Above: Euglena, a microscopic single-celled alga is a common inhabitant of wet tree holes. There are many
species of Euglena and some are extremely flexible, changing shape as they move in characteristic euglenoid
movements. Euglena swims by means of its whip-like flagellum. Many Protozoa may also be seen under the
microscope, such as ciliates like Paramecium and Amoeba. Under the microscope the woodland becomes a very
bizarre and alien scape! Euglenoids often have green chloroplasts for photosynthesis.
Many ancient trees have hollow trunks, depending on species. Tree holes are an important part of the ecosystem
since they support a variety of life. Rot holes form when bark is damaged, either by wind, animals or lightning or
by pollarding, coppicing or pruning. Often, the tree will form scar tissue (calluses) which will slowly close over the
wound, over many years, preventing infection, but sometimes fungi take root and rot the dead heartwood. Even if
the wound closes over, fungi may have gotten inside and will slowly rot away the heartwood. This is fine for an old
thick tree, since it loses weight and so is more stable in high winds and the fungi break down the heartwood and
leave a nourishing compost inside the hollow trunk, into which trees grow roots down the inside of their trunks, top
absorb and recycle the valuable nutrients released.
Pans are shallow depressions in the tree, lined by unbroken bark, and a result of the natural growth of the tree.
They often form when overcrowding of branches distorts the trunk or its branches, perhaps as they fuse or graft
Spaces may also appear beneath a tree where soil erosion exposes the main roots, or where the tree grew over an
obstacle, such as a dead tree, which has rotted away.
Rot holes and pans are found frequently in a number of hardwoods, such as beech, ash, oak and hornbeam, but
are less common in conifers, since conifers produce copious resin which seals wounds very quickly and prevents
their infection, though some conifers may have them, including the silver fir.
Dry tree holes harbour a different ecosystem, and are frequented by centipedes, spiders and overwintering
ladybirds and they make excellent homes for larger animals. Large holes may harbour owls, smaller holes starlings,
blue tits, great tits, nuthatches and pied flycatchers. These birds may modify the hole by lining it with oak leaves,
bark or grass, according to species. Holes high in the tree may be the home of squirrels or bats, holes lower down
may be the homes of mice, stoats and wildcats.
If you have access to a microscope then why not take a sample of water and sediment from a tree hole and take a
look - you never know what you may find!
Click here to see what else might be living inside tree holes!