One basic weakness in a conservation system based wholly on economic motives is that most members of the land community have no economic value. Yet these creatures are members of the biotic community and, if its stability depends on its integrity, they are entitled to continuance.
When one of these noneconomic categories is threatened and, if we happen to love it, we invent excuses to give it economic importance. At the beginning of the century songbirds were supposed to be disappearing. Scientists jumped to the rescue with some distinctly shaky evidence to the effect that insects would eat us up if birds failed to control them. The evidence had to be economic in order to be valid.
It is painful to read these roundabout accounts today. We have no land ethic yet. But we have at least drawn near the point of admitting that birds should continue as a matter of intrinsic right, regardless of the presence or absence of economic advantages to us.
A parallel situation exists in respect of predatory mammals and fish-eating birds. Time was when biologists somewhat overworded the evidence that these creatures preserve the health of game by killing the physically weak, or that they prey only on "worthless species".
Some species of tree have been rid out of the party by economics-minded foresters because they grow too slowly or have too low a sale value to pay as timber crops. In
To sum up, a system of conservation based solely on economic self-interest is hopelessly lopsided. It tends to ignore, and thus eventually to eliminate, many elements in the land community that lack commercial value but that are essential to its healthy functioning. Without the uneconomic pats.
参考答案及点评：
1. Scientists jumped to the rescue with some distinctly shaky evidence to the effect that insects would eat us up if birds failed to control them.
参考译文：科学家们紧急行动起来以拯救这些鸟类。他们提出的理由大意是说，如果鸟儿不能控制昆虫，昆虫就会把我们吃掉。然而，这种理由显然站不住脚。
分析：英语句子的特点是句子结构复杂。然而，万变不离其宗，只要找出句子的主干，整个句子的意思就会一目了然。本句的主句是scientists jumped to the rescue，其后带有一个由with引导介词短语，作方式状语，其中又套有一个 that 引导的同位语从句。根据汉语句子结构短小的特点，在翻译技巧上，可以采取分句处理，即把原文的一个句子拆译为若干小句。另外，distinctly shaky 是作者的评述，根据汉语习惯，一般放在所评述的对象后面，因此在翻译时建议改变原文顺序。在语言点上，jump在这里的意思是“匆忙”；shaky的意思是“靠不住的”；to the effect是个成语，意思 是“大意”，常用于间接引用时。
2. But we have at least drawn near the point of admitting that birds should continue as a matter of intrinsic right, regardless of the presence or absence of economic advantages to us.
参考译文：但我们至少开始承认，繁衍生息是鸟儿天生的权利，与其是否对我们人类有经济上的好处没有关系。
分析：句子的主干结构是we have drawn near the point。draw是一个多义词，在这里的意思是“移动”，“行进”，draw near的意思是“接近”；point也是一个多义词，根据上下文，这里应该理解为“程度”；a matter of意思是“事情；问题”，a matter of intrinsic right可直译为“天生的权利问题”；整个that从句是admit的宾语。与前句一样，在翻译技巧上，可以采用拆译。
3. Time was when biologists somewhat overworded the evidence that these creatures preserve the health of game by killing the physically weak,or that they prey only on "worthless species".
参考译文：曾几何时，生物学家们反复强调，这些生物是为了维持食物链的正常运行而捕食弱小生物的，它们捕食的只不过是“毫无价值的物种”。
分析：Time was，是一个固定搭配，可以翻译成“曾几何时”； somewhat“有点”，表示程度；that these creatures preserve the health of game by killing the physically weak和that they prey only on "worthless species"这两个从句都是the evidence的同位语，起说明解释作用。
4. In
参考译文：在生态林业较为先进的欧洲，不具有商业价值的树种被视为原始森林群落的成员，因此而受到适当保护。
分析：句子的主干是the noncommercial tree species are recognized as members of the native forest community；where forestry is ecologically more advanced是定语从句，对Europe起修饰作用，to be preserved是不定式短语，对主句起补充说明作用，隐含一种因果关系；such指前面的members of the native forest community。 在语言点上，within reason是一个固定搭配，意思上“在合理范围内”；native forest community是一个专业术语，意思是“原始森林群落”。
5. It tends to ignore and thus eventually to eliminate many elements in the land community that lack commercial value but that are essential to its healthy functioning.
参考译文：这种环保制度往往忽视并进而最终消灭大自然群落中许多不具商业价值但对于维持生物群落健康运行至关重要的成分。
分析：句子的主干为it tends to ignore and eliminate many elements；两个that定语从句的先行词都是elements，由于关系密切，可以译为定语短语；it指前面提到的“完全基于经济上的私利的环保制度”，可简译为“这种环保制度”。