Beech Leaf Disease Reaches the Beech Forest at Cape Cod National Seashore

At the far end of Cape Cod, the Beech Forest outside Provincetown is an unlikely place for beeches, and a disease first recorded in Ohio in 2012 has now reached them. Park staff at Cape Cod National Seashore confirmed beech leaf disease in the forest in 2022.

Dark bands between the veins of leaves affected by beech leaf disease, which may be visible only when looking up at the leaves with light shining through them. NPS photo: Kristin Vinduska.

A forest that is an anomaly

A forest of beeches at the very end of the Outer Cape is somewhat of an anomaly: beeches typically need shelter from strong winds, access to water and deeper soils, and those are rarely found there. The land took shape when ocean currents picked up sand from Cape Cod's southern beaches and laid it down in long, parallel spits stretching north. Sediments that collected in the troughs between the spits made the rich soil where the beeches grow. The trees were spared when European colonists clear-cut the area, which left a desert-like landscape of eroding dunes with sparse poverty grass.

Beeches matter to the forest. Their nuts have been a culturally important food for Indigenous people traditionally associated with the area, and they feed black bears, deer, squirrels and many kinds of birds. The trees also shade the plants and animals of the understory. Losing them could change the canopy's structure and the mix of species, and could reduce services such as water filtration, biodiversity maintenance, carbon sequestration, and aesthetic, historic and recreational value.

The disease

Where beech leaf disease came from and how it spreads are still a mystery. Many beech species can be infected, including the American beech of the Beech Forest. The cause is thought to be a non-native foliar nematode, Litylenchus crenatae mccannii, a microscopic roundworm with a smooth, unsegmented body that feeds on a plant's outer surfaces or burrows into its tissue.

A nematode, a microscopic roundworm. Photo: Harold Grieb, U.S. Department of Agriculture.

This nematode feeds on the buds and leaves of the beech. When buds are attacked, the leaves are damaged before they even emerge and the tree cannot use them; it eventually drops them, spending valuable energy along the way. The tree's vigor falls, which can leave it open to secondary pests and, eventually, kill it.

The nematode's year, as the page describes it, runs like this. From August, juvenile and adult nematodes leave the leaves and spend the winter mostly in buds, occasionally in leaf litter. When the buds open in spring, none are found in the symptomatic leaves until late June or early July, yet DNA-based evidence confirms the nematode is there, presumably as eggs. Numbers rise through the fall and the cycle begins again, as more nematodes spread by unknown routes and more trees weaken. At certain times of year, leaves full of nematodes can be seen under a microscope.

What the seashore found

Staff noticed the disease in the Beech Forest in 2021 and confirmed it in 2022 during forest monitoring surveys, which run on a five-year rotation. They then set up five more monitoring plots there, to be checked every year. Each is a one-hundred-meter square broken into four modules; staff identify the species in the modules to estimate cover, and record tree density and diameter at breast height, which shows each year's growth. The disease has affected a large portion of the forest. Drought-filled summers or other environmental stress may be making the beeches more susceptible and contributing to their decline.

What happens next

No one knows what the future holds for beeches in the northeast. Seashore staff think the forest can recover, with native tree species replacing the beeches: despite its name, the wider forest is dominated by other species such as oak and pine. Recording what grows in the understory should show what might fill the gaps, and counting beech seedlings and saplings will give a better picture, year by year, of how much of the forest the disease has reached.

How the disease spreads, and how long symptoms take to develop, have not been confirmed. Birds may carry it, the page says, because it has turned up in random, secluded places, and it was found at the end of Cape Cod before anywhere else on the Cape, a hub for migratory birds. In the forest, other tree-dwelling animals and insects could move it from tree to tree.

Staff have looked into treatments, but most would be hard to use because of the risk to groundwater quality, and recovering trees could in theory be infected again. If some beeches are naturally resistant or tolerant, they could replace the susceptible ones. Researchers in Massachusetts and other affected states run forest monitoring programs to study how the disease moves and what treatments might work.

Symptoms to look for

• Dark bands between the veins of the leaves
• Cupped, deformed or shriveled leaves, which may be smaller than usual
• Thick, leathery leaves, unlike the papery texture of healthy ones
• Premature leaf drop
• Aborted buds, leaving sparse leaf cover
• A thinning canopy

These signs can appear at different stages of infection.

Leaves with beech leaf disease. NPS photo: Kristin Vinduska.

Healthy beech leaves, for comparison. NPS photo: Kristin Vinduska.

Infected leaves can be thick and leathery, unlike the papery texture of healthy ones. NPS photo: Kristin Vinduska.

Anyone who sees these symptoms can help by reporting them. The Massachusetts guide the page quotes asks for details of the location, the symptoms and their severity, and for pictures of the tree, all of which help officials track how the disease progresses in the Commonwealth.

Sources

• National Park Service, Cape Cod National Seashore, Beech Leaf Disease at Cape Cod National Seashore, written by Kristin Vinduska, NPS; the original's calling a nematode an insect is not repeated here; rewritten in hubnx's own words.