First Week of April: Trees

A roundup of quick Sidewalk Nature updates: one warning and three wonders.

Trouble with Double

Kwanzan cherry trees don’t feed pollinators or birds. They look great two weeks of the year but they don’t support our foodweb. Prunus serrulata ‘Kwanzan’ / ‘Kanzan.’

My concern is that when people have room to plant one tree, this is the one they’ll want. It is cultivated for pretty, and pretty it is, but it doesn’t have nectar, doesn’t make fruit, and as a nonnative congener, its leaves support only a fraction of the Lepidoptera species a native Prunus / cherry can.

But at the Cherry Blossom Festival this month, festival-goers can walk away with a free Kwanzan cherry tree from the Nashville Tree Foundation.

Also on offer are Yoshino and Okame cherry trees. From what I’ve read, Yoshino and Okame do have nectar and pollen. Yoshino makes fruit (bird food), Okame is sterile (no fruit). Both trees have single flowers, not Kwanzan’s doubles. Double / pompom blooms are bred for show, and even if they do produce nectar or pollen, some insects won’t be physically able to negotiate the extra layers to reach it.

Listen to Doug Tallamy about the trouble with doubles: “If you have a double flower, those are all sterile. If you have anything that’s really, really showy, be suspicious that energy has gone into enlarging the bracts or changing the color, and it takes energy away from pollen and nectar production.” (as interviewed by Margaret Roach at “A Way to Garden” (link).

Let’s phase out Kwanzan cherry trees from local giveaways.

In a big place like Vanderbilt or Centennial Park with mature oaks, maples, elms, tulip poplar and other natives, a few Kwanzan cherries aren’t going to matter much. 

*But in a little yard with room for one tree, a homeowner needs a tree that can pull its weight in the foodweb, or they’ll have to “borrow” ecosystem services from the yard next door.*

I stood underneath one of these pompom cherries at Vanderbilt last week and did not observe a single insect, but behind me on the same sidewalk was a native redbud mobbed with bees, flies, wasps of all sizes, all making a living. 

See the article “Nectar and pollen production in ornamental cultivars of Prunus serrulata” (link) with this quote: “The double flowers of P. serrulata ‘Kanzan’ offered only tiny amounts of nectar and pollen. The total mass of sugars was 0.59 mg per flower and that of pollen 0.08 mg per flower…Therefore, if pollinator-friendly arrangements are made in urban areas, these cultivars should not be planted.”

We have run out of time and room to plant just for pretty.

In contrast, our native Black cherry (Prunus serotina) has flowers with nectar and pollen, fruit that feeds birds, mammals, turtles, insects, and leaves that “make” 320 different Lepidoptera species in Nashville (as a caterpillar host plant).

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Redbud Fruit

If you’re sad the recent rain knocked flowers off a redbud, look closely to find what’s left on the tree: developing fruit. Those mini pea pods are adorable.

Redbud nectar is popular with bees, flies, and wasps, so all the flowers usually get pollinated, and a fertilized flower will drop its extra bits as the ovary swells into a tiny pea pod, which grows into a bigger pea pod, which holds the seeds that make new trees.

Redbud flowers are a delicious nibble as is, but to me, the pods aren’t great raw. Even young, tender, green ones need a short blanch, which is too much trouble to do more than once.

But the important thing about a redbud is how it can feed our whole foodweb with all its parts, and how it can be a gorgeous street tree for the rest of us, all year. 

Especially if it’s not a cultivar that messes around with leaf color. Red or purple leaves are an anti herbivory tactic, and butterflies and moths will not lay eggs on them. So if you want your redbud to make new butterflies, go green.

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Cedar apples!

Not real apples, and not a real cedar, but galls on a juniper (Eastern red-cedar). They arrived late this year, unlike the Crossvine and the chiggers, who are both weeks too early.
Cedar apples are a fascinating fruit of spring, but fruit only in the sense of fruiting sporangium.
Spore horns!
Tentacular, gelatinous, telial arms!

The chocolate brown galls were dormant all winter, but yesterday’s rain triggered each little pimple to sprout a slimy, orange tentacle.

They do this because of their partner in slime: a nearby tree in the apple family.
The two plants pass to each other the perfect ingredients for Cedar Apple Rust, a.k.a. Gymnosporangium juniperi-virginianae, which I can never spell without cheating.

If you’ve got a nearby Eastern red-cedar, run out and look. The orange will start drying any minute. Tentacles shrink and get crispy, and a few days later will fall off to leave the chocolate brown galls all bare and pimply again.

The lifecycle of the Cedar-Apple Rust is fascinating, and I love these wacky things, but I admit that if I owned an orchard, I would not be as pleased to see them, as they can result in spotty apples that customers might not buy. 

But I don’t own an orchard, so I can celebrate this weird and wonderful sign of spring.

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Twig Watch

Here’s a quick, general reminder to find your nearest tree with low branches.
What is happening on it?
April is prime baby-leaf time. They grow up fast, so please hurry to see oak leaves the size of a pinky fingernail,
or hackberry leaves the size of a lacewing wing,
or sycamore leaves, sugar maple leaves, and redbud leaves shockingly small, fresh, and perfect.

Like these Shumard oak leaves emerging from winter buds along with male catkins. The pollen paints the street yellow!

This oak’s branches are too high to see, but squirrels drop twigs on the sidewalk every day this time of year. They gnaw on lots of things to file their incisors—which never stop growing—but they also enjoy spring salads at the tip of a twig.

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Bio:
Joanna Brichetto is a naturalist and writer in Nashville, the Hackberry-tree capital of the world.
She writes about everyday marvels amid everyday habitat loss at SidewalkNature.com and Instagram (@Jo_Brichetto); and her essays have appeared in Short Reads, Brevity, Ecotone, Fourth Genre, Hippocampus, The Hopper, Flyway, The Common, The Fourth River, and other journals.
Her book is forthcoming from Trinity University Press: This is How a Robin Drinks: Essays on Urban Nature.