假设来解说黄杉数量的降低。 One hypothesis is that the yellow cedardecline 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 andkilling yellow cedars, so this insect is a good candidate for the cause of thetree’s decline.
其间一个假设以为黄杉数量降低是由以衫皮甲虫为代表的寄生害虫致使。这种甲虫据了解是 以杉树皮为食，而其幼虫则以木质有些为食。史上不乏关于甲虫腐蚀和致使黄杉大量逝世的 记载。由于，这种甲虫很可能是黄杉数量削减的缘由。 A second hypothesis attributes the declineto brown bears. Bears sometimes claw at the cedars in order to eat the treebark, which has a high sugar content. In fact, the cedar bark can contain as muchsugar as the wild berries that are a staple ofthe bears’ diet. Although thebears’ clawing is unlikely to destroy trees by itself, their aggressive feedinghabits may critically weaken enough trees to be responsible for the decline. 第二种假设以为是棕熊致使了黄杉数量的削减。熊有时会扒下黄杉的树皮用以食用，由于黄杉树皮还有很高的糖分。事实上，黄杉树皮的含糖量同棕熊首要使用的野生浆果相差无几。虽然棕熊扒树皮的行为不会直接致使黄杉的逝世，可是它们这种破坏性的觅食行为却由于降低了树木的生命力，而直接致使黄杉数量的削减。 The third hypothesis states that gradualchanges of climate may be to blame. Over the last hundred years, the patternsof seasonal as well as day-to-day temperatures have changed in northwestern NorthAmerica. These changes have affected the root systems of the yellow cedartrees: the fine surface roots now start growing in the late winter rather thanin the early spring. The change in the timing of root growth may havesignificant consequences. Growing roots are sensitive and are therefore likelyto suffer damage from partial freezing on cold winter nights. This frozen root damagemay be capable of undermining the health of the whole tree, eventually killingit.
第三个假设是气候的缓慢改变致使了黄杉数量的削减。在曩昔的一百年里，在北美西北部，无论是季节性的气候替换仍是每天的气温调理都发生了改变。这些改变对黄杉根系产生了影响。曾经，黄杉的表面细根是初春开端成长的;而如今却在晚冬就开端成长。根系成长时刻的改变可能会形成十分严峻的结果。重生的根系都十分灵敏，因此十分简单由于冬季夜晚有些结冰的温度遭到损害。这种根系冻伤表象可能会致使全部树木健康状况降低，并逐步致使逝世。
托福归纳写作阅览有些需求提取的观念是： - Main point: 有三个假设解说黄杉数量削减 - Sub point 1: 杉皮甲虫的腐蚀 - Sub point 2: 棕熊的破坏 - Sub point 3: 气候改变对根系的影响 最后，托福代报名预祝大家考试顺利