one basic weakness in a comservation system based wholly one economic motives is that most members of the land.community have no economic value.yet these ereatures are members of the biotic community and ,if its stability depends on its inteyrity,they are entitled to continuance.

When one of these noneconomic categories is threatened and,if we happen to love it .we invert excuses to give it economic importance.at the beginning of century songbiras were supposed to be disappearing.(46scinentists jumped to the resure with some distimctly shaky evidence to the effect that insects would eat us up of birds failed to control them),the evideuce had to be conbmic in order to be valid.

It is pamful to read these round about accounts today .we have no land ethic yet ,(47but 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 advantage to us)

A panallel situation exists in respect of predatory mamals and fish-eating birds .(48time was when biologists somewhat over worded 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 read out of the party by economics-minded foresters because they grow too slowly .or have too low a sale vale to pay as imeber crops (49in europe ,where forestry is ecologically more advanced ,the ncommercial tree species are recognized ad members of native forest community ,to be preserved as such ,within reason)

To sum up:a system of conservation based solely on economic self-interest is hopelessly lopsided.(50It 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.

46.科学家们赶紧拿出某些明显站不住脚的证据前来救驾，大致说的是如果鸟儿不能控制害虫的话，害虫就会把我们吃掉。

47.但是我们至少已经几乎承认了这样一种观点：那就是鸟儿的生存是它们的固有权利，不管它对我们是否有经济利益。

48.曾几何时，生物学家总是重述以下的这条证据：这些生物是为了维持食物链的正常运行去捕食弱小的生物或“没有价值的物种”。

49.在生态林业较为先进的欧洲，没有成为商业化对象的树种被视为原始森林群落的成员适当地加以保护。

50他容易忽视并最终消灭很多缺乏商业价值的物种，然而这些物种对于整个生物群落的健康运行是至关重要的。