I was born into a family that was poor but still had a sweet tooth. So tapping sugar maple trees was one of the ways we could satisfy that sweet tooth without going broke in town. But while the sugar maple is the most commonly tapped tree, there are many other trees that can be used to make syrup with. The only reason that sugar maples are used is because of its high sugar to water content in its sap. It can have 2, 3 or even 4 percent sugar. What this means is that it takes about 40 gallons of maple sap to make 1 gallon of syrup. That's a whole lotta boiling down to do, but other trees can be used the same way, you'll just need more sap to get syrup is all.
Most maples can be used to get maple syrup if you live in a climate that has a winter and then warm days and cold nights in the spring. The silver maple is the most common maple in most urban settings. This is a tree that grows fast and people wanted those tall trees fast so they line many streets and drives. The wood is inferior because of how fast the trees grow, but boil down the sap and it tastes just the same as sugar maple syrup. You'll just need more sap to get the same syrup. The nice thing is that silver maples tend to give off more sap than sugar maples so often you'll get the same amount of syrup with just a bit more work.
The box elder tree is considered to be a weed tree by many people. If you've ever had to keep a fence line clean here in Wisconsin, you've probably cut out your share of box elder trees. They can take over a clear space in a matter of a few years. But the box elder tree is a member of the maple family and while it take a good amount of sap to make syrup (about 60 to 70 gallons of sap to make 1 gallon of syrup), most people can not tell the difference between box elder and sugar maple syrup. Box elder trees also can produce a great deal of sap so often a person can get the same amount of syrup from box elders as they do from sugar maples. Again, it will just take more boiling. Really though, sitting around a fire with friends, boiling sap and every now and again taking a cupful of sweet sap out of the pans and putting a tea bag in it is a fun thing to do. Most people in the North East part of the U.S. can find box elders quite easily.
Leaving the maple family there are still many trees that give us syrup and these can often be used in warmer climates. The black walnut tree doesn't need the hard winters of the north to produce sap. It just needs a dormant time and as things begin to warm up it's sap will rise up from the roots. Many people will read about how the black walnut has poisons in it. Yes, it does, but in minute traces in the spring sap. A potato is more toxic than black walnut sap. This will not taste like maple syrup by the way, but it is sweet and has an earthy flavor to boot. I like my maple but we tap a couple black walnut trees every year just to have that unique flavored syrup to cook with if we need a sweetener in the dish.
Shagbark hickory is a tree that can be used for syrup throughout its range. Here in the north or where it goes dormant it can be tapped just like any other tree. If you live in a place where it doesn't get cold though you can cut into the inner bark and boil this in water for a very long time. Shagbark's sugars stay fresh unless they go to the roots where they turn to starch (yuck). So if you have shagbark around you can get a wonderful sweet, smokey syrup no matter if you've never suffered though a long cold winter.
Then there are the birches. Up north here we have the paper birch. This is the last tree of the spring season to tap. Because of it's light color, this tree protects itself from budding too early and it's sap rises up just as maple season is finishing. A couple things about tapping birch; 1) it takes a horrible amount of sap to make syrup and the trees are kind of stingy with their sap. It can take over 100 gallons of birch sap to get 1 gallon of birch syrup. and 2) birches contain salicylic acid, the forerunner to aspirin. Birch syrup is GREAT for getting rid of headaches and to take down swelling, but if you are allergic to aspirin, it may not be safe for you to ingest it. Besides that birch syrup is wonderful to taste. It has a delicate, sweet, and slightly minty taste. Anyway, our paper birch does.
If you are lucky enough to live in the south you may have a sweet birch tree near you. This tree gives a very, very good tasting, minty syrup. You can get it from tapping or more likely you would get it from boiling lots and lots of twigs for a long time until you extracted their sugars and then boiled that down to make a thicker syrup. I've traded for sweet birch syrup and now I'm looking to plant a grove of them up here by the creek. It is just so good and has been used as pain medicine by southern American Indians and granny women for hundreds if not thousands of years. If you have some near you, get out and give it a try...you lucky person. lol
There are other trees that can be tapped for syrup, poplars, which usually grow in dense stands, make a sweet syrup. Again, like the birch it does have salicylic acid, just not as much. Elms and hackberries are also tapped but I have never done it and I certainly wouldn't do it to an American Elm as they are so rare now adays and an injury could spread disease. But most areas have plants that can be used to get sweet syrup. All living things contain sugars, it just depends on if we like the flavor of those sugars or not. See if any of the old ones around you may know of how they satisfied their sweet tooth before cane sugar was transported in on ships from far away.