Sycamores, Trees of Wonder

If you were to decide to learn only one tree in your life, I would recommend learning the sycamore (though I don't recommend learning only one tree).

A stately sycamore between our outdoor classroom and playground.

A friend once told me that sycamores are easy to recognize because they are the only tree that wears pants.  A sycamore's upper limbs are white and appear to be uncovered, and its lower trunk is covered with brown, patchy bark - the sycamore's pants.  Sycamore bark consists of three layers: the outer is brown, the middle is greenish and the inner bark is white.  Sometimes you can see all three layers together in a camouflage-like pattern.  The outer two layers peel off of the upper limbs, leaving bone-like white branches that look spectacular against a blue sky.  Scientists aren't sure why the upper bark peels off, but some people think it falls off to prevent vines from being able to grow up into the treetops. 

Sycamores tend to grow near water, and since their white branches are visible from a distance, they are useful for finding water if you are ever lost in the forest.  Early explorers used them to find water sources across North America, but they used sycamores for lots of other things too.  Sycamores are very fast-growing, so they produce a lot of wood.  Though sycamore wood is twisty, it is extremely strong and light, and Native Americans and settlers both used it to make just about everything you can make out of wood.  Before North American forests were logged, most forests contained trees that were a lot older, therefore they were bigger than trees we have now.  Old sycamores tend to be shockingly enormous compared to other trees, and they are often hollow (here's a medium-sized one, and possibly the world's largest), so sometimes they were used by people as a shelter or to corral animals.

A drift of sycamore seeds and a few pieces of fallen sycamore bark.

The sycamore tree at our school is making a mess right now.  While more northern parts of the country still have snowdrifts, here in Middle Tennessee, we get drifts of sycamore seeds.  Sycamores hold their seed balls (technically fruits) up on their branches all winter, but now the seed balls are dispersing their seeds.  Every ball contains hundreds of wind-dispersed seeds that each have a few feathery hairs to catch the wind.  Some of the seed balls break apart while they are on the tree, and the seeds are dispersed from high in the sky.  Many seed balls fall onto the ground as well.  Mostly the seed balls break apart when they fall off the tree.  The seeds are only loosely-held together, so the seed balls usually smash to smithereens on impact with the ground.  If you're lucky, you may find a whole seed ball, which is exceedingly enjoyable to break apart for yourself.

A sycamore seed ball with a few seeds falling out.

 If you lightly crush the seed ball, you can see how the seeds fit together so tightly. 

A lightly-crushed sycamore seed ball.

Once you have completely crushed the seed ball, look for the hard structure inside.  That structure is the base of where the seeds are produced, and it looks like the strangest type of seed or fruit you've ever seen, but it's neither seed nor fruit, just stem.  Many naturalists have been confused when trying to identify these structures when they find them without the surrounding furry sycamore seeds.

A fully-crushed seed ball.

Soon our sycamore will look very different.  It will be covered with giant plate-sized sycamore leaves, but you will still be able to recognize it by its beautiful white branches.

Turdus migratorius, American Robin

The robins are here!  For such a pretty and lovable bird, they have a very unflattering scientific name: Turdus migratorius.  The migratorius part isn't so bad, and robins are indeed migratory birds.  But why the name Turdus?  Scientific names are in Latin, and 'turdus' means 'thrush' in Latin, which is a bad deal for the robin.  A thrush is a type of bird that is usually small and plump and searches for food on the ground.  Bluebirds and wood thrushes are other common Middle Tennessee thrushes.

A male robin.

Robins are grayish with rusty undersides.  The males' heads are darker than their backs, and their underbellies are usually brighter than females'.  Last week a male and female were getting to know each other at our outdoor classroom. 

A female robin.

 In Nashville, this time of year robins are just finishing up their winter migration.  Robins group together near the end of winter into massive flocks (did you notice them a couple weeks ago?), then they migrate to follow food sources and warm weather.  They may not migrate straight north like most other migratory birds do - they just go wherever life is good for robins, which explains why we have some robins here year-round.  At the end of the winter migration, birds form pairs and begin to find a home range to nest in.  They may come back to the same place as last year, but they may not.

A female robin between the two Japanese quinces.

Robins are generalists in both nesting and in feeding.  They build nests in a variety of habitats, from landscaped yards to meadows to forests.  They eat a variety of insects, worms and fruits, depending on what is available to them to eat.  In the spring and summer, they tend to eat more insects, and in the fall and winter they eat more fruit and berries.  This time of year, you are likely to see the cliché of a robin with a worm dangling from its beak.  Robins can usually find their food and shelter requirements around where humans live, so they tend to be very familiar to us.

A female foraging for ground insects or worms and a male sitting on the fence.

If the male and female I saw at our outdoor classroom become a pair, they will have 2-3 broods of baby robins this spring and summer.  The female will soon start building a cup-shaped nest of three layers: twigs first then mud then grass on the inside.  She will probably lay 3 light blue oblong eggs in the nest a couple of days after it is finished.  The female sits on the nest for 12-14 days, getting up every once in a while to turn the eggs or go get food.  The male might bring her some food or might not.  The female's belly has a patch of skin with extra blood vessels that keep the eggs warm as she sits on them.  If the eggs get too cold, they will die.  When the eggs hatch, the female tosses the egg shells out of the nest and broods (sits) for another 3-4 days.  After that, the hatchlings are able to keep themselves warm enough without being sat upon constantly.

Both parents feed the hatchlings after they escape their eggshells.  For the first few days, the menu is regurgitated food the parents already ate.  And if that isn't gross enough, after that the parents bring soft-bodied insects and worms to feed the poor little birds.  The hatchlings beg and peep like mad for their food, so they must like it.  Begging is an important skill for robin hatchlings, because the most aggressive peeper with the longest neck and widest-open beak will get the most food and is most likely to survive to adulthood. 

At two weeks old, the robins usually fledge (leave the nest).  They still don't fly well or know how to find food, so the parents hop around them on the ground alerting them to danger and bringing them insects and berries.  At first, the mom feeds the fledglings, but then when they are starting to become independent, the dad will feed them, and the mom will go and build a new nest for the next brood.  The fledgeling stage is very dangerous for the birds because the young ones can't fly yet.  They might become the food that a mother hawk brings home to her hatchlings, or they might fall prey to a cat.

There are many types of birds at our outdoor classroom right now.  Next time you go, try to count the different types of birds you see.  Last time I was there, I saw 3 kinds.  Pay special attention to the robins, and see if you can figure out what they are doing when you see them (feeding? gathering nest materials? searching for a good nest site? fighting off other birds? or are they watching you?).   

What ARE Coconuts Anyway???

On my marathon visit to the Chicago Field Museum, I geeked out most over the plant models.  There are cases and cases of gorgeous models of representative members of lots of plant families.  I, of course, amused myself by trying to guess what family was represented in each case without looking at labels.  It turns out I have forgotten quite a bit of Botany since my days at MTSU.  Time for a little refresher course.

The plant models didn't photograph well, due to the dim light, glaring glass, and lack of likely appeal of subject matter to the rest of the world.  However, I couldn't resist taking this picture of a coconut model:

Coconut model at the Field Museum.

Coconuts are completely strange to most people who live in temperate climates.  We don't tend to eat lots of them, and we rarely even see them.  If we see them, they are big brown woody balls in the produce section, or they are tiny flakes of sugary white in the baking aisle.  When we go to the beach and a real coconut washes up on shore, we don't believe people when they tell us what they are.  Well, here's your chance to stop feeling so uninformed when it comes to coconuts.

Coconuts are the fruits and seeds of the coconut palm.  A complete coconut is green or brown, oblong and bigger than a football.  The brown woody thing in the produce section is the innermost part of the fruit plus the seed of the coconut.  The whole fruit is made of layers of fibrous husk called coir.  The fruit is less dense than water, so it floats.  You may have noticed that the scratchy brown doormat outside your front door is made of coir.  Coconut palms often drop their fruit where waves can wash them into the ocean, and the fruits can then be dispersed out around the world to grow somewhere else.  The outermost two layers of the fruit are removed before whole coconuts are brought to our stores.

Field museum coconut model with labels.

Each coconut fruit contains one giant seed, which is almost entirely white with a paper thin layer of seed coat around it.  The seed contains an embryo, which can grow into a new palm, and endosperm, which is a food source for the growing embryo.  When the seed is first formed, the embryo is microscopic, and the endosperm fills up most of the space inside the seed.  The early embryo is slightly sweet and crunchy.  As the coconut starts to get larger, the endosperm becomes somewhat more gelatinous and is known as green coconut meat.  When the seeds are nearly mature, the endosperm forms solid endosperm around the outer edge of the seed and liquid endosperm inside the seed - coconut meat and coconut water.  A mature coconut seed will also contain some air, which helps it float in the ocean.  All stages of coconuts can be eaten, and they all taste coconutty, slightly sweat and delicious.  Coconuts contain a high proportion of saturated fat, unusual for a plant but much more common in butter and animal fats.

If a coconut escapes consumption by a human and floats off to a new land, it will begin to germinate.  The embryo enlarges into a root and a shoot, and it escapes the hard coconut shell through structures called eyes that look like dimples on the surface of the coconut.  As the embryo starts to grow, it forms a mass inside the coconut called a coconut apple.  The mass is soaks up the nutrients from the endosperm and transfers those nutrients to the growing shoot and root of the embryo.  The coconut apple is also edible - in fact it's considered quite delicious, though I have unfortunately not tasted it.

Writing about coconuts is definitely making me want to conduct some field research about the gastronomic virtues of the various stages of coconuts!  Anyone up for a Caribbean vacation?

Maples in Early Spring

If you live in the temperate eastern United States, and you only know one kind of tree, it's probably going to be a maple.  Everyone knows maples.  People either recognize and love maples' unique, pointy leaves, enjoy maple syrup, admire bright fall maple trees, or played with maple helicopter seeds as kids.  Few people know what maples are up to this time of year, though.

Even without leaves, maples are very busy this time of year.  Look at the ends of the branches on this maple tree below:  there are lumps all along the branches.

Swollen maple buds ready to pop.  Early March.

Those lumps are flower buds.  Many maples flower and fruit before they leaf out.  Here is a closeup of maple flowers:

Mid March, maple flowers.

Maple flowers are pollination generalists.  Some are pollinated by insects and bees, some are wind pollinated, and some are self-pollinated.  From the tree's perspective, it pays to be flexible with pollination strategies if you bloom very early in the growing season, because it's difficult to insure that insects will be out when you're ready to bloom.  Insects are really the best pollinators.  They are great at pollinating over long distances with small amounts of pollen, but they require warmer temperatures to do their work.  Wind pollinates cheaply - you don't have to feed it nectar or a portion of your pollen to get it to carry your pollen to another flower.  But wind isn't very specific in direction, so you usually need to make a lot of pollen if you are using wind (more on this next time!).  Self pollinating is convenient, but let's face it, you don't get much genetic variety if you make kids using only your own genes. 

Either way, lots of pollination has happened, because the maples in Chicago are LOADED with maple fruit.  Notice I called these helicopter things seeds earlier in the post, and now I'm calling them fruit.  I didn't want to alarm you earlier, but here's how this works:  fruits are plant parts that hold seeds.  An apple fruit has seeds in it, and so does a cucumber, and so does a maple fruit.  The maple fruit consists of a wing and a case around the actual seed.  Open up the swollen end of the fruit, and you will find a sticky seed (and you can stick the fruit on your nose or fingers like we did when we were kids).

Maple fruits (samaras) in late March.

Maple fruits are winged, and they are adapted to being carried far away from their parent tree by the wind.  They do indeed work like helicopters - their wing catches the wind and spins them along to hopefully sunnier ground than the ground just under their parent tree (maples are indeed shade trees).  There are many types of fruits out there: berries, capsules, hesperidia, drupes, pepoes, etc.  Fruits with wings are called samaras.  Both maples and ash trees have samaras to carry their seeds away.

New (red!) maple leaves, plus some maple samaras, late March.

Above you can see some new leaves just starting to grow on this maple. I had to look hard to find maple leaves on this type of maple tree - they mostly have only fruit right now.  Below you can see two pictures of early leaf growth on a Japanese maple.  Japanese maples seem to usually leaf out before they set fruit.

Japanese maple leaf buds opened and showing the new expanding leaves, late March.

Slightly older Japanese maple leaves, late March.