The story of a mass extinction

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PLoS Biology just published my paper on how the meteorite that killed the dinosaurs affected plants. You can read the paper here (Plant Ecological Strategies Shift Across the Cretaceous–Paleogene Boundary), or read an excellent popular summary here (A Plant’s Guide to Surviving the Chicxulub Impact). There’s also media coverage in Newsweek, The Daily Mail, and several other outlets.

Instead of repeating these stories about the science, I want to share a little about how this project came together. It has been a long road. The project was first conceived some time in late 2009, when I was in a first-year graduate school class on ecology, and had the good fortunate to hear a paleobiology lecture from Karl Flessa while also reading on my own about fossilized leaves. I was already interested in learning about plant functioning from leaves, so it wasn’t much of a jump to start thinking about analyzing fossil leaves.

Over the next year or two I was able to refine some ideas, with good support from Brian Enquist and my dissertation committee, and started calling around to different museums asking about their fossil collections. Peter Wilf pointed me to Kirk Johnson at the Denver Museum of Nature and Science, where there existed an exquisite collection of fossils spanning the Cretaceous-Paleogene boundary. Perfect.

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I flew up there for the first time in early 2012, and spent several hours examining the collection. I still remember waiting for two hours for a bus in east Denver on a cold snowy night. It looked good, so I wrote a grant to the Geological Society of America and got some funding to come back a second time. That summer I spent a week at the museum, passing long days in the museum basement, examining every single fossil in the collection, then photographing many of the better-preserved one.

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Analyzing the images took the better part of the summer, and then the first manuscript appeared later in the year. It went through dozens of revisions, was joined to another project, then split up again. A bloodbath of Track-Changes in Microsoft Word.

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Then Dana Royer got in touch in 2013. He was interested in the same topic and had already measured some complementary things on the same fossils. We joined our datasets, re-wrote the paper, did a dozen more revisions. We submitted it to Science and made it through one round of review, but were rejected after some pushback on the dataset. We tried again at Nature, where we were rejected without review.

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Some more revision followed, and the paper was next submitted to PLoS Biology. We went through a few rounds of peer-review to address some questions of bias in the dataset, and finally got the paper accepted over the summer. The last few weeks have been filled with correcting proofs, final figures, coordinating popular press articles, and getting in touch with the media.

It’s wonderful to see this project finally finished. The final project is nothing like I had first imagined it, but I have learned so much about paleobiology and met some wonderful scientists along the way. And I’m glad to be done with the endless manuscript revisions!

Where the musk ox live

Winter is coming to Dovrefjell. The high peaks are already covered in snow, and the plants of the lowlands have changed to turn gold and red for autumn. On this landscape the musk ox (Ovibos moschatus) is also preparing for winter.

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For me the musk ox has always been a mythical sort of animal, a reclusive inhabitant of far-flung northern lands. On this fieldwork trip to Norway I have finally had a chance to see them. They are shaggy brown creatures, difficult to spot at a distance in the heaths and meadows of these glacially-carved mountains. Up close they look like they are wearing a rug, because their long hair sways around their legs as they walk. I can’t imagine what it is like for them in the depths of the snowy winter, but they are still engaged in the important business of eating the season’s plants and lichens.

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The musk ox has not been in Norway for more than a century. It was re-introduced from a Greenland population in the late 1940s and early 1950s, but perhaps deserves to call this area its home. The species once had a far wider range, reaching in the Pleistocene as far south as New Mexico. Since that time its range had dramatically contracted until this active human intervention. So why has the musk ox disappeared?

Two major hypotheses are climate change (we are no longer in an ice age) and human over-hunting (I have had it in sausage form, and can report it tastes very nice). Anyway, the discussion is very controversial, but a recent paper by Lorenzen et al. has suggested that climate change is a sufficient explanation for the disappearance of this species. There are many areas in today’s world where the animal might be able to live, but which it has not yet re-colonized – one justification for the last century’s reintroduction. Certainly these landscapes feel cold enough to me – while the ice age is long over, there are still glaciers and ice nearby.

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The existence of this animal here challenges me to think about the shadow of the past, and the roles of climate change and human action in shaping these landscapes. We live in the shadow of a very different earlier world.

BMC Ecology photo contest – landscape ecology

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I recently won a photography contest that I forgot I had entered. The image is of an endorheic lake basin at the Racetrack Playa in Death Valley, California. The contest is run through the academic journal, BMC Ecology. They say:


Section Editor Michel Baguette was equally impressed by the variety of ecosystems that the image depicts in this inhospitable part of the world, and the adaptations that species must exhibit in order to survive there:

“I am puzzled by the regular organization of the vegetation, typical of plants growing on a poor soil. I also like the juxtaposition of different ecosystems (desert, lake, mountains).”

It’s a beautiful and stark place. Here’s another image from the rock outcrop in the center of the basin. It is an endless vista of dry mud flats.

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You can read about all the other winning entries at the BMC Ecology website – there are some great images and stories!

Find the bird

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Last weekend I climbed Treasury Mountain, a massif of marine shales rising more than thirteen thousand feet above sea level. The endless slopes of loose scree are nearly bare – but not completely. Can you find the white-tailed ptarmigan (Lagopus leucura) in this photograph? The species lives on alpine tundra throughout the year, and is nearly invisible in its summer plumage.

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I have heard they are very tasty, but have never had the heart to find out.

Sharing with others

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This summer I’ve been living in the Rogers Boggs cabin at the Rocky Mountain Biological Laboratory. There are four bedrooms, but I haven’t had any cabinmates for the past few days. That doesn’t mean the place is empty. I’ve been sharing it with a few wild visitors.

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A family of mule deer (Odocoileus hemionus) has been hanging around the cabin. The mother of this fawn has realized that there no need to worry about predators with so many people around.

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There are also two adult yellow-bellied marmots (Marmota flaviventris) living in the townsite. This one likes to spend time on a rock next to my window.

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A few of the animals come closer. I found this mountain bluebird (Sialia currucoides) trapped in my wood stove this morning. I think it flew in the chimney and couldn’t get back out. I was very surprised to find it when I opened the stove door, but it immediately flew out, and then away.

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The chipmunks (Tamius miniumus) are the boldest. They come in through the window and sit on my couch eating flowers.

One even licked me a few days ago. I’ll miss this place when the field season is over.

Installing a research site

Every day of the last week I have climbed the same mountain, bringing up cargoes of steel nails, aluminum tags, meter tapes, string, sandwiches, water, and everything else needed to install a long-term plant census site. The hike in is three miles and climbs from 9000′ to 11700′, rising from subalpine meadows through spruce forest to an alpine scree field.

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Here’s what the installation process looks like. First, assembling equipment. I have fifty plots at the site, and each needs its corner points to be permanently marked. Each plant in each plot needs a permanent tag. This means lots of aluminum strips and metal nails hammered into the ground. A recycling shed provides much of the raw materials – then backpack-manageable quantities of metal are stowed in a pack and hiked up the mountain.

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At the site, I lay out meter tapes to designate baselines for census plots.

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Then metal nails go into the ground to demarcate each plot, and nylon string is laid to mark plot boundaries. The string will probably be destroyed overwinter from ultraviolet radiation or animal nibbling, but it can easily be replaced. I’m more worried about frost heaving destroying the corner makers.

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This is the final layout. Each plot is four square meters in area and includes a wide alley so I can walk through the site without trampling the delicate vegetation.

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Next up is the census. Each plant gets its own permanent tag, nailed into the ground near its rooting point. I am mapping, sizing, and tagging every individual in every plot. It means a lot of tags, and a lot of nails.

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I’m a little over half finished with the initial census. Some plots are bare, and some have more than a hundred individuals. Some are less than a half centimeter tall and others form a low mat covering almost a square meter. They are all beautiful.

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The field days are long and hard, but I don’t mind. If the site survives the winter, the science will be good. If it doesn’t, I will try again. In the meantime I am enjoying the scenery.

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(Thanks to Guadalupe Flores and Jordan Stark for their invaluable field assistance).

The perils and promise of selecting a research site

I’ve been trying to choose a research site in the Rockies for several months. It’s not easy. I want to study how alpine plant communities respond to disturbance, and I want to study it in the long term. This means I need to choose a research site that I won’t regret a decade from now. There are some constraints. It has to be on national forest land, but not on land designated as wilderness, because I plan to disturb and manipulate the ecosystem. It has to be within hiking or hitchhiking distance of the Rocky Mountain Biological Laboratory. And it needs alpine vegetation. There are only a few areas that meet these criteria. I spent the past few months with maps and GIS tools identifying some candidates, then took the past few days to see what they looked like up close. Here’s how it went down.

My first choice was the top of Virginia Basin (approximately 12200′ elevation). It’s the green valley in this photo, glowing in a stray sunbeam. It only takes a few hours to hike up from the research station, and not many tourists pass through the area.

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The trouble is that despite its high elevation, it is barely an alpine site. Willows and meadows extend nearly to the top of the saddle which forms the top of the basin.

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Most of the species are subalpine, and the density of plants was higher than I had wanted.

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The site also didn’t smell so great. Right next to my imagined research site was a recent elk kill, and the odors weren’t so attractive. I didn’t relish the idea of working there.

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My second choice was a peak across the valley from Virginia Basin, here seen from the same location as the previous photograph. This is Gothic Mountain, approximately 12500′ elevation. Most of its upper reaches are unambiguously in the alpine zone.

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I climbed it today, and was pleased with the plants I saw. Many of my favorite alpine species are there.

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The trouble is that the site is not easy to reach. It is a long three or four hour hike, with most of the upper sections being on loose talus or scree. There is significant exposure in a few places, and it takes almost an hour to get from the summit down to an area that would be safe from lightning. Any research sites would have to be on steep slopes. I decided the site was too risky to be worth using.

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My final option was Mount Baldy, elevation approximately 12800′. I dropped down a ridgeline from Gothic and checked it out.

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Finally, I got lucky. I found a ridgeline covered in shale that supported exactly the kind of alpine plant community I was looking for.

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The site doesn’t require any scrambling to reach, has beautiful views, isn’t visible from any trail, and includes many interesting species like this columbine.

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So I took its coordinates with a GPS, then hiked a few miles back down the valley to a well-deserved rest. Tomorrow I will start setting up the research site. The investment in time to find the right place has not been small, but when your commute to work looks like this, it all seems worth it!

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