Forest the Preserver; Fire the Destroyer

Forest and Bird, Issue 59, 1 February 1941, Page 3

Forest the Preserver; Fire the Destroyer

(By Lucretius.)

Appropriately placed native forests are a country’s greatest asset; for the forest is the greatest preserver of the soil, and our very existence depends on the soil and its continued fertility. Many past civilisations have perished as a direct result of wanton destruction of their forests. Who has not seen pictures of the ruins of fine cities in North Africa, Asia Minor, Persia, China, etc., etc.? Did Darius, the great Persian conqueror, build his huge palace at Persepolis in an uninhabited waste? China 2,500 years ago had abundant forests; to-day wood is very scarce indeed in China, such forest as remains are being confined to almost inaccessible mountains. Destruction of the forest in the catchment areas of the ancient Mesopotamian irrigation system, the finest ever known, resulted in the formation of desert. The Mediterranean countries all show striking evidence of the dire results following deforestation. In Karst, for instance, naked rocks are found where once was forest. The country knows nothing but drought, all the rain that falls being lost in rock fissures or evaporated from the hot rock.

Until 1852 the foothills of the Himalayas in the Punjaub were used as hunting grounds and were covered in forest. In that year the British annexed the Punjaub and handed over these foothills to the villagers. Fire, the axe and the goat soon destroyed the vegetation. This area is now an oft-quoted example of the effects of accelerated erosion a fertile wooded land which fifty years later was well-nigh useless. The French Niger Colony is now largely desert, but two hundred years ago this huge tract of land had forests and its peoples were prosperous.

Innumerable other examples of the consequences of spoliation of the forests might be drawn from Africa, Asia, America and Australia. No continent has not suffered.

In New Zealand the impoverishment of our native forest resources by fire and improper management is a matter of immediate concern; it is the concern not only of the timber merchants, but of manufacturers, bankers, farmers

and indeed every one of us. Already in this country, barely a hundred years old in white man’s history, far too much of it has gone. It behoves us not to be heedless of the lesson of the Punjaub and other places where the forest has been destroyed. Soil eroded is soil lost, maybe for ever. But it is well to remember that the soil, with its bacterial and other minute life, the vegetative covering and the animals living therein, constitute one whole, whose parts cannot be considered as separate entities. Vegetation certainly grows on the soil, yet were it not for vegetation there would be no soil. Soil consists of more than disintegrated rock and water; it has an organic part, the humus, derived mostly from decayed vegetation. All vegetation helps to form soil and to protect it from being washed away by excessive rainfall or being blown away by wind, but the best form of vegetation for protecting the soil is forest in its natural condition, especially where the terrain is rough.

Trees, as everyone knows, act as protection against wind, but their action against other erosive agents is not so well known. The canopy of leaves and branches prevents the beating effect of rain falling directly on the soil. Leaves drip for as long as an hour or more after rain has ceased falling. Dew and mist condensing on the leaves act in a similar manner. When the water has dripped from the leaves it falls on to the litter of leaves and other debris on the forest floor. This litter, together with the underlying humus, absorbs the water, preventing a rapid run-off, and gradually passes it down to the deeper layers of soil and subsoil, where it is held as an underground reservoir. A large quantity of the underground water is absorbed by the roots and returned to the atmosphere as vapour from the leaves, but most of it seeps through the soil to the streams. Streams arising in forested regions remain clear, and their water content does not vary much throughout the year. Thus it is that forests are the great controller of floods, and by far the least expensive. One hundred and fifty years ago the local

laws governing the forests of the French Alps were repealed and clearing for grazing purposes began. Erosion of the soil followed, and in a short time 800,000 acres of farm land were ruined by silt and debris and the population of 18 departments were reduced to poverty. Between 1845 and 1901 the population was reduced by 50,000. In 1856 enormous floods caused great loss of life and damage amounting to close on £8,000,000. In 1860 reforestation measures were begun, but failed; but in 1882 a colossal scheme for restoring the native forest cover at the headwaters of the flooding rivers was evolved in order that the mountain torrents might be curbed. Up to 1900 66 million francs had been expended, with satisfactory results, and it was then estimated that the work would be completed by 1945 with a further expenditure of 115 million francs. At the present time almost all the torrents have been brought under control, and the erosion is now no longer a menace. French engineers after many experiments have come to the conclusion that forest cover is the best way of controlling erosion and that the existence of forested headwaters is the only effective way of controlling river flow.

New Zealanders should bear in mind what happened in France when the forest protecting the headwaters of many of their important rivers was destroyed. A few trees wantonly destroyed cost millions of francs and years of time to replace, and it was necessary for the well-being and safety of the people of France to have them replaced.

In the higher levels of New Zealand forests prevent the freezing of the ground (a very potent erosive force where the soil becomes

exposed) and delays the melting of snow. These two effects of the forest in preventing erosion at high levels and floods lower down are very important, though rarely mentioned.

It is very essential therefore that all high country clothed in natural native vegetation should promptly be declared inviolate reservations.

And now that summer is here, the bush fire is also here. Let people be careful not to start fires which might spread to forest or other vegetative covering of the soil.

Fire, by destroying forest cover, causes excessive water run-off and spells destruction to all forms of wildlife. It kills trees and thus destroys the protective canopy. Those trees it does not kill it damages, and insect pests complete the ruin. It burns the undergrowth, the invaluable litter on the forest floor, and destroys the underlying humus. When the covering is burnt off the soil is exposed and unprotected, so that it soon dries out, its structure and life are destroyed, and it seriously erodes when rain falls or the wind blows. Water is no longer absorbed, but runs off rapidly, an agent of destruction. Silt-laden streams contain little or no aquatic life, the silt is deposited where it is not required, the bed of the stream is raised when the velocity of the water is lowered, floods are caused, etc., etc. One small fire might cause untold damage if allowed to spread.

New Zealanders, don’t let your forests burn, keep them growing! They protect the soil, from which we derive our nourishment, and which is our country’s and our Empire’s first line of defence.