Ponderosa Pine Mortality 



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Volume 

 ■ Trees 



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 100.000 s 



Year 



Ponderosa pine losses from 

 western and mountain pine 

 beetle in eastern Oregon have 

 been substantial, particularly in 



the early I 990s. Source: Cooperative 

 Aerial Survey, Oregon Department of Forestry 

 and USDA Forest Service. 



Old ponderosa pine is killed by pine beetles. West- 

 ern and mountain pine beetles have been important 

 mortality agents of ponderosa pine in pine and mixed 

 conifer stands, in connection with drought and high 

 stand densities resulting from the suppression of natural 

 fires. On the Fremont National Forest, more than 14,000 

 large pines were killed in 1992, and another 18,000 in 

 1994. Throughout eastern Oregon, losses have been 

 significant because old, yellow-barked pines are under- 

 represented across the forested landscape and the "old- 

 growth" character of mixed conifer stands is drastically 

 altered by the loss of larger overstory trees. 



Western Larch 

 The greatest threat to western larch is 

 the lack of forest disturbance — ^Fire sup- 

 pression and partial cutting maintain forest 

 floor conditions that prevent larch from suc- 

 cessfully regenerating. In the absence of dis- 

 turbance, larch stands are gradually taken 

 over by species more shade-tolerant than larch, 

 such as grand fir and Douglas-fir. Only the 

 re-introduction of fire or periodic mechanical 

 disturbance can create the proper seedbed for 

 larch. Furthermore, larch seed crops are usu- 

 ally poor because of dwarf mistletoe infections, 

 frost damage to conelets, and feeding by west- 



ern spruce budworm. 

 Seed production is thus 

 inadequate for either 

 natural regeneration or 

 nursery-grown seedlings. 



Pines 

 Distribution of pine 

 is affected by fire — ^Pon- 

 derosa pine once covered 

 large areas of the Blue 

 Mountains and the east- 

 ern Cascades that are 

 now mixed conifer for- 

 ests. Disturbance from 

 fire played a crucial role 

 in maintaining the domi- 

 nance of ponderosa pine 

 and stand health by re- 

 ducing tree densities. 

 Fire suppression in pine 

 stands results in higher 

 densities, reduced tree 

 vigor, and greater sus- 

 ceptibility to bark beetles, 

 particularly in places 

 where pine forests inter - 

 grade with desert, like 

 the southern flank of the 

 Blue Mountains. Lodge- 

 pole pine is an important 

 serai species that colo- 

 nizes disturbed sites in 

 the grand fir zone in the 

 Blue Mountains and frost 

 prone areas in central 

 Oregon. Although it is an aggressive colonizer, 

 it can be replaced by shade-tolerant species 

 such as grand fir in the absence of fire. In ar- 

 eas dominated by lodgepole pine but with in- 

 frequent fire, dwarf mistletoe has a significant 

 effect on stand vigor. 



Mountain pine beetle is still evident in 

 lodgepole pine — ^In eastern Oregon, the m,ost 

 conspicuous incidence of bark beetle activity 

 in pines has been mountain pine beetle in 

 lodgepole pine. Although outbreaks of this 

 species are infrequent — every 60 years — they 

 always kill the largest trees in the stand and 

 produce enormous quantities of fuel. In cen- 



Oregon — 37 



