I'm Erika Zavaleta, and this is Ecosystems of California.
California's subalpine ecosystems are the highest elevation systems that are still
dominated by trees.
Subalpine forests are defined at their upper limit by treeline and
they exist in an environment of short growing seasons, extremes of wind,
desiccation, cold and drought, and poorly developed soils.
Their lower limit is to defined variably.
Where they meet montane forests, depends on things like
the history of fire in a region, and the opportunities for subalpine species to
expand down into gaps created in the montane forest, by disturbances like fire.
Moisture arrives to these systems almost entirely in the form of snow,
which is a challenge because that snow becomes available very briefly as water
before the dry summer arrives.
For our visit to subalpine forest,
we've decided to focus on the Ancient Bristlecone Pine Forests
of the White Mountains in far eastern California.
There are many different kinds of subalpine forests in
the state defined by a variation of climate and soils.
But the Bristlecone Pine Forest here, exists on these ancient dolomite soils.
I'm in a dolomite fell field here.
An environment marked by a lot of rock as well as these poorly developed soils.
These dolomite substrates, the rock itself, are pre-Cambrian in origin.
They're 600 million years old.
They're part of an ancient sea floor and were laid down in sediment,
calcium carbonate originally, in the shells of ancient animals.
And over many, many years, these sedimentary ocean floor bottoms were
lifted up by larger tectonic forces that created both the Sierras,
which are dominated by granite, to our west, and the White Mountains,
which are dominated by these sedimentary rocks.
Dolomite is nutrient poor.
It's unusual in chemical composition.
And so there are not very many things that can grow here.
The understory is unusually sparse.
Even for a subalpine forest there aren't very many plants growing
besides the bristle cone pines.
And those that are mostly herbaceous plants and not woody species.
The ancient bristlecone pines,
themselves, have an number of adaptations to deal with these extreme settings.
They can hold on to individual needles for up to 50 years.
Which is much, much longer than your typical conifer,
and their needles have this very waxy resin, this coating, to protect them.
That's because a long period can go by, in which, there aren't water or
nutrients available for the tree to invest in making new needles.
They grow really, really slowly.
They grow most slowly on a slope like the one I'm standing on.
These trees are growing slowly, and putting down really,
really dense resinous wood as a result.
And so turns out that the very oldest trees are the ones
in the harshest environments, like this hill slope.
This tree, behind me, looks dead for the most part.
But a small portion of it Is being supported by a thin strip of cambium that
is carrying water and sugars up and down in the living bark, the cambium.
And supporting just a small portion of the canopy of the tree.
So most of it has died back and that small portion of living canopy
doesn't require as much water or nutrients to persist.
So trees on this slope are on the order of 3 to 4,000 years old, potentially.
And another adaptation to these extremely harsh environments that bristlecone pines
exhibit is that they can remain reproductive for thousands of years.
So over much of that long life span they can still produce cones.
And that's important because replacement in an environment like this
can happen really, really infrequently.
So the ability to try to reproduce over many thousands of years,
gives individuals the opportunity to hit, what might be a once in a century
opportunity, to reproduce successfully and produce ceilings.
Bristlecone pines are famous for their longevity.
They're the oldest known non-clonal living organisms on Earth.
And, in 2012, an individual in this area,
in the White mountains was dated at 5,062 years old.
An individual even older than that, 5,200 years old was described
earlier in the 20th century, elsewhere in the Great Basin.
Because they grow slowly, their growth rings are really, really small.
But because they grow in this really extreme environment, in this high
elevation, arid setting on really nutrient poor dolomite soils, their growth is
sensitive to changes and variation in climate, and other conditions.
And so, because of that, study of their tree rings, dendrochronology,
has been a valuable way to reconstruct climates throughout the great basin
region over the past 11,500 years.
So dating all the back all the way into Pleistocene.
And the way that scientist have gone back, beyond the ages of oldest
living trees, and into the 6,000 odd years before that,
is by cross-dating rings in living trees with rings in long dead trees.
That haven't decomposed because it is so high and dry here.
And so they're able to line up rings in living individuals
with rings from wood on the forest floor.
And to reconstruct through those overlapping sections a continuous record
of 11,500 years.
The other thing that bristle cone pines have allowed,
and that have really revolutionized our understanding of history,
is that in the past people dated major events in ancient history
using radio carbon methods directly on artifacts.
So for instance, a piece of a pottery shard from Mesopotamia,
would be dated using radiocarbon methods.
But scientists weren't able to take into account how variations in the earth's
atmosphere, over thousands of years, affected those radiocarbon dates.
And so, when I was a kid in school, the dates that we were
taught were all under estimates of how long ago various things happened.
So it turns out that when you radiocarbon date tree rings
in that 11,500 year old record.
So that you know exactly how old you're looking at, so
you can recalibrate the carbon-14 dating scale.
That shifted dates of many events, ranging from the advent of metal tools in Europe,
to the time of the Pyramids and the rise of civilization in the fertile crescent.
It moved them back earlier in history.
Thanks to the information provided in these trees.