77" 



THE TROPICAL AGRICULTURIST. 



[May I, 1886, 



perfectly white again ; a small piece of the leaf or 6talk, 

 boilod with ftu old fowl or tough piece of meat, makes 

 it quite teuder. — Journal of the Society ft/" Arts. 



THE INFLUENCE OF FORESTS 

 CLIMATE. 



ON 



The third Dumber of I'rtermatm's MitllicUnngeii for 

 this yrar contains an article by Herr A. Woeikof on 

 the inlhience of forestK on climate. The commence- 

 ment of a scientific investigation of this subject was 

 made when the Bavarian fore.st meteorological stations 

 were established, and when Prussia, Alsace-Lorraine, 

 France, Switzerland, and Italy followed the example. 

 As a general rule it jnay he. laid down that in the 

 warm seasons, as between forests and places close at 

 hand which are treeless (1) the temperatures uf the 

 earth ami air are lower in the former, (li) their vari- 

 ations are less, (3) the relative humidity is greater. 

 After examining observations as to evaporations, Herr 

 Woeikof states that the influence of forests in dimin- 

 ishing evaporation from water and the soil is so great 

 that it cannot be accounted for alnne by the lower 

 temperature of the hot months, the greater humidity, 

 or even by the shade. An important influence, which 

 lias hitherto been but little appreciated, is the pro- 

 tection from the wind afforded by the trees, and this 

 the writer regards as more important than all the 

 others togethi'r in reducing the degree of evaporation. 

 With regard to the influence of forests on rain and 

 snowfall, there is as yet only a single series of observ- 

 ations supplying comparative statistics, and extending 

 over a sutficiently long period. These were taken in 

 the neighbourhood of Naucy, and they show an im- 

 portant iufluerce of forests in increasing the rainfall. 

 It might appear that the effect of forests on rain in 

 the climate of Central Europe in winter would be 

 small, for the difference between the temperature and 

 humidity of the forest and the open is very little, 

 and the quantity of moisture in the atmosphere is 

 small. But the observations show that it is at this 

 time of the year that forests get much more rain. 

 This the writer attributes to the clouds being lower, 

 the resistance which the forest offers to the move- 

 ment of the air, and to the moist west wind. Forests 

 retain rain by undergrowths of grass, moss, &c., much 

 better than open ground, and let water oif superficially 

 only after a heavy rainfall ; the remainder filters up- 

 wards slowly, and much of it is used for the evaporation 

 of the trees. Although forests, especially thick, luxu- 

 riant forests, cannot exist without certain supplies 

 of moisture, yet it is the same to them when the 

 supplies come, for they retain what they get and use 

 it over a long period. One example of this is the 

 Lenkoran forest on the west coast of the Caspian, 

 where the vegetation is more luxuriant than in any 

 other part of Europe, yet very little rain falls in 

 summer, but the rainfall in autumn and winter is 

 great. The water is stored up by the forest, and is 

 used in evaporation during the heat of summer. Humid- 

 ity of the atmosphere, however, is not inconsistent 

 with a high temperature, as the Ked .Sea shows ; 

 but in forests the humidity is due to the evaporation 

 of the leaves — in other words, to a process by which heat 

 is converted into work, and hence the coolnes.s. Herr 

 Woeikof then endeavours to ascertain the influence 

 of forests on the climatic conditions of their neigh- 

 bourhoods in the western jiarts of the Old A\'orld, 

 between the 38th and .52nd degrees N. latitude, the 

 placi'S selected being in all cases in the open. Thus 

 for the &-nd degree eight stations are taken between 

 Valentia in Ireland on the west and the Kirghiz steppes 

 on the east ; for the 50tb, Ouernsey on the west, 

 SemipalatinsU on the east, and thirteen stations, and 

 soon for each two degrees of latitude to 38". The 

 general result of the observations in fifty stations in 

 six different degrees of latitude is that in Western 

 Kurope and Asia large forests have a great influence 

 on the temperature of places near them, and that by 

 their influence the normal increase of temperature 

 u wi^ travel eastward from the Atlantic Ocean to the 



ioteriur of the coutiiwot is oot mervly iaterruptvd, 



but they give places far removed from the coast a 

 cooler summer than those actually on khe sea. A 

 striking example of this is Bosnia. An examination 

 of the statistics shows (1) that in Bosnia the summer 

 is 2''5 to 4'5 cooler than in Herzego\'ina ; (2) even 

 on the island of Lissa, in the full influence of the 

 Adriatic .Sea, the summer temperature is more than 

 a degree higher than that of Bosnia, which is separated 

 by lofty mountain rauges from the sea. Bosnia owes 

 this comparatively cool summer to its great forests, 

 while Herzegovina is almost disafforested. To sum up ; 

 forests exercise an influence on climate which does 

 not cease on their borders, but extends over a large 

 or smaller adjacent region according to the size, kind, 

 and position of forest. Hence man by afforestation 

 and disafforestation can modify the climate around 

 him ; but it is an extreme position to hold that by 

 afforestation the waste places of the earth can be 

 made fertile. There are places incapable of being 

 afforested, which would not give the necessary nourish- 

 ment to trees. — Xature. 



TIMBERS OF UPPEB ASSAM. 



It will be easily understood that in a country where 

 the temperature of the plains and low hills never falls 

 below 45 degrees F., and never rises above lUO degrees 

 F., with an average rainfall of 120 inches a year, veget- 

 ation cannot but be of the most luxuriant character 

 and extreme variation. In fact, one of the characteristics 

 of Upper Assam is its interminable jungles constituted 

 in places by thick forests of colossal trees, and in others 

 by impenetrable cane or bamboo groves. As a rule, 

 cane jungle will grow in swampy ground where water 

 lodges for several months, and sometimes all the year 

 round. Bamboo jungle will grow in low lands flooded 

 occasionally, but where the water does not remain for 

 any length of time. Forest jungle generally grows in 

 dry soil, and one or other of any special trees seems to 

 prevail according to the different altitude of the ground, 

 or perhaps it would be better to say according to the 

 different degrees of moisture retained by the soil. The 

 prevalence, however, of any special tree is by no means 

 strikingly apparent. In spite of favourable ground, 

 and the gregarious tendency of jiearly all forest trees, it 

 seems that a great variety will grow and flourish side 

 by side in a way which would seem quite incongruous 

 in our country. The only clear fact in these forests 

 is the total absence of certain species of trees under 

 peculiar circumstances. Thus Nahor and Makahi, as 

 will be seen hereafter, are never found in low lands, 

 especially if .subject to occasional floods, while Uriam 

 and HoIIock are never found in high, well-drained 

 lands. However, as a rule, one may sLind in one of 

 these forests surrounded by trees growing as thickly 

 as possible, and he will fimi it difticiiit to detect half- 

 R-d'>zeii trees of one species. This fact considerably 

 enhances the wild beauty of the Assam jungles, but it 

 has been up to the present time a great drawback, 

 from a mercantile point of view, to the proper utiliz- 

 ation of the tindier. For the pnrpo.se of collecting one 

 kind of t'mber it npces.sitate.s going a great distance 

 through initrodden jungle, and after havmg found and 

 cut ii^ to the smallest size, elephants are required for 

 the purpose of dragging it olt- This process, of course, 

 causes a large portion to be va.sted, which under other 

 circumstances would be very valuable. The Assam 

 Railways and Trading Company, amongst other con- 

 cessions, obtained from the Government of India, have 

 the monopoly of the timber trade for U miles along 

 each sidr of their line, which runs from Makum .lunc- 

 tion to IMar^iherita (a distance of 23 miles), and the 

 fippcinien.T on' view at the Health Esbibition c^ime from 

 these forests, wliinli extend, practically, uninterrupted- 

 ly from end to end of the al)ove-mentioned portion of 

 the line. When the Company first commenced work 

 in opening out the country, little or nothing waskaown 

 as to the re.d value of ma^iy of the timber ^, and as 

 the Company's works depended so much on thcni, they 

 had to start at the beginning, and thus acquired an amount 

 of iuforniatioa which will prove very valuable for the 

 future of the timber trade of that country, The follow* 



