Fall Frost

Frost on a Hairy Leaf
Copyright © 2012 Andrea Liberatore

Frost on a Leaf
Copyright © 2012 Andrea Liberatore

Frost Damage on a Tomato
Copyright © 2012 Andrea Liberatore

Evergreens take hardiness
to the Extreme
Two-needle Pinion Pine
Copyright © 2009 Linda Kervin

Fall has descended in earnest across Utah. Leaves have flashed their colors and dropped to the ground. Juncos have replaced the flycatchers on my backyard’s best perches, and my garden has been cleaned up and tilled under. As I watched the fall weather affect plants in my vegetable garden, I began to wonder about the different reactions they had to the changing temperatures. My tomatoes and squash turned brown and wilted at the merest suggestion of cold temperatures. Other plants, like kale, carrots and onions are still bright and fresh, even after an early snowfall. What is it about some plants that allow them to withstand frost, while others succumb right away?

Frost occurs when the temperature of an object – in this case a plant leaf – falls below the dew point of the air. Moisture from the atmosphere collects on the surface of the leaf and freezes when temperatures drop below 32 degrees. Just seeing frost on a plant doesn’t necessarily mean it will die – it’s the internal tissue temperature that counts. Like humans, plants are made mostly of water – upwards of 80-90% in an herbaceous plant like lettuce. When temperatures drop, the water inside plant cells expands as it freezes, tearing cell walls and causing irreparable damage.

The amount of harm done to a plant depends on many different factors and is generally referred to as a plant’s hardiness. Species or individuals that are more compact will incur damage at a lower temperature than others due to their reduced surface area. Those growing close to the ground are more protected by their proximity to the warm earth. Plants with darker colored leaves such as the deep greens of spinach and chard may be hardier because their leaves absorb and retain heat better than lighter-colored leaves. Fuzzy or hairy leaves also fend off cold temperatures better than their smooth counterparts.

Perhaps the best defense of all is found in plants that protect themselves with natural antifreeze. When frost hits these plants, the relatively pure water in the space between leaf cells freezes first, which in turn draws more water out of the surrounding cells. The remaining cellular fluid contains a high concentration of sugars and other molecules, which reduces the fluid’s freezing point and protects the cell’s contents from ice.

Evergreens, of course, take hardiness to the extreme, utilizing a number of different tactics to remain alive and photosynthesizing throughout the winter. These tactics include compact leaf size, a thick leathery consistency, and a waxy coating that both insulates and prevents water from escaping into the dry winter air.

Frost damage to less hardy plants can be postponed by human interventions such as covering with blankets, but as the cold spells get longer and more frequent, damage is inevitable. Everything has its season, and now is the time to harvest the last of those hardy fall greens and tuck the garden in for the coming winter.

For the Stokes Nature Center and Wild About Utah, this is Andrea Liberatore.

Images: Courtesy &
            Copyright 2012 Andrea Liberatore
            Copyright 2009 Jim Cane
Text:     Andrea Liberatore,
            Stokes Nature Center in Logan Canyon.

Additional Reading:

Savonen, Carol (2012) Some plants make natural antifreeze to cope with winter’s wrath. Oregon State University Extension Service. Available online at: http://extension.oregonstate.edu/gardening/node/847

Farmer’s Almanac (2012) A Gardener’s Guide to Frost. Almanac Publishing Co. Available online at: http://www.farmersalmanac.com/home-garden/2008/09/22/a-gardeners-guide-to-frost/

Huber, Kathy (Feb 16, 2002) What Happens When a Plant Freezes. The Houston Chronicle. Available online at: http://www.chron.com/life/gardening/article/What-happens-when-a-plant-freezes-1635570.php

Utah’s Glacial History

Moraine with erratics, Photo Courtesy and Copyright Mark Larese-Casanova, Photographer
Moraine with erratics
Photo Courtesy & Copyright
Mark Larese-Casanova, Photographer

Little Cottonwood Canyon, Photo Courtesy and Copyright Mark Larese-Casanova, PhotographerLittle Cottonwood Canyon
Photo Courtesy & Copyright
Mark Larese-Casanova, Photographer

Hi, this is Mark Larese-Casanova from the Utah Master Naturalist Program at Utah State University Extension.

It is amazing to see just how much of an impact the large amount of snowfall from last winter still has on the annual cycle of nature. Of recent note, wildflower blooms in the mountains seem to be at least 2-3 weeks behind normal schedule. Hiking through snow in late July had me thinking about colder times when Utah’s mountains were covered with ice that flowed as glaciers.

The most recent period of glaciation in Utah occurred between 30,000 and 15,000 years ago when Utah’s climate was, on average, up to 30?F cooler. At times during this period, much of the western half of Utah was covered by Lake Bonneville, which contributed tremendous amounts of moisture as snow throughout Utah’s mountain ranges. As the snow accumulated at high elevations, its sheer weight caused it to recrystallize into ice. Once the masses of ice became heavy enough, gravity pulled them down slope, carving out characteristic U-shaped valleys.

At the top of the valleys, where the glaciers formed, we can often find large, bowl-shaped cirques. In the Wasatch Range, the Little Cottonwood Canyon glacier formed at the top, creating Albion Basin, and reached the mouth of the canyon where calved icebergs into Lake Bonneville. The Uinta Mountains contained such large glaciers that even many of the mountain peaks are rounded.

As temperatures warmed during the end of the last ice age, glaciers receded and left behind large piles of soil and rocks, known as moraines. Terminal moraines at the end of a glacier’s path, can act as natural dams to create lakes. Enormous boulders, known as glacial erratics, can often be found discarded along canyons.

While glaciers don’t currently exist in Utah, there are several permanent snowfields in shaded high mountain areas. So, if you’re feeling a little nostalgic and missing that extra long winter we had this year, you still a chance to hike up above 9,000 feet and cool your toes in the snow.

For Wild About Utah, I’m Mark Larese-Casanova.


Images: Courtesy & Copyright Mark Larese-Casanova
Text:     Mark Larese-Casanova, Utah Master Naturalist Program at Utah State University Extension.

Additional Reading:

Utah Geological Survey http://geology.utah.gov/surveynotes/gladasked/gladglaciers.htm

Parry, William T. 2005. A Hiking Guide to the Geology of the Wasatch and Uinta Mountains. University of Utah Press.

Stokes, William Lee. 1986. Geology of Utah. Utah Museum of Natural History.

The smell of rain

Electron micrograph showing
the filamentous structure of
Photo Courtesy:
Soil Science Society of America

Spring is my favorite season. I love watching our landscape turn from brown to green, the first butterfly sighting, and the rain. During a recent April shower, I stepped outside and inhaled that magical springtime scent – the smell of rain. Which got me thinking – what is that smell, anyway?

What seems like a simple question, begs a complicated answer. That smell, however, does have a name – petrichor – and there are many things that contribute to its scent. One of the biggest culprits may actually be soil bacteria – mostly from the genus actinomycetes – which grow in unfathomable concentrations in soils all around the world. These bacteria play an important role in decomposition and soil health. Periods of relative dryness trigger their reproductive cycle, causing the production of spores, which are considerably more drought-tolerant. When rain finally does fall, the spores are launched into the air, where they may eventually reach our nose. Scientists have identified the chemical compound responsible for the spore’s odor and have named it geosmin, which literally translates to ‘earth smell.’

Humans noses are particularly sensitive to geosmin, but we’re not the only ones. Camels, too, are sensitive to its smell and some scientists believe this helps them find oases in the desert. Our ability to detect this odor might be a throwback to our nomadic ancestors for whom finding water in a vast landscape was of utmost importance.

But the scent trail doesn’t end with geosmin. The chemical compound ozone may also be a part of petrichor especially after a thunderstorm, as ozone is produced by lightning. Another aroma is provided by chemicals called volatile oils which are produced by all plants, and which collect on the ground during dry periods. With rain, they evaporate into the air, contributing to the musty, earthy odor. Acidic rain has also been shown to create scents by reacting with chemicals on the ground such as spilled gasoline. And further complicating the matter is the fact that rain hitting the earth throws dust and other particles from countless sources into the air.

If all of these smells are around us all the time, why is it that they are distinctly associated with rain? The answer lies in the properties of odors and how they travel. Everything that produces a scent is releasing chemical compounds into the air. The ability to evaporate – or volatility – of these compounds increases with the heat and moisture levels of the air around them. The humid air that produces rain creates ideal conditions for conveying scents to our noses.

In the end, it’s not the rain itself that causes odor, but the interaction of water and a number of chemical and organic compounds. Test this theory at home by throwing a bucket of water on the lawn or a hot driveway to see if you can recreate the smell of rain. Likewise, smell a stick, leaf, or rock when it is dry, then wet it and see how the odor changes. For those seeking answers to the origins of the smell of rain, it’s often best to follow your nose.

Thank you to the Rocky Mountain Power Foundation for supporting the research and development of this topic.

For the Stokes Nature Center and Wild About Utah, this is Andrea Liberatore.

Images: Photo Courtesy Soil Science Society of America
Text:     Andrea Liberatore, Stokes Nature Center in Logan Canyon.
Special thanks to Joel Martin from the Utah Climate Center

Additional Reading:

National Public Radio (2007) The Sweet Smell of Rain. All Things Considered, August 11 2007. Interview of Dr. Charles Wysocki by Debbie Elliott. Transcript available online at: http://www.npr.org/templates/story/story.php?storyId=12716163

Gerritsen, V.B. (2003) The Earth’s Perfume. Protein Spotlight, Issue 35. Accessible online at: http://web.expasy.org/spotlight/back_issues/035/

Gerber, N.N, and Lechevalier, H. A., (1965) Geosmin, an Earthy-Smelling Substance Isolated from Actinomycetes. Applied Microbiology. 13,6. Accessible online at:

Live Worldwide Network for Lightning and Thunderstorms in Real Time, Blitzortung, http://en.blitzortung.org/live_lightning_maps.php?map=30

Snow Pack Dynamics

Snow Layers
Click image for more information
Forest Service Avalanche Center
Jim Conway, Graphic Artist
Depth Hoar
Click image for more information
and a deformation animation
Forest Service Avalanche Center
Jim Conway, Graphic Artist

Water is our planet’s magical molecule, changing states faster than a presidential candidate. Snowpacks vaporize, ice melts and re-freezes, lakes evaporate, and cooled water vapor condenses back as clouds, snowflakes and hoarfrost. The muffled silence of the winter snowpack belies its dramatic pace of transformation.

In his book entitled “Life in the Cold”, author Peter Marchand explains the dynamic nature of the snowpack. Within a few hours after a snow storm, destructive metamorphism sets to work on the newly fallen snow. The delicate crystalline structure of each snowflake is quickly degraded. The intricate flakes transform to amorphous icy grains. Wind, warmth and compression accelerate destructive metamorphism, leaving a firmer, denser snowpack. At the surface, not only does snow strongly reflect the weak warmth of winter sunlight, but on a clear night, it radiates energy, greatly cooling the surface.

Meanwhile, the soil beneath the snowpack is typically warmer than the overlying snow, which is why springs can run all winter long. Three feet underground, soil temperature is within a few degrees of that location’s average annual air temperature. Sandwiched between the warm soil and the cold air, the blanket of snow is a great thermal insulator; fresh snow is the equal of fiberglass insulation. As a result, soil warmth transforms snow deep under the snowpack into water vapor. This moisture spreads through air spaces in the snowpack, following the thermal gradient to the chilly snow surface. As the moisture vacates the lower layers, a brittle porous layer develops in the snowpack. Termed “depth hoar”, it is weak, icy and prone to collapse. When the heavy overlying snowpack shifts, the crumbly depth hoar can release an avalanche, a powerful reminder of snowpack transformations for any backcountry traveler.

Come spring, every particle of Utah’s snowpack undertakes its final transformation. Some sublimates to waft away on warm springtime winds. Most of it melts away to feed the groundwater, springs and streams that give us cool relief on a hot summer day and provide the precious water that every Utahn depends on.

This is Linda Kervin for Bridgerland Audubon Society.


Graphics: Courtesy Forest Service Avalanche Center, http://www.fsavalanche.org/
Text: Jim Cane, Bridgerland Audubon Society

Additional Reading:

Life in the Cold by Peter Marchand:http://www.upne.com/9619460.html

Forest Service National Avalanche Center, Avalanche Awareness Website: http://www.fsavalanche.org/

Depth Hoar: http://www.fsavalanche.org/encyclopedia/depth_hoar.htm

Utah Avalanche Center: http://utahavalanchecenter.org/