148 



Garden and Forest. 



[Number 266. 



the open, the water-supplies, under the influence of higher 

 temperatures and unchecked winds, are more readily exhausted 

 or reduced to a minimum where evaporation and transpira- 

 tion of the soil covering plants does not increase proportional 

 to temperature increase, it becomes evident that the forest 

 retains for a longer time a water-supply which is easily 

 available. 



The observation that both absolute and relative humidity 

 are increased in the forest is a new and important fact, which 

 had not been apparent from the observations of the German 

 stations situated under the infl uence of an oceanic (the Baltic and 

 Atlantic) climate, which is characterized by high relative humid- 

 ity and only occasional high temperatures, while the Austrian 

 stations are situated near the region of the pontic dry climate. 

 In such a climate the dry air is capable of taking up additional 

 water-supplies from the forest, and since the latter has also a 

 cooling effect, both absolute and relative humidity of air cur- 

 rents passing it are increased, while in the oceanic climate the 

 absolute moisture, already high, cannot be increased, and only 

 the cooling effect of the forest affects the relative humidity. 

 This important difference in general climatic conditions must 

 be kept in view when discussing forest-influences. In com- 

 paring forest and open field, the kind of cover of the latter 

 must also be taken into account. During the early develop- 

 ment of meadow-growth and of crops, while they are green, 

 they furnish by transpiration more water to the air than the 

 forest. Since, therefore, during this season the open soil 

 loses both by evaporation and transpiration more water than 

 the shaded forest-soil, the latter is able to supply moisture 

 when that of the field-soil is exhausted and begins to absorb 

 moisture from the atmosphere, especially when, with the rip- 

 ening of the crops, the plants cease to transpire much water. 

 Hence, the difference of absolute humidity appears greater in 

 the forest, especially in dry seasons. 



The decrease in absolute humidity above the forest-crown 

 must, of course, take place at about the same ratio as above 

 the field, but altogether the observations seem to show that 

 the enriching of the air with moisture above a forest-cover 

 can extend to a considerable height. These conditions of 

 moisture and temperature above the forest lend countenance 

 to the claim that the possibility of precipitation over large 

 and dense forest-areas is greater than over open fields. 



As far as the temperature and moisture conditions of forest- 

 areas may be communicated to adjoining fields, further light 

 is promised from the radial stations in Austria. The results 

 from these have only just been published, and I will refer to 

 them at some other time. Theoretically, there are various 

 objections to the assumption th^ the influence, if any, is an 

 appreciable one. But we know that meteorological theories, 

 more than others, are liable to be at fault and unsatisfactory in 

 many respects, probably on account not only of the compli- 

 cated nature of the phenomena with which they deal, but also 

 of the defects in methods and means by which the data have 

 so far been collected. 



It is hardly a conclusion, but at least an impression, that 

 seems to come from looking at results already presented that, 

 as a climatic factor, the forest of the plain is apparently of 

 more importance than the mountain forest, the more potent 

 meteorological influences of the mountain elevation obscuring 

 and reducing in significance the influence of their cover, 

 while for soil and water conditions the mountain forest is of 

 considerable importance. r. c c- 



Washington. D. C. ^- ^- FemOW . 



Correspondence. 



On the Local Segreg-ation of Trees. 

 To the Editor of Garden and Forest : 



Sir, — In the first of Professor Sargent's highly interesting 

 and instructive papers on the Forest Flora of Japan, he tells us 

 that " the segregation of arborescent species in Japan ... is 

 the most striking feature of the silva of that country" ; and he 

 says that in Yezo are " probably more species of trees growing 

 naturally in a small area than in any other one place outside 

 the tropics" ; in support of which statement he gives a list of 

 forty-six species and varieties (forty-three species and three 

 varieties) which he noticed " in ascending a hill which rises 

 only 500 feet above the level of the ocean." To these he adds 

 thirteen species " growing within five miles of this hill," 

 making " in all sixty-two species and varieties, or more than a 

 quarter of all the trees of the empire crowded into an area 

 only a few miles square." 



Unless the list given by Professor Sargent is a very incom- 

 plete one, I think it can be proved that at least one locality in 

 the eastern United States is even richer than Yezo in respect 



to the number of species of trees growing in a restricted area. 

 In the Proceedings of the United States National Museum for 

 1882 (vol. v.) I published lists of trees found by me growing in 

 limited areas of forest in south-eastern Illinois and south- 

 western Indiana, which I reproduce here, although, to save 

 space, they are presented in a different form, names of the 

 species being omitted, and a summary of the number of spe- 

 cies and genera found on each tract, with the size of the tract, 

 being substituted. For convenience, the tracts are designated 

 as " a" and " b." 



Number of Number of 

 Tract. Locality. Area of tract, genera. species. 



a. Wabash County, Illinois, 50 acres. 24 46 



b. Knox County, Indiana, . 75 " 29 52 



Both these tracts were absolutely level ground, the first 

 varied only by a creek which meandered through it, and the 

 second bordered by a wooded swamp along one edge. Within 

 half a mile of locality "a" there were identified twelve addi- 

 tional species and five additional genera ; while within three 

 miles in a nearly opposite direction were found seventeen ad- 

 ditional species and five additional genera, making a total of 

 seventy-five species and thirty-six genera — against sixty- 

 two species and thirty-two genera of the Japanese list — 

 growing on very much less than five square miles of ter- 

 ritory.* 



In locality " b" an enumeration of the species of trees grow- 

 ing on a separately enclosed tract of only twenty-two acres in 

 extent, about eight acres of which had been partially cleared, 

 showed forty-four species, belonging to twenty-five genera, to 

 be growing there, or two species and more than one genus for 

 each separate acre of ground. I am quite certain that the two 

 localities referred to are by no means exceptionally rich in the 

 number of species for that region ; in fact, I am sure that five- 

 mile-square areas might be selected in the valley of the lower 

 Wabash which would produce a still larger number of species 

 and genera ; but it would be necessary to include within their 

 limits a greater variety of surface — that is, to include not only 

 the usual bottom-land forest, but also swampy tracts, river- 

 banks and a portion of the river-bluffs. 



In his second article on the forests of Japan, Professor Sar- 

 gent calls attention to the great difference in the undergrowth 

 which covers the ground beneath the forests in the two re- 

 gions, which he says is so great that it " must at once attract 

 the attention of the most careless observer." This under- 

 growth, he says, in America is composed of a great number of 

 shrubs, while " in Japan the forest-floor is covered . . . with a 

 continuous, almost impenetrable, mass of dwarf Bamboos of 

 several species." Now, this latter character of undergrowth 

 is exactly what is found in parts of the Mississippi valley, ex- 

 cept that only one or two species of arborescent grass, instead 

 of several, constitute the nearly impenetrable undergrowth. 

 Large areas of forest in southern Indiana and Illinois (though 

 farther northward t in the former than in the latter state) have 

 the ground chiefly occupied (where not destroyed by horses 

 and cattle) with a very dense growth of the "Switch-cane" 

 (Arundinaria tecta), growing, as do the Bamboos of Japan, 

 from three to six, though sometimes ten or more, feet high ; 

 and the parallelism is carried still farther by another feature 

 mentioned by Professor Sargent in connection with Japanese 

 forests, these very forests of southern Indiana and Illinois be- 

 ing " filled with climbing shrubs, which flourish with tropical 

 luxuriance"; though many of the genera are different, our 

 forests having, of the larger or higher growing vines, repre- 

 sentatives of the genera Vitis (five species), Cissus, Ampelop- 

 sis, Wistaria, Celastrus, Calycocarpum, Rhus, Bignonia, Te- 

 coma and Aristolochia, most of which ascend to the tops of 

 the tallest trees, frequently more than 100 feet from the 

 ground, and the largest stems of Vitis, Tecoma and Rhus 

 sometimes measuring a foot in diameter. 



With all these elements of similarity, however, there are 

 equally marked points of difference between the forests of 

 Japan and those of the region under consideration. Most con- 

 spicuous is the absence of evergreens in the latter, there being 

 among the seventy-five species representing the silva of the 

 southern Illinois-Indiana area described above not a single 

 evergreen tree. In fact, the general absence of evergreens, 

 both among trees and shrubs, is a conspicuous feature of these 



*The genei-a represented were as follows: Llriodendron, Asimina, Tilia (two 

 species), iEsculus, Acer (three species), Negundo, Gleditsia (two species), Gymno- 

 cladus, Cercis, Prunus (two species), Pyrus (two species), Crataegus (four species), 

 Amelanchier, Rhus, Liquidambar, Nyssa, Cornus, Viburnum, Diospyros, Fraxi- 

 nus (five species), Sassafras, Catalpa, Ulmus (three species), Celtis (two species), 

 Morus, Platanus, Juglans (two species), Carya (seven species), Quercus (thirteen 

 species), Fagus, Carpinus, Ostrya, Betula (two species), Salix (two species), Populus 

 (three species) and Taxodium. 



t To a distance of several miles above the mouth of the White River. 



