The Community of Trees 



107 



seeding from trees left standing is de- 

 pended upon. When small trees grown 

 in nurseries are planted in forests, it is 

 usually to correct some mistake in land 

 management, such as the clearing for 

 farms of land not suitable for farming 

 or the accidental burning over of for- 

 ests; or it is done to alter drastically 

 the type of forest that grew naturally. 



Agriculture tends the growing crop 

 by tilling the ground to reduce the 

 competition of weeds. In forestry, til- 

 lage is almost never used except during 

 the earliest stages when trees are raised 

 in nurseries and planted in the forest. 

 Rather, the weed trees are cut. Some- 

 times they can be used. The weeds a 

 farmer pulls are rarely useful. 



Agricultural crops are mostly an- 

 nual ; the forest crops, almost never. In 

 agriculture, one crop is removed with 

 comparatively little thought of the one 

 to follow. In forestry, there is emphatic 

 need to consider the next crop. It is 

 the chief duty of silviculture to devise 

 methods for harvesting forests in such 

 a way that a new crop will be assured 

 so that plenty of seed of the wanted 

 species will be shed on the ground and 

 conditions will be right for their germi- 

 nation and the growth of the seedlings. 



The tools of silviculture are the ax 

 and fire-fighting equipment the ax 

 to modify natural succession to man's 

 needs, and the fire-fighting equipment 

 to keep forest fires in their places. 



In order to understand more inti- 

 mately what silviculture is and to get 

 its relation to natural forest succession 

 clearer, let us go back to the com- 

 munity of trees. And to make it easier 

 let us consider specific forests. 



First, a tract of loblolly pine in the 

 Carolina Piedmont. A great deal of lob- 

 lolly pine grows in this region, but we 

 have evidence that it is not the climax 

 forest. Loblolly is intolerant of shade, 

 and the new seedlings cannot grow be- 

 neath the old trees, which change the 

 environment by shading the ground 

 and by adding moisture-holding humus 

 to it. Shady, cool, moist, humus-cov- 

 ered ground is a hard place for loblolly 

 seedlings to get started. Those condi- 



tions favor the shade-enduring hard- 

 woods, oaks, gums, and hickories. A 

 little study of surrounding areas will 

 show that loblolly is a pioneer species 

 on abandoned fields and burned-over 

 areas. Its seeds are light and winged, 

 and mature trees can seed large areas 

 in a single season. Consequently all 

 trees in a stand of loblolly are likely 

 to be about the same age. These facts 

 indicate that loblolly forests are the 

 result of disturbances in the natural 

 succession. Further proof comes from 

 the forests along the creeks where fields 

 have never been cultivated and where 

 fires burn less readily. These forests are 

 hardwoods. 



Hardwoods are evidently the climax 

 type in the Carolina Piedmont, or at 

 any rate they are a higher stage in suc- 

 cession than loblolly pine. But hard- 

 woods are not what we want to grow 

 there. Pine is better suited to a greater 

 number of products than hardwood, 

 and it grows faster. So the job of 

 silviculture is to devise a method of har- 

 vesting our tract of loblolly to get an- 

 other crop of the same species started. 



That can be done by clear cutting 

 the stand except for the trees necessary 

 to produce the seed for the next crop. 

 Clear cutting will lay the ground open 

 to the hot sun. It will dry out. Much 

 of the moisture-holding humus will 

 disappear and again conditions fa- 

 vorable to pine seedlings will prevail. 

 It is true that to perpetuate loblolly 

 pine we must push nature backward a 

 step. But consider how much further 

 back we would go to raise a crop of 

 tobacco: To do that, every vestige of 

 natural growth would be removed first 

 and later kept out by tillage. 



Another example: An acreage of 

 northern hardwoods in Michigan 

 the sugar maple, yellow birch, beech. 

 Seedlings of those species can grow in 

 the shade cast by their parents, and all 

 ages of trees, from seedlings to vet- 

 erans, grow together. Remnants of the 

 original forests evidently undisturbed 

 for many tree generations are of this 

 type. We must suppose that northern 

 hardwoods are one of the climaxes 



