1965b). Many times during late June, July, and August, on south and west aspects, min- 

 eral soil surface temperatures exceed 152° F, considered potentially lethal to very 

 young seedlings (Baker 1929). Soil moisture measured at 6-, 12-, and 18-inch depths 

 in a mulching study showed that beneath weed-free surfaces on south- and west- facing 

 slopes the wilting point was commonly exceeded at depths to which tree seedling roots 

 penetrated. The moisture deficiency accounted for mortality of some outplanted stock 

 (Hall 1971) . 



Additional causes of mortality of natural seedlings less than 3 years old are 

 fungi, cutworms, birds, rodents, deer, hail, washing, and burying by eroding soil. 

 Damping-off is frequently responsible for extensive mortality in newly emerged seedlings 

 (Foiles and Curtis 1965b), but is virtually impossible to control under forest condi- 

 tions. In plantations, apart from drought, animals--hares , gophers, and porcupines-- 

 probably account for most losses during the first 3 years, but are commonly sporadic 

 in their attacks . 



Losses After Establishment 



Logging. — Ponderosa pine advance growth occurs to some extent in nearly all stands 

 of the species. Because reproduction is so difficult to establish, damage to it must 

 be avoided. Some stand damage from logging is inescapable, but planning can lessen 

 the degree of understocking caused by it (Mowat 1940; Curtis 1955a; Barrett 1960). 

 High intensity of cut can result in significantly lower stocking of advance reproduc- 

 tion after logging. On an 838-acre experimental cutting in central Idaho, tractor 

 size, cutting method, and initial volumes varying from 10,000 to 20,000 board feet per 

 acre produced no differences in initial and postlogging stocking, but heavy cutting 

 caused significantly greater damage to the understory than light cutting (Foiles 1962) . 



Damage to young stands by logging can be reduced by (1) felling trees up or down 

 slopes on areas to be logged by jammer and angled to skid trails in areas to be cat 

 skidded; (2) felling a group of trees in one direction and, if possible, in one place; 

 (3) skidding logs by tractors at right angles to contours and down ridges wherever 

 feasible; and (4) removing all limbs on large trees before skidding to avoid raking, 

 bending, and breaking of seedlings and saplings. The number of chokers should be 

 limited to from three to five, depending on the size of the logs, to prevent the load 

 from fanning, making an unnecessarily wide skid trail, and skinning tree bases. To 

 see that these practices are observed, enlisting the interest of the woods boss and 

 crews in management objectives is far superior to relying on supervision. This 

 approach is more educational and enduring in its effects. 



Fire. --Vires are a constant threat to any forest stand. Even fast-moving surface 

 fires can wipe out the youngest age classes completely (Connaughton 1936) . They occur 

 frequently and are difficult to control in the ponderosa pine type. Fortunately, 

 State, federal, and private fire control organizations are prepared for these annual 

 emergencies with revised fire plans and the latest equipment. Management plans for 

 reproduction stands should include fire protection. 



Disease. — Diseases are potential agents of severe damage to young trees and stands. 

 Diseases that cause only occasional damage under ordinary circumstances may cause wide- 

 spread destruction under certain favorable conditions. Dwarfmistletoe is often preva- 

 lent on certain habitat types, but it can be controlled silvicultural ly with available 

 guidelines (Boyce 1961; Childs 1963; Leaphart 1963). Root-infecting fungi such as Fomes 

 annosus and Armillaria mellea cause both mortality and growth loss in young pines. 

 Most root diseases spread from the stumps of cut trees into adjacent stands; therefore, 

 these diseases may become more widespread with increasing application of thinnings. 

 E ly troderma needle cast causes considerable damage locally, and is occasionally wide- 

 spread on ponderosa pine. Unknown pathogens have been suspected of causing mortality 



