NUTCRACKER BITTERSWEET
Whitebark pine wouldn’t survive without the help of the Clark’s nutcracker
Whitebark pine restoration is naturally tied with the Clark’s nutcracker (Nucifraga columbiana), a bird that co-evolved with the tree species over a similar range across North America’s western mountains. Together, they form a “mutualistic” relationship — although each species benefits from the other, whitebarks simply could not survive without nutcrackers.
Since its cones do not open on their own, whitebark pine’s reproduction depends on nutcrackers’ ability to pry the cones open, as well as their dogged determination to collect and bury thousands of seeds every year in caches. Some studies estimate a single bird stores close to 100,000 seeds annually, an effort aided by the bird’s specially designed throat pouch for carrying seeds. Nutcrackers will somehow remember where most of those seeds are buried, even though they’re distributed across the landscape in multiple caches of no more than 15 seeds each, usually less.
Luckily for whitebarks, the nutcrackers won’t come back for every cache, and they also just happen to bury the seeds at a perfect depth for germination, which is why whitebark pine often grow in little clumps out of abandoned seed caches. Seeds cached by red squirrels, on the other hand, rarely germinate because they’re usually buried too deep.
“Nutcrackers are the unsung heroes and keystone dispersers,” says U.s.-based researcher Diana Tomback, who began her career studying nutcracker seed-dispersal behaviour. She says that as pine populations decline due to blister rust, it leads to reduced cone production, which in turn means a higher proportion of seeds are eaten by nutcrackers (and other animals) rather than being buried. That’s why management intervention is required to ensure genetic resistance in whitebark pine — to some extent, it’s replacing the seed dispersal services of nutcrackers.
“It may be centuries before we see full whitebark recovery,” says Tomback, “But if we can get blister rust-resistant genomes out there, and then let nutcrackers do the heavy lifting, it will work.”—f.l.