So I'm gonna be discussing changing ecosystems and the ecology of change but
at the outset, I promise there was no sharing of slides ahead of time there'll
be a little redundancy in my first few slides here, but I would like to say
congratulations to the whole Odum School. I mean it's just incredible to think
that it's been 50 years already in the making and here we are today.
The Institute as has been mentioned previously really was a vision ahead of
its time and the reason that we are where we are is that there has been
effective leadership all along the way. As we heard earlier institutional
support from UGA, the Institute wouldn't be where it is without that and we had
tremendously committed faculty, many of whom are here today who devoted their
entire careers and and grew as scientists at this place. So it's a
really remarkable accomplishment. So I did just do a little bit of walking down
memory lane. All of my pictures are slides or photos which I have
photographed but the Institute when I first started so this is my first year,
February 1981. You will notice an absence of vegetation around that building it's
strikingly different. Those of you who were -- how many of you were in the
Carroll's? Your offices in the Carroll's? A number of you. Right, so this is these
are the Carroll's this is my side of the building not the other side where Kim
and Bob were. That's my desk. I wish my desk was as cleaned today as it is then.
Our courtyard, I mean that was such a wonderful place to read our papers for
class. I mean taking your paper out and sitting out in the
courtyard or having potlucks. And then again the absence of --whoopsy
[computer alert]
Here we go. Gotta get the pointer right.
That's where we used to play volleyball on Fridays
and drink beer so things have changed again as well but what I really value so
much in my own training and the experience I had here was that we had
such leading thinkers present training us as young scientists, as early career
scientists, and representing the science of the times. That's my copy of Odum's
Ecology book which I had as an undergraduate. It's why I applied to the
University of Georgia. As in New Yorker going to Georgia was not considered to
be the best thing from my family members. It was awesome
however but we were lucky to have so many people leading in so many areas.
I have names here and if there are any I omitted it's simply by a lack of
remembering it's not my intention, but I mean Gene Odum and Frank for ecosystem
ecology. Sustainability a term now that was that was new then. Systems ecology
and modeling: Bernie Patten and Dick Weigert,
long-term research: so D.A.C. , Wayne Swank at Coweta, and Judy.
Biogeochemical cycling: Bruce Haines, Carl Jordan,
Microbial loop which was new in marine
systems and marine ecology: Larry Pomeroy, Jim Porter,
Aquatic ecology: Judy Meyer, Karen Porter especially
Agroecology: was new D.A.C. and Dave Coleman were leading a
lot of that effort and then
landscape ecology: Frank Golley, Vernon Meentemeyer in geography
and Ron Pulliam with a lot of his source sink ideas.
As was mentioned previously, these areas and these leaders who are pioneering in
their thinking. They were holistic. They were integrative and collaborative.
Now not only were they leading thinkers but they were thoughtful leaders, leading us
by example. This was mentioned previously but Georgia has five prior ESA
Presidents among its faculty. That is the only institution to have that. We grew up,
as young scientists, being trained to contribute back to our discipline
to help serve the societies upon which we depend and from which we benefit.
Frank was also leading a lot of the International connections by his service
as as president of INTECOL. And also I feel like it's appropriate for me to
give a couple of personal notes of gratitude to some of these faculty who
influenced me so much of my development. Frank was my mentor, my adviser.
He was extraordinary as a mentor for a young scientist and I would not be where I am
today. I would not have evolved in my science without that that training.
Susan Bratton who's pictured here was the person who taught me field ecology.
She was on my committee. She was from the Park Service co-op unit. They funded my
research as well.
But as a female scientist, she along with Judy and Karen
There WERE women scientists here that was unusual. There were few in
the ranks of the faculty so I am greatly appreciative for both Susan on my
committee but the others as well Gene was on my committee he also hired
me as a postdoc when I had no other offers but it was also a wonderful opportunity.
Larry Pomeroy accepted me as a student,
which many of you may not know, I had done my undergraduate honors thesis on
phytoplankton limitations -- limitation of silica on phytoplankton in Long Island Sound
and unfortunately I learned I didn't want to sit by a microscope so I
got here naively and said I don't really want to do that and he was very gracious
D.A.C. was head of Graduate Admissions and was really really just delightful in
helping to recruit me. And Bernie Patton I would call out as well.
The course on systems ecology, I don't know how many of you have had Bernie's class
in systems, quite a number of you.
It was highly influential and really changed my thinking and in a good way
So I'm going to be talking today though about science.
And I will be talking about the ecology of change. I will mention however that
UGA has continually evolved with the times after 50 years it's still at the
forefront addressing many of the contemporary problems we face in ecology
but as has been mentioned by Peter and others, we're currently in a time of just
unprecedented rates of change and some of the changes that we are observing and
in all of the systems in which we work are big. That is there qualitative differences
and they happen really fast. They're abrupt changes and I think these
are all things that lead to surprising outcomes where we say
"Geez, we didn't expect that!"
And I think it's also one of our biggest challenges in contemporary
ecology. Regardless of the level of biological organization or a sub
discipline or the scale .
So that's going to be kind of my theme again following
up a little bit on the rates of change that Peter so nicely set up. This is from
Will Steffen's paper updating some of the big drivers globally have change.
There's socio-economics on this side, Earth system trends on the other. Details don't -
aren't critical but what I'd like to just focus your attention is
since 1950, that exponential, that hockey stick curve that you see in so many different
drivers. So this is fundamentally changing the way our ecological systems
are responding and I apologize for the the acronym here ahead of identifying it
but A.C.E.S. standing for abrupt change in ecological systems are happening all
around us the more we look for them, the more we see them. And they're continuing
to surprise. So whether it's lakes suddenly turning from clear to turbid or
eutrophic or coral reefs that are going from these beautiful colorful diverse
systems into areas where they're dying or rangelands for example where we're
seeing increased densification of woody vegetation and bareness on the ground
from what had been a a thriving rangeland system.
So abrupt change when I
talk about that. It's things that are abrupt in time or relative to the speed
at which the drivers are changing. If you think about some response, a driver or a
state you think about time. It could be a step function but it's big and it's
happening quickly. It could be a little bit, slightly different sorts of changes
but we're talking about big changes that happen quickly. Oftentimes these involve
tipping points or thresholds. Where again, if we have our response or our state on
the Y and we have some kind of controlling driver on the X where if
you're near that threshold, a very slight change in the value of that driver,
can cause a really large change in response. It may be a threshold. It may
also be a hysteretic or bifurcation alternative state type dynamic. Where
when you release the driver, you push it back the other way, you can't just get
the system to recover quite well. It's very difficult in practice to
distinguish those two. And I would say one of our big picture questions in
ecology is ' when where and why are these kinds of changes going to be happening
in our systems? Can we anticipate them? Can we figure out ways to avoid the ones
that we don't want? Can we diagnose them when they happen? So, we're actually
involved currently in a project that's focusing on this general area across
systems, timescales, spatial scales, terrestrial, aquatic. A group of five
faculty and a cluster hire of four postdocs so we've been trying to think
through this very generally and it's really challenging and surprisingly so
actually once we once we get into it. So, the abrupt changes are hard to
diagnose because of several factors. One is they can be caused by many different
causes - that didn't make sense - They can arise from many different
causes. So we can have really rapid changes in the driver so the driver
changes rapidly in the system responds. We can have changes in disturbance
regimes like fires, hurricanes, floods. The types of things have been very
much in the non-fake news this year. We can have stochastic variability or
increased patterns or changes in variance in drivers even in the absence
of a changing mean. In real world systems, we have multiple drivers interacting
with each other changing simultaneously so it's really
hard to disentangle what happens in the end. Thresholds are particularly thorny
because it's really hard to anticipate them before you pass them and see that
you go down that slope and finally, the theory. We have a lot of theory to
address these things but the theory has really outpaced the real-world
applications. When you try to figure out how do I take some of these ideas that
are out there and apply them in the system in which I work.So, I'm going to
be telling you a story about fire, climate, and forest resilience and a
story about abrupt change so I just want to put a little context for when I talk
about disturbances and drivers what I mean. So, if we start here and we have a
system or state or any any of whatever your favorite response might be
we may have disturbance events that happen in time, they happen to be equally
spaced here this is just a cartoon. So, they affect the system, the system recovers.
They affect the system, the system recovers. This is kind of like the normal state of being
that the system is accustomed to. However, there are ways in which the changes in
these these dynamics or their interactions may lead to situations
where the system doesn't recover. So, maybe the disturbances become so
frequent in time that the system can't recover and maybe it crashes.
Maybe the intensity of the disturbance or the size of the disturbance is
increasing over time and again causes a disruption of the disturbance recovery
cycle and then we have may have changing drivers interacting with disturbances
that again can operate to tip the system. So, conceptually that's where I'm
thinking but I'm going to take you on a trip to Greater Yellowstone today so out
of Georgia and off to the western US. This is a place that I've worked in for
almost 30 years now. It is one of the largest intact wildland-ecosystems in
the temperate world. It's located in the northwest-corner of Wyoming, centered on
Yellowstone National Park, surrounded by other parks and wilderness areas.
I also want to just acknowledge here briefly that I'll be talking about work that is
done in collaboration with my students and colleagues and funded by a variety
of different sources. So, Yellowstone is really well-known to most of you.
How many of you have been there? Okay so all of you. How many of you that have been
there and remember seeing blackened trees? oh good okay so handful of you or I'd
say maybe half of you have been. So, most people go out there and they're
familiar with the wildlife the thermal features and the scenery and all of that.
Yellowstone is dominated primarily by forests. It's about 80 percent forested.
Most of those forests are middle elevation dominated by lodgepole pine.
There are spruce fir forests at the higher elevations that are cooler in
and at the lower elevations that are warmer and drier
we have Douglas fir and Aspen. Now, still a little hard to see in here with the lights,
but in the summer of 1988, Yellowstone had very very big wildfires
and these fires were the ones that were on the news every night, much as
California has been throughout the fall. At the end, the forests looked like this.
And as I like to say, this picture I took this in October of '88 it is a color
picture just looking like it's black and white.
So, it looked like the area was quite devastated, however, we have learned and
I'm going to walk you through a little bit of the foundational work because I
need to establish that before talking about some of the change.
So, I've been studying these fires since 1988 and I'm just going to be do a little bit of a
whirlwind about what we have learned since then and then how we're thinking
as we look ahead. So, is actually not new in the system and I've had fun
reading some of the early reports of the journals of the explorers that were
surveying that country for the first time and in one quotation here from
Langford who ended up being the first superintendent of Yellowstone. They
talked about going through breaking camp, traveling along the edge of the Firehole
River, passing through a long stretch of fallen timber blackened by fire for
about four miles so my colleague Bill Romme has done the dendro work and the
fire history reconstructions in Yellowstone and this was likely the 1862
fire that happened right in that area that is reported. So, fire has been there
even since euro-american settlement, however, since 1988 we've also learned
that infrequent, stand-replacing fires meaning the fire comes through burns
through the canopy of the trees kills the trees this is very different than
the coastal longleaf pine or loblolly pine types of systems.
These kinds of fires are business and as usual so throughout the
past 10,000 years so throughout the Holocene fires have recurred at one to
three hundred year intervals some variation over time in that system.
Importantly they're driven by climate, not by fuels. So, fuels are generally
always available but most summers have climates that are too cool and too wet
to burn. So, when you get that infrequent summer like 1988, it makes all the fuel
available and the fire just continues goes through the landscape and resets
the system. So, the 1988 fires are notable in the West actually in in fire ecology
for sort of ushering in the new normal or the new era of wildfire in the west
in which we are living now each year. So nonetheless the size and the severity of
the 1988 fires were really surprising to scientists and managers alike because we
hadn't seen others that big and and that severe during the 20th century. Largely
side comment, because the climate was too cool in too wet we didn't have the
burning conditions happen. These fires burned under very severe droughts, very
high wind and I always have to mention they were not caused by past fire
suppression. This is a different system than the southwestern ponderosa pine or
even some of the savanna type settings that we have in the east. And for a
budding landscape ecologist, they gave a wonderful opportunity to study a
landscape scale creator of pattern that we can't do experimentally. Shown here is
the outline of Yellowstone. The red areas are the perimeters of the fires so they
affected about a little bit more than a third- almost 40% of Yellowstone. So, I got
to go up in a helicopter in October of 1988 which is really fun it was when
they were still firefighting and I was out there trying to figure out
what the research would be and what things look like and get the hypotheses
together for an NSF proposal so I'm gonna again do a quick run through some
of the main messages from 25 years of work. One is that the fires created a
really complex landscape mosaic. We're accustomed to this now any time you have
a big disturbance you know it's gonna be heterogeneous. We didn't know that at the
time, which sounds kind of silly but flying over in the helicopter and seeing
this kind of pattern. Where we have different patches of highly, very
severely burned areas where all the trees are killed, islands of green trees
that are missed by the fires, and then these brown perimeters here where you
have the trees killed but they didn't burn off for the needles. So, very complex
spatial mosaic which in turn influenced successional patterns. We also were
surprised that the vegetation recovered really rapidly. Like much more rapidly
than we expected, and if you -- the sequence this is October in '88, this is two years
later you can see the flowering, the robust flowering and the understory
vegetation recovering. By 15 years, these are all the little lodgepole pine trees
and they start out by recruiting the very first year after fire.
Little baby seedlings but they come in really early.
The understory vegetation re-sprouted primarily
and that was also a surprise so the fires didn't burn down into the
soil very deeply which we were surprised at initially, and so in many cases you
can see here these are lupins you can see this is a very well-developed root
that the plant has restarted from. So, we did a lot of excavating at the time but
basically in 89, the plants re-sprouted. In 1990, two years after fire, they
flowered and in 1991, we had a huge recruitment of seedlings of native flora.
So, non native plants did not increase which was not what we expected based on
what was known previously.
In general, species
richness at a plot level increased for about five years or so this is from
widely dispersed plots around the park. There was a still strong influence of
the abiotic template so the composition was kind of similar initially following
the fires but then it diverged based on the elevation, the topography, the soils
and the like and there was a strong effect of ecological memory.
So, the species that came back were largely the species that were present before the
fire because of all these autogenic mechanisms. The abundance of the
lodgepole pines was, I would just say, astonishing. So, they come back really
fast but the variation was so much more than we ever expected. Everything from a
sparse forest coming back so that's about 500 or so trees per hectare to
over 400,000 actually over 500,000 stems per hectare. I don't know how -- for
those of you who aren't familiar with that means right now we can't walk through them
because they're so dense then just extremely densely packed.
So, this is all the same stand age coming back after the same event but very very
big differences in the structure in the ecosystem.
Largely due to variation in whether the trees bore serratinous cones those are the
kinds of cones that remain closed until they're heated and then they release
their seeds but that trait varies across the landscape in ways that we didn't
know. We kind of serendipitously spanned the gradient and then also this
variation in fire severity had an influence on these patterns.
So, when we most recently re-sampled these at 24 and 25 years after the fire, we still have
this variation on the landscape. It's kind of what it looks like it's some
really challenging sampling conditions right now because the trees are really
dense. You can't you can't run a bearing. You can't sight very far and all of the
pre-fire coarse wood, the standing snags, standing dead they've all fallen.
So, you have standing down up to your nose trees that you can't see through
and you're trying to swim your way and climb your way through to do your sampling.
It's a really good place to send undergraduates of graduate students
So, these trees are also really productive. Their actually
their net primary productivity is higher than the mature stands at this point.
The numbers here that are showing for averages for those of you who know- think
in those terms are there. But suffices to say they are really really
productive and even in those high density areas where you'd think they'd
be out competing each other already, they're not. So, the quantity of trees at
the ecosystem-level trumps the quality of the trees at the tree level so if you
have three or four hundred thousand trees per hectare as is shown here even
though each individual tree is smaller than where they're they're open grown at
the ecosystem level that is huge amounts of productivity. These patterns
of differences in stand structure set up a pattern across the landscape, a mosaic
of process rates. And so this is ten years post-fire. The patterns are
still similar but there is variation in the total above-ground net primary
productivity and we have a mosaic. This is the southern portion of Yellow Stone
of process rates that's due to the patterns that were set up following the disturbance.
We also know that that mosaic persists
for over 150 years.
This is work by one of my former PhD students Dan Kashian
just showing you that the density of trees per hectare goes down over time so
by the time you're at 200 years following a fire, it's about 1,200 trees
per hectare but this is the coefficient of variation among stands of the same
age so the variation remains high and then it settles in by about 200
So,
those initial patterns really set the stage for how the system behaves for a very
long time.
I also want to talk briefly about nitrogen dynamics.
I avoided that with great success while I was a graduate student
I did not do any biochemistry and
I got really interested in it in the 1990s because wondering
what does this mean for the function of these systems. So, started doing it then
but surprisingly there wasn't very much known about nitrogen cycling following
this kind of fire. Almost everything had been done on prescribed, low-severity
fires. So, we did a bunch of stuff on it and two main points.
One is that despite what you have learned from the Hubbard Brook examples and what we all
teach in undergraduate ecology, this system did not lose much nitrogen
following the big fires of 1988. We kept thinking our data were wrong.
Okay going back, going back and back back again.
But the microbial community in the soils is
really tight it's holding on to the nitrogen that's remaining in that system
and we know that from laboratory incubations using
pool dilution. Where the consumption the grabbing by the microbes exceeds what's
the net production and also from field incubations that are year-long resin
core incubations. So, the microbes in the system really hold on to the nitrogen.
By about fifteen years, the plants those rapidly growing lodgepole pines that I
showed you they're really effective at competing with the microbial community
in the soil they're also mycorrhizal and they become a very strong sink for
nitrogen so they start to sequester it and then similarly to what I showed you
for carbon or for productivity this variation and tree density that I was
showing you, also sets up a landscape mosaic a foliar and and and nitrogen
cycling rates. As of twenty five years, we still have no evidence that nitrogen is
limiting productivity in this system which is very surprising and counter to
what conventional wisdom would be. The foliar nitrogen concentrations are still
surprisingly high.There is a negative relationship between productivity and
nitrogen availability. That's opposite what you would expect if and
availability was associated with increased productivity and over time all
pools of nitrogen in the system have increased and I will say we have very
few, we don't have alder, we don't have like here you have black locust Seca we
know we don't have a nitrogen fixer that's dominant so where it's coming
from is something we're still working on. So, basically the consequences of those
big fires have been very well studied. We've we've studied them to death.
I shouldn't say that because it's a lot of fun to still try to track it. We know the
narrative. So, this is from National Geographic almost two years ago now
We know the narrative so we have the fires and then we have the
recovery and then we have the forest coming back just like that cycle that I
showed you at the beginning. So, the bottom line native vegetation ecosystem
ecosystem processes recovered rapidly without intervention. Yellowstone is well adapted
to these kinds of fires.
Thank you very much lots of resilience.
One of the ways that we depict this in another way and I'll
use this again later is by these ball and Cup Diagrams so if this is my
Yellowstone forest, the fires can come around and they they move that ball
around in this basin but they don't push it out, so the system you know moves out
but it comes back moves out and comes back whether or not it can flip to
another state is one of the things that we're starting to think about.
So, we know going back to the issue of change that both climate and our fire regimes are
changing. The paper that Leroy Westerling published in 2006 in Science was the
first one to show the statistically significant relationship between climate
change in the West and the occurrence of fires.
So, we were having large -
an increased number of large fires high severity fires in the West and it's
associated with the warming temperatures, with the earlier snowmelt in the spring,
and then the lengthening of the fire seasons so this is all stuff you've been
hearing on the news as well associated with California.
Leroy updated this these bars here are the numbers of fires that're large in the west.
Idec the bars of the decadal means and you can see them marching steadily
up and that's continuing. So, we started thinking about the effects of climate
change in Yellowstone in like really in the 1990s so
The first paper Bill Romme and I wrote came out in 1991. It's before we had the
the sophisticated climate models or the predictions nor even really enough data
yet to say that the trends were clear. So, it was really more of a thought exercise
about what would happen and so you know we laid out that yes well a warmer and
drier climate would increase fire activity. If we had more fires it probably
would reduce the net age of the stands across the landscapes and again it might
shift the vegetation upslope just because of the cooler conditions at
higher elevations. So, we did probably over ten years or so more than that
actually because too through 2009 a lot of different modeling approaches where
we really kind of I you know I put the hammer here because we really tried to
hammer the system based on all the variability that we had seen throughout
the records from the Holocene so what happens if we make the fires as frequent
as they were observed and the like. So, in all of those cases we know that climate
and fire had changed in the past that it would change in the future.
In all cases when we were doing our modeling explorations the forests were
recovering just finds it was very consistent with what we had seen
following the 1988 fires and we knew that those were not catastrophic.
So again, it did not change the conclusion that Yellowstone is well adapted to
these large severe fires and it was likely to be in the future.
Or is it?
So, the thing when I talk about abrupt change sometimes we have changes in our
conceptual understanding as well and this was a watershed for me.
So, Leroy and I were at the same conference and he put this map up of
the moisture deficit in 1988, the year of the big fires and the redder, the drier,
so that's where it's more arid with the drought conditions are the worst and you
can see in 1988 it centered right on Yellowstone we know what happened then.
And then he showed this for the projections for 2090.
Where it's both more intense and that red throughout the West. That is out of
the box. That is beyond what we had considered because it's beyond what we
had seen in the Holocene. It goes outside of that range and although we had been
really thinking we hadn't thought than anything that severe could be in our
futures so it really started changing our understanding
our thinking about what might happen.
So, Leroy and I were able to get with a
couple of other colleagues some joint fire project funding to start looking at
what those implications might be and for the Yellowstone area this suggested that
we see spring summer temperatures up by four to six degrees C and that's the
time period where it matters for fires by the mid 21st or the end of this
century. The water year deficit is driven not so much by a change in precipitation
but by that warming which is tending to dry out the system. This is a bit of a
complicated figure and I'll just make a couple of points from it but we looked
at what that would mean with many like with ten thousand replications and such
from different climate models looking at the log area of area burned
on the Y and then time on the X. The area burned in the 1988 fires is here and all
of the vegetated area of Greater Yellowstone is here. These colors are
showing the observations which match well the median and then the whole full
range of observations over the fires over the projections. Basically, what it
says is by mid-century, we're getting very few years with no fire and the
weather conditions associated with big fires are happening essentially all the time.
It doesn't say there will be fires it's based on the weather conditions
because there are a few feedbacks here. So, the the nugget here is that the novel
the fire regime in the future could be novel relative to the to the Holocene to
the past 10,000 years and these changes are much greater than what had
previously been considered and we would have few years without fire.
Fires would no longer be climate limited so we would have the climate available
for those big fires all the time which remember I said it was quite different
from the beginning eventually fuels would have to be limiting to the fires
and what would happen to the fire severity remains to be seen.
So, this has really sent us on a new investigation of what might be happening
throughout the West so we know again that fire activity will increase but the
details about how that will play out remain the subject of very intense
research by not only our group but others.
How many fires? How much area will burn?
When will these changes happen? Where will we see them?
Are there going to be tipping points that lead to fundamental changes in those systems?
So, this is hard to do because by their nature these high severity fires are
infrequent at any given place. It's not like you can easily go out and get lots
of replication. Trees live a long time and so there can be very
long time lags involved before you see changes but the fires themselves can
potentially trigger an abrupt change in that whole fire and recovery cycle.
So, what do we do in the face of these challenges?
So, I would say for this and
many of the other big, wicked problems we face we can't put our heads in the sand
and ignore them we actually need to take advantage of all of the sort of tools in
our toolkit so observations across a disturbance characteristics are across
space, long-term study where we can look at the dynamics as they change,
experiments, and then also process based models. It's going to be really important
I think that we try really hard to identify the nonlinearities or the
thresholds that might be associated with abrupt change and that we understand the
mechanisms or we test hypotheses about the mechanisms that could be
underpinning such changes so we've been doing that in the Yellowstone system
asking how does the warming temperature plus the changing fire, going to effect
the forests in the future and I'm going to walk you through three different
mechanistic hypotheses about what might play out. The increase in fire frequency
affecting the supply of seeds, the fire size affecting the delivery of seeds
into burned area, and the drought affecting establishment.
So, first of all frequency of fire and seed supplies, so we have
conifers they're obligate seeders, they have to produce cones that's the source
of the seed that comes in whether they're serotinous or non-serotinous.
If the re-burns occur before the trees have matured, you lose your seed source, and so
that could lead to a failure of the ability of the system to recover, so
following the 1988 fires, it's mostly large trees big mature trees long
interval fire that set up this variation nonetheless but still a lot of recovery
following the fires. However, we are now starting to see re-burns of those areas
that burned in 1988. So, in 2016, it was not in the news because there were fires
burning in the West everywhere else that were more-- of a greater threat
But we had the most area burned in Yellowstone since the 1988 fires.
This picture shows the fires of 2016 burning in some of my study areas the 28 year old lodgepole
pine stands, so we were just out there a year ago sampling with with rapid
funding from NSF and this is what some of these look like and again it's a
little bright, so you can still see there is this mosaic just like I showed you
from my helicopter picture but we also have areas like this we were calling
them "stump towns" because all of the coarse wood and all of the young trees
were consumed in some of these places. It's greater severity than we had seen
following '88, so in areas, this is I haven't even analyzed the data, this
is really the back of the envelope stuff but in places where we had kind of like
the normal stand replacing fire, the trees that came back after the '88 fires
this density is matched by what's coming back after 2016, however, in the areas
that look like this I mean they're just remarkable you can
these lines here these are ghost logs so that's where the coarse wood had been
on the ground but it was completely consumed and you can see there's no
above-ground trees. We had to use a stick to poke to try to recreate
what the densities were because all that was left with stumps. We have there 99%
reduction in the regeneration so these- we really did lose the seed sources so
in addition to the frequency this variation in severity is also playing a
role I think in what will come back. In terms of fire size if we change the
patch sizes and for species like Douglas fir that do not have a canopy seed bank
then fire size may influence whether or not seeds can disperse into these areas.
This is post '88 fire data but here's surviving Douglas fir trees and then we
have coming down the hillside here little post '88 ones coming back in but
essentially if you're more than 100 meters from a live tree, a seed source
there's very little regeneration and especially if you're on a dry position.
So, patch size will matter and then drought is associated with the fire but
drought can also affect the ability of the trees to establish and grow following a fire.
So, if we think about the mature forest big trees can handle a
lot; little trees not so much. Just like in your garden when you're planting
flowers or vegetables you've got to baby them in the beginning.
So, the tolerance
for the mature trees of environmental conditions is much broader than it is
for seedlings.
So, we've been looking, we took advantage, well again one of my
former PhD students Brian Harvey, we looked at fires throughout the Northern
Rockies that were followed by three years of above average temperature so
lower moisture and then normal or wetter conditions and we found that indeed we
see fewer trees in the dry post fire years and also on south-facing exposures
where it would be would be drier. So, there's evidence for all of these
mechanisms coming into play. We're also doing experiments. One of my current
students, Winslow Hansen, we are in the process of writing up this paper for
ecological monographs but we've done both greenhouse experiments and field
transplant experiments where we're growing seeds and post-fire soils of
current climate and then in places in the landscape today where the future
projected climate is is apparent today some of the lower elevations and those
data are also showing that at the low elevations over four years field study
we have much reduced success in terms of tree establishment. So, we're getting this
from from multiple angles. So, my question is then are we potentially seeing
forests in transition where instead of this historical condition that I showed
you we may be making this Basin more shallow by warming the climate and then
with the changes in the fire have the ability to perhaps change the system to
a non forest or deciduous forest State?
So what that would look like is do we
have Yellowstone transitioning from this landscape which is what you see now if
you're out there to something that has a whole lot more open type vegetation
maybe an expansion of some of the lower elevation grasslands expansion of Aspen
and of douglas-fir. So, one of the challenges even with these kinds of
field studies is we kind of get what we're given by the weather and the
conditions that we have but when we're trying to understand the suite of
factors that could affect novel conditions in the future in novel
systems it's it remains challenging and when we go to use models that exist that
are empirically based they're based on the past not on the future so we may be
seeing climate conditions and fire regimes that are quite different from
what we have seen in the past and we want to know how multiple interacting
driver can shift us to different different
positions so therein comes the role for modeling.
So, we are now using a model
called "Iland" developed by my collaborator Rupert Seidl who's in
Vienna which is a process based model, individual based model but scalable that
represents trees and landscapes and disturbances and spatial dynamics and
such so I just want to mention what it is I'm not going to go through the details.
One of my students has already parameterize this model for our Yellowstone
tree species. This is just showing in the gray lines actual simulations
from our stands based on the '88 fires. In the red dots showing field data that we
have from plots so we have the model behaving well and then I mentioned these
factors. We would like to look at how they interact with one another and so we
have conducted a factorial experiment with the model looking at several
two species but two forms of one fire return interval from the lowest observed
in the Holocene to shortest that we've observed in the field, varying distances
from seed source, and then climate periods that are the historical mid 21st
century and late 21st century and looked at all the combinations of those and
I'll just show you one output here that's all this paper is being revised
now we have minor revision for ecology so hopefully it'll come out year.
But for each of our species what I'm showing here is a state space of
where in red post-fire regeneration has failed and we were very conservative
about that that's less than 50 trees per hectare so that means you're really
you're not even in a savanna by that point and then where it's
successful as a function of distance to seed source the return interval of fires
and the climate periods. So, you can see the various combinations that give you
the possibility for having a non forest coming in at the end. So, in all cases
distance to seed source matters a lot fire return interval is especially
important if you have an aerial seed bank and the like so we're trying to
explore what sets of conditions might be there and then we'll look for where
those might happen on the landscape. So, the bottom line for this I think that
affects all of us no matter what systems that we're working in is that what we've
observed in the past even the deep past even if we go back ten thousand years
can inform us about mechanisms but it may not be enough to help predict the future
In my case, I think forest state may be less resilient in the future as
we have climate warming and we have change in fire regimes I always like to
make sure that I'm not really sounding like the sayer of doom. Yellowstone is not
going to be destroyed it will still have native species it is still one of the
best places on earth to observe how nature is responding to the changes with
minimal human impact, additional. We will see changes in the age the type the
extent location of forests and I think by focusing on mechanisms particularly
when we have long-lived species and time lags involves that may help us with
early detection and again following my theme here I think anticipating when
where and why we're likely to have these big abrupt changes is a challenge that I
think we should all be considering in our systems.
So, I'm going to end this in
my last slide here but a couple of extraneous comments that are geared
particularly towards the early career people who are in the room and I think
we have- these are some of the lasting lessons I got as a student here that
have helped me I think throughout my career but some of them are are looking
forward a little bit. One is always have good questions. You can push to ask a
good question regardless of the system, regardless if it's applied or basic
research or any of that and follow the things that are really exciting to you.
I mean you should want to get up in the morning and go to work and figure out
what new whatever the problem is you're working on so really really push on the
questions.
I think also don't get caught up and having just one one tool
like you see every hammer -- every problem is a nail because all you have is a
hammer you have the opportunity to hear, to learn diverse approaches use them and
appreciate them in your work so whether it's experiments comparisons long-term
data, modeling, remote sensing, the list goes on however in the world of big data
and fancy statistics that some of us have to catch up on and learn as we go
retain your close association with the real world system if you're modeling or
doing statistics your work will be better informed by knowing your system.
If you're down in the weeds with your system you may be also better informed by
taking the broader modeling approach but use them together but don't lose the
connection and then finally in the world of fake news which we live in right now
which is very very disturbing two things that I think are really important with
the advance of the advent of predatory journals and the like strongly support
the value of peer-reviewed science the system is not perfect but I don't think
we have a better one and then also get involved in your scientific society
support the professional organizations that are advocating on behalf of all of
us and all of our science. You can see I'm passionate about it so with that note I will say
thank you very much. I really am honored to have had the
chance to attend and talk to you.
Thank you!
[applause]
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