A Walk in the Woods with John O’Keefe, Forest Ecologist at Harvard Forest in Petersham, MA

Jennifer Berglund 00:04

Welcome to HMSC Connects! Where we go behind the scenes of four Harvard museums to explore the connections between us, our big, beautiful world, and even what lies beyond. My name is Jennifer Berglund, part of the exhibits team here at the Harvard Museums of Science and Culture, and I'll be your host. For this year's summer solstice episode, I'm speaking with John O'Keefe, a recently retired forest ecologist and coordinator of the Fisher Museum at the Harvard Forest in Petersham, Massachusetts. It's a museum of forest history and ecology that aims to explain the complex history of the New England landscape. Today, John is going to take us on a journey through the woods at solstice, highlighting the magnificence of New England's forests and the challenges they face. Here he is. John O'Keefe, welcome to the show!


John O'Keefe 01:13

Thanks very much. Looking forward to it.


Jennifer Berglund 01:19

What inspired you to become a forest ecologist?


John O'Keefe 01:25

Well, I took a fairly circuitous route to becoming a forest ecologist. I had an undergraduate; I majored in sociology at Harvard College, and then graduated in '67, and faced the Vietnam War, and joined the Peace Corps. Spent time in Lisutu in South Africa. [I] came back a bit early because my dad was dying, but still was facing the draft and managed to be accepted into a pilot training program in the Massachusetts Air National Guard. And so, through [the] much of the 1970s, for six years, I spent flying over New England, and I had always been interested in nature, walking in the woods, and looking down flying around, I saw that New England was almost all forest, and decided that would be interesting to learn more about those forests. When I was done, I actually took a bunch of courses through Harvard Extension in biology, and then was accepted into a master's and then a Ph.D. program in forest ecology at UMass in Amherst.


Jennifer Berglund 02:42

You have been working on this leaf emergence and flowering study for over 30 years, which is amazing. Describe what that study is all about and what you've observed over the last 30 years.


John O'Keefe 03:01

Shortly after I started working at Harvard Forest, I was sort of looking for a way to get myself out on a regular basis walking through the forest and tried to come up with a research project that might involve that. And as a grad student at the University of Massachusetts, I had helped one of my advisors set up a study on one of the University of Massachusetts forests to observe the timing of leaf emergence on deciduous trees and also the time of leaf senescence or drop. And senescence means the basically dying of the leaves on deciduous trees in the fall preparing to go dormant for the winter. So, the tree or shrub essentially shuts down, stops photosynthesizing, goes through a process where the leaves form an abscission layer surface at the base of the leaf where the bud for the next year's leaf is developed. And then as the fall progresses, the leaves change color and drop off, which, of course is our fall foliage season which is a major event across this part of Massachusetts. It's part of this annual cycle of leaf emergence and growth in the spring, growth through the summer, and then as the days shorten, and it gets colder, the plants prepare to go dormant for the winter. And I mentioned mountain laurel being an evergreen broadleaf tree or shrub and we are right near the northern range limit of both mountain laurel and all of the other rather taller evergreen broadleaf plants because they can't survive when it gets too cold. Those of you who might have rhododendrons in your yard, may notice that on those really cold winter days, the leaves of the rhododendron are really tightly curled up to try and expose the minimum amount of surface to the sun. Because there is no moisture available for photosynthesis, because the ground is frozen. And it's basically the lack of moisture. The cold creates, essentially, a lack of available moisture in the winter. So, the plants…that's their way to shut down for the winter, the evergreen trees have much less surface area, and another, sort of, way of protecting themselves—the needles are able to get largely shut down the attempt of photosynthesis during the winter. They have sort of an anti-freeze system.


Jennifer Berglund 06:03

What have you observed over these many decades?


John O'Keefe 06:10

Interestingly, not much change. I have observed a huge amount of year-to-year variation. And when I started in 1990, I wasn't really thinking that I was going to be focusing on a climate change study. But over the 30 years, because the timing of these events, the leaf out and leaf color and drop in the fall, are controlled by climate. It's part of an area of science called phenology, which is the timing of biological events that are driven by climate. So, these events such as leaf emergence, leaf senescence, migration, hibernation, all of these that are ultimately biological events driven by climate, are seen as ways to look for the impacts of climate change. So, after 5 or 10 years, the study became of more interest because of its potential to record changing climate. And so, I started, you know, focusing a little bit more on that aspect of it rather than just observing what was happening. And that I think, is actually why I wanted to do it, I wanted to have a good reason to get out and wander around. It's always the set path through the forest, because I'm looking at the same trees year to year, but I hadn't put it in that really larger context initially. It was probably more to get myself to look closely and analyze the trees and this process of leaf emergence, especially, which although I had, you know, done a lot of work working in the woods, on university forests for my dissertation, you don't look that closely at every tree. And so having initially I started with over 30 species that I was tracking, on about a weekly basis through the spring and then in the fall, I learned a tremendous amount about how each of the species went through this process of leaf emergence, depending on the type of bud and how the bud expanded and when it flowered, where the flower appeared, timing of what flowering and, you know, fruit development, seed development over the course of the growing season. So, you know, that was sort of my initial focus. But then over time, with the increasing awareness of how the climate was changing, it became also a study to look at how that might be affecting the timing of the growing season, and leaf emergence and senesence in the fall. And, at times, it has appeared that the growing season has been getting longer in my observations. And there are many other now observations done, both around the world and across North America, both with citizen observations, citizen and scientist observations, but also using satellite imagery and what are now called phenocams, which are basically surveillance cameras looking out at a forested landscape, and using the changes in the color recorded by those cameras to track leaf emergence and then leaf color change and senescence in the fall and drop. But those are really definitely showing changes in climate. My study actually has not shown a significant change in spring leaf out.


Jennifer Berglund 10:22

What kinds of major changes have New England's forests experienced since you started working as a forest ecologist?


John O'Keefe 10:32

Well, actually, since I've been a forest ecologist, the major changes that the forests have experienced have largely been driven by pests and pathogens, and mostly introduced ones. Of course, the other change that the forest is experiencing, sort of, with pulses is clearing for development. That really is a function of how the economy seems to be doing at a given time. We went through a big burst, you know, in the 90s and 2000s. And it slowed down and was beginning a little bit…but the biggest change right now is introduced pests and pathogens, major ones being the hemlock woolly adelgid, which sort of was coming through southern and central New England, starting in the late 1980s, to the current time. And then, in the last decade or so, it has been the emerald ash borer. Two insect pests. The hemlock woolly adelgid kills hemlock trees by inserting a stylet feeding tube into the base of the needles and sucking out the photosynthate so the tree doesn't get it. The needles die, fall off, and the tree eventually succumbs to not having enough food produced. The emerald ash borer is an introduced boring insect that bores through the stem of the tree and lays eggs in galleries, and that prevents the movement of sap and food up and down in the tree and it essentially girdles the tree, and that also weakens the tree, and the tree dies from lack of function. When I first started my research at the University of Mass[achusetts], we were in the middle of a major gypsy moth outbreak in the end of the 1970s and early 80s. So we had three or four years of extreme defoliation of the oaks in our area, which caused a large amount of mortality. Gypsy moth was introduced to Massachusetts in the 1860s, and since then has gone through cycles of, sort of, eruption, major damage, and then kind of slowing down a lot. There have been a couple of attempts to control it with fungus and a virus. And these have had some effect, but they're somewhat weather dependent on how their effect acts on the insects or the caterpillars. And so, when the weather conditions aren't conducive to developing the fungus and virus, we tend to go into another small outbreak. We had an outbreak three and four years ago now in central Mass[achusetts] that seems to have dropped down again. It's still around, it hasn't been as bad as it was in the early 80s since then. But, the hemlock woolly adelgid has definitely largely eliminated hemlocks across much of southern New England. The adelgid, as introduced to North America from Asia, has some cold tolerance limitations. So very cold snaps in the winter can kill almost all of the adelgids. Not all, but almost all. And then it can take quite a while for them to build up again after that. So, that has really reduced its spread, or the rate of its spread, into northern or north central and northern New England. But, we, you know, exacerbated by warming climate…we haven't been getting those cold snaps in southern New England. And so that has allowed it to gradually keep moving north, and it's been at Harvard Forest for a couple of decades at this point. And we have a major hemlock area in the center of one of our main tracks at Harvard Forest where we're tracking the impact of the adelgid as it kills the hemlock trees. And what we're seeing is that as the hemlock trees die, they're generally replaced by black birch. There's black birch…some black birch, in almost every hemlock stand. It's the major associate with hemlock in our forests in this region. And it seems very adept as the canopy thins and more light reaches the floor of the forest than the birch seedlings take advantage and get established. And as the hemlock gradually die, the birch come in. And what we don't know is whether that's a temporary transition and the birch will gradually be replaced, or whether the birch will form another forest for a period of time, more or less as a single species. It's interesting that, you know, hemlock and black birch are extremely different species. One is a conifer that has needles that are very acidic and very slow to decompose and forms a dense deep litter layer on the forest floor, builds up a lot of stored carbon. Black birch has very rapidly decomposing leaves that drop every fall, but then decompose, so it doesn't build up that litter layer. So the whole ecosystem in these forests changes as that transition occurs from hemlock to black birch.


Jennifer Berglund 16:21

That is very interesting. You had mentioned when we had spoken previously, that the hemlock groves in the Harvard Forest are dangerous places to walk now. It used to be that there were trails going through that area. But now that the hemlocks are dying, there are hazards above.


John O'Keefe 16:43

Right, right. And in fact, you know, my trail that I, my phenology observations, actually goes through the hemlock stand, and I'm very careful walking. In fact, we had a research project that we would sometimes bring visitors out to see and talk about the hemlock changing, the forest changing, and hard hats are required for visiting that part of the forest because of the danger of falling branches. And you know, if it's very windy, you could even get occasional trees coming over. So that trail, which was one of our major interpretive nature trails has been moved. And so it's no longer part of our visitor experience at Harvard Forest. We explain it in other ways.


Jennifer Berglund 17:35

You mentioned that you have some citizen science projects. And did you say that you have one that's tracking the woolly adelgid through New England?


John O'Keefe 17:46

Yes, yeah, we have actually three major citizen science projects, one of which is based on my phenology study, where we have schools and teachers and students across southern New England, even down into New York City. We have a teacher, who is observing the timing of leaf emergence and leaf drop in a protocol that's largely based on my study at Harvard Forest. Another is tracking where they have hemlock trees available near the school site looking at the presence or absence of the woolly adelgid. And then once it is there, tracking its development and impact on the hemlocks. And in fact, several of the schools that have been doing this over almost 20 years of the study, have had the hemlocks on their school's site be infected by the adelgid. The adelgid has arrived and is now starting to affect those trees. Whereas when the project was started, I think there were only one or two sites where the adelgid was present.


Jennifer Berglund 18:57

I see.


John O'Keefe 18:58

And the third is actually setting up plots, 10 meter by 10 meter plots, on the forest adjacent to the school or that the school has access to, and measuring the trees on an annual or every second or third year basis, to have the students observe how the forest is growing and changing over time.


Jennifer Berglund 19:23

How can other schools get involved?


John O'Keefe 19:27

They should go to the Harvard Forest webpage and look for a section on it called "Schoolyard Ecology". There's a link on our webpage, how to get more information to try and start one of these projects in your local school. We've had thousands of students involved over the nearly 20 years, and hundreds of teachers. On the webpage you can see the map of involved schools, and, you know, what projects they're working on and for how long.


Jennifer Berglund 20:04

Many of our listeners are nature lovers who enjoy springtime and New England's forests, and the summertime. What kinds of things should they be on the lookout for around [summer] solstice?


John O'Keefe 20:19

We're recording this a little bit before solstice, but right now what's happening is that the forest in the past week and a half, the leaves have emerged and are now rapidly growing. And by the solstice they will be pretty much at their full size. What's happening also right now is that our wind pollinated species, and most of our forest trees are wind pollinated. And for those of us who have seasonal allergies, that's fairly obvious. Right now, we're recording sort of third week in May, and the oaks are in flower and the birches have just finished flowering. And in a week or so, by early June, the pines will be shedding that pollen; pines don't flower in the technical sense. But right now, my car, each morning when I go out to it, I have to run the windshield wipers to clear off the pollen that has settled on the windshield overnight. So the car is sort of covered in this yellow green dust. And you know, that's one of the important things that happens. And we actually often don't think of our trees and forests as flowering because they are wind pollinated. We notice the apple trees and the quote "flowering trees" like the mountain laurel, or shrubs like mount laurel I mentioned, and the cherries, black cherry. But all of the trees do flower and pollinate, and because it's wind pollinated, we don't often think of the flowers as flowers, per se. But in fact they are. And that's one of the things that, you know, I've really gotten into observing as part of my phenology study is I've really noticed a lot more detail about this whole process of the leaves emerging and the flowers emerging on some species. In fact, [in] several species, the flowers emerge before the leaves to facilitate the transfer of pollen, with the leaves not getting in the way. Doesn't matter for insect pollinated species, but for wind pollinated species, it's actually beneficial to have the pollen moving from the male to the female flowers without leaves getting in the way to trap the pollen. But the timing actually, to my mind, one of our most interesting trees is striped maple, which is a tall shrub, short tree. And it has a very interesting emergence. It has just two leaf scales, they split, and then an inner covered part of the leaves, another scale, starts to grow out. It grows about an inch and a half, and then it splits and the leaves pop out. And if it is going to flower, if it's getting enough nutrients and sunlight to flower, it then has a hanging group of flowers that emerge at the same time as the leaves, the leaves are very small then so it's easier for it to pollinate. And striped maple is very interesting because it actually has two genders. There are male plants and female plants, but that is more of a timing sequence. When the tree or shrub starts to flower it typically flowers male. As it reaches maturity and is about to die, it shifts and flowers female and produces seed for several years. And then typically, the plant dies. It's capable of surviving as a very small plant with two or four leaves for several decades in the understory waiting for enough light to start growing and flowering, and then going through that flower cycle. So it's one of the things that I really enjoyed learning as I started studying my phenology at the forest.


Jennifer Berglund 24:46

What's your favorite thing about the forest around Solstice?


John O'Keefe 24:54

Oh, the fact that, you know, it's just getting really vibrant and green, and the trees are basically just fully leafed out. And so they're, you know, at maximum growth and maximum photosynthesis. Actually, right around then early to mid-June, the red maples are dropping their seeds. And so this year is actually a really big seed year for red maples in our area. And so, the trees are just loaded with these red, you know, what people think of as helicopters. It's interesting that the red maple seed drops in June and germinates over the summer. And the sugar maple seed develops all summer into the fall, and then is dropped in the fall and sits on the forest floor and germinates in the spring. Similarly, the oaks, the red oaks, and there is a group of oaks: red oak, black oak, scarlet oak, that are in the red oak group and their acorns fall in the fall, sit on the ground, and then germinate. And they're actually just germinating now…last year was an incredibly a big red oak acorn year as well. And so we have lots of little acorns, germinating red oaks, right now with the first leaves just emerging. The white oaks actually dropped their acorns in the fall and they, a little earlier, and they germinate in the fall. And actually, are there as little seedlings in the spring already.


Jennifer Berglund 26:54

What do you hope your work does to inspire people to enjoy forests everywhere?


John O'Keefe 27:01

Well, I hope that, you know, by thinking about what I've done, and my sort of route into studying the forest, and phenology, it will encourage other people just to get out and look at the forest around them, the trees and plants around them, and actually look for the changes that are happening. I know, you know, growing up, I spent a lot of time in the forest and was somewhat aware of what was happening, but not really focused on it at all. And I think that, the more you can try and get yourself to look at it in a closer way, focus on a couple of trees, maybe track when the leaves emerge in the spring, and when they senesce and change coloring, drop off in the fall…get a much better appreciation of what's really happening in nature around you. I just think it, you know, it's fascinating. And I think that it's really a good way to get people to relax a little bit more, and think about, you know, what's really happening in the world around them. And maybe a little less focused on the news that you're bombarded with every day. Because that can be pretty depressing and really enjoying what's happening, even if it may be buggy, is really a good way to feel better.


Jennifer Berglund 28:42

John O'Keefe thank you so much for being here. This has been really fun.


John O'Keefe 28:46

No, thanks for having me. And I've really enjoyed it and hope other people do, too.


Jennifer Berglund 28:56

Today's HMSC Connects! podcast was produced by me, Jennifer Berglund, and the Harvard Museums of Science and Culture, and edited by Emma Knudsen. Special thanks to the Harvard Forest and to John O'Keefe for his wisdom and expertise. And thank you so much for listening. If you liked today's podcast, please subscribe on Apple Podcasts, Spotify, PodBean or wherever you get your podcasts. Happy solstice! See you in a couple of weeks!


Transcribed by https://otter.ai