A LESSON FROM NATURE

Forest and Bird, Issue 52, 1 May 1939, Page 12

A LESSON FROM NATURE

BIRDS AND SOIL

WHEN one visualises the difference between barren and alluvial soil, it is evident how such factors as the washing away of the top soil, i.e., sheet erosion, must inevitably destroy almost all bird life as it does all living creatures.

Roger T. Peterson in an article appearing in “Bird Lore,” the official organ of the National Association of Audubon Societies, U.S.A., entitled “The Good Earth,” says:—

“ The soil is alive. Men, birds and other creatures depend upon it, so it should be treated well.” Then Mr. Peterson goes on to describe a walk in the country by a dozen children accompanied by their schoolmistress, in the following manner: —

A Walk in the Country.

One Saturday morning a dozen members of the Junior Audubon Club took the dirt road north of town, the one that goes to the river. Some of the best “birding” spots near town could be reached by the wood trails that lead off this road. One open glade that ends in a cow-pasture was always good. This morning when they crossed the little brook and this charming spot they were more conscious than ever of the number and variety of things that lived there. Some people could have taken this same walk and, being too busy with thoughts about themselves, would have seen nothing but the grass and the —but not these young people. Their eyes were keen and they saw many things. A Flicker flew from a large anthill where it had been grubbing with its long bill; a little party of sulphur butterflies hovered around a wet, muddy spot on the path. A male Song Sparrow sang from a bush top and dashed after another Song Sparrow that trespassed on his territory. Chiomunks scampered under the rocks of an old stone wall. Dragonflies hawked the air, and everywhere there were living things, crawling, hopping, or flying.

It had never occurred to the class until today how much the soil had to do with the lives of these creatures. Many of them foraged

amongst the plants or scratched or grubbed in the debris at the grass roots. The soil seemed to have a great fascination for them. The teacher commented on this, and one of the boys suggested that they take a sample of the soil so that they might see what was in it. The small trowel and the pail used for transporting plants to the school garden came in handy. A handful of surface dirt and debris from an open grassy spot revealed an ant, a tiny spider, and several other small creatures. This looked promising, and it was dumped into the pail and a section of earth 12 inches long, 6 inches wide, and 4 inches deep was carefully scooped out with the trowel and dumped in with it. They found by probing deeper into the soil that only an occasional grub or earthworm could be found deeper than 3to 4 inches. Most of the small animal life lived near the surface. One-half square foot of soil would be quite enough to analyse, so a piece of cloth was tied tightly over the pail to prevent anything from crawling out. What was in the Soil? The pailful of earth was put on the centre of the work-table and each student carefully picked over a handful of it at a time, on his piece of cardboard. If an insect or worm was found, it was picked up with tweezers and dropped into a little glass medicine vial. With twelve people working it did not take long to run through the whole pail. The pail itself and its cloth covering were carefully examined, too, so that nothing would be missed. Some of the tinier things could be very easily overlooked. There were several very tiny, pale insects that could hardly be seen, so small were they. - These were springtails, and they were very hard to catch, too, because they would jump when the tweezers touched them. When the job was finished, one of the boys offered to try to analyze the contents of the vial, with the help of several good books on insects and other invertebrates from the library.

His analysis showed the following: — Earthworms . . . . . . 2 Sowbugs .. . . . . . . 6 Centipedes . . . . . . 3 Millipedes . . . . . . 10 Mites . . . . . . . . 6 Spiders . . . . . . . . 1 Ants . . . . . . 15 Fly pupae . . . . . . 30 Aphids . . . . . . . . 4 Beetles . . . . . . . . 4 Springtails . . . . . . 14 Unidentified . . . . . . 20 Total 115 One hundred and fifteen invertebrates in a half square foot of earth! Two hundred and thirty per square foot! What would that be per acre? That was easily determined on the blackboard. 43,560 (sq. ft. per acre) X 230 1306800 87120 10,018,800 Over 10,000,000 small animals to the acre! No wonder the soil is such a favourite feedingground. Micro-organisms. It was noted that most of the insects were in the ground debris and in the top 3 to 4 inches of soil. If a small sample of this same rich surface soil were placed beneath a powerful microscope, great numbers of tiny organisms could be seen, tiny plant and animal forms. These are micro-organisms ; millions or even billions exist in a single gram of soil. These micro-organisms are perhaps as necessary as anything on earth. Without them life would stop. They form the link between the living and the dead. They transform dead plants and animals into a condition on which living plants and animals can be nourished. The micro-organisms, insects, birds, mammals, man himself, and his crops are all dependent on one another. They all get their life from the soil and return to the soil when they die. Birds and the Soil. If the life-giving topsoil were to go and the land be made lean, it is logical that birds would be less common, too. A good bird population, then, is “a sign of healthy land.” Scientific studies have shown that not only are the animals dependent on the soil but that the soil is dependent on animal life.

As animal activities in soils increase, soilstructure, fertility, and cover are improved. Vertebrate animals, such as the mammals and the birds, often have as great an effect on the soil as the lower forms of animal life.

“The Topsoil is Like Frosting on a Cake.”

The top layer of earth, which is so full of organic life, has been likened to the frosting on a cake. Some people eat the frosting off the cake first. We have eaten much of the frosting of topsoil off and are getting down to the less palatable subsoil. When the topsoil goes, everything that depends upon it is affected —the small creatures, the birds, and man and his crops.

Erosion is Licking off the Frosting. Much of this loss of topsoil has been the result of erosion or a wearing away by wind and water, the teacher explained. To demonstrate water erosion in its simplest form, she used a large piece of wallboard propped up to present a slight slope. She took a watering-can and sprinkled a quart of water at the top. It slid off almost instantly. Next she placed an old piece of thick carpet on the board and repeated the sprinkling. (She got her idea from Stuart Chase’s “Rich Land, Poor Land.”) Very little water ran through, at first, and the dribble continued for some time. The wallboard, she explained, was hillside with a slope; the can of water was rainfall, and the bare surface, ploughed fields. The carpet was natural ground-cover, either grass or woodlands. Over the bare fields, improperly ploughed, the water comes down, taking with it the rich topsoil. In the second instance, the water sinks into the cover and is released slowly. Very little, if any, soil is washed away. Much Erosion is Man-made. The teacher explained that most of this loss of land was due to man’s mistakes and carelessness. He cut the timber completely off slopes that should have been lumbered more carefully, if at all. Without protection, the soil was washed from the rocks by the rain. Trees cannot grow on bare rocks, nor can rocks hold water, so as the years went on the gullies on the slopes were cut deeper and deeper. Meadows were burned on purpose, and forests by accident. The burning killed the

organic life in the topsoil, burned the humus, and set the stage for erosion. Farmers placed too much livestock in their fields. Instead of putting three or four cows on a small piece of land, they pastured twenty or more. The cattle ate all the ground-cover, and packed the earth so hard that the rain could not sink in but ran off the surface, washing the dirt with it.

These were but a few causes of erosion, the teacher said. She wrote them down briefly on the blackboard, so that the children might put them in their notebooks. 1. Careless lumbering. 2. Fire. 3. Overgrazing of livestock. 4. Improper ploughing. 5. One-crop farming. Dust Storms and Floods. Erosion of a field here and a hillside there seldom caused much comment. The process was a gradual one that went on unnoticed except by the farmer, who found, sooner or later, that he

could no longer grow a paying crop on his land. But the newspapers carried stories of dust storms and great floods. This was big news, for it often meant the lives of many people. These catastrophes were called acts of God, over which man had no control. A few people knew otherwise. They could clearly trace these events to the eroded fields and hillsides. The rain fell, and instead of soaking into the ground, was carried away into the little brooks, whose banks could not always hold the unnatural rush of water. Erosion had set in there, too —and so on into the big rivers. Instead of wandering slowly towards the sea, the water rushed down in a hurry. Great floods were caused by 100 much water reaching the same place all at once. When the drier months came, the water was gone prematurely from the little brooks and streams. They became dry and the soil parched. On the great plains the powdery, exhausted soil was whipped into the air by hot summer winds and literally whole farms were blown away.