Wind and Sagebrush

Wind and Sagebrush: Mountain big sagebrush (Artemisia tridentata subsp. Vaseyana) in flower - Photo Courtesy and Copyright Dr. Leila Shultz
Mountain big sagebrush (Artemisia tridentata subsp. Vaseyana) in flower – Photo Courtesy and Copyright Dr. Leila Shultz

Wind and Sagebrush:Three-tip sage (Artemisia tripartite) with visible yellow flowers. - Photo Courtesy and Copyright Dr. Leila ShultzThree-tip sage (Artemisia tripartite) with visible yellow flowers. – Photo Courtesy and Copyright Dr. Leila Shultz

Hi, I’m Holly Strand of the Quinney College of Natural Resources at Utah State University.

By late summer, most of Utah’s flowering plants have fizzled out for the year—those that remain are looking pretty spent. But not true for the sagebrush. It’s show time for over 20 types of sagebrush of the Intermountain West.

Like grasses and conifers, sagebrush plants are pollinated by the wind. They have no need for the specialized traits designed to attract live pollinators. Instead, they have evolved other strategies to survive and multiply.

For instance, wind-pollinated plants don’t need showy, colorful petals to attract insects or birds. The wind is going to do its job anyway regardless of visual cues. Thus sagebrush flowers are very small and nondescript. In fact, when passing by flowering sagebrush you might not even notice that it’s in bloom. Look for long spikes with clusters of tiny flower heads. The pale yellow flowers are concealed by petal-like bracts, which are the very same color as the rest of the plant.

While the flowers of sagebrush lack in beauty, they make up in quantity. A single flowering stem of the most common sagebrush—known simply as big sagebrush–can hold hundreds of flower heads that produce a massive amount of pollen. Most wind-blown pollen grains won’t end up anywhere near the female part of another plant. So to make up for this risky method of fertilization, individual plants must produce greater volumes of pollen. In contrast, plants with live pollinators get door to door service during fertilization. Far less pollen is needed to get the same job done.

Scent is another way for plants to attract live pollinators. Species pollinated by bees and flies have sweet scents, whereas those pollinated by beetles have strong musty, spicy, or fruity odors. However, the iconic western scent of the sagebrush has absolutely nothing to do with pollination. Instead, the pungent aroma of the sagebrush is a by-product of certain chemicals produced in the leaves. These chemicals evolved to repel animals and to reduce the odds of being eaten or grazed.

The chemicals—bitter terpenes, camphors and other secondary compounds–—peak in early spring. But as the late-summer flowering period approaches, the chemicals start to break down. By winter, browsers like deer and elk can nibble on the protein-rich seed heads without getting a nasty aftertaste.

Thanks to botanist Leila Shultz for sharing her knowledge of sagebrush. For a link to the online version of Leila’s book Pocket Guide to Sagebrush, go to www.wildaboututah.org
If you’d like a hard copy of this Pocket Guide, send an email to wildaboututah@gmail.com We have 5 copies to give away to listeners from across the state.

For Wild About Utah and the Quinney College of Natural Resources, I’m Holly Strand.

NOTE: The copies are gone. You can view the book as a .pdf here or check here for the next printing from http://www.sagestep.org/pubs/brushguide.html.

Credits:

Photo Courtesy & Copyright 2007 Dr. Leila Shultz
Text: Holly Strand, Quinney College of Natural Resources at Utah State University

Sources & Additional Reading:

Dudareva, Natalia. 2005. Why do flowers have scents? Scientific American April 18. http://www.scientificamerican.com/article/why-do-flowers-have-scent/

Shultz, Leila. 2012. Pocket Guide to Sagebrush. PRBO Conservation Science. http://plants.usda.gov/java/
As pdf: http://www.sagestep.org/pubs/pubs/sagebrush_pock_guide.pdf

Shultz, L. M. 2006. The Genus Artemisia (Asteraceae: Anthemideae). In The Flora of North America north of Mexico, vol. 19: Asterales, pp. 503–534. Flora of North America Editorial Committee, eds. Oxford University Press. New York and Oxford.

USDA, NRCS. 2012. The PLANTS Database, National Plant Data Team, United States Department of Agriculture (USDA), Natural Resource Conservation Service (NRCS):
http://www.plants.usda.gov

VanBuren, R., J. C. Cooper, L. M. Shultz and K. T. Harper. 2011. Woody Plants of Utah. Utah State University Press & Univ. Colorado. 513 pp.

Virga

Click to view information from the : Virga courtesy and Copyright 2010 Kevin Connors
Virga
Courtesy & Copyright 2010 Kevin Connors

Virga

August is the perfect month to observe virga in Utah, for it is the monsoon season here. Moist subtropical air is flowing northward from the Pacific Ocean and the Gulf of California. When this warm, moist air is driven upward by convection and mountains, towering thunder heads result.

Below the bellies of these dark clouds you sometimes see grayish windswept curtains or streamers that do not reach the ground. Meteorologists call them “virga”, virga spelled with an “i”, from the Latin for “streak”. The word “virga” is absent from the prose of Mark Twain and the exploratory reports of John Wesley Powell because the word “virga” was only coined 70 years ago.

Click to view information from the : Virga in Cache Valley courtesy and Copyright 2010 Jim Cane
Virga in Cache Valley
Courtesy & Copyright 2010 Jim Cane

These picturesque virga are descending precipitation. One might guess it to be rain, but most meteorologists agree that it is frozen precipitation which is melting and evaporating as it drops through our dry Utah air. Like a home swamp cooler, evaporation in virga causes cooling which leads to the chilly downdrafts that accompany our summer thunderstorms. In the humid tropics, rains can be lukewarm, but our summer cloudbursts are goose-bump cold, owing to the same evaporation which yields virga.

Virga are a tease for parched summer landscapes, a herald of wild fires ignited by dry lightning, and a generator of dust storms as downdrafts scour dusty salt flats. But mostly, the curtains of precipitation that are virga are a fleetingly beautiful element of our western summer skies, well worth a pause and a picture, especially if you are lucky enough to see one accompanied by a rainbow or a fiery sunset.

Click to view a larger picture of Virga in Tucson, AZ Courtesy & Copyright 2010 Julio Betancourt, Photographer
Virga in Tucson, AZ
Courtesy & Copyright 2010 Julio Betancourt

This is Linda Kervin for Bridgerland Audubon Society.
Credits:

Photos: Courtesy & Copyright 2010 Jim Cane
Courtesy & Copyright 2010 Julio Betancourt
Text: Jim Cane, Bridgerland Audubon Society

Additional Reading:

Jetstream, an online school for weather, NWS NOAA Southern Regional Headquarters, Ft worth, TX,
http://www.srh.noaa.gov/jetstream/index.htm

Click to view a larger picture of Virga in Tucson, AZ Courtesy & Copyright 2010 Julio Betancourt, Photographer
Virga in Tucson, AZ
Courtesy & Copyright 2010 Julio Betancourt

Fire weather : a guide for application of meteorological information to forest fire control operations, Mark J. Schroeder and Charles C. Buck, USDA Forest Service, http://training.nwcg.gov/pre-courses/S390/FireWeatherHandbook
/pms_425_Fire_Wx_ch_01.pdf

The Book of clouds, John A. Day, Sterling, 2005, http://www.amazon.com/Book-Clouds-John-Day/dp/1402728131

Wind, Hold on to Your Hat!

Graphical Forecasts – Central Rockies
NOAA National Weather Service
Western Regional Headquarters

Hi I’m Holly Strand.

On a recent camping trip on Utah’s Colorado Plateau, my brother and I were buffeted by strong sand-blasting winds for two days straight. Setting up camp was nearly impossible. Strong gusts ripped the tent away from us. Catching only the guylines, we flew the big green tent like a kite through the sagebrush. Eventually we pulled it down and got stakes in the ground. Unable to make a fire, we ate a cold dinner and tried to sleep –until the tent collapsed under the persistent onslaught of meteorological Furies. The next day, the sand-infused wind whipped us painfully as we descended into Horseshoe Canyon. Dust devils pursued us along the canyon floor.

Arriving home I read up on the cause of our discomfort. In simplest terms wind is caused by air moving from high to low pressure. The steeper the air pressure gradient—that is –the change in air pressure per unit distance–the stronger the resulting wind speed. Differences in air pressure are often caused by localized warming of air temperature. The warm air rises creating a spot of relatively low pressure ; then cooler air from a high pressure region rushes in to replace it.

Wind tends to blow much more forcefully near a frontal boundary. And our camp was located very close to the low pressure center of a stationary front. Although the wind was a nuisance, it was probably only blowing around 35 miles an hour. Meanwhile the record in Utah is 124 miles an hour –a wind gust measured at 11000 feet Snowbird. The strongest wind gust here in Logan was 94 miles an hour. Compare this to the highest wind on record anywhere—a gust measuring 253 miles per hour on Australia’s Barrow Island during a tropical cyclone. The record in the United States is 231 miles per hour on top of Mt. Washington in New Hampshire. Higher wind speeds than these may occur in tornadoes, but anemometers tend to malfunction at extreme speeds .

Luckily, we don’t have to worry much about tornadoes. Utah ranks very low in terms of tornado frequency. We average 2-33 a year with most of them occurring May through August. Utah tornadoes tend to be small and not last very long. Whirlwinds or dust devils are much more common. About 90% of them occur in the West Desert where there is plenty of loose, dry dust and sand to swirl around in the air.

Thanks to Marty Booth of the Utah Climate Center for help in developing this Wild About Utah episode.

For Wild About Utah, I’m Holly Strand.

Credits:

Photos: Courtesy US NOAA
Text: Holly Strand

Sources & Additional Reading:

National Weather Service (NOAA) “Dust Devils” http://www.wrh.noaa.gov/fgz/science/dustdvl.php?wfo=fgz [Accessed June 15, 2011]

National Weather Service (NOAA) Jetstream Online School for Weather. “Origin of Wind” http://www.srh.noaa.gov/srh/jetstream/synoptic/wind.htm [Accessed June 15, 2011]

National Weather Service (NOAA) Daily weather maps http://www.hpc.ncep.noaa.gov/dailywxmap/ [Accessed June 15, 2011]

Utah Climate Center http://climate.usurf.usu.edu/

Pope, Dan and Clayton Brough (eds.) Utah’s Weather and Climate. 1996. Salt Lake City: Publisher’s Press. http://www.amazon.com/Utah-Weather-Climate-D-Pope/dp/1567131743

http://www.photolib.noaa.gov

Virga: Teasing Rain

Virga courtesy and Copyright 2010 Kevin Connors a.k.a Virga teasing rain
Virga
Courtesy & Copyright 2010 Kevin Connors

Virga: Teasing Rain

August is the perfect month to observe virga in Utah, for it is the monsoon season here. Moist subtropical air is flowing northward from the Pacific Ocean and the Gulf of California. When this warm, moist air is driven upward by convection and mountains, towering thunder heads result.

Below the bellies of these dark clouds you sometimes see grayish windswept curtains or streamers that do not reach the ground. Meteorologists call them “virga”, virga spelled with an “i”, from the Latin for “streak”. The word “virga” is absent from the prose of Mark Twain and the exploratory reports of John Wesley Powell because the word “virga” was only coined 70 years ago.

Virga in Cache Valley courtesy and Copyright 2010 Jim Cane
Virga in Cache Valley
Courtesy & Copyright 2010 Jim Cane

Virga: Descending Precipitation & Downdrafts

These picturesque virga are descending precipitation. One might guess it to be rain, but most meteorologists agree that it is frozen precipitation which is melting and evaporating as it drops through our dry Utah air. Like a home swamp cooler, evaporation in virga causes cooling which leads to the chilly downdrafts that accompany our summer thunderstorms. In the humid tropics, rains can be lukewarm, but our summer cloudbursts are goose-bump cold, owing to the same evaporation which yields virga.

Virga are a tease for parched summer landscapes, a herald of wild fires ignited by dry lightning, and a generator of dust storms as downdrafts scour dusty salt flats. But mostly, the curtains of precipitation that are virga are a fleetingly beautiful element of our western summer skies, well worth a pause and a picture, especially if you are lucky enough to see one accompanied by a rainbow or a fiery sunset.

Virga in Tucson, AZ Courtesy and Copyright 2010 Julio Betancourt, Photographer
Virga in Tucson, AZ
Courtesy & Copyright 2010 Julio Betancourt

This is Linda Kervin for Bridgerland Audubon Society.
Credits:

Photos: Courtesy & Copyright 2010 Jim Cane
Courtesy & Copyright 2010 Julio Betancourt
Text: Jim Cane, Bridgerland Audubon Society

Additional Reading:

Jetstream, an online school for weather, NWS NOAA Southern Regional Headquarters, Ft worth, TX,
http://www.srh.noaa.gov/jetstream/index.htm

Virga in Tucson, AZ Courtesy and Copyright 2010 Julio Betancourt, Photographer
Virga in Tucson, AZ
Courtesy & Copyright 2010 Julio Betancourt

Fire weather : a guide for application of meteorological information to forest fire control operations, Mark J. Schroeder and Charles C. Buck, USDA Forest Service, http://training.nwcg.gov/pre-courses/S390/FireWeatherHandbook
/pms_425_Fire_Wx_ch_01.pdf

The Book of clouds, John A. Day, Sterling, 2005, http://www.amazon.com/Book-Clouds-John-Day/dp/1402728131