Category Archives: Climate and weather

Cloud forest trees drink water down

By John Upton

One of the first things that every botany student learns is the simple process by which trees drink water. The water enters the roots from moisture in the soil and is sucked up the trunk through straw-like xylem to the leaves, where some evaporates. The combined effects of water tension and water cohesion inside the xylem and evaporation from the leaves keeps the water flowing against the force of gravity.

Researcher Greg Goldsmith simulates clouds in a laboratory to study foliar water uptake / Courtesy: Drew Fulton (Canopy in the Clouds)

A study of trees growing on Costa Rican mountains revealed that some high-altitude species can pull switcheroos on this widespread drinking system. When the soil is parched and their canopies are saturated by clouds, these trees use their leaves to suck water out of the air and then send the moisture back toward their trunks.

“Water is still moving along a gradient from areas with more water to areas with less water,” Greg Goldsmith, a tropical plant ecologist at the University of California, Berkeley and lead author of the study, which appeared this month in Ecology Letters, told me. “It’s just a different gradient.”

The clouds that nurture these cloud forests are evaporating as the planet warms, meaning the cloud-drinking strategy could doom those trees that rely upon it. That would be bad news for the birds and other wildlife that live in cloud forests, which are some of the world’s most striking and biodiverse ecosystems.

“The phenomenon of water from clouds entering leaves — foliar water uptake — indicates a much tighter relationship between clouds and cloud forest plants than previously known,” Goldsmith said.

Tropical mountain cloud forests are renowned for their high biodiversity but are threatened by climate change / Courtesy: Drew Fulton (Canopy in the Clouds)

Mushrooms make it rain in the Amazon

By John Upton

It’s not enough for mushrooms to simply produce spores. A little more than one-third of the world’s known fungal species, including mushrooms, puffballs and rusts, use a neat canon-ball trick that sends those spores sailing through the air toward newfound territory.

Clouds forming over the Napo River, Peru / Flickr: Photographer 23

This trick relies on the detonation of a fluid-filled sac to send so-called ballistospores airborne. It turns out that this neat trick not only helps fungus spread: Scientists recently discovered that these explosions may help keep the rain falling over the Amazon rainforest.

Water cannot condense into a rain drop unless it has something solid, a “seed,” to grow around, such as a speck of dust or a grain of pollen. Lawrence Berkeley National Laboratory researchers searching for the seeds that help clouds form in the Amazon think they have found what they were looking for.

They reported in Science late last month that potassium salts coalesced with organic material to form the seeds that create the Amazon’s clouds. Based in part on an abundance of ballistospores in the atmospheres, the researchers think the salts are squirted out when these spores are ejected from fungus during the night.

“The source of potassium could only have been natural forest organisms,” researcher Mary Gilles said in a press release published by the Lab on Monday.

Fungi are already known to play a critical role in breaking down old wood and leaves on the forest floor, recycling the nutrients and making them available for plants and animals; and now it appears that they also help to keep the Amazon wet and rainforesty. A pretty neat trick.

Mushrooms form ballistospores in their gills / Flickr: jo-h

Fungus-infected forests heat the planet

By John Upton

Forests suck carbon dioxide out of the air. They use solar energy to combine the carbon dioxide with water droplets to form sugars that fuel plant growth. During that chemical reaction, known as photosynthesis, waste oxygen is released back into the air.

So the effects of widespread deforestation by lumberjacks and bulldozers are relatively easy to understand. Less forests means more carbon dioxide, which heats the planet, and less oxygen for us to breathe.

New research has revealed that deforestation can take an even more sinister turn when it’s performed by a fungus. Fungal pathogens and fungus-like diseases are stealthily felling forests across the world. Forests at Big Sur disappeared in less than a decade after sudden oak death moved onto their turf. Cypress canker, native to California, is destroying trees across Europe. Dutch elm disease has forever changed the landscape on the East Coast.

Trees in Yale Myers Forest, CT, may look healthy, but many are rotting from the inside. Heart rot fungus breaks down the wood into substances that are consumed by bacteria, which further break the material down into methane. / Flickr: morrowlong

These symptoms of a sick planet do more than merely strip the earth of some of its greatest carbon sponges. Scientists have discovered that fungus disease can cause some of the wood in infected trees to break down not into carbon dioxide (CO2), but to break down anaerobically with the assistance of bacteria into methane (CH4), which is a far more potent and damaging greenhouse gas.

The university researchers measured methane levels in Connecticut woodlands infected by heart rot, a fungus disease, and reported in the journal Geophysical Research Letters that concentrations were so high in some places that it was flammable. Methane concentration in the air is normally less than 2 parts per million, but the researchers discovered levels in some trees that reached more than 160,000 parts per million. The average methane concentration in the forest was 15,000 parts per million.

The ailing forest was releasing enough methane to counteract the climate-cooling benefits of nearly one-fifth of the carbon dioxide it was absorbing, researchers calculated.

The researchers point out that their study covered just one forest, and one type of fungus disease. This particular disease is unique in that the trees often appear outwardly healthy while they rot away from the inside. But they warn that other fungal diseases that are laying waste to woodlands around the world could have similar effects.

“I think it’s fair to say that wood-rotting fungi in general could lead to this effect,” lead researcher Kristofer Covey, a Ph.D. candidate at Yale University’s School of Forestry, told me. “It’s hard to say if more aggressive fungal pathogens could lead to further emissions or not.”

Now is a terrible time to be losing forests. They are needed to help soak up all the carbon we’re pumping into the atmosphere when we burn fossil fuels. So this discovery comes as a double-whammy: Not only are we losing carbon-storing forests to fungus, but the fungi are taking carbon that had been stored in the trees and helping to turn it into a particularly potent greenhouse gas that further accelerates the rate of climate change.

The discovery offers one more reason to protect our forests from fungus diseases. Unfortunately, the problem has become so rampant that there is very little that we can do about it.

Climate change — megadroughts may fuel American monsoons

By John Upton

Vast regions of the Northern Hemisphere are currently being saturated by monsoons. In many warm climates, including parts of India, Australia and Africa, intense summertime storms satisfy much of nature’s and farmers’ yearly thirsts for water in weeks- to months-long blitzes.

A monsoon in Arizona / Flickr: Arizona Parrot

For most of the year, winds blow dry air from North American deserts over Arizona, New Mexico and Texas. But as these southwestern states heat up in July and August, the winds shift and begin flushing vast volumes of water into the region from the gulfs of California and Mexico, fostering the North American Monsoon.

These winds carry moisture overland, but they can’t make it fall from the sky. Clouds must be seeded with tiny particles before they will dissolve into falling rain, and a major seeder of clouds worldwide is dust. Dust can also induce rainfall by altering atmospheric temperatures.

Researchers at the Pacific Northwest National Laboratory in Washington recently used computer models to determine that heating effects of desert dust boost North American Monsoon rainfall by 40 percent. The dust’s seeding properties likely have further impact.

“Our next plan is to include this seeding effect in the model,” lead researcher Chun Zhao told me.

The discovery, published earlier this year in the journal Atmospheric Chemistry and Physics, suggests that monsoons could counterintuitively grow more intense if climate change produces a terrifying phenomenon that’s forecast to afflict the region: Megadrought.

“The deserts during the megadrought will expand outwards, which means creating more desert surface area,” Zhao said. “Our simulations imply that megadrought may emit more dust and increase the precipitation over the Texas and Arizona regions.”

Tortoises, toads and other creatures native to the southwest are well adapted to the wild weather extremes wrought by the region’s seasons. This new research suggests that these extremes are set to exacerbate as the climate changes. There’s a good chance that the rugged creatures of the desert will adapt better to these extremes than we do.

New Mexico during monsoon season / Flickr: Rohit Chhiber


Arctic trees could heat the planet

By John Upton

Trees and shrubs suck water up from the earth and into their leaves through super-thin straws in their trunks called xylem. When sunlight hits a leaf, it causes some of that water to evaporate, which in turn draws more water up from the roots through the xylem. This solar powered plumbing system keeps plants hydrated, allowing them to combine carbon dioxide from the atmosphere with water from the soil to create sugars essential for their growth. This process of photosynthesis also releases waste oxygen, which is breathed by animals and fungi.

Tundra swans migrate north to breed in Arctic tundras / Flickr: chiptape

But the system starts to fall apart when temperatures drop below freezing and the water turns to ice. Some plants produce antifreeze, and some have evolved to seize on short growing seasons when melted water is briefly available, but most simply cannot survive in the Arctic or Antarctic. Either the frozen water is too rigid to move through the xylem, or water freezes and thaws inside the plant, creating deadly bubbles that wreck its insides.

That’s the main reason that tundras are so barren — water in the soil is often locked up as ice that is useless to most plants, especially to tall trees.

As tundras heat up and ice wanes, forests are blooming in new places. Logically, one would expect these new and expanded forests to slow climate change by sucking up the atmosphere’s burgeoning carbon dioxide supplies and turning them back into oxygen.

But a new study published in the journal Climate Nature Change suggests that such logic might not prevail. That’s because the soils of tundras are home to vast reservoirs of carbon that could be stirred up and spewed back into the atmosphere by the return of the forests.

The researchers compared carbon levels in the heathlands of tundras in northern Sweden with those in nearby birch forests, which are replacing the heath as Earth heats up. They discovered that the amount of carbon stored in the low-lying heath vegetation and in the soil beneath it exceeded the amount stored in the forests’ plants and soil.

“Counterintuitively,” the researchers wrote in the paper, “increased plant growth in the European Arctic could result in C (carbon) being released to the atmosphere, accelerating climate change.”

To explain this counterintuitive result, the researchers found that frenetic plant activity in birch forests during the summer growing season triggered the decomposition of old organic matter in the soil, causing the ecosystem to leak more carbon than it captured.

Lead researcher Iain Hartley, a geography lecturer at the University of Exeter, warned that more studies are needed in a wide range of Arctic environments to determine whether expanding forests will indeed exacerbate global warming. (Unlike many other arctic tundra environments, those studied by the researchers lacked a permafrost.) But the findings point to that as a major risk.

“At the moment, the results are relevant to a particular change in vegetation,” Hartley told me in an email. “There is a lot of further study required to try and work out how carbon storage will change as forest colonises tundra in different areas of the Arctic.”