- Welcome, everybody.
My name's Alex Balial.
I'm with the FEMC.
It's my pleasure to introduce Katlyn Schulz,
a graduate student at the University of Maine.
Katlyn will present the effects of harvesting
on lowland northern white-cedar stand structure
and composition.
- All right, thanks for the introduction, Alex.
Like she said, I'm a master's student
at the University of Maine,
and I'm going to be presenting on management impacts
on sustainability of lowland northern white-cedar.
So to begin, northern white-cedar's
a boreal conifer tree species
that's distributed throughout the northeastern United States
and the southeastern part of Canada,
which you can see on the map to the left.
It's a slow-growing, shade-tolerant,
and long-lived tree species,
and although this tree has a lot of economic,
cultural, and ecological value in the region,
it's also one of the least studied commercial tree species
in North America, so that makes any new information
on the species really valuable.
My master's project will focus on the effect
of harvesting on lowland northern cedar stands,
which are characterized by wet, swamp-like environments.
Around 70% or more of the stands are made up of cedar,
and the rest is a mix of deciduous and evergreen species.
These ecosystems are extremely sensitive
to environmental changes,
and they can be greatly impacted by human activity.
Since the early 1900s, the cedar population
in Maine has been steadily declining,
and the cause has been attributed mainly
to poor management practices and excessive harvesting.
Cedar is really challenging to manage,
and even more so in sensitive lowland ecosystems.
One of the biggest reasons it's challenging to manage
has to do with all the seasonal flooding
that occurs every spring.
Cedar has very specific water requirements
in order to regenerate, and it can rot and die
if they're exposed to too much water.
Additionally, as a shade-tolerant species,
cedar grows really slowly, so its growth is suppressed
under the canopy for many years by its competitors.
Finally, cedar is a preferred winter browse species
for forest mammals like deer and bear,
so those that can establish
and grow are often eaten in the winter.
The combination of all of these factors makes it
extremely difficult for cedar to thrive
after they're harvested,
and it's causing the population to decline.
My study will focus on assessing the impact of harvesting
on two of the challenges to cedar regeneration recruitment,
which are in in bold.
In order to understand if harvesting positively
or negatively impacts cedar regeneration sites,
it's equally important to look at the impact of harvest
on both cedar and its main competitors.
This will help them determine if harvesting creates
environments that will promote future cedar regeneration,
or that of its competitors.
Cedar's main competitor
in the lowlands stands is balsam fir,
which is an extremely common and widespread tree in Maine,
but it has a lot less ecological
and economic value than cedar.
Although it's a native tree, it's considered to be needy
in many core stands across Maine,
because it's really fast-growing,
has a lot less specific site requirements than cedar,
and their regeneration often dominates the forest floor.
The biggest problem for lowland cedar is competition
and canopy suppression.
Therefore, my study is focused on managing cedar
in lowland stands, which again, is challenging to do.
Previous research conducted in upland
and mixed stands suggests that
partial harvesting might be an effective treatment
for lowland stands, because it retains a large portion
of adult trees dispersed throughout the stand,
which has proven effective in promoting growth,
regeneration, and recruitment.
Therefore, the overarching goals of my study are
to determine the conditions that are associated
with cedar and fir regeneration in lowland stands,
and then increase our understanding
of how partial harvesting impacts structure, composition,
regeneration, and associated micro-climates
in the lowland stands to determine
proper management procedure.
For this study, three lowland cedar sites
throughout Maine were selected, which you can see labeled
as stars on the map to the left.
All three of the sites had a history
of unspecified partial harvesting prior to the mid 1900s,
with no known harvesting since then.
The middle image is of one of our sites,
so each of our sites had one treated stand,
and around one to three control stands,
and within each of those stands were
around four to five fixed-radius plots that we took
measurements in, and then two to three mil-plots
within those spots.
To achieve the first objective,
a partial harvesting treatment was applied to one stand
in each of the three lowland cedar sites.
The two images to the left show the density of the stand
before and after a harvest,
and it was treated by an irregular shelter with treatment
that had a target removal of 40% stand basal area removal
of trees over 4.5 inches in diameter at breast height.
The harvest was meant to thin the stand,
capture mortality, improve the growth
of the best cedar trees, and improve
overall stand vigor and quality, while maintaining
structural complexity, and opening the cedar,
or opening the canopy for cedar regenerations.
Next, we took measurements, and conducted them
on three sites to determine the conditions
that are associated with cedar regeneration and fir,
as well as to assess the impact of harvesting
on those conditions, and the composition
and structure of the stand.
Pre-harvest measurements were conducted
the summer before the harvest,
which took place in the winter,
and then post-harvest measurements were conducted
the summer after the harvest.
My thesis is part of multiple ongoing projects
in which all of these measurements
on the site were assessed.
However, today I will be reporting some preliminary results
from the first stage of analysis for the measurements
that are related to my thesis, and these are in bold.
So now we're gonna move on to the results
of the pre-harvest conditions of the stands.
So before the harvest took place,
trees per hectare was calculated to determine
the species composition of understory,
which is the seedling and sapling layer,
and then the overstory, which is the tree layer.
For this graph, trees per hectare is on the Y axis,
and size, class, and species is on the X.
It was found that in a majority of the stands,
fir dominated the understory.
In both the understory and the overstory,
all the other tree species,
like spruce and birch were minor components of the stand.
It was only in the overstory that cedar composed
a majority of the species composition,
and this is what classified these stands as cedar swamps.
Oop.
This finding directly contradicts the findings
of similar cedar studies in the region,
which found that cedar dominated the overstory
and the seedling layer,
while fir dominated the sapling layer.
In these studies, a recruitment bottleneck was observed
between the cedar seedling and sapling class,
and it was determined that their growth was limited
by things such as light availability,
browsing, or competition.
However, for my study, the limited cedar regeneration
in the seedling layer suggests that regeneration
and establishment is being limited
by a lack of suitable microsites,
rather than a recruitment bottleneck.
One potential explanation for the lack
of suitable microsites for cedar could be related
to micro-topography, or the topographic variability
of the soil surface.
For this study, we identified three different types
of micro-topographic positions,
mounds, which are the raised areas,
flats, which are the level areas,
and then pits, which are the sunken areas in the ground.
After averaging all the sites together,
we found that mounds consisted around 33%
of the landscape, flats around 48, and pits around 18%.
In the wetland conditions of the lowland cedar stands,
mounds are thought to be particularly valuable
in landscapes, because they're significantly less saturated
than flats and pits, and this helps to reduce
mortality from flooding.
Therefore, we expect to find both cedar
and fir positively associated with mounds,
and negatively associated with flats.
To assess the association of fir and cedar abundance
with positions, the occurrence of a pit, mound, or flat
on a landscape was compared with the actual positions
of cedar and fir seedlings found on a flat level
for each management unit.
This was done using a Chi-squared test,
and standard residuals and P values
that were generated were average to the stand,
site, and then study level.
Results were recorded at the site level,
and then across all sites.
This figure on the slide is a heat map
that helps to visualize the association
of seedling abundance with positions.
Micro-topographic position is on the Y axis,
and then three different study sites are on the X,
as well as the division between fir and cedar seedlings.
Finally, the standard residuals,
which are denoted by the different colors, indicate
if the seedlings are associated
with a certain position or not.
Green indicates that more seedlings would be found
more often than expected by chance,
whereas red indicates the opposite.
The white color indicates that seedlings are found
as often as expected on a certain position,
and then stars in the right-hand corner indicate
if results were statistically significant.
What we found was different than when we expected.
Fir seedling abundance was found to have
a greater association with mounds than cedar,
which you can see by the two dark squares
with stars on the left.
This is compared with cedar, which has a lesser association
with mounds, which you can see
by the two light green squares and only one star.
This finding directly contrasted many of the studies
that have found a strong association of cedar with mounds.
One explanation could be that fir is dominating,
and out-competing cedar on the mounds.
Additionally, mounds consisted of an average of only 33%
of the landscape, but other studies have suggested
that cedar regeneration required at least 70%
of the landscape to be composed of mounds
in order for cedar to avoid interest-specific competition.
So next we'll move on to pre versus post-harvest conditions
of the overstory.
So in order to determine if partial harvesting impacted
stands' structural attributes and regeneration,
pre and post-harvest conditions
for eight variables were compared and tested,
using linear mixed effects models,
using a random effect for plot
within each treated management in it.
We calculated the difference
between pre and post harvest variables at the plot level,
and then determined if the difference was
significantly different than zero.
So for these next few graphs,
the pre-harvest conditions will be
on the left side of the graph,
and the post-harvest conditions will be on the right.
This first graph involves basal area,
which was significantly reduced after the harvest.
The second graph reveals a significant decrease
in canopy cover, around 20%,
from pre-harvest to post-harvest conditions.
However, you can see that, while the reduction
in basal area indicates that the stand was thinned,
and the canopy was open, it wasn't really opened that much.
Canopy cover is still around 70%, and this still mimics
the relatively shaded conditions that cedar prefers,
so it's a good thing.
This next graph looks at the change in trees per hectare
from pre to post-harvest.
This graph is divided by species, with cedar on the left
in red, and fir on the right in blue.
As we learned from the previous graphs,
the treatments resulted in the overstory being
significantly thinned.
However, even though it was thin,
there was not significant declines in cedar or fir,
or at least consistently across all plots.
This means that our objective,
which was to thin the stand while opening
the canopy proceeded regeneration,
and maintaining structural complexity was achieved.
So next we'll move on to pre versus post-harvest conditions
in the understory.
So in assessing how understory conditions changed
from pre to post-harvest, we were able to better assess
the suitable micro-site conditions
for cedar or fir where either increased or decreased.
The first graph deals with coarse, woody debris.
The panel on the left shows a significant increase
in coarse, woody debris and decay class one,
which is usually newly-cut wood
that hasn't started to decay yet,
and this is likely driven by the presence of new stumps.
However, interestingly enough,
after we corrected for multiple comparisons,
we found that the difference was not
statistically significant.
This is because a majority of the stands experience
little to no change in wood volume after the harvest,
which you can see on a histogram to the left.
The reason why the previous graph seemed to be
statistically different was because some plots were in areas
that were impacted by the harvest, and some are not,
and we're gonna have to analyze this further.
Coarse, woody debris in decay classes four to five were not
significantly increased.
The retention, of course, woody degree can increase
micro-topographic variability,
and as wood progresses into higher decay classes
like four and five, it retains levels of moisture
and temperature that are suitable for cedar regeneration.
For the next graph, you can see that
the percent of mounds did not significantly alter
after the harvest, which is also good.
There was a concern that
the mechanized harvesters could cause damage
to micro-topography within a stand,
and this reduced the number of seedlings that regenerate
and survive each year, but this didn't happen.
Finally, with this last graph,
you can see that the trees per hectare
of seedling, of cedar and balsam fir seedlings were not
significantly changed by the harvest.
There was initially a concern
that cedar ceilings might be damaged
by harvesting equipment, but these results indicate
that they were not, which is also good.
And also just to clarify, we didn't expect to see
an increase in cedar regeneration.
There was only a year in between the survey periods,
and that's not long enough to see if there was an effect
on regeneration and recruitment due to the harvest.
So what does all of this mean?
So our results show us that stands are dominated by fir
in the understory, and cedar in the overstory,
which is different than a lot of the stands in the area.
The conditions of the stand may not currently support
cedar regeneration and recruitment.
This could partially be due
to micro-topographic variability.
And then our treatment objective,
which was to thin the stands,
while maintaining structural complexity was achieved.
And then during the harvest, it did not significantly alter
things that support cedar regeneration,
like coarse, woody debris, the percent of mounds,
or seedling density in the understory.
So we can use all of this to come up
with some implications for management.
So we recommend that the micro-topographic variability
and volume of coarse, woody debris is increased
after a harvest.
That can be done by leaving the wood and logs
generated from harvest on the site.
We also recommend using a minimum number of skid trails
to not damage micro-topographic conditions.
And then all of this will help us to create guidelines
for lowland cedar stand management in the future.
So a big thank you to my two advisers,
Jeanette Allogio, who helped with data analysis,
field crew, who helped me collect data for this project,
and then my sponsors and committee members.
So that's my presentation.
Does anyone have any questions?
- [Participant] I have a question.
I unfortunately came in just a little bit
after this started.
I'm curious, how long are you planning on continuing
the observational component of this study?
- Yeah, that's a good question.
So this study has been going on for a couple of years,
and it will continue to go on after my master's project.
So we have, it should go back.
I can, first up, oh, there we go.
We have control stands and treated stands,
and so the treated stands will,
our treated stands will be compared to our control stands,
I think a couple of years down the line.
Yeah.
- [Participant] And then how long would it take
to actually determine the effect
on population of more mature trees?
Just, I don't know the biology of the species.
- Well, part of our goal was with
like, these treatments was to like thin the stand,
and improve the growth of current cedar trees,
so I think the plan for this study is to go back in,
like, in another five years,
and assess the conditions of the current trees,
and then see if there have been like,
regeneration, or proven effects of the harvest.
- We've got a question in the chat, a couple, actually.
The first, Sean Hagan says, asks,
do you think tipping the harvested trees
prior to cutting wood would enhance the pit
and mound levels post harvest,
thus enhancing cedar regeneration?
- That could be.
That wasn't like, a goal of our study,
or something that we tried to implement,
but I've definitely taken a couple of classes
that have suggested that, you know, like,
like, small gaps that are created by tree tipping can be
suitable for regeneration.
We've also seen like, out in the field, like,
like, the mounds that are created by tipped trees,
like, a lot of cedars like to establish on those mounDs,
so that could be a possibility,
and something to look in to.
- And then sort of an addition to that question,
Rick Morals asked if there's an assessment
of blow-downs post-harvest,
or if there's any plan to measure that over time?
- I do not believe so.
Yeah, if anyone has any additional questions,
it can show my email down here.
katlynschultz@maine.edu.