Conifers at the Crossroads
by Renee Galeano-Popp

It’s a long story. Some say it all started with the colonists and the Pine Tree Riot of 1772 in New England. But first let’s talk about white pines. White pines are in the Strobus subgenus of Pinus and are characteristically 5-needled. White pines include Bristlecone (P. aristata), Limber (P. flexilis), Southwestern White (P. strobiformis) and Whitebark (P. albicaulis) in the Rockies.

Eastern White Pine (P. strobus) is reported to be the tallest tree in eastern North America with pre-colonial estimates at around 230 ft. (Cox, 2003). Diameters have been reported as great as 5 ft. It was highly valued by the colonists who used it heavily for constructing their towns, villages and even exporting it to far away countries. They sent boatloads (50 trees at a time) back to England where the King had them used for masts on ships of the Royal Navy.

The King prized them so much that he had laws passed in the colonies reserving all eastern white pines over 12 inches diameter to be marked for use solely by the king. The colonists responded with defiance, arrests and widespread protest cuttings of pines. It was the Pine Tree Riots and skirmishes like it that eventually led to the Revolutionary War. In fact, the first flag flown by the colonists against the British was the Pine Tree Flag (Murrow, 2013). When all was said and done, eastern white pine forests paid a high price.

Enter the fungus White Pine Blister Rust (Cronartium ribicola) (WPBR). As a rust, it has a complex life cycle involving an obligate alternate host. The alternate host for WPBR is Ribes (gooseberries, currants) and just about any Ribes species will do. Recent studies have also found that paintbrushes (Castilleja spp.) and louseworts (Pedicularis spp.) may also serve as alternate hosts (USFS, Undated). WPBR is believed to be native to Asia and was first detected and described from western Russia in 1856 (Hummer, 2000). Once a North American white pine is infected, it may take some time but most will die of the disease. Outbreaks were noted in England on seedlings that had been brought from North America for cultivation and also in nurseries in Germany.

By the mid-1800s, the demand for eastern white pine lumber and the improvement of logging equipment had accelerated the regional depletion of the forests. A premium was placed on nursery stock. Tariffs were removed and because there was no visible sign of disease, large numbers of white pine seedlings were imported to the U.S. for reforestation (Hummer, 2000). By the mid-1890’s and early 1900’s signs of infection became visible. The newly formed U.S. Forest Service recorded that several million infected seedlings from Germany had been shipped to more than 226 locations here in the U.S (Hummer 2000).

At around the same time (1910) a shipment of eastern white pines from Europe was received in Vancouver, Canada (Hummer, 2000). The rust was identified there in 1921 and over the next 20 years it had spread through much of the western U.S.

The earliest strategy to combat this deadly disease was to eradicate Ribes, develop a public awareness campaign and to place quarantines in high value areas where Ribes plantings were then prohibited. Enter the Civilian Conservation Corps. The first blister rust camp was established in Idaho in 1924. Men were commissioned to dig out or spray herbicide on Ribes plants. Fungicides were added in 1957 but the program ended in 1967 and left management of the situation to “natural factors”. Certain areas, such as the northeast, reportedly now have few wild Ribes as a result.

WPBR has been known in the Yellowstone area since the 1940’s (Newcomb and Six, 2001). By the 1990’s, WPBR was found in Nevada, New Mexico and South Dakota. In 1998, it was confirmed in northern Colorado around Red Feather Lakes (Hummer, 2000). As of this writing, this non-native disease has become a resident in 38 states.

The threats posed by WPBR are direct, indirect and cumulative. The disease directly kills trees. Parts of the west have seen mortality rates reach more than 90% in some areas. In Glacier National Park, white pine blister rust has killed 44% of the whitebark pine trees. According to published sources, 75% of Glacier’s remaining whitebark pine trees are expected to die within the next 20 years (USDI-NPS, 2006).

Indirect effects result from the loss of vigor and decreased seed production that support the biodiversity of the high elevation Rocky Mountains. Grizzly bears depend on whitebark pine seeds and species such as Clark’s nutcrackers and red squirrels are more widespread examples. Scientists refer to the direct and indirect effects of WPBR as having a cascading effect because they affect so many trophic levels in the ecosystem.

Cumulative impacts are also at play in this scenario. Here we look at the one-two punch. Mountain Pine Beetles (MPB) kill mature trees and they do it very quickly. WPBR will kill mature trees slowly but can decimate seedlings very quickly. Not only does this result in reduced seed production, MPB can kill the few rust resistant trees that might be present in an area and the WPBR can kill off any seedlings left in the aftermath of a MPB epidemic. Even though MPBs are native, there are a host of conditions causing them to become more virulent and in combination with WPBR our high elevation pine ecosystems are at great risk.

Although whitebark pine does not occur in Colorado, it is in Wyoming just north of us. Moreover, it is the flagship for all North American white pines at the “conifer crossroads.” According to the US Fish and Wildlife Service (Undated) cumulative threats to the whitebark pine include habitat loss and mortality from white pine blister rust, mountain pine beetle, catastrophic fire and fire suppression, environmental effects resulting from climate change, and the inadequacy of existing regulatory mechanisms. While individual trees may persist, given current trends the Service anticipates whitebark pine forests will likely become extirpated and their ecosystem functions will be lost in the foreseeable future. On a landscape scale, the species appears to be in danger of extinction, potentially within as few as two to three generations.”

So, the question becomes: will researchers and foresters be able to slow the mortality and mitigate the threat WPBR poses to Colorado’s high elevation pines before it’s too late? In addition to natural selection, there is a multi-state, multi-agency effort to find natural resistance in our white pines. Scientists at the USFS Rocky Mountain Research Station in Fort Collins look for possible resistance in bristlecone and limber pines, collect seed and germinate them in the lab. They inoculate the seedlings with WPBR and wait to see if their hunches are right. If so, seeds from resistant trees are preserved and ultimately used to breed resistant strains for propagation.

That means there is hope.

But before we end this story, we might note that other species of blister rust are native to our local ecosystems. For example Comandra blister rust (Cronartium comandrae) is an endemic disease of “hard pines” (as opposed to the soft white pines) in North America (Johnson, 1986). The alternate host in Colorado is bastard toadflax (Comandra umbellata). In our area, it especially hits Ponderosa and Lodgepole pine. However, unlike a non-native disease, our pines are adapted to Comandra blister rust meaning that it does not have the same mortality or infection rate that WPBR does. That too is good news.

Cox, S. 2003. White Pine Blister Rust: The Story of White Pine, American Revolution, Lumberjacks and Grizzly Bears.

Hummer, K. 2000. History of the Origin and Dispersal of White Pine Blister Rust. HortTechnology 10 (3).

Johnson, D. 1986. Comandra Blister Rust. Forest Insect and Disease Leaflet 62. USDA Forest Service.

Murrow, P. 2013. The Pine Tree Riot. Journal of the American Revolution.

Newcomb and Six, 2001. White Pine Blister Rust in the Greater Yellowstone Area. University of Wyoming National Park Service Research Center Annual Report: Vol. 25, Article 20.

US Forest Service, Undated. High Elevation White Pines.

USDI-NPS, 2006. Whitebark Pine: The Decline of a Keystone Species. Resource Bulletin.

USFWS, Undated. Whitebark Pine.