Cold-Resistant Trees

9 May, 2023

The Appalachians are an old, worn-down mountain chain that runs down the eastern side of North America. The ecology of the Appalachians is fascinating. For example:

Ecologists have tested many species of Appalachian trees to see how much cold they can survive. As you’d expect, for many trees the killing temperature is just a bit colder than the lowest temperatures at the northern end of their range. That makes sense: presumably they’ve spread as far north—and as far up the mountains—as they can.

But some other trees can survive temperatures much lower than that! For example white and black spruce, aspen and balsam poplar can survive temperatures of -60° C, which is -80° F. Why is that?

One guess is that this extra hardiness is left over from the last glacial cycle, which peaked 20,000 years ago—or even previous glacial cycles. It got a lot colder then!

So, maybe these trees are native to the northern Appalachians—while others, even those occupying the same regions, have only spread there since it warmed up around 10,000 years ago. Ancient pollen shows that trees have been moving north and south with every glacial cycle.

I learned about this issue here:

• Scott Weidensaul, Mountains of the Heart: a Natural History of the Appalachians, Fulcrum Publishing, 2016.

I bought this book before a drive through the Appalachians.

To add some extra complexity to the story, David C. writes:

I’d love to understand more and reconcile that with the fact that none of these trees do well above around 4500 ft in the northern Appalachians (New Hampshire).

and Brian Hawthorne writes:

Don’t forget that all the tree species had to move back into the areas that were under the last glacier.

Serpentine Barrens

19 February, 2021


This is the Soldiers Delight Natural Environmental Area, a nature reserve in Maryland. The early colonial records of Maryland describe the area as a hunting ground for Native Americans. In 1693, rangers in the King’s service from a nearby garrison patrolled this area and named it Soldiers Delight, for some unknown reason.

It may not look like much, but that’s exactly the point! In this otherwise lush land, why does it look like nothing but grass and a few scattered trees are growing here?

It’s because this area is a serpentine barrens. Serpentine is a kind of rock: actually a class of closely related minerals which get their name from their smooth or scaly green appearance.

Soils formed from serpentine are toxic to many plants because they have lots of nickel, chromium, and cobalt! Plants are also discouraged by how these soils have little potassium and phosphorus, not much calcium, and too much magnesium. Serpentine, you see, is made of magnesium, silicon, iron, hydrogen and oxygen.

As a result, the plants that actually do well in serpentine barrens are very specialized: some small beautiful flowers, for example. Indeed, there are nature reserves devoted to protecting these! One of the most dramatic is the Tablelands of Gros Morne National Park in Newfoundland:

Scott Weidensaul writes this about the Tablelands:

These are hardly garden spots, and virtually no animals live here except for birds and the odd caribou passing through. Yet some plants manage to eke out a living. Balsam ragwort, a relative of the cat’s-paw ragwort of the shale barrens, has managed to cope with the toxins and can tolerate up to 12 percent of its dry weight in magnesium—a concentration that would level most flowers. Even the common pitcher-plant, a species normally associated with bogs, has a niche in this near-desert, growing along the edges of spring seeps where subsurface water brings up a little calcium. By supplementing soil nourishment with a diet of insects trapped in its upright tubes, the pitcher-plant is able to augment the Tablelands’ miserly offerings. Several other carnivorous plants, including sundews and butterwort, work the same trick on their environment.

In North America, serpentine barrens can be found in the Appalachian Mountains—Gros Morne is at the northern end of these, and further south are the Soldiers Delight Natural Environmental Area in Maryland, and the State Line Serpentine Barrens on the border of Maryland and Pennsylvania.

There are also serpentine barrens in the coastal ranges of California, Oregon, and Washington. Here are some well-adapted flowers in the Klamath-Siskiyou Mountains on the border of California and Oregon:

I first thought about serpentine when the Azimuth Project was exploring ways of sucking carbon dioxide from the air. If you grind up serpentine and get it wet, it will absorb carbon dioxide! A kilogram of serpentine can dispose about two-thirds of a kilogram of carbon dioxide. So, people have suggested this as a way to fight global warming.

Unfortunately we’re putting out over 37 gigatonnes of carbon dioxide per year. To absorb all of this we’d need to grind up about 55 gigatonnes of serpentine every year, spread it around, and get it wet. There’s plenty of serpentine available, but this is over ten times the amount of worldwide cement production, so it would take a lot of work. Then there’s the question of where to put all the ground-up rock.

And now I’ve learned that serpentine poses serious challenges to the growth of plant life! It doesn’t much matter, given that nobody seems eager to fight global warming by grinding up huge amounts of this rock. But it’s interesting.


The top picture of the Soldiers Delight Natural Environmental Area was taken by someone named Veggies. The picture of serpentine was apparently taken by Kluka. The Tablelands were photographed by Tango7174. All these are on Wikicommons. The quote comes from this wonderful book:

• Scott Weidensaul, Mountains of the Heart: A Natural History of the Appalachians, Fulcrum Publishing, 2016.

The picture of flowers in the Klamath-Siskiyous was taken by Susan Erwin and appears along with many other interesting things here:

Klamath-Siskiyou serpentines, U. S. Forest Service.

A quote:

It is crystal clear when you have entered the serpentine realm. There is no mistaking it, as the vegetation shift is sharp and dramatic. Full-canopied forests become sparse woodlands or barrens sometimes in a matter of a few feet. Dwarfed trees, low-lying shrubs, grassy patches, and rock characterize the dry, serpentine uplands. Carnivorous wetlands, meadows, and Port-Orford-cedar dominated riparian areas express the water that finds its way to the surface through fractured and faulted bedrock.

For more on serpentine, serpentinization, and serpentine barrens, try this blog article:

Serpentine, Hiker’s Notebook.

It’s enjoyable despite its misuse of the word ‘Weltanschauung’.

Diary, 2003-2020

8 August, 2020

I keep putting off organizing my written material, but with coronavirus I’m feeling more mortal than usual, so I’d like get this out into the world now:

• John Baez, Diary, 2003–2020.

Go ahead and grab a copy!

It’s got all my best tweets and Google+ posts, mainly explaining math and physics, but also my travel notes and other things… starting in 2003 with my ruminations on economics and ecology. It’s too big to read all at once, but I think you can dip into it more or less anywhere and pull out something fun.

It goes up to July 2020. It’s 2184 pages long.

I fixed a few problems like missing pictures, but there are probably more. If you let me know about them, I’ll fix them (if it’s easy).

Salar de Uyuni

22 January, 2016


I just learned about the Salar de Uyuni: the world’s largest salt flat, located in southwest Bolivia. It’s about 10,000 square kilometers in area!

It’s high up, near the crest of the Andes, 3,600 meters above sea level. Once there were permanent lakes here, but no more. This area is a transition zone: the eastern part gets rain in the summer, but clouds never make it past the western part, near the border with Chile. Further west comes the the famously dry Atacama Desert.

The Salar de Uyuni is high, but still it lives up to the name ‘salt flat’: its salt crust varies in height by less than one meter over the entire area. It’s so flat that people use it for testing equipment that measures altitudes.

Why is it so flat? Because the dry crust covers a huge pool of brine that is still liquid! This brine is a saturated solution of sodium chloride, lithium chloride and magnesium chloride in water. As a result, Salar de Uyuni contains over half of the world’s lithium reserves!

In the rainy season, the Salazar de Uyuni looks very different:

And when it’s wet, three different types of flamingos visit the Salar: the Chilean flamingo, the rare Andean flamingo, and the closely related but even rarer James flamingo, which for a while was thought to be extinct!

Flamingos eat algae that grow in the brine. This is why they’re pink! Newly hatched flamingos are gray or white. Their feathers become pink only thanks to carotene which they get from algae—or from crustaceans that in turn eat algae. Animals are not able to synthesize these molecules!

Carotene comes in different forms, but here is one of the most
common: β-carotene. I like it because it’s perfectly symmetrical. It has a long chain of carbons with alternating single and double bonds. Electrons vibrating along this chain absorb blue light. So carotene has the opposite color: orange!

It’s not just flamingos that need carotene or related compounds. Humans need a chemical called retinal in order to see:

It looks roughly like half a carotene molecule—and like
carotene, it’s good at absorbing light. Attached to a larger protein molecule called an opsin, retinal acts like a kind of antenna, catching particles of light. Humans can’t produce retinal without help from the foods we eat. Any chemical we can use to produce retinal is called ‘vitamin A’. So vitamin A isn’t one specific chemical: it’s a group. But beta carotene counts as a form of vitamin A.

Speaking of humans: people sometimes come to have fun in the Salar de Uyuni. There are hotels made of salt! And thanks to the featureless expanse of salt, you can take some amusing trick pictures:

Click on the pictures to find out more about them. For more on the Salar de Uyuni, try:

Salar de Uyuni, Wikipedia.

Puzzle: What kinds of algae, and other organisms, live in the brine of the Salar de Uyuni when it rains? How do they survive when it dries out? There must be some very interesting adaptations going on.

Khumbu Icefall and the Valley of Silence

27 April, 2012

National Geographic has a blog written by people who are now climbing Mount Everest. Here’s Sam Elias training in the Khumbu Icefall near the Everest Base Camp:

As usual, it’s the Sherpas who impress me most:

Years of experience, or maybe the mountain itself, had told the Sherpas that passing through the Ballroom on this day was not a good idea, something would happen. “Big ice will fall.” Panuru’s words echoed in my head. “How do they know?” I wondered.

I was sitting in my tent fitting my crampons onto my boots when I heard it. I know the sound now. Before, when the loud rumbling began I instinctively thought of a giant semi barreling down a highway. But there are no vehicles here.


Every year, the route through the Khumbu is set by the “ice doctors,” a small team of Sherpas who take mortal risks to navigate the safest passage through the Icefall, putting up ropes in the steep sections and stretching ladders across the abyss-like crevasses.

Crossing the ladders is an adventure for some. For the Sherpas, setting them up is a job.

Khumbu Icefall

Suppose you take the southeast route to Mount Everest, on the Nepal side. When you climb up from Base Camp, the first thing you’ll hit is the Khumbu Icefall, a crazy and ever-changing mass of ice at the bottom of the Khumbu Glacier:

As the National Geographic blog put it:

Like a gargantuan bulldozer, the Khumbu glacier plows down off the Lhotse Face between Mounts Everest and Nuptse. Dropping over a cliff just above Base Camp, this mile-wide river of ice shatters into building-size blocks and steeple-size spires called seracs. It’s riven with cracks called crevasses that can be hundreds of feet deep. To reach our expedition’s two goals — the Southeast Ridge and the West Ridge, which both begin atop the Khumbu glacier in the Western Cwm — we must travel up through this labyrinth of raging ice.

To cross the crevasses, you use bridges that the Sherpas have made by lashing ladders together with rope. Here’s Nima Dorje Tamang crossing one. The clouds are like a ceiling… but there’s no floor:

The picture above is again from National Geographic.

The glacier advances about a meter each day around here. Most climbers try to cross before the sun rises, when the cold keeps things frozen. As the intense sunlight warms things, the icefall becomes more dangerous. Blocks of ice tumble down the glacier from time to time, ranging in size from cars to houses… and sometimes entire large towers of ice collapse. They say bodies of people who die in here sometimes show up at the base of the icefall years later.

Here’s Kenton Cool talking about the Khumbu Icefall. “It can implode underneath you, it can drop on you above – or god forbid, you can fall into its inner depths, never to be seen again.”

And this is photographer Leo Dickinson speaking about the dangers of this place. Look at the fellow poking at snow with a pick around 0:58, revealing that it would be deadly to step there!


The Valley of Silence

Suppose you succeed in crossing the Khumbu Icefall—including the last crevasse, shown in this photo by Olaf Rieck. Then you have reached the Western Cwm, also known as the Valley of Silence:

In the middle background is Lhotse. At far right you see a bit of Nuptse. And at left there’s Sāgārmatha, also known in Tibetan as Chomolungma… or in English, Mount Everest.

‘Cwm’, pronounced ‘coom’, is Welsh for a bowl shaped valley, also known as a ‘cirque’. This one is a 4-kilometer-long valley carved out by the Khumbu Glacier, which starts at the base of Lhotse. It’s the easiest way to approach Everest from the southeast. However, it’s cut by massive crevasses that bar entrance to the upper part: here you must cross to the far right, over to the base of Nuptse, and through a narrow passageway known as the Nuptse corner.

It’s called the Valley of Silence because it’s often windless and deathly quiet. On days like that, the surrounding snow-covered slopes surrounding are so bright that the valley becomes a kind of solar oven, with temperatures soaring to 35 °C (95 °F) despite an elevation of 6000 to 6800 metres (19,600-22,300 feet). But when sun turns to shade, the temperature can plummet to below freezing in minutes!

The photo above was taken by the Moving Mountains Trust. See the people? You may need to click for a bigger version! For more, see:

• Alan Arnette, Life in the Western Cwm.

Want to go further? When you’ve reached Base Camp II near the top of the Western Cwm, you still have 2300 meters to climb… and now it gets steep! I’m sorry, I’m quitting here and heading back down—it’s my bedtime. Good luck!

For more

Cut your carbon footprint. Travel virtually:

Mount Everest summit—interactive 360 degree panorama.

Reality Maps viewer for Everest.

Michael Murphy writes:

I had become intrigued by the story of Marco Siffredi, a French snowboarder who was the first to successfully descend Everest on a snowboard via the Norton Couloir. His second attempt to descend a far more serious route, the Hornbein Couloir ended in his demise.

[….] I used Reality Maps to trace his route. It is no wonder he did not make it.