At the beginning of century songbirds were supposed to be disappearing.

The evidence had to be economic in order to be valid.

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 advantage to us.

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 non-economic categories is threatened and, if we happen to love it, we invert excuses to give it economic importance.

It is painful to read these round about accounts today.

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.

A parallel situation exists in respect of predatory mammals and fish-eating birds.

Here again, the evidence had to be economic in order to be valid.

It is only in recent years that we hear the more honest argument that predators are members of the community, and that no special interest has the right to exterminate them for the sake of benefit, real or fancied, to itself.

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 timber crops.

Time 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.

In Europe, where forestry is ecologically more advanced, the non-commercial tree species are recognized as members of native forest community, to be preserved as such, within reason.

Moreover some have been found to have a valuable function in building up soil fertility.

That interdependence of the forest and its constituent tree species, ground flora, and fauna is taken for granted.

It assumes, falsely, I think, that the economic parts of the biotic clock will function without the uneconomic parts.

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.