REPORT ON FORESTS. 9 



termed insolation or excessive heating by the rays of the sun 

 falling directly upon it. The influence in lessening the quan- 

 tity of water evaporated from the surface also is recognized, 

 although it is offset by the transpiration of water by the leaves 

 of the tree and drawn up by the tree from the ground-water. 

 The most important beneficial influence of the forest is as a 

 wind-break, and in reducing the sensible effects of extreme heat 

 and severe cold. The moderating and softening influences of 

 forests are known, but are not so well recognized as they ought 

 to be by students of climate and by the people generally. The 

 shelter of a narrow belt of trees or of woods against the dry 

 parching winds of summer and the cold waves of winter is not 

 only a comfort to man, but also a protection to many of the more 

 delicate forms of vegetation and to some farm crops. Hence the 

 value in an agricultural district of wood-lots which may serve as 

 wind-breaks. In sand)'^ soils high winds tend to move the loose 

 grains and to form shifting bodies of sand or dunes, which bury 

 vegetation in the march and tend to produce conditions like 

 those of a desert. Hence in a country whose surface is sandy, as 

 that of southeastern New Jersey, timber belts are necessary to 

 arrest this movement. Frequent fires have, in places, made so 

 barren a soil that this desolating dune-formation is appearing 

 and is threatening to widen its reach. 



The influence of the forest upon the stream-flow of any 

 country is mainly upon the discharge or rate of flow, and not 

 upon the total volume of water which runs off in the streams, 

 and the layer of vegetable mold or humus of the soil is in the 

 nature of a sponge, taking up the water and holding it, thereby 

 reducing the flow in the case of light rains and yielding a con- 

 stant supply after heavier rainfalls.* The study of the subject of 

 stream-flow in New Jersey points to the necessity of a forest 

 cover in order to protect the soil and prevent it being carried 

 away into the streams, and making the water turbid and filthy, 

 and in providing a bed of leaf-mold and humus to hold the water 



* The woodlands of our day are largely of coppice growth and of small trees as compared with the 

 giants of the original forest. The layer of humus was then large, due to the accumulation of decaying 

 tree-trunks and the litter of many seasons, and the more dense growth of ferns and other shade-loving 

 plants. The thicker hed of humus was ahle to hold a larger volume of water and its influence was cor- 

 respondingly greater than it is to-day, when the forest litter is scanty — perhaps the growth of a few 

 seasons only. Fires hurn over woods so frequently that there is practically no humus such as the 

 original forest had. The total area of swamps also has been reduced largely and the catchment basins 

 are now mountain-tops and hillsides, rather than valleys and swamps. 



