A nurse log is a fallen

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

which, as it decays, provides

ecological facilitation Ecological facilitation or probiosis describes species interactions that benefit at least one of the participants and cause harm to neither.Stachowicz, J. J. 2001. Mutualism, facilitation, and the structure of ecological communities. BioScience 51 ...

to seedlings. Broader definitions include providing shade or support to other plants. Some of the advantages a nurse log offers to a seedling are:

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

thickness,

leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall, or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that has fallen to the ground. This detritus or dead organic material and its constituen ...

mycorrhizae A mycorrhiza (; , mycorrhiza, or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere, the plant root system and its surroundings. Mycorrhizae play ...

, disease protection, nutrients, and

sunlight Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...

. Recent research into soil pathogens suggests that in some forest communities, pathogens hostile to a particular tree species appear to gather in the vicinity of that species, and to a degree inhibit seedling growth. Nurse logs may therefore provide some measure of protection from these pathogens, thus promoting greater seedling survivorship.

Occurrence

Various mechanical and biological processes contribute to the breakdown of

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidit ...

in fallen trees, resulting in the formation of niches of increasing size, which tend to fill with forest litter such as soil from spring floods, needles,

, mushrooms and other flora. Mosses also can cover the outside of a log, hastening its decay and supporting other species as rooting media and by retaining water. Small animals such as various

squirrel Squirrels are members of the family Sciuridae (), a family that includes small or medium-sized rodents. The squirrel family includes tree squirrels, ground squirrels (including chipmunks and prairie dogs, among others), and flying squirrel ...

s often perch or roost on nurse logs, adding to the litter by food debris and scat. The decay of this detritus contributes to the formation of a rich

humus In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...

that provides a seedbed and adequate conditions for germination. Nurse logs often provide a seedbed to conifers in a temperate rain forest ecosystem. The oldest nurse log fossils date to the earliest

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

, approximately 300 million years ago.

References

Books

* Montagnini, Florencia, and Benedict, Carl F. Jordan (2005). ''Tropical Forest Ecology: The Basis for Conservation and Management'' (1st ed.). Berlin: Springer. . * Noss, Reed F. (Ed). ''The Redwood Forest: History, Ecology, and Conservation of the Coast Redwoods'' (1999). San Francisco: Island Press. * Mathews, Daniel (1999). ''Cascade-Olympic Natural History'' (2nd ed.). Portland, Oregon : Raven Editions.

External links

{{commonscat, Nurse logs * Mangan, Scott A., et al
"Negative plant–soil feedback predicts tree-species relative abundance in a tropical forest"
''

Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...

'', New York, 2010-June-25. Retrieved on 2010-June-25 Dead wood Ecology