Role in the ecosystem
Squirrels not only use the forest to live and eat, but also help the forest in its process of renewal. In years of high seed production, particularly those species that are prefered by squirrels (hazel, beech, chestnut, stone pine, Scots pine), squirrels store part of the collected seeds.
It is a nice experience to see a squirrel take in its mouth a nut fallen on the ground, start looking around, stopping to dig a small hole 2-4 inches deep with the front legs so to place the nut with the help of the muzzle and cover it with earth. This behaviour is called "caching" or "hoarding". In autumn, when the nuts or cones of conifers are ripe, the squirrels may take up to an hour to hide groups of 1-5 seeds rich in energy in holes dug in the ground. Many of the hidden seeds will be recovered by the animals in winter and spring, but some will be forgotten. The seeds left in the ground will have the chance to germinate and give rise to a new plant.
The caching behaviour of seeds by squirrels is very important for the renewal of many tree species, particularly plants that produce heavy seeds that have few chances to sprout when they fall near the parent plant. In this case, the squirrels promote germination by hiding the seeds far from the trees. Much of the renewal of chestnut trees in mixed forests, for example, depends on the squirrels, as well as the renewal of the stone pine is related to the action of seed dispersal conducted by nutcrackers and squirrels; squirrels also help the renewal of beech, hazel and, to a lesser extent, oaks.
The red squirrel eats many mushrooms, including the hypogeous ones (truffles and similar species). This action is very important because the fungi are essential for the growth of many plants. Between the roots of plants and the subterranean fungal filaments (hyphae), in fact, a symbiosis is established: the fungus gives water and minerals to plants and receives from them processed organic matter. When the squirrel eats the mushrooms, it ejects the spores (the reproductive part) in the feces. Falling onto the soil, they can germinate, giving rise to a new fungus and a new association with plants. Squirrels, mushrooms, and trees are thus linked by very complex mutual ecological relations which altogether ensure the presence of the rodent, but also of plants and fungi.
The grey squirrel has a strategy for the storage of seeds and the consumption of mushrooms that is quite different from the red squirrel, so the replacement of native species with the American species could have negative effects on the composition and functioning of the woods.