March 29, 1893.] 



Garden and Forest. 



147 



very large flowers. Sweet Peas require abundance of water 

 during the dry season and ought to be closely picked ; all 

 seed-pods, especially, being picked off, to keep them contin- 

 ually in bloom. 



Varieties of Sweet Scabious are among the most useful bor- 

 der plants grown, and are universal favorites. They are rather 

 tall and should have at least one foot of space ; the flowers 

 are aster-like, on long stems, varying in color, from white to 

 the deepest crimson. Ten-weeks Stocks for bedding and cut- 

 ting are indispensable. Dwarf Bouquet are the best for bed- 

 ding ; for cutting, the large-flowered pyramidal are to be pre- 

 ferred. Stocks had better be transplanted when small into 

 boxes or pots, from which they are more easily shifted into 

 blooming quarters ; if left in the seed-bed, crowded, until 

 large, they are established only with great ditflculty. 



The Chinese Aster, a beautiful summer and autumn flower, 

 repays good culture. The first sowings should be pricked off as 

 recommended for Stocks; subsequent ones may be made 

 thinly where the plants are intended to bloom. The Comet 

 strain, now in five or six colors, including white, I consider 

 the best for all purposes. It is comparatively dwarf in habit, 

 very early, and bears an immense number of loose flowers, 

 after the form of a Japanese Chrysanthemum. It is superior 

 to the Pagony-flowered and the Victoria, being of loose con- 

 strucdon, and does not sufl"er nearly so much from heavy 

 rains. The Pompone, Quilled and Dwarf Bouquet are general 

 favorites. 



Wellesley, Mass. -' • JJ- J^- 



The Forest. 



Notes on the Climatic Influence of Forests. 



WHILE writers on forestry and friends of the forestry 

 movement have been advocating reform in the public 

 treatment of forests on the ground of their conjectured cli- 

 matic importance, a thorough investigation of the question by 

 scientific methods and careful systematic measurements has 

 been made in Europe, where well-established forest-adminis- 

 trations rendered possible such work on an extensive scale — 

 such a scale as is necessary for conclusive results. 



The question of practical importance is not so much as to 

 the effects of the forest upon the general climate, but as to the 

 local modification of climatic condidons produced thereby. 

 We are not concerned as to whether the total rainfall over the 

 continent is increased, but whether the distribution of precipi- 

 tation in time and quantity over and near a forest-area is influ- 

 enced by its existence ; whether we or our crops feel its 

 absence or presence in our immediate neighborhood. 



We can readily understand that an effect upon climate, if 

 any, must be due, in the first place, to the mechanical obstruc- 

 tion which the forest-cover presents to the passage of air cur- 

 rents and to the action of the sun's rays upon the soil ; that it 

 must result from a difference in insolation and consequent dif- 

 ferences in temperature and evaporation over forest and field ; 

 and that this influence can become appreciable only when 

 large enough air columns of different characters areopposed to 

 each other, capable of producing local currents of air which 

 may intercommunicate the characteristics of one area to the 

 other, or else of changing the character of passing air currents. 

 The size and character of the forest-growth, its density, height, 

 situation and composition are much more important in deter- 

 mining its influence than has been hitherto supposed. It is 

 not trees, but masses of foliage, which may be effective. 



The most important contributions toward a solution of the 

 question of climatic forest-influences are the observations at 

 tliree sets of forest-meteorological stations, established in 

 Switzerland, Germany and Austria. The systems, made up of 

 double stations, one within, the other without, the forest, but 

 under similar conditions otherwise, cannot finally decide the 

 question of the climatic influence of the forest, but they may 

 furnish preliminary data, in establishing the differences be- 

 tween meteorological conditions in the forest and in the open, 

 from which finally the reaction of one upon the other may be 

 deduced with the aid of additional observations in radial sta- 

 tions, such as have been more recently established in Austria. 



The observations in the forest-meteorological stations of the 

 Canton Berne, lately published, comprise nineteen years at 

 three sets of stations, the longest systematic series of observa- 

 tions so far recorded. Only the temperature observations of 

 air, soil and tree-interior are so far published, with results 

 which permit of the following conclusions : The air tempera- 

 tures taken three metres above ground are found in the forest 

 lower for mean annual as well as mean monthly, except during 

 winter months. The difference is greater at 4 p. M. (time of 



daily maximum) than at 9 A. M., and increases as the season 

 temperature increases, reaching its maximum in July, then 

 decreasing toward fall ; in winter the air temperature in the 

 woods is nearly the same as in the open, or, at least, only 

 slightly warmer. The evergreen forest seems to exert greater 

 cooling influence than the Beech-woods. Altogether, the 

 range of temperatures through the year is from two and a half 

 to three degrees, Fahrenheit, greater in the open. 



The soil-surface in the open in summer is warmer, in win- 

 ter colder than the air; in the forest, on the contrary, the sur- 

 face temperature is always lower than the air temperature, 

 and the forest-soil shows at all depths during spring, summer 

 and autumn lower temperatures, but in winter either the same 

 or slightly warmer than the open. The greatest difference is 

 found at the surface, the Spruce-forest at Berne exhibiting the 

 greatest cooling effect to the extent of nine degrees, Fahren- 

 heit, while the warming effect in winter ranges only fronione 

 to two degrees. 



At 9 A. M. no difference was found between tempera- 

 tures breast-high and in the crown of the trees, but at 4 

 o'clock the crown shows higher temperature, except in winter, 

 when it is as cold as, or colder than, the lower parts. The 

 trees are always colder than the surrounding air and colder 

 than the air in the open, especially in summer. This may be 

 one of the factors which help to cool the air temperature in 

 the forest and possibly induce condensation of moisture- 

 laden air currents. The range of tree temperatures is smaller 

 than that of air temperatures. 



From the observafions at the German stations, sixteen in 

 number, which extend through now eighteen years, the most 

 interesting result regarding forest-influence upon rainfall may 

 be cited at the station of Lintzel. This station is situated in the 

 great Lueneburg heath, a prairie-like country, which, during 

 the existence of the stations, has been reforested, so that on an 

 area of twenty-five Square miles the following change took 

 place : 



Before reforestation. After reforestation. 



Field and meadow, 12 per cent. 10 percent. 



Heath, 85 " " 10 " " 



Forest, - - - - 3 " " (old) 80 " " 



The reforestation took place at the rate of 1,000 to 1,500 acres 

 a year at first, afterward more slowly, until 8,000 acres were 

 under forest. 



Comparing the rainfall observations with those from stations 

 outside of the forest-conditions, but near enough to be avail- 

 able for comparison, the following changes took place at Lint- 

 zel. While at first the rainfall was only about eighty per cent, 

 of that at the other stations, it increased as follows : 



1882. 1883. 1884. 1885. 1886. 1887. 1888. 

 81.3 86.3 95.2 99.8 100.6 103.7 I03-9 



So that finally it rose from a deficiency of nearly twenty per 

 cent, to an excess of nearly four percent. 



The observations at the Austrian stations cover a period of 

 eight years. These stations, of which there are three sets, are 

 radial, that is to say, there are several sets of instruments in 

 the open at varying distances and in different directions from 

 the forest, by which arrangement, it is to be hoped, not only 

 the difference of meteorological conditions, but also the 

 influence, if any, of forest-areas, may be determined. These 

 observations are especially valuable, because they have been 

 taken at various heights above the soil, and, therefore, indi- 

 cate the differences in vertical distribution of these meteoro- 

 logical factors of temperature and moisture. Comparing the 

 air temperatures of forest and field at the same height above 

 the soil, namely at sixteen, thirty-six and forty-eight feet, we find 

 in the day-time the same temperature, lower below, higher 

 above the crowns than at corresponding heights in the open, 

 while in the night the temperature in and above the crowns is 

 lower. Yet the differences are not very great. 



The absolute humidity is always greater in and above the 

 forest. This excess is smallest toward morning and reaches its 

 maximum at noon, then decreases again. The difference at 

 noon is 0.55-0.63 inches, with calm air. The relative humidity 

 at all heights and at all times is higher in the forest, the differ- 

 ence in calm weather at sixteen feet reaching as high as 

 thirteen to thirteen and a half per cent, in the mean of obser- 

 vations. At forty-eight feet it is less, yet in the hours toward 

 morning it is still ten and nine-tenths per cent, greater than 

 over the open. In regard to the humidity of the air, it is note- 

 worthy that in the forest the relative humidity increases and 

 decreases at the same time with the absolute humidity, while 

 usually in the field they have opposite progressions. This 

 leads to the conclusion that the forest is at the same time a 

 source of atmospheric water-supply and of cooling. Since in 



