27 



lings and saplings which would have produced the forest of the fu- 

 ture. In the years 1907, 1908 and 1909, 2,455 fires occurred in the 

 State of Pennsylvania, and burned over 484,987 acres. The esti- 

 mated amount of damage was almost |1,000,000. It is also esti- 

 mated that the average annual direct loss from forest fires within 

 Pennsylvania is |500,000. 



Three kinds of forest fires are usually recognized: Surface fires, 

 which burn the surface layer of leaves, grass, twigs, and some trees; 

 Ground fires , which burn through soils with abundant vegetable ma- 

 terial; and Crown fires, which burn through the crowns of trees. 



Many fires can be prevented by educating the people concerning 

 the real value and significance of the forests. Vigilant patrol dur- 

 ing the danger season, the construction of fire- towers, telephone lines, 

 roads, fire-lanes, compartment lines, and the proper disposal of com- 

 bustible material, help to minimize the fire danger. 



The damage which man does in the forest is very noticeable to his 

 fellowman, while that done by other agents often goes unnoticed. 

 Due to the development of our biological sciences in the recent past 

 we are beginning to appreciate the extent of the damage done by 

 such agents as insects and fungi. 



The organic agencies which damage the forest are plants or ani- 

 mals. The principal types of plants which do damage to the forest 

 or to the products of the forest are parasitic flowering plants, as the 

 mistletoe, and fungi which cause the decay of wood. The extent of 

 damage which fungi do to trees as well as construction timber is 

 usually underrated. They may be found upon living or dead trees, 

 stumps, logs, railroad ties, and construction timber in bridges, 

 houses and barns (Figs. 29-32). The Chestnut Bark Disease is an 

 example of a parasitic fungous disease which attacks the Chestnut 

 tree, doing enormous damage. 



Many different kinds of animals do damage to the forest. Domes- 

 tic animals, as cattle, sheep, goats, and hogs, and wild vertebrates, 

 as deer, rabbits, squirrels, mice, and beavers, are among the most im- 

 portant damaging agents. 



Next to fire, insects are the most destructive enemies of the forest. 

 They may infest young seedlings in the nursery, the fruit or seeds, 

 the twigs, the cambial bark, and the wood. They also do consider- 

 able damage by attacking the leaves. Complete defoliation is not 

 uncommon. 



The damage from inorganic agents may be in the form of wind- 

 fall, wind-break, snow-break, excessive cold, excessive heat, shifting- 

 sands, erosion, floods, and noxious gases. 



Proper protective measures can sometimes be carried out success- 

 fully by the individual, but in other cases the co-operation of the 

 nation, state, or municipality may be required. Organizations or 



