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NATURE 



[November 29, 1894 



tier of our States and Territories, we meet a different set of 

 skirmishers following up the huge cacti and agaves, which to- 

 gether with the tree yuccas, penetrate into the very desert. In 

 these regions the mesquite or algaroba and others of the acacia 

 tribe form the second phalanx, as it were, gradually advancing 

 their lines in spite of adverse conditions. In other regions the 

 pine, satisfied with but scanty favour of soil moisture, and the 

 spruce, able to sustain life in shallow soil, and the lir, in the 

 higher, colder, and wetter elevations, sometimes much stunted, 

 form the skirmish line. These improve the soil in its moisture 

 conditions by their shade, and by the foliage and litter falling 

 and decaying they deepen the soil, forming a humus cover. The 

 duff that is found covering the rocky subsoil of the Adirondacks 

 is formed in this way at the rate of about one foot in 500 years. 

 They are soon followed by the birch, maple, elm, and ash, and 

 in moister situations by the oak — first, that hardy pioneer, the 

 black oak tribe, and then the more fastidious white oak, with 

 whom the slower but persistent hickories, beeches, and other 

 shade-enduring species begin to quarrel for the right of occu- 

 pancy of the ground, until the battle is no longer that of the 

 forest against the elements and lower vegetation, but between 

 the mighty conquerors themselves. This struggle we can see 

 going on in our primeval forests, wind, storms, and decay acting 

 as allies now to one, now to the other side, and thus changing 

 the balance of power again and again. 



In this struggle for supremacy between the different ar- 

 borescent species the competition is less for the soil than for the 

 light, especially for tree growth. It is under the intluence of 

 light that foliage develops, and that leaves exercise their functions 

 and feed the tree by assimilating the carbon of the air and 

 transpiring the water from the soil. The more foliage and the 

 more light a tree has at its disposal, the more vigorously it will 

 grow and spread itself. 



Now the spreading oak or beech of the open field finds close 

 neighbours in the forest, and is narrowed in from all sides and 

 forced to lengthen its shaft, to elevate its crown, to reach up 

 for light, if it would escape being overshadowed, repressed, and 

 perhaps finally killed by more powerful densely-foliaged 

 competitors. 



The various species are differently endowed as regards the 

 amount of light which they need for their existence. Go into 

 the dense foiest and see what kinds of trees are vegetating in 

 the dense shade of the older trees, and then go into the opening 

 recently made, an abandoned field or other place, where the 

 fall benefit of light is to be had by all alike, and one will find 

 a different set altogether occupying the ground and dominating. 

 In the first case there may be found, perhaps, beech and sugar 

 maple or fir and spruce ; in the second case aspen, poplar, 

 willow, soft maple, oak or pine, tamarack, &c. 



All trees thrive ultimately best in full enjoyment of light. 

 But some, like those first mentioned, can at least subsist and 

 their foliage functionate with a small amount — they are shade- 

 enduring kinds, usually having a dense foliage, many leaves, 

 and each one needs to do but little work — and exert considei» 

 able shade when fully developed. Those last named, however, 

 are light-needing kinds, and having less foliage, cannot exist 

 long without a considerable amount of light. 



To offset this drawback in the constitution of these latter, 

 nature has endowed them as a rule with the capacity of rapid 

 height growth, to escape their would-be suppressors ; but again, 

 what they have gained in the rapidity of development they 

 lose in the length of life. They are mostly shortlived species, 

 while the shade-enduring are generally slower growers, but 

 persistent and long-lived. Some kinds, like most of the oaks, 

 stand between the two ; while exhibiting a remarkable capacity 

 of vegetation in the shade, they are really light-needing species, 

 but comparatively slow-growers and long lived. One of the 

 same species behaves also somewhat differently under different 

 soil and climatic conditions; for instance, as a rule, the light- 

 needing species can endure more shade on moist soils, and the 

 thadc enduring require more light on drier soils. 



In liie earliest stages of life the little seedlings of most trees 

 require partial shade, and are quite sensitive in regard to light 

 and conditions. Some have such a small range of light and 

 shade endurance that, while there may be millions of little 

 seedlings sprouted, they will all perish if some of the mother 

 trees are not removed and more light given ; and they will 

 pcri-sh equally if the old growth is removed too suddenly, and 

 the delicate leaf structure, under the influence of direct sunlight, 

 is made to exercise its functions beyond its capacity. 



Left to itself the forest grows up, and as the individual trees 

 develop, each trying to hold its ground and struggling for light, 

 a natural thinning lakes place, some trees lagging behind in 

 growth and being shaded out, until in old age only as many 

 trees remain as can occupy the ground without incommoding 

 each other. 



This struggle among the individuals goes on during their 

 entire life. Some few shoot ahead, perhaps, because of a 

 stronger constitution or some favourable external cause, and 

 over-tower their neighbours. These, lagging behind, fall more 

 and more under the shading influence of their stronger neigh- 

 bours until entirely suppressed, when they only vegetate until 

 they die. The struggle continues, however, among the dominant 

 class, and it never ends. 



Thus the alterations of forest growth take place, oak follow- 

 ing pine, or pine following oak ; the poplar, birch and cherry 

 appearing on the sunny burns, or the hickory, beech, and 

 maple creeping into the shadier pine growths. While in 

 the eastern forests under natural conditions the rotation of 

 power is accomplished in at least from 300 to 500 years, the old 

 monarchs of the Pacific, towering above all competitors, have 

 held sway 2000 or more years. In this warfare, with changes 

 in climatic and soil conditions going on at the same time, it may 

 well occur that a whole race m.iy even be exterminated. 



The study of the form.itive period of the forest is necessary in 

 order to show clearly that the virgin forest is a product of long 

 struggles, extending over centuries, nay, thousands of years. 

 Some of the mightiest representatives of the old families, 

 which at one time of prehistoric date were powerful, still 

 survive, but are gradually succumbing to their fate in our era. 



The largest of our eastern forest trees, reaching a height of 

 140 feet and diameters up to twelve feet, the most beautiful and 

 one of the most useful, the tulip tree (Liriodendroii lulififiia), 

 is a survivor of an early er.i, once widely distributed, but now 

 confined to eastern North -Vmerica, and doomed to vanish 

 soon from our woods through man's improper partisanship. 



Others, like the Torreya and Cupressus, seem to have suc- 

 cumbed to a natural decadence, if we may judge from their 

 confined limits of distribution. So, too, the colossal sequoias, 

 remnants of an age when things generally were of larger size 

 than now, appear to be near the end of their reign, while the 

 mighty taxodium or bald cypress, the big tree of the East, still 

 seems vigorous and prosperous, being able to live with wet feet 

 without harm to its constitution, weird with the grey tillandsia 

 or .Spanish moss. 



Having thus scanned through the traditions of unwritten 

 history of the battle of the forest, having seen some of the 

 combatants in the struggle, and learned something of their 

 methods of conquering the earth and each other, we may take 

 a look at the condition of things on the North American con- 

 tinent as it presumably was in the beginning of historic times 

 or within our century. 



As far as occupancy of the soil by the forest is concerned, 

 we find that the struggle had not yet been determined in its 

 favour everywhere. While a vast territory on the Atlantic side 

 and a narrower bell on the Pacific Coast, connected by a broad 

 belt through the northern latitudes, was almost entirely under 

 its undisputed sway, and while the backbone of the continent, 

 the crest and slopes of the Rocky Mountains, was more or less 

 in its possession, there still remained a vast empire in the 

 interior unconquered. 



Of parts of this territory we feel reasonably certain from 

 strong evidences that the forest once occupied them, but has 

 been driven off by aboriginal man, the firelnand taking sides 

 with the grasses, and the buffalo probably being a potent 

 element in preventing re-establishment. In other parts it is 

 questionable whether the lines along the river-courses, the 

 straggling trees on the plateaus and slopes, are remnants of a 

 vanquished army or outposts of an advancing one. In some 

 parts, like the dry mesas, plateaus and arroyos of the interior 

 b,asin and the desert-like valleys toward the southern frontiers, 

 it may reasonably be doubled whether arborescent flora has 

 more than begun its slow advance from the outskirts of the 

 established territory. 



Certain it is that climatic conditions in these forestless regions 

 are most unfavourable to tree growth, and it may well be ques- 

 tioned wbttther in some parts the odds are not entirely against 

 the progress of the forest. 



Temperature and moisture conditions of air and soil deter- 

 mine ultimately the character of vegetation, and these are 



NO. 1309, VOL. 51] 



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