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Squirrels & Wildlife

Are Squirrels Beneficial to the Environment? Yes, Hugely

Squirrels plant most of the oak trees they forget about, spread fungi that trees need, and feed every predator above them. The full ledger.

By Zakaria 2 min read Save to Pinterest — opens Pinterest in a new tab
An acorn splitting open and germinating among dead leaves on the forest floor
Photo: artverau, Pixabay Content License, via Pixabay
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Squirrels are among the most effective tree planters in the northern hemisphere, and they do it entirely by forgetting where they put things.

What they actually contribute

roleeffect
Seed dispersal and cachingregenerates oak, hickory, walnut, beech
Mycorrhizal spore dispersaltree nutrient uptake
Prey basehawks, owls, foxes, martens, bobcats
Cavity and drey creationreused by owls, bats, flying squirrels
Soil disturbancesmall-scale aeration and litter turnover

Where the ledger flips

regiongrey squirrel status
North Americanative keystone disperser
Britain, Irelandinvasive; displaces red squirrels
Parts of Italyinvasive, spreading
Red squirrel range (Eurasia)native, same ecological role

Squirrelpox is the mechanism, not competition alone

Greys carry squirrelpox and are largely unaffected by it; reds that catch it usually die. That, more than direct competition for food, is why the British red squirrel retreated so fast after greys were introduced in the nineteenth century.

The bark-stripping cost

Late spring and early summer, when sap is running, greys strip bark from young broadleaves — sycamore, beech and oak especially. A fully girdled stem dies. In a mature mixed woodland the planting benefit swamps this; in a commercial plantation of fifteen-year-old broadleaves it does not, which is why forestry views the same animal very differently from ecology.

The useful thing a garden can do

Leave a dead or dying tree standing where it is safe to do so. Cavities in standing deadwood are the limiting resource for squirrels, owls, bats and woodpeckers alike, and nothing you plant replaces one for fifty years.

Common questions

What is the main ecological benefit of squirrels?

Tree planting, by accident. A grey squirrel caches thousands of nuts a year in separate single-nut holes and fails to recover a substantial share of them — estimates commonly run from a quarter to well over half. Each forgotten acorn is an oak seed planted at the right depth, away from the parent tree. Oaks, hickories, walnuts and beeches depend on this far more than on wind or gravity.

Do squirrels do anything besides spread seed?

Three more things that matter. They disperse the spores of mycorrhizal fungi, which tree roots need to take up nutrients, through their droppings after eating underground truffles. They are a core prey species for hawks, owls, foxes, martens and bobcats. And their nest cavities and abandoned dreys are reused by owls, bats, wood ducks and flying squirrels.

Are grey squirrels beneficial everywhere?

No, and this is the honest qualification. In Britain, Ireland and parts of Italy the Eastern grey is an introduced species that has displaced the native red squirrel, largely by carrying squirrelpox without being harmed by it, and it strips bark from young broadleaf trees at a scale that affects forestry. The same animal that is a keystone seed disperser in North America is a damaging invasive in Europe.

Do squirrels damage trees?

Some, mainly through bark stripping in late spring and early summer when sap is running, which can girdle and kill a young tree. Set against that, the same population is planting replacements continuously. In a mature mixed woodland the net effect is strongly positive; in a plantation of young broadleaves it can be negative enough to matter commercially.

Is it true squirrels forget most of their nuts?

They forget some, but less than the popular claim suggests. Squirrels use spatial memory and scent, and recovery rates in studies are often good. The figure that matters ecologically is not the proportion forgotten but the absolute number — a squirrel caching several thousand nuts leaves hundreds in the ground even at a high recovery rate, and that is enough to regenerate a woodland.

Should I encourage squirrels in my garden?

In their native range there is no reason not to tolerate them, and feeding is a separate question from encouraging. In Britain and Ireland, where greys are invasive and reds are protected, deliberately feeding greys is discouraged and in some contexts regulated. Either way, a garden with mature trees supports squirrels whether you feed them or not.

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