Tree hollow

A tree hollow or tree hole is a space inside a tree trunk or branch. These hollows are most often found in old trees, whether they are still alive or not. They can be seen in many forests and woodlands. Hollows give a home to many living things, like fungi and animals.

Hollows form because of natural forces that put pressure on the tree. These forces can include wind, fire, heat, lightning, rain, or even insects like ants or beetles. Sometimes trees make hollows by dropping lower branches as they grow older. Animals can also shape hollows more with 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 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 important for many wildlife species, especially when animals depend on them. Animals use hollows to rest, to raise their young, to stay warm or cool, and to help them travel. They choose hollows based on how big the entrance is, how deep it is, and how well it keeps them safe from the weather. In Europe, scientists study 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 space inside a living tree. These spaces form when a tree branch breaks and makes a hole in the bark, showing the sapwood. Over time, fungi and bacteria soften the wood, making a room inside the tree. These rooms can fill with water, creating homes for many animals. Birds like woodpeckers and bluebirds, as well as insects, live in tree hollows.

Non-excavated hollows

Non-excavated hollows form naturally in trees after damage and decay. This can happen because of fungi, insects, fire, or weather. These hollows are not made by animals. They happen when the tree weakens over time. Events like lightning strikes, heavy snow, or large animals like red deer bumping into the tree can cause them.

There are several types of non-excavated hollows. Knotholes happen when a branch breaks off. Chimneys form when a stem breaks and leaves an opening facing upward. Cracks appear when the trunk splits apart. Trunk holes are spaces that develop in the main stem of the tree. 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 things made by people instead of natural tree hollows to live in. For example, 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 all over 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, some of these animals are rare or threatened because hollow-bearing trees are being removed. Threats include cutting down trees for timber or firewood, and land clearing. Pests like the common myna also compete for these homes.

In parts of Russia, China, and Korea, Asian black bears use large tree hollows for winter and to give birth. However, these areas face 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.