Our Llviiii^ Rt'sotirrrs — Terrestrial Ecosystems 



229 



northern range, many whitebark pine stands 

 have declined by more than QO'/r (Fig. la). The 

 most serious threat to the tree is from white pine 

 blister rust (Cromiriiwn ribicola). a non-native 

 fungus that has defied control. Fewer than one 

 whitebark pine tree in 10.000 is rust-resistant. 

 Mortality has been rapid in areas like western 

 Montana, where 42'/f of whitebark pine trees 

 have died from the disease in the last 20 years; 

 89% of the remaining trees are infected with 

 rust (Fig. 3; Keane and Amo 1993). Although 

 drier conditions have slowed the spread of blis- 

 ter rust in whitebark pine's southern range, 

 infection rates there are increasing and large 

 die-offs are eventually expected to occur (Fig. 

 lb). 



Before fire suppression, whitebark pine 

 stands burned every 50-300 years. Under cur- 

 rent management, they will bum at 3,000-year 

 intervals. Without fire, serai whitebark pine 

 trees are replaced by shade-tolerant conifers and 

 become more vulnerable to insects and disease. 



Repercussions 



The alarming loss of whitebark pine has 

 broad repercussions: mast for wildlife is dimin- 

 ished and the number of animals the habitat can 

 support is reduced. Such results hinder gri/zly 

 bear recovery and may be catastrophic to 

 Yellowstone grizzlies for whom pine seeds are a 

 critical food. Predicted changes in whitebark 

 pine communities include the absence of refor- 

 estation of harsh sites after disturbance and the 



Whitebark pine 



■ Major subalpine corrponent 

 D Minor component 

 ■ Isolated occurrence 



Whitebark pine mortality 

 ■ 51%- 100% dead 

 @ 21% -50% dead 

 no%- 20% dead 



Whitebark pine infected with 

 blister rust 



■ 51% -100% infected 

 D 20% - 50% infected 

 Infection rate unknown for 

 rest of range. 



Fig. 1. (a) Natural distribution of wtiitebark pine (Arno and HolT 1989: Olgilvie 1990) with 

 mortality zones. Mortality level is the proportion of trees dead from all causes since presettle- 

 ment. (b) White pine blister rust infection rates in whitebark pine. Blister rust is present but 

 infection rates are unknown in Canada and the southern l_Inited States. 



lowering of treelines. In addition, stream flow 

 and timing will be altered as snowpack changes 

 with vegetation. 



Implications 



Whitebark pine will be absent as a function- 

 al community component until rust-resistant 

 strains evolve. Natural selection could be speed- 

 ed with a breeding program like that developed 



Ki'.;. 2. llr.ildiN whitebark pine stand in Yellowstone 

 Naliun.Ll I'.uk nut yet affected by the introduced disease 

 white pine blister rust. 



Fig. 3. Dead whitebark pine trees 

 in Glacier National Park. 



