The Broadleaf Papers

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Trees have stories to tell, their annual growth rings cataloging changes in the environment, including climate. Many tree-ring scientists focus on conifers, but Neil Pederson, a scientist at Lamont-Doherty Earth Observatory, believes that the less-studied broadleaf trees in temperate forests, such as magnolia, tulip-poplar, maple and birch, have much to teach us.
Updated: 16 min 54 sec ago

Fire on the Mountain, Fire in the ‘Burbs

Wed, 11/20/2013 - 11:19

I walked out of the house Thursday morning when my nose detected it – a forest fire! Having worked for two years in the piney woods of southwest Georgia, I had become accustomed to and, actually, come to love forest fires. That classic line kept coming into my mind, “the scent of fire in the morning reminds me of healthy forests.” The scent can be better than a campfire. It can be a little sweeter. That morning, it filled the entire town. Firefighters were just beginning to quench the fire. As of Saturday night, it had burned about 40 ha (ca 100 acres), but was still uncontained on its northern end. I might have been one of the few people to be thrilled to be in a smoke-filled town. It reminded me that we lived in a heavily forested area, and an active ecological event was playing out just up the hill.

It was fascinating to see the coverage of this fire. There were many resources thrown at it. It is understandable. Clausland Mountain is beautiful, beautiful enough that it is ringed by expensive houses. Twenty-six fire units, composed of about 150 firefighters, were actively fighting the fire (about one fire unit for every 1.5 hectares (3.8 acres)). Two helicopters were brought in to douse the flames. The breathless words of the reporter are fascinating as well, “remote areas” and “extremely dangerous.”

The large response is what happens in the wildland-urban interface, especially outside of one of the largest cities in the world. The conflict between humans and ecological processes has been on the rise as we move out into natural areas and as we become more aware of important ecological processes that maintain ecosystems and the services they provide for humanity. Fire is one of these processes.


 N. Pederson

The aftermath of the November 2013 Clausland Mountain Fire. Photo: N. Pederson


So, Sunday we went on a hike to see the impact of the fire. Bushwhacking, we went into the northern end where the fire was still smoldering (though the fire took care of many bushes). It is steep and the ash makes the slope a bit slippery. Much of the leaf litter was consumed, though not completely. In some places, logs were consumed down to the mineral soil. Death shadows are evident. The potentially severe rainstorms approaching from the west should put out the fire. (Update: they did.)


 N. Pederson

Death shadow of a consumed tree. This tree was dead before the fire. Photo: N. Pederson


It will be interesting to see how the forest responds. Fire is an important ecological process. It reduces the disease and pest load in an ecosystem; it is an antiseptic in a way. It favors some plants more than others. Like me, fire favors blueberries! Oak trees in the eastern United States do not seem to be regenerating very well over the last 40-50 years. The re-introduction of fire is today’s response to a lack of oak regeneration. Much money is being spent on prescribed fires and education about fire. The lack of oak regeneration seems complex. It is said that the rise of mesophytic species, the species “taking the place” of oak, is changing the forest in such a way that it ecologically dampens the forest, making it hard for fire to take hold. However, the re-introduction of fire doesn’t seem to be having its hypothesized impact – oaks still do not seem to be regenerating in experiments employing fire, while mesophytic species seem to be handling the fire pretty well. Important for the context of this ecological scenario, many changes have occurred in the forest over the last 50-100 years, all of which could be a factor of a reduction in oak regeneration – increased deer populations, loss of important megafauna, and changing land-use and cultural patterns (Hello Smoky Bear!). And, climate change might be playing a direct role in the “mesophication” of the East.

One physical mechanism has been detected – flammability of and differential drying of forest fuels (leaves). Fire is a very physical process. The variation in forest fuels, especially the finer fuels that carry fire in wetter regions, plays an important role in flammability. Thinner leaves absorb moisture more easily. Large, curling leaves, especially lobed leaves, dry faster. Curling leaves make the duff (or “litter”*), the fuel layer, fluffier, allowing better oxygenation of fire, to literally fuel the fire even more. One hypothesis for why eastern forests burn less is the loss of the great American icon, the American chestnut tree. Research by Morgan Varner supports this hypothesis.

It will be especially interesting to see how the Clausland forest responds to this fire. It is getting much wetter in this part of the world. Deer populations are high because of the high human density and the amount of forest preserve in the county (there is no hunting in the area, and deer have learned home gardens are a smörgåsbord). And, the diversity in this little patch of woods is pretty amazing. On our 0.5-mile hike, if that (our 2-year-old doesn’t hike great yet), I spotted 13 major broadleaf tree species, one conifer, the fading eastern hemlock, and two small tree species (I wasn’t even trying to seek out species; there must be more). Amazingly, yellow birch, a boreal species more common to the Adirondacks, New England and southeastern Canada, is mixed in with pignut hickory and sweet birch, species more common to Virginia.


 N. Pederson

Yellow birch in a scorched landscape. This tree is more ‘at home’ in the far north. Seeing it here and in a fire is a pretty neat thing. Photo: N. Pederson

The understory might respond a little differently, though in the little patch we hiked, the wineberry looked just fine. Guess we’ll have to go back out and hike a little more next spring. Shucks.



A pictorial of the aftermath of the November 2013 Clausland Mountain fire.


 N. Pederson

The fire line created to slow the fire; the “litter”* layer was swept away to starve the fire of fuel. Photo: N. Pederson

 N. Pederson

An eastern hemlock snag on fire. Eastern hemlock is dying of hemlock woolly-adelgid over much of the eastern U.S. This one died recently and was being consumed by the fire. Photo: N. Pederson


 N. Pederson

Fire flow on the north toe of the Clausland Mountain fire. Note the patchiness of the fire. Patchiness in fire severity scales across the landscape. While it can, fire doesn’t always consume everything. Photo: N. Pederson


 N. Pederson

Waves of fire consumption. Photo: N. Pederson


 N. Pederson

This section of Clausland Mountain is diverse – we counted >15 tree species without trying. Photo: N. Pederson

We met a colleague and his wife on the trail. They were out to check out the fire. They live near the burn and watched the fire grow and the efforts to stop the fire. She noted that it was like a ring of fire. Absolutely!


* = really? Can we get rid of the term “litter”? Fallen leaves, twigs, branches, bud scales, etc., enrich the soil by returning nutrients back to the Earth and increasing the soil’s ability to retain moisture. If that is “litter,” call me trash.


The Pluvial Continues… Has the Long Rain Epoch Begun?

Sun, 09/15/2013 - 20:04

It was midday. It was dark. It was June! It was pouring. We were sitting in my folk’s cabin in the Adirondacks when my dad groaned, “This is depressing”. Later on that same day, a hometown friend made a similar exclamation. Elizabeth’s update triggered a deluge of similar sentiments. During that discussion, she made reference to The Long Rain. It was the perfect comparison. Judging from the sentiment in our cabin, in the newspapers, and on Facebook, Central New York was on the edge of insanity because of the unrelenting rain.

 N. Pederson

A deluge during the Long Rain of June 2013 at Black Rock Forest. Photo: N. Pederson


It was too early in the season to write this post. Predicting future rainfall is like trying to predict Dennis Rodman’s next career move: It will move in a new direction, but no one can pinpoint the trajectory. But now, as Cortland and Macoun apples grace us with their presence, we can now safely say that summer is over (I do not care what the tilt of the Earth says. It is apple season!). In fact, the Northeast Regional Climate Center and NOAA have completed an early overview of this past summer’s climate. Their conclusion regarding precipitation in the Northeastern US? The Pluvial continues.

 it was wet in the NYC region. Image from NOAA's climate summary page. Hat Tip to Stockton Maxwell for sharing this graphic with me.

NOAA August and Summer 2013 summary of significant events. Hint: it was wet in the NYC region. Image from NOAA’s climate summary page. Hat Tip to Stockton Maxwell for sharing this graphic with me.


Actually, these overviews typically discuss climate of just the most recent month or season year or versus the “climate normal.” While useful, these summaries do not paint the full picture. Consider this: A climate normal is often based on a recent 30-year period, like 1970-2000. Now consider this: Instrumental records for the Northeastern U.S. (below) and analyses for the Catskills region and southern New York State, here and here, indicate that since the 1960s drought, the region has seen a substantial increase in precipitation; in fact, hydroclimate seems quite unusual since 2000. Now really consider this: A tree-ring reconstruction of moisture availability indicates that the recent wetting comes at the end of a 120-180 year trend (and maybe longer). So, the daily comparisons on TV or other media sources are typically based upon recent climate and ignore the past. Thus, based upon paleo records, the full picture indicates that we are sitting in one of the more unusually wet periods of the last 500 years.

Northeastern US summer precipitation from 1895-2013. 2013 is the second wettest summer on record for the entire region. Data and image procured from NOAA.

Northeastern US summer precipitation from 1895-2013. 2013 is the second wettest summer on record for the entire region. Also note the only two years since 2002 are below the average since 1895. And, they are marginally below the mean at best. Data and image from NOAA.


I return to this topic because of: 1) the many implications of this climatic shift and, most importantly, 2) what seems to be a limited amount of public awareness of how wet it has become in recent decades (though this awareness is growing). The substantial change in moisture across the Northeastern U.S. (the draft of the 2013 3rd assessment is here) is more commonly known in the scientific literature, but it seems to be less well-known outside of that community. For example, under the tab “Climate Change” on the Northeast Regional Climate Center’s excellent web resource, one can only find minimum and maximum temperatures when seeking to understand how much the climate has changed. An increasing trend in precipitation just doesn’t seem to grip the attention of most people like an intense heat wave or drought. In fact, an editor remarked to a freelance writer that they’d only do a story on the change in precipitation in the NYC region if “they were painting the lawns green on Staten Island.

For the people in Vermont, the Catskills, Mohawk Valley, and those wishing to use beaches in the summer along the coast, this seems a bit short-sighted. Excess rain is costly. It costs the people still trying to rebuild in the Catskills from the flooding of 2011 (and it isn’t just the two tropical storms that triggered the flooding – new research indicates that because the soils were saturated, the impact of Irene and Lee were worse than they might have been in other times). It costs people in Vermont wanting to rebuild their cultural heritage. It will cost all of us in NY State if tax breaks are given to expand flood relief measures in five counties and restoration and reconstruction of managed water systems; climatic change disregards political boundaries. It might cost us if we are managing forests for a long-gone climatic era. It further erodes trust between country and city folk as well as citizens and their government. Tragically, it costs lives.

So, as we become aware of the impacts of additional rainfall (and certainly there are additional costly impacts than what is listed above), we need to know that precipitation is likely to increase over the coming century. Model projections indicate it is likely that the Northeast will get wetter and have more extreme rain events. This doesn’t mean we will not experience droughts in the future, nor does it mean each summer will be like 2011 or 2013. And, these model projections could be wrong. But, our state of knowledge indicates that these Long Rain conditions could become more common.

This shouldn’t be viewed as more environmental doom and gloom. Humans have enormous brains and know how to use them! See: Klaus Jacob. We have the ability to prepare for potential adversity. And, if it isn’t clear by now, humans are one of the more adaptable and flexible animals on the planet. Heck, we might even celebrate wetter conditions with some enormous fun. And, from my Broadleaf perspective, the Northeast could become a temperate rainforest with bigger trees and a denser forest.* Folks spend enormous money to experience such things.

 N. Pederson

Dario Martin-Benito and Javier Martin-Fernandez in the Oriental beech dominated Colchic temperate rainforest in the Mtirala National Forest of the Republic of Georgia. Photo: N. Pederson







* unless future warming overwhelms our rain wealth and stunts the future forest…. apologies. It is hard to avoid all of the potential doom and gloom…


Out of the Woods

Mon, 05/06/2013 - 19:38

By Ana Camila Gonzalez

When we walked into the Sheraton in Springfield, Massachusetts we were greeted by none other than a wall full of cross sections from trees perfectly sanded to reveal the rings.

No way” I say. “I forgot the camera!” says Neil.

We were just walking into the Northeast Natural History Conference, along with Dario and Jackie from the Tree Ring Lab. When I pictured my freshman year of college last summer, I pictured a lot of things. I did not picture getting to go to a conference to present a poster on my own research.

On the first day we listened to talks given by people who dealt with everything from conservation science to birds and berries and beetles. I’ve gone to multiple talks at Lamont, but those talks are mostly geared towards graduate students, so I’m always the slightest bit lost listening to them. This conference seemed to be geared towards a wider audience: I could actually understand the talks. I couldn’t believe it at first. After the first day I knew a little more about a wide range of topics: I can now tell you about the reproductive cycle of a lobster, what kind of fruits allow birds to fly farther during migration and even the life cycle of an Emerald Ash Borer in a tree.

I also learned more about the research process, since many people were presenting research projects that we weren’t already familiar with. I thought there was only a specific set of proxies for climate, but I found that people are continually finding more and more. I listened as someone described how they were using a mountainside as a proxy for climate change, and I realized that one of the great things about environmental science is that you can use the world as your lab, in many cases literally.

That afternoon during lunch we were told to make sure our GPS systems were safely hidden in our car. We were warned that we had to realize that we were now in a “big city.” We joked at our table—all being from New York—about how Springfield didn’t seem like a big city at all. I liked the thought, however, of a field of science where so many people are able to work in small rural towns that they do see Springfield as a big city. Want to know a secret? As much as I like school in the Big Apple, and I see myself living the city life for a while after school, I don’t see myself living anywhere with a population over five thousand after that.

Everyone in the lab was scheduled to present the next day. I was scheduled to give a poster, but Jackie, a Senior undergrad at Columbia, was scheduled to give a talk: we were both freaking out in the hotel room that night, but she probably had more justification. That night Jackie, Neil and Dario went through their talks while I made a big deal over how to cut my poster. Jackie ended up cutting it for me; my hands were too shaky. I must have asked a million questions to prepare that no one ever actually asked me, but by the end of that night I felt ready. “At least I’m not giving a talk!” That didn’t really calm Jackie’s nerves.

The next morning we had an awesome breakfast, I bought a piece of flan for no apparent reason, and we headed to the conference. I set up my poster and less than a half hour later sat to watch Jackie, Dario and Neil give their talks back to back. They were all wonderful, and some questions were asked that sparked some good conversation. Someone made a comment about baldcypress, and my ears turned up at the corners. She was mentioning how incredibly sensitive it was to drought, and I have to admit I got a little too excited. I talked to her afterwards: “That makes so much sense! I’ve been trying to cross-date this batch of baldcypress for so long, and it seems like every drought year thus far has produced either a narrow, missing or micro ring, and yeah, like you mentioned, isn’t it crazy that they’re so sensitive…” yeah, I was a little over-excited. It worked out well, because I had to go stand by my poster directly afterwards.


 N. Pederson

Ana paying great attention to her inquisitor. Photo: N. Pederson.


This is it. I’m standing by my poster. Someone comes up to me. THEY’RE GOING TO ASK ME SOMETHING I CAN’T ANSWER… THEY’RE GOING TO… Hey, so can you tell me a bit about what you did?

Wait. Really? I can do that!

The rest of the poster session went well. I was asked more than “can you tell me about your poster,” but it wasn’t half as bad as I had imagined. There were many questions I could answer, and there were many that I couldn’t. I ended up liking the questions I couldn’t answer more, however, because they told me what to do next. The same scientist who I had talked to previously about the baldcypress caught me off guard when she told me she’d look forward to reading about my findings in a paper. I hadn’t thought about it before, but I guess that’s my next step: take the unanswerables and answer them.

All in all, I learned more than I ever thought I could at the North East Natural History Conference, and walked away with much more than just natural history.  I’m more excited than ever for what’s to come.


 N. Pederson.

Dario, fully coming out of the woods at the Northeast Natural History Conference. Photo: N. Pederson.




Ana Camila Gonzalez is finally out of the woods. She has, essentially, completed her first-year as a student in environmental science and creative writing at the Tree Ring Laboratory of Columbia University and Lamont-Doherty Earth Observatory. She has completed her blogging on the process of tree-ring analysis, from field work to scientific presentations…for now. We are happy to announce that she will be working with us for Summer 2013.

Visual Skateboarding

Fri, 04/05/2013 - 18:57

By Ana Camila Gonzalez


“You can do math on excel?” I ask. I immediately imagine a face-palm response, but Dario, one of my advisors, is nice enough to hide it. I’ve collected tree core samples, I’ve prepared them and cross-dated them. Now what?

Oh, right. The Science.

 N. Pederson

Science! Photo: N. Pederson


I guess I never really understood there could be so much involved in answering a question. When I imagine the scientific method I’ve learned since the sixth grade, I somehow imagine a question that can be answered with a yes or no. If I let go of this apple, will it fall to the ground? Hypothesis: yes, it will. Experiment: yes, it does. Conclusion: yes, it will. To the credit of my high school science teachers, it’s not that they didn’t make it perfectly clear that the why and the how are just as important as the yes or the no. I just couldn’t imagine that you’d have to explain why the apple falls with four different figures: haven’t you seen an apple fall too?

Dario is helping me understand how to analyze the data from the black oak samples I have already been working with for some time now. I know these samples. Or at least I think I know these samples. I’m learning there’s more to know about them than I initially thought.

We’re analyzing the climate response, which proves to be exactly what it sounds like. We have recorded measurements of climate (precipitation records, temperature records) and a proxy for tree growth (our ring width measurements!) and by comparing those we can see how a tree population responds to a range of climactic conditions. Alright. I can do this. I’ve made graphs before.


So we’re going to find correlations,” says Dario.

Click on an empty cell.” I start to make a scatter plot; I think what we’re going to do is look at the slope of a line of best fit.

So we’re going to see if the correlation is positive or negative?” I ask.

Yes, but we also have to see if the correlations are significant.” Isn’t any correlation higher than a zero significant? They’re showing a relationship. 

Dario continues, “Any correlation above a 0.2 or so is significant for the hundred years of ring width and climate that you have for this analysis.” I learn how to use the =correl function to compare the populations to temperature and I have to say I’m disappointed. I thought 0.2 sounded so low, but some of my data is showing a much lower correlation, and the data that is significant only ranges from about really close to 0.2 to 0.38 or so. I wanted to see a 0.5 correlation like I did between tree samples within a species as I was cross-dating. Comparing precipitation to ring width gives me slightly higher correlations, a few in the 0.3 range, but I’m still feeling underwhelmed.

No, but it’s still significant! It matters!” Dario tells me to make a scatter plot comparing precipitation to ring-width measurements over time at both sites. At first it looks like a ball of yarn, but as I mask the plot out I can see why those 0.3 correlations are significant. I follow each curve, visually skateboarding up and down the peaks and valleys and noticing that I’m going up and down a lot of very similar hills as I do so. What’s most rewarding is looking for years I know are drought years (1966 and 1954 were big droughts) and seeing relatively low measures of precipitation and ring width during those years. I knew while I was cross-dating that those years were important when I saw how small the rings were, but now I can prove it. Like the apple falling, I can’t just say that because I see the rings are small those were dry years. I have to compare it to precipitation records, temperature records, and, dare I say it, the Palmer Drought Severity Index (I have to admit I don’t entirely understand the mechanics behind the index, but I understand that dryness is a composite of precipitation and temperature forcings).

Dario, over multiple days, teaches me a few more nuances of Excel and helps me understand the ARSTAN program and how we use it to make our ring-width measurements more effective as proxies for tree growth. He mentions this would all be easier if I knew how to use R. I make a mental note: learning R is the next step. If I thought that was scary, now I have to put this information on a poster. That real people will see. At a real conference.

Neil shows me a few poster examples, and the message is clear. Show your data instead of describing it in words. That also means I’ll have to explain my data by actually… talking… about it. Gulp. The North East Natural History Conference is next weekend, but I feel like I’m ready. I understand the why and how after analyzing my data. At least I understand it enough to give an answer better than yes or no.




Ana Camila Gonzalez is a first-year environmental science and creative writing student at Columbia University at the Tree Ring Laboratory of Lamont-Doherty Earth Observatory. She will be blogging on the process of tree-ring analysis, from field work to scientific presentations.