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White Pine Blister Rust in the Interior Mountain West

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White Pine Blister Rust in the Interior Mountain West White Pine Blister Rust in the Interior Mountain West Kelly Burns1, Jim Blodgett, Dave Conklin, Brian Geils, Jim Hoffman, Marcus Jackson, William Jacobi, Holly Kearns and Anna Schoettle Introduction and Rocky Mountain Regions (Colorado, Wyoming, White pine blister rust is an exotic, invasive disease South Dakota, and Nebraska), and the eastern of white, stone, and foxtail pines (also referred to as portion of the Northern Region (central Montana white pines or five-needle pines) in the genus Pinus and North Dakota) (see Fig. 2). The infection front and subgenus Strobus (Price and others 1998). lies within this region and a large portion of its Cronartium ribicola, the fungus that causes WPBR, susceptible white pine population has not been requires an alternate host - currants and gooseberries challenged by the disease. This publication provides in the genus Ribes and species of Pedicularis and some background on the high elevation hosts and Castilleja (McDonald and others 2006, Zambino and others 2007) - to complete its life cycle. White pine synthesizes current information onthe distribution blister rust was discovered in western North and impacts of white pine blister rust in these more America in 1921. It is thought that the disease was recently infested areas. A summary of current and accidentally introduced on infected eastern white ongoing efforts for managing the disease is also pine (Pinus strobus) nursery stock shipped to provided. Vancouver, BC from Europe in the early 1900s but the specific details are unclear. Since then, the disease has spread throughout the distributions of most western white pines. Although all of the North American white pine species are susceptible to white pine blister rust (Bingham 1972, Hoff and others 1980), it was once thought that the remote, dry habitats occupied by the noncommercial, high elevation white pines would not support rust establishment. Unfortunately, white pine blister rust can now be found in many of these areas. Over the past decade, members of the Central Rockies White Pine Health Working Group have collaborated to monitor the spread and establishment of white pine blister rust in the high elevation white pines of the Interior Mountain West - the broad region that encompasses USDA Forest ServiceIntermountain (Utah, Nevada, and southern Idaho), Southwestern (Arizona and New Mexico), In: Adams, J. comp. 2010. Proceedings of the 57th Western International Forest Disease Work Conference; 2009 July 20-24; Durango, CO. Forest Health Technology Enterprise Team Ft Collins, CO 1Kelly Burns, Plant Pathologist, USDA Forest Service, Rocky Mountain Region, Forest Health Figure 1. Distribution of high elevation white pine Manaagment, Lakewood Service Center, 740 Simms species that grow in the Interior Mountain West. Street, Golden, CO 80401 [email protected] 57 Hosts Limber pine is widely distributed in the west from White pines are well distributed within the forested Alberta and southeastern British Colombia to New areas of the Interior Mountain West (Fig. 1). Pine Mexico, and southeastern California with isolated hosts in this region include whitebark pine (Pinus populations in North Dakota, South Dakota, albicaulis), limber pine (P. flexilis), Rocky Nebraska, eastern Oregon, central Arizona, and southwestern California (Burns and Honkala 1990). Mountain bristlecone pine (P. aristata), Great Basin Limber pine has a very wide elevational distribution bristlecone pine (P. longaeva), and southwestern as well, ranging from 2,850 feet in North Dakota to white pine (P. strobiformis). These species grow at 12,500 feet in Colorado (Burns and Honkala 1990). high elevations and are especially important because In the Northern Rocky Mountains, limber pine of their unique ecological and cultural generally occurs at lower elevations. In the characteristics. They provide cover and regulate Southern Rocky Mountains, limber pine has a very snow and runoff on steep, rocky sites where little wide elevational range, from the grassland-forest else can grow; their seeds are an important food ecotone at 5,250 ft to the subalpine-alpine ecotone at source for corvid bird species, small rodents, grizzly 11,482 feet and everywhere in between (Schoettle bears, and other animals; and they are some of our and Rochelle 2000). Limber pine seeds are wingless oldest and largest pines. (or nearly wingless) and rely on the Clark’s nutcracker for dispersal. In contrast to whitebark Whitebark pine is widely distributed in two broad pine, limber pine cones open upon seed maturity. Its sections within western North America – from the seeds also provide food for squirrels and may Coast Range of British Columbia into the Cascade therefore affect prey populations of the Canada lynx. and Sierra Nevada Mountains and from the Limber pine tends to be one of the first species Canadian Rockies to the Middle Rocky Mountains established after fire on dry sites and can facilitate of Wyoming. Scattered outlying populations occur the establishment of other species that eventually within and around these sections. The species is a replace it on the more mesic sites. This species can major component of high elevation, timberline tolerate very harsh, exposed sites and can reach ages forests of Idaho, Montana, and western Wyoming. over 1,000 years. Infected limber pines were first The seeds of whitebark pine are large and wingless observed in central Montana in 1944 (Riley 1944), and enclosed in a cone that does not open upon southern Idaho in the 1940s (Krebill 1964), and ripening. Clark’s nutcrackers extract the seeds and central Wyoming in 1959 (USDA Forest Service serve as the primary dispersal mechanism. A number 1959, Brown 1967). of scatter-hoarding birds and small mammals contribute slightly to seed dispersal. Many species of Southwestern white pine is distributed in the wildlife, such as red squirrels and grizzly bear, rely mountains of western Texas, New Mexico, Arizona, on whitebark pine seeds as an important part of their and southwestern Colorado, but most of its diet. Blister rust-infected whitebark pines were first distribution is in Mexico. Limber pine and observed in the Coast Range of British Columbia in southwestern white pine hybridize where their 1926 and in the Northern Rocky Mountains n 1938 distributions overlap, so distribution and range (Childs and others 1938). Mortality caused by the information is somewhat unclear. The species disease is greatest in whitebark pine stands of the generally occurs as a minor component of mixed- Northern Rockies where infection levels are variable conifer and spruce-fir stands, and higher elevation but frequently greater than 70 percent (Kendall and ponderosa pine stands, but may become dominant on Keane 2001, Schwandt 2006). The incidence in the high elevation, cool sites. In New Mexico and more recently infected Greater Yellowstone Ecosystem is estimated to be 25 percent (Greater Arizona there are more than 30 geographically Yellowstone Whitebark Pine Monitoring Working isolated populations. Like limber and whitebark Group 2006). pine, southwestern white pine seeds are essentially wingless, but the seed dispersal mechanisms are not fully understood. White pine blister rust was 58 discovered on southwestern white pine for the first Impacts of White Pine Blister Rust in the time in 1990 in southern New Mexico (Hawksworth Interior Mountain West 1990). Since then, the disease has been observed in White pine blister rust impacts all phases of the the northern and western parts of the state (Conklin regeneration cycle. The disease affects trees of all and others 2009) and more recently in Arizona ages and sizes and could potentially eliminate white pines from certain ecosystems and landscapes. (M.L. Fairweather personal communication). The Young trees are especially susceptible and cone disease has not been reported on southwestern white potential is greatly impacted on infected large trees pine in Colorado, Texas, or Mexico to date. when most or all of the cone-bearing branches are killed. Although the impacts of the disease are Great Basin bristlecone pine occurs in eastern similar in the high elevation and low elevation white California, Nevada, and Utah. It grows high in the pine species, there are some important differences. mountains from 6,760 feet in Nevada up to 12,000 The white pine species of the Interior Mountain feet in California. The species has a remarkable West grow high in the mountains with broad valleys ability for surviving under adverse conditions and is separating populations - this limits gene flow and slow-growing and very long-lived. For example, changes the dynamics of disease spread. one tree in Great Basin National Park in eastern Nevada is estimated to be 4,950 years old – the It appears likely that aeciospores can disperse very oldest living single organism in the world. Even long distances in upper level air currents to eventually infect pines (Frank and others 2008). though the distribution of Great Basin bristlecone Opportunities for such long distance spread are rare pine overlaps with other susceptible white pine since climatic conditions must be favorable at both species no infected trees have been observed to date. the source location and the target location at the It is the only five-needle pine species in the United appropriate time (Frank and others 2008). States that remains uninfected. Conditions suitable for intensification are also Rocky Mountain (RM) bristlecone pine’s infrequent, but thought to be associated with large- distribution
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