Of Tree Cores and Climate

Dr. Ailene Ettinger is a Putnam Fellow at the Arnold Arboretum in Boston. Her current research examines factors that may influence a tree’s response to warmer or colder years. Through an analysis of tree core samples and individual traits, she hopes to improve scientists’ ability to predict the climate sensitivity of plant species.

What is the focus of your research?

I’m trying to understand how plants will respond to forecasted changes in climate due to global climate change. How do individuals respond to warmer years vs. colder years? Does their growth change a lot in warm vs. cold years? That relationship is what I call climate sensitivity. Right now, there’s a lot that we don’t understand. For example, over the past hundred years temperatures have already warmed a little, and in some places trees have responded to that warming by growing faster. In other places, they’ve responded to that warming by growing slower and in still other places, their growth hasn’t changed. The bottom line is that we’re really not good at predicting yet how species will respond to warming, but we would like to be. Whether trees respond by growing more, by dying more frequently, or by growing less could have dramatic impact on the earth.

What brought you to Arnold Arboretum?

It’s such an old arboretum and there’s a great diversity of species planted. The Arnold Arboretum offers the chance to study how growth has been affected by climate going back over the past hundred years across many, many species. I’m studying about 80 different species. Normally, to get this number of species in the same size area as the Arnold Arboretum, you’d have to go to the tropics because the species diversity in New England and other temperate areas is much lower than it is in the tropics.

What information are you collecting to investigate this topic?

I started collecting tree growth data which I could correlate with climate to understand climate sensitivity. Then, what I actually want to do, what I think is missing, is to be able to predict that climate sensitivity, so I’m looking to see if there are particular traits that lead to more climate sensitivity or less climate sensitivity. [Ettinger’s research examines multiple characteristics of trees as possible predictors of climate sensitivity: phenology (focusing mostly on bud burst and leaf out dates), leaf mass, wood density, native climate range (warm or cold climate) and phylogeny (tree species that are more closely related, in the same family or genus).]

How are you collecting data for your research?

Here in the temperate zone, trees make these annual rings because they grow more slowly during the cold winters. Last year, we collected increment cores from each of the trees. You drill into the tree and pull out the straw sized piece of wood. This is a way of looking at annual growth, how much a tree grows each year going back in time, without causing any damage to the tree. Because the tree grows more or less symmetrically, we try to go just to the middle in order to get as many years of growth as possible. By measuring the ring widths, I can look and see how much the tree grew each year and I can correlate that with climate data.

How many cores do you have?

We collected about 400 cores from the arboretum.

Have you found anything significant for New England?

Once you collect a tree core, there’s actually a lot of work that needs to be done to process it before you get the data out. I’m still analyzing the data and don’t yet have the climate sensitivity estimate. Contact me in six months and I might know more.

How do you see your results being used by researchers or resource managers?

There are two ways that I could see it being used. One is just simply to identify species that may be more sensitive to future climate change. We might find that one species doesn’t seem to be that affected by warmer years, so that might be a good species to plant in newly forested areas. On the other hand, you want to avoid species that have high climate sensitivity if growth is negatively impacted by temperature, for example. The other way that I can see this affecting management is through predictions that people are trying to make about how the world will continue to warm in the future. My results could affect climate models [by providing insight into the role of trees in the carbon cycle and ecosystem.]

Is there a particular aspect of your research that you enjoy the most?

I love the field work. I like being outside and I’ve loved getting the chance to see such a great diversity of species. I love looking at data. It’s exciting to find out what the patterns are. I also really love working with people who are not scientists. I learn a lot from people who, for example, walk in the arboretum and notice how species, from birds to trees, are changing. They usually have great questions and great insights.

How is citizen science a part of your work?

I was only able to collect phenology data for the two years that I was at the Arnold Arboretum, but there are many people who walk there every day. They can provide valuable data [by] continuing to collect the phenology data that I was collecting. This year, we launched a citizen science project called Tree Spotters, looking at tree phenophases. All the data is collected through the National Phenology Network [in Nature’s Notebook]. We just started that project this year as a pilot and next year we’re hoping to expand it to more volunteers. This is going to be really great to get additional long term phenology data.

I have also been involved in studying citizen science methods as a whole. What kinds of citizen science projects are out there? What do they offer to science? How much biodiversity are they measuring? Can they be used to help us understand things like climate change? How diverse are these projects? We’re really interested in helping people understand the resource of citizen science.