Along the coast of Maine a special cold-adapted forest ecosystem thrives: the coastal spruce fir forest. The cool air that blows off the ocean provides an ideal environment for these colder species, but their future, like many, is uncertain. In this episode, we’re traveling through time to understand how coastal spruce fir forests in Acadia have changed over the past sixty-six years.

Episode 2: Place-based Science | The Coastal Spruce-Fir Forest

Narration: If you stepped into the spruce-fir forests of Acadia National Park early last summer, these are some of the bird songs you might be greeted with.

*Golden Crowned Kinglet, Dark Eyed Junko, Black Throated Green Warbler, Winter Wren and Red Breasted Nuthatch songs play*

Black Throated Green Warblers are small boisterous birds that are one of the most common summer residents of the coastal spruce fir forest. *Black Throated Green song plays again*

While the current soundscape of Acadia may seem normal to us, it is pretty different from even sixty-six years ago. It may even be quieter than it used to be, but most of us might not realize that when we step into the forest. Sixty-six years ago in 1959, you might have heard a completely different song.

*bird songs start playing*

You probably would have heard three times as many black throated green warblers.

*Black Throated Green songs play*

Some birds weren’t even detected in 2025 that you might have heard back in 1959 like the Bay Breasted Warbler.

*Bay Breasted Warbler song plays*

Others, like the yellow rumped warbler, noticeably declined.

*Yellow Rumped Warbler song plays* Our sense of what a forest in Acadia sounds like is based on our present experiences. In reality, we may be experiencing something called shifting baseline syndrome. A shifting baseline is a gradual change in what we accept as normal for the environment. These changes happen slowly and usually over generations so they are imperceptible to most people. But this change doesn’t go unnoticed by everyone, especially ecologists who devote their lives to studying trends and asking questions.

*music starts*

Welcome to Sea to Trees. My name is Julia Rush. Today we’re traveling through time to understand how coastal spruce fir forests in Acadia have changed over the past sixty-six years. In 1959 a PhD student named Ron Davis recognized a gap in literature on coastal spruce fir forests in Maine and conducted surveys of different locations to characterize these under-studied ecosystems. Today, researchers at Schoodic Institute and the University of Maine are revisiting Ron’s surveys to try to uncover the story of the coastal spruce fir forest and understand the future of these ecosystems in the face of climate change.

{Gillian Audier}: So I'm recreating surveys that were done by a researcher in 1959 named Dr. Ron Davis.

Gillian Audier is this year's Gero Fellow in Science Research at Schoodic Institute. She spent this summer retracing Ron Davis’ steps on Mount Desert Island to resurvey bird populations in coastal spruce fir forests.

{Gillian A}: He went to a bunch of different locations around MDI and just downeast Maine in general, to study lots of things, including bird populations.

She took me to one of the inventory sites in Blackwoods Forest on Mount Desert Island this summer to show me how she conducted surveys of the forest’s bird population. This site is just off of the Park Loop Road in Acadia National Park and about a two minute walk through the woods.

{Gillian A}: Once you get off the road, there's, like, just a really thick area of deciduous trees, and you kind of have to crash through and like it's really crowded, but then once you get through, it's like just a whole different biome, and it's so quiet right there, even though the roads here.

As we reached the survey site we were surrounded by bright green moss blanketing the forest floor. The moss was soft under our feet making each footfall nearly silent and almost acted like soundproofing, softening the noises of the forest. Tall, straight, grey-barked trees watched over us as they swayed gently with the ocean breeze. We could hear far-off lobster boats chugging as they worked and the buoy bell clanging in the bay. Gillian ventured here three times throughout June and July to collect her data.

{Gillian A}: So there's five different locations. This is one of them, Blackwoods, and at each location we have five to six different flags, which are each about 150 meters apart. And I just go to each of these flags, and I wait a little bit so the birds get used to my presence, and then I spend the next five minutes trying to be as quiet as possible and not moving around or making too much noise, and I just record every bird that you hear or see.

A point count survey is a research method used in ornithology, the study of birds, to sample a population. The flags marking each point count location are spaced out from each other to avoid repeat birds while sampling a larger area of the forest.

{Gillian A}: And then you hike to the next one, and you do it at each of the sites, and it all has to get done before nine AM because because, well, that's when Ron Davis stopped it. I'm trying to replicate it as closely as he was. But also, even, like, by like, eight, a lot of the bird activity has died down. It's pretty surprising how quickly they they start to, like, become less active in the day.

She had to get an early start to reach Mount Desert Island by sunrise from Schoodic, but was usually greeted by familiar voices.

{Gillian A}: I would usually leave at like four thirty AM and by the time I got here would be like five thirty to six, so pretty early it would be like the first couple sites were definitely louder, but it was always the same, like ten to fifteen birds.

While we were in Blackwoods we sat and listened and, even though it was much later in the day, we heard some of those songs.

{Gillian A}: Right now we're listening to Golden crowned kinglets, which is that, like, squeaky, high pitched one, and then that loud, kind of, like car alarm one, that's the red breasted Nuthatch. And those two guys you just, like, constantly hear, they never stop talking.

*Red Breasted Nuthatch sings*

{Gillian A}: That's the Nuthatch.

When it came time to evaluate her data, Gillian found that Ron heard more birds overall back in 1959 than she did in 2025. There were some species Gillian didn’t detect at all that Ron heard and recorded. Conducting a resurvey of existing datasets like this is one way ecologists attempt to identify shifting baselines. In this case they were looking to evaluate changes in bird populations and were able to determine a decline in birds. But you have to have an older dataset to compare your data to in order to detect those changes.

{Gillian A}: And it's pretty unique to have a data set to recreate from like, such a long time ago. So that's that's pretty valuable to have data from, you know, six decades ago. That's not the most common thing, and to be able to go to like those exact locations again.

In terms of natural history, sixty-six years is a pretty short amount of time considering the Earth has existed for billions of years. But sixty-six years is a long time ago for us. In 1959 Dwight D. Eisenhower was the president of the United States, the first ever Barbie doll was put on display at the American Toy Fair, and the Sound of Music debuted on Broadway. The world of ecology was pretty different too which presents some challenges for anyone resurveying Ron’s original study.

{Camilla Seirup}: Dr. Davis published in his thesis these little hand drawn maps of the sites. They're very professionally done, but he didn't have access to GIS information at the time. So he hand drew his site maps.

Camilla Seirup is a biologist for the Northeast Temperate Network which is part of the Inventory and Monitoring division of the National Park Service. In the summers of 2020, 2021, and 2022, as a graduate student at the University of Maine, Camilla resurveyed trees and soil at the sites Ron established in 1959. Today, ecologists use GIS, or Geographic Information Systems, to track their data collection and mark their research sites. But without access to that technology, Ron had to work analog.

*music starts*

{Camilla S}: One site in particular that was quite a challenge was the Beech mountain site. The calculated GPS location put us on this slope with very little spruce, and it didn't match the description, there was a lot of white pine and cedar. And, you know, it's been sixty years, maybe things had changed, but on his little hand drawn map, he had a boulder pointed out on it, which felt pretty permanent, and also, if it was obvious enough or prominent enough to be on this map, we figured we should be able to find it. I decided we should go back out in the field, take a closer look around, or really widen our search area. And we found it. We found the boulder, and there's this perfect strip of spruce that, I mean, I think that we located that site down to the meter. It was really amazing. So that was a challenging, but a really fun part of the project, just trying to figure out where he'd been.

Once she found all of the inventory sites, Camilla conducted her own resurvey. Her aim was to look at changes in forest structure in these coastal spruce sites. Because Ron didn’t just survey the birds in his initial sample, he took a wide inventory of the forest. Along with bird populations he sampled insects, small mammals, soil, and trees.

{Camilla S}: His work was this landmark study. He was the first one to delineate this coastal spruce population. And what's notable about that is that red spruce is a cold, sort of cold adapted species, and so for the most part, in the United States, its range is in northern and high elevation sites, but it has this sort of, this local range extension down the coast of Maine, facilitated by the ocean.

Camilla started by taking inventory of the trees in each of these sites.

{Camilla S}: So every tree in the plot was measured for diameter. We looked at its general health and got its x y coordinate so that I could generate a map, and I have maps of the stem locations across the whole the plot. We also identified the species, measured it or assessed its status, so whether it was alive or dead

She also measured and counted saplings, seedlings, and dead trees, estimated the percent cover of plants on the forest floor and took soil samples and tree cores. All of these pieces of data worked together to give Camilla a pretty large snapshot of the overall health of the forests. Camilla was able to compare her data to Ron’s and look for changes.

{Camilla S}: I titled my thesis sixty years of change in coastal spruce, but I think it's notable, like what didn't change, and that's that all the sites remained spruce.

Camilla found that red spruce remained dominant in sites that were predominantly red spruce back in 1959 and it actually increased across all sites. Red spruce is the most common tree species in coastal forests in Downeast Maine. But it’s also believed to be sensitive to changes in temperature and precipitation patterns. The climate is changing and the Gulf of Maine is one of the fastest-warming parts of the global ocean. Some models suggest that red spruce could lose almost all of its habitat in the United States in the near future. Camilla’s findings that red spruce has persisted was surprising considering its sensitivity and dire predictions. But there’s still a lot of uncertainty, and we can’t know for sure what the future holds for red spruce.

{Camilla S}: Resurveying and in general, long term monitoring is really important, because without it, we just don't know how resources are changing over time. You don't know where you've been, and you don't know where you are now, and you can't develop trends and projections for where you might be in the future. So a very critical piece of research.

The studies by Gillian and Camilla and subsequent observations are possible because of the initial inventory Ron took back in 1959. And like Gillian said, it’s pretty special to have access to such an extensive ecological survey from over sixty years ago. What’s even more special is being able to speak with the scientist who conducted the surveys in the first place to discuss your findings.

{Gillian A}: I don't remember what, how far along in the process we were when I last talked to you, I think we were still just planning everything. But since then, we've, yeah, recreated your bird surveys as closely as possible. Followed all the same methods.

Gillian and I visited Ron at his home in Orono in January so she could share her findings with him and talk about how her resurvey went. We were greeted at the door with a warm welcome from Ron and his dog Gingah before sitting down to chat. Gillian shared how the surveys went and that her findings suggest a decline in overall bird abundance in these coastal spruce fir forests.

{Dr. Ron Davis}: Well, I've heard, of course, about declines in bird populations, but I find it very sad.

Bird populations are declining all around North America so Ron wasn’t very surprised by Gillian’s data. But he wasn’t expecting that someone would be revisiting his research over sixty years later.

{Ron D}: One of the reactions I have is a sense of delight. That somebody like you is resampling what I did back in the late fifties, which was a long time ago, and I'm fortunate to have lived long enough to see that. And I was also delighted by what Camilla did. That's very satisfying for somebody like me.

Even though much has changed, Ron’s motivation for working in ecology aligned with Gillian’s and they immediately connected over their love of nature.

{Ron D}: I was always motivated by the beauty of the ecosystem. If it weren't for that, I probably wouldn't have done the work {Gillian A}: Yeah, {Ron D]: I like being in nature, and that's a very important part of the motivation for doing the kinds of things that I do. {Gillian A}: Me too {Ron D}: And I like being in nature because it's refreshing and inspiring, and it makes me feel good. {Gillian A}: Yeah, I totally agree.

Although Ron didn’t think anyone would revisit his work back when he was doing his initial inventory, he was thinking about the future.

{Ron D}: I always felt that it was very important to establish ecological baselines for future comparisons to in order to evaluate the impact of environmental changes that humans have made and will continue to make in the future.

Shifting baseline syndrome is real and we face it whenever we step into a forest and are greeted by fewer birds than there used to be. And these resurveys provide us with even more context and information, but we can’t predict the future of these forests in the face of climate change.

{Ron D}: Trees are long lived and they don't respond very quickly, so we don't really know, despite Camilla's results, just what effect it's going to have. We’ll have to wait another few decades. So you'll be around. *laughs* You might be around, but I won't.

While we have an idea of some of the changes that these spruce fir forests in Acadia have undergone over the past sixty years, there are still many unanswered questions about why those changes happened. Studies like Gillian’s and Camilla’s help clear away some of the fog that obscures the stories of these places but the future can never be certain. Predictive models can change as conditions evolve and time passes. Some of our questions are answered while new ones spring up.

*music starts*

Each ecosystem in Acadia is unique and faces its own challenges. There is no one answer of how to help these ecosystems. What we do know is that each restoration plan and research method here in the Park requires careful, inclusive science. Providing the time and space for scientific inquiry was part of the original mission of Acadia when it was first established as a National Monument in 1916. Of course science looks different today – we don’t have to hand-draw maps of research sites – and science will continue to change and it’s up to us to see the glimmers of hope that come from scientific inquiry. Like maybe bringing native plants and Wabanaki harvesters back to the Great Meadow will inspire more relationship building and healing for indigenous communities in National Parks around the country. Or maybe studying microtopography in summit restoration will help scientists on other low elevation mountains restore their summits. Maybe red spruce will stay resilient to climate change and Ron, Gillian, and Camilla’s data will help future generations understand that resiliency.

Understanding the history of this land and our own role in it, acknowledging the very real threats our ecosystems face and continuing to ask questions, helps us move forward into a brighter future. Because if we don’t know where we’ve been and we don’t know where we are now, how will we know where to go in the future?

Thank you for listening to Sea to Trees, a podcast from Schoodic Institute at Acadia National Park, a nonprofit partner of the National Park Service, inspiring science, learning and community for a changing world. Acadia National Park is on traditional lands of the Wabanaki, people of the dawn. A big thank you to this episode's guests Gillian Audier, Camilla Seirup, and Dr. Ron Davis. Birdsong recordings in this episode are courtesy of Matthew D. Medler and Cornell Lab of Ornithology Macaulay Library and Laura Sebastianelli. Once again, thank you to all of the guests on each episode this season. And thank you to everyone who has contributed to this season along the way. Sea to Trees is written and produced by me, Julia Rush, and edited by Catherine Schmitt and Sarah Luchini. The cover art was created by Sarah Luchini. Sea to Trees is possible through generous support of the Cathy and Jim Gero Acadia Early-Career Fellowship, the National Park Foundation, National Park Service, and Schoodic Institute.