24 FOREST INFLUENCES. 



and imi^ortance so far as relates to the suitability of a climate for resi- 

 dence and agriculture. 



The solution of these two problems is very much complicated by the 

 variety of conditions of the forest itself. The forest, woods, or wood- 

 lands may vary in extent all the way from the Amazon forest, which 

 covers a large part of South America, or the corresponding forests of 

 tropical Africa, to the woodlot of the farm, the grove, or the i)ark. In 

 density of tree-growth they vary quite as widely. The openings in 

 forests are esjiecially subject to forest climatic action, as any one knows 

 who has found himself in a tropical forest glade at the hottest hour of 

 the day; and these openings vary in form and in size all the way from 

 the forest gallery or swale through the oak oi)enings and little prairies 

 to the regions where the prairies x^revail and the forest is reduced to 

 islands of woods or to fringes along the streams. In height the trees 

 range from upwards of 300 feet to the low coppice or brush of a few 

 feet elevation; some forests are of fairly uniform height, like the north- 

 ern forests of firs and spruces, while others are composed of plants of 

 all heights from the herb to the forest giant. This is mostly the case 

 with the tropical forests where the giants are scattered between high 

 and low trees and open glades, so arranged that the sunbeams, not- 

 withstanding the density of the vegetation, sift through to the soil 

 itself. In undergrowth, in i^ersistence of leaves, and in quantity of 

 shade, there is also every possible variation. 



The eifect of a mixed forest of deciduous trees must differ from that 

 of an evergreen forest with needle-shaped leaves, and this again from 

 forests of such trees as flourish in Australia, New Holland, and else- 

 where, whose leaves stand more vertically so that the shade bears 

 little relation to the leaflness. Such trees are found in numy ])arts 

 of the world; our own Kentucky coffee tree, is of this sort, and the 

 lack of shade under a tree of this kind in full leaf in July is always a 

 surprise. 



Again, the litter accumulating in the forest has an important influ- 

 ence on its action, and the effects of the forest must be also much modi- 

 tied by many factors which determine its condition but are not strictly 

 a part of it, such as the soil on Avhich it grows, the abundance or 

 scarcity of water, the slope of the land, the altitude above .sea level, 

 the latitude, and the prevailing degree of cloudiness. Any of these 

 peculiarities may sensibly modify not only the clinuite of the interior 

 of the forest but also the influence which the forest may exert on the 

 climate of adjacent territory. 



The literature (»f forest meteorology is already a large one. Liiffel- 

 holz-Colberg published in 1872 a catalogue of the publications on the 

 significance and importance of the forest, and since the issue of that 

 catalogue the literature of the subject has grown at a rapid rate. 

 Nearly all the publications to which he refers bear on the meteorological 

 aspects of the forest. The longer bibliographical references given by 



