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How Do Squirrels Affect Oak Trees? Planting and Damage

Squirrels plant red oaks by caching bitter acorns they never recover — and strip bark from young oaks. The two effects pull in opposite directions.

By Zakaria 2 min read Save to Pinterest — opens Pinterest in a new tab
Two green acorns in their cups on an oak branch among lobed leaves
Photo: Couleur, Pixabay Content License, via Pixabay
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Squirrels plant oaks and injure them, and which effect you see depends entirely on whether you are looking at a woodland or at one young tree in a lawn.

Why the acorn choice matters so much

white oak acornred oak acorn
Tanninlowhigh, bitter
Germinatesautumn, within weeksspring, after dormancy
Squirrel behavioureats it nowburies it
Consequencelittle dispersaldispersed and planted

A cached white oak acorn would sprout and spoil as a food store. The squirrel is making a storage decision on taste, and oak woodland composition follows from it.

Bark stripping, and when it happens

periodsquirrel foodrisk to oaks
Autumnfresh mastlow
Wintercacheslow
Late springcaches gone, mast not arrivedhighest
Summergreen acorns, fungi, budsmoderate

Trees roughly 10 to 40 years old, with smooth thin bark and sap running, take the damage. Mature oaks with thick fissured bark are largely left alone.

A complete ring of stripped bark is fatal

Phloem carries sugars down from the leaves. Sever it all the way round and everything above the strip dies, however healthy the crown looks that season.

Those green twigs on the lawn in August are not storm damage

Squirrels cut leafy twigs to get at unripe acorns and drop the rest. Clusters of fresh green oak twigs with cut ends, appearing in dry calm weather, are the signature.

Common questions

How do squirrels affect oak trees?

In two opposing ways. They are the principal dispersal agent for acorns, carrying them away from the parent canopy and burying them at planting depth — and the ones they never recover become the next generation of oaks. At the same time they strip bark from young oaks in late spring, which can ring and kill a sapling outright. On a woodland scale the planting dominates; on a single young tree in your garden, the bark stripping is what you will notice.

Why do squirrels bury red oak acorns and eat white oak acorns?

Tannin and germination timing. White oak acorns are low in tannin, palatable, and germinate within weeks of falling — a cached one would sprout and be lost, so squirrels eat them immediately. Red oak acorns are high in tannin, bitter, and stay dormant until spring, so they are worth storing. The result is that squirrels selectively cache exactly the acorns that can survive being cached, which is why red oak regeneration depends on them so heavily.

How many buried acorns actually become trees?

A small proportion of a very large number. Squirrels recover most caches by smell rather than by remembering locations, but studies put the forgotten fraction anywhere from about a quarter to three-quarters depending on species, year and food abundance. Most forgotten acorns are then eaten by other animals or rot. The survivors are still enough to regenerate an oak woodland many times over.

Why do squirrels strip bark from oaks?

Mostly in late spring and early summer, when they take the sweet sap-rich layer beneath the bark during the gap between winter caches running out and the new crop arriving. Young trees with thin smooth bark — roughly 10 to 40 years old — take the worst of it. A strip right round the trunk severs the phloem and kills everything above it.

Can you protect a young oak from squirrels?

A spiral guard or wire mesh sleeve around the lower trunk protects that section, though squirrels will work higher up a tree they can climb. Keeping other food available does not reliably help and tends to raise local squirrel numbers. For a single specimen tree, a mesh sleeve extended up the main stem is the practical measure.

Do squirrels eat acorns before they ripen?

They take green acorns off the branch through late summer, well before natural drop, which is one reason a garden oak can appear to produce almost nothing. They also cut and drop whole leafy twigs with acorns attached — the clusters of fresh green twigs that appear on lawns in August are usually squirrel work rather than storm damage.

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