220 WOOD AND FOREST. 



western forests differ radically from the eastern forests and why the 

 forest of Australasia is sharply distinct from any other forest in the 

 world. 



Any one or several of these factors, soil, moisture, heat, and light, 

 may be the determining factor in the make-up of a forest, or it may 

 be that a particular tree may survive, because of a faster rate of 

 growth, thus enabling it to overtop its fellows and cut off their light. 

 The struggle for survival is constant, and that tree survives which can 

 take the best advantage of the existent conditions. 



Besides these topographical and climatic factors which help deter- 

 mine the distribution of trees, a very important factor is the historical 

 one. For example, the only reason by which the location of the few 

 isolated groves of big trees in California can be accounted for is the 

 rise and fall of glacial sheets, which left them, as it were, islands 

 stranded in a sea of ice. As the glaciers retreated, the region gradu- 

 ally became re-forested, those trees coming up first which were best 

 able to take advantage of the conditions, whether due to the character 

 of their seeds, their tolerance, their endurance of moisture or what- 

 ever. This process is still going on and hardwoods are probably gain- 

 ing ground. 



Besides these external factors which determine the composition 

 and organic life of the forest, the trees themselves furnish an impor- 

 tant factor in their methods of reproduction. These, in general, are 

 two, (1) by sprouts, and (2) by seeds. 



(1) Most conifers have no power of sprouting. The chief ex- 

 ceptions are pitch pine and, to a remarkable degree, the redwood, 

 Fig. 67. This power, however, is common in broad-leaved trees, as 

 may be seen after a fire has swept thru second growth, hardwood 

 timber. Alfho all the young trees are killed down to the ground, the 

 young sprouts spring up from the still living roots. This may hap- 

 pen repeatedly. Coppice woods, as of chestnut and oak, which sprout 

 with great freedom, are the result of this ability. The wood is poor 

 so that it is chiefly used for fuel. 



(2) Most trees, however, are reproduced by seeds. Trees yield 

 these in great abundance, to provide for waste, nature's method. 

 Many seeds never ripen, many perish, many are eaten by animals, 

 many fall on barren ground or rocks, and many sprout, only to die. 

 The weight of seeds has much to do with their distribution. Heavy 

 seeds like acorns, chestnuts, hickory and other nuts, grow where they 



