White Pine Blister Rust Surveys in the Sangre De Cristo and Wet Mountains of Southern Colorado

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Biological Evaluation R2-06-05

White Pine Blister Rust Surveys in the Sangre de Cristo and Wet Mountains of Southern Colorado

Photo: Anna Schoettle, RMRS

Kelly Sullivan Burns USDA Forest Service Rocky Mountain Region

February 2006 White Pine Blister Rust Surveys in the Sangre de Cristo and Wet Mountains of Southern Colorado

Biological Evaluation R2-06-05

February 2006

Prepared by:

______Kelly Sullivan Burns Forest Pathologist, Lakewood Service Center (LSC), Forest Health Management

Approved by:

______Jeffrey J. Witcosky Entomologist and Leader, LSC, Forest Health Management

and

______Frank J. Cross Group Leader, Forest Health Management

USDA Forest Service Rocky Mountain Region Renewable Resources P. O. Box 25127 Denver, CO 80225-0127

2 INTRODUCTION

White pine blister rust (WPBR), caused by the fungus Cronartium ribicola, is an exotic, invasive disease of white, stone, and foxtail pines in the subgenus Strobus. The disease was accidentally introduced into the Pacific Northwest in 1910 and since then has spread nearly throughout the range of western white pines. White pine blister rust has a complex lifecycle involving five different spore stages and an alternate host, currants and gooseberries in the genus Ribes1. Pine hosts in Region 2 include limber pine (Pinus flexilis), Rocky Mountain (RM) bristlecone pine (P. aristata), whitebark pine (P. albicaulis), and southwestern white pine (P. strobiformis). White This WPBR canker will eventually girdle pine blister rust causes cankers which result in the tree. mortality of the portion of the branch or stem above the canker. Trees weakened by blister rust become susceptible to other damaging agents such as bark beetles. White pine blister rust may significantly impact reproductive potential by killing off cone-bearing branches. Small trees are easily killed because infections generally occur close to the main stem and ultimately girdle the tree. More detailed information on WPBR biology is available on the Forest and Shade Tree Pathology website (Worrall 2006): http://www.forestpathology.org/dis_wpbr.html.

Limber and RM bristlecone pine are well distributed within the Sangre de Cristo and Wet Mountains (Biery 2003). High elevation white pines serve many important ecological functions. They provide food for wildlife, stabilize slopes, and maintain cover on harsh, rugged sites where little else could grow (Schoettle 2004b). They are some of the oldest and largest pines in the Rocky Mountain Region and are especially valued because of their unique cultural and ecological characteristics. White pine blister rust may result in greatly altered and even devastated ecosystems. For example, in heavily impacted areas, reduced post-fire reforestation and reduced sustainability of bird and wildlife species may result. On sites where limber pine is the only tree species present and mortality is high, hydrologic changes and slope instability could occur.

Rocky Mountain bristlecone pine is a high elevation species which grows on dry sites. The range of RM bristlecone pine is almost entirely within the state of Colorado, with populations extending south into northern New Mexico and a disjunct population in the San Francisco Peaks of northern Arizona. In the Sangre de Cristo and Wet Mountains, RM bristlecone pines are often found mixed with other species such as aspen (Populus tremuloides), Engelmann spruce (Picea engelmanni), limber pine, and/or ponderosa pine (Pinus ponderosa) (Biery 2003). They are commonly found on rocky sites, ridges and

1 Recently, researchers identified naturally occurring C. ribicola infections on non-Ribes species hosts including Pedicularis racemosa and Castilleja miniata (Zambino et al., In Press). This new discovery could dramatically affect our understanding of WPBR epidemiology.

3 open parks on southeast to west aspects from 9,000 to 12,000 ft in elevation. Bristlecone pine is common throughout the Sangre de Cristo Mountains and on the west side of the Wet Mountains.

Limber pine has a broad elevational range growing from below the lower treeline up to upper treeline (Schoettle 2004). Small amounts of limber pine occur in most stands in the Sangre de Cristo and Wet Mountains, but it becomes codominant near ridges and on rocky, south aspects between 8,500 and 10,000 feet in elevation (Biery 2003). Limber pine is gradually replaced by RM bristlecone pine at higher elevations and on the westward side of mountains. Limber pine is often a minor component of stands dominated by other species and is more common in the Wet Mountains where elevations are generally lower. In the Sangre de Cristo Mountains, limber pine-dominated stands are most common in the southeastern portion of the range forming an intermediate belt between lower elevation and subalpine forests (Alington 1998).

WPBR was discovered for the first time in Colorado in 1998 just below the Colorado- Wyoming border north of Red Feather Lakes (Johnson and Jacobi 2000). Presumably, the disease spread south into Colorado from Wyoming where the disease has been present for decades (Brown 1978). Other parts of Colorado had not been surveyed extensively until an Evaluation Monitoring project was initiated in 2001, Monitoring White Pine Blister Rust Spread and Establishment in the Central Rocky Mountains (J.L. Harris and J.T. Hoffman, unpublished data). Surprisingly, field crews discovered WPBR in the Sangre de Cristo and Wet Mountains of southern Colorado, nearly 200 miles from any other known infection zone. The closest outbreak area to the south is on Gallinas Peak on the Cibola National Forest in central New Mexico (Conklin 2004). Infections in southern Colorado were found primarily on limber pine, but infected RM bristlecone pines were also observed for the first time in their native range (Blodgett and Sullivan 2004a, Blodgett and Sullivan 2004b). Great Basin bristlecone pine (Pinus longaeva) is the only native North American five-needle pine that remains uninfected. The distribution of WPBR in the central Rocky Mountains is displayed in Figure 4.

It is unclear how Cronartium ribicola dispersed such a long distance. Possible theories include long distance spore dispersal in upper-level air currents or via infected nursery stock (either Ribes or white pine). Research suggests that it is likely that an isolated infestation in New Mexico is the result of a single introduction by long-distance atmospheric transport from infected areas in the Sierra Nevada Mountains (Frank and Geils, unpublished data). Atmospheric conditions capable of transporting spores were analyzed for transport capacity and then compared to dates on which surface conditions occurred that were conducive to fungal infection. Results demonstrate that necessary atmospheric conditions are common and surface conditions that coincide with these atmospheric events are rare, but do occur in the vicinity of the New Mexico infestations. It is possible that a similar situation occurred in southern Colorado.

A canker growth rate model was developed which uses maximum canker length as a surrogate for canker age allowing managers to estimate the duration of WPBR infestations in limber pine (Kearns 2005). Mean longitudinal growth rate of actively

4 growing branch cankers was 3.3 inches per year. In 2005, the USFS and Colorado State University scientists measured over 600 WPBR branch cankers along the Mosca Creek Trail in the Great Sand Dunes National Park and Preserve (GRSA) as part of a pruning study. Maximum canker length was 36 inches suggesting that the disease has been present in that valley since 1993. The longest canker observed in the Wet Mountains was 16 in (this study) signifying that the disease was introduced on the pine host around 1999.

The potential distribution of WPBR for white pines in Colorado was modeled using data from Wyoming limber pine plots, extensive Ribes plots installed throughout Wyoming and Colorado and PRISM climate data (Kearns 2005). Only the PRISM climate data were selected using classification and regression tree (CART) analyses to model the relationship between the site and climate variables and the presence or absence of rust for the state of Colorado. Important classification variables were May relative humidity, May minimum temperature, May precipitation and August minimum temperature. Results suggest that approximately 50 percent of Colorado’s white pine stands are at risk for WPBR establishment. This includes a significant portion of the Sangre de Cristo and Wet Mountains of southern Colorado. An analysis of the model and how it can be applied locally is available on the Rocky Mountains Region’s Forest Health Management website (http://www.fs.fed.us/r2/fhm/).

Objectives

In light of the new infestations in southern Colorado, a more in-depth survey was initiated in 2004 to supplement the Evaluation Monitoring survey initiated in 2001. The purpose of this study was to delimit the current geographic extent and intensity of the southern Colorado infestation, to determine the incidence of the disease on RM bristlecone pine and to establish long-term survey plots in and around the Sangre de Cristo infestation to monitor distribution, rates of spread and intensification and ecological impacts of the disease. An additional objective was to create a GIS database of recent USFS (Region 2, 3 and 4) and CSU survey locations that can be used to map the current distribution of WPBR and locate areas for future surveys and monitoring. This report provides results from all USFS Forest Health Management surveys conducted in the Sangre de Cristo and Wet Mountains of Colorado between 2003 and 2005.

METHODS

Study Area

This study was conducted in the Sangre de Cristo and Wet Mountains of south-central Colorado (Figure 2) encompassing portions of the San Carlos Ranger District of the San Isabel National Forest, the Conejos Peak Ranger District of the Rio Grande National Forest and the GRSA. The Saguache Ranger District of the Rio Grande National Forest, the Huerfano State Wildlife Area and BLM lands bordering the San Isabel National

5 Forest were visited on reconnaissance trips however no plots were installed in these areas.

Site Selection

The distribution of white pines in both mountain ranges was mapped out by querying existing USFS Rocky Mountain Resource Information System (RMRIS) and Common Vegetation Unit (CVU) vegetation datasets using ArcGIS software2. Survey sites were selected through GIS queries of vegetation datasets, advice from Forest and Park personnel and field reconnaissance. Survey locations were selected arbitrarily; we attempted to survey stands representing the variety of site conditions that occurred while covering an extensive geographic area. The occurrence of WPBR was not a selection factor. Access was very difficult in both mountain ranges, particularly the Sangres. As a result, we were limited to surveying stands that could be reached, monumented (long- term plots) and surveyed in one day. Plots were located at least 150 feet from major roads. Long-term monitoring plots were located at least 50 feet from major trails.

Survey Procedures

Survey methods were adapted from those developed by Smith and Hoffman (2000) and the Whitebark Pine Ecosystem Foundation (2004). Temporary survey plots were installed throughout the Wet Mountains while long-term monitoring plots were installed in most survey locations in the Sangre de Cristo Mountains. All long-term monitoring plots were monumented with rebar at the centerpoint of the beginning, center and end, and all white pines within the plot were tagged at breast height. Survey methods were otherwise the same in both ranges. UTM coordinates (NAD27, Zone 13) were recorded at the centerpoint of the beginning, center and end of each plot. Trees were not destructively sampled. Infected trees observed outside of plots and in areas that were not surveyed were noted and GPS coordinates were collected and used to analyze the geographic extent of the outbreaks.

Plots were belt transects, approximately 50 feet wide by 200 feet long, and were established along the slopes contour with a random starting point. Transect width and length were adjusted so that approximately 30 live trees greater than 4.5 feet tall were present in each plot and plot slope, aspect and site conditions were relatively uniform from one end of the plot to the other. Stems that forked below breast height were considered separate trees. A variable radius plot was established at the centerpoint of the beginning, center and end of each plot to collect data on stand composition. A fixed

2 Vegetation datasets available for the Rio Grande and San Isabel National Forests included Rocky Mountain Resource Inventory System (RMRIS) and Common Vegetation Unit (CVU) data. Portions of forests had recently updated datasets available (e.g. the Wet Mountains) while other portions had outdated and/or incomplete data (e.g. Sangres). We found that most of the vegetation datasets, particularly the RMRIS and older versions of CVU, grossly underestimated white pine coverage and misclassification of polygons was common.

6 radius (1/300 acre) subplot was established at these same three points to examine regeneration composition and WPBR occurrence on host trees smaller than 4.5 feet tall.

Site information collected included: elevation, slope, aspect, transect length, transect width, transect bearing, stand structure, slope position, the three most common overstory species, the three most common ground species, regeneration presence/absence, blister rust presence/absence on regeneration, maximum needle retention for the dominant white pine species on the plot, and Ribes species present in the plot and their density (0%, 1- 6%, 7-12%, 13-25%, >25%). Variables collected for each white pine within transects included: white pine species, DBH, total height, tree status (healthy, declining, dying), crown class, percent of the crown with cones, number and size of branch cankers, distance to the main stem on the most lethal branch canker, number, size, and location of stem cankers and other damages and their severities. A blister rust damage severity rating was assigned to infected trees based on the distance from the bole of the tree to the nearest (most lethal) canker (see Table 1).

Table 1. White pine blister rust damage severity codes (Smith and Hoffman 1998).

Severity code Distance from the Damage Main stem 1 > 24 inches Minor 2 6-24 inches Moderate 3 < 6 inches or on main stem Severe

Data Management and GIS Work

Field data were collected using a handheld datalogger/GPS (GeoExplorer III). All data were downloaded into an Excel file for storage. A geodatabase was created from UTM coordinates and includes summary data such as rust incidence and rust severity for each plot. These data were combined into a single geodatabase that includes all central Rockies surveys and observations completed between the years of 1995-2005. Data analysis was conducted using SAS software.

RESULTS

Ninety-two plots within the San Isabel National Forest, the Rio Grande National Forest and the GRSA were surveyed from 2003 to 2005 (Figure 2). Thirty-six plots were established in the Sangre de Cristo Mountains; twenty-six of these were monumented for long-term monitoring purposes (Figure 3). Fifty-six plots were established in the Wet Mountains. Plots ranged in size from 0.05-0.61 acres, with a mean of 0.23 acres. The

7 average length and width of transects were 202 ft and 50 ft, respectively. There was an average of 38 live limber and/or RM bristlecone pine trees per plot. Plots were located on a variety of aspects, slopes and slope positions.

Limber pine occurred on 92 percent of all plots. The most common species occurring with limber pine based on variable radius plots were bristlecone pine, aspen, Douglas-fir (Pseudotsuga menziesii), ponderosa pine, Engelmann spruce and white fir (Abies concolor). Less common associates were Rocky Mountain juniper (Juniperus scopulorum) and lodgepole pine (Pinus contorta). Bristlecone pine occurred on 44 percent of all transects. Bristlecone pine was most commonly associated with Engelmann spruce, limber pine, aspen, ponderosa pine, Douglas-fir and white fir. In both mountain ranges, limber pine occurred more commonly below 10,000 ft in elevation while bristlecone pine occurred more frequently above 10,000 ft.

Over 90 percent of all plots surveyed had white pine regeneration in them. Infected regeneration was observed in 10 percent of all plots with infected trees. Forty-one percent of all trees surveyed had cones and on average 41 percent of trees per plot had cones.

White pine blister rust is present in both mountain ranges; however the infestation is more concentrated in the Sangre de Cristo Mountains than in the Wet Mountains (Figures 2, 5 and 6). Disease intensity (proportion of infected trees per plot) in the Sangres is greatest on the west side of the range in the GRSA (Figure 5) while in the Wet Mountains disease intensity is greatest on the east side (Figure 6). The highest recorded disease intensity in both ranges was in the Wet Mountains about 5 miles west of Beulah, Colorado. White pine blister rust is currently impacting limber pine more extensively than bristlecone pine; only 1 infected bristlecone pine was observed in all plots combined. No white pine blister rust-caused mortality was observed within plots.

WPBR intensity (proportion of infected trees per plot) and plot elevation were inversely correlated (P = 0.0002). The incidence (presence or absence) of WPBR was greater in plots below 9,800 feet in elevation based on chi-square analysis (P = 0.01). The mean elevation of plots with rust was 9,233 while the mean elevation of plots with no rust was 10,066, a statistically significant difference (P=0.03).

Potentially lethal WPBR infections, including stem cankers and cankers within 6 inches of the main stem, occurred on 53 percent of all infected trees. While trees of all sizes were infected with WPBR, potentially lethal infections occurred most frequently on trees less than 6 inches in diameter (Figure 1).

Results are summarized by mountain range in the following sections.

45 Minor damage 40 Moderate damage Severe damage 35

30 ees r T

of er b 20 m u

N 15

0 < 2 “ 2”-5.9” 6”-12” >12” Diameter Class

Figure 1. White pine blister rust damage severity on infected white pines by diameter class (Minor = closest canker is more than 24 in from stem, Moderate = closest canker is between 6 and 24 in from stem, Severe = closest canker is less than 6 in from the stem or on the stem).

Sangre de Cristo Mountains

One thousand seventy-three limber pines and 432 bristlecone pines were inspected within formally surveyed plots (1,505 total). Most of these trees appeared healthy (89%) but a small portion were declining (6%) or dying (5%). Bristlecone pine was present in 61 percent of all plots and limber pine was present in 92 percent of all plots. Thirty-nine percent of all plots had only limber pine while 8 percent had only bristlecone pine; fifty- three percent had both species present. The mean elevation of all plots was 10,105 and ranged from 9,219 ft to 11,719 ft. Limber pine occurred in plots at all elevations while bristlecone pine did not occur in plots below 9,440.

Twig beetles (Pityopthorus spp.) were the most common damaging agent observed and were found on 9 percent of all trees formally surveyed; most (90%) of these trees were limber pines. White pine blister rust was the second most common damaging agent after twig beetles and was found on 8 percent of all trees. Three percent of all evaluated white pines were recently attacked by mountain pine beetles and needle cast fungi (Bifusella spp. and Elytroderma deformans) were observed on 2 percent of all trees. Other common damages included broken and dead tops, lightning scars, hail damage, and decline and dieback of unknown cause.

9 Geographic Distribution of WPBR

In the Sangre de Cristo Mountains WPBR is most common and intense in and around Mosca Pass in the Mosca Creek and May Creek drainages but the disease front extends north approximately 7 miles and south about 5 miles. The northern edge of the disease front occurs near Medano Pass where very low infection levels were observed. No infected trees were observed in the survey areas north of Medano Pass including Music Pass, South Crestone Creek, Hermit Pass, Cloverdale Basin and Hayden Pass. Similarly, very low infection levels were observed near the southern end of the disease front which lies in the Huerfano State Wildlife Area on the east side of the range and near North Arrastre Creek on the west side of the range. No infected trees were observed in the Upper Huerfano River, Zapata Creek, Holbrook Creek and Spanish Peaks survey areas. Most infected trees were observed within the GRSA and on the San Carlos Ranger District, San Isabel National Forest; however, a single infected tree was observed on the Rio Grande National Forest just south of the GRSA boundary along North Arrastre Creek and infected trees were also observed on BLM lands near the USFS boundary on North May Creek and on BLM and State lands in and around the Huerfano State Wildlife Area.

Incidence and Severity of WPBR

WPBR was observed only in the vicinity of Mosca and Medano Passes. Seventeen plots were established in the Mosca Pass area and 8 plots in the Medano Pass area. Ninety-four percent (16/17) of plots surveyed in the Mosca Pass area had infected trees in them. The incidence of the disease declines to the north near Medano Pass where only 25 percent of plots established had rust-infected trees. The mean disease intensity (percentage of infected trees per plot) of WPBR within survey plots in the Mosca Pass area was 14 percent. The highest recorded disease intensity was 56 percent and occurred along Mosca Creek on the west side of Mosca Pass within the GRSA. Disease intensity was lower in the Medano Pass area where on average only 1 percent of trees within plots were infected. The highest disease intensity in the Medano Pass area was 6 percent and occurred near Dry Lake. Considering plots with WPBR-infected trees only, average disease intensity was 14 percent and ranged from 1.2 to 56.3 percent.

Ninety-two percent of all infected trees had branch cankers and 31 percent had stem cankers. Potentially lethal infections, including stem cankers and cankers within 6 inches of the main stem, were observed on 60 percent of all infected trees that were surveyed in 2004 or later (these data were not collected in 2003). Branch cankers ranged in size from 1 to 24 inches in length and were 8.7 inches on average. The mean number of branch cankers per infected tree was 2.6 and the mean number of stem cankers per infected tree was 0.35.

The mean elevation of infested plots was 9,731 and no diseased trees were observed above 10,076 ft.

10 Ribes species present in plots, in order of abundance, included R. cereum, R. inerme and R. montigenum. Ribes species occurred in 69 percent of all plots. Although Ribes plants outside of transects were not formally surveyed, their presence was noted in every drainage visited. Spore structures (telia) typical of a Cronartium species were observed on Ribes leaves in the vicinity of all plots with WPBR; however, we were unable to positively identify the rust as C. ribicola in the field3.

Wet Mountains

One thousand four hundred ninety-nine limber pines and 484 bristlecone pines were inspected within formally surveyed plots (1,983 total). Most of these trees appeared healthy (97%) but a small portion were declining (2%) or dying (1%). Bristlecone pine was present in 24 percent of all plots and limber pine was present in 76 percent of all plots. Seventy percent of all plots had only limber pine while 7 percent had only bristlecone pine; thirteen percent had both species present. White pine blister rust was observed in 21 percent of all survey plots. The mean elevation of all plots was 9,579 and ranged from 8,040 ft to 11,684 ft. Limber pine was present in plots at all elevations while bristlecone pine was not observed below 8,800 ft.

Twig beetles were the most common damaging agent and evidence of them was observed on 9 percent of all trees examined; most (88%) of these trees were limber pine. Physical damages such as broken and dead tops were observed on 7 percent of all trees and white pine blister rust was recorded on 5 percent of all trees. Other common damages included lightning scars, hail damage, animal damage, and decline and dieback of unknown cause. Mountain pine beetle activity was observed on less than 1 percent of all surveyed trees.

Geographic Distribution of WPBR

White pine blister rust is scattered throughout the Wet Mountains with the highest disease intensity approximately 4.5 miles west of Beulah, Colorado. The most northern observation of the disease was on Holt Mountain where field crews found a single infected sapling (this is about 10 miles north of the epicenter). Five survey plots were established in the vicinity of the infected tree but no other infected trees were observed in the Holt Mountain area. The most southern observation was along the Greenhorn Trail approximately 3 miles west of Rye, Colorado and about 12 miles south of the epicenter. Again, this was a single infected tree and no other infected trees were identified in the area. Most infected trees were located east of State Highway 165. No infected trees were observed along the western slope of the range.

3 The distribution of our native pinon blister rust (Cronartium occidentale) overlaps with that of C. ribicola throughout Colorado. The two fungi look very similar macroscopically and thus are difficult to differentiate in the field.

11 Incidence and Severity of WPBR

Twenty-one percent (12/56) of all survey plots had white pine blister rust-infected trees in them. Five percent of trees per plot were infected on average. Considering infected plots only, the average percentage of infected trees per plot was 26 percent (range 2.9 to 79.2), almost twice that of the Sangres. Disease intensity was greatest east of Bishops Castle and west of the town of Beulah. One plot in this area had a disease intensity of 79 percent which was higher than what was observed in the Sangre de Cristo Mountains.

Ninety-two percent of infected trees had branch cankers while 30 percent had stem cankers. Potentially lethal infections, including stem cankers and cankers within 6 inches of the main stem, were observed on 40 percent of all infected trees. The average number of branch cankers per infected white pine was 1.7, lower than that observed in the Sangres, and the average number of stem cankers per infected white pine was 0.32. Branch cankers ranged in size from 1 inch to 16 inches in length and were 6 inches on average.

The mean elevation of infested plots was 8,690 and ranged from 8,040 to 9,311 ft.

Ribes species were present in 30 percent of all established plots; however the incidence of Ribes and the incidence of WPBR were not correlated. The most common Ribes species occurring in plots were R. cereum (15 %), R. montigenum (14%) and R. inerme (2%).

Incidence of White Pine Blister Rust on Bristlecone Pine

The distribution of white pine blister rust on bristlecone pine is concentrated within the Mosca Creek drainage in the southern portion of the Sangre de Cristo Mountains within the GRSA. No infected bristlecone pines were observed in the Wet Mountains or in areas outside of GRSA in the Sangre de Cristo Mountains; this includes both the Rio Grande and San Isabel National Forests. Bristlecone pines co-occurred with infected limber pines in half of infested plots within the Sangre de Cristo Mountains yet only 1 infected bristlecone pine was observed in all plots combined. Limber pine was the only white pine species present in all infested plots in the Wet Mountains. However, the incidence of WPBR in bristlecone pine is high along the Mosca Creek Trail within the GRSA in areas that were not formally surveyed because of the limited number of host trees and their proximity to the trail.

Blodgett and Burns (see FHM report: RCSC-13-04) reported that 75 percent (6 of 8 trees) of bristlecone pines along the Mosca Creek Trail were infected with WPBR in a 2004 survey. Region 2 Forest Health Management and Colorado State University conducted pre-treatment surveys as part of a pruning project aimed at protecting and preserving white pines along the Mosca Creek Trail and found WPBR infections on 29 percent (4/14) of bristlecone pines examined, but trees with severe infections were not

12 included in the survey so the overall incidence would be significantly higher than 29 percent (Willian R. Jacobi and Kelly Burns, unpublished data). The vast majority of infected bristlecone pines occur within 0.10 mile of the trail within the valley bottom; only 2 infected trees were observed on the hillslopes above the trail.

Generally, symptoms of WPBR were more inconspicuous on the bristlecone pines observed in this study than on infected limber pines making the disease much harder to identify, particularly in the early stages of infection. Frequently, cankers observed on bristlecone pine were less swollen and resinous and produced fewer and more sporadic aecia than what was observed on limber pine (see photo above). Because of this, it is important that surveys are conducted during peak sporulation (late May-early June) when cankers are most visible.

WPBR stem canker (left) and branch canker (right) on bristlecone pine. Note lack of swelling and resin, and sporadic aecia.

Distribution of White Pine Blister Rust in the Central Rocky Mountains (GIS Database)

A GIS database was created to display the current distribution of white pine blister rust in the central Rocky Mountains based on recent surveys by USFS Regions 2 (this study, Blodgett et al. 2005, Blodgett unpublished data, Harris and Hoffman unpublished data, Geils unpublished data), Region 3 (Conklin 2004, Conklin unpublished data), Region 4 (Smith and Hoffman 2000, Newcomb 2003, Guyon unpublished data) and Colorado State University (Kearns 2005) (Figure 4). The purpose of this database and map are to locate areas that need to be surveyed or resurveyed in the future. GIS files are available by request.

DISCUSSION

This is the first comprehensive survey of the status of limber and bristlecone pine health in the Sangre de Cristo and Wet Mountains of southern Colorado. Long-term monitoring plots were established to assess changes in the incidence and intensity of WPBR and its ecological impacts over time. WPBR is well established in both the Sangre de Cristo and Wet Mountains and because white pines and Ribes co-exist in both mountain ranges it is likely that the disease will continue to spread and intensify.

Twig beetles were the most common damaging agent in all plots Twig beetle combined. Twig beetles attack many damage on a coniferous species and generally small branch. damage small twigs and branches in Note exit holes. the lower crown. Normally these insects contribute to self pruning of shaded-out or storm-damaged branches, however, when trees become stressed during periods of drought twig beetles can kill whole trees or portions of trees and may indicate conditions suitable for increases in other bark beetle populations such as mountain pine beetle. The most prominent symptoms of twig beetles are “flagging” of terminal branches and small circular exit holes on the twigs with boring dust around the entrance hole. Twig beetle flagging may be confused with WPBR flagging. By carefully inspecting the branch symptoms the two can be easily distinguished in the field.

The incidence of the WPBR is greater on limber pine than on bristlecone pine, in fact, no infected bristlecone pines were observed in the Wet Mountains. This may be explained by the propensity for bristlecone pine to grow at higher elevations where the incidence of the disease is significantly lower. All infected bristlecone pines were observed along Mosca Creek at low elevations and in the valley bottom where climatic conditions may be more conducive to the fungus. It is also possible that bristlecone pine is less susceptible to the disease. Studies are currently underway testing the susceptibility of both tree species in greenhouse studies and preliminary results suggest that limber pine is more susceptible (Kegley and Kearns 2004).

Results suggest that ecological impacts of white pine blister rust are beginning to occur in the Sangre de Cristo and Wet Mountains. Small trees had a higher frequency of severe infections suggesting that mortality of small trees is occurring and can be expected. Small trees are particularly vulnerable to this disease because the distance the fungus needs to travel from foliage, the point where infection occurs, to the main stem is small compared to larger trees and small branches and stems are quickly girdled. Impacts to larger trees are evident as well. WPBR infections in limber and bristlecone pine occur throughout the crown (Kearns 2005, Jacobi and Burns, unpublished data). This is unlike western white pine and sugar pine in which infections tend to occur near the ground where the microclimate is more conducive for infection. The implications of this may be severe as more cone-bearing branches are girdled and killed further affecting regeneration potential.

WPBR is more widely distributed in the Wet Mountains extending approximately 20 miles from north to south as compared to an extent of about 12 miles in the Sangres. Additionally, the highest disease intensity recorded was in the Wet Mountains yet it appears that the disease has been present in the Wets for a shorter period of time based on maximum canker lengths (Kearns 2005). Spread and intensification of WPBR is strongly influenced by the distribution of hosts and microclimate. The Wet Mountains are generally lower in elevation than the Sangres and limber pine is a more common

14 component.

The incidence of WPBR is currently low in both the Sangre de Cristo and Wet Mountain ranges. It can be expected that the incidence and severity of the disease will continue to increase, and spread will occur over time. Low elevation sites will likely be more impacted than high elevations sites and climatic conditions will affect spread and intensification. The Rocky Mountain Region is currently developing a WPBR Management Guide that includes information on the biology and distribution of the disease as well as management recommendations that may reduce impacts of white pine blister rust. The management guide will be available on the Rocky Mountain Region’s Forest Health Management website (http://www.fs.fed.us/r2/fhm/) in the near future.

ACKNOWLEDGEMENTS

This project could not have been completed without the help of many others. Special thanks to Meg Halford, Michlele Laskowski, Russell Beam, Phyllis Bovin, Anna Schoettle, Bill Jacobi, Brian Geils, Mike Smith, Ed Biery and Jim Worrall. Data contributed by Jim Blodgett, Jim Hoffman, J.J. Smith, John Guyon, Dave Conklin, Dan Ryerson, and Maria Newcomb was used to develop the Central Rockies WPBR distribution map. Funding was provided by the USDA Forest Health Monitoring, Evaluation Monitoring Program.

15 REFERENCES

Alington, C. 1998. Fire history and landscape pattern in the Sangre de Cristo Mountains, Colorado (M.S. thesis, Colorado State University, Fort Collins, Colorado). 55 p. Biery, E. 2003 Common vegetation communities of the Pike and San Isabel National Forests. Unpublished report. Blodgett, J.T., Schaupp, W.C., and Long, D.F. 2005. Evaluation of white pine blister rust and mountain pine beetle on limber pine in the Bighorn National Forest. USDA Forest Service, Rocky Mountain Region, Renewable Resources. Biological Evaluation R2-05-08. 18 p. Blodgett, J.T. and Sullivan, K.F. 2004a. First report of white pine blister rust on Rocky Mountain bristlecone pine. Plant Disease 88: 311. Blodgett, J.T. and Sullivan, K.F. 2004b. Letter to the Superintendent of Great Sand Dunes National Park and Preserve. USDA Forest Service, Rocky Mountain Region, Renewable Resources. Service Trip Report RCSC-13-04. 2 p. Brown, D.H. 1978. Extension of the known distribution of Cronartium ribicola and Arceuthobium cyanocarpum on limber pine in Wyoming. Plant Disease Reporter 62: 905. Conklin, D.A. 2004. Development of the white pine blister rust outbreak in New Mexico. USDA Forest Service, Southwestern Region, Forestry and Forest Health. Biological Evaluation R3-04-01. 15 p. Draper, M.A. and Walla, J.A. 1993. First report of Cronartium ribicola in North Dakota. Plant Disease 77: 952. Geils, B.W., Conklin, D.A., and Van Arsdel, E.P. 1999. A preliminary hazard model of white pine blister rust for the Sacramento Ranger District, Lincoln National Forest. Research Note RMRS-RN-6. USDA Forest Service, Rocky Mountain Research Station: 6 p. Hawksworth, F.G. 1990. White pine blister rust in southern New Mexico. Plant Disease 74: 938. Johnson, D.W. and Jacobi, W.R. 2000. First report of white pine blister rust in Colorado. Plant Disease 84: 595. Kearns, H.S.J. 2005. White pine blister rust in the central Rocky Mountains: Modeling current status and potential impacts (Ph.D. diss., Colorado State University, Fort Collins, Colorado). 243 p. Kearns, H.S.J. and Burns, K.S. 2005. Distribution, incidence, and severity of white pine blister rust on the Medicine Bow National Forest. USDA Forest Service, Rocky Mountain Region, Renewable Resources. Biological Evaluation R2-06-01. 18 p. Kegley, A. and Kearns, H. 2004. Assessing rust resistance in limber pine seedlings: A test underway. Nutcracker Notes. Issue 7. 18 p. Lundquist, J.E., Geils, B.W., and Johnson, D.W. 1992. White pine blister rust on limber pine in South Dakota. Plant Disease 76: 538. McDonald, G.I.; Richardson, B.A.; Zambino, P.J.; Klopfenstein, N.B.; Kim, M.-S. 2006. Pedicularis and Castilleja are natural hosts of Cronartium ribicola in North America: A first report. Forest Pathology. In Press.

16 Newcomb, M. 2003. White pine blister rust, whitebark pine, and Ribes species in the Greater Yellowstone Area. (Master’s Thesis, University of Montana, Missoula, Montana). 73 p. Schoettle, A.W. 2004. Ecological roles of five-needle pines in Colorado: Potential consequences of their loss. In: Sniezko, Richard; Samman, Safiya; Schlarbaum, Scot; Kriebel, Howard. Eds. Breeding and genetic resources of five-needle pines: growth adaptability and pest resistance. 2001 July 24-25; Medford, OR. IUFRO Working Party 2.02.15. Proceedings RMRS-P-32. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. Pp. 124-135. Smith, J.P. and Hoffman, J.T. 2000. Status of white pine blister rust in the Intermountain West. Western North American Naturalist 60: 165-179. Van Arsdel, E.P. and B.W. Geils. 2004. The Ribes of Colorado and New Mexico and their rust fungi. FHTET-04-13. Fort Collins, Colorado: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, 32 p. Worrall, J. 2006. Forest and Shade Tree Pathology. Online textbook: www.forestpathology.org.

Figure 2. Location of white pine survey sites and the distribution of white pine blister rust in the Sangre de Cristo and Wet Mountains, Colorado.

Figure 3. Location of 26 long-term monitoring plots in the Sangre de Cristo Mountains.

Figure 4. Distribution of white pine blister rust in the central Rocky Mountains based on over 1000 surveys conducted between 1997 and 2005 by USFS Region 2 (this study, Blodgett et al. 2005, Blodgett unpublished data, Harris and Hoffman unpublished data, Geils unpublished data), Region 3 (Conklin 2004, Conklin unpublished data), Region 4 (Smith and Hoffman 2000, Newcomb 2003, Guyon unpublished data) and Colorado State University (Kearns 2005).

Figure 5. Close-up of the white pine blister rust outbreak area in the Sangre de Cristo Mountains showing the outbreak extent and intensity (percentage of infected trees per plot).

Figure 6. White pine blister rust distribution and intensity in the Wet Mountains.