Winter severity index shows few real trends
In 1975, Wisconsin began to keep track of the severity of winters in the northern third of the state. Our severity index was arrived at after testing several different procedures.
We presently use the number of days with a minimum temperature of zero degrees Fahrenheit or below as a measure of winter air chill and the number of days with 18 inches of snow or more on the ground to estimate the snow hazard. Days when both conditions occur together are scored a two.
The daily scores are added together from Dec. 1 through April 30 to arrive at our winter severity index.
The U.S. Department of Commerce weather data was initially used to calculate the WSI but starting in the winter of 1986-87 weather data was collected at 35 Department of Natural Resources stations across the north.
During the winters of 1999-2000, four of the reporting stations were dropped while one was added. Presently there are 32 stations active in this effort. The reporting stations range across the state from Grantsburg, Barron, Spooner, Prentice, Merrill, Tomahawk, Antigo, White Lake and points north.
Values of WSIs were extrapolated back to the winters of 1960-61 to provide a historical look for almost 50 years.
Winters are considered "mild" if the calculated WSI is less than 50, moderate if 50 to 80, severe if between 80 to 100 and very severe if the WSI is greater than 100. These designations are based on observed associations between WSI and winter deer mortality, fawn production and buck harvest during the following year.
The region-wide winter last year (2008-09) was rated moderate with an average score of 60.5 (+/- 3.3). A 30-year average is 60.9 (+/- 4.7). Last year 52 (87 percent) of the generated points were temperature points and most were accumulated during December and January.
An outdoor writer from southern Wisconsin in 2008 tried to make a tie to the WSI data from the winters of 1960-61 through 2008-09 and global warming. Looking at the same information he elaborated on, there is absolutely no trend or indication that the winters are getting less severe in the area from which the data is generated.
Two of the lowest WSIs (less than 20 WSI) were in the winters of 1986 and 1997. Winters that were scored as very severe (greater than 100 WSI) occurred in 1968, 1970, 1971, 1978, 1981, 1985, 1995 and 1996. In the year 2000 the severe WSI level was reached. While the number of data points observed is relatively low, the data appears for each year to be random in intensity.
Keep this in mind if you are planning to sell your warm winter clothes, skis and snowshoes. This might be the year we reach the very severe WSI level again!
Following a fresh snow like we experienced last week, one has the opportunity to get outdoors and observe what and who is making an impression in your neighborhood.
Rabbits and squirrel tracks are easily discernable. The three prominent claw prints of the pheasant and the larger three toed tracks of the turkey make their presence known. It is interesting how turkeys march from one place to the next in "herds" at times all moving in the same direction.
Deer tracks often come in multiples also. While the bucks are mostly loners this time of the year, the does and fawns will herd up. Size of the hoof imprints tell the young from the old. When the snow gets deeper, animals will utilize the same paths and runways will be opened.
When I was a kid, everyone in my circle of friends would search out these runways and snare a few rabbits for mom's cooking pot. There are small bird tracks galore in and around the bird feeders. Ground feeding birds can be differentiated from the perch feeders. Cat tracks and dog tracks can be identified in relationship to fox and coyotes. I have seen all in the confines of our city limits.
If one is lucky and observant enough, one can see in the outlines left in the snow, a true drama unfold. A mouse, rabbit or pheasant track can be followed into a clearing and suddenly disappear. The only thing left is a small area of disturbed snow and the indentation of spread wing tips indicating the place where the animal met its fate and a raptor had lunch. The story of a fox or coyote also setting up the dinner table can be read in a fresh snow.
Getting out after a fresh snowfall can be a very rewarding experience!
WPA of the Week
Oak Ridge WPA Aspen Stands
The Oak Ridge Waterfowl Production Area is located about six miles northeast of New Richmond. The WPA is managed by the U.S. Fish and Wildlife Service at the St. Croix Wetland Management District and in combination with adjacent state wildlife area land, provides more than 585 acres of habitat that benefits many species of wildlife.
This winter, the Fish and Wildlife Service will be cutting approximately 15 acres of mature aspen on the Oak Ridge WPA as part of an effort to regenerate the young aspen forest. If you have wandered around the aspen stand in the northwest corner of the WPA, you have probably noticed many fallen aspen trees in the forest.
With time, these mature aspens have started to fall over and are slowly being replaced by other tree species. Unfortunately, aggressive species such as box elder, Siberian elm and buckthorn have started to establish themselves in this forest. Compared to aspen, these species provide little wildlife value.
Often called "popple," aspen is a clonal species, meaning that many trees grow from a single seedling, spreading through an extensive root network. Root suckers send up new stems which may be located 90 to 120 feet from the parent tree.
Young aspens do not compete well in a shaded forest so an effective technique to regenerate the aspen stand is to cut the mature aspens which opens up the canopy and allows the young aspen to thrive in the sunlight. This "young forest" benefits many species that use early successional habitat including woodcock, ruffed grouse, deer, brown thrasher and golden winged warbler.
Woodcock prefer these young stands of aspen that provide lots of overhead cover and protection from predators. Ruffed grouse use these young aspen stands for brood rearing, the thick whip-like vegetation providing protection for the young. Aspen buds are also a very important winter food for ruffed grouse. With time, this aspen stand will change from a shrubby sapling stage to a mature forest again, benefiting many different species of wildlife over the next 50 to 60 years.
If you would like more information about the St. Croix Wetland Management District, visit our Web site at http://www.fws.gov/midwest/StCroix/.