No one should go through the fall season without stepping outside to admire the colors of nature. Albert Camus, a French philosopher, once said, “Autumn is a second spring when every leaf is a flower.” If you’re wondering what causes our trees to turn colors in the fall, check out our previous blog on Fall Foliage. Fall hikes are a great time to get out and admire the colors, to observe animals preparing for winter, and to squeeze in as much Vitamin N(ature) as you can in the mild temps of autumn. Make your fall hikes a learning opportunity for your family by practicing your tree ID skills along the way! In this blog, we’ll learn some basic tree identification skills and fun facts about some of the most common types of trees in our neck of the woods – central Minnesota.
A variety of characteristics help identify certain types of tree: size, shape, colors, textures, bark, branches, twigs, leaves, flowers, smells (!) and many other minute details we won’t even get into. For the basics, we’ll be focusing mostly on the leaves, but even so, it’s good to get in the habit of observing all the parts! A Dichotomous Key is my favorite tool for easy tree ID. The word Dichotomous comes from the Greek word dikho, meaning in two. So in a dichotomous key, it asks you a question and you have to choose one of two answers. While I happen to love the key found in the guide Minnesota Trees by David Rathke, he also has a simplified online version that has fewer words, and more pictures – so it’s great for families! It’s free, so just print it out and you’re on your way! Please keep in mind, this guide is for common, native Minnesota trees. That means some trees won’t be in the guide, especially ones that have been planted or introduced to this area.
The first question you have to ask yourself about a tree is: Is it coniferous or deciduous? Coniferous trees (right) have needle-like leaves which they retain all year (except for tamaracks), while deciduous trees (left) have broadleaves (the more “typical” leaf shape), which they drop in autumn.
Since leaves are quickly disappearing from our trees, let’s start with a few of the most common deciduous trees. The first question is: Are the branches/leaves alternate or opposite? Examine the leaves on a twig or the twigs on a branch. Now – stick your arms straight out to either side. Do they look like that? Then they’re opposite. Or do they look more like if you stuck your right arm out and your left leg out? Then they’re alternate! We have considerably fewer trees in Minnesota that are opposite – so identifying this right away rules out many options!
Next, look closely at the leaves. There are two main types: simple leaves are made up of a single leaf, whereas compound leaves are made up of several leaflets all on one leaf stalk. Closely examine the edge of the leaf which can be smooth, toothed (which can be big or small), double toothed (different sizes), or lobed.
Here is a simple dichotomous key for the deciduous trees. The highlighted ones are more commonly seen species that we’ll discuss in more detail.
The Maples
The most common opposite-branched trees in Minnesota are our maple trees, of which we have 6 native species. Maples are of course known for their sap which we turn into syrup, and for their “helicopter” seeds (samaras) which we delight in throwing into the air! Maples are a very important food source for many types of birds and mammals. They often produce spectacular fall colors – a variety of reds, oranges, and yellows – and contribute substantially to the tourism industry. Since it’s fall, we’ll focus a lot on the maples. Here are the types common in our area:
Boxelder: Compound leaves with 3-5 leaflets that are irregularly toothed and often have three shallow lobes. The samaras are long, v-shaped pairs that can be seen on the tree in autumn. Fun facts about boxelders:
Only maple with compound leaves!
It was once widely used for windbreaks in the prairie region because it is easy to transplant and can survive temperature and weather extremes. However, it’s brittle branches often leave it damaged after storms and it rarely lives past 100.
The female trees often attract boxelder bugs, a little red and black beetle. Can you find any?
Red Maple: Simple, toothed leaves with 3-5 lobes. The samaras are wide v-shaped pairs that can be seen on the tree in the spring. Fun facts about the red maple:
One of the first trees to flower in the spring, providing an important pollen/nectar source for spring bees!
Like other maples, these trees are a very important food source for wildlife! They make prolific seeds that are favored by small mammals like squirrels and chipmunks, and larger mammals like rabbits, deer, and moose browse on the twigs and leaves.
Known as a “tonewood” which means the wood carries sound waves very well. This makes this tree sought after for many different instruments, including violins, violas, bass, and guitars.
Sugar Maple: Simple, 5-lobed leaves with few very pointy edges. The samaras are more u-shaped pairs and can be seen on the tree in the autumn. Fun facts about sugar maples:
Have the highest sugar content of all the maples, meaning you need less sap to produce syrup. Still, it takes about 40 gallons of sap to make 1 gallon of syrup.
A stand of sugar maples is called a sugar bush. Maples should be between 30-40 years old before they are tapped for sap. A single mature tree can produce about 25 gallons of sap each spring.
Seeds have a germination rate of 95%! Sugar and red maple are some of the only seedlings that can survive in the completely shaded forest floor. You can find tons of tiny seedlings during the summer!
Silver Maple: Simple, 5-lobed leaf with deeper lobes and even more points on the edges than sugar maples. The samaras are u-shaped pairs that can be seen on the tree in the spring, and fall singly to the ground. Fun facts about the silver maple:
This is a tree that likes to have its feet wet! It can be found in low, moist areas and along river beds.
Like red maples, these trees flower very early in the spring, making them an important food source for pollinators.
Seeds reach maturity only 3 weeks after pollination. Seeds drop to the ground about the time spring meltwater is receding, leaving a very rich soil of silt deposits – an excellent seedbed!
The Oaks
Oak trees have alternate branching and simple, lobed leaves. We can thank our oaks for acorns, which are an extremely important food source for a variety of wildlife! Oaks do something we call mast-fruiting, which means they synchronize the timing of their acorn crop and yield with other oaks of the same species in their geographic area. A large crop year is followed by 2-3 years of very little or even no acorn production. Want to know why? Watch the video below.
These trees can grow to be very old (some white oaks can live between 500-600 years) and very large! The wood is hard and is frequently used in making furniture. We have 7 native species of oak, but we’re just going to break them down into two categories.
Red Oaks: Simple leaves with pointed lobes and “bristles” or a little point at the end. I remember this by thinking if it’s pointed, I could poke myself and draw blood, blood is red. A little morbid, but it works for me! Fun facts about red oaks:
Acorns take two years to mature, dropping to the ground their 2nd autumn and germinating the following spring.
Red oaks appear to be on a 2-year cycle for acorns, with large crops occurring in most areas of Minnesota during even years.
The acorns of red oaks are high in tannic acid, making them bitter tasting. This can be toxic in high amounts but can be reduced by boiling the acorns. Native Americans traditionally made flour from the acorns and used tannic acid from oak trees to tan deer hides.
Northern Red Oaks and Pin Oaks can be difficult to tell apart, even more so because they hybridize quite frequently.
White Oaks: Simple leaves with rounded lobes and no bristles. Fun facts about white oaks:
Acorns mature at the end of the first growing season, fall to the ground in autumn, and germinate immediately!
White oaks appear to be on a 3-year cycle for acorns, with large crops occurring in most areas of Minnesota in 2000, 2003, 2006, 2009, etc. The cycles of all oak species aligned in 2000, making a very large acorn crop!
The acorns are lower in tannic acid, making them less bitter than red acorns and preferred by most wildlife.
Before the use of steel, white oak was frequently used in ship construction, including in the USS Constitution!
Fun Fact about Squirrels: Squirrels acorns from both types of oaks, but they have a preference for which ones they eat first! Squirrels eat acorns from white oak first, leaving the red oaks for later in the winter/spring. More about that in our Fall Feeding Frenzy Blog!
The Birches
Minnesota is home to 5 native species of birch trees. They have alternate branching with simple, double-toothed leaves. They tend to be fast-growing, short-lived pioneer species. Our birch leaves turn yellow in the fall. Birch trees are historically significant for multiple reasons, including the use of birch bark for writing. The oldest dated birch bark manuscripts go back to the 1st century CE! The most common birch in our region is fairly well known.
Paper Birch: Simple, double-toothed leaves, but most people identify it by the white, papery, peeling bark. Fun facts about paper birch:
Native Americans had many uses for many parts of the birch tree. The bark was prized because it was light-weight, strong, waterproof, flexible, and easy to strip from trees. It was used in making canoes, wigwam covers, bowls, baskets, moose-calling horns, utensils, and more!
Traditionally this tree has many medicinal uses, including uses in treatments for gout, cough/cold, pulmonary diseases, constipation, burns/wounds, and is even being studied in cancer research.
The oils in birch bark make it an excellent fire starter, even when it is wet. It is easy to peel into thin layers, making it easier to catch on fire. It also prevents the bark from decaying quickly, which is why you can often find large pieces of birch bark in the woods and shake out the rotten wood from the inside. Note: these make excellent “cannons” when placed vertically in a campfire, but adult supervision advised!
The Aspens
Aspens are likely the most abundant tree group in Minnesota, even though we only have 4 native species. They have alternate branching with simple, toothed leaves. Their leaves have flat stems (petioles), unique to this group! Aspens are an important species in the forestry industry and recently, fast-growing artificial hybrids have been developed for large-scale biomass and fiber production. Their leaves are a bright yellow against blue skies of autumn. Trembling and big tooth aspen are the most common in our area, but cottonwoods are too neat to leave out!
Cottonwood: Simple leaves with large teeth. They can be distinguished from other aspens by their squared-off base and the elongated tip. Fun facts about cottonwoods:
The most massive tree species in Minnesota! This is a “live fast, die young” species and is thought to be the fastest growing tree in North America. While some trees can live up to 200 years, most trees show considerable damage by the time they reach 100 due to their very brittle branches. Some trees can reach up to 150 feet and have a diameter of 6-8 feet!!
Prefers moist locations and is typically found on floodplains and along streams, rivers, and lakes.
Light cotton-like seeds (which can be so numerous from large trees it almost looks like snow) are dispersed by wind and water and are the only way this tree reproduces.
Bigtooth Aspen: Simple leaves with, you guessed it, very large teeth! Fun facts about the big tooth aspen:
Like many other aspens and willows, the bark of this tree has a compound called salicylic acid in it, which is the main ingredient of aspirin!
Seedlings of bigtooth aspen are somewhat rare. More often, the tree reproduces through a method called root suckering, which is when it sends up new sprouts from shallow roots to make a clone tree.
Bigtooth aspen is an important Minnesota timber species, used for pulp, paper, and oriented strand board (like plywood).
This aspen, as well as many others, are important food sources for wildlife and are favored by grouse, deer, moose, rabbits, and beavers.
I saved my favorite for last! Everything I continue to learn about this tree is amazing!
Trembling or Quaking Aspen: Simple leaves with very small teeth. The flat stem causes the leaves to “tremble” in the wind, which is where it gets its name. Fun facts about trembling aspen:
This is the most widespread tree in North American and the most common tree in Minnesota!
Prolific reproduction from root suckers. Because of this cloning ability, a quaking aspen is actually the largest organism on earth! The largest colony of aspen, named Pando (Latin for I spread), is made up of over 47,000 trees and covers over 100 acres in Utah. All of these trees are clones and are connected through one massive root system, technically making it a single living organism!
Individual quaking aspen trees do not live that long. However, a system of clones can live a very long time! There is one clone group in Minnesota estimated to be over 8,000 years old!!
The bark of quaking aspen often has a noticeable green tint to it. Research has shown that this actually comes from active chlorophyll – the same pigment in green leaves responsible for photosynthesis! Scientists believe the tree’s ability to photosynthesize using the bark is particularly useful in the early spring season before leaf out and is likely a large reason why this tree can live so far north and at high altitudes!
Stay tuned for Part 2, where we’ll delve deeper into Minnesota’s common coniferous trees!