Take a walk in a winter forest and you can’t help but notice beech trees. Silky smooth bark and sand-colored dry leaves stick out like Christmas lights against a dull and gloomy background. While every other leaf drifted to the forest floor months ago, beech leaves hold tight like cat hair on a sweater.
It’s called marcescence – these leaves that just won’t drop – and it’s common in oak and beech (the trees are close relatives). But why keep the leaves? Are these trees just photosynthetic versions of hoarders?
One possible reason may be to protect that bud, the thin tapered structure often described as “cigar-shaped.” Inside the scaly covering are the beginnings of the new year’s growth. Hungry deer can ruin a tree’s plans for spring. But with beech trees, deer tend to get a mouthful of dry leaves whenever aiming for a yummy bud. (1)
What about attacks from smaller enemies? Insects seem to prefer infesting trees with leaves hanging on over winter. R. Karban decided to yank all the leaves off a few dozen small oaks and compare infestation levels of a tree-noshing wasp. (2) His numbers indicate that wasps prefer leaf-hoarding trees three-to-one compared to his denuded ones.
I believe Nature is constantly sending messages of wisdom if we’ll just listen. In this case, perhaps she’s saying “every action has an upside and downside, but with diversity, there’s always hope for a better future.”
- Svendsen, Claus R. 2001. Effects of marcescent leaves on winter browsing by large herbivores in northern temperate deciduous forests. Alces 37(2): 475-482.
- Karban, R. 2007. Deciduous leaf drop reduces insect herbivory. Oecologia. 153: 81-88.
Watch out, squirrel. You’ve got competition this autumn.
Acorn gathering and burying is often considered a squirrel hobby. Turns out, Blue Jays (Cyanocitta cristata) are pretty good at it too. Okay, really good.
Blue Jays have a pouch in their throat they can use to hold acorns (up to 5!). When they reach a caching site, the birds will spit up the acorns and bury them one at a time under leaves or in the dirt.
One study showed that Blue Jays were responsible for relocating more than half the acorns in a forested plot. (1) That’s over 130,000 acorns! And yes, the birds usually remember where they’re hidden. They’ll often place the morsels near “beacons” like rocks or fences.
Another study suggested that the birds were the most likely culprit in the spread of oaks after the last Ice Age (2). Most trees with heavy seeds returned slowly to the barren lands left when the glaciers retreated. But the oaks came back quickly. Squirrels couldn’t do that, but Blue Jays could.
- Darley-Hill S and Johnson WC. 1981. Acorn dispersal by the blue jay. Oecologia. 50(2) 231-232.
- Carter JW and Adkisson CS. 1986. Airlifting the oaks. Natural History. 95(10) 40-48.
By the way, Lego(R) came out with a bird series this year – and it includes the blue jay. They should add a small Lego acorn to go along with it.
See that tiny bump on the branch? You’re looking at a mom protecting hundreds of babies. Well, actually, the mama Oak Scale insect (Parthenolecanium quercifex) is dead now, but her exoskeleton is still harboring those little eggs underneath. When those baby Scales hatch around the end of May, the tiny darlings will move out to the oak leaves and begin to SUCK THAT POOR TREE DRY. They sniff out the precious sugar-water flowing through veins in leaves, insert their straw-like mouth parts and drink up. As the year progresses, Scales grow and mate. Mama lays her eggs beneath her and dies, making way for next May’s new generation.
(These are the eggs… um, on my kitchen table. Didn’t realize they’d pop out like that when I lifted the mama Scale off. Oops.)
In the insect’s defense, healthy trees can resist Scale infestations. Some leaves and twigs may fall off – that’s all. But trees that are weakened (by physical damage, drought, chemicals, etc.) can be killed by the insects.
Cool Climate Change research recently found that densities of Oak Scale are up to 13x higher in warm urban areas! (1) Since things are getting toastier here on Earth, we may want to get more familiar with the life & times of the Oak Scale.
1. Meineke EK, Dunn RR, Sexton JO, Frank SD (2013) Urban Warming Drives Insect Pest Abundance on Street Trees. PLoS ONE 8(3): e59687. doi:10.1371/journal.pone.0059687
A little dead White Oak (Quercus alba) leaf. Did you know you can prepare the acorns from this tree and grind them into flour? Oak pancakes!