All right, thanks everyone for being here.
If you came to see Bill Keaton's talk,
I'm sorry to disappoint you that I am not Bill,
but he unfortunately at the last minute
had to miss the conference today.
I know he's sorry he can't be here with everyone,
but I'm a PhD student in his lab
and he asked me to give his talk for him.
So I'm gonna be talking about some research
that our lab has been doing over the past several years
looking at how riparian forest structure
impacts woody debris in streams.
And this is a project that was primarily led by Bill
and then a former master student, Hannah Kirkmeyer.
And I've been involved in kind of the later stages.
So just to give you some background
a little bit on Woody debris,
it's obviously a very popular topic right now
after all of the flooding this summer.
But large woody debris
has a lot of really important functions within streams.
It creates habitat complexity,
which can be important for fish
and macro invertebrate habitat
that provides sites for nutrient processing
and increases the roughness
or the complexity of the stream channel,
which has important implications for flood resilience.
If you look at the photo here on the right,
that's from Hubbard Brook Experimental Forest,
and you can see all that wood in the stream
is really creating a much more complex
and rough environment.
Now, a lot of research has shown that
large wood recruitment to streams is positively correlated
with forest age and structural development.
The figure here on the bottom left shows on the X axis,
the stand age of riparian forests.
And then on the Y axis,
the frequency of woody debris and streams.
You can see there's a very strong relationship here
where older forests store more wood at in their streams.
And as forests age undeveloped structurally,
the recruitment of wood two streams happens
both through density,
dependent mortality like south thinning
and through density independent mortality
such as disturbance gaps.
But where this gets a little more complicated
is because structural development
that provides a lot of wood to streams
occurs over multiple pathways
depending on disturbance type, stand conditions,
all sorts of things.
Typically, you know, we think about stand development
in northern hardwood Conifer forest is following
sort of the classic old field succession model
like you see at the top of this figure
where trees come back, they grow,
and then eventually later in succession
you have the development of gaps and downed wood.
But in recent years, in recent decades,
we've learned that there are many more complex pathways
through which stand development can occur.
A couple of which are,
that are theorized are shown here in the middle
and bottom panel of this figure.
But despite the fact that we know
there are these multiple pathways of stand development,
we don't have great paradigms
to understand exactly how they work.
And so this made us interested in,
okay, how does stand development under different pathways
impact wood loading and streams?
And we know that one place that there is a
sort of unique stand development pathway occurring
is at the Hubbard Brook Experimental Forest,
thanks in large part to some work by Charlie Coville
who I see out there.
Hubbard Brook was partially harvested
in the late 1800s and early 1900s,
leaving some remnant trees that many of which remain today.
And so this led us to wonder,
how does stand development
associated with such partial harvesting
and the retention of large trees
impact large woody debris recruitment into streams?
So to look at this, we, as I mentioned,
went to the Hubbard Brook experimental forest.
It's a mature forest.
And the land use history, as I was mentioning,
involved a lot of heavy logging for spruce trees
at the turn of the 20th century
and then some logging as well of hardwoods.
But this left a number of undesirable hardwoods
and left advanced regeneration release
creating these legacy trees,
like you can see in this image here.
This creates a forest that has a variety of tree sizes
and some horizontal complexity.
I mean nothing approaching old growth,
but it has some complexity
as you can see in this photo here,
variety of tree diameters
left some large trees that are old enough and big enough
to have epicormic growth.
And then what we're interested in,
these large trees eventually fall over
and often recruit into streams
like you see with this ash tree here,
and remain in the stream,
adding a lot of woody debris
and also collecting a lot of wood
that would otherwise move through the system,
creating a debris dam like you see in this photo.
So because of that,
and what we know about this recruitment process,
we hypothesize that forest structure
and particularly legacy trees
are influencing the variability that we'd find
in wood loading and streams across Hubbard Brook.
So to assess this, we selected 13 headwater streams
in the Hubbard Brook Valley.
Each reach that we sampled was 300 meters long.
These were all first or second order streams,
so about three to five meters in width.
And they were unmanaged.
We had field crews go out
and they sampled all of the wood within the stream reaches.
And to count as large wood,
a piece of wood must be at least 10 centimeters in diameter
and at least a meter long.
And then the field crews also sampled the riparian forest
setting up four random plots at each site
to assess forest structure and composition.
So then we could understand how that played a role
in the wood loading.
So to get into some of the results first about wood loading,
these two figures here show you
each stream reach that we sampled.
And on the top is the volume of woody debris in the stream
and on the bottom is the frequency of woody debris.
So that's number of pieces per 100 meters of stream length.
And we broke each stream up into 50 meter sub-segments
to try to understand some of the variabilities.
That's why you see there are error bars
and ranges on these graphs.
But the first thing to notice here
and kind of the most important thing
is that there's a lot of variability.
There's variability between stream reaches.
So those black bars are the medians.
You can see those vary quite a bit
from a stream like falls to one like Cushman.
But then there's also a lot of variability
within each stream.
So individual 50 meter segments
varied a lot within this broader 300 meter long reach.
And then to understand how forest structure
impacted that variability,
we found we ran Bayesian generalized linear mixed models,
which is kind of a mouthful
and analyzing these 50 meter sub reaches of the stream.
And then we made models using
28 different predictor variables of forest structure
and stream geomorphology.
And then within those models,
we picked out the most parsimonious model
describing the wood, loading the wood,
the frequency and volume of wood in these streams
using the expected log predictive density.
So what do we find?
This here, this figure on the right is,
there's a lot in here,
but basically what it's showing is
each of those panels is one of the predictors,
one of the parameters that was included
in the best fitting model to describe woody debris volume
in these streams.
But among these, so among these nine,
one of the most important ones
is the one that's circled up there,
which is the density of big trees in the riparian forest.
And big trees in the northeast
and kind of the east in general
are trees greater than 50 centimeters in diameter.
So what you can see in that circled panel,
these are marginal effects graphs,
which basically means it's showing you the impact
of each parameter on woody debris volume.
So in that circled one,
you can see there's this a positive relationship here,
meaning that a higher density of big trees
in the riparian forest is related strongly
to the volume of woody debris in the stream.
There's a number of other things involved in this model.
I don't have time to get into all of those.
But another interesting one is on the bottom right,
which hopefully you can read there,
that's the standard deviation of basal area
in the riparian forest.
And that's interesting 'cause you can see there is,
again this positive relationship
where a higher standard deviation in the riparian,
basal area in the riparian forest led to
or is related to more wood in the streams.
So this suggests that maybe there's some element
of patch complexity within the riparian forest
that plays a role in increasing woody debris volume as well.
Then when we go on to look at the frequency of wood,
this was the best model describing wood frequency.
So again, that's number of pieces of wood
per stream length, unit of stream length.
And again here the most important predictor in this model
was the density of big trees,
again with a positive relationship.
So we're seeing that big tree density increases
or is related to increasing wood volume
and frequency in the streams.
There's a couple other things in here I just wanna point out
that we're still trying to untangle.
So if you look, you see that quadratic mean diameter
is included, that's the top left panel I think.
And there's a positive relationship there
which would suggest that okay,
larger trees are important
for increasing wood volume and streams.
However, if we go back and look here,
we can see that when we're looking at
volume rather than frequency,
the bottom middle panel is quadratic mean diameter
and there's actually a negative relationship here.
So there seems to be something weird going on with that
where it's negatively related to wood volume in the stream,
positively related to wood frequency in the stream.
So still sort of untangling that and why that might be.
And then also there's this very interesting
negative relationship with dead tree density
and woody debris volume in the stream.
Our hypothesis about this is you might think,
okay, if you have more snags in the riparian forest,
you'll have more wood in the stream.
But our hypothesis about this negative relationship
is that there's maybe a time element here.
So perhaps what is happening is
in a forest that has few snags in the riparian zone,
there perhaps used to be more snags
that have already recruited into the stream.
So that stream would have fewer snags in the riparian area
but more in the stream.
So that's our hypothesis.
We haven't directly tested it,
but an interesting relationship there.
So our main conclusions, what are the takeaways here?
The big one is that remnant old legacy trees
appear to enhance and be related to
woody debris volume and frequency
in low order streams at Hubbard Brook.
This makes a lot of sense conceptually
because if these images on the left
are not from Hubbard Brook,
they're from actually old growth forests.
But you can see how when these large stems
recruit into the stream, they're very stable.
So when you have a big tree that falls in,
it often stays there for a long period of time.
These also have a lower surface area to volume ratio,
which means decomposition occurs more slowly
and they're very important for collection
of lots of smaller pieces of wood,
so creating debris dams.
And so basically these large trees
and their eventual recruitment into streams
may translate into effects on
wood related in-stream processes.
As I mentioned, we think that there's,
that this might be partially related
to some atypical stand development pathways at Hubbard Brook
and we're looking into that.
And then from a management perspective,
retention forestry that keeps big trees in riparian zones
may be important for long-term wood benefits.
I just have about 30 seconds left
so I'm not gonna go into this in a lot of detail,
but this is just sort of an idea
to show you what we're continuing to work on.
We're interested in how the riparian forest now
is impacting the functions
provided by these woody debris in the stream.
So we're doing some research
into the carbon stored by this wood in streams.
We're finding again here, big trees,
very important for the carbon storage of wood in streams.
And then on the right here,
we did an analysis comparing the carbon stored
in wood in streams at mature forest,
so at Hubbard Brook
compared to an old growth forest
and found that the old growth forest
stored about five times the amount of carbon.
So this may have future implications
for carbon dynamics and streams
as well as the potential uses a natural climate solution
as forests age and develop.
Let's see.
And I just want to acknowledge our funders,
McIntire-Stennis and National Science Foundation,
all the field crews who helped out
and Hubbard Brook.
-Thanks. -(audience claps)
Thanks for that. That's great.
Very interested in hearing more findings
as you develop them.
So you talked about structure.
Did you also look at diversity, composition,
anything about species in those riparian zones?
And can you comment on some of the preliminary findings?
Yeah, so we have those data.
In terms of this analysis,
the main thing we looked at was the percent conifer,
just because that is, I mean it's a compositional metric,
but it has a strong relationship to structure as well.
Lemme just go back and see.
I don't think that was in,
that was in the model describing woody debris volume.
So there's a negative relationship
between the percent conifer and woody debris volume.
We haven't dived into that too much.
We do have those data.
So it'd be something interesting to look into.
Thanks for that presentation.
Question for you about the snag density
and asking you to look into your crystal ball
and the slide that had the ash on it.
So that potential time lag or anything,
what do you see as the impact of emerald ash bore
on ash trees and then having impacts on our streams?
Yeah, I mean I think that's gonna have a really big,
there's gonna be a large flux of these trees to the streams.
There's been some research done in,
I think West Virginia looking at hemlock (indistinct)
and how that impacted hemlock forests.
And there was a bit of a time lag, I believe,
from actual infestation
and death of the trees to recruitment.
But that I would imagine is gonna speed up
some of this process of wood recruitment
especially 'cause at a lot of places,
the ash trees are some of the larger trees
left in the riparian forest.
So that may add more large stems to the stream,
which then have this effect of
sort of fueling more wood recruitment
by being stable and forming debris dams.
So as much as we don't wanna lose the ash trees,
I think there may be some benefits to streams.
Hi, have you looked at any correlations
between the amount of large woody debris in the stream
and the in-stream biodiversity,
the macro invertebrate communities or anything like that?
That is something we are starting to do some research on.
We have had someone from Plymouth State come out
and do some sampling on some of these streams.
Don't have any data on our sites.
But my understanding is that
generally having more wood in the stream
does increase macro invertebrate densities.
I'm not sure about diversity.
I would imagine it does,
but I haven't read any studies on that.
Yes, I'm very happy to see that
you have took land use history into account
at Hubbard Brook.
I'm Charlie Cobra by the way.
And it's very interesting.
Hubbard Brook is unique in its land use history
and not only in general but its specific sites,
the different cuts at different times,
at least three different cuts and salvage cuts and whatever.
And it's basically is produced a force that's an oddball.
An oddball that's a hundred years after major management.
And I wonder if that episodic history
is affecting what you have here.
I think it's a wonderful case history
but I don't know how generalizable it is.
All the yellow (indistinct) are falling out.
It's probably overshot the basal area to begin with.
And do you think this process that you're describing
is generalizable to either the original landscape
or the current landscape that's being managed
in a more intense way?
I think it is.
I think as you mentioned though,
because of the unique history at Hubbard Brook,
I think much of the landscape in the Northeast
doesn't have as high a density of these remnant trees.
And the relationship may be harder to pull out
just because there's not enough legacy trees left
to have a huge impact.
But I think at sites
where there was partial harvesting or minimal harvesting,
I think this probably is generalizable to those sites.
And I would imagine that as stand development continues
and we start to have more of these large trees
in places that were clear cut or old ag,
that there would be,
that this relationship would start to be important,
but that may not be for several decades
at sites that were clear cut.
Alrighty, we'll do one more question.
This is Chris Campy, Windham Regional Commission.
I'm here as a planner, not a forester.
But one of the things
I think we need to get the research out quickly
is about the benefits to woody debris and streams
and the impact on flood flows
'cause quickly, right now after these events,
trees are viewed as the enemy
and woody debris is viewed as the enemy
because logically you see it piled up
against culverts and bridges
and trees are viewed as, that is a bad thing.
But what's not necessarily being considered as upstream,
how much stuff is getting caught
by the debris that's already there,
by the standing trees that have been left to stand there
and how that dynamic works.
So just to plea to all of you,
get out in front of your road foreman,
your road crews, your select boards,
you know, maybe specific training
through Vermont local roads and other things
'cause you know, there's this view,
I mean, I think we in this room recognize that,
you know, we need more trees and we need bigger buffers
and we need, you know, to accommodate the flood events
that we've gotten that are coming.
But the intuitive understanding is not that
this is a good thing.
So just wanted to put that out there as a cautionary tale
'cause we're living it right now.
Thank you.