Whitebark pine and Clark’s nutcrackers.
Keystone species are plants or animals that are so critical to an ecosystem that the landscape would dramatically change without them. In the subalpine forests in our region whitebark pine (Pinus albicaulis) is a keystone species, as is Clark’s nutcracker (Nucifraga columbiana). Most interestingly, both are tied together in a key mutualism. Nutcrackers rely on whitebark pines as a crucial food source, the pines rely on nutcrackers to disperse and plant their seeds, and many, many other species of plants and animals benefit from that mutualism between tree and bird.
Whitebark pine grows in high elevation forests close to treeline. In Canada they occur only in BC and Alberta. They’re long-lived, typically 500 years, often more than 1000 years. Sizable cone production begins at 60-80 years of age, peaks at 250 years. The seeds are a rich source of food for squirrels, chipmunks, bears, chickadees, woodpeckers, and many others.
Whitebark pine is dependent primarily on Clark’s Nutcracker to disperse seeds. The cones do not open to release the seed; rather the seeds must be removed by the birds and cached in the ground. Other birds also remove seeds, in lesser amounts: Stellar’s jay, pine grosbeak, common raven. Red squirrels harvest whitebark pine cones, too, and are major seed dispersers.
Nutcrackers feed on whitebark pine seeds almost exclusively when they are available and store the seeds for use throughout the year. Nutcrackers have a sublingual pouch that can hold up to 150 seeds, an adaptation that is unique among birds. With a full pouch nutcrackers fly to a suitable site (sometimes more than 10 km away) where clusters of up to 15 seeds are cached 2 to 3 cm below the soil surface. Each bird stores 30- to 100-thousand seeds each year. Those not retrieved to be eaten have the opportunity to germinate and grow.
Whitebark populations are currently in major decline throughout their range. Several factors are involved, in particular mountain pine beetles (Dendroctonus ponderosae) and a human-introduced disease, white pine blister rust. Whitebark pine is now classed as endangered by COSEWIC (Committee on the Status of Endangered Wildlife in Canada). Sadly, as the trees disappear, so do nutcrackers. Nutcracker populations are in serious decline throughout much of their range, too.
Resources:
Gustave Alexson. Soul mates: nutcrackers, whitebark pine, and a bond that holds an ecosystem together. Living Bird, autumn 2015.
Gail Wells. Clark’s nutcracker and whitebark pine: Can the birds help the embattled high-country pine survive? Science Findings 130, USDA. 2011.