Fire Ecology: East vs. West

Note: This program first aired on July 20, 2013.

I recently had the good fortune to travel to the Rocky Mountains, specifically the greater Yellowstone ecosystem. For people like many of my friends and me, East coast kids that we are, the mountainous west has long held an almost mythic standing in our minds. Besides the fact that it lacks an ocean, on its face the west seems to have everything an outdoorsy girl could want: bottomless powder skiing, endless trail running, essentially perfect weather all the time, no biting insects, wide open spaces, and more truly high mountains than you could climb in a lifetime. At the end of a solid two weeks of downpours and fog, or when the blizzard ends in rain, sometimes Maine doesn’t quite stack up.

There’s something Maine has though, that the West doesn’t, and it influences the biological community we find here, and minimizes our exposure to one of the more unpredictable, and frankly terrifying natural phenomena out here. I’m referring of course to water, we’ve got it, in spades, and to wild fires, which are pretty rare here in the Pine Tree State, but oh so common out west.

Fire ecology is a complicated topic; it includes factors like climate, weather, forest type and age, tree species, fuel load, and human management. All of these factors can change from year to year, and day to day, and some, like human management decisions, have had repercussions that are felt for decades. So bear with me when I simplify these factors in an attempt to get to some ground truths. Maine is a forested state, and the reason we have so much forest is that we have so much water, specifically, precipitation. Remove human interference and given enough time essentially the entire state would be forested (with a few odd and extremely localized exceptions). The west is different. It gets much less precipitation, and much of what it does get is in the form of snow fall. At certain elevations that is enough precipitation to support forest, but above and below those elevations, temperatures combine with water stress to yield treeless landscapes.

The first lesson you learn in fire fighting school is about the fire triangle, the three components required for a fire to burn. The first is oxygen, chemically a fire is the exothermic reaction that occurs when the carbons and hydrogens that are combined in any kind of carbohydrate molecule recombine with oxygen. No oxygen, no fire. The second leg of the fire triangle is an ignition source. Something has to ignite the fire, lightening and human carelessness are common sparks. The third leg is fuel, which brings us back to our two forests, east and west. Forests anywhere are nothing if not fuel for fires. The frequency and intensity of fires that occur, and they will occur, depends on the volume and flammability of the fuel; just how dry is it? Here in Maine we carry a potentially high fuel load, but it seems our flammability must be fairly low, as the average presettlement rate of fire return was something well over 1000 years. The disturbances to the forests here tend to be small scale (even the fires). The transitional “Acadian” forest that covers much of Maine is not particularly fire adapted as a result, though it is sandwiched between the much more fire adapted boreal forest to the north and oak forests to the south. Western forest and woody shrub communities tend to have much shorter rates of return for fire frequency, a few hundred years for high intensity stand killing fires, and just decades for lower intensity ground fires. The trees in these forests are adapted to high fire frequency, to the point where some of the species are actually dependent on fire at some point in their life cycle. Looking beyond the fact for a moment that as a result of climate change, summers are supposed to get hotter, winters warmer, droughts worse, and precipitation events heavier but less consistent, all of which will potentially lead to more fuel, we have to look at the other way human choices are impacting the effects of wild fires.

It is scarcely two weeks since 19 firefighters were killed in the line of duty in the Yarnell fire north of Phoenix, Arizona. They were working just beyond what is called the Wilderness Urban Interface*, the zone where housing butts up to forest vegetation. This is the big topic of conversation in western fire management circles, as housing development pushes further and further into naturally fire prone dry forest and shrub areas. And it is easy to sit here in Maine and shake our heads at those silly folks building houses in burnable canyons in Colorado and Arizona, but when I look out my window, you know what I see? Trees, and only trees. It turns out that I live in the wilderness urban interface too, though it is a stretch to call West Sedgwick urban. There is actually more housing in the WUI on the East coast than anywhere out west. The problem is that many western ecosystems are so much more fire adapted, they are supposed to burn. And as anyone who has argued with Mother Nature knows, its hard to stop her when she is doing what she is supposed to. So when the humidity is so high it is hard to breath, or the fog so persistent that things start to mildew, or the rain so torrential you can’t see across the yard, I thank my lucky stars I live in Maine, and although I know wild fire could certainly happen here, I don’t have to treat it as inevitable, as I think I would if I were living the western dream, enjoying that fluffy Rocky Mountain snow and hiking all those 14,000 footers. It was fun to visit, but I’ll take our vibrant, almost decadent temperate lushness here anytime.

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*The Wilderness Urban Interface is also known by its acronym WUI, pronounced “woo-eee”, but that was just too silly to say on the air.

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References:

The human toll of wildfires: http://www.nytimes.com/interactive/2013/07/02/us/firefighter-victims.html#AndrewAshcraft

The Yarnell fire outside Prescott AZ is just one example of the complicated intersection of climate change, human fire management, and unpredictability in nature http://www.nytimes.com/2013/07/07/us/a-painful-mix-of-fire-wind-and-questions.html?ref=earth

Issues of development in fire prone areas (much like issues of building along an increasingly flood prone coastine…) http://www.nytimes.com/2013/07/06/us/homes-keep-rising-in-west-despite-growing-wildfire-threat.html?pagewanted=1&src=un&feedurl=http://json8.nytimes.com/pages/science/earth/index.jsonp

Precipitation info for Yellowstone: www.nps.gov/yell/planyourvisit/weather.htm

Precipitation info for Maine: http://www.currentresults.com/Weather/Maine/average-yearly-precipitation.php

Nice overview of wildfire mechanics: http://science.howstuffworks.com/nature/natural-disasters/wildfire.htm

A good radio piece on the Wilderness Urban Interface (WUI) from Colorado College: http://radiocoloradocollege.org/wildland-urban-interface-where-the-wilderness-meets-civilization/

Yellowstone Afterglow

Note: This program first aired on July 13, 2013.

Last weekend I was in Montana, for a wedding. We were near Bozeman and the north entrance to Yellowstone National Park, surrounded by high country, open meadows and mountain ranges with names like the Crazies, the Absarocas, the Gallatins, and the Bangtails; a landscape so dissimilar to our home territory of coastal Maine. The air was different, the sun was different, it was a nice change of pace from the fog and damp we left behind.

We had one day after the wedding to explore before flying home, and we chose to make a lightening fast tour of the northern part of Yellowstone National Park, a place I have longed to see but never had visited. I especially wanted to soak in a hotspring; hotsprings being one of the few things Maine lacks that would make it perfect in my mind. Maine formed as the result of plate tectonics and volcanic activity, but the last of this was 200 or more million years ago. Yellowstone, in contrast, is located over a hot spot, a place where the Earth’s crust is particularly thin (3-5 miles in this case). A plume of magma is able to come unusually close to the surface of the Earth as a result, and can influence conditions on the surface. Conditions I was hoping to participate in, like a hot spring. The relatively recent nature of Yellowstone’s volcanic activity (a little over half a million years ago), the size and scope of this activity (described in the literature as “cataclysmic” and “massive”), and the thinness of the crust have ensured the profusion of geothermal features that make Yellowstone unique.

Hot springs result from a special set of circumstances. Water is a requirement, a spring is simply a spot at the surface where water emerges. Proper plumbing is key, the underlying geology must be fissured in such a way that all cracks lead to that one spot where the water is funneled out. Heat is also requisite, and the heat in this case comes from the interior of the Earth, resulting from the radioactive decay of elements like uranium and thorium in the mantle and core, elements trapped there since the earth formed 4.6 billion years ago. Here in Maine our main impediment to having hot springs is the plumbing. We have plenty of water, and there is certainly heat below the crust under our feet. The problem is the crust is too thick, and while it may be cracked, those cracks aren’t connected in such a way as to allow water to sink and get heated and then make it all the way to the surface.

In Yellowstone, precipitation and the melting alpine snow pack drain into the bedrock , which in much of the park is made up of rhyolite, a extrusive volcanic rock that gives us a clue about the nature of Yellowstone’s significant volcanic past. Many minerals are dissolved into this water as it flows deep below the surface, and surprisingly there are bacteria deep in the Earth’s crust that make use of these minerals. The most notable are the anaerobic hydrogen sulfide producing bacteria, which use the sulfur in the water in their metabolism, and produce the smelly hydrogen sulfide gas that is associated with many hot springs.

The spring I went to was called the Boiling River, and while it has a dramatic name, it is a fairly mild mannered thermal feature, by Yellowstone standards. The spring simply emerges out of the ground and forms a short water course before it drains into the Gardiner River. You soak at the narrow interface on the edge of the river where the hot spring water meets the cold river water. You remember the age old question about having your feet in the oven and your head in the ice box? Its kind of like that when you first get in. I would just get in a comfortable spot and the turbulence of the river’s flow would send a burst of cold river water into my lap, like a peal of laughter from the mountains. The characteristic orange mineral build up lined the edge of the spring’s flow, and the rocks were covered with blue green mats of heat loving extremophile bacteria. A perfect last quarter moon hung in a bright blue sky, and we were slightly veiled by the steam that rose around our heads. As I soaked I reveled in this heat that was not from the sun or the woodstove or any other earthly (as we know it) source, but from the deep mystery that is the interior of this rock we ride around the sun. Elements from an exploded star, coalesced into a planet. Elements that are still active, 4.6 billion years later, still releasing energy,  pumping heat into water, water I was sitting in as it emerged from a crack in the ground. I couldn’t stop grinning, even though there were tears in my eyes.

And now I am returned home smelling a bit like sulfur, dreaming of alpine meadows and steaming rivers, and basking in the Montana afterglow.

References:

The National Park Service Yellowstone website: http://www.nps.gov/yell/naturescience/geothermal.htm

Nice overview from a Canadian website associated with Banff National Park: http://www.mountainnature.com/geology/HotSprings.htm#Origin

Some nice local knowledge from a park gateway community business owner: http://www.pineedgecabins.com/yellowstone-guide-book.htm *Note: I have never stayed at this place and have no affiliation with the business. This is not any kind of endorsement, I just like the “guidebook” they have on their website.

Fledging Day

Note: This program first aired on June 29, 2013.

The other morning I got a phone call. It was my niece, saying, “Sarah, Sarah, I found a baby bird on the lawn! I watched it for twenty minutes and it is still there, can I keep it for a day?” I told her to leave it where it was, and that I would be right over. When I arrived we found not one but two baby chipping sparrows, staying quite still in the grass, minding their own business, and two adult chipping sparrows, noisily and nervously flitting about in the trees above. The date was June 14, what many Americans celebrate as Flag Day; for me now it will always be Fledging Day.

Merriam Webster defines fledge, the verb, as “to acquire the feathers necessary for flight or independent activity, also to leave the nest after acquiring such feathers”. The word can also be used as a transitive verb, which simply means it has an object, as in “to rear until ready for flight” or, my favorite, “to cover with or as if with feathers or down”. The definitions make me feel that it is as much about getting the feathers as it is about leaving the nest, which may be, because you can’t leave the nest until you have the feathers.

The little chipping sparrows we found were in fact fledglings, young birds who, under the care of their parents, having grown sufficient feathers, made the leap from the nest into the big world beyond. These sparrows, like most small song birds, are what is called altricial at hatching, meaning they are tiny, without feathers and with eyes closed. They can’t keep themselves warm, and are dependent on their parents for everything. They look like little fetuses, which is essentially what they are. They will live in the nest for days to weeks as they grow, for example, those chipping sparrows were in the nest for about 10 days before they fledged. The rate at which these babies develop is quite amazing, it seems like you could literally watch them grow. For altricial birds, fledging means growing enough feathers to leave the nest, not necessarily having the ability of full flight.

On the other end of the baby bird spectrum (and it is a spectrum) are birds who are precocial at birth, meaning they have feathers, open eyes and are capable of movement when they hatch, and may or may not feed them selves from the start. Ducks and other shore and water birds exemplify this pattern. The babies may not be able to fly immediately, but often they can swim.  For precocial birds, they have fledged when they can actually fly.

It is curious that there is such a difference in the stage of development of baby birds when they are born. This difference is a result of evolution. Nature has presented a problem to birds everywhere, namely “How do we keep our vulnerable young from getting eaten by some hungry predator?” (truly, the problem that faces all parents in the world). For birds, evolution has produced two quite elegant solutions, based on resource availability, and with pros and cons to each. Song birds migrate great distances to come to habitat with sufficient food resources and nesting areas. They have evolved to put their energy into simply getting here and getting down to the business of mating as soon as possible. Energetically that means that they put relatively little into their eggs, and the less you put into an egg, the less you are going to get out of it, hence the helpless altricial young. They are able to invest less bodily energy into egg production because once the young are born, they are able to collect plenty of food to feed them; the parents’ investment is on the outside of the egg shell. This is still a dangerous strategy, though, as finding a nest full of baby birds is like winning the lottery for a predator. It’s a concentrated source of nutrition, those tasty little niblets are all in one handy spot, the nest. Hence the speed with which these babies grow. Evolution has favored the fastest periods of in nest development, because the whole time they are in the nest, those baby birds are easy targets.

Precocial birds eliminate the possibility of having all of the young eaten in one predator attack, by dispersing them from the nest as soon as possible, mainly, as soon as they hatch. Individually they may be picked off, but they won’t all go together in a big gulp. The trade off for this in the physiological preparation of the parents. Their investment, particularly that of the mother, is on the front end of the nesting process; she must eat enough while developing the eggs to create a big fat juicy yolk laden egg. An egg like that contains enough nutrition to grow a baby bird that has feathers and run around as soon as it hatches. This strategy works really well, but obtaining that kind of nutrition on the front end is clearly not an option for many kinds of birds. The process of evolution has guided different bird species in different circumstances in different directions, and hatchling development is a perfect example of this. Happy Fledging Day everyone!

References:

Richard Sibly, et al, Energetics. Lifestyle and reproduction in birds PNAS, April 24, 2012  http://www.pnas.org/content/early/2012/05/17/1206512109.full.pdf

Mary Holland Naturally Curious 2010, Trafalgar Square Books—This fantastic book is also a popular blog and an email list serve: http://naturallycuriouswithmaryholland.wordpress.com/

Paul Ehrlich et al, The Birder’s Handbook: A field guide to the natural history of north American birds, 1988, Simon and Schuster. A classic, with detailed species accounts and a wide array of content essays.

One of the most comprehensive bird websites out there, from the Ornithology Lab at Cornell University http://www.birds.cornell.edu

The information about the evolutionary strategies of precocial vs. altricial young came from the Stanford University bird website: http://www.stanford.edu/group/stanfordbirds/text/essays/Precocial_and_Altricial.html They seem to have an active on campus birding community.

A Robin's Life Work

Note: This program first aired June 22, 2013.

I’ve had the pleasure of watching a pair of robins nesting this spring. For the past several years, they have taken to nesting on human made structures around an outbuilding at my house; on window ledges, on top of propped up ladders, on exposed beams. I’ve watched them in the past, but I’m ashamed to say that I didn’t really pay attention to them, due to a mix of caution and frank snobbery. Part of me didn’t want to disturb them, and part of me thought “oh, well, they are just robins. Robins are everywhere, they are so common, there’s nothing special about them.” This is a trap that naturalists everywhere fall into, we want to spot the rare bird, be the first to find the unusual flower, identify the large mammal tracks. So caught up are we with the excitement of the uncommon that we become blind to the more ordinary friends we see around us on a daily basis; the dandelion, the daisy, the sparrow, the robin.

This year I let go of my pretension. I was in a class, and one of our assignments was to watch a bird for an hour and record our observations. Because I am both an over achiever and an over scheduler, I needed to find an easy bird to observe, something close to home, something predictable, something like a robin nesting on a window ledge right out my front door. I decided that an hour was clearly not long enough, I would watch them during their entire nesting cycle, and document what I saw (that’s the over achieving part). What I learned is that every creature, every organism, every entity out there has something to teach us, if we are willing and open to learn it.

Several weeks ago, the robins began building their nest; The female builds the nest, with help from her mate. I didn’t know that from watching, a little back ground reading never hurt anyone. The pair struggled to construct the nest out of dry grass during high winds. It seemed futile to me. Then it rained, the ground became wet, mud formed. Robins construct a substantial part of their nests from mud, and these robins didn’t make any progress on their nest building until spring weather favored them with some building material. Suddenly, from what looked like a sloppy pile of mud on a window sill, a beautiful grass lined nest was formed. Next the female seemed to be testing out the nest, sitting in it some times leaving it other times. I realized she was preparing to lay eggs. One day I saw an egg in the nest, and worried that she had abandoned it, as she was not there every time I looked. Again, just as suddenly there were four eggs in the nest, and she was sitting consistently. Robins, like many birds will delay the incubation until all the eggs in her clutch are laid, so they all hatch at the same time. Her spotty attendance to the nest was what I was observing, by not sitting on the eggs she was keeping them cool so they wouldn’t start to develop.

The book said that the eggs would hatch in 12 to 14 days, so I marked the range of due dates on my calendar. The first due  day two eggs had hatched, the second day a third egg had hatched, and by the third day all four had hatched. That meant that the first two had a two day head start on the last hatchling, and I wondered how that would play out in nest dynamics. The book also said that they would fledge in 14 to 16 days, meaning they would grow from helpless pink featherless grubs to fully feathered birds in about two weeks. I couldn’t believe that, so I decided to photo document their growth, with a single picture each day. It turns out that a photo really is worth a thousand words. By day 12 the largest nestling had fledged. By day 13 the next one had. Today is day 14. I fully expect that by the end of today when I go out and look, the nest will be empty.

In watching these animals, who I am so grateful to for accommodating my curiosity, I was given a gift. I saw how fast those babies grew, and thought of all of my friends and their children, and my young niece and nephew. I watched the mother sit faithfully on the nest for two weeks, and then saw the father return to share feeding responsibilities with the mother once the eggs had hatched. I was aware of the parents’ alarm when I would approach the nest for my lightening fast once daily photo, observing how the young would immediately lower themselves in the nest in response to their parents’ calls. When darkness fell each night, I would imagine the mother robin, sitting on her nest in the dark, with only her self between her babies and the unknown and hungry night beyond. Raising those babies is truly a robin’s life work. What kind of person am I if I am not awed by that?

As we enter this period of summer’s bounty and ease, pick something, anything, anything you will see on a daily basis, don’t wait for the Blackburnian warbler or the rose pogonia. Watch it until it brings you to your knees. I promise you, your life will be richer for it.

References:

The Birder’s Handbook Paul Ehrlich et al, 1988 Simon and Schuster, the Bible for concise  go to info about North American bird natural history.

Nice little website about robins, including opportunities for citizen science. http://www.learner.org/jnorth/tm/robin/EggstraEggstra.html

The History of Maine Part 12: Humans and the Future of Maine

Note: This program first aired on June 15, 2013.

We’re spending a few weeks here on the world around us, tracing the deep history of Maine, from its geological genesis to the current day. We’ve reached the end of this series with a look the general trends of the human impacts on the Maine landscape.

If we had to summarize what happened to Maine as a result of human impact we could summarize it thusly: forest, farm forest. As we have said previously, the post glacial biotic community here is forest, at least in the current climatic regime. That is no surprise, follow the 45th parallel around the globe and what you will find is temperate forest world wide. The composition of that forest has changed over the past 12,000 years, but in the face of any disturbance, trees are what grow back here. We can consider European settlers as a major disturbance to this forest community, their direct impact peaked in the late 19th century, that is the “farm” part of the forest, farm, forest pattern. Since that time for a number of social and economic reasons, the forests have returned (not that they ever actually went that far in the first place).

European settlers first arrived in Maine in the early 17th century and for nearly 150 years enjoyed a precarious existence, eeking out a living tied to the coast line and coastal rivers and estuaries and warring with each other, and with the native population, which had been decimated soon after the Europeans arrived by European pathogens. By 1670 a whopping 3500 English settlers lived along the coast and coastal rivers, west of Penobscot Bay, with additional French settlers to its east. The low population numbers and the instability caused by constant conflict kept the impact of these new human colonists fairly low. Deforestation was strongly limited to the immediate coast, and up river valleys, and consisted of clearing for subsistence agriculture, and targeted harvesting of oak for barrels and white pines for ship masts.

Here is where geopolitics influences ecology. Once the American Revolution settled things and relative stability spread across the area, the population of “not yet Maine” grew dramatically. With this population increase came significant increases in land clearing and forest harvesting. It is important to take a moment and parse out these various levels of human impact. Land cleared for agriculture could be one of three things; land cleared for pasturing grazing animals, land cleared for hay fields and land cleared for tillage and the planting of crops. At its peak in the late 19th century, Maine was as much as 15% cleared for these uses (a number that has only gone back down from that time). Cutting in the forest was targeted at white pine for lumber, hemlock for the tanneries, oaks for barrels and ship building, and other hard woods for fuel wood, for both Maine and the Boston market. Forestry at that time was targeted, clear cutting was not part of the system, and wouldn’t be until the late 20th century.

This boom continued in the 19th century, until the time of the civil war and just after. At that point farms began to be abandoned with amazing speed, as the rail roads opened up the mid west (and their deep rich more easily farmed soils) and the economic center of gravity in America shifted from the Northeast westward. Forestry changed as well, as the best lumber logs became harder and harder to find, it was only the advent of the pulp and paper industry in the late 1800’s that kept the forest industry alive in the state. So Maine, the pine tree state, achieved its cleared land maximum just after the civil war, and has been growing trees back ever since. Even the spruce bud worm out break of the 1970’s and the change to industrial land ownership and subsequent clear cutting  in the second half of the 20th century have not managed to change the undeniable fact, in Maine, if you turn your back, a tree will sprout. It was only through constant back breaking vigilance that Maine was as cleared as it was in the mid 19th century.

Will it always be so? I doubt it. If there is one constant on Earth it is change. Now our actions will be influencing the Maine landscape well beyond clearing for agriculture or cutting trees in the forest. As climate changes in the coming decades, I doubt that Maine will become a treeless landscape, but a thousand years from now? Who knows? The biotic community we see around us is a result of the average temperature and the amount of water that falls from the sky, both factors that stand to be significantly altered by changing climate. So it seems that the tale of humans’ impact on the Maine landscape isn’t finished after all.

And thus concludes our look into the deep history of the Maine landscape. The tale may not be done, but this series is. Keep your eyes open and read the signs in your own neighborhood. You will be amazed, as I have been, where that story takes you.

References:

If this kind of history floats your boat, I can’t recommend this book enough: Andrew Barton and friends The Changing Nature of the Maine Woods. Readable and excellent!

A classic: William Cronin’s Changes in the Land. This one looks at the impact of Native Americans on the primeval forest, and is definitely weighted more towards southern New England. Lots of good information though.

Colin Woodard’s The Lobster Coast provides a comprehensive overview of the history of the people in Maine, particularly along the coast. Though “lobster” is the unifying theme, there is a tremendous amount of environmental history is this book. Very readable, super interesting.

Curious about the future? Check out this report from the UMaine Climate Change Institute: “ Maine’s Climae Future” http://climatechange.umaine.edu/files/Maines_Climate_Future.pdf

The History of Maine: Part 11 First Humans in Maine

Note: This program first aired on June 1, 2013.

We’re spending a few weeks here on the world around us, tracing the deep history of Maine, from its geological genesis to the current day. We’ve reached the third and final (for now) chapter in Maine’s deep history, and it is one we all have a hand in. Before we dive in though, lets quickly recap first two aspects of the existence of the Maine landscape.

About 600 million years ago the very faintest hints of the beginning of Maine were in the air. As a result of the constant movement of the Earth’s tectonic plates, coastal sediments were accreted on to the edge of the North American plate, and volcanic activity added new igneous rock to the mix as well, both above and below the surface. Additionally, little bits of continental plate that likely originated on the ancient European continent also became plastered to the edge of North America. By bits and pieces, the crust of Maine was formed. Two million years ago, the northern hemisphere entered an ice age, and continental glacier after continental glacier advanced over the Maine landscape, scouring and smoothing, and dumping the rocky sediment that challenges gardeners throughout the state.

The last glacier retreated from the state between 15,000 and 13,000 years ago, and the Maine landscape was likely recolonized with Arctic tundra plants, which were then rapidly outcompeted by a forest community as climate continued to warm. Paleopollen analysis indicates that the post glacial environment was mainly forested (with a variety of community compositions). So the types and sizes of trees may have been somewhat different, but after the glaciers left, Maine didn’t look shockingly different than it does today, at least to the casual observer. Botanists and foresters may argue this point, but I think it is important to understand that in the big picture, Maine is solidly a forest community.

It is likely that as soon as there was large game in the post glacial forest, people were here as well. There is archeological evidence to support this. And while there were multiple native cultures that flourished at various times during this post glacial epoch, current thinking posits that the native populations here had a relatively low population density (relative to southern New England or the southeast US), due to an almost entirely hunter gatherer lifestyle. Agriculture was  used in more southern regions, and in far southern Maine, but not in the majority of the state. So, early native populations had some kind of impact on the Maine environment, but it was strongly limited by the low population density and lifestyle. Geographically, evidence suggests that the native populations were concentrated on the coast, so for vast stretches of Maine, while there may have been human activity in the past 10,000 years, it left little impact.

In terms of human impact, European colonization was the turning point. It began in earnest in 1607 with the failed Popham colony, and the various French and English 17th century trading and fishing outposts. These early developments were entirely coastal, as transportation was water based. Just think about that for a moment. There were no roads, just overland foot paths. If you wanted to get anywhere you got in a boat. Think about how access to transportation, in this case, the water, must have guided settlement, and in fact, limited it to the thinnest of strips right along coastal waterways and eventually, up major rivers as well. European’s ties to the water, as well as conflict with the native populations kept the majority of human impact along the coast for nearly 200 years.                                     

We’ll look at what happened next, next week, when we finish the chapter of the human influence on the Maine landscape, and perhaps even peer into the future.

References:

Terrific new book by Andrew Barton and friends The Changing Nature of the Maine Woods. Readable and excellent!

A classic: William Cronin’s Changes in the Land. This one looks at the impact of Native Americans on the primeval forest, and is definitely weighted more towards southern New England. Lots of good information though.

Recently Maine Public Broadcasting did an interesting call in show about the first people in Maine. Listen to it here: http://www.mpbn.net/OnDemand/AudioOnDemand/MaineCalling/tabid/288/ctl/ViewItem/mid/3682/ItemId/28278/Default.aspx

The History of Maine Part 10: Sea Level and the Coastline

Note: This program first aired on May 25, 2013.

We’re spending a few weeks here on the world around us, tracing the deep history of Maine, from its geological genesis to the current day. We left off last week looking at some of the landscape features the glaciers left as they retreated 13,000 years ago here in Maine. That period of deglaciation had another profound impact on the Maine landscape, particularly the one most people know Maine for: the coast.

When we look at the location of the coast line, we are really looking at the edge of the water relative to the elevation of the landscape. If the landform is low, the water can move in, if the land form is high, the water is pushed out. There are two factors here that can change, the amount or volume of the water (the more water there is, the more three dimensional space it takes up, the higher it rises relative to the land, if all things are equal), and the level of the land (this is trickier to get your head around, but just remember that the crust of the Earth is floating, just like a ship at sea—the heavier the boat, the lower it floats. Solid crust floats on the more plastic layers of the Earth below.)

When we look at these two things relative to glaciation, we see the complicated and variable history of Maine’s coastline in the past 13,000 years. When glaciers form, they form from water, generally liquid water that evaporates into the atmosphere and then falls back to Earth in solid form. Where does all that liquid come from? The ocean, so overall we see a drop in global sea level when large continental glaciers form, because so much liquid water is taken up out of the ocean. At the height of the last glacial advance, it is thought that sea levels in our neck of the woods were 300 to 400 feet lower than today as a result of this (a level that would have easily exposed the continental shelf, had it not been covered by ice).

The amount of water isn’t the only thing that can change however, remember, the actual relative level of the land can as well. Remember the ship I mentioned, when it is heavy is floats lower in the water, when it is empty it floats at a higher level. The crust that underlies the state of Maine is like that ship. And what could make the crust heavier than normal? How about 10,000 feet of solid ice? That would do it. The continental glacier was so large and massive, it caused the crust to become less buoyant and float a bit lower on the underlying mantle. The crust was literally depressed into the Earth. As a side note, this is happening today in Antarctica, much of that continent is actually below sea level as a result of the weight of its ice cap.

So that is how the stage was set when the last ice age began to end here in Maine, about 13,000ish years ago. Just like a trampoline with some one sitting on it, the Earth’s crust is deformed by the weight of the glacier, and there was less water in the ocean. That less water in the ocean bit was changing fast though, as the glacier was melting quite rapidly. All of that melt water returned to the ocean, which rose quite rapidly in response. And as the glacial melted, it relived the pressure on the underlying crust, and just like a trampoline when you bounce off it, the crust rebounded. These two events didn’t happen simultaneously though, the glacier melted a great deal faster than the Earth rebounded, which meant, the ocean water easily covered the newly exposed but still depressed landscape of Maine. This event is called the Marine Incursion and at its maximum the coastline was as far inland as Medway, near Baxter State Park. Soon though the Earth’s rebound caught up with the rising ocean, and then some (again, think of our trampoline; a bouncer gets pushed up above the equilibrium level before coming back down). At the height of the crust’s rebound, sea level was much lower than it is today, as the land rose up above the level of the ocean. During this period, about 11,000 years ago, much of the Gulf of Maine, in particular Georges Bank on the edge of the continental shelf, was dry land. Terrestrial fossils, including trees and mammoth tusks have been recovered from Georges Bank, and the Gulf of Maine was a shallow inland sea cut off from the Atlantic Ocean. Soon thereafter though, the rebound eased and even subsided a bit, and the rising ocean caught up. The present day coastline was more or less established in the last few thousand years, as the rapid changes that resulted from deglaciation ended and temporary equilibrium was restored.

Maine has what is called a drowned coastline, and I hope now you can see why. Next week we will look at the third major force that shapes the Maine landscape, us.

References:
D. W. Caldwell Roadside Geology of Maine 1998

Harry Thurston The Atlantic Coast: A Natural History 2011

David L. Kendall Glacier and Granite 1987

The Maine Geological Survey makes its surficial geology map available on line, in a printable 11x17 inch format. It has lots of good info on the results of the last glacial advance and retreat, and it’s free!
http://www.maine.gov/doc/nrimc/mgs/pubs/online/surficial/surficial11x17.pdf

Super nerds unite: check out the Maine Ice Age Trail, and you too can tour Hancock and Washington counties looking at gravel pits (I’ve done it, its awesome). http://iceagetrail.umaine.edu/ also includes an excellent overview of the last ice age in Maine http://iceagetrail.umaine.edu/content/iceageinmaine/iceageinmaine.php