322 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1939 



but make the effort. Enrichment instead of depletion of environment 

 should be his conscious goal; and when that ideal steadily prevails, 

 there will be a different, a far more satisfactory tale to tell of man's 

 progress in getting along with nature. 



The phrase "balance of nature" admittedly is a figure of speech, 

 but it is a justifiable one. Balances always tip up and down before 

 they equalize. The balance of nature is such a tipping balance 

 because all animal and plant populations are ever fluctuating. But 

 just as truly as does a weighing balance, that of nature seeks 

 equilibrium. 



This is no more difficult to understand than if the grass is scanty 

 here and lush yonder, grazing animals will feed there; automatic 

 equalization takes place at once. If sumac bushes along the edge of 

 the woodlot are shaded out, cottontails, which feed so much on their 

 bark, may have to leave the dying thickets and come perchance to a 

 hedge near the garden where they may do damage. If mice in grass- 

 land are killed by burning, weasels that would prefer to feed upon 

 them may be forced to look elsewhere for food, possibly in the chicken- 

 yard. If some isolated, densely branched, and prickly trees, as thorn- 

 apples or red haws, are preserved or grown, kingbirds will build 

 their nests in them and from these airy castles harass crows, hawks, 

 and buzzards, so that they no longer can do as they please ; the king- 

 birds will also consume thousands of insects during the summer. 



The operations of nature's balance are going on before our eyes all 

 the time. To realize it we need only to take a little thought as to 

 causes and effects. Everything that happens has a cause and pro- 

 duces an effect, and these effects in turn become causes. The far- 

 reaching effects of a hard winter or of a drought are familiar 

 examples. As a result of such climatic severities, trees may die at 

 once or be so injured that they succumb later. Every tree that perishes 

 has been host to many kinds of insects that must then find another 

 home or die. The insect populations have regularly paid an endur- 

 able toll to various predators and parasites. These must now levy 

 their tax elsewhere or cease tO' exist. The trees that die have shaded 

 the ground; now the sun strikes through their leafless branches 

 stimulating to rapid growth plants previously suppressed and seeds 

 that have been waiting, possibly years, for this opportunity to sprout, 

 grow, and reproduce their kind. 



Each new thing attracts a company of dependents, so that under 

 the dead tree a plant and animal society very different from that 

 previously dominant may come to rule. The lifeless bole and 

 branches themselves provide homes and food for fungi, insects, and 

 other organisms that could not successfully attack the tree in life. 

 Each being in the association depends upon others, and prepares the 



