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An Ancient Partnership Put in Danger

Clark's nutcracker in a whitebark pine | Photo: chloesview/Flickr/Creative Commons License

Bad news for lovers of alpine trees in East California: the whitebark pine has been added to the global Endangered Species list. The tree, which grows above 7,000 feet in the Eastern Sierra and a few desert mountain ranges, is threatened by a warming climate and related insect infestations, as well as an exotic fungal disease. But it's not just the tree in danger. If the tree goes, one of the most interesting ecological partnertships in the West dies out as well.

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The International Union for the Conservation of Nature downgraded the whitebark pine's place on its Red List from "Vulnerable" to "Endangered" this month in a sweeping review of conifer species, and there was bad news for other California trees as well. The giant Sequoia of the western Sierra Nevada also went from Vulnerable to Endangered, as did the Monterey pine and, rather shockingly given its relative prevalence throughout Northern California, the coast redwood.

The downgrading of the whitebark pine, Pinus albicaulis, isn't so shocking. It's been in trouble for a while. Two years ago, in response to a lawsuit by environmentalists who wanted the whitebark protected under the U.S. Endangered Species Act, the U.S. Fish and Wildlife Service (FWS) put the tree into its notorious "warranted but precluded" category. That category covers those species that FWS agrees deserve and need protection, but which the agency lacks the resources, the funding, or the will to protect, or all three.

Canada, which holds a majority of the tree's present range, has been a bit more proactive. The whitebark pine was listed as endangered under that nation's Species at Risk Act in June 2012, the first tree in western Canada to gain that sorry status.

Range of the whtebark pine | Map courtesy FWS

What's threatening the tree? Many populations of whitebark pine are being hit hard by infestations of the mountain pine beetle, which bores beneath the bark of the trees to lay its eggs. The larvae hatch out and start eating, and between their efforts and a deadly pathogen that usually comes along for the ride, the blue stain fungus, a successful infestation can kill a tree within a month. The beetle reproduces more quickly in hot, dry weather. Historically, in the whitebark's alpine redoubts, the beetles have taken two years after hatching out to reach reproductive maturity. As the landscape warms, the beetles can reach egg-laying age in just one year, ramping up the pace of destruction. In some former strongholds for the whitebark such as the Greater Yellowstone area, experts predict the tree will be functionaly extinct in this decade.

As if that weren't enough, another fungal disease threatens the trees. White pine blister rust, an Asian fungal disease introduced in timber shipments, has been infecting trees in California since the 1940s.

And, of course, even without these two major threats, whitebark pines stand to lose much of their habitat as the world warms. For one thing, climate change means more fiires, and whitebark habitat is especiially susceptible to fire. Even without fire, though, when the landscape below 7,000 feet is just a little too warm for your comfort, a warming world means you have to either go uphill or move north. That's not as easy for a tree as it is for more mobile life forms. They can't migrate themselves. Trees must disperse their seeds as best they can, and with luck some of those seeds will germinate in more copacetic surroundings, preserving the species. Many other species of pines have little membraneous "wings" on their seeds, which catch the breeze when they fall out of their pinecones and allow the seeds to travel. They might not be as air-worthy as dandelion seeds or even winged maple samaras, but it helps.

Whitebark pine seeds have no such aerodynamic accessories. They're wingless. That means that without help, the pine's seeds don't fall far from the tree. fortunately, unlike some trees, whitebark pines do have partners who distribute their seeds.

That partner is the Clark's nutcracker (no relation to the author), Nucifraga columbiana, which mainly makes its living by harvesting whitebark pine seeds, which it collects in prodigiious amounts and stores in caches across the landscape.

Clark's nutcrackers are marvelous birds. Members of the corvid family and thus relatives of ravens, crows, and jays, Clark's nutcrackers are forbiddingly intelligent. They extract ripe seeds from whitebark pine cones with their beaks, test them with a couple of "clacks" of the beak to see if they're likely to withstand months of storage, and then when they have gathered a crop-full -- as many as 150 seeds, though usually more in the 50-60 range -- they fly off to store those seeds in a safe spot in a buried cache.

Here's where that prodgious intelligence comes in handy. A typical Clark's nutcracker caches somewhere between 30,000 and 90,000 whitebark pine nuts in a season, depending on the harvest. (The trees have good years and lean years.) A single cache usually holds three to five seeds buried an inch or two deep. The birds cache their seeds anywhere from right next to the tree to more than 10 or 12 miles away.

That's up to 30,000 caches a year made in a territory that can extend over more than 300 square miles, and as far as we can tell your standard Clark's nutcracker can remember where every single cache is for six months, and that memory slackens only a bit by nine months. There's some thought that the birds get through lean years by recalling the locations of caches made in years past.

That's an impressive feat of memory as compared to certain other Clarkes who forget where their keys are mere moments after cacheing them in plain sight on the dining room table, and it's the foundation of a whole web of ecological relationships. Clark's nutcrackers aren't the only animals who eat the cached seeds. Jays will follow the nutcrackers and raid the caches. Alpine squirrels sniff out the caches, as do larger animals. Some, like Yellowstone grizzlies, are quite a bit larger. There's some thought that cached pine seeds are so important to grizzlies that they get desperate in years of bad seed production. Whitebark pine seeds run about 2,700 calories per pound, mostly in the seeds' fat content. When caches of whitebark and other pine seeds are scarce, bears seeking to put on fat for hibernation have to turn to other, less-efficient food sources, including tourists.

And of course even with the Clark's nutcracker's astounding memory, and even with the entire rest of the animal world helping diig up the caches, a lot of cached seeds go unrecovered each year. Some of them germinate. Some of those seedlings survive to maturity. Within 20 years, they start producing seeds of their own and the cycle continues.

The partnership between nutcracker and pine is so efficient that before the beetle and the fungus started getting out of control, whitebark pines were considered a colonizer species. They'd be the first trees to germinate in burned areas, atop landslides, and in other disturbed areas, courtesy of its partner the nutcracker. Slow-growing trees, whitebarks can live for centuries, tying the alpine soil down and acting as the base of an extensive food chain.

Whitebark pines | Photo: Richard Sniezko | US Forest Service

That's when things are good. In our new world, in which we import new, voracious fungi and change the planet's temperature, the whitebark ecosystem is unraveling. Studies show that when a certain percentage of the whitebarks in a forest stop producing cones, the nutcrackers pick up and leave. That's a problem, as few other animals can open the tree's cones without destroying the seeds within.

The trees can't reproduce without the nutcrackers, in other words. Nutcrackers aren't quite as dependent on the pines: they can eat other pine seeds, though they don't like them, and they are known to hunt for insect larvae and other such fatty food alternatives. Endangering the trees doesn't necessarily mean a death sentence for the birds.

But it does mean a death sentence for the relationship, one that works well enough that both tree and bird were able to spread into North America from their central Asian origins over the last several million years.

Our whitebark pines in California are the southernmost in the species. The farthest-south trees for which CalFlora has records, one near Whitney Portal and the other a few miles south of triple Divide Peak, were reported more than 50 years ago and may not be there anymore. (There are certainly whitebarks still in the area, one well-known example being the last tree you pass as you climb to Whitney's summit on the John Muir Trail.) The species' stronghold in California is in the Yosemite high country, though they do edge into the desert where altitude permits, with records from the Mono Craters, Glass Mountain north of Bishop, and the northern summits of the White Mountains.

In North America, the southernmost edge of a species' range is where you'd sensibly look for individuals who are best equiped to handle heat and drought and all their attendant ills. It may be that California's desert mountaintops hold the key to the preservation of an ecosystem that extends northward for more than 1,000 miles.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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Great post Chris. The Sierra Nevada offers the most extensive habitat and thus largest population centers of whitebark pines in the state. However, the species also grows in northern California in much more fragmented and isolated stands. I'll be mapping and assessing these little-known populations this summer as part of a conservation assessment for the state. I am looking for feedback and input on these populations, as well as information about other outlier populations in the Sierra Nevada, so we can better understand this species at its southern range extension. I encourage readers to check out my collective research on the species range and provide feedback if you have it: http://blog.conifercountry.com/2013/07/07/whitebark-pine-in-northern-california.aspx