Pinus albicaulis

Whitebark Pine trees typically begin producing cones at between 30 and 50 years old.  Therefore, three generations is at least 90 years.  From the sample surveys conducted throughout Whitebark Pine range, it is clear that Whitebark Pine populations have decreased more than 30% in the past three generations, or 90 years.  In addition, if the trends continue and threats are not mitigated we can expect to see a greater than 30% population reduction in the next three generations of Whitebark Pine.  Hence the species is listed as Vulnerable based on past and future population decline. The threats are described below.

Whitebark Pine populations have been threatened by blister rust infections since the early 1900s when the non-native fungus was introduced to North America. As predicted at that time, the fungus spread throughout the range of Whitebark Pine and is now nearly range wide. There is nearly 100% mortality in infected trees. Infection is increasing and expanding: along coastal ranges surveys’ have shown blister rust in up to 100% of trees sampled with a mean infection rate in forests sampled at 42.5%.  RockyMountain populations also range up to a 100% infection rate, with most infection rates between 29 and 82 percent.  It is expected that infection rates will increase, especially in light of the favourable conditions being created by climate change.

A more recent threat to Whitebark Pine is the Mountain Pine Beetle whose infestations are at record high levels within Whitebark Pine communities.  Although the beetle is native to North America, the habitat of Whitebark Pine has historically been too severe for outbreak populations of Mountain Pine Beetle.  Extensive modelling combined with recent observation show that the higher-than-normal levels of Mountain Pine Beetle activity in Whitebark Pine forests is a result of atypically warm temperatures brought about by global climate change.  In the Greater Yellowstone Ecosystem, a high altitude environment, Mountain Pine Beetle populations have only been recorded as present in the past 4-5 years.  Surveys in 2006 in this area indicate 77% mortality of Whitebark Pine trees >5 inches dbh from beetles (Gibson 2006).  In Northern Idaho surveys conducted in 2000 documented loss of 45% – 82% of the Whitebark Pine to beetle kill and from 33%-87% of the remaining trees were infected with blister rust (Kegley et al. 2001). The beetle infestation is a new threat and more survey work throughout the range is called for.

In addition to these two major threats, a policy of fire suppression in North America has caused a major loss of regeneration sites throughout the range of Whitebark Pine.  For example, in SW Montana, Whitebark Pine communities covered 14% of the land area around 1900, in 2001 it was reported that there were no longer stands dominated by Whitebark Pine, and stands with cone bearing trees had declined by half.  Most stands remaining in the US West are climax communities.  Fewer than 10% of the stands sampled in central Montana have any Whitebark Pine regeneration younger than fifty years old (Keane et al. 1994).

Whitebark Pine is a keystone species of the upper subalpine ecosystem and serves several important ecological functions throughout its range, such as protecting watersheds, promoting post-fire forest regeneration, and providing an important food source for wildlife. In the Greater Yellowstone Ecosystem Whitebark Pine seeds and ungulates are considered the two most important foods of the grizzly bear. Whitebark Pine has the largest seeds of all conifers in its range, having about 52% fat by weight and a supplying high-energy food source for wildlife, particularly valuable for animals during cold weather and for bears who need a source of fat for hibernation. 

Whitebark Pine is facing three major threats that are working together to reduce the population:

1. White Pine Blister Rust:  This disease specific to five-needled pines is caused by a fungus, Cronartium ribicola, which was introduced in the early 1900s. Since introduction of the fungus, blister rust has steadily spread throughout the range of Whitebark Pine and in some areas mortality has reached 90%.
   
2. Mountain Pine beetle epidemic:  This native pest, Dendroctonus ponderosae, is at record high levels within Whitebark Pine communities.  There is currently an epidemic throughout western North America and warming temperatures have allowed the beetles to move into normally protected high altitude forests.
3. Fire exclusion: Stand replacement fires provide Whitebark Pine a successional advantage over other conifers because its seeds are planted by nutcrackers throughout the burned areas. Since about 1929 fire exclusion has led to extensive successional replacement of Whitebark Pine by shade-tolerant species and in some areas sampled, there are no Whitebark Pine trees under 50 years old.