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Sycamores Are A Champion Streamside Tree In Our Watersheds

By Julianne Schieffer, Penn State Extension Regional Urban Forester

After late frosts this spring, in July we notice this ancient native tree species finally springing forth. Let’s look at the natural history of this adaptable tree to appreciate how it successfully survives as a champion streamside tree.

Fossil evidence exists that the Sycamore tree family has thrived for over 100 million years on our planet. The ancient Greek word sūkomoros’ (meaning ‘fig-mulberry’) likely influenced its common name sycamore.

The Latin name Platanus refers to broad, either referring to the plant’s broad leaf or the flat pieces of bark that explode off annually as the tree grows.

The relatively recent common name of button ball or buttonwood tree tells us that early colonists used the center of the fruiting structure and the wood for buttons. The fine-grained wood can be finely milled without cracking; perfect for producing long-lasting clothing and shoe buttons.

The fruit, really an aggregate of achenes around the hard “button” center, remain attached over winter and then shatter apart upon hitting the ground in spring.

The individual achenes resemble a small badminton shuttlecock with spikey hair around the barely weighted center seed, squeezing it point first into tight spaces like road cracks.

As a streamside tree, the sycamore’s fruit floats, and the light structure allows wind to disperse it. Mammals like muskrats, beavers, and squirrels and birds such as purple finch, goldfinch, chickadees, and dark-eyed junco also relish the seeds.

Remember the hard freezes in mid-April and May? Since late frosts tend to kill sycamore buds, the damaged trees characteristically have long dead twigs with bushy masses of leaves around their bases by midsummer.

Frosts and low temperatures in the North, and dryer conditions further west probably limit the sycamore’s natural Eastern North American range. Many of our sycamore trees exhibited this damage in 2020 and have since re-foliated.

Although low winter temperatures may also injure the cork cambium of the bark, the overall health of the tree remains unaffected.

However, sycamores still face damage from the naturally occurring fungus Apiognomonia, which causes sycamore anthracnose. The term anthracnose refers to dead areas on leaves, twigs, or fruit.

This fungus attacks as young leaves unfurl and forms large, irregularly shaped dead areas along leaf margins, veins, and in between. The ends of twigs may be killed back 8 to 10 inches. Cankers or dead areas may develop on the tree trunk and main branches.

Affected leaves fall early in the season only to be replaced by new leaves mid-season. Killing buds, young shoots, and leaves, stimulates new bud formation and more bud death and twigs results in a “witches' broom” proliferation of branch ends and an overall contorted branching pattern across the tree canopy.

Weather like frequent rains and cool temperatures promote the disease. Little or no anthracnose will occur if average temperatures during bud break are above 60 degrees. Few trees die from this yearly attack. Anthracnose may weaken a tree, however, making it susceptible to attack by other diseases.

Frost damage can both mimic and complicate anthracnose symptoms.

How does the sycamore tolerate these stresses that thwart healthy growth? One way is the presence of many dormant buds beneath the bark.

As a bud or twig dies back, other buds become released from their dormancy to take over thereby giving creating that witches’ broom or heavily twiggy appearance. This becomes a common identification feature for the species.

Or, in the case of heavy flooding along a waterway scouring vegetation from the banks and leaves off trees, a sycamore can rely on its ability to re-foliate along its entire living surface to continue to survive.

Another unique feature is how the base of a leaf stem encircles next year’s bud until the leaf drops, thereby protecting it from infection and bad weather until fall. The tiny buds then continue their growth in spring as another interesting protective leaf feature takes over.

After bud break, you may have also noticed that a sycamore twig develops peculiar little modified leaves called stipules encircling its buds or at twig junctions. These stipules protect the newly forming buds from damage.

Another tree with ancient lineage, the tulip poplar, employs the same tactic but loses its stipules after the leaf unfolds. Imagine the stipule as a little umbrella shielding water or wind containing the fungal spores of the fungal invader from the bud.

Finally, let’s get up close to the fuzz which completely coats new twig growth and all young leaves.

The “stellate” or “star shaped” hair, when looked at head on; can lodge into our nose tissues to cause irritation and allergies upon inhalation. However, the hairs at the leaf's margins, seen from their side, reveal that they're more "plumose," or "feather-like,".

Such hairs certainly protect the developing leaf's delicate tissue from water evaporation, intense sunlight, temperature extremes and physical damage. Surely an insect would think twice about chewing into that hair or finding a good foothold.

But how about a fungal spore gaining access to the actual leaf surface? This hair remains on the sycamore during the period when it is most susceptible to the anthracnose fungus.

Despite the environmental and biotic stresses hitting our sycamores, its long record and effective countermeasures assure us that it will remain one of the fast growing and largest diameters tree species in our area.

Small plant features add up to long-lived success!

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(Reprinted from Penn State Extension and Watershed Winds newsletter. Click Here to sign up for your own copy.

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