Sam Cox
November 2000
 

INTRODUCTION

Whitebark pine, Pinus albicaulis, is a five-needled species which is found in alpine areas of the northern Rocky and Sierra Nevada Mountains. It is a major component in alpine ecosystems of western Montana, central Idaho and northwestern Wyoming, as well as the Cascades in central Washington. Its importance in the ecosystem is primarily from the large seeds it produces yearly which are a staple for grizzly and black bears in alpine areas in the northern Rockies. The seeds are also an important part of the diet for red squirrels, and Clark's nutcrackers (Mattson and Reinhart, 1994). Whitebark pine requires about 50 years to achieve sexual maturity and produce seeds, after which it will produce large amounts of seed for the next 200-300 years. A stand is naturally replaced about every 300 years. Whitebark pine is not shade tolerant, but is a natural climax species because of its hardiness to cold, windy conditions and above-average fire-resistance. 

Unfortunately for the white bark pine, anthropogenic activities of the last century have severely undermined its success. Fire suppression has allowed shade tolerant, fire-intolerant species such as fir and spruce to flourish and compete with whitebark pine where before they were kept in check by frequent, low intensity fires (Morgan, et al., 1994). White pine blister rust, an imported pathogen of five-needled pines, kills 97-99% of infected whitebark pines (Hoff, et al., 1994). Predictions of global warming indicate that whitebark pine will be forced out of much of its southerly range by rising temperatures and changes in precipitation patterns (Mattson and Reinhart, 1994). The tree's own slow-maturing habit means that it cannot adapt rapidly to changing conditions and will probably be out-competed by firs and spruces after ecological disturbances . 

In Montana, 14% of a 200 hectare area was dominated by whitebark pine in 1900, compared to 0% now. That same study calculated a 54% white bark pine decline (Arno, et al., 1993). Major declines of whitebark pine have occurred in the Bob Marshall Wilderness and Glacier National Park in northwestern Montana. Since 1971, whitebark pine basal area in the Bob Marhsall Wilderness has declined 20%, and the number of living trees has declined 30% each decade, primarily as a result of white pine blister rust (Keane and Morgan, 1994). Mortality of whitebark pine in Glacier National Park has exceeded 90% of infected trees, and almost 50% park-wide are dead (Kendall, 1994). The highest incidence of infection has occurred north of the Canadian-US border, although whitebark pine is a minor species there (Hoff, et al., 1994). Yellowstone National Park has been relatively free of white pine blister rust, but it is present. It is unclear if mortality there will be as extensive as it has been in more northern areas.

Management of forests over the past century has hindered rather than helped whitebark pine, as well as most forest ecosystems (Keane, et al., 1994; Monnig and Byler, 1991). Changes in procedures are necessary to alleviate pressure on this species. Understanding current pressures is prerequisite to prescribing proper management policies.
 

WHITE PINE BLISTER RUST

The biology of white pine blister rust is complex, since the fungus has multiple life stages and alternate hosts. The fungus attacks all North American five-needled pine species with close to a 100% infective rate (Table 1). Wild Ribes species serve as the alternate host. The fungus infects Ribes and produces spores which infect the needles of certain pines. The fungus mycelium grows toward the stem, where it enters the cambium and continues to spread, causing death of tissues as it progresses. It forms white aecia: spore producing fruiting bodies that stand out from the trunk and give the characteristic bubbled appearance. The fungus will progress farther each year until the trunk of the tree is girdled and dead (Agrios, 1997). 

Table 1. Infection rates among North American five-needled pines
 

White pine blister rust was introduced to western North America in 1910 on seedlings of western white pine grown in British Columbia that originated from Europe, where the rust is endemic. The disease was first noticed affecting native white pines in 1921. The first infected whitebark pine was found in 1922 in the arboretum of the University of British Columbia. The first natural whitebark pine to show infection was found in 1926 in British Columbia (Hoff, et al., 1994). 

Given the economic importance of western white pine, a major effort at control was launched by the United States Department of Agriculture. Removal of Ribes species (currants and gooseberries), the alternate host, was the primary control effort, followed by removal of infected trees and application of fungicides. The entire effort proved futile, as the fungal spores leap-frogged containment efforts and traveled hundreds of miles to infect suitable hosts. The infective range of the fungus, combined with the vast wilderness of the western US, proved too large to overcome (Monnig and Byler, 1991). By 1960, the fungus had spread throughout the natural range of whitebark pine. Mortality of whitebark pine seemed to be higher than white pine, and one study reported only one in 10,000 whitebark pines were resistant to the rust (Bingham, 1983). Hoff, et al. (1994) concluded this was due to 1) higher susceptibility of first year whitebark pine needles and 2) longer regeneration time of whitebark pine needles (5.3 years) as compared to other susceptible pines. Nevertheless, resistant individuals have been located in Idaho and Montana. This gives hope that a breeding program will be able to successfully incorporate resistance into replanted stock, much like the success with white pine. Even with resistant stock on hand, however, it will be perhaps hundreds of years before whitebark pine makes a comeback in areas where it has been removed from the ecosystem.  During this time, drastic changes to forest ecosystems are likely, and perhaps irreversible. 
 

FIRE SUPPRESSION

Fire suppression exacerbates the losses to blister rust because it allows competitors to inhibit whitebark pine regeneration. Fir and spruce will grow more quickly than pine and shade it out. Normally, fires will remove fir and spruce, but not the fire-resistant whitebark pine. Fires also retard the spread of dwarf mistletoe and mountain pine beetle, which are also damaging to whitebark pine but, in the case of the latter, not to fir or spruce. Whitebark pine regenerates more successfully on burned sites than do other conifers, but less successfully on undisturbed sites. Thus, the suppression of fire has resulted in fewer regeneration sites, more competition, and more pestilence for whitebark pine. All of this has greatly contributed to recent decline. 
 

GLOBAL WARMING

Climate change is likely to impact whitebark pine significantly over the next century. Long life span and late maturity of whitebark pine limit its ability to adjust rapidly to change. Three models showed that under current projections of a doubled CO₂ level, whitebark pine will be reduced to less than 10% of its current range in Yellowstone National Park, where it is a major component of alpine and subalpine ecosystems (Mattson and Reinhart, 1994). The warmer climate will favor less-hardy species which heretofore have been restricted to lower elevations by temperature, but will likely find more opportunities to compete with whitebark pine at higher, more rugged locations. Whitebark pine will be less successful at regeneration, and future stands are likely to be more mixed. Implications of this decline are severe, since bears in this area rely heavily on whitebark pine seeds for food year-round. 
 

MANAGEMENT POLICIES

Management options for whitebark pine are few. The least intrusive policy is to allow natural fires to burn uncontested, or strategically ignite areas to remove fire-intolerant species such as fir and spruce. This will allow whitebark pine to regenerate more successfully, as well as improve individual tree health which should result in more seed production and increased ability to fend off pathogen attack. Additionally, since whitebark pine regenerates well in burned areas, an increase in burned areas will lead to an increase in seedlings, and an increase in the odds of rust-resistant seedlings becoming established. 

A second, more costly method is to implement a plan of replanting resistant stock in the original range of whitebark pine utilizing seeds, seedlings, grafts or rooted cuttings. This method is more intrusive and more expensive, but may be required if natural regeneration fails to produce a substantial amount of resistant seedlings. Resistant stock is not yet available, but is expected to be ready for planting soon (Hoff, et al., 1994).

In the absence of fires, mechanical removal of competing conifers may be useful to establish whitebark pine stands. In clear-cut areas where potential regeneration is high, removal of fir and spruce will be mandatory if fire is excluded from the system. Since human structures have become so dispersed throughout whitebark pine's range, prescribed fire is often not an option.

Given that natural replacement of whitebark pine stands takes about 300 years, timber harvest should not exceed 3% each decade in order to avoid complete depletion of seeds (Morgan, et al., 1994). In light of the forecasted global warming and subsequent whitebark pine decline, Mattson (1992) recommends a moratorium on white bark pine harvest lest the species be wiped out completely from many areas.

NATIONAL PARK MANAGEMENT POLICIES

National Park policy is generally more restrictive than other land-use codes, and forbids intervention into natural ecosystems unless the problem is clearly man-made. Park policy is aimed at ecosystem health, not timber production. Any intervention should be congruent with natural processes (Kendall, 1994). Planting of seeds and resistant stock is usually not appropriate, but in this case it is, since the rust is an introduced pathogen. Therefore, resistant stock planting and prescribed fire may be used in conjunction with mechanical removal of competitors to allow whitebark pine to regenerate, live healthy and continue to be the climax species in fire-prone areas. However, planting resistant stock is cost-inhibitive and intrusive, and is likely to be, at best, a small component of whitebark pine conservation strategy. Also, mechanical removal is not in line with the Park Service policy of mimicking natural processes, and is expensive as well. Fire is a natural component of the white bark pine ecosystem and will serve to allow naturally-resistant whitebark pines to establish themselves free from competitors.  Prescribed fires are not very popular with the public, especially in highly visible areas of national parks. Therefore, it will be difficult to implement such a plan on a scale large enough to save whitebark pine in many areas. If too much time passes, too few whitebark pines will remain to produce the required number of seeds for natural selection of resistant seedlings to be effective.
 

CONCLUSIONS

Whitebark pine has been severely impacted by fire-suppression and white pine blister rust in the 20th century. Predicted global warming over the next hundred years will further hasten species decline. Ecosystem impacts will be severe since many species rely on whitebark pine for food. Management should focus on eliminating competitor species through prescribed fires and/or mechanical removal. Allowing natural selection to produce rust-resistant seedlings seems to be the only economically-viable way to produce enough resistant trees to replace the losses incurred up to this point. National Parks should vigorously address this problem in order to maintain natural ecosystems, and focus more on the health of the ecosystem than on tourist approval. 

REFERENCES

Agrios GN. 1997. Plant Pathology, 4th ed. Academic Press. San Diego, CA pp 378-380.

Arno SF, ED Reinhart, JH Scott. 1993. Forest Structure and landscape patterns in the subalpine  lodgepole pine types: a procedure for quantifying past and present conditions. USDA  Forst Service Report INT-294. Ogden, UT.

Bingham RT. 1983. Blister rust resistant western white pine for the Inland Empire: the story of  the first 25 years of the research and development program. Gen. Tech. Rep. INT-146.  Ogden, UT. USDA Forest Service.

Hoff RJ, SK Hagle, RG Krebill. 1994. Genetic Consequences and Research Challenges of Blister  Rust in Whitebark Pine Forests. In: Proceedings of the International Workshop on  Subalpine Stone Pines and Their Environment: The Status of Our Knowledge. USDA  Technical Repot INT-GTR-309. Ogden, UT, USA pp 118-126.

Keane RE, P Morgan. 1994. Decline of Whitebark Pie in the Bob Marshall Wilderness Complex  of Montana, USA. In: Proceedings of the International Workshop on Subalpine Stone  Pines and Their Environment: The Status of Our Knowledge. USDA Technical Report  INT-GTR-309. Ogden, UT, USA pp 245-252.

Kendall KC. 1994. Whitebark Pine Conservation in North American National Parks. In:  Proceedings of the International Workshop on Subalpine Stone Pines and Their   Environment: The Status of Our Knowledge. USDA Technical Repot INT-GTR-309.  Ogden, UT, USA pp 302-307.

Mattson DJ, DP Reinhart. 1994. Bear Use of Whitebark Pine Seeds in North America. In:  Proceedings of the International Workshop on Subalpine Stone Pines and Their Environment: The Status of Our Knowledge. USDA Technical Repot INT-GTR-309.  Ogden, UT, USA pp 212-219.

Monnig E, J Byler. 1991. Forest Health and Ecological Integrity in the Northern Rockies. USDA  Forest Service Report FPM 92-7.

Morgan P, SC Bunting, RE Keane, SF Arno. 1994. Fire Ecology of Whitebark Pine Forests of the  Northern Rocky Mountains, USA. In: Proceedings of the International Workshop on  Subalpine Stone Pines and Their Environment: The Status of Our Knowledge. USDA  Technical Repot INT-GTR-309. Ogden, UT, USA pp 136-140.