Immune Response in Hemlocks

Immune Response in Hemlocks

==============================================================================
TOPIC: Immune Response in Hemlocks
http://groups.google.com/group/entstrees/browse_thread/thread/2701053d4edf0a2a?hl=en
==============================================================================

== 1 of 4 ==
Date: Wed, Nov 14 2007 8:46 am
From: Josh

ENTS,

After collecting a couple of dozen cores from hemlocks heavily
infested with adelgids in the past three years, I have made an
observation: many of these trees continue to produce large growth
rings, despite their infestation, even into their last year of life.
Some even seem to increase their radial growth in the period of
adlegid infestation. It is possible that I am misinterpretting this
pattern. I suppose all infested trees could be "dropping" rings, and
I'm actually seeing pre-adelgid growth, but I don't think so.

Is it possible that the adelgid is so foreign to eastern hemlocks,
that the trees don't even recognize them as a threat, and their immune
response is not triggered. Normally, when a plant is attacked by an
herbivore, it increases it's production of secondary compounds to make
its growth, and in this case, fluids, less palatable to its
assailant. If our hemlocks are failing to physiologically "recognize"
adelgids, could there be a way to stimulate their immune systems to
put more of their energy into creating secondary compounds, and less
of it into producing lignin (wood). Just a thought. Has anyone else
seen a comparable trend in hemlock growth rates post adelgid
infestation? All responses appreciated.

Josh

== 2 of 4 ==
Date: Wed, Nov 14 2007 9:03 am
From: James Parton

Josh,

I have wondered about this as well. While surveying the hemlocks in
Cataloochee I have often wondered about the rings, whether the trees
add them ( grow ) at this time of great stress. If one cut a treated
survivor down years from now whether the ring count would be accurate.
It surprises me that they would add rings at this time. Will or Jess
may be able to add to this.

James Parton.

== 3 of 4 ==
Date: Wed, Nov 14 2007 1:12 pm
From: "Will Blozan"

Josh,

I think Dave Orwig posted this same observation a few years back. Maybe
since no energy is going into leaves it all goes into wood until the tree
runs out of stored energy?

Will

== 4 of 4 ==
Date: Wed, Nov 14 2007 1:15 pm
From: "Jess Riddle"

Hey Josh,

Most of the hemlock cores collected for Tsuga Search did not show the
pattern you're observing. I typically saw two or three very narrow
rings at the end of the core. Some cores were missing rings, but I
think two years was the most skipped and some trees in each stand had
a ring for every year. I think there were exceptions that did not
show a dramatic decline in growth, but I can't remember the details
now.

Jess

==============================================================================
TOPIC: Immune Response in Hemlocks
http://groups.google.com/group/entstrees/browse_thread/thread/2701053d4edf0a2a?hl=en
==============================================================================

== 1 of 6 ==
Date: Wed, Nov 14 2007 2:49 pm
From: Lee Frelich

Josh et la.:

There must be missing rings. The amount of wood a tree can make to cover
the trunk with a new sheath is proportional to the leaf area. Wood growth
on a tree starts where the branches enter the trunk, and proceed downward
from there to the base of the tree. Trees that have been severely
defoliated might still put on a ring high on the trunk, but that ring would
likely disappear or become discontinuous near the base of the tree. Unless
the second law of thermodynamics has been repealed, I can't see any way a
hemlock could get the energy to make more wood as the foliage disappears.
Hemlocks don't have big stores of materials to use in case of emergency.

Immune systems are mechanisms to detect and destroy foreign proteins at the
molecular level, and are the main form of interaction between
microorganisms and animals. Immune systems don't occur in trees, although
as you point out some trees have inducible defenses in the form of
secondary compounds. The inducible defense mainly occur in trees with short
leaf lifespans, for example oak trees (leaf lifespan 4-7 months) defoliated
by insects can grow a new set of leaves with secondary compounds. Hemlock,
on the other hand, has a long leaf lifespan of 2-4 years, which makes it
more difficult to respond to defoliation. The loss of foliage is a greater
blow to the tree in a hemlock than a species with shorter leaf lifespan,
since it represents a much bigger investment of resources by the tree.

Resistance to insects and other herbivores has many different mechanisms,
such physical, chemical, and phenological. I haven't seen any reports on
why western hemlock and Japanese hemlock are not killed by the adelgid
(although they probably exist somewhere) and we would have to know that to
try to induce resistance in eastern hemlock.

Lee

== 2 of 6 ==
Date: Wed, Nov 14 2007 3:48 pm
From: "Neil Pederson"

Josh, ENTS,

here is one citation I know of that might help your answer question: Impact
of the Hemlock Woolly Adelgid on Radial Growth of
Eastern Hemlock in Pennsylvania. Donald D. Davis, Matthew S. Fromm, and
Matthew D. Davis.

It is available here: http://www.treesearch.fs.fed.us/pubs/27819

I've not read it yet. Hope to in the next 2 weeks. Hope it helps - it is an
interesting question & observation. From the NA Dendroecological Fieldweek,
I seem to recall a reduction in ring widths in hemlock, but these may have
been mostly suppressed individuals. Is that correct, Jess? If so & in
conjunction with Jess' observation from the Tsuga Search trees, Josh, you
may be 'missing' rings.

neil

== 3 of 6 ==
Date: Wed, Nov 14 2007 4:44 pm
From: Josh

Thanks Will, Jess, Lee, and Neil,

Neil, from the article you pointed toward " Severely infested trees
exhibited a short-term, spike in growth immediately prior to a
precipitous growth decline that eventually lead to mortality."

Such a spike in growth to a sick individual that should be putting
it's resources towards inducible defenses could be catastrophic miss-
appropriation of energy, and part of a feed-back loop that leads to
their demise. This is what I think I may be observing.

Josh

== 4 of 6 ==
Date: Wed, Nov 14 2007 6:08 pm
From: Josh

Reading the entire article, I now see that the authors attribute the
early infestation spike in growth to increased light from the needle-
drop of neighboring trees, and perhaps increased nitrogen from the
same source. It seems like they too believe in the second law of
thermodynamics Lee. Well, I'm not about to argue with 300 years of
well validated physics. I do think there could be some strange
hormonal stuff going on with hemlocks infested by the adelgid, and
that could contribute to their mortality.

Josh

== 5 of 6 ==
Date: Wed, Nov 14 2007 6:31 pm
From: Michael Davie

I believe that one of the presenters at the adelgid symposium, who had
been looking into the terpenoids present in hemlocks, had posited the
differences in terpenoids might make the difference in susceptibility.
I'll have to look at the proceedings to see if I'm remembering
correctly; one thing I do remember is that his english was not very
good and most of what he was saying was not only over my head but
nearly incomprehensible anyway. This may be related:
http://pubs.acs.org/cgi-bin/abstract.cgi/jafcau/2003/51/i08/abs/jf021028s.html
Mike

== 6 of 6 ==
Date: Wed, Nov 14 2007 9:10 pm
From: James Parton

Jess & Josh,

This would have been more of what I expected. Missing rings or very
close rings due to lack of or slow growth due to infestation.

James P.

== 2 of 4 ==
Date: Thurs, Nov 15 2007 6:10 am
From: "Will Blozan"

Mike,

A student at Warren Wilson College is trying to study the terpene stuff as
well.

Will

== 3 of 4 ==
Date: Thurs, Nov 15 2007 7:13 am
From: David Orwig

Josh, you may also be observing dynamics in tree growth reflecting
changes in HWA populations, which also fluctuate on the tree. For
example HWA may be quite high on the tree for several years, then the
quality of resources declines and/or some other factor like cold temps
causes reductions in HWA populations. If the next year is good for
hemlock growth, the tree may be able to have a better year, which then
makes it better for the HWA, which subsequently rebound. Certainly the
dynamic i point out may not be happening down south, but has occurred in
southern New England.

DAVE ORWIG

David A. Orwig, Ph.D.
Forest Ecologist
Harvard University
324 North Main Street
Petersham, MA 01366
978-724-3302 ext.250
http://harvardforest.fas.harvard.edu

== 4 of 4 ==
Date: Thurs, Nov 15 2007 2:29 pm
From: Josh

Lee,

All the hemlocks I have cored have been old - at least 160 years.
Most have been in association with other hemlocks, but I can think of
one exception, a 317 year-old tree in the Pigeon River Gorge amongst
hardwoods. I'll take a look at that one when I get the chance.

Josh

== 2 of 2 ==
Date: Thurs, Feb 7 2008 9:53 pm
From: James Parton

Ed,

But why is the Chinesis clean of hwa while the Canadesis is covered?
I know the Chinese hemlock evolved with hwa and obviously has some
degree of immunity to it. Does it have a natural compound that the
adelgid dislikes that the Eastern & Carolina hemlocks lack? There is
a reason why the bugs favor ours so much, but I am sure the
professionals have noticed and thought about this already.

JP

==============================================================================
TOPIC: Immune Response in Hemlocks
http://groups.google.com/group/entstrees/browse_thread/thread/71238e57ab560859?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Feb 10 2008 10:07 pm
From: Andrew Joslin

I'm not a forestry expert and I'm looking forward to an expected
emphatic response from Will and others. Based on my observations of
young hemlocks in dominant hardwood forest over the last ten years of
HWA moving into woods in my area I predict the following: cutting
down the hardwoods will have zero impact on helping the hemlocks
resist HWA. It may actually hasten their decline since they are
adapted to the lower light levels under the hardwoods and will suffer
additional stress on top of what HWA is already doing to them. I
understand the release phenomenon caused by opening the canopy but
that requires healthy hemlocks to take advantage, not stressed out
hemlocks fighting against HWA. The end result of the recommended
strategy will be zero large hardwoods and zero hemlocks, what's known
as a lose/lose outcome.

I'm surprised what seems like continued denial by "experts" as to the
well documented prognosis for eastern hemlock exposed to HWA, they
just can't fight it. I don't care how optimal the growing conditions
are. I've seen the healthiest possible groves go under. Will's photos
from the Smokies should be enough to convince. The hemlocks in the
Smokies are growing in the most optimal habitat known for the species
in its range and it looks like they've been nuked! The only natural
phenomenon that's proven to keep HWA exposed hemlocks from going
under are colder average winter temperatures in more northern
locations and that only prolongs the death process.
-AJ

From: Jonathan Wagar
Sent: Sunday, February 10, 2008 11:05 PM
Subject: [ENTS] Re: Immune Response in Hemlocks

Greetings ENTS!

First, I'd like to say that this is my first post and I really enjoy reading your list! Thank you for sharing your tree knowledge and insights!

I have a related question about HWA and forest management and was wondering if anyone could point me in the right direction.

I manage a large nature preserve located in the Highlands Region of Northern NJ. We have several nice, young hemlock stands that are starting to decline due to HWA. Like a lot of young hemlock stands in the area, hardwoods are the dominant canopy tree. A forester recently recommended that we cut down all of the dominant hardwood trees to release the hemlocks and give them a fighting chance against the HWA. He felt that the hemlocks have a better immune response with less competition. What I have read here seems to contradict his statement.

My question is, does his recommendation have any basis in research? We are willing to try just about anything to try to save our hemlocks, but other local well-stocked hemlock-dominant forests (i.e. no supposed hardwood competition) seem to be infected with HWA at the same rate as our young stand. In most cases, I feel that doing any type of active tree cutting in this area of New Jersey is extremely problematic if a goal is regenerating a native forest. Contrary to our best efforts, we have extremely high deer densities and major problems with non-native invasive plants. There is absolutely no native tree regeneration in natural forest canopy gaps in our forests. But maybe that is for another post....

Thanks in advance for your advice!

Jon Wagar

== 2 of 4 ==
Date: Mon, Feb 11 2008 5:53 am
From: "Will Blozan"

AJ,

NAIL ON THE HEAD!

Will

== 3 of 4 ==
Date: Mon, Feb 11 2008 6:00 am
From: "Joseph Zorzin"

That forester was probably just trying to get his chainsaw teeth into a nice overstory of hardwood. The lies that some foresters tell are just amazing. If he was a service forester or extension forester- it could just be ignorance, but if a consultant or mill forester- I bet he saw a nice profit. It's such selfish advice that gives the forestry profession such a black eye.

Joe

== 4 of 4 ==
Date: Mon, Feb 11 2008 12:16 pm
From: "Jonathan Wagar"

Thank you everyone for you response! That is pretty much what I figured and
it was very helpful to get your thoughts. - Jon Wagar

Home