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N-P

N

nitrogen-fixing plant

A plant that can assimilate and fix the free nitrogen of the atmosphere with the aid of bacteria living in root nodules.

nodule

Nitrogen-fixing root swelling of characteristic shape and size for particular leguminous species that contain rhizobia. If the rhizobial strain is effective, atmospheric nitrogen can be fixed and is readily utilizable by the plant.

normal-aged forest

A forest composed of a series of age classes in proportions that permit sustained yield by felling under an appropriate system.

nursery stock

Shrub or tree species grown in a plant nursery for planting out elsewhere.

O

open forest

A 'forest' where the canopy is not closed and a large proportion of the area does not carry trees.

organic farming

The production of crops from land that does not receive and has not received (for a stated period of time) any inorganic inputs (fertilizers, pesticides, and so on).

ornamental

Any tree or plant that is planted for its beauty. This does not mean that it has no other uses. For example, Chlorophora excelsa is often planted as an avenue tree along roadsides (in Uganda); its stately appearance in no way diminishes its usefulness for timber. Ornamentals with other uses in agroforestry are the Cassias and Senna spp.

overstorey

The portion of trees in a forest stand forming the upper crown cover.

P

palm

Member of the Aracaceae (previously Palmae) family, containing over 200 genera and more than 2700 species, many of them economically important for food, fibre, canes, waxes, wood, thatch, and so forth.

permaculture

'Permanent agriculture'. The design and maintenance of sustainable, ecologically favourable, energy efficient agricultural and horticultural systems. The concept includes not only agroforestry but the integration of organic farming principles and intermediate technology, the use of renewable resources and recycling, the exploitation of biodiversity, conservation and habitat protection,as well as social and institutional well-being. It can be applied to urban as well as rural environments.

pest

In the general sense, an insect pest, fungal or viral pathogen, weed, or avian or mammalian pest (birds, rodents).

pH

A numerical measure of the acidity, or hydrogen ion activity, of a soil. The neutral point is pH 7.0. All pH values below 7.0 are acid and all above are alkaline. A change of one unit in pH value represents a tenfold change in hydrogen-ion concentration. pH represents the `intensity' of acidity, not the total exchangeable hydrogen or 'quantity' of potential acidity.

plant nursery

A specially prepared site for germinating seeds and looking after seedlings and young plants under conditions favourable for their growth and development. Facilities for vegetative propagation are also often present.

plant population

The number of plants per unit area. Sometimes referred to as 'plant density 'or 'planting density'.

pollarding

Cutting back in more or less systematic fashion the crown of a tree but leaving a main trunk to 1.5 m or so, with the object of harvesting small wood and browse, of producing regrowth beyond the reach of animals or of reducing the shade cast by the crown.

practice

In agroforestry, a particular use of land involving woody and non-woody plants in some spatial (simultaneous) or temporal (sequential) arrangement. For example, hedgerow, intercropping, homegardens, shifting cultivation. Sometimes referred to as an agroforestry 'technology'. An'agroforestry system' is a specific example of a practice.

propagate

To increase the number of a given plant type. Propagation can be by seed, root sucker, stool, stump, root, stem or leaf cutting, grafting, layering or by micropropagation.

provenance

The place in which any stand of trees is growing. The stand may be indigenous or non-indigenous.

pruning

1.     The process of cutting back growth of plants, including roots, but more particularly, side branches of trees, or the sides and tops of hedges.

2.     General term to describe the removal by cutting of buds, stems, or entire branches.

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