Soil And Trees
The natural rain-forests were one of the great surpluses ofNature but they are now alarmingly depleted and the trees are being used up at everincreasing speed. And this is the time when their restoration and expansion has becomemost critical for the safety and preservation of the total environment.
The deepest soil on the face of the earth was in the naturalrain forests. The forest soils were not always the most fertile when judged on theircapacity to produce in abundance the feeds of the high quality complete proteins.But they were tremendously absorbent.
Rain forests once grew wherever the conditions for their developmenthad been suitable. They needed an adequate and regular water supply, mild to hotconditions with no long dry periods. The trees did not usually intrude into the greatfertile grasslands because these were subject to drought.
Trees and the deep soil of the forest are critical in landscapedesign for the city and for the countryside--in the City Forest and the strip forestsfor the farm and grazing lands.
In nature the deep soil and the trees created each other becausethe climatic conditions were right--and no doubt they took their time about it! Thereis no such deep absorbent soil where it is needed for City Forests but there is needfor hurry! However the responses of the inhabitants of the soil to good conditionsand abundant food, are very rapid. These things can be promoted and controlled. Aswas said, fertile soil has been developed from poor soil and subsoil many times,in a space of only three years. For the development of the soil for the City Forestthere is this difference; the objective is not eight or even sixteen inches of soilbut the rapid development of four feet, five feet or more, of fertile and absorbentsoil.
The preparation of the land for water flow and for the plantingand irrigating of the soil and the trees are soil making procedures. There will beno waiting around for these things to happen. The natural responses will again berapid.
Some experiments of the author in growing trees and experiencesto do with rain forests are recounted in order to confirm the validity of the CityForest and the strip forests for their role in landscape design.
A hundred or more trees were planted a year after the purchaseof the farm, (1943). The ground was opened up with a post hole digger; the youngtrees were watered for a time. The planting was a failure.
Immersed in the problems of water, no further attempts weremade to grow trees for a few years. But becoming interested later in the treatedround post type of fencing, it was decided to grow a perpetual forest of fence posts.This planting was so successful that in three years there were more trees ready forposts than could be used. When some of the trees were cut, a selected sucker wasleft to grow from each stump. They were large enough for posts in only two more years.The trees were spotted gums, (Eucalyptus maculata).
Of course this planting had been done differently, because inthe meantime something had been learned from our soil experiments.
The poor shale derived soil, the exposed subsoil and the yellowshale was torn-up with an early version of chisel plow and sown as for a pastureand soil development programme and managed as such for a year. There was one significantchange; the area was chiselled when dry enough after every fall of rain for the oneyear. In the successive cultivations the chisels penetrated a little deeper. Thelines for the rows of trees were deeply ripped--16 inches. By the end of the yearthe clovers and grasses had become healthy looking and vigorous, the poor soil materialnow looked like soil for seven inches down and there were some earthworms to be seen.In this moist soil the young six leaf seedling trees were planted after having beenwatered the evening before in the tubes in which they were grown by the New SouthWales Forestry Commission. They received no water at planting time and only rainthereafter. The soil between the tree-rows was chiselled twice during the year afterplanting, by which time the roots of the young trees had gone down over 20 inches.Two years after tree planting the soil was found to be loaded with various grainand thread-like fungi, the character of the earthworms had changed to big and fatand clover plants persisted among the trees. I had not seen such forest soil sincedigging in the rain forest of Queensland's Atherton Tableland before the Second WorldWar.
But this notable instance of soil making, which was repeatedwith other tree plantings, could be considerably accelerated. For instance, it wasdone on poor soil-material--sub-soil and shale--without irrigation and with lessthan an abundant rainfall. The ripping for the rows of trees was 16 inches deep;it is quite practical nowadays to rip to 50 inches and more. The depth of chisellingbetween tree rows did not exceed eight inches; it could likewise be ripped to 50inches deep. Special plants would keep the earth aerated; many plants will go downto wherever the moisture is. No fungi spores were added; perhaps the best could beintroduced. The earthworms arrived on their own accord; maybe the world's largestearthworms from the Gippsland rain forest of Victoria could be introduced and wouldgrow longer than their recorded 11 feet. Very fortunately, earthworms are not over-sensitiveto the chemicals of industry and agriculture. To multiply these factors there isthe effect of irrigating the soil and the trees with the wonder-water from the city.
A great surplus of fertility would rapidly develop in the soilof the City Forests. It would also physically increase by the addition of dusts fromthe atmosphere filtered by the leaves and washed to the surface by the rain. Othermatter would be extracted from the effluents by the soil processes and by the treesthemselves, to return to the soil in the leaf-fall. Although indeterminate at themoment, the surplus of top fertility soil which would be available for sale to homegardeners, and for parks, gardens and plant nurseries, would be big business. Itwould require 20,000 acres or even up to 40,000 acres to use for optimum profits,the waste water from a city of 2,000,000 people. A large area? Perhaps, but certainlyno giant in rain forests--or in grazing properties.
Even Sydney, a city of high priced land, has much larger areasin reserves and so-called parklands which are little seen and rarely used. True,much of it is apparently worthless sandstone shelf country. Its 'water shape' isalso poor. But the requirements of the rain forest are principally a place for thetrees to stand up and adequate water. Sandstone country can be cultivated, if notby rippers then certainly by explosives. We had experience of this kind of 'cultivation'in 1951. A particular contract called the removal of 20,000 tons of sandstone dailywhich we lifted and dumped to the side with a dragline excavator--after "cultivation"with explosives. When each 'shot' of a ton of explosives was fired, a near-by observerwould hear only a dull whoosh and see the section of land lift en masse and settleback again . The surface was so little disturbed that motor vehicles continued totravel it. But no matter how heavy the deluge, no water ran off and none formed poolson the explosive-cultivated land . Incidentally this contract was planned in 1950,and designed to operate on these same principles of 'complete water control' evenif the rainfall was extremely high. 1951 turned out to be the year of the "widespreadbig wet." The nearly incessant rain eventually closed every coal mine, bothunderground and open-cut, in New South Wales, while our job did not lose a day.
There are other experiences relevant to the 'impossible' natureof sandstone shelf country. Firstly, years ago the author designed a machine to pulverisescrub, the smaller timber and the surface boulders of rock strewn rural land andcoined a new word to name it, the 'tritter'. Drawn by the ordinary farm tractor,it turns at a low cost such things as lumps of sandstone into sand and dust to leaveplenty of fine material to grow grass and trees. Tracks through rough country havenowadays been called "tritter trails". The tritter is marketed world wideby new owners. Secondly; sandstone country is frequently of 'poor water shape' whichmeans that the three shapes of land--main ridge, primary valley and primary ridge--arenot smoothed over and rounded off. They can be smoothed over and made suitable forrapid irrigation with the minimum of rock-moving. A cheaper and better method forconstituting natural water shapes would be to use the garbage which is in plentifulsupply. Indeed the garbage disposal problem could be solved for centuries to comeby using it to turn the rocky gorges of the sandstone shelf country into luxuriantlyforested valleys.
This 'worthless' sandstone shelf country can be converted todeep soiled rain forests with little delay and produce as well as timber, plentyof surplus fertile soil for sale.
In 1948 the reserved remnant of a Kauri rain forest was seenin New Zealand immediately after heavy rain had ceased. The soil appeared merelymoist. The forest remnant is a tourist attraction; the forest soil appeared to bedeep. It was evident that the surface of the man-made grassland which surroundedit was much lower. A notice stated also that the grassland was once forest land.The height was lost through erosion by water, compaction and shrinkage. Such a forestwould take-in dozens of inches of flood-type rains and discharge it gently from springsof clear water to the streams and the river.
Camped in the rain forests of New Guinea before the Second WorldWar, one of the bugbears was getting wood to burn in the cooking fire. One of themost used expressions around the camps was "Wind 'im fire" which is pidgeonEnglish for 'blow-up the fire' (to stop the stinking acrid smoke). But higher upthere grew one special tree, an Australian eucalypt. When first seen I hurried to'wash' my face in its leaves. After months in the smelly forest below, the urge wasirresistible.
The vanishing rain forests of Australia do not have the unpleasantsmell of many tropical forests. For the City Forest even the perfume could be chosenby planting a few special trees.
These natural rain-forests and others visited around Australia,the two islands of New Zealand, the Pacific Islands, Europe and America; whereverthey remain, have in common the great water absorbtion capacity to stop any amountof rain-fall in its tracks; to take in water very quickly and to release it slowlyin springs of clear water. A region which is covered with good grassland soil doesnot produce heavy floods, but covered with deep forest soil floods are not possible.Flood control is merely one coincidental of landscape design. There is another thatwould belong to the City Forests and is even more significant; they would be fireproof.