Occurrence

Occurrence [ Ecology ]
(Also: Element Occurrence )

Dictionary of botanic terminology
index of names

The number of possible appearances of an element.

In ecology an occurrence is a general term describing the amount of elements of biodiversity (e.g. species or ecological community) found in corresponding but separate environments, divided by a natural barrier.
For example the number (or presence) of separate population of a given species (including sub-species, varieties and hybrids) found in a landscape, area of land and/or water.
An element occurrence has conservation value for the element: it is a location important to the conservation of the species or community. For a species, an element occurrence is generally the habitat occupied by a local population (identified by geographic and habitat information, number of individuals, age and dimension of the colony etc) What constitutes an occurrence varies among species. For an ecological community, an element occurrence may be the area containing a patch of that community type.

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Holdfast roots [ Botany ]
Dictionary of botanic terminology - index of names

Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.

Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans), develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994