If squirrels disappeared entirely, the ripple effects would touch everything from forest regeneration to the diets of hawks and foxes to the health of underground fungal networks that keep trees alive. Squirrels sit at a busy intersection in ecosystems around the world, and removing them would create gaps that no single animal could easily fill.
Forests Would Lose a Key Tree Planter
Squirrels are scatter hoarders. They bury nuts and seeds across wide areas, and the ones they forget to retrieve germinate into new trees. This isn’t a minor contribution. Oaks, walnuts, hickories, hazelnuts, chestnuts, and certain pines all depend on animals like squirrels to move their seeds away from the parent tree and into soil. Eastern gray squirrels, for example, will bury a hazelnut faster than they can eat one, making caching the default behavior for large portions of their diet.
Many of these tree species have evolved specifically to encourage this. Acorns from red oaks contain high levels of bitter tannins that discourage squirrels from eating them immediately, nudging the animals to bury them instead. Black walnuts have convoluted inner structures that make on-the-spot eating tedious, again favoring burial. Without squirrels performing this service, fewer seeds would end up in the right conditions to sprout. Over decades, that would visibly change the composition of temperate forests, with oak, walnut, and hickory regeneration slowing or shifting to rely entirely on gravity and water, which disperse seeds far less effectively.
Underground Fungal Networks Would Shrink
Beneath the forest floor, vast networks of mycorrhizal fungi connect to tree roots and supply them with water and nutrients they can’t access on their own. These fungal networks are essential for seedling survival, forest productivity, and overall tree health. Squirrels, particularly flying squirrels, play a surprisingly important role in keeping these networks thriving.
Northern flying squirrels are fungal specialists. Their diet is dominated by underground fungi, and as they travel through the forest and deposit fecal pellets, they scatter viable fungal spores into new areas of soil. Because northern flying squirrels maintain large home ranges, they spread spores across wide stretches of forest. Losing them would limit how far and how quickly mycorrhizal fungi colonize new ground, which in turn would slow tree growth and make forest regeneration harder, especially for young seedlings that depend heavily on fungal partnerships in their first years.
Other animals eat fungi too, including birds, reptiles, and other small mammals. But few do it as consistently or across as wide an area as squirrels, making them difficult to replace in this role.
Predators Would Lose a Reliable Food Source
Squirrels are prey for a long list of predators: hawks, owls, goshawks, foxes, coyotes, bobcats, weasels, and snakes all eat them regularly. In mainland Europe, goshawks count red squirrels among their important prey items, and the relationship is similar across North America with red-tailed hawks and barred owls feeding on both tree and ground squirrels.
That said, most of these predators are generalists. Goshawk diets during breeding season, for instance, are roughly 79% birds like pigeons, crows, and game birds, with squirrels making up a smaller share. So squirrel extinction wouldn’t likely cause the collapse of any single predator population. What it would do is remove one reliable option from the menu, forcing predators to increase pressure on other prey species like rabbits, songbirds, and voles. That redistribution of hunting pressure could trigger its own chain of population shifts, particularly in ecosystems where squirrels are abundant year-round and serve as a buffer prey species during lean months.
Grasslands and Soil Would Change Too
It’s not just tree squirrels that matter. Ground squirrels are ecosystem engineers. Cape ground squirrels in semi-arid grasslands, prairie dogs’ close relatives in North America, and other burrowing species physically reshape the landscape. Their digging moves nutrients from deeper soil layers to the surface, loosens compacted ground, and creates cooler, moister pockets where seeds can germinate.
Research on Cape ground squirrel burrows found that burrow sites had greater plant cover and species richness than surrounding areas, particularly for disturbance-dependent shrubs. Those shrubs, while rarely eaten by the squirrels themselves, provide valuable forage for antelope and shelter for invertebrates and small mammals. Ground squirrel feces also deposit nitrogen into surrounding soil, further enriching the area. Without these burrowing activities, semi-arid grasslands would lose pockets of biodiversity that support a wider community of animals.
Cities and Parks Would Feel It
In urban environments, squirrels are one of the most visible and ecologically active wild mammals. Their disappearance would create a mix of benefits and losses that might surprise people.
On the positive side, urban trees would suffer less bark stripping damage, a common problem caused by gray squirrels gnawing on trunks and branches. Bird feeders would become far more productive for their intended visitors. Studies in the UK found that gray squirrels at feeding stations can reduce the amount of food birds manage to eat by over 90%. Squirrels also raid bird nests, eating eggs and chicks, so songbird nesting success would likely improve in parks and gardens.
On the other hand, cities would lose an effective and free waste removal service. Research has shown that eastern gray squirrel abundance is a main driver of littered food removal in urban parks. Where squirrels are plentiful, dropped food is cleaned up faster and more completely. Without them, parks would see more food waste sitting on the ground, potentially attracting rats or other less welcome scavengers. Cities would also lose the seed dispersal squirrels provide in parks and urban green spaces, potentially making it harder for urban tree canopies to regenerate naturally over time.
The Gaps Other Animals Can’t Fully Fill
Jays and crows also scatter-hoard nuts. Mice and chipmunks cache seeds. Other small mammals eat fungi and dig burrows. So some of what squirrels do would continue at a reduced level. But the scale matters. Squirrels exist on every continent except Antarctica and Australia, numbering in the billions globally. They cache enormous quantities of seeds, disperse fungal spores across large home ranges, aerate soil over vast areas of grassland, and serve as prey for dozens of species simultaneously.
No single replacement species does all of these things at the same volume. Jays cache acorns but don’t eat fungi or dig burrows. Chipmunks hoard seeds but cover far less ground. Rabbits feed predators but don’t plant trees. The loss would be distributed across many ecological functions at once, each one slightly degraded, and the compounding effect over years and decades would reshape forests, grasslands, and urban green spaces in ways that would be slow to notice but difficult to reverse.