One sure sign of spring is when maple sap starts to run.

The first task in maple tapping is finding the suitable tree. In the summer time, sugar maples are easy to identify with their distinctive five-lobed leaves, like those seen on the Canadian flag. In the winter, it's harder, but you can pick them out by noting that the pointed buds on the slender twigs are opposite each other, and by the oval shape of the tree when it's growing in clearings.

Maple sap starts to run when the nights are below freezing and when the days are warm. The sap isn't actually running all the way from the ground, since the ground is frozen; rather, the sap in the tree is warmed by the changing season. By the time sap actually flows out to the budding tree leaves, it has changed to the point where it is no longer suitable for turning into syrup.

For small scale syrup production, you drill a hole into the tree at about chest height, tap it with a small peg called a spile, and hang a bucket or bag on the hook on the spile to catch the sap that drips out. Large-scale production uses a series of tubes between the trees and a system of pumps to capture the sap into large containers.

Trees to be tapped should be at least 18 inches wide, healthy, and well exposed to the sun; traditionally, you place the tap on the south side of the tree to catch the sun. If you are tapping a tree in multiple years, make certain to move the tap each year to get best results.

The City of Ann Arbor has 5,359 sugar maples in public parks and on the municipal right of way. The city calculates that each 16-inch diameter residential sugar maple tree provides $149 in benefits every year, including savings on energy in the summer from the shade, improved property values, improvements to storm water handling and air quality. What they don't measure is the value of the sap from a sugar maple.

A typical healthy tree in a good year will produce about 10 gallons of sap. When you boil this down, you'll get about a quart of maple syrup, with a market price of $20 for a quart or more depending on where you buy it and how fancy the bottle is.

If you don't have sugar maples in your yard, or if you do and want to see how syrup is produced before you make a go of it on your own, there are a couple of area parks which run maple sugaring programs.

The Hudson Mills Metropark north of Dexter along the Huron River combines a tour of their sugarbush and tree tapping ($2) with an all you can eat pancake and sausage breakfast. Registration is required for this Saturday and Sunday event during the season, call 734-426-8211 or 800-477-3191 or visit www.metroparks.com for details. The breakfast runs from 9 a.m. to 2 p.m., and there are three programs at 10 a.m., 11 a.m., and noon. A Metroparks day or season vehicle permit is required.

On March 13, naturalist Tom Jameson will lead a maple syrup program at 1:30 p.m. at the Gerald Eddy Discovery Center & Waterloo Recreation Area in Chelsea. Make reservations at 734-475-3170; you'll need a state motor vehicle permit.

Snow's Sugarbush is in Mason, about an hour west of Ann Arbor. They host an annual maple sugar festival, where you can see their entire commercial sugaring operation from trees to finished products. This year's season runs until April 18, and the festival features a pancake breakfast. Contact them at 517-676-1653 for details or see www.snowssugarbush.com .

Edward Vielmetti grew up with big pans of maple sap boiling in the front yard. Contact him at 734-330-2465 or edwardvielmetti@annarbor.com.