40 LOCALITY AND FOHEST VKOETATION. 



it is capal)k' of holding ti large (juantity of water, which 

 it gradually gives up to the lower layers of the soil ; it 

 loosens too firm a soil, and gives somewhat more consistency 

 to a soil which hy itself is too porous ; finally it moderates 

 the extremes of cold and heat. The poorer a soil the more 

 important is the preservation of tlie humus, provided it is 

 not acid. 



5. Summarji. 



Summarising all the demands which forest trees make on 

 the soil, it may he said that all species like a soil M-hich is 

 minerally rich, deep, porous, fresh, warm and rich in humus, 

 such as a mild loam with a good layer of humus. Some 

 species find the necessary conditions more on one class of soil 

 than on another ; for instance, oak, beech, ash, elm, maple, 

 and Austrian pine, like a certain quantity of lime in the soil, 

 probably less on account of its chemical composition than of 

 the physical qualities which an admixture of lime produces. 

 ]\rost coniferous trees, on the other hand, are more frequently 

 found on loamy and sandy soils. 



Though all trees like a good fertile soil, the several species 

 differ considerably as to the minimum of fertility on which 

 they can thrive ; that is to say, some are more exacting in 

 their demands than others. In this respect the following 

 scale is suggested : — 



Least €.ractiii;i air .- Austrian pine, Scotch pine, Weymouth 

 pine, birch, poplars, tree willows, mountain ash, acacia, 

 mountain pine, white alder. 



Moderately exactimi are : Spruce, Cembran pine, larch, 

 common alder, lime, osiers, horse chestnut, hazel, 

 hornbeam, Norway maple, Douglas fir. 



Most cxactinfi are : Silver lir, beech, sweet chestnut, sessile 

 oak, sycamore, ash, elm, and pedunculate oak. 



It will be observed that the valuable broad-leaved species 

 are, on the whole, more exacting than the soft broad-leaved 

 species and the conifers. 



