Tree sex

Beyond the birds and the bees

text and photography by Tom Kimmerer

Over the next few weeks, billions of public sex acts will take place and few of us will notice.

It’s time for tree sex. Time for the air to fill with the flowery aroma of tree sex, with clouds of pollen and with bees, flies, beetles, moths, butterflies and hummingbirds doing the trees’ bidding.

We all know the showy flowers like yellow-poplar, locust and magnolia. But most trees have very subtle, small flowers that we scarcely notice. Sometimes we smell a sweetness in the air without noticing the abundant, tiny flowers on nearby trees.

Sex in trees is complicated, more so than in people. Depending on the species, a tree might be all male or all female; male and female in the same tree; male on Tuesday and female on Wednesday. A tree may even start out as male and become female decades later.
If you are fixed to the ground, you can’t go out on dates. So how does tree sex happen? One thing is for sure – trees don’t have sex with themselves. Even if male and female flowers are on the same tree, the female flowers will reject the advances of its own pollen. No inbreeding allowed.

Trees would have trouble finding suitable mates if it weren’t for the dating services provided by wind and animals.

Wind is not a reliable matchmaker. Trees like birches that depend on wind have to produce billions of pollen grains and fling them into a passing breeze. Each pollen grain has only a tiny chance of landing on a receptive female flower of the same species at the right time. Yet most of the trees in the Bluegrass toss their pollen into the wind – that’s why our cars are often dusted with pollen in the morning. It’s also why many people suffer from allergies in the spring.

The clouds of pollen in the air and the thick coatings on streets and cars are impressive, but it is even more impressive that enough of these pollen grains manage to land at random on the right flower at the right time so that the tree can bear seeds.

Some trees leave less to chance and enlist the services of animals. There are over 200,000 animals, mostly insects, that pollinate plants. Of course, bees are the most familiar, but it’s not just honeybees. There are bumblebees, carpenter bees, mason bees, even a tiny bee the size of a pin head. Then there are the flies, butterflies, moths and beetles. Birds and bats get into the game, and sometimes even monkeys will carry pollen from one tree to another.

Trees play elaborate games to attract pollinators, offering bright colors, sweet nectar, and smells ranging from pleasant scents to the stink of rotting meat. Flowers are specially constructed not only to attract animals, but to efficiently put pollen on their bodies and ensure that it rubs off on a willing female flower. Some flowers even go so far as to imitate the reproductive organs of insect pollinators. All this elaborate behavior is in the service of one thing: sex.

Red maple has to be the closest thing to a porn star among trees. Red maple will do anything for sex. The flowers are tiny – many people hardly notice them – but brightly colored, and creating a subtle sweet smell to attract the earliest spring insects. Leaving nothing to chance – what if the insects are late to the party? – red maple also casts pollen into the wind.

Red maples have as many as five different genders. Some red maples are male, some are female. But others have male and female flowers on the same tree, often with male flowers high in the tree and female flowers lower. Some have ‘perfect’ flowers that have both male and female sex organs in the same flower. And some trees like to switch it up – male for a few years, then female for a while, back and forth.

Whatever their sexual identity, red maples are really good at finding mates. Beetles, bees, flies and wind move pollen from tree to tree, and fertilization takes place. The winged fruits grow quickly and are mature a few weeks after pollination. One tree may bear tens of thousands of winged fruits, which are tossed into the breeze to float away like tiny helicopters.

What if there are no insects, or an inadequate breeze? Red maples have a fallback plan. They are self-fertile – that means they can mate with themselves, the male parts fertilizing the adjacent female parts. This is usually not allowed in tree society, but red maples are an exception.

And even if all attempts at sex fail, red maples have a second backup plan – they can simply produce more stems from the same root system, which we call stump sprouting.

All this wild sex seems to work for red maple – it is one of the most successful trees in eastern North America.

Nearly every tree you see is engaged in some kind of sex in the spring. As you walk around town, or go for a hike in the woods, see if you can spot signs of tree sex.