RECOVERING VULNERABLE LIMBER PINES

Limber pine trees often occur in the montane and subalpine regions of the Rocky Mountains. They speckle the landscape from their northernmost reach of Alberta and British Columbia southward to New Mexico and California.

These resilient conifers prefer warm, dry, and well-drained slopes from 850 m to 1900 m in elevation, displaying a particular affinity for coarse, gravelly soil. In Alberta, limber pine stands are comprised of single trees or widely spaced groups and can be observed on more gently rolling terrain, rocky outcrops, and ridges. Often exposed to severe winds, and when coupled with shallow, moisture-deprived soils, they grow into gnarled but naturally sculpted figures on the landscape.

The limber pine is a shade-intolerant species that acts as an influential early establisher following fire disturbance. They often facilitate the growth of other plants and encourage the biodiversity of an area.

Mature limber pines are typically less than 15 m in height with a rounded, many-branched crown. In wind-influenced areas, the trees can be stunted to less than 5 m, whereas sheltered trees in ideal conditions can grow straight-trunked up to 20 m.

The needles of a limber pine tree are slightly curved, are dark green in colour, and grow in bundles of five clustered at the tips of the branch. The light brown to greenish-brown seed cones are oblong in shape and grow to about 7-15 cm in length at maturity. Cones open to release their wingless, brown seeds which fall to the ground beneath the tree. Pollen cones are yellowish in colour and grow to about 15 mm long.

Like its whitebark pine cousin, limber pine wields significant influence over the ecosystems in which it is found. Due to its interconnection with other organisms, the potential extinction or significant decline of limber pine could have far-reaching consequences, impacting the entire ecosystem.

With roots that anchor the soil, limber pine stabilizes slopes and controls erosion.

These pines contribute to water supply in headwater streams. Snow accumulation during winter months amongst the trees on the otherwise bare slopes is slowly released as snowmelt into the surrounding environment. This prolonged release of water maintains a more steady and sustained flow downstream for communities, wildlife, and vegetation and contributes to the resilience of headwater ecosystems.

Limber pine holds the heavy title of a ‘keystone mutualist’, which is a species so intricately linked with other organisms that its extinction or significant decline would have cascading effects throughout the entire ecosystem. Its seeds are a food source for many animals like the red squirrel, as well as black and grizzly bears, who, in return, occasionally disperse limber pine seed throughout the landscape.  Almost all successful limber pine regeneration, however, results from dispersion by one particular bird species – the Clark’s nutcracker.

Photo by Getty Images

The Birds and the Trees

Clark‘s nutcracker is the avian ally equipped with a beak tailor-made for extracting and dispersing limber and whitebark pine seed. These jay-sized birds begin their limber pine seed harvest mid-summer in strategic preparation for the harsh winter and early spring months ahead.

Utilizing their long, sharply pointed beak to chisel seed from cone, nutcrackers are able to harbour up to 100 seeds under their tongue in a special pouch. These clever birds have astounding spatial memory and bury or ‘cache’ the limber pine seeds singly or in clumps of up to 20 at a time. Caching refers to the practice of the nutcracker storing excess seeds in various locations, often many kilometers away from the source tree and throughout their expansive territories for later feasting. A single nutcracker can make and mentally map up to 30,000 caches in a year.

Come spring, overlooked seeds have the chance to germinate, and if located in good microsites, they may give rise to new limber pine seedlings.

Hidden Handshakes
Limber pines have a vibrant underground social network. Thanks to mycorrhizal fungi, these trees exchange nutrients in secret, sub-terrestrial handshakes. The thread-like mycelium welds to the tree roots and reaches into the soil where it offers the tree an efficient transport of nutrients like phosphorus and nitrogen. In return for its fungal friendship, the mycorrhizal fungi are provided with carbohydrates that leak from the roots.

Alberta is at risk of losing 90% of its limber pine trees within 100 years, as well as the ecological benefits they provide.

These trees are adapted to living on slopes that many other tree species find too inhospitable. The roots of limber pines aid in stabilizing soil and preventing erosion, thereby influencing water retention. Furthermore, the canopy structure of limber pines helps regulate snowmelt by providing shade and reducing direct sun exposure on the snowpack. This shading effect slows down the melting process, influencing the timing and amount of water released into downstream runoff.

Preserving limber pine is not just about saving a species; it’s about safeguarding a vital resource that is indispensable for human and wildlife communities alike.

White pine blister rust

Limber pine are entangled in a silent battle with a human-introduced fungus called white pine blister rust that affects five-needle pine trees. Native to eastern Asia where it evolved alongside rust-tolerant trees, the fungus was introduced to Canada in the early 1900s.

The fungus persists by alternating between the five-needled primary host and a secondary host in the currant family (Ribes species) to complete its life cycle. It infects the needles of these pines, then grows down into the main stem where it disconnects the water and nutrient supply, killing the tree. Although the fungus may take years to fully kill the tree, the fungal growth begins affecting the crown of the tree and its cone production, initiating the cascading collapse of its ecological function.

A very small percentage of five-needle pine trees have natural resistance to this disease and these special trees are key to successful recovery of the species across its range.

Coordinated monitoring actions are carried out throughout the province to detect these resistant trees. The seeds of these trees are tested over the course of 7 years in a designated facility. Successful rust-resistant seedlings are used in restoration efforts with the goal of planting trees that will eventually produce an ongoing supply of rust-resistant offspring, contributing to a more resilient population.

Those equipped with a keen eye can identify a tree that has been infected with white pine blister rust even when it is not sporting an actively fruiting canker. Three of the following five signs must be observed on a single tree to have confidence in the assessment:

Wildfire Suppression

Wildland fire suppression encourages the growth of shade-tolerant species of trees which can form dense stands and outcompete limber pine. High-severity fires can also negatively impact limber pine trees due to their thin vulnerable bark.

The locations of known rust-resistant trees have been identified in government databases as high-value resources and are currently protected from wildfire whenever possible by the Government of Alberta’s Wildfire Management Branch. Prescribed fires are conducted as conditions and resources allow to reduce fuel load buildup and create open caching sites for Clark’s nutcrackers.

Mountain Pine Beetle

Limber pine are susceptible to the infiltration of the voracious, wood-boring mountain pine beetle (MPB). The MPB burrows beneath the bark of a mature tree where it destroys the conductive tissues the tree needs to function. Their larvae feed on the tree’s phloem, which acts as part of its circulatory system.

Although rust-resistant trees are critical for seed protection, they are still susceptible to MPB. Envelopes of special compounds are strategically placed on these high priority trees to send chemical signals into the surrounding environment that discourage MPB attacks on such trees.

Climate Change

Although adapted to environmental extremes, the limber pine is susceptible to extended periods of severe drought, or unfavorable conditions for tree growth and survival.  Climate-induced changes in alternate food sources for Clark’s nutcracker can also negatively affect the bird’s populations, further exacerbating impacts on limber pine as the species are inherently linked.

Cattle often avoid the conditions where limber pines tend to grow; however, they may search for shade relief underneath larger trees, forage in flatter, sparsely treed sites, or travel through limber pine stands toward preferred grazing areas. As limber pine presence on the landscape diminishes, landowners can support the success of limber pine trees, where possible, by diverting cattle to other areas with better forage quality.

Diverting or minimizing cattle presence at sites where limber pine seedlings, saplings and mature trees grow would promote regeneration and maintain cone production within these stands. Consider using drift fencing, salt blocks, water, or shade-relief structures to guide cattle away from these sensitive areas and towards pastures with higher quality grazing. If grazing within these sites is necessary, consider a shorter rotational grazing period, for example, utilizing 25% of the yearly forage production followed by a longer rest period.

Please see the Resources section for more information on beneficial management practices in limber pine stands.

Those with limber pine on their land can support the stewardship of this species by reporting tree locations in the iNaturalist app to help refine species range maps.

Planting rust-resistant trees

The WBRA partnered with the Whitebark Pine Ecosystem Foundation of Canada and landowners in 2022 and 2023 to plant limber pine seedlings on private land within WBR. These weren’t just any seedlings, but carefully reared, rust-resistant specimens to foster a more resilient population.

Their health will be monitored regularly, following standard protocols, to evaluate how well they are surviving in their new habitat and to compare the white pine blister rust screening results to field outcomes.

Recovering Vulnerable Limber Pines Workshop

In 2022, interested WBR residents and Jodie Krakowski of the Whitebark Pine Ecosystem Foundation of Canada (WPEF-C) took to the slopes to learn while nestled amongst the needles. Jodie shared her knowledge about this species, its threats, and conservation actions underway to support their survival.

Workshop participants were taught white pine blister rust identification and saw it firsthand in the field. They were invited to consider future actions they can take to promote the stewardship of this species. This included reporting tree locations in the iNaturalist app to help refine species range maps. Those in attendance were also taught how to avoid direct damage or impacts to trees and beneficial management practices for grazing in limber pine habitat.

Limber Pine Land Camp

In May 2023 the WBRA once again teamed up with WPEF-C, now alongside the Livingstone Range School Division and Destination Exploration, for two days of shared learning with some caring and intrepid high school students from the region.

The days centered around experiential learning, where students were immersed in a limber pine ecosystem to better learn about the threats these species are facing, as well as the conservation and restoration efforts. Students were able to explore real-life monitoring and recovery activities such as seedling surveying, tree-coring, and white pine blister rust health assessments.

Scratchy Fingers Event

In November 2023, the WBRA hosted an event to support limber pine recovery and restoration efforts. Participants constructed cone cages that will be used by WPEF-C scientists in the 2024 field season to protect the seeds of rust-resistant trees from the Clark’s nutcracker.

The event was abuzz with conversation and discussion about limber pine and ended with a tour to Waterton Lakes National Park to observe the seedling orchard growing the beginnings of future limber pine forests.

For more information on limber pine you can visit the White Bark Pine Ecosystem Foundation of Canadas website here.

Their site is an excellent resource for information about the conservation, restoration and stewardship action of whitebark and limber pine in Canada. Check out their one-pager for farmers and ranchers with limber pine on their land.

Living Legacy: Saving Alberta’s Limber Pine

This short film, produced in co-operation with the Whitebark Pine Ecosystem Foundation of Canada, explores the plight of the Limber Pine in southwest Alberta. These trees play an important role in the foothills ecosystem. They provide food and shelter for animals, help mitigate and maintain soil moisture, and provide an array of system services. The trees are at risk though…endangered even…due to a host of anthropogenic factors. Learn more about this iconic tree species and how organizations like the WBR and WPEF-C are working to save these beautiful trees.

We want to acknowledge and send out a huge thank you to the supporters of our Recovering Vulnerable Limber Pine Project, Alberta Conservation Association, Environment and Climate Change, Livingstone Range School Division, Parks Canada, and Whitebark Pine Ecosystem Foundation of Canada. Also, a big thank you to Burke Creek Ranch and Waldron Ranch for their contribution to supporting the next generation of limber pine trees! Together, our project helps raise awareness of limber pine conservation and contributes towards recovering this endangered species in southwestern Alberta. Finally, many thanks to the landowners who gave access to their properties and continue to provide learning opportunities and information that will help inform our collective efforts to support local limber pine populations.