thank you so much for your time.
>> Thanks for having me, Ali.
John: Next Saturday is the
autumnal equinox, the beginning
of astronomical fall in the
northern hemisphere.
For some, though, fall doesn't
really begin until leaves change
color.
But scientists say climate
change is affecting both the
timing and intensity of fall
foliage.
Earlier I spoke with bill
Keeton, a professor of forest
ecology and forestry at the
university of Vermont.
I asked him to explain why
leaves change color in the fall.
>> It's really a delicate dance
between many factors that are
driving both the onset of the
fall foliage, as well as the
intensity of the color that we
see.
Basically what happens is that
the trees sense the onset of
winter as the contrast between
daytime temperatures and
nighttime temperatures increases
and as the length of the day
shortens and as they sense that
onset, they begin shutting down.
And they try to reabsorb as much
of the energy that's stored in
leaves as possible.
These are sugars and
carbohydrates that the trees
have been producing all summer
long.
And as this is happening, the
chlorophyl in those leaves,
chlorophyl is a catalyst for
photosynthesis and important for
all of life on Earth.
It makes vegetation appear green
to our eyes.
The chlorophyll is beginning to
degrade, and as this happens, it
reveals other chemicals that
have been in the leaves all
summer.
So these are the same chemicals
that you find in bananas that
make them appear yellow and
Oranges that make them appear
Orange.
At the same time this is
happening, the trees are trying
to buffer those leaves and hang
on to them as long as possible
so that they can absorb as much
of the energy stored in those
leaves as possible.
And to do that, they produce
another group of chemicals
called anthocyanins.
These anthocyanins give us the
reds and the purples that we
find in some species like maples
and oaks, and add a lot of
diversity to the color that we
see on the landscape.
John: And that process you've
just described, how is that
affected by climate change?
>> First of all, there's pretty
good evidence that climate
change, especially our warming
Summers, is delaying the onset
of fall foliage.
There's even some research
that's suggested that the onset
of fall foliage may have been
delayed by as much as a month
over the last century.
The other thing is the climate
change can dampen the intensity
of the fall foliage.
And this happens particularly
after extreme droughts or after
Summers like we've just had,
with really extreme rainfall and
wet, saturated soils.
So these types of climate
extremes create stresses in
trees, which can interfere with
the production of some of these
chemicals that give us color and
can interfere with the overall
productivity and health of
trees.
John: One of the things we've
seen this summer has been record
wildfires, putting a lot of
particulate matter into the air,
into the atmosphere.
Does that affect the trees and
the foliage in any way?
>> We don't have conclusive
evidence on this yet, but
there's some evidence that, yes,
in some parts of the eastern
U.S., ash and particulate matter
on leaves can interfere a little
bit with photosynthesis and
reduce the overall productivity
of trees, which could have a
ripple effect down the road on
foliage, on color.
But with the mega fire situation
increasing year by year in the
western U.S., and now across
boreal, northern Canada, this
may change into the future.
There are major differences
around the country in terms of
how climate change seems to be
affecting forests.
So, for example, in the
southwest and part of the
intermountain west, we've just
come out of one of the worst
droughts in something like 1200
years.
A ten year plus drought.
And that certainly impacts tree
health, tree growth.
Whereas in the northeast where I
live, our climate seems to be
getting rainier and wetter.
We think that our rainfall has
increased by something like 21%
in the last couple of decades
and our winters especially are
getting a lot warmer and
rainier.
So these changes affect tree
health, tree productivity, and
their ability to produce some of
these compounds that give us
fall foliage.
John: We know that forests and
trees actually take greenhouse
gases out of the atmosphere.
So does this become in any way a
vicious cycle that that as
climate change hurts the trees
and forests, that they take less
green, fewer greenhouse gases
out of the atmosphere, making
climate change worse?
>> We think that over the near
term of maybe the next 50 years
or so, the combination of longer
growing seasons, because we have
warmer Summers, and higher
concentrations of carbon dioxide
in the atmosphere might actually
increase forest productivity.
Again, over the next several
decades.
But over the very long term of
maybe the next century, we might
see those positive effects of
climate changes overwhelmed by
extreme climate conditions like
drought and excessive rainfall.
John: Is there anything can be
done now to mitigate the that
long term loss?
>> For example, we can conserve
forests by conserving healthy,
complex forests, particularly
older forests, I might add, that
are able to buffer their own
climate beneath their canopies.
This might help forests resist
some of these climactic changes.
There are also a lot of things
that foresters can do to make
those forests more resilient to
climate change.
For example, reducing the
stocking or the density of trees
to make them less prone to
drought.
Of course, in the west, all of
the various techniques that we
use to support and restore
natural fire regimes.
So things like reducing fuel
loading and the use of
prescribed burning, all of these
things can make our forests more
resilient to climate change.
John: Bill Keaton from the
university of Vermont, thank you
very much.
>> My pleasure.
Thank you for having me.
♪♪