Kelly S. Burns

Distribution of Ribes, an alternate host of white pine blister rust, in Colorado and Wyoming

Abstract Ribes (currants and gooseberries) are alternate hosts for Cronartium ribicola, the invasive fungus that causes blister rust of white pines (Pinus, subgenus Strobus) in the Rocky Mountain region of Colorado and Wyoming. The location, species, and density of Ribes can affect the spread and impact of this potentially serious forest disease. We assessed the distribution and density of Ribes growing near white pine stands for 15 study areas in Colorado and Wyoming with 1258 survey plots of two types, an intensive white pine/Ribes survey and an extensive Ribes survey. Species present, total numbers of stems and bushes, average number of stems per bush, and average stem length were recorded. Various Ribes species were present in all study areas across a range of elevations. The most frequent and common species were R. cereum, R. inerme, R. lacustre, and R. montigenum. Densities and probabilities of occurrence were related to site variables and varied by Ribes species. The most common predictive variables included type of dominant overstory, elevation, and general plot classification such as riparian area. The predictive information provided can be utilized by tree health specialists for risk rating of forests and in planning white pine blister rust mitigation projects. We expect that other areas in Colorado and Wyoming with similar site characteristics will have similar distributions and densities of Ribes and thus have similar risks to white pine blister rust.

Restoration planting options for limber pine (Pinus flexilis James) in the Southern Rocky Mountains1

Abstract Limber pine Pinus flexilis James populations in the southern Rocky Mountains are threatened by the combined impacts of mountain pine beetles and white pine blister rust. To develop restoration planting methods, six P. flexilis seedling planting trial sites were installed along a geographic gradient from southern Wyoming to southern Colorado. Experimental treatments included: high or low overstory canopy density from existing trees, presence/absence of a nurse object, and presence/absence of hydrogel. Of the P. flexilis seedlings planted, 72% were alive after four growing seasons. There were interactions between nurse object, seedling height at planting, and percent canopy cover that affected the number of healthy seedlings. Denser canopy cover was positively correlated with healthier planted seedlings and hydrogels had no effect. Nurse objects promoted healthier seedlings, particularly when canopy cover was low (0–50% cover), and the specific orientation to the nurse object affected seedling health under all levels of canopy cover. In conclusion, for best growth and survival in the first four years after planting, P. flexilis seedlings should be planted under an overstory canopy and on the north or west side of a nurse object, particularly if the canopy cover is low or absent.

Regeneration for resilience framework to support regeneration decisions for species with populations at risk of extirpation by white pine blister rust

Natural forests are increasingly invaded by nonnative pests and pathogens that threaten host species with population extirpation and cascading ecological impacts. The regeneration for resilience (R4R) framework provides a decision structure to prioritize limited resources and utilize artificial and natural regeneration management to offer the best likelihood of success in positioning stands and landscapes to support multi-generational self-sustaining host populations in the presence of the nonnative invader by (1) increasing host population size to offset invader-caused mortality, (2) increasing the frequency of genetic resistance traits in host populations in habitats that enable their expression and durability to retard future mortality and facilitate population sustainability and recovery, and (3) maintain host genetic diversity, adaptive capacity, and population connectivity. This application is designed for conditions where the nonnative invader is expected to be a persistent threat, the host species naturally has some genetic resistance to the invasive species, and the forest host populations are integral to support valued ecosystem processes and services. The R4R framework has been developed for application in high elevation five-needle pine ecosystems of North America impacted and threatened by the nonnative pathogen Cronartium ribicola that causes the lethal disease white pine blister rust (WPBR). Several examples using the R4R framework to integrate information on current forest condition, WPBR risk or hazard, genetic resistance to WPBR, and host population dynamics and silvics to prioritize areas and design interventions are discussed. Effective management of forest regeneration dynamics can increase forest resilience and adaptive capacity to mitigate impacts of invasive species.