EFFECT OF THE DROUTH ON FOREST TREES 225 



dences in the form of exudations of pitch from the holes of the beetles 

 lead to the conclusion that vigorous trees are often able to overcome 

 their enemies, and a search in the inner bark reveals the dead beetle or 

 larva "drowned" by the pitch. When the tree's vitality has been reduced 

 from any cause the tree is likely to suffer attacks by fungi or by insects 

 or by both at once, and in its low stages of vitality it may not be able 

 to overcome its enemies. 



In most portions of Nebraska drouthy conditions have prevailed dur- 

 ing several years; consequently the vitality of most trees has been re- 

 duced below normal. Disease from various sources is extraordinarily 

 common and unusually virulent. Many requests for advice are being 

 received by the forestry department and by the department of entomology 

 of the state university. If drouth of an intensity and endurance as great 

 as the one just experienced should occur during each summer for several 

 or many summers, it is not unlikely that disease would practically ex- 

 terminate our trees. But such a calamity as protracted drouths during 

 a considerable number of consecutive years, while possible, is not prob- 

 able, as human experience by white settlers in Nebraska for a half cen- 

 tury bears witness, and that such a misfortune has not occurred during 

 the past three or four centuries is evidenced by the presence of our native 

 trees. These trees have become adapted to Nebraska climate and there- 

 fore to occasional periods of summer drouth. We may look to them to 

 best survive the rigors of such seasons as recently experienced. The 

 trees imported from wetter climates would naturally be the first to feel 

 the strain of drouth here. The green ash, the bur oak, and, in the Pine 

 Ridge, the western yellow pine, and throughout the state the American 

 elm, hackberry and red cedar, among others, should, and I believe do, 

 show less distress than other only partially acclimated species. It seems, 

 however, that an unusually large number of boxelders in Lincoln have 

 succumbed to borers during the summer. In general, it may be safely 

 asserted that severe drouths reduce the vitality of trees, thus rendering 

 them more susceptible to the attacks of decay and of insects. 



SUPPRESSED TREES. 



Recently, while walking along the bluffs near the Missouri river, the 

 writer noticed many dead trees, killed since they leaved out last spring, 

 for the dried leaves were still clinging to the branches. Upon examina- 

 tion in most instances it appeared that the dead trees were suppressed 

 trees, or those overtopped by neighbors. During normal years the most 

 of these suppressed trees would have survived. Evidently the most of 

 these would die, but the drouth reduced their vitality until the endurance 

 limit was passed, and great numbers promptly succumbed. As a result, 

 then, of the drouth our natural forests and plantations have suffered the 

 loss of many of their suppressed trees. These trees do not possess the 

 vitality of the dormant trees, and when a hard season comes they are the 

 first to die. Insects and decay in this case are not necessarily present 

 or are not the immediate cause of death. The trees simply "burn up" for 



