At the top of a ridge, a whitebark pine forest is in the fight of its life. Photo courtesy Ecoflight (ecoflight.org) I grew up under the influence of great trees, including the magnificent aspen and ponderosa forests of southern Colorado. In later life, I've spent extensive time in places like the exotic southern beech forests of New Zealand, and have marveled at the ancient bristle cone pines of the Great Basin.

But no other tree, no other forest, has captured my imagination like the whitebark pine. I’ve thought about this some; I’m not sure if I love the whitebark because of where it lives, or I love where it lives because of the whitebark. Either way, this tree that can live—no thrive— for centuries in the highest, most remote, and seemingly inhospitable of landscapes, has assumed a role central to my being.

To some, the measure of a tree is board feet, and its value can be found on the bottom line of some corporate ledger. These folks might not find much of interest in what follows. For others, though, the measure of a tree is the biological community it supports, and the bottom line is the ecosystem it builds.

I should note here that ecosystem ecology is itself a confluence of scientists who bring their individual areas of expertise together and harness a broader range of thinking. That’s what modern systems ecology is all about, understanding how and why threads converge and form a more elaborate, interconnected mosaic.

Forests are the predominant land cover in the Greater Yellowstone Ecosystem and you could say they are foundational, like water and soil, to the ecosystem’s richness of life. But Greater Yellowstone is a matter of forests within forests within forests and forces affecting one can affect the others and the creatures living in and beneath them.

Shortly after I retired from the Research Branch of the U.S. Forest Service in 2006 — seemingly few Americans realize that science has been, and continues to be, an important pillar of the agency — the U.S. Fish and Wildlife made the decision to remove the Greater Yellowstone grizzly population from protection under the Endangered Species Act.

I had looked forward to an idyllic retirement of fly fishing Yellowstone’s backcountry in summer, and skiing it in winter, but that was not to be , primarily as a result of the delisting decision. Why? Because my background in understanding a lot about wild forests, what kills them and the things they produce that other animals rely upon, brought me directly into the discussion of whether removing this iconic population of bears from federal safeguarding was a wise idea.

Whitebark seeds had been identified as the most important food resource for Yellowstone’s grizzly population, so, the condition of whitebark forests was central to the question of whether or not the population could be considered as truly recovered, and I was deeply involved in litigation that challenged the appropriateness of this decision.

The document that the Fish and Wildlife Service used to base their delisting decision vastly understated the extent of whitebark mortality that had occurred in the Greater Yellowstone. The impact of climate warming had altered the high elevation habitat of whitebark to the point that mountain pine beetles, previously limited by harsh conditions of the high mountains, could effectively exploit whitebark — and they were doing so with a vengeance. In an attempt to understand more fully the level of mortality that had occurred , Wally Macfarlane , Willy Kern and myself conducted an aerial assessment of whitebark mortality for the entire Greater Yellowstone Ecosystem

The Greater Yellowstone is the southern extent of whitebark’s distribution in the interior Rocky Mountains. Typically, as the limits of a species distribution is approached, conditions deteriorate to the point that its competitive success, and presence on the landscape, is dramatically reduced. How is it, then, that these magnificent forests have come to occupy such a vast area and play such a significant role in the ecology of this very special place?

Grizzly bears, humans and whitebark pine all colonized North American from Siberia. In fact, all three crossed the Bering Land Bridge at various times during the Pleistocene. Although it is easy to understand how highly mobile animals like grizzlies and humans were able to capitalize on ephemeral events like the opportunistic appearance of the Bering Land Bridge, it is difficult to understand how a tree might do the same. Knowing a little whitebark ecology helps explain this mystery.

Whitebark is one of a group of trees known as stone pines. Worldwide (circumpolar) there are five varieties, all originating in the Russian Far East, Siberian stone pine being the most likely origin species from which the others diverged. Plant taxonomy can be confusing, but the stone pine are defined by one unique attribute, among all the pines their cones remain forever closed unless actively opened by some external force – and therein lies one of the most fascinating stories in co-evolutionary ecology.

The closed (indehiscent) cones of whitebark contain a valuable reward for any animal willing to expend the effort required to obtain the large, highly nutritious seeds contained therein, and all of the stone pines have an associated crow-like bird that is specially adapted to harvest this valuable prize.

In the case of whitebark, the associated corvid is the Clark’s nutcracker. This amazing bird has specialized sublingual pouches that hold a dozen or more of these valuable seeds which the bird then conceals in shallow caches excavated in the soil. No less remarkable than a bird remembering the exact location of thousands of these seed caches, is the reproductive strategy of a tree that is tied almost exclusively to over-provisioning by this co-evolved bird. The tree feeds the bird, and the bird, in turn, plants new trees.