Tree hollow

A tree hollow or tree hole is a semi-enclosed cavity which has naturally formed in the trunk or branch of a tree. They are found mainly in old trees, whether living or not. Hollows form in many species of trees, and are a prominent feature of natural forests and woodlands, and act as a resource or habitat for a number of vertebrate and invertebrate animals. A river red gum, with hollows. The younger trees surrounding it would generally not yet have developed hollows suitable for vertebrate species.Hollows excavated by the lesser spotted woodpecker (Picoides minor). Also fungus, which may also help in the formation of hollows through the decomposition of heartwood. A tree hollow or tree hole is a semi-enclosed cavity which has naturally formed in the trunk or branch of a tree. They are found mainly in old trees, whether living or not. Hollows form in many species of trees, and are a prominent feature of natural forests and woodlands, and act as a resource or habitat for a number of vertebrate and invertebrate animals. Hollows may form as the result of physiological stress from natural forces causing the excavating and exposure of the heartwood. Forces including wind, fire, heat, lightning, rain, attack from insects (such as ants or beetles), bacteria, or fungi. Also, trees may self-prune, dropping lower branches as they reach maturity, exposing the area where the branch was attached. Many animals further develop the hollows using instruments such as their beak, teeth or claws. The size of hollows may depend on the age of the tree. For example, eucalypts develop hollows at all ages, but only from when the trees are 120 years old do they form hollows suitable for vertebrates, and it may take 220 years for hollows suitable for larger species to form. Hollows in fallen timber are also very important for animals such as echidnas, numbats, chuditch and many reptiles. In streams, hollow logs may be important to aquatic animals for shelter and egg attachment. Hollows are an important habitat for many wildlife species, especially where the use of hollows is obligate, as this means no other resource would be a feasible substitute. Animals may use hollows as diurnal or nocturnal shelter sites, as well as for rearing young, feeding, thermoregulation, and to facilitate ranging behaviour and dispersal. While use may also be opportunistic, rather than obligate, it may be difficult to determine the nature of a species' relationship to hollows—it may vary across a species' range, or depend on climatic conditions. Animals will select a hollow based on factors including entrance size and shape, depth, and degree of insulation. Such factors greatly affect the frequency and seasonality of hollow use. Especially in Europe, entomologists are interested in the use of hollows by invertebrates. One beetle associated with hollow trees, Osmoderma eremita, has been given the highest priority according to the European Union's Habitat Directive. A tree hollow is a cavity in a living tree. Tree holes can be caused when an injury to the tree, such as breakage of a limb, creates an opening through the bark and exposes the sapwood. The sapwood is attacked by fungi and bacteria, which form a cavity in the bole of the tree. The resulting cavity can fill with water, thus becoming a type of phytotelma. Therefore, there are wet and dry tree holes. Tree holes are important habitats for many animals, such as Ceratopogonidae, Chironomidae, the common merganser, toucans, woodpeckers, and bluebirds. Tree holes can be important in the maintenance and spread of some diseases, for example La Crosse encephalitis. Hollows may be an adaptive trait for trees as animals provide the host tree with fertilizer. Animals have been found to use artificial structures as substitutes for hollows. For example, pygmy possums in the chute of a grain silo; or pardalotes in the top, horizontal pipe of a children's swing. Purpose built nest boxes, such as birdhouses and bat tubes, are also constructed for conservation and for wildlife observation. The size of the nest box, entry hole and placement height may be chosen in consideration of certain species. Natural hollows are still generally preferred for habitat conservation.