Tree hollow

A tree hollow or tree hole is a semi-enclosed cavity that forms naturally in the trunk or branch of a tree. These hollows are mostly found in old trees, whether they are still alive or not, and can appear in many different kinds of trees. They are a common sight in natural forests and woodlands, and they provide an important home for many living things, including fungi and various animals.

Hollows usually form because of natural forces that put stress on the tree. These forces can include wind, fire, heat, lightning, rain, or even attacks from insects like ants or beetles. Sometimes trees also create hollows by dropping lower branches as they grow older, leaving open spaces where the branches once were. Animals often help shape these hollows further using their beaks, teeth, or claws.

The size of a hollow often depends on how old the tree is. For example, eucalypts start forming hollows when they are young, but only when they reach about 120 years old do they create hollows big enough for animals to use. It may take as long as 220 years for a tree to develop hollows large enough for bigger animals. Hollows in fallen trees are also very important for animals like echidnas, numbats, chuditch, and many reptiles. In streams, hollow logs can give shelter to aquatic animals and help them lay eggs.

Hollows are vital for many wildlife species, especially when animals depend on them and cannot live without them. Animals use hollows to rest during the day or night, to raise their young, to keep warm or cool, and to help them travel and spread out. They choose hollows based on how big and shaped the entrance is, how deep it is, and how well it keeps them insulated from the weather. In Europe, scientists are especially interested in how tiny animals, such as invertebrates, use hollows. One beetle called Osmoderma eremita, that lives in hollow trees, is protected under European Union laws.

Description

A tree hollow is a cavity inside a living tree. These hollows often form when a tree branch breaks and creates an opening in the bark, exposing the sapwood. Over time, fungi and bacteria break down the wood, forming a space inside the tree. These spaces can sometimes fill with water, creating wet or dry habitats for many animals. Birds like woodpeckers and bluebirds, as well as insects, all make their homes in tree hollows.

Non-excavated hollows

Non-excavated hollows form naturally in trees after they have been damaged and decayed by things like fungi, insects, fire, or weather. These hollows are not made by animals digging them out, but rather by the tree itself weakening over time. They can be caused by events such as lightning strikes, heavy snow, or even large animals like red deer bumping into the tree.

There are several types of non-excavated hollows. Knotholes happen when a branch breaks off from the main stem of the tree. Chimneys form when a stem breaks and leaves an opening facing upward. Cracks appear when the trunk of the tree splits apart. Trunk holes are cavities that develop in the main stem of the tree, and if they are narrow and long, they are called slits. These natural hollows often become homes for many birds and other small animals.

Artificial hollows

Animals sometimes use man-made objects instead of natural tree hollows to live in. For instance, small animals like pygmy possums might stay in the chute of a grain silo, and birds called pardalotes can be found in the top part of a children's swing pipe. To help wildlife, people build special homes called nest boxes, such as birdhouses and bat tubes, which are made to suit different animals. These boxes are placed at certain heights and have entry holes of specific sizes.

Tree hollows can also be made by people using tools like chainsaws. By cutting into a tree and covering the hole partly with wood, these spaces become safe homes for animals like mammals and birds. Unlike nest boxes, these artificial hollows last longer and offer better protection from temperature changes. Natural hollows are still the best for habitat conservation, but these man-made options are helpful when natural ones are scarce.

Around the world

Conservation of animals that use tree hollows is important around the world. In North America, birds like the eastern bluebird need nest boxes because there are fewer natural hollows. In Scandinavian forests, many bird species depend on dead trees with hollows, but these trees are becoming scarce.

In Australia, many animals such as birds, mammals, reptiles, and amphibians rely on tree hollows. Sadly, about 100 of these species are rare or threatened because hollow-bearing trees are being removed. Threats include cutting down trees for timber or firewood, land clearing, and animals like cattle that damage trees. Pests like the common myna also compete for these valuable homes.

In parts of Russia, China, and Korea, Asian black bears use large tree hollows to spend winter and give birth. However, these areas face serious threats from deforestation and hunting, which destroy the trees bears need. Efforts are being made to restore some damaged trees, though it remains a challenge.