Wind Chill

Wind Chill

By:  Steve Roark

TN Dept. Agriculture, Forestry Division

The humorist Carl Hurley once said that he wished they had never invented the wind-chill factor given in weather reports.  “Use to when they said it was 29 degrees it felt like 29 degrees”, he commented.   “But now they say it’s 29 degrees with a wind chill of 20 and you freeze to death!”

The wind-chill temperature was adopted by the National Weather Service to reflect the cooling effect of wind on cold days.  In theory, the wind-chill temperature is the temperature in still air that would cause the same rate of heat loss from exposed skin as that brought about by prevailing winds.  For example, a 10 mile-per-hour wind on a 20-degree day has the same chilling effect as a 3-degree day with no wind.  Hence the wind chill temperature is 3 degrees.

Cold man.jpg

The original formula used to determine wind-chill temperature was developed from research done in the 1940s.  To determine rates of heat loss, scientists sealed a thermometer in a plastic bottle of water and timed how long it took the water to freeze under a variety of wind speeds and air temperatures.  The freezing times were later converted into a chart of temperature equivalents. But the whole point of wind chill is how it impacts your comfort, and the thermal properties of a plastic bottle do not resemble those of human flesh.

To resolve this, a scientist named Osczevski literally stuck his head in a refrigerated box with sensors on his cheeks until his skin temperature came close to the freezing point.  His reasoning was that any attempt to revamp wind-chill should start with the face, which is the most exposed part of the body, and therefore most vulnerable to frostbite.    In 2000 Osczeyski created a mathematical model of heat transfer in the human face and tested it with volunteers who braved fierce strong winds in a wind tunnel.

The result was a gentler wind-chill prediction.  A 20-degree day with a 10 mph wind now has a wind-chill rating of 9 degrees instead of 3.  It turns out that there is not much difference between the old and new formulas at low wind speeds, but at higher speeds the new formula is quite a bit warmer.  The Weather Service adopted the new calculation method, and so less teeth chattering temperatures are given.

For the record, the normal temperature of the skin is 94 degrees F.  Exposed skin becomes uncomfortable when it cools to around 59 degrees, and painful at 50 degrees.  Below that skin temperature starts to feel numb, and under certain conditions, frostbite can occur within minutes.  Skin freezes at 23 degrees.




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The Shape of Snow

The Shape of Snow

By: Steve Roark,

TN Dept. Agriculture, Forestry Division

Snow is a weather event that is either loved or loathed, with not much middle ground. There is no denying however that a gently falling snow is a beautiful, serene sight.  As with most things in nature, snow is a more complex phenomenon than it appears.

Snow starts high in the frozen tops of large thick clouds, where minute ice crystals form from water vapor in temperatures below minus 40 degrees. These crystals gradually grow and cling together until they become heavy enough to fall as snowflakes.  If the temperature stays below freezing all the way, the snowflakes reach the ground intact, growing larger on their way down.


Snow crystals come in a variety of forms, including needles, hexagons, columns, prisms, and six-pointed stars.  The shape depends on the air temperature in which they fall.  The star-shaped crystal what everyone mentally pictures as a “snowflake”, and is technically called a “dendritic crystal”. They form in fairly moist air at temperatures around 5 degrees F. The old saying that no two snowflakes are alike is technically true.  The growth of crystals involves a complicated mix of evaporation, condensation, sublimation (the direct conversion of water vapor to ice), and deposition around a tiny hexagonal ice nucleus.

The shape of snow readily demonstrates its origin as water.   All snow crystals are six-sided, a shape derived directly from the triangular template of the water molecule.  The central oxygen and its two bound hydrogen atoms form a bulbous triangle, the basic unit of all shapes of frozen water.

Dry powdery snow falls when temperatures are so low that the falling crystals do not melt and refreeze when they touch each other and so do not form large soft flakes.  Dry snow is very light and ideal for skiing.  Wet snow is composed of crystals that have melted and refrozen together to form fluffy, soft flakes.  It sticks together and makes good snowballs and snowmen.  Around 36 inches of dry snow and 7 inches of wet snow have a water content equal to 1 inch of rain.




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Rudolf the Red Nosed Rein…..dear?

Rudolf the Red Nosed Rein…..dear?

By Steve Roark

TN Dept. Agriculture, Forestry Division

By now you have no doubt heard the obligatory Rudolf the Red Nosed Reindeer song ten times on the radio or department store sound systems.  The assumption is that because Rudolf is depicted with antlers that he’s a he, and that may be correct. But if you will allow me some natural history holiday fun, it’s possible that Rudolf is a her.


Okay, let’s talk antlers.  They are of course those spiky things growing out of the heads of members of the deer family, whom science guys call Cerviadae.  The family includes deer, elk, moose, and our topic the reindeer, also known as caribou in North America. Antlers are extensions of the animal’s skull, and made of true bone. They are grown by the males each year and then shed off, and their function is sexual. Their size is attractive to females, and they are used as weapons to fight off other male suitors.

Reindeer however, are the exception, with both the male and female growing antlers.  The likely reason is that the antlers are not only used in the procreation process, but also used to clear away snow to reach vegetation to eat.  Females also use them fend off threats and defend feeding area, which in snow country is critical.

So now we come to it. Once the reindeer cows are pregnant, the bull’s testosterone level drops,  triggering the changes that make the antlers fall off, which normally takes place in November or early December. This suggests that reindeer with antlers on Christmas Eve are female.  But it turns out that young adolescent males keep theirs a little longer, so it’s indeed possible that Rudolf could be a young male, as the song and cartoon suggests. But the older reindeer on Santa’s sleigh pulling team could very well be females…. and pregnant.  Just saying.


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Holiday Crafts from the Forest

Holiday Crafts From The Forest

By: Steve Roark

TN Dept. Agriculture, Division of ForestryPine cone decorations

Many celebrate the Christmas season by decorating our homes.  Local woodlands contain many trees, shrubs and plants that can be used to create decorations that look and smell “back to nature”.  With all the pressures of shopping and socializing that comes with the season, it’s nice to take a quiet walk in the woods, gather some greenery, and create something with your own hands.

What follows is a list of trees and plants that can be used in making holiday crafts. Some are easily found, while others may take some looking.  But that’s part of the fun.  Wherever you look though, please be courteous and get permission from the landowner.

Pines:  All of our pine species provide nice greenery for making wreaths, center pieces, and garlands.  They also add a fresh smell to the home.  Virginia pine is probably the easiest to find, for it is very common in fence rows, old abandoned farmland, and along road cuts where soil has been exposed.  It has roundish pine cones that are good craft material.  Short leaf pine is also fairly easy to find especially on dry ridge tops mixed in with hardwoods.  It has an egg shaped cone around two inches long.   White pine is not easy to find naturally growing in the woods, but it is found in almost any neighborhood as a landscape tree.  It has soft blue green needles in bundles of five.  It has narrow shaped cones 4-6 inches long.  Many cones have resin droplets dried on them that look and smell great.

Hemlock:  This one is also a popular greenery plant, but is prone to lose its needles when it gets dry.  The needles are small (less than an inch long) and flat.  The cones are delightfully small and are usually found in great numbers under or on the tree.  The cones are great for all kinds of ornaments and decorations, so let your imagination and glue gun run wild.

Eastern red cedar:  Easy to find growing in every fence row in the area. The foliage adds a spicy odor to the home.  Try to find branches with the small, blue, berry like cones hanging on them to add color to the greenery.

American holly:  Holly has been revered and used for holiday decorating for thousands of years.   It produces beautiful red berries in the winter that are striking with the green foliage.  Holly can be found throughout our area, but is not real common.  Look for it in mixed hardwood stands on moist, well-drained, low areas. You’re also likely to find some variety of holly growing in the neighbor’s landscape, so you might be able to collect it close to home.




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Christmas Trees: Real or Plastic

Christmas Trees: Real or Plastic ?       

By: Steve Roark

TN Dept. Agriculture, Forestry Division

Being “green” is in vogue these days, so as the holidays approach you may be pondering over which is better for the environment, a real tree or an artificial one. It’s a personal choice, but here are some facts to consider.

Artificial trees have these positive attributes:  They don’t require water, don’t mess up the floor with needles, and can be reused for several years, preventing the need to cut a tree annually.  On the other hand, they are plastic and therefore use a nonrenewable resource, as you can’t grow more petroleum.  They are mostly produced overseas, so you can’t “buy American”. Finally, the global transportation of the trees requires a heavy use of fossil fuels, again eating into non-renewable resources.

Christmas trees.jpg

Real trees do require extra care and work getting needles swept up, and you have to kill the tree in order to use it, unless you buy one with roots.  But, Christmas tree farms intentionally grow trees to be cut, and replant trees to replace cut ones.  Live trees are a renewable resource: you can grow more.  They are also biodegradable and eventually decay back to the soil. This can be encouraged by taking your tree to a recycling center that chips it up for mulch.

Some fossil fuels are consumed by tree farmers to grow their crop. However, during the 5 to 10 years it takes to grow a Christmas tree, it takes up carbon dioxide and produces oxygen.  They also provide some wildlife habitat benefit and beautify a landscape.

There are lots of factors to consider when choosing real or artificial, but from an environmental standpoint, real trees have some advantages, and if you buy from a local tree farm you also support the local economy.   And you just can’t beat the smell of a live tree in the living room.




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Bird Survival In Winter

How Birds Survive In Winter

By: Steve Roark

TN Dept. Agriculture, Forestry Division

Many birds remain in our area during the winter.  Songbirds (also called passerines) have a normal body temperature of 107 degrees Fahrenheit, and appear to go about their business on cold days in comfort.   They have a number of adaptations to keep them warm.

A thick covering of body feathers provide birds with effective insulation.  They often fluff them on cold days, which helps trap warm air.  A chickadee has approximately 2000 body feathers and has muscular control over all of them.  Raising feathers to trap heat and lowering feathers to cool down allows birds to adjust to varying temperatures.   Birds also remain relatively dry when it rains or snows because they coat their body and flight feathers with oil secreted by a gland at the upper base of the tail.  The oil is very water repellent and permits the bird’s body to remain relatively dry even during a rainstorm. bird fluffed up.jpg

To stay warm while roosting, birds will seek shelter to protect them from wind, rain, and cold nighttime temperatures.  Tree cavities are used by several species. The brown creeper, nuthatch, wren, and bluebirds will often roost in groups to share body heat.  Finches, sparrows, crows, blue jays, and doves roost in dense clumps of cedars or pine.  The thick cover of evergreen branches helps reduce wind chill and provides a warmer surrounding for birds.  These thermal shelters should be included when developing wildlife habitat on farms and forests.

Birds spend more time foraging during the winter than they do in summer to keep the body heat engine stoked to remain warm.  When temperatures are extremely cold, birds may opt to remain inactive, because the energy lost in foraging is too costly.

Having bird feeders is an enjoyable way to help birds during the winter.  Provide high energy feeds such as suet and sunflower seeds.  Once you start feeding birds, don’t stop until warmer weather.  The sudden end of a food source is stressful.


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Tree Addictions

Tree Addictions

By: Steve Roark

TN Dept. Agriculture, Forestry Division

 Trees provide thousands of products we use every day and they are a great blessing to our society.  Some tree products are even addictive and consumed in large amounts.  Take chewing gum for instance.  A few decades ago the chewy part of gum was obtained from a tree called the Sapodilla that grows in Central America.  The sap from the tree is called chicle, and was the mainstay of the chewing gum industry until after World War II, when synthetic gums largely replaced it.  Gum chewing is a common habit and some folks are never without it.

Another very popular vice is chocolate. The main flavor ingredient is from the Cacao tree, another tropical plant that produces squash-like pods that contain the all-important cocoa seed.  Chocolate is blamed for the mass consumption of empty calories that are eaten in place of more nutritious, less fattening foods.  But a silver lining of chocolate is that the dark variety does have antioxidants and some positive nutritional components. But to get the benefit you have to go with dark-dark chocolate, like 75% cocoa content. Chocolate is also a source of caffeine, an addictive stimulant. “My name is Steve, and I’m a chocoholic.”

Speaking of empty calories, another heavily consumed product is soft drinks, of which the dark colas (the ones with caffeine) are the most popular.  Coca-Cola, Pepsi-Cola, Royal Crown-Cola, all the cola drinks use the nut from the Kola (also called cola) tree for that popular cola flavor.  The tree grows in western Africa and is a cousin of the Cacao tree.

Those who cannot face the day without that morning cup of coffee should give thanks to the Coffee plant, a woody evergreen shrub grown in Africa and the tropical Americas.  The roasted seed (they are technically not beans) provides that all-important jolt of caffeine people have grown to depend on.


coffee cup of photo


Iced and hot teas are also popular caffeinated beverages consumed by half the world population.  It originates from the young leaves and leaf buds of the Tea plant, which grows in many Asian countries.  There are several varieties of Tea Plants, but all are woody evergreen trees that can grow 50 feet tall, but are normally cultivated in plantations to only grow to around waist high.

The recent energy drink craze is like coffee on steroids.  The caffeine source for these high octane beverages varies, but one common source is Guarana, obtained from seeds off a vine by the same name, which grows in the Amazon forest.

No doubt this will change your caffeine habit (whatever form it is), but the reason all of these plants produce caffeine is that it acts as a natural toxic pesticide to protect it from insect attack. So you are consuming something considered poisonous in the plant world….something to talk about at the breakfast table.


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