NATURAL NATIVE FORESTS

Taupo Times, Volume I, Issue 20, 28 May 1952, Page 2

NATURAL NATIVE FORESTS

t » CONTROL SOIL EJROSION In a good forest the tree tops usually* are close enough to touch and form a closed canopy; and frequently small trees, shrubs and other forms of lesser vegetation make up a thin or thick undergrowth. Anything less is not first-class forest and is not likely to provide such good protection for the land beneath. The leaves, the, twigs, branches, ' and stems of a forest expose innumerable little surfaces, aggregiatlng, under good conditions, an area several times greater than that of the ground beneath. This Iposely thatch - ed roof often 100 feet or more in thickness, is the first line of protection against soil* erosion and excessive run-off. Driving rains be»at j upon this roof; the raindrops spatter, and the water slips gently down the stefris . or drips intermittencly to the ground. As much as half an | inch of rainfall may be completely | mtercepted by this intervening ! thatch. Part of (this intercepted | water is l6st by evaporation and so I never reaches the ground. | The main forest buhvarks against erosion and run-off, however, are I still lower down. Covering the for- ! est floor is a hlanket of woods Jit- | ter — a mass of leaves, iwigs iand | fragments of bark, in various stages of disantegration. It is not always a smooth blanket, for beneath it are an endless s'eries* of little depressicns. These catch part of the water that penetrates the thatch roof overhead and restrains much of it from runniffg away. . The blanket performs a double function — that of absorbing part of the water and like a | sieve directing the remainder dowri- | ward to filter slowly to the soil beheathi This all-important blanket of vegetative material exerts a powerful influence on the soil in several ways, making it more permeable j to water. | %

The surface of the soil is kept rnoist and absorbent,' even in winter when exposed soil is deeply frozen. The iitter and humus form the principal habitat for a vast population of organisms important to soil building and conditioning. From the standpoint of soil protection, this covering of the forest floor is the most effective element of the forest complex. Here is the gateway to I water storage in soil and underground channels. Its function is to filter water, keep it olear, and so keep it moving downward into the soil. Muddy water, such as gathers on bare surfaces, dogs the channels, tflows infiltration, and changes beneficial percolation to harmful run-off. ' In any system of sound land use, it is essential that excessively steep slopes, such as usually prevail bout the head-water of numerous streams, be kept in some dense cover, preferably forests or grass. Trees make the most effective cover for vast areas of mtountain and hili country, where it is not easy to establish and maintain an adequate cover of grass. The contrary is true, of course, with respeet to the use of grass in those areas not climatically , suited to rapid J tree growth. Conibihations of tre.es and grass, as w^l as combinations of trees and shrubs, have important places for special conditions vin the control of run-off and erosion.

(From ''Soil Conservation,>, by

Dr

H. H.

Bennett),