A tree throw or tree hole is a bowl-shaped cavity or depression created in the

subsoil Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus. The su ...

by a

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 ...

. They are formed either by the long-term presence and growth of tree roots or when a large tree is blown over (as a windthrow) or has its stump pulled out which tears out a quantity of soil along with the roots. The resultant hole will often slowly fill with organic material and can be identified during

archaeological Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. The archaeological record consists of Artifact (archaeology), artifacts, architecture, biofact (archaeology), biofacts or ecofacts, ...

fieldwork. The pit left in the ground after a rootwad is removed can be several meters across and deep. Fresh tree throws also provide a degree of shelter amongst the roots for animals. Some also contain evidence of prehistoric human activity such as flint tools suggesting that they were sometimes used by people in the distant past. Tree throws expose

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 ...

-poor,

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

-rich soil. Over time the hole will fill with rain water, fallen leaves, animal excrement and other organic matter which over time becomes a habitat for decomposers which soon form a community on the thick organic layer and so are able to nurture certain types of organisms. Tree throws contribute to bedrock weathering and

soil formation Soil formation, also known as pedogenesis, is the process of soil genesis as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order ( anisotropy) within soils. These alteration ...

, and why it is fastest in soils of intermediate thickness. In thin soils, fresh bedrock fragments are a large proportion of the upturned rootwad, but trees are sparse; in deeper soils less rock is upturned, but trees are more common, and in soils deeper than the depth of roots, no bedrock is upturned. The advent of trees roughly 370 million years ago led to dramatic ecosystem changes, as before then bedrock weathering was too slow to maintain thick soils in hilly terrain. Pits from tree throws, together with mounds from decaying fallen trees, are part of the characteristic

pit-and-mound topography Pit and mounds are small, persistent microtopographical features that present themselves after a disturbance event occurs and uproots trees via windthrow. The uprooted tree falls, and a pit forms in the forest floor where the root mass and associa ...

old growth forest An old-growth forest or primary forest is a forest that has developed over a long period of time without disturbance. Due to this, old-growth forests exhibit unique ecological features. The Food and Agriculture Organization of the United Natio ...

References

Archaeological features Soil science {{archaeology-stub

See also

References