Testing Glacier Influence on the Whitebark Pine Blister Infection

In 2011, the U.S. Fish and Wildlife Service called for the protection of whitebark pine trees as endangered species due to an alarming rate of decrease in their population. Pinus albicaulis, the species name for whitebark pine, are conifers native to the mountains of the western U.S., particularly the Rocky Mountains in Wyoming. Fear of the complete disappearance of the whitebark pines in the Greater Yellowstone Ecosystem has motivated a group of scientists including Lynn Resler, an associate professor at Virginia Tech, to conduct field research to determine the environmental variables influencing the blister infection, one of the causes of pines’ disappearance. Resler’s latest study in Grand Teton National Park indicates that the pines’ proximity to a glacier has likely not contributed to the blister infection rate among the whitebark pines, contrary to the findings from an earlier modeling study conducted in 2011 with data from Glacier National Park.

A grove of whitebark pines in Crater Lake National Park, Oregon (Source: US Department of Agriculture).

Unlike many other plant species in the Greater Yellowstone Ecosystem, whitebark pines can survive in harsh environments and are capable of growing at the highest treeline elevation within the mountain range. Today, in the western United States, whitebark pines are facing extinction but have still not been listed as the endangered species by the Environment Protection Agency. The decline of whitebark pines is attributed to a number of different factors, but the introduction of blister rust infection, a fungal disease caused by the pathogen Cronartium ribicola, has been thought to be one of the major causes. Native to Asia, blister rust was introduced to North America in the 20th century and rapidly spread across the western United States.

Canker created by the blister rust infection on the whitebark pine (Source: Global Trees Campaign).

In order to understand why glaciers could potentially affect the rate of blister rust, Resler notes that it is essential to understand the lifecycle of the rust. White pine blister rust has two hosts: white pines, the primary host, and gooseberries or currants, the alternative host. Its life cycle starts in the fall, when the spores (basidiospores), reproductive cells of fungus from the infected alternative hosts, germinate to white pines.

As germination takes place on the surface of the pine, the fungus enters through the stomata (micro-scale pores) of the leaf needles or any opening on the pines from wounds. The fungus then grows on the twigs of a branch, often causing swelling on the infected branch and creating cankers. It takes a few years for the fungus to kill the branch, turning it into an orange/red color. When the blisters finally rupture, they infect the alternative hosts, causing the cycle to repeat itself.

The lifecycle of the blister rust infection from the primary host to the alternative host (Source: The American Phytopathological Society).

“What is important for germination of a particular spore type in the blister rust lifecycle—based on the literature—is cool temperatures and high humidity for a certain sustained period of time,” Resler told GlacierHub.

Blister rust favors areas with cool and moist air near the sources of moisture, such as streams. However, the treelines the pines inhabit are usually very dry.

“Because many treelines of the Rocky Mountains are quite dry, it would seem that at treelines where glaciers are present, glaciers, depending on local winds, could provide the necessary moisture conditions for spore development,” she added.

Her study in 2011 (conducted in collaboration with her former student, Dr. Smith-McKenna), supported that hypothesis; Resler and a group of scientists examined the whitebark pines at six alpine treelines in Glacier National Park, Montana, divided into 30 different sampling quadrats for the purpose of the study.

They measured the number of cankers on each Whitebark pine to assess the severity of the blister rust in different quadrats. They then created a high-resolution DEM (digital elevation model) to develop topographic variables and derived different environmental variables in the sample locations based on GIS (Geographic Information System) and field examination.

By doing so, the team attempted to identify variables that affect the blister infection rate, based on the density of cankers in each quadrat and its proximity to individual variables. Her model indicated that proximity to glaciers was an important correlate of infection rate at her selected sites, with a higher density of cankers compared to sampling areas farther away from the glacier.

An image of Schoolroom Glacier (Source: Glaciers of the American West).

However, Resler indicated that her study in 2015, as well as a few of her subsequent studies, did not agree with this finding from her 2011 paper.

In 2015, Resler published an annual report based on her preliminary findings at alpine treelines of Grand Teton National Park, Wyoming. The results of her study showed that the proximity to the Schoolroom Glacier, a small glacier in Grand Teton National Park, did not affect the infection intensity.

“The presence of the Schoolroom Glacier didn’t really seem to contribute to higher infection rates, as compared to our other study areas,” she said. She also sampled blister rust extensively at Parker Ridge near the Columbia Icefields in Alberta, Canada and compared it to the rust in dryer locations on the Rocky Mountain Front, only to find that the areas near the Icefields show lower infection rate.

 

An image of whitebark pine skeletons (Source: Oregon Hikers).

“We do not have enough information to conclude that glaciers, specifically, contribute to blister rust infection rates at this time. More focused studies (on the glacier’s influence on the blister rust) would be necessary,” Resler said.

The reduction of the pines threatens wildlife that is largely dependent on the pines as their source of food. As Resler indicates, whitebark pine is a keystone species whose seeds are a major food source for different species of wildlife including grizzly bears and Clark’s nutcracker.

Whitebark pine is also a foundation species, with a role in stabilizing the ecosystem and structuring the basis of the community for many other organisms: its canopies shade the snowpack, thereby prolonging snowmelt and consequently regulating downstream flows, contributing to the protection of the watersheds.

Determining the degree of influence that different environmental variables have on the rate of blister rust infection is crucial for the fate of different species that are dependent on the pines. Without an effort to deter the spreading blister rust, we may no longer be able to see diverse bird species visiting the partly-opened cones of the pines, left with the gray skeletons of whitebarks.

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Roundup: Microbial Mats, Hidden Heat, and Tree Infection

Benthic Microbial Mats in Meltwater from Collins Glacier

From Polar Biology: “Most of Fildes Peninsula is ice-free during summer thereby allowing for formation of networks of creeks with meltwater from Collins Glacier and snowmelt. A variety of benthic microbial mats develop within these creeks. The composition of these microbial communities has not been studied in detail. In this report, clone libraries of bacterial and cyanobacterial 16S rRNA genes were used to describe the microbial community structure of four mats near a shoreline of Drake Passage. Samples were collected from four microbial mats, two at an early developmental stage (December) and two collected latter in late summer (April). Sequence analysis showed that filamentous Cyanobacteria, Alphaproteobacteria, and Betaproteobacteria were the most abundant ribotypes.”

Learn more about the microbial mats here.

Microbial mat on a sandy depositional surface (Source: GSA).

 

Geothermal Heat Flux Hidden Beneath Greenland Ice Sheet

From Nature: “The Greenland ice sheet (GIS) is losing mass at an increasing rate due to surface melt and flow acceleration in outlet glaciers… Recently it was suggested that there may be a hidden heat source beneath GIS caused by a higher than expected geothermal heat flux (GHF) from the Earth’s interior. Here we present the first direct measurements of GHF from beneath a deep fjord basin in Northeast Greenland. Temperature and salinity time series (2005–2015) in the deep stagnant basin water are used to quantify a GHF of 93 ± 21 mW m−2 which confirm previous indirect estimated values below GIS. A compilation of heat flux recordings from Greenland show the existence of geothermal heat sources beneath GIS and could explain high glacial ice speed areas such as the Northeast Greenland ice stream.”

Learn more about the hidden heat flux here.

Aerial Image of Greenland Ice Sheet (Source: NOAA).

 

Blister Infection on the Whitebark Pine in the Greater Yellowstone Ecosystem

From University of Wyoming National Park Service Research Center: “Whitebark pine is a keystone and foundation tree species in high elevation ecosystems of the Rocky Mountains. At alpine treelines along the eastern Rocky Mountain Front and in the Greater Yellowstone Ecosystem, whitebark pine often initiates tree islands through facilitation, thereby shaping vegetation pattern. This role will likely diminish if whitebark pine succumbs to white pine blister rust infection, climate change stress, and mountain pine beetle infestations. Here, we established baseline measurements of whitebark pine’s importance and blister infection rates at two alpine treelines in Grand Teton National Park.”

Read more about the blister infection on Whitebark pine here.

Whitebark pine on the Continental Divide of the the Greater Yellowstone Ecosystem, which includes Yellowstone and Grand Teton National Parks (Source: Taisie Design).
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