Oak Tree Habitat, pt.2

In the last blog, we discussed oak trees as a keystone species, substantially affecting the types and abundance of other species in their habitat.  There are 400-500 species of oaks worldwide, supporting an extraordinary 2,300 wildlife species not including fungi, bacteria, and other microorganisms.  Oak trees in all stages of life and death have numerous biotic relationships with wildlife.

^{Badger in tree cavity by Byrdyak, Getty Images||Golden millipede in Lagos by efeghali, Getty Images||Neanura springtail by Henrik_L, Getty Images||Pileated woodpecker in oak tree by mtruchon, Getty Images||Slug & rollie pollies by Sonya Kate Wilson, Getty Images||Wood Mouse in tree cavity by byjohn, Getty Images}

Fungi are often identified as attacking oak trees, but they can have very beneficial relationships.  Fungi growing in the ground assist an oak tree in getting nitrogen, phosphorous, and other nutrients out of the soil, and in return get carbon and energy from the sugars in the tree’s sap.  Oaks provide a place to live for over 700 species of lichens, plus uncounted liverworts and mosses.  Lichens covering the oak’s surface help to keep them free of fungal infections and invasive insects.  Liverworts and mosses help oaks to retain water and release it into the soil over a long period of time.  As oak limbs fall and decay, water retention softens the wood providing food and habitat for decomposers.

Fallen oak leaves are slow to decompose due to their tannin and lignin content, both preservative compounds.  Leaf litter, composed of several layers of fallen leaves, becomes habitat for many millions of species including millipedes, springtails, woodlice, slugs, beetles, ants, and other organisms that feed on decaying plants.  Through their activities, the creatures of the leaf litter help to return nutrients to the trees.

Acorns, with high amounts of fats, proteins, and carbohydrates, are one of the healthiest and most sought after foods in the woodland.  White oaks, living between 200 and 300 years, will produce about 3 million acorns during their lifetime.  Many bird species eat acorns, but oak trees enjoy a special relationship with blue jays, whose beaks are strong enough to pry an acorn open.  In autumn, blue jays enjoy feeding on acorns, but also cache them for winter, burying several at a time under a few inches of soil in various locations up to a mile from the originating tree.  Although blue jays cache large quantities of acorns, they can only remember and retrieve about 25% of them, allowing many new oak trees to grow and spread into new areas.

Oak trees support 31 mammal species who consume acorns for food, use the tree for shelter, or use the surrounding habitat for hunting.  Gray squirrels and red squirrels favor acorns in the autumn and throughout the winter from caches hidden in nearby locations.  They remember far more cache locations than blue jays, but there are still uneaten acorns that will germinate in spring to start new trees.  Acorns are also a favorite food for badger, deer, wild board, and wood mouse. 

Oak trees offer shelter for many species.  Squirrels often build their nests high up among the leaves that provide protection from weather and predators.  Dead branches, especially those with cavities, may remain on the tree for many years, providing excellent roost sites for bats.  Open limbs, leafed areas, and cavities all provide nest sites for a variety of birds.  In addition, the many insects drawn to oak trees provide a ready source of food for all of these nesters.  Humans have been acorn consumers for millennia.  Raw acorns, high in tannin content, can be toxic in larger quantities; but, properly prepared, acorns are high in calories, vitamin C, starch, magnesium, calcium, phosphorous, and antioxidants.  They have been a food staple in many cultures and can be found in the records of ancient Greeks, Iberians, Japanese, and English.

Oak trees have many direct and indirect relationships with insects, which we will explore in the next blog.