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.
Map of whitebark pine distribution in Greater Yellowstone. After attacks by mountain beetles, blister rust, drought and wildfire, whitebark is barely hanging on, most notably in the high and cold reaches of the Absaroka-Beartooths in the northeast corner of the ecosystem and the Wind River Range in the southeast.
The
4,653 aerial photographs that resulted from this survey reinforced just how
spectacular the whitebark forests of the Greater Yellowstone really are, and
just how extensive the threat was to their very existence. Subsequent,
independent research has corroborated our finding that the level of mortality was
unprecedented in the ecological history of these forests. Perhaps even more
interesting, from a scientific point of view, was documenting the dramatic extent
of climax (forests in which whitebark vastly dominates any other tree species)
whitebark forests in this 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.
Clark’s nutcracker extracting seeds from a whitebark pine cone. Photo courtesy U.S. Forest Service
So a corvid
moved whitebark seeds from Siberia to North America approximately coincident
with grizzlies and humans. Both indigenous humans and grizzlies utilized large
quantities of pine seeds, as do residents of Siberia to this day. However, the
association between bears, humans, and stone pines goes back much further, back
to time beyond memory – pine nuts litter the floor of caves that were occupied
by Neanderthals.
The ancient association between humans, bears and trees has
resulted in a rich indigenous tradition of creation stories and mutual respect.
At least until recently, whitebark pine seeds have been identified as the most
important food for Yellowstone’s grizzlies, and in fact, grizzlies in
Yellowstone were more dependent on pine nuts than anywhere in the world outside
of Siberia.
Imagine, as have others,
what it was like for the early humans arriving on a totally wild and
uninhabited continent. Theirs for the taking, except that it was already
occupied by animals like Arctodus simus,
the short faced bear. Beasts like the short faced bear would have been
intimidating in the extreme for humans and grizzlies alike.
For whitebark,
occupation of a new land also was fraught with significant challenges. Other
pines were there, already well established and extensively distributed south of
the Pleistocene continental ice sheets. Whitebark is supremely adapted to cold,
harsh conditions, but they are not particularly effective competitors with
other conifers. Many of the attributes that result in amazing survival
capabilities have simultaneously resulted in reduced competitive ability.
It is the colonizing and survival capability of whitebark
that have resulted in some of themost impressive of all whitebark
forests paradoxically found in the southern most extent of its range. In all of
the Rocky Mountains there are no whitebark south of the Wind River Range. Other
five-needle pines that are distant cousins, yes, but no whitebark.
The Greater
Yellowstone of 15,000 years ago was an island of ice surrounded by more
moderate, intact forested ecosystems; and as the Pinedale ice receded, the
emerging landscape provided a superb opportunity for an effective colonizer
like whitebark.
As the ice receded, whitebark was the first tree that
followed and replaced alpine tundra. As climate continued to moderate,
whitebark at lower elevations was displaced by other conifers, resulting in the
gradual migration of whitebark into ever higher and harsher climatic zones. In
the present day Greater Yellowstone Ecosystem, whitebark occupies the most
remote, the most rugged and harshest reaches of the ecosystem.
Observes Logan, "The most ancient whitebark seem to grow in the most unlikely places imaginable, like this giant growing out of solid rock. They just hang in there year after year after year, protected by their hostile environment from competition from other conifers. Note the crown has been lost and subordinate limbs are starting to dominate."
Because of
its inaccessible location, slow growth, and soft wood, whitebark has never been
an important commercial species, and in the GYE, it has never been intensively
managed.
The ecological processes that have shaped whitebark forests are
largely intact since the last ice age. Hence, these expansive, climax whitebark
forests remain much the same as they were in Lewis and Clark times, and in
fact, long before European intrusion. It can be argued, that in aggregate, the
whitebark forests of the Greater Yellowstone are among the largest expanse of
old-growth forests remaining in America outside of Alaska.
So, these
ancient trees and magnificent forests resulted from the intricate interplay of
geology, ecology, animal behavior and intelligence – and on it goes. A species
like whitebark is considered an indicator species because it integrates the
entire ecosystem, and what happens to whitebark is an indication of the health
and resilience of the entire community it supports.
In addition to the
ecological significance of whitebark, these forests are a direct link to the
very foundation of human culture, not to mention the human colonization of North
America and subsequently the Greater Yellowstone. Perhaps it is this, the
ecological and cultural context that is being lost with the demise of
Yellowstone’s whitebark forests that breaks the heart of this “dispassionate”
old scientist.
Authors Note: Much of this article was
excerpted from a chapter by Jesse A. Logan and William
W. Macfarlane in the forthcoming The
Shining Mountains: A Journal/Atlas of the Absaroka-Beartooth Wilderness.
About Jesse Logan
Jesse Logan is literally a man of the woods. Much of his former career as a civil servant was spent studying why forests of the American West live and die. He amassed an impressive body of work publishing papers as a researcher. He is also revered, even among millennial-aged telemark skiers, for his ability to hold his own off-piste with wayfarers a third his age.
