intercept more rainfall than open canopies and coniferous trees intercept more 

 than deciduous trees. 



During an average growing season about 80% to 90% of the incident 

 precipitation that falls on a forest reaches the ground (Likens et al. 1977). 

 Stemflow averages about 5% of the incident precipitation, although it may be 

 as high as 107o to 16% for smooth-barked species (beech) or as low as 1% for 

 rough-barked species (sugar maple; Horton 1919; and Geiger 1965). Much of the 

 water reaching the ground is held in the soil by organic matter, absorbed in 

 the tree roots and transpired through the leaves. About 607o of the rain 

 falling on a deciduous forest in New Hampshire becomes runoff. The remainder 

 is either evaporated or transpired. Following deforestation, streamflow may 

 increase 25% to 40%. This not only affects the water supply in the soil but 

 also causes increased loss of nutrients and soil particles as well (see 

 "Logging Effects" below). 



Soils 



Forest soils consist of four basic layers (also called horizons). The most 

 important of these ecologically is the organic layer, or forest floor, which 

 consists of fresh or partially decomposed organic matter. Below this is the A 

 horizon, which consists of mineral soil to which organic matter has been added 

 by leaching and mixing and from which clay, iron, and aluminum have been 

 removed by leaching. The B horizon has concentrations of clay, iron, 

 aluminum, and humus leached from the A horizon. Finally, the C horizon 

 consists of weathered material, which may or may not resemble the bedrock 

 (depending upon whether or not it has been transported by water, glaciers, or 

 wind) . 



The formation of soils under Maine's softwood stands is strongly influenced by 

 the acidity of the foliage. As a result of this acidity the main decomposer 

 organisms are fungi, which also produce acid and depress the activity of soil 

 organisms (see "Decomposers" above). Slow decomposition and poor mixing of 

 the organic matter into the soil results in large accumulations of litter, 

 which rest on top of the mineral horizons. These are the so-called "mor" 

 soils. The mineral soil is also affected by the acidity, which causes a 

 greater leaching of clay, organic matter, iron, and aluminum from the A 

 horizon, which is deposited in the B horizon; a process known as 

 "podzolization." 



Under hardwood stands the lower acidity of the litter results in an organic 

 layer formed under different circumstances. Bacteria replace fungi as the 

 major decomposer organisms and animal activity, which is closely tied to 

 bacterial activity, increases and nitrification is accelerated. Decomposition 

 is rapid and much of the organic matter is rapidly and thoroughly mixed with 

 the top layers of mineral soil by soil invertebrates and through leaching, so 

 that only a thin layer of litter rests on top of the soil. These are the so- 

 called "mull" soils. Organic matter content of the mineral soil is higher 

 than in softwood stands and leaching of elements is reduced somewhat. 



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