Looking into tropical treetops. Two books examine life webs at roof of rainforest

Life Above the Jungle Floor, by Donald Perry. New York: Simon & Schuster. 171 pp. $16.95. The Enchanted Canopy: A Journey of Discovery to the Last Unexplored Frontier, the Roof of the World's Rainforests, by Andrew W. Mitchell, foreword by Gerald Durrell. New York: Macmillan.288 pp. $24.95. A new, but probably not the last frontier lies in the tops of tropical forests, which until recently have been inaccessible for close study. Views from airplanes and satellites have given an impression of a green vastness, now rapidly disappearing to meet the needs of burgeoning populations and their demand for agricultural land or wood products or minerals. But huge question marks hang over the scene.

What happens to the climate when tropical forests disappear?

What happens to the ground when trees disappear?

What happens to the people when they lose their firewood, some of their food and water?

What was in the forests that we may never know about? Or is the whole business simply another stage of earth's history, which has already seen much rise and fall of species, much geological and climatic change?

The effort to find some answers to these questions in the tropical treetops has begun in earnest. Biologists spin webs like Spiderman or build aerial walkways so they can see and study the intricacies of life there. Only in the past hundred years have the means been available to get scientific exploration off the ground into very near space.

But no more. Read ``Life Above the Jungle Floor'' for an account of one man's view from the top story of Costa Rica's forests; thrill to the excitement of hanging by a thread to inspect the inside of a gigantic, hollow, wild cashew tree and confront its varied inhabitants. Hold your breath with Donald Perry as he strings his web among the tallest, strongest trees, and commits himself to a swing into the void between them, hoping and praying the lines will hold. Drop with him into a realm previously familiar only to the birds.

Perry tells his story well, tucking in pertinent biological history, facts, and his discoveries as he narrates his adventure. He calls the canopy ``an intricate factory of evolutionary ideas that has transformed the earth's life. The influence of this habitat can be found in the aquatic flight of penguins, in a can of mixed nuts, in the wing of a bat, in a parrot's communication, and in the development of the human mind.'' Read on in the book for his elaboration and justification of the statement.

Perry took most of the excellent photographs to illustrate specific points. The publisher has provided a format with page and type laid out for easy reading, in contrast to many current books - including ``The Enchanted Canopy.''

That book has a wider scope than does ``Life Above the Jungle Floor.'' It surveys the tropical treetops around the world, with more history and more biological information - maybe more than you ever wanted to know - than Perry provides. Andrew Mitchell is a naturalist and television producer who worked with David Attenborough on ``The Living Planet'' television series. He tells how they filmed the episode in which Attenborough hoists himself up into the canopy in Venezuela, and of Andrew Field, who pioneered the rope trick in that part of the world.

But Field is only one of quite a few pioneers now, some of whom have managed to construct semipermanent walkways and platforms for long-term visits to the canopy world. Mitchell tells about early attempts to make canopy observation safe and relatively easy, noting both successes and failures, and moves on to present projects and future plans.

The big pitch, however, is made by both authors for preservation of the world's tropical forests. They argue from the botanists' and biologists' viewpoint, pleading for the chance to know and measure and record as soon as possible, lest the myriad species disappear.