The Pamphlet Collection of Sir Robert Stout: Volume 6
7. On the Relation between Rainfall and Forest
7. On the Relation between Rainfall and Forest.
Captain Campbell-Walker, in his able and exhaustive paper (Appendix to Trans. N.Z. Inst., Vol. ix.) "On the Climatic and Financial Aspect of Forest Conservancy as applicable to New Zealand," after enumerating and illustrating many ways in which the presence of forests undoubtedly tends to ameliorate the climate of a country, as well as to increase and conserve its water-supply, and therefore its productivity, "records his opinion that so far nothing has been found to establish the theory that extensive denudation will of itself cause a marked decrease in the rainfall" (Par. xxviii.), "although the facts as he has seen and compared them in this colony almost convince him that forests have a direct influence on the amount of it." However—he significantly goes on to ask—"May not the presence of the trees be the effect of the rainfall, and not the cause of it? "and confesses that he feels no kind of certainty one way or the other, but takes comfort from the fact that Dr. Brundis, the Inspector-General of Forests in India,—no mean authority,—and doubtless many others, have like himself failed to make up their minds about the matter. page 311 He even avers "that statistics in this colony tend to prove that the rainfall has increased at stations in the neighbourhood of which woods have been extensively cut down."
Now, I firmly believe that this attitude of mind on the important subject in question is precisely that of many thoughtful people. They feel that there is an intimate relationship between rainfall and forest, but are not prepared to assign priority of existence to either. Nevertheless the usual opinion originated by those who clearly perceive the beneficial effects of an arboreous covering, and the evils resulting from the wanton destruction of such covering, in most newly-settled countries, has been that rainfall will be very seriously affected by deforestation and largely increased by reforestation. To this dictum quite lately more than one authority much more competent to form an opinion than myself has demurred. I follow on the same side, and venture to discuss the question in a somewhat novel fashion.
I have prepared, and have now before me, two maps of Now Zealand—the one showing approximately by degrees of shading the average annual rainfall in the different parts of the colony; the other showing, also approximately, from the information supplied by Captain Walker while acting as Conservator of Forests in New Zealand (Report on Forests: C.—3, Appendix to Journals H. of R., 1877), where the great forest-areas principally lie, and the comparative extent of them. The similarity between the two maps is evident at a glance, so much so indeed that, with some trifling exceptions, principally on the eastern side of the Islands—in Cook County and the Province of Marlborough, e.g.—it may be said that the more darkly shaded areas in the two are nearly coincident; and it is impossible to do otherwise than conclude that between rainfall and forest there is, in some way, the connection of cause and effect.
To construct, even roughly, a map of the forests of New Zealand is no easy matter: no authentic map of that character is in existence; and the materials for constructing one, as supplied by the source already indicated, are neither precise nor adequate. There is pretty accurate information as to the amount of forest which was in the hands of our Government in 1877; but at that time very much had already teen alienated, especially of kauri, totara, and other commercially valuable timber, and of course a large quantity still remaned in the possession of the Natives.page 312
|Total Area of Province. Acres.||Acres in Forest.|
|Auckland||9,449||per cent, of||16,650,000=||1,573,258|
|Hawko's Bay||11.803||per cent, of||2,187,000=||252,230|
|Taranaki||83.003||per cent, of||3,050,000=||2,521,896|
|Wellington||57.142||per cent, of||7,200,000=||4,114,224|
|Nelson||14.434||per cent, of||6,700,000=||967,278|
|Marlborough||19.301||per cent, of||3,000,000=||579,030|
|Canterbury||4.306||per cent, of||8,693,027=||374,320|
|Westland||62.809||per cent, of||3,045,700=||1,912,973|
|Otago and Southland||8.729||per cent, of||15,038,300=||1,312,693|
There are marked discrepancies between these figures of 1886 and the ones previously quoted from Captain Walker's report of 1877. In some cases those of the later date are much larger than those of the earlier. This might arise from the the former including forest-lands already alienated by the Crown and also those areas of woodland still possessed by the Natives. The discrepancy, however, in the case of Nelson is too great to be accounted for in this way. I have no means page 313 whatever of explaining it. In any case the figures are very large, and clearly show that there is a vast area of fores still left in the colony, which certainly deserves the credit that it possesses of being, as regards arboreous vegetation, one of the richest portions of the globe; but the destruction that has gone on since European settlement began must have been enornous if we may judge from an estimate made by Sir J. Hector and quoted in the "Encyclopædia Britannica," to the effect that in 1830 there were probably 20,370,000 acres of forest in New Zealand. That the area should have diminished by at least one-third in less than fifty years shows the immediate recessity of steps being taken towards forest-conservation. This, however, by the way.
The above figures, and the map drawn in accordance therewith, show us pretty clearly that the great forest-areas in New Zealand are on the western side of the Islands—on the western slopes—and, if they are below 4,500ft. in height, on the summits of the mountain-chains. The densest forests, as far as the North Island is concerned, would seem to be in the Taranaki Province, of which more than four-fifths is forest-clad, and in the Wellington Province (on the Tararua and Ruahine Ranges), of which more than half the surface is so covered; and, as regards the South Island, the Province of Westland has proportionately and absolutely the greatest amount of forest-area, as much as three-fifths of its surface being forest. There are vast areas of wooded country also at the extremities of the colony—that is, in the Provinces of Auckland, and Otago and Southland. In Nelson and Marlborough the mountain-ranges are less elevated generally, and more broken, and the forest spreads over the land extensively, hut with large bare areas intervening, so that the proportion of area forest-covered is riot so large as in the districts previously named. Canterbury and Hawke's Bay, with their naked plains and comparatively sparsely-timbered hills, and a very extensive bare area in the interior of Otago, are absolutely and relatively the poorest in forest of all the provinces, and these are precisely the areas which are most subject to warm north-westers and have least rainfall, being most protected by mountain-chains against the prevalent rain-bringing or equatorial winds.
Similarly, a rainfall map prepared on the basis of authentic statistics shows that the greatest rainfall in New Zealand occurs on the western slopes of the Southern Alps and the mountain-ranges in Taranaki; and, generally speaking, the colony has its heaviest precipitation on its western side—as so frequently occurs elsewhere in corresponding latitudes—and there is less and less as the eastern shores are approached. Heavy rains also occur over the extreme northern and southern areas; and local circumstances bring about exceptionally-heavy page 314 rainfalls in various other districts of limited area, particularly in the Provinces of Nelson and Wellington, and on the east coast of Southland. The conclusion is inevitable. Rainfall and forest must, as a general rule, be related to one another as cause and effect; and, though the two may have reacted on one another to a limited extent, yet for the most part the rainfall has brought about the forest, rather than the reverse.
Mountain-ranges as a rule are, as is well known, better covered with forests than level country. I do not think this arises, as Darwin supposed, because plains are in themselves less favourable to the development of arboreous growth than broken and hilly country; for some of the most extensive and dense forests in the world extend over areas level as a table. Mountain slopes and summits—particularly if at all formidable—are little interfered with by man or cattle, and there growth goes on more or less comparatively undisturbed; and, as good drainage and various aspects and different kinds of soil in such situations are sure to be found, there various forms of vegetable life, suitable to the climate, through the instrumentality of birds and winds spring into existence. But the main cause why woods thrive on mountains better than on plains is that rainfall increases, within certain limits, 3 or 4 per cent, for every 100ft. of elevation.
Captain Walker, as if arguing desperately against his own convictions, asks, if forests follow rainfall, "Why should not rain have fallen and forests been created on the eastern slopes of the mountains on which the clouds laden with moisture from the Pacific first impinge? "The answer is conveyed in the question. Bain has not fallen on the eastern slopes of our Alps, because in this latitude the rain-bringing winds are western, and comparatively little rain comes from the east at all. The rain from the west has been intercepted by the mountains, and, as there has been little rain, forests have not been called into existence on the eastern slopes, except in a few places where low passes have permitted the moisture to cross to the leeward side.
That woods do undoubtedly tend to the equalisation of temperature, screen the soil from the sun, check evaporation (which in open country is five times as great as in woods) particularly from pools and streams, render the air about them to some extent cooler and moister than it would be otherwise through the immense surface that the leaves expose to radiation and copious evaporation, and mechanically bind the soil and check the running-off of moisture from its surface—all this, in addition to their grace and beauty of form and colour,—for I share all Lord Beaconsfield's enthusiasm about trees,—must be granted. I will even go further and say that, in consequence of some of the effects herein just enumerated, there page 315 would be a slight increase of the rainfall in a country if forests could be grown to occupy a large area previously bare. In France it has been computed that 5 per cent, more rain falls over woodland than in the open; but one would like to examine this calculation closely and see if here also effect has not been put for cause, and cause for effect.
Besides, all kinds of trees are certainly not equally beneficial as regards conserving moisture or giving shade or cooling the air. Some plants—sunflower, e.g.—pump water out of the ground enormously; and the drying capacity of the Eucalyptus, as far as the ground around it is concerned, is considered one of its special and peculiar virtues. Even in the case of other trees, the amount of moisture which they draw up from the ground by their sometimes far-reaching spongioles is really enormous. True it is that transpiration and consequent evaporation are constantly going on during growth, and sometimes are so copious that an individual tree will perspire its own weight of water in twenty-four hours; and this undoubtedly does render the air around cooler and moister, though it must be remembered the ground is proportionately robbed of its moisture. According to some people, trees are as good as artesian wells, and will draw water from heaven as Franklin's kite drew electricity from the clouds. They certainly do draw water in large quantities, but it is rather from the earth than from the sky.
That forests, in a wide sense, operate to materially change the climate of a country, as many have contended, I believe therefore to be a serious mistake, resulting from the confounding of cause and effect. The power attributed to trees of drawing rain from heaven is a matter indeed on which many people have held the most extreme views. James Brown, in "The Forester," says, "It is in the power of man to alter, modify, and regulate the climate in which he lives to suit the various kinds of crops he cultivates." One gentleman I know—a well-known litterateur of a city in Australia, and the editor of its leading journal—who always entertained the idea that the miraculous virtue of drawing rain lay especially in the Melia azedarach or white cedar. This, therefore, he largely planted in the grounds attached to his house, but it is needless to say that the rainfall over his few acres was not sensibly larger than that of the locality generally. Such notions remind one of the old story of King Canute and his courtiers on the sea-shore. Professor Tate, of Adelaide, who holds vews similar to my own, in a lecture delivered by him some years ago went so far as to say that "European experience bused on records kept since 1688, and extending up to the present day, failed to prove that the rainfall had decreased as the trees had been destroyed, and that a similar remark might be ap- page 316 plied to the United States, covering a period of sixty-six years." Per contra, our later visitor, Mr. David Christie Murray, told me a short time ago that in the Ardennes, where he had lived for many years, it had been observed that the rainfall had been seriously affected by the destruction of the indigenous forest.
There is a good deal of evidence—much of it more or less untrustworthy—on both sides of the question; but I believe the balance falls on the side of the views which I have expressed, and this is what we should expect from a priori considerations. The powers of nature which determine general weather are too Titanic for man to hope to overcome. He does not even thoroughly understand them yet, for meteorology is the newest of the sciences. But what knowledge we do possess goes to show that nine-tenths of the rain that falls is cyclonic, and thus general weather depends on widely-operating physical laws, which man will best recognise his own interests by bowing to as inevitable. In India, where at one time they largely held the notion that they could by reforestation modify an extremely hot and, considering their requirements, dry climate, after large experience in this kind of work they have entirely changed their views, and no longer struggle to avert the inevitable or accomplish the impossible. Some of the British colonies, however, still attempt this feat. They have so long repeated the ordinary phrases about forests causing rain that they have come to believe them eternal verities.
As long as the configuration of New Zealand has been what it is, the prevailing western winds have deposited their precious burden on the western sides and summits of the Southern Alps, and on those portions of their eastern flanks and the country beyond to which they could travel without mounting more than, say, 4,000ft. This is one of those wide and general features of climate depending on our latitude (the "roaring forties"), our insular position, and the existence of a high range of mountains running from north to south near the western shores. To alter this feature in any material way whatever, man is perfectly impotent; and, where the rain falls heavily, there the forest heavily covers the land; where less heavily, there the trees grow in patches; where very lightly, there the shady woods are wanting, and the plains are treeless. Above, say, 4,500ft. forest-growth ceases, and stunted vegetation only is found; for at that height cold checks growth, and, instead of rain, for the most part snow falls.
Of course, the nature of the soil and other circumstances are factors of the greatest importance; but, generally speaking, in a country unoccupied by civilised man the forest-areas will be the areas of heavy rainfall. A good map showing clearly the forests of New Zealand, if we took into account the woods page 317 destroyed by settlers and accidental fires, would exhibit the main features of the annual rainfall. In countries that have been long settled and cultivated it is impossible to determine what were the areas of virgin forest. It is only in a country such as ours, just placed in the hands of civilised man, and where the aboriginal inhabitants have not been given to felling and clearing on an extensive scale, that such an inquiry becomes possible; and, as to determining or helping to determine what are or have been the areas of greatest precipitation, it may surely be considered, next to exact meteorological statistics, as of paramount importance.
Certainly different kinds of trees require different degrees and amounts of moisture, as of heat, light, and elevation, to develope them. Some, indeed, seem specially adapted by nature for dry climates and positions: they have hairs covering their leaves, which thus attract a larger proportion of dew, or their leaves are needlelike, or set on edge, so that during a drought the sun has less effect on them. It would almost appear as if the Eucalyptus when grown in a moister climate than that in which it is indigenous alters its habit of growth. In New Zealand here, its leaves grow less edgewise, more open and flat to the sky, as if they felt they could safely expose themselves to a less powerful sun in a climate where moisture is happily so plentiful as to temper materially his ardent days. But all these are quite exceptional characteristics of particular species, and are instances of modification of form to protect life and accommodate it to its environment.
It would be quite possible to bring out the truth of the proposition submitted as to the relationship between rainfall and forest by a survey of the surface of the earth genenlly. Some instances could be given which pointedly confirm the theory: e.g., the northern and eastern portions of the Island of Madagascar, where the climate is moist, are clothed with magnificent forest, whereas elsewhere in the island the vegetation is remarkably scanty, there being only a narrow arbore-ous belt along the shores. But it is very difficult to conduct the inquiry as to the earth generally with precision, because there are large areas in the world over which the extent of woodland is very imperfectly mapped out, or, indeed, known; and unfortunately, too, these are precisely the regions where the rainfall is conjectured rather than measured. Moreover, where the forest-area and the mean annual average of rain are well known and duly recorded, there the condition precedent that the forest be indigenous and virgin does not obtain; for the countries referred to have been so long settled that few spots, if any, are left in true primitive wildness. Similar uncertainty, indeed, may exist as to the reading of such cases as Makatu Island, in the Fijis, where the windward and pre- page 318 sumably rainy side is densely wooded, while the leeward side is timberless. Moseley, the naturalist of the "Challenger" expedition, thinks the forests there are owing to heavier rainfall; but we have no meteorological statistics from the island, and, as the windward side is the steeper of the two, it may be that the natives, though barbarian, in bygone days have cleared the leeward side for cultivation. The Island of Madeira, as the name implies, was once entirely timber-covered: now, however, through ruthless destruction by Zargo and others, the island is bare except on one side, and that is the windward and rainy. Fire is powerless in a land of incessant rain, or, if it temporarily succeeds, the damage done is speedily repaired.
It is believed that before human inhabitants became numerous in the world its surface was almost entirely covered with forest. Possibly at that remote period—and the latest inquiries into the question of the antiquity of man show that it must have been very remote indeed—the mean annual rain-all on the earth was everywhere considerably greater than it is now. Whether that was so or not, in our own day the most extensive natural forests in the world would seem to be generally, though not exclusively, in those parts where the rainfall is known or conjectured to be heavy, if not the heaviest.
For example, the greatest and most productive forests on earth are in America; and that Continent, as a whole, has undoubtedly a humid climate. British America has 900,000,000 acres of valuable timber. British Columbia and the Washington and Oregon Territories of the United States are densely timbered, and the immense Sequoia (Wellingtonia) gigantea, is only found where the western slopes of the Nevada Range intercept the heavy western rains from the Pacific. Passing to South America, we find in the silvas of the western portion of the great plain of the Amazon an area of nearly a million English square miles covered with impenetrable forest and jungle (Brown's "Forester"). In all these lands the rainfall is heavy, in some parts very heavy. Loomis (map, Amer. Jour, of Science, 1882) shades them so as to show a mean annual average of at least 50in., and often over 7 Sin. In Neeah Bay, Washington Territory, the amount is 123in.; in Blockhouse, Oregon, 96in.; in Halifax, N.S., 54in.; in New Westminster, 58in. What it is in the forests of Brazil, particularly in the uplands towards the Andes, I cannot discover, but it must be very large, for, the latitude being tropical, the trade-wind striking against the eastern flanks of the mountains must cause immense precipitation. The Andes are clothed with forest along their entire length either on one side or both sides, because the mountains catch the eastern, rains page 319 in one latitude and the western in another. Contrast with this luxuriant arboreous vegetation—resulting, as I contend, from heavy rainfall—the barrenness of Peru and northern Chili, the treeless condition of the pampas of La Plata, Banda Oriental, and Patagonia, and the deserts of Utah and Nevada, in all of which countries the mean annual rainfall is less than 10in. (6in. at Fort Bridger, Utah; 5in. at Fort Churchill, Nevada; 4in. at Mendoza, La Plata; and 0in. at Lima).
Darwin, in his "Journal of Researches" (p. 46), à propos of the entire absence of trees in Banda Oriental, notices many of the above facts respecting South America, and discusses the question with which we are engaged at some length. He thinks, as I have already remarked, that extremely level countries such as the pampas seldom appear favourable to the growth of trees, and that this may be possibly attributed to the force of wind or kind of drainage. The fact is, however, that quite recently the Eucalyptus globulus has been extensively planted in different parts of the pampas, and, being a tree that can stand drought well, it succeeds despite the pampero, even better than in Australia, becoming both richer and denser in foliage. But, apart from this experimental proof that Darwin was in error on this point, it must be observed that the most extensive tracts of level country with which we are acquainted are flanked on their western sides by mountain-chains cutting off the oceanic winds and rains (Guyot's "Earth and Man "); and this factor, from the point of view of one who believes that rainfall determines forest, is not to be lost sight of. I confess I do not see that the argument as to force of wind and drainage in level tracts is very cogent. Darwin himself subsequently records that he found little or 110 vegetation whatever on the Sierra de la Ventana—a group or chain of hills 3,000ft. high on the eastern side of the Patagonian plain and at no great distance from the South Atlantic. Now, the treeless uniformity of Patagonia ought to have been broken by this elevated ground, if Darwin's reasoning was conclusive; for shelter would be found either on one side or another of the chain, and drainage would be generally good on its slopes. Darwin refers to Maclaren's article in the "Encyclopædia Britannica "as "inferring with much probability that the presence of woodland is determined by the annual amount of moisture," and emphatically says that, confining our view to South America, we should certainly be tempted to believe that trees flourished only under a very humid climate, for the limit of the forest-land follows in a most remarkable manner that of the damp winds. He seems, however, to attach importance to the fact that the Falkland Isles can boast of few plants deserving even the title of bushes. Such carefulness about making wide generalisations is eminently page 320 characteristic of the great naturalist. A trifling exception like this, however,—and even though many more might be given,—could be probably accounted for by quite exceptional circumstances, such as being swept by cold and stormy oceanic winds, which accounts similarly for the stunted vegetation of our own Chatham Islands, and does not appear to justify hesitancy about accepting a law which is widely and generally observable. Forest argues heavy rainfall, but heavy precipitation of rain must be accompanied by other circumstances to result in the growth of wide areas of timber.
Of the Dark Continent and its forests our information—though, thanks to the attention which this part of the world has of late been receiving, not by any means meagre—is as yet only general. Of exact statistics we have scarcely any; but the explorations of recent travellers—particularly the indefatigable and indomitable Stanley—show us that almost impenetrable woods fill up the heart of the land, more or less from the Atlantic Ocean to the Indian; and Loomis's map gives us a rainfall of over 75in. for the whole of this wide tropical belt. Northward of it stretches from the Atlantic to the eastward of Central Asia—only broken by the Hindoo Coosh and the Himaleh Mountains—a vast treeless desert, almost rainless.
In India, owing to the beneficial action of the monsoons, a copious rainfall of above 75in. is found along the coasts and at the base of the stupendous chain to the northward, with very excessive precipitation in certain limited areas—Cherapungi, e.g., in Assam, where the fall is over 600in. in the year. The valuable forests of pine, box, sal, teak, ebony, and deodar therefore here are very extensive, and now all are most carefully conserved—not so much with the view of securing a continuance of the rainfall as for the sake of preserving and economizing national wealth. As regards teak (Tectonia grandis) it is well known that it grows best where the rainfall is heaviest. Burmah, Java, Sumatra, and Borneo, as regards rain and forest, are equally liberally endowed by nature. All have a truly tropical average of over 75in. (213in. at San donay, Burmah; 220in. at Buitenzorg, in Java; and 181in. at Padang, Sumatra); and all are remarkably well wooded. Siberia, north and north-east of the Altai Mountains, is one enormous forest. It has, however, only a moderate rainfall of from 10in. to 50in. according to locality. The forest here, therefore, does not cause heavy precipitation. But it must be remembered that this is a high latitude, and evaporation is comparatively small. A little rain, therefore, under such circumstances is very effective. The same remarks apply to a large part of Russia in Europe. Japan, again, is well wooded and has a rainfall of over 65in. On the other hand, the page 321 steppes of Tartary and Mongolia are nearly treeless, and have less than 10in. of rain in the year.
In Europe, man's action has been powerful enough to completely alter the face of the land, but we know from history that till comparatively recent times it was covered with forest, and this may be presumed to have been the effect of the rainfall with which the Continent is blessed, through its latitude, its being intersected by great oceanic areas, and the action of the Gulf Stream and the Return Trades bringing copious moisture from the Southern Hemisphere—a rainfall coming more or less throughout the year, very heavy in particular spots, but not tropically heavy anywhere, yet quite sufficient, considering the high latitude, to promote vigorous arboreous growth almost in every comer.
Australia has a poor mean average of rainfall throughout its vast interior (5in. at Alice Springs, 6in. at Charlotte Waters), the greater part of which lies within an anticyclonic region of high pressure and the dry south-east trades. This is a land, therefore, subject to very severe droughts, periodically blighting the face of nature from the 18th to the 30th parallel of latitude, and occasionally embracing the whole continent; and as a consequence—though Darwin ("Journal of Researches," p. 47), with scantier information than we possess, speaks of the whole of Australia in spite of its arid climate as being covered by lofty trees—I believe we should be correct in saying that the interior for many thousands—yes, even hundreds of thousands—of square miles is nearly absolutely treeless. Along the eastern coasts and mountains the rainfall is heavier (48in. at Brisbane, 49in. at Sydney: compare 20in. at Adelaide and 25in. at Melbourne), and the arboreous vegetation is more profuse; while the Australian Alps in the southeastern corner, being within the area and influence of the cyclonic depressions that pass along the southern coast in regular succession, are covered with Eucalyptus woods, and there the massive E. amygdalina attains its gigantic size.
This review is too cursory and sketchy, but, when taken in conjunction with the more careful examination of the rainfall and forest of New Zealand, previously given, it may perhaps he considered enough to give semblance of truth to the proposition that the native forests of a country are located in those districts blessed with abundant rainfall, and by the said rainfall are mainly brought into existence. That a reflex action of forest in producing rain also may exist to a limited extent, I quite believe; but, as I have implied, I think it is a power supposed by most people to be much greater than it actually is. Of course, also, what constitutes sufficient abundance of rain for arboreal development depends on latitude and several other circumstances.page 322
A notice in Research of the 1st October, 1889, states that Dr. Hamberg, of the Central Meteorological Institute of Stockholm, has been detailing in a public address the results of his thirteen years' experience and investigations on the influence of forests upon climate. These were carried on at numerous stations—some on free open land, some on forest-clearings, and some in the depths of woods—and related more especially to temperature, humidity of air, and rainfall. He found that temperature was more equable under trees than on free land, and on free land than in clearings; and that, while forests afforded shelter against cold and cutting winds, they did harm on the whole in respect to the sun's heat by depriving the earth of it, and fostering frost through lowering the temperature on the ground on clear nights. As regards the moisture of the air and the rainfall, his researches went to show that in Sweden, at all events, forests are simply without influence. In Gothland, e.g., the new forests, presumably extensive, had not increased the rainfall in the least. He concluded that climate rested on a more solid basis than that of forests, and that forests deserved preservation for more weighty reasons than their influence on climate. At the meeting where this address was given, Baron von Kroemer agreed with the views of Dr. Hamberg, and went so much further as to say that even as regards protection trees were not always desirable, for in Scania, e.g., corn dried much more quickly after rain on free land than in clearings. There is no doubt that in a cold country like Sweden the beneficial effects of forests would be less than in a tropical country like Ceylon, e.g., where Colonel Clarke, after many years of observations, came to the conclusion that "forests make climate more equable, increase the relative humidity of the air, and perhaps increase the rainfall," and also regulate the water-supply, making springs more sustained and rivers more continuous giving besides protection against strong winds, and preventing the soil from being washed away by heavy rains (Nature, 18th October, 1888). This is pithy testimony given by an authority who commands attention; but there is nothing in that testimony which militates against my views, herein expressed.
The proposition which I have endeavoured to establish is one which some people will be disposed to regard as so self-evident as to need no demonstration. It is one which, nevertheless, is frequently lost sight of when the relationship between rainfall and forest is discussed; and it can be maintained quite consistently by those who hold, as I do, that the wholesale destruction of the forests of a country must be, as a rule, prejudicial in various ways to its future interests; though in the process of settlement such destruction, or at all events a large page 323 part of it, is inevitable. Indeed, I often think that, even for the sake of preserving old types of the fauna and flora of the land, it would be well if blocks of country here and there, not neessarily very extensive, were, like the Suli lands of Timor, eld inviolably sacred as against axe or gun, or destructive insrument of any kind. To deny, however, that reforestation wold materially increase rainfall is quite a different thing from daying that deforestation must in some respects prove calamitus. Let us plant trees by all means where the ground cannot otherwise be more profitably employed. By so doing we sail clothe the earth with beauty, and shelter it alike from, he bitter blast and the fiery sun, and conserve its refreslng moisture for the benefit of plants and animals. But we sall not materially affect the mean annual rainfall, for that is determined by the operation of cosmic laws which neither he wisdom nor the will of man can change.