Ghosts of Ancient ForestsMay 14 2018
Scientists working on the outer coast of Southeast Alaska recently discovered an ancient forest exposed by glacial retreat. In late May, they’ll return to the site.
Could these trees reveal how life how life has responded to past warming? Could they provide insight into how life will respond today?
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FIELD NOTES FROM THE ANCIENT FOREST, PART II
Reports from Dan and Ben say the sampling went smoothly, which is as good as it gets when it comes to field science in “rather Icelandic” conditions. They cut dozens of cross-sections from the ancient trees.
“Because the standing dead trees in the buried forest were completely entombed in glacial outwash," Ben wrote "the outer divots and inner pockets of logs were stuffed with sand and gravel.” The cutting quickly wore down several chainsaw chains that they’d brought for backup. Phillip and Ben spent hours twisting increment borers into live trees on the moraine to collect samples of the core—from the outermost rings to the inner pith.
Ben deemed 16-day trip a success. They cored about a hundred living trees from the surrounding area and cut about ninety cross-sections from trees in the ancient forest. Strapping the slabs to external-frame backpacks, Dan, Ben, and Phillip hauled about six hundred pounds of wood down to the beach for pickup on the flight out.
In the end, Ben came up with three scientific goals from the treasures taken from the outer coast:
First, construct a time series of the rates at which the trees grew and examine their demise toward death. He wants to know whether the patterns of growth and death correspond to any past climatic events.
Second, see if (and how) the growth rates of yellow-cedar trees responded to the relatively balmy conditions of the Medieval Warm Period (MWP). “Just like the Little Ice Age,” Ben says, “the Medieval Warm Period was not a monolith over space and time.” Occurring roughly 900-1000 AD, “It was well-pronounced and fairly straightforward in Europe, but the specifics are still being defined elsewhere including the North Pacific.” Dr. Greg Wiles of The College of Wooster Tree Ring Lab calls the MWP a natural warm period relative to today. “Today’s warming is fundamentally different,” due to the influence of our human activity, but how the trees responded during that time might reveal something about how they’ll respond to future conditions. Given the extent of yellow-cedar mortality throughout many parts of southeast Alaska and British Columbia, the species is currently under consideration for listing under the Endangered Species Act.
Lastly, Ben wants to determine how the different tree species on the moraine responded to the local cooling and warming as the glacier advanced and retreated in the 19th and 20th centuries. He thinks the historic, localized changes in climate could serve as a test for how these different species may respond to the abrupt climate change expected to come. What does their future in a warming world hold?
He’s headed back to the La Perouse forest this week and installing some temperature devices that will collect hourly temperatures for a year. With any luck, we’ll return next summer with results from the wood samples and collect the current those devices for an understanding of the current conditions.
FIELD NOTES FROM THE ANCIENT FOREST, PART I
Ben said the weather on the outer coast was a constant source of entertainment. Some form of rain—whether it was a sprinkle, a steady downpour, or an intermittent burst—persisted for the first six days.
“At one point late in this soggy episode,” he wrote me, “my mind was operating with the assumption that it wasn’t raining anymore, but that was only because the rain was rather light. I guess the mind works on relative terms. It was raining, just not that hard.”
A storm ripped through the camp, which was exposed on open outwash gravel, and belted the team with raindrops the size of marbles. The deluge split one of the cook tents in two. The next day, Ben, Dan, and Phillip, an undergraduate student at the University of Alaska Fairbanks helping with the field work, moved their base to a more protected spot. It never blew like that again, however, and the spells of blue sky began to persist for longer.
Spring came over the course of days. “The 4am bird chorus at the end of the trip was only a series of tentative solos at the beginning,” Ben recalled—Swainson’s and Varied Thrushes, Yellow Warblers, Tree Sparrows, and Winter Wrens in concert with one another. Spruce tips broke free from what were initially tight buds.
And the glacier crossing? Well, that part wasn’t necessary.
"After passing over the proposed glacier route, it was apparent that the ice was riddled with too many crevasses to pass safely," Ben wrote in his field notes. "Fortunately, the creek draining the glacier, normally a raging torrent, had now transformed into a sleepy brook, allowing us to pass to the study area with relative ease…. When we arrived at the glacier it was apparent what had happened. House-sized icebergs that had once floated in the lake stood grounded. The lake, which normally fed the creek, was dry, having finally tapped into the inner plumbing of the glacier that dammed its southern side. It was now draining below the ice. This product of glacier retreat graced us with the ability to stroll from the forest to the beach, a route we needed to use for hauling wood samples to where the plane could land on the beach. Without this auspicious lake-draining, we would have spent days bushwhacking through the old-growth forest with heavy packs where our land speed usually averages 0.3 miles an hour."
ON THE COAST
Last time we were in touch, the packing list from Ben looked something like this:
bowl, mug, spoon, first-aid kid with signal mirror, fire starter, 10-degree sleeping bag with water resistant cover, sleeping pad, 3-season freestanding tend, tarp (for over the tent), lightweight drybags, long underwear, extra socks, fleece-jacket, wind-shirt, hiking pants (non-cotton), nylon rain gear, PVC rain gear, leather boots (sturdy ones for crampons), Xtratufs (for stream crossings), gaiters, neck gaitor, warm hat, gloves, knife, sunglasses.
It was a pretty standard backpacking list, although the multiple types of rain gear as well as the multiple tiers of rain protection at night (rain resistant cover, tent, tarp over tent) were good indicators of the anticipated challenges. I took a look at the weather projections online before they flew out of Yakutat on the May 29th —a ten-day front predicted.
“Looks damp for the foreseeable future,” Ben wrote.
The brief updates I’ve received over email since their departure are more uplifting. They’re carrying inReach devices, which can send a lat/long location along with 160 characters of text.
May 27: L. Weather rather icelandic. creek dry, which is lucky becse glacier impssable. cook tent & phillips tent blown down last pm. Found spectclr ice cave. D | Dan Mann sent this message from: Lat 58.496608 Lon -137.297473
In the planning stage, there had been two possible routes to the ancient forest—across a creek and through downfallen trees and brush or via the glacier. If the creek had been too high to cross and the glacier also impassable, there wouldn’t have been any other way. Lucky.
May 27: Non buried cedar snags look like died long ago n at same time. Is that unusual? cored a hem and looked up to find a well fed porcupine | Benjamin Gaglioti sent this message from: Lat 58.496586 Lon -137.297924
Hem—hemlock species, either Mountain or Western. It’s difficult to distinguish the two species with trees that have died a long time ago, but both are known to co-exist with yellow-cedar. Snags are dead trees—and Ben is interested in identifying the timing of their death. Yellow-cedar (Callitropsis nootkatensis) is of particular interest because recent research has revealed this species’ vulnerability to climate change. The loss of snowpack, which acts as an insulator, makes these trees susceptible to injury from sudden cold events. Even amidst the loss of snow and increasing temperatures, extreme cold events still persist along the coast. Could the conditions that caused these trees to die long ago in this one place be similar to the conditions triggering death of this tree across the archipelago?
June 2: L. Guess we should have done a coms check before we left town. Did u get my earlier email? Dan | Dan Mann sent this message from: Lat 58.496618 Lon -137.297516
I tried another 160-character response to confirm.
Nearly ten days have passed with these few words to fill the silence. I’ve spent enough time on the outer coast to know that anything can happen out there—quick turns in weather, failed data missions, bear charges, and food shortages, just to name a few. But the latest news is great news as far as I can tell:
June 7: L. Back in Yak this arvo. On scale of 1 to 10 [10 best] this a10. Ben will tell you more. D | Dan Mann sent this message from: Lat 59.548355 Lon -139.71704
Not sure what “arvo” means, but the location shows they’re back in Yakutat. I'm looking forward to hearing more about "The Ten".
PRESERVING THE PAST
Rocks. Lake sediments. Tree-rings. Ice-sheets. Corals. Shells. Microfossils. What the paleoclimatologist (paleowhat?!) finds today paints a picture of the past and, perhaps, offers clues for how climate may shape life in the future.
“What’s unique about this place, this discovery” Dan says of the La Perouse forest, “is that we have a chance to look at two systems—both the forest dynamics and the glacial dynamics.” Typically, paleoclimatologists, like Ben, are looking to reconstruct past climate from proxies, such as rocks or tree-rings. But this project is about more than past climate. It’s also about how life responded.
“There’s a bunch of different ways for recording when glaciers got bigger,” Ben told me. Radiocarbon dating allows scientists to determine the age of an object containing organic matter based on its chemical properties. “You could date boulders, for example, to see when they were unearthed by the ice and started receiving direct sun,” Ben says. But tree ring dates are more precise.
Each line in a core documents a year of growth. Wider rings mark the years with conditions for better growth; narrow rings distinguish the times of stress and hardship. Take one tree and match the rings up with the next tree—maybe an older one—and you start building a chronology of events back in time. Finding young trees that are growing near the face of a glacier can indicate retreat. Abrupt changes in the symmetry of the cores in a forest can indicate tilting caused by advance, ice-contact, or even death. So Ben and the team are after slabs—not just simple cores—for the more complete records at La Perouse.
“It’s a bit circular,” Ben admitted to me about his thoughts on the study during recent preparations. “We’re looking for what the trees can tell us about the timing of glacial advance and retreat and advance and retreat again,” but also “for how the trees themselves responded to changing climate conditions.” The ice and trees—the forest still standing and the ancient layer below—hold the same climate history.
Preliminary data suggests the ancient forest below dates back to 600 A.D., not long after the end of the Roman Era. Then there are the dead trees above, crushed and tilted and scarred by the ice that came with the Little Ice Age just over a century and half ago. What’s in between lies the Medieval Warm Period, or what scientists call the MWP for short.
“Today’s warming is different,” Greg Wiles told me in conversation about the MWP. “The rates are quite a bit different. But the medieval warm period was a natural warm period relative to today.” Some scientists consider it the closest analog we have for considering the consequences of future warming.
Ben and the team’s field technician, Phillip, are in Fairbanks getting ready to head south the archipelago. Yesterday, they packed food and shipped saws to Yakutat. Today, they’re packing in fresh greens while they can. Weather permitting, they’ll load up Wednesday for the flight to La Perouse.
UP NEXT: More on the medieval warm period and the many confusing aspects of historical climate. And the gear? What’s on the list for La Perouse?
THEN AND NOW: THE ICE IN 1899 AND THE FORESTS TODAY
“Though a wanderer himself, John Muir didn’t ride a glacier from to Yosemite or Alaska. But in a metaphorical way, he did. Raised in northern geographies that harbored the ghosts of glaciers—Scotland and Wisconsin—he became a keen observer. He developed ice age eyes….He regarded the long views, the wisdom of rocks.” – Kim Heacox, John Muir and the Ice that Started the Fire
Most people think of John Muir (aka the “Father of National Parks”) and the California Sierra Nevada, but in the four expeditions he made to the north, Muir left behind a legacy in Alaska as well. In 1899, Edward Harriman, a wealthy American in the railroad industry, arranged for an expedition from Seattle to Siberia and back. Muir was one of his top picks for the interdisciplinary team of scientists, artists, and photographers on board. The descriptions and illustration the team put together are some of the earliest known records of the La Perouse glacier. Even back then, the team noted the ice abutting forest—and remnants of a forest shaped by the glacier coming and going.
The Harriman Expedition report from June of 1899 notes: “The remnant of timber standing east of the stream valley was separated from the glacier at the time of our visit, by a belt of barren ground from 100 to 200 yards wide. This ground was occupied by bouldery till containing bruised and macerated branches and trunk fragments, and the margin of the timber showed unmistakable evidence of recent attack by the ice.” What was curious to the explorers back then would only become all the more relevant to another interdisciplinary team one hundred and seventeen years later.
“We didn’t go there in 2016 looking for the forest,” Dan told me. “I was interested in the old stuff—a section of an old marine terrace that the geologist on the expedition also described.” Over his years of working in Alaska, Dan has searched for evidence of the route the people who first populated the Americas took from Siberia. He’s looking for when and where the “the ice gates open”—when deglaciation occurred on the order of 14,000 or 15,000 years ago (maybe even more).
But the creek was flooded that year, so Dan and the team couldn’t cross over to the terrace the way they’d planned. “We went over the glacier just to get there just an easier way, and when we came around the corner, it looked like a field of telephone poles there, sticking out of the ground. We just stumbled upon them.”
Ben says that when they got down from the ice and walked about amidst the trees, they see that perhaps there were two forests left behind. The first appeared to be a relatively recent remnant of the Little Ice Age, the second perhaps from long ago.
UP NEXT: A bit about the role of paleoecology in understanding climate as the team preps for the return to La Perouse. How does the science work? What can a tree core reveal about the past?
THE TEAM AND THE PLAN
There’s pretty much one pilot you want if you’re going to try to a land plane on the outer coast anywhere within striking distance of Yakutat, Alaska. His name is Hans Munich, and his experience flying the northern reaches of the Alexander Archipelago once saved me from rationing a couple days of emergency food over a week of waiting. Dr. Ben Gaglioti, our project lead from Columbia University’s Lamont-Doherty Earth Observatory, calls him a “man of few words”. But then, who wants chatting for this kind of flying? Weather turns quickly. Rain comes and goes. Thick fog settles, rapidly restricting visibility across the mountainous terrain. Where Hans decides that he can land is where the La Perouse expedition begins. Then to reach the recently exposed forest, the rest is by foot—fording creaks, bushwhacking through downfall, or crossing the ice of the glacier itself.
Funded in part by National Geographic, our team brings together scientists with a range of expertise. Ben is a paleoecologist and paleoclimatologist, which means he studies climate from long ago, past environmental conditions, and their relationships with ancient organisms. He focuses on the last 40,000 years, mainly at high latitudes and works with lake sediments and tree-rings for a window into past. I’m on the other end of the spectrum when it comes to time. I focus on the present and the future in light of climate change—what impacts we’re seeing and will continue to see, how people (and other species) can adapt to a rapidly changing world. I’m an ecologist and social scientist by training.
“Tell me why you turn to the past,” I said to Ben over the phone during one of our recent conversations.
“I want to understand what happened the last time things suddenly warmed up," he replied, "and make discoveries about the Earth’s systems that aren’t available from short-term observations.” Ben acknowledges the role of human activity in the unprecedented rates of warming today but also sees an opportunity to learn from the past. Climate has always been changing. (More on this complicated topic later.)
Dr. Dan Mann from the University of Alaska Fairbanks is a geologist and paleoecologist who studies how climate changed during the last ice age and, to some extent, how it shaped the world we know today. Then there’s Dr. Greg Wiles, an expert in glacial geology and tree-ring analysis. Greg and I aren’t going to the coast for various reasons. His role comes into play once that bush plane makes it out with tree cores and slabs for analysis. I’ll help with the science from afar and write. I spent six years studying how forests on the outer coast of Southeast Alaska are impacted by climate change and how people are coping with the changing environment. Now I work on climate adaptation -- helping people plan for the future, or respond, today, to impacts in their local environment. So, I too, thought maybe there was something to learn from the past.
UP NEXT: What did the ice at La Perouse look like when John Muir traveled the rugged coastline in 1899? What were Dr. Mann and Dr. Gaglioti doing out there in 2016, when they first discovered the recently exposed forest?
In 2016, a team of scientists traveled to the outer coast of Southeast Alaska in search of evidence of a strip of land that was ice-free thousands of years ago. They were looking for clues to solve a persistent mystery: if people first populated the Americas by migrating from Siberia to Alaska, what route did they take? They made a surprisingly different discovery.
Forced by changing stream conditions to take an unexpected route along the La Perouse glacier, they spotted an ancient forest once buried by ice—now exposed by recent glacial retreat. Snapped in places and leaning away from the ice, giant ghosts of an old-growth forest remained.
Samples later confirmed that these trees, and others, well-preserved a layer below, recorded a long history of glaciers coming and going. Some trees by the La Perouse Glacier dated back to the Little Ice Age. Others lived over a millennium ago. The rings inside could be used like fingerprints trapped in time, revealing when they died, under what climate conditions, and where the glacier reached back then.
Now, researchers are headed back. The plan is to harvest cross-sections and core samples from the sentinels on the outer coast, and via bush plane, ship out the history preserved in the wood for study. The question at stake: What can we learn about our warming world from what the melting ice leaves behind?