- Jeff Ward is the Chief Scientist
with the Department of Forestry and Horticulture
at the Connecticut Agricultural Experiment Station
and, today, is presenting "Multiyear Defoliations
in Southern New England Increases Oak Mortality".
Jeff, take it away.
- So yeah, I'm gonna be talking about some research
we started before we joined FEMC,
but I think it's really gonna highlight the importance
of longterm monitoring, policy monitoring long-term time.
I can end up looking at questions
you've probably never even thought of when you set it up.
And if you've never seen severe gypsy moths defoliation,
that was a stand last year in Western Connecticut
and that picture was taken at the end of June.
So at the very beginning, I just want to thank
all of our great partners in setting up this study
and, especially, Alenka Mora and Sarah Sullivan,
we'll close a lot of field work,
and my right hand, JP Barsky.
So here's the take home message.
I like putting up the beginning.
First of all, multi-year defoliation events
are really important, where you're gonna see,
as far as oaks, is you're gonna see
the loss of lower canopy oaks,
you're gonna see the loss of white oaks,
and you're gonna see the loss of low vigor red oaks
and there's a new thing that we found recently.
I'll try to get that to the end.
So what was our previous knowledge about that?
Well, we actually set up, our oldest research plots
go back to 1927 that we measure every 10 years.
So we're able to measure ingrowth, death mortality,
and then when we have an event happen, like defoliation,
we're able to see what the impact of that is on the forest
and was fortunate on this forest
is or unfortunate, I should say,
is there's some pretty severe defoliation.
We had three years of, you know,
40% or more defoliation back in the '60s,
two years in the '70s, and one year
of big defoliation back to the 1980s.
And one of the take-home message, if you look in the bottom,
you can see the measurement period we had
and if you look in the side,
that's mortality of upper canopy oaks
and notice, that only goes up to 40%.
I'll explain why in a second.
But we had three years,
three years of repeated defoliation.
We saw that we had close to 35% of all oak trees died
for repeated defoliation.
With two years of defoliation
back in the '60s through the mid '70s, we had around 50%
and then with one year defoliation,
the oaks really can tolerate one year defoliation
and the periods without defoliation,
upper canopy oaks we had, you know,
less than 1% mortality on average.
Compare this to the upper canopy oaks.
Compare the lower canopy oaks, the upper canopy oaks.
Lower canopy oaks, those trees are already stressed
because they aren't getting as much sunlight,
much, much higher mortality.
In fact, the first period we had,
the first multi-year period we had back in the mid '60s,
we lost over 85% of the lower canopy oaks
were killed by the defoliation induced mortality.
And even when we only had two years,
we still had close to half of those
trees that survived then died.
So that's one of the big things there.
And commonly, as Judy said
if you're in the earlier session,
gypsy moths, by themselves, don't kill the oak,
but they start to decline spiral
where you can get on malaria root rot,
two-lined chestnut borer,
and, eventually, the oak tree dies.
Oops, (indistinct).
One of the things we also found from that earlier study
is that white oak mortality was much higher.
The white oaks, white chestnut oak,
mortality is much higher than for the red oaks,
for northern red, black, and scarlet.
And mortality was also a higher per codominant oaks
than they were for dominant oaks.
So if were a red oak, even with repeated,
you know, defoliation,
if you were in the dominant crown class,
you only had about 10% mortality,
but then if you look at codominance,
now we're getting up to 40%.
So there's a real, you know,
a real difference between crown classes
because trees which are up in the sunlight
are, generally, able to produce
more carbohydrates so they have greater starch reserves
to be able to refoliate after oak.
I'm sorry, after gypsy moth defoliation.
One of the other things we found
is that faster growing trees, back then,
the faster tree grooves, the more likely it was
to be able to survive repeated defoliation.
This held for the dominance, the red triangles,
for the codominance, the orange triangles,
and, also, for intermediate,
so long as they had at least a 10th of an inch
in diameter growth on average every year.
So the first bottom line from that study
is that multi-year defoliation
has removed the lower canopy oaks.
They remove less vigorous oaks,
the ones that are growing slower
and especially removed white oaks.
One thing we did see back there,
for time, I wasn't gonna go into this.
Surviving trees did recover and 20 years later,
we really didn't see that
they had higher mortality over time.
So those who survived were able to do well.
And then we went through a 30-year period
without a major outbreak
and this was actually right after,
the last big defoliation
was right after I came here in the late '80s.
So most of foresters are really put worrying about LDD
and that's what the new name is for gypsy moth.
It's now, I can never pronounce that,
so you can read it down there,
but really nobody worried about it,
but wouldn't you know it,
we had the hungry, hungry caterpillars came back
and they just completely defoliated
thousands and thousands and thousands of acres,
especially in Connecticut, Rhode Island,
and Eastern Massachusetts.
And here's a map that was produced by the US Forest Service,
where you can see just how extensive
all the defoliation was and if you look at the areas
that are sort of a deep, dark red color there,
those were areas, I'm sorry, the red areas were,
brighter red, were areas that had two years in a row
repeated defoliations and we had some stands
in Connecticut, at least, so we had three years
of repeated defoliation.
So those trees really got hammered.
It was also compounded by something else
is going on at the same time.
Similar to back in the 1960s,
we had an extended period of drought.
If you look back in the '60s, there were four years straight
when we had pretty severe drought characteristics
during the growing season.
If you look at what we had back between 1915 and 1918,
we had, again, four years in a row where we had
pretty moderate to severe drought situations
during growing season.
So the trees were hit with a one, two hammer.
They were hit with both the drought, which weaken them,
and then they were hit by defoliators.
So in response to this,
because the trees now are also 30 years older
and trees are like people.
They do have a lifespan and a lot of our oaks,
the scarlet and black oaks,
are probably getting towards late middle age.
And just like a lot of us of a certain age,
we're not quite as resistant to insects and disease.
Well, not insects and diseases, but for us diseases,
and are more likely to have issues.
So we set up 29 study areas and we look at over 3,000 oaks
and on all of these study areas, the ones we chose,
these were areas where we had 10 years data
prior to the defoliation outbreaks.
So I want you to recall that we've talked about before.
I didn't show you this exact graph,
but we look at mortality of the red oaks,
the red triangles, and the white oaks, the the blue circles,
back during the '60s and '70s,
white oak tended to have much higher mortality
than the red oak did.
Well, we did the preliminary one analysis.
We found that, "Hey, something's different."
Also the red oaks are dying
almost at the same rate as the white oaks.
Like I said before, we're speculating right now,
but we think one of the differences
are these trees are getting older.
It's kind of interesting.
A side note back in the 1930s,
when they did a study of LDD and mortality,
they called that part of Eastern Connecticut,
Western Rhode Island, they called them gypsy moth proof,
even though there's 50 moth going through there,
they didn't see trees die.
The difference was those trees were 90 years younger
back in the 1930s when they looked at that data.
The one thing we did find is that, again,
the more defoliation hit, the more severe it was
and persevere, we said it had to have
at least two years of defoliation,
you saw much higher mortality levels.
And I said, blackouts, especially,
are probably getting towards, you know,
late middle age, early senescence
so it became much more susceptible to defoliator,
which deployed some at the exact wrong time of the year,
right in the spring, right when they're using
all of their stored energy to produce those new leaves.
Now they have to pull on their reserves
and if they don't have the reserves,
they aren't gonna be able to recover as quite as well.
And this is just a screenshot.
This has taken two years after defoliation ended.
And you could see this one here flying around
thousands and thousands of acres of dead oaks.
Those aren't defoliated oaks, those are dead oaks
because the defoliation period had ended.
So how do the stands recover, crystal ball?
Well, the one thing we found in the past,
just a little drawing, showing that
whenever you look at a stump,
you can see the trees really had slow growth
during those periods, gypsy moth defoliations,
as you would expect because now they have to use
all their starch reserves not to grow,
but to try to produce new leaves
and new buds for the following year,
but then they recovered and we saw pretty wide growth rings.
But again, those trees were 30 years older.
So what's gonna happen in the future?
We're really not quite sure.
The other thing we saw in the past,
it was we saw a real upsurge, a real surge,
in the growth of, down our way, it's mostly red maple,
was some sugar maple, and especially black birch
coming into these stands where the overstory oak had died.
There weren't as many beech coming in,
'cause we didn't have this many beech at the beginning,
but over the last 30 years, beech had increased.
And as Judy has said in the previous talk,
we have a new bugaboo out there.
We really don't know what's gonna happen
because of beech leaf disease.
In this past year, I saw several stands
where all the understory beech were dead
and in some of the stands,
25% of the overstory beech had died in one year.
So that's a very scary disease.
Maybe the only good thing,
I don't know if it's because of climate
or weather or just pure luck,
but it seemed to be restricted
to within 30, 40 miles of Long Island Sound.
The other thing to note, too,
is when we saw the recovery in the past,
this is before deer density was high
and before the days this species became an issue
and invasive species, I mean, Japanese barberry,
multiflora rose, stiltgrass, bittersweet,
these are all having a real impact
on how these forests are gonna recover going forward.
So the second bottom line, as we saw before,
multi-year defoliations remove the less vigorous oaks.
They remove lower canopy oaks
and they remove the white oaks,
but because the trees are older now,
we're seeing increased mortality of red oaks
and, unfortunately, I think that's gonna be likely the norm.
And as I said, surviving trees recovered well in the past.
How are they gonna do going forward as they're older?
We just don't know.
And the one thing you can see
is defoliation induced mortality.
Mortality comes after defoliation,
whereby defoliation
can increase in succession of maple and birch down our way
and probably beech.
Now, you might be thinking,
those of you who are up further North,
well, you don't have to worry as much about gypsy moth.
But gypsy moth likes to feed on an oak,
but it also loves aspen and I know aspen
is the species we're trying to maintain,
not so much for timber value,
but because it has some real important wildlife values
and gypsy moth love aspen.
So with that, I'm gonna stop sharing my screen
and if anyone has any questions,
be more than happy to answer you.
- [Judy] We do have a couple of questions in the chat box.
- Sure.
- [Judy] The first one, "Can we comment on the potential
for prescribed fire as a tool for encouraging oak region?"
(laughs)
- That's a little off subject.
Prescribed fire, I think would work pretty well,
but you're gonna have to have repeated prescribed fires.
Reason why we can't really use prescribed fire
as a tool down here in Connecticut
is because of air quality.
We're just very much an urbanized state.
Even though we're close to 60% forest cover,
we also are the fourth,
most densely populated state in the country.
So that's really a tool that's not in our toolbox anymore.
- [Judy] Another question in the chat box.
"What do you think the mechanism
is underlying the greater vulnerability
of older red oak trees?"
- Ah, boy, I wish I could answer that.
I'm not a tree physiologist.
I think part of it is as the trees get older,
they have to support a lot of,
you know, tissues on the branches and on the trunks
and those are nonproductive tissues so they,
you know, they're, I don't want to say they're parasites
because they're holding up the leaves,
but, you know, when you start getting
bigger and bigger branches, it takes more and more energy
just to maintain those branches
and the trunk space.
And there's probably some other physiological reasons,
but like I said, I'm not a physiologist
so I don't know how to answer that.
- [Judy] Okay, thank you.
There's a couple more in the chat box.
"I noted you used PDI in our FH reports
and Vermont's Drought Monitor product is often referenced.
What are people's favorite tools for looking at
and quantifying drought as it relates to tree
and forest health?"
- Well, I'm gonna look at some of the modern parts,
you know, I'm an old timer.
So I still use the Palmer Drought Index.
I like looking at the growing season.
The reason why I look at growing season
and not overall during the year is,
as far as I've known,
every year, the soils become completely recharged
with moisture over the winter because you don't have
the leaves pulling all the moisture out of the ground
that we get enough snow and rain
and soil moisture fully recharges.
So I like looking at, you know,
the drought during the actual growing season.
So there's a question I can,
actually, I can start reading now.
Jeff Foran asked for one about,
"Why the higher mortality for white oak?"
I think part of it is LDD preference.
Why does some of them have as many tannins in their leaves?
And gypsy moths,
you know, the tannins in leaves are primarily
a defense against insect herbivory.
So the gypsy moth, preferentially, where I've seen it,
will feed on the white oaks
and then preferentially feed on aspens.
Then they'll move on to the red oaks
and then the red maples
and they'll feed on pretty much everything except ashwood,
since we've lost most of the ash, to a pauper or sassafras,
and a real surprise,
I've seen areas where every tree is stripped
except for sassafras and American chestnut.
- [Jerry] Jeff, this is Jerry in New York.
Great presentation, thanks for that.
I'm wondering what you think the role is for,
(laughs)
what you think the role is for a time,
obviously, you mentioned drought,
but, you know, we in New York have had periods of drought
and not had the same outbreak
that you guys in Connecticut and Rhode Island had
in the same types of stands.
So is that a bigger role for maybe the national enemies,
(indistinct) or what do you think?
- I'll tell you, it's really interesting.
If you really dive into the literature,
it seems like drought during outbreak
exasperates mortality, but drought per se
doesn't set up a gypsy moth outbreak.
But a drought allows, and (indistinct), the fungus,
to, it's not so much drought as you really need to have,
you know, multi-day periods during May.
So fungus is pretty much always out there,
but it'll hit the early instars
and then it'll bioamplify in those early instars
and then if you've got more repeated periods
of high humidity and high moisture,
the fungus will, I'm pregnant to say this 'cause I'm not
a fungus guy, but it'll sporulate
and it'll spread to the later instars
and that's when you start seeing the massive die off
and you start seeing the caterpillars
falling out of the trees
and the woods smell like rotten meat when it gets that bad.
- [Judy] There is a comment in the chat box, too.
- Yeah.
"The timing of the leaf out, red oak, white oak."
I was gonna say, well, at least down here,
they tend to leaf out pretty close to each other
within a couple of days.
And I'll tell you, man,
that could be,
I just honestly don't know.
The one scary thing that would happen when we had,
you know, a couple of years of drought
before we had this last outbreak of defoliators,
and I shouldn't say the first year of defoliation,
we also had, the same time, with gypsy moth,
there was a co-outbreak of forest tent caterpillar.
And they were both covering all of the tires
while we were out in the woods.
But when both arborists and foresters
were trying to drop trees,
when you drop, especially the white oaks,
if you're a harvest tree, when it hit the ground,
the entire tree would shatter.
There's very little bucking was needed on the trees.
Arborists were saying when they were up there
bringing down trees that were dead around folks' houses,
the branches would just sometimes just shatter
before they'd even cut all the way through the limbs.
So it became a bit of a riskier proposition
to actually be working out in the woods at that time.
- [Judy] Thank you, Jeff, for that presentation
and for all the questions and the answers.
We'll see people at the next talk.
- Take care, everyone.
Thanks for listening.