A survey of limber pine (Pinus flexilis James) to determine the geographic distribution, incidence, and severity of white pine blister rust (WPBR) throughout 13 study areas in central and southeastern Wyoming and northern Colorado was conducted from 2002 to 2004. The majority (81.1%) of the 18 719 surveyed limber pines >1.37 m tall were classified as healthy, 13.5% were declining or dying from various causes, and 5.4% were dead. WPBR was present on 278 (55%) of the 504 survey plots. Incidence of the disease ranged from 0% to 100% and averaged 15.5% over all the plots and 28.0% on the infested plots. Likelihood of infection by WPBR was significantly greater for limber pines in larger diameter classes. Incidence was negatively correlated with elevation and positively correlated with geographic position, with more northerly and easterly plots having higher incidences of WPBR. Incidence varied by slope position and did not vary by aspect, slope configuration, or degree of canopy closure. The current level of infestation in central and southeastern Wyoming and northern Colorado has been attained within the past two to four decades. With time, the pathogen may spread to currently uninfested white pine populations and intensify throughout its current distribution impacting valuable ecosystems.Résumé : Un inventaire du pin flexible (Pinus flexilis James) a été réalisé de 2002 à 2004 dans 13 zones d'étude situées dans le centre et le sud-est du Wyoming et le nord du Colorado pour déterminer la répartition géographique, l'incidence et la sévérité de la rouille vésiculeuse du pin blanc (RVPB). La majorité (81,1 %) des 18 719 pins flexibles échantillonnés de plus de 1,37 m de haut ont été classés comme sains, 13,5 % dépérissaient ou étaient mourants sous l'effet de diverses causes et 5,4 % étaient morts. La RVPB était présente dans 278 (55 %) des 504 places-échantillons. L'incidence de la maladie variait de 0 % à 100 % et atteignait en moyenne 15,5 % dans l'ensemble des places-échantillons et 28,0 % dans les places-échantillons infectées. Les risques d'infection par la RVPB étaient significativement plus élevés pour les pins flexibles dans les classes de diamètre supérieures. L'incidence était négativement corrélée avec l'altitude et positivement corrélée avec la position géographique : les places-échantillons les plus au nord et les plus à l'est avaient les plus fortes incidences de RVPB. L'incidence variait selon la position de la pente mais non selon l'exposition, la configuration de la pente ou le degré de fermeture du couvert. Le niveau actuel d'infection dans le centre et le sud-est du Wyoming et le nord du Colorado a été atteint au cours des deux à quatre dernières décennies. Avec le temps, le pathogène pourrait progresser vers les populations de pin blanc non infectées et l'infection pourrait s'intensifier partout où la maladie est actuellement présente et affecter des écosystèmes de grande valeur.[Traduit par la Rédaction]

Cronartium ribicola, the introduced pathogen that causes white pine blister rust (WPBR), continues to spread to additional limber pine populations in the Southern Rocky Mountains of Colorado and Wyoming. Because WPBR can severely impact ecosystems, forecasts of its potential distribution and incidence would be useful to land managers. Site and climate data from long infested study areas in Wyoming were fit with two regression models [logistic and classification and regression trees (CART)] to determine the environmental conditions associated with the distribution of WPBR. These models were then used to map limber pine stands at risk of infestation by C. ribicola throughout Wyoming (where it has long occurred) and Colorado (where it is just becoming established). Although variables representing vegetation and landform could identify infested plots, 1-km-scale climate variables for monthly temperature and moisture were better predictors of current WPBR distribution and were available for mapping expected future distribution across the region. Of 280 485 ha where limber pine was projected to occur in Colorado, 41% was forecast by the logistic model to be at risk of infestation, and 53%, by the CART model. Of an estimated 782 229 ha in Wyoming with limber pine, the logistic model projected 61% to be at risk; CART projected 79%. Additional regression models were fit with site and climate data to predict WPBR incidence (per cent of trees infected) and intensification (incidence/age of the oldest canker). Nearly one half of the plot-to-plot variation in incidence was explained using environmental variables readily available to land managers. Although mean plot incidence increased over time, mean intensification decreased 50% per decade. This work provides managers with several tools to reduce uncertainty over the expected distribution and incidence of WPBR, but surveillance and monitoring remain prudent activities for supplementing forecasts of WPBR epidemics.

Epidemiological studies of white pine blister rust on limber pine require a temporal component to explain variations in incidence of infection and mortality. Unfortunately, it is not known how long the pathogen has been present at various sites in the central Rocky Mountains of North America. Canker age, computed from canker length and average expansion rate, can be used to estimate infestation origin and infection frequency. To investigate relationships between canker lengths and canker ages for limber pine, we collected live white pine blister rust branch and stem cankers from three locations in Wyoming and two locations in Colorado. We quantified relationships between various measures of canker length and an estimate of canker age based on dendrochronological analysis. Total branch canker length was strongly, negatively correlated (r = )0.79) with the first year of incomplete, annual ring formation (canker age). Mean longitudinal canker expansion rate was 8.4 cm year )1 for branch and stem cankers where branches distal to the canker were either dead or alive. Annual longitudinal canker expansion, however, was significantly greater on a stem or branch where the portion distal to the canker was alive (11.5 cm year )1 ) rather than dead (7.1 cm year )1 ). For branches or stems, proximal expansion rate (i.e., toward or down stem) averaged 4.9 cm year )1 . The circumferential canker expansion rate (around branch or stem) was greater for stem cankers (8.3 cm year )1 ) than for branch cankers (6.2 cm year )1 ). Additional site and host tree covariates did not improve prediction of canker age. Two simple linear equations were developed to estimate a canker age from total length of a canker with the distal portion either alive or dead. An appropriate sample of canker ages can be used to determine how long a limber pine stand has been infested with white pine blister rust and how frequently infections have occurred.

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Thirty discrete black stain root disease (BSRD) mortality centers, caused by Leptographium wageneri (Kendr.) Wingf. var. wageneri, were examined in 1999 to determine the effects of BSRD on the composition and structure of piñon–juniper woodlands at the tree, shrub, and herbaceous plant levels and on tree-seedling regeneration. In these recently formed mortality centers, the majority (68%) of all piñon (Pinus edulis Engelm.) was dead, 76% of piñon were affected by BSRD, and 70% had evidence of piñon ips bark beetle (Ips confusus Leconte) attack. BSRD mortality centers had a mean area of 0.28 ha (range 0.07 to 0.63 ha). There were no statistically significant (p > 0.05) differences in shrub composition, cover, or diversity between mortality centers and the unaffected surrounding woodlands. Herbaceous plant cover was significantly greater (p < 0.001) within mortality centers and frequency responses were species specific. There were no significant (p = 0.629) differences in the density of piñon regeneration inside mortality centers compared with outside mortality centers. The pathogen was regularly isolated from piñon roots dead for 5–8 years and once from a root dead for 16 years. The rate of radial expansion of mortality centers averaged 1.1 m/year (0.07 SE). The rate of mortality center expansion was not significantly (p > 0.05) related to available water-holding capacity, percent organic matter, pH of soils, piñon density, or any other site data recorded.

Cronartium ribicola is a non‐native, heteroecious, fungal pathogen that causes white pine blister rust (WPBR) on all white pines, including Pinus flexilis James (limber pine). The pathogen continues to move southwards and eastwards in the Rocky Mountains of Colorado and Wyoming on populations of limber pine. We examined the progression and intensification of WPBR on limber pine in recently invaded areas (<40 years) by combining historical accounts of disease occurrence with recent large‐scale monitoring projects to describe the epidemic in this region. Using epidemiological information, we provide spread rate, disease incidence, disease rate increase, severity, infection density, disease intensity, frequency of infection events and mortality for this pathosystem across 27 study areas in Wyoming and Colorado. Over the past four decades, WPBR spread through Wyoming and Colorado at 7.7–10.6 km/year. Epidemiological parameters varied both within and between mountain ranges. Sites were classified into four epidemic types defined by length of time the pathogen has been present and disease incidence. Disease rate increase (increase in per cent disease incidence per year) ranged from 0% year−1 to 3.2% year−1 and varied depending on temporal scale. Average disease severity was 4.1 cankers per infected tree, and disease intensity (disease incidence × severity) averaged 112. Infection episodes occurred fairly consistently at 1‐ to 3‐year intervals at most sites, and by 2012, WPBR caused mortality of >2.5% of all limber pine trees (>1.37 m tall) surveyed. Future monitoring and restoration activities may use epidemiological information to prioritize sites for management actions in conjunction with other published models and monitoring data.

We examined the persistence of pinyon pine (Pinus edulis Engelm.) standing snags and downed logs in southwestern Colorado pinyon-juniper woodlands. The time since death of pinyon pines killed by bark beetles, black stain root disease, or unknown causes in three study areas in southwestern Colorado was determined through monitoring of permanent plots and dendrochronological crossdating methods. The structural condition and form of the trees was recorded and related to the time since death. Pinyon snags may persist for up to 25 years, with persistence of intact snags averaging 8.4 years and broken snags averaging 13.2 years. Sound logs had been dead for a mean of 9.8 years, whereas more fragmented logs had been dead for a mean of 14.4 years. Extremely fragmented trees had been dead for 16.2 years. There was no statistically significant difference in the time since death for snags versus logs in similar condition classes. A simplified rating system to determine the number of years dead for pinyon pine based on form and condition is provided. West. J. Appl. For. 20(4):247–252.

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