Hanging On

Most winter trees fall into one of two categories we readily recognize. There are the deciduous trees, whose leaves fall off in winter, and there are the evergreen trees, who keep their leaves throughout the winter. But there are trees that don’t squarely fit into these categories.

beech-6

In the photo above, you are looking at an American Beech, which is a deciduous tree. And although its leaves have wrinkled and faded, they hang on tenaciously to the tree. Take a walk in the Sheldrake woods and you’ll notice them right away, like a ballroom of debutantes frozen in time, not ready to hang up their petticoats for the season.

beech-2

 

There is a name for what these trees are doing: marcescence, or the retention of dead plant organs. In deciduous trees autumn triggers a chemical change that makes the tree grow a layer where the leaf stems connect to the branch. This layer creates a separation between the leaf and the branch, and prevents water and nutrients from reaching the leaf. That separation, also known as abscission, is the reason leaves change color, shrivel, and fall off. But in marcescent trees such as oaks, beeches, and witch hazel, even though the abscission layer forms, and the leaves shrivel and fade, they do not fall off.

Why? Why would a tree want to hold on to dead leaves that can no longer produce food?

This is one of those delicious questions that we actually do not know the answer to. There are theories, but in the absence of sufficient testing, we cannot say which is correct.

Hypothesis #1: Protection from browsers

It is possible that marcescent leaves may provide cover for tree buds from large browsing herbivores such as deer or moose. Crumbly zero-nutrition leaves may provide a layer of deterrence, since animals would have to eat through the leaves to get to the nutritious buds and twigs they like to eat, if they can even see them through the leaves!

beech bud
This beech tree bud is protected by its tough wrapping and pointy tip, and is also tucked away between the tree’s dead leaves.

In support of this theory is that marcescent leaves are primarily found on lower branches and young trees, whose buds are within reach of browsers.

beech full
In the above follow the trunk of the beech tree with the marcescent leaves. You will see that all the leaves appear in the lower branches. The upper and middle branches are bare.

Hypothesis #2: Strategic decomposition

A second theory posits that there is an advantage to dropping the dead leaves in the spring, as new growth finally pushes off the old leaves. Marcescent trees such as beech and oak traditionally grow on infertile soil. It’s possible that by dropping the leaves in the spring, they will decompose at the time when the tree most needs the organic compost to spur new growth.

Personally I find this explanation less convincing, for it does not explain why only the younger trees or lower branches sport the dead leaves. Also, decomposition in winter is very slow due to the shorter hours of sunlight and the dormancy of many decomposers, so I am not certain there is much to be gained by waiting until spring to drop to the ground.

Hypothesis #3: Evolutionary vestiges

The first trees were all evergreens, keeping their waxy leaves through winter. As they succeeded and spread, they evolved to suit the different climates in which they found themselves. Some found it advantageous to shed their leaves over winter, to avoid freezing or depleting their nutrient store, and deciduous trees were born. It is possible that marcescent trees such as beeches and oaks are an evolutionary halfway point–deciduous trees that retain their (dead) leaves through the winter. Perhaps these clinging ghosts are an evolutionary vestige, like the human appendix or tailbone, which serves no function but has persisted over time. Lending support to this explanation is the fact that some beech and oak species are evergreens. The Southern Beeches are 43 species of evergreen trees and shrubs that until recently were classified in the same genus as beeches (They now have their own genus, Nothofagaceae, which translates to “bastard beeches.”). Their fossil record dates back to the Cretaceous period. Among oaks, the Quercus ilex is an evergreen.

What do you think? Which do you find most convincing? Whatever the explanation, take this time to walk in the woods and enjoy the rustle of the wind rattling these stubborn stragglers.

Jelly Fungus Among Us

ears
Photo credit: Svetlana Wasserman

They looked like a group of butterflies resting on a branch. But as I approached, the purplish wings morphed into something gelatinous, fleshy, and etched with veins. I touched them. There was something human and macabre about them, like severed decaying ears. I had mistakenly thought that winter was not a great time for mushrooms, but the rain of the previous day had launched an abundance of them.

ears-4
Photo credit: Svetlana Wasserman

What I was seeing was a member of an entire subgroup of mushroom–the jelly fungus, or for you Latin speakers, Basidiomycota. These particular ones are an example of Auricularia auricula, otherwise known as the Jelly Ear fungus. Perhaps not so pretty to look at, they perform a vital public service by decomposing dead wood. When weather is dry, they shrivel and harden, like an old cork. But once the rain returns, they quickly reabsorb water and recover their shape, size and color, and can begin to produce spores. This ability to dry, rehydrate, and revive with a small amount of moisture is a remarkable adaptation, allowing these fungi to endure.

Not ten paces from the first jelly fungus, I came across another oddity. Creamy yellow layers folded in and out of themselves, like buttercream roses. This was also a jelly fungus, growing right amid the turkey tail mushrooms that had already colonized this decomposing log (Some speculate that this fungus actually feeds on the turkey tails).

 

witch-butter
Photo credit: Svetlana Wasserman

This particular fungus is called witch’s butter. Legend originating in Eastern Europe holds that this mushroom was hung on doorposts by people to rid themselves of a witch’s curse. Piercing the fungus was said to banish the curse.

Like other jelly fungi, witch’s butter is very absorbent, and after a rain it can soak up so much water that it looks more like a slime. Once the water evaporates, the fungus shrinks back and the fruiting body remains dormant until the next rain.

witch-butter1
Photo credit: Svetlana Wasserman

Two sunny side up eggs? No, this is also witch’s butter fungus, but with more water absorbed than the one above. In case it is making you hungry, witch’s butter is edible, although allegedly tasteless. Its gelatinous consistency makes it a good soup thickener and if you are an adventurous eater, you can find these for sale at Asian groceries.

The next time it rains don’t miss the opportunity to seek out the jelly fungus among us, at Sheldrake or another woods near you.

The Hidden Lives of Leaves

Svetlana Wasserman

decomposition-11

During the warmer months, tree leaves inhabit the world above our heads, giving us shade and a pleasant rustle as they soak up sunlight and convert it to food. But as they swirl to the ground on these November days, the leaves reveal their hidden lives, if we care to look.

Pick up a leaf. If the surface has started to wear away, you’ll discover a jumble of tiny veins twisting and merging that may remind you of a map of lower Manhattan. This is the inner skeleton of the leaf. It provides both structural support for the leaf and is also part of the hydraulic system that transports water and nutrients from the tree roots to the leaves, and sugars from the leaves back down to the rest of the tree.

decomposition-14

These gossamer remains of the leaf are the handiwork of myriad decomposers, large and small. For example, while photographing these leaves, a tiny transparent worm smaller than one letter on my newspaper crawled out, and I could see the contents of the leaf it had been chewing inside its body.

decomposition-3
Do you know how tiny this worm is? The bar under it is part of one letter in a newspaper.

This little worm, along with slugs, snails, millipedes and miles of fungal roots are the workhorses that clear our forest floors of fallen leaves, and recycle the nutrients from the leaves back into the soil. That is one reason gardeners should consider mulching their leaves instead of relying on gas blowers to take them away. The mulched leaves provide premium free fertilizer! Instead of having your tax money used to pay composters to process the leaves, and then sell them back to you as mulch, you can ask your gardener to mulch mow your leaves, and make your own for free. Extra leaves can be blown or raked into a compost pile for the future.

slug
This slug works at rates far more favorable than your gardeners!

The fallen leaves reveal not only their beautiful inner structure, but also how important they are to sustaining forest life. Pick up a leaf and you are bound to see signs of it having provided room and board.

decomposition-9

Oak leaves, such as the one pictured above, support more life forms than any other native trees. They host hundreds of species of insect, supplying many birds with an important food source.

decomposition-21

The bumps on these leaves are galls made by the eggs of a small midge which lives inside. When the insects hatch, the leaf that hosted them becomes their food and in turn, they become food for birds and their squalling babies. These galls cause no harm to the tree, and are quite beautiful in spring when they are plump and pink.

oak-leaf-gall
Oak leaf gall in summer. Photo credit: Randy Rosenberger

Next time you are outside take a moment to pick up a few leaves. Look for signs that they have nurtured insects. Admire the remaining latticework, not only highly functional but hauntingly beautiful as well.

decomposition