WHITE PINE BLISTER RUST

The long term sustainability of high elevation ecosystems in the presence of the rust will depend on the level of genetic resistance in the populations and the ability of the trees to grow, reproduce and reforest an area after disturbance. Therefore the overarching long term goal of management is to increase the level of rust resistance in the populations. More than likely a combination of strategies will be most effective in developing, refining, and implementing effective management options to sustain high elevation white pine ecosystems in the presence of white pine blister rust. For instance, prepare the landscape before infection by creating diverse age class structure; promote natural regeneration from resistant trees after infection; and augment, if needed and available, with artificial regeneration of selected genetic resistant seedlings. Since many management strategies are currently untested, site-specific treatments are experimental at this point. Therefore, it is strongly encouraged to work closely with forest health specialists in developing and implementing treatments.

1. Preserving high value trees
   1. Pruning
   2. Chemical
2. Restoring ecosystem integrity in impacted areas
   1. Natural regeneration
   2. Artificial regeneration
3. Sustaining ecosystem integrity and preparing landscapes for infection
   1. Natural regeneration
   2. Artificial regeneration

Preserving high value trees

A high value tree may be an individual that is integral to a campground, cultural site or residential or commercial landscape or otherwise has characteristics that are deemed valuable such as resistance to other pests or pathogens, historical/cultural significance, extreme age or morphology, etc. For a tree of this type, survival of the individual is paramount and its ability to produce seeds for wildlife or reforestation is secondary. In these cases, removal of the infected portions of the tree through pruning before the disease compromises the tree may be a management option.

Other high value trees could be any individual with rust resistance. For a tree of this type, survival of the individual is paramount because of its ability to produce seeds for wildlife and reforestation in the presence of the rust. These trees should be protected from other damaging agents such as mountain pine beetle (link), wildfire (link), draft mistletoe (link), etc.

Pruning

A strategy for local short - term management of white pine blister rust in high value/use locations such as trailheads, campgrounds, cultural sites, and residential, is to prune/remove infected branches. This approach is limited; it can be used to keep individual trees alive yet it does not promote the development of rust - resistant or rust - tolerant trees on the landscape.

Pruning infected branches can prevent white pine blister rust infections from spreading into the trunk, where it will girdle and kill the tree. Another benefit of pruning lower branches is that it will increase air circulation and sunlight penetration to the lower portion of the tree; therefore decreasing the most favorable conditions for blister rust infection to occur.

As a conservation strategy, pruning is very labor intensive and may not be feasible over large areas of the landscape. It is best used to save high value individuals and is not a practical option for increasing the long term sustainability of high elevation forest stands.

Sources: 110, 109

Chemical Control

Currently there are no chemical methods to control white pine blister rust.

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Restoring ecosystem integrity in impacted areas

Restoration of impacted sites may include augmenting the impaired regeneration cycle and accelerating the establishment of rust resistant trees such that the ecosystem over time can become self sustaining in the presence of the rust. Actions can include promoting natural regeneration if the seed supply is adequate and supplementing with artificial regeneration using rust - resistant seedlings.

Promoting natural regeneration

In the early stages of infestation or in areas that have some trees with heritable rust resistance promoting natural regeneration from those resistant trees will increase the frequency of resistance on the landscape.

Natural regeneration - use of fire

High elevation white pines regenerate on disturbed sites more successfully than within intact forests; stand - replacing and mixed severity fires are the most common disturbance that promotes regeneration in these species. Widespread fire suppression has resulted in fewer regeneration sites and more competition for high elevation white pines. Some experts believe that the maintenance of native fire regimes is the single most important management action to ensure conservation of high elevation white pines.

Allowing naturally ignited fires to burn uncontested when appropriate, or strategically ignite areas to remove fire - intolerant species (spruce, fir, lodgepole) in a responsible manner may be beneficial to these ecosystems. The burned areas provide conditions suitable for successful natural regeneration of white pines. In due course, this serves to improve individual tree health resulting in more seed production and increased ability to fend off native pathogen and pest attack.

There are various prescribed fire techniques that can be implemented. Research has shown that on some sites Ribes ssp. populations proliferate after a fire and may therefore increase the blister rust hazard; researchers are studying this trade - off to help decision makers.

Sources: 97, 113

Natural Regeneration - using silvicultural thinning

Tree cutting/thinning can be used on a local scale to mimic the effects of natural disturbances or augment fuel loads for prescribed fires. There are various cutting techniques that can be adapted to specific site conditions and desired outcomes.

When human structures and infrastructure are dispersed throughout the high elevation white pine forests, prescribed or natural fire is often not a viable option. Tree cutting can be used as an alternative to recreate forest conditions that were historically common after major disturbances like fire.

Commonly, this often involves removing other conifers (fir, spruce, and lodgepole) in small patches and leaving behind cone - producing white pines. These openings are located strategically in areas where sufficient white pine seed sources exist to produce regeneration. Coincidently, these openings can also provide and improve wildlife habitat.

Sources: 111, 97, 113, 85

Supplement with Artificial regeneration

If the disease has impacted the stand such that few cones and seeds are being produced, providing regeneration opportunities may not be enough. The process of planting seedlings into an area is called artificial regeneration. Seedlings are grown in a tree nursery and transplanted into the field. Depending on the management objectives and the source of seeds to produce the seedlings, artificial regeneration can be used to:

1. Speed reforestation after a disturbance,
2. Change the species composition of the next generation of trees on that land, and/or
3. Improve the quality of the existing species on the land.

In the case of blister rust and high elevation white pines, the first and third objectives would apply. Through silviculture (thinning or prescribed fire) openings in the forest can be created and the improved seedling stock (with resistance to the rust) can be outplanted.

Sites occupied by high elevation white pines are often dry and harsh and it may prove difficult to achieve successful establishment of transplanted seedlings.

However, this strategy may be the only option in situations where mortality from rust is high and natural regeneration fails to produce a substantial amount of naturally rust resistant seedlings. When there is not a sufficient rust resistant seed source, artificial regeneration is an important and vital component of a high elevation pine conservation effort.

Artificial Regeneration - Identifying improved seedling stock with rust resistance

In areas that are heavily infected with blister rust there may be individual trees that have fewer cankers than others - these trees are suspected to have resistance to the rust and are called "phenotypically resistant" or "plus" trees. If the resistance is heritable, then seedlings grown from the seed of plus trees would also have some resistance. Confirmation of heritable rust resistance can be determined through scientific study and screening and would further increase their value. Seed from plus trees in the field can be used in direct seeding efforts or to generate seedlings for outplanting in the rust - impacted areas near the plus trees.

Once identified plus trees are high value trees and protection from other stresses may be warranted (protection from fire, mountain pine beetle, mistletoe, etc).

In areas not yet impacted, plus trees can be identified through screening of their seedlings using artificial inoculation studies. This work has begun for some species.

Artificial Regeneration - Developing improved seedling stock with rust resistance

Through the breeding program, where the pollen from one plus tree is used to fertilize the cones of another plus tree, seeds with greater resistance to the rust can be developed. The resistant seed can be grown in orchards and the seeds from those trees used for artificial regeneration. This approach has been used successfully for lower elevation white pine species; its application for high elevation white pine species may be more problematic. Some challenges include:

• Plus trees have not yet been identified for all the high elevation white pine species.
• It takes 30 - 50 years for a high elevation white pine seedling to mature to produce a cone.

Efforts have begun in this area.

Sources: 1, 112, 113, 115, 85

Artificial Regeneration - Seed collection

Seed collection supports several strategies used in managing the threat from white pine blister rust. Cones and seeds are collected from healthy high elevation white pines for planting, gene conservation (ex situ collections), and rust - resistance screening programs.

Seed collections require effort and skill and should be taken on by professionals with the necessary resources and knowledge of cone biology and the collection planning process. Poor planning can lead to injury to the tree, cones, or collector. Choosing regions and individual trees to collect seed from must be done carefully. The valuable seeds that are collected must be stored under environmentally controlled conditions to retain viability for future applications.

Sources: 112

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Sustaining ecosystem integrity and preparing landscapes for infection

We now know that extreme site conditions and high elevation do not reduce the susceptibility of high elevation white pines to threats like white pine blister rust. Some areas already demonstrate the devastating potential of these threats to alter the landscape. In other locations the threats are still at low levels or not yet present. In the later case, proactive strategies may help to increase overall health and resilience in these forests and mitigate impacts once the pathogen invades.

The primary objective of proactive management is to prepare the landscape to accelerate the establishment of rust resistant trees upon infection and sustaining ecosystem function during the process.

In order to develop proactive management options it is critical to collect and integrate information from many disciplines. For instance, information is needed on pathology, genetics and ecology of both the rust and the pines. Even though much information is still lacking, using what we do know and striving to collect new information will help in devising strategies to sustain white pine ecosystem function and maintain the species existing distribution.

Promote natural regeneration

Creating small regeneration sites, using fire or silviculture, before the rust arrives will result in mosaic of patches - the undisturbed areas would sustain ecosystem function and the opened areas provide the young trees for efficient rust - resistance selection upon invasion of white pine blister rust. The age - class diversity on the landscape will promote early identification and selection of rust resistant trees that are well adapted (native) to the site. Supplementing natural regeneration with artificial regeneration using rust - resistant seedlings, if available, would further advance the goals. Silviculture and/or fire can be used to generate the regeneration sites, as described in the former section.

Archiving genetic diversity

The highly selective mortality caused by white pine blister rust may reduce genetic diversity within the pine species - this effect is called a genetic bottleneck. Archiving seeds and pollen from population before the rust invades will preserve the diversity for future use in breeding programs or conservation projects.

Sources: 1, 112

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