Forest Vines to Snow Tussocks: The Story of New Zealand Plants
Structurally, the tropical rain forest is considered to have five strata; three tree layers, a layer of shrubs and a ground layer of herbaceous plants. This contrasts with most temperate forests where, at most, three strata are recognised; tree, shrub and ground.
The uppermost layer of very tall trees in the tropical rain forest is often discontinuous and the individual trees are referred to as emergents. This might be taken to imply that the 'emergents' grow through and above the canopy formed by the second tree layer, but studies indicate that many of them are light-demanding species which establish themselves early in a forest's history, grow rapidly, and initially form a continuous layer. As the lower forest layers close up, the forest floor becomes more shaded, many emergents cease to regenerate, and in time the highest tree stratum becomes discontinuous as old emergents die and are replaced only sporadically in canopy gaps.
In the conifer broadleaf forest five strata can usually be recognised, although they are lower in stature than their tropical equivalents:
|(a)||Emergent trees (30-40 m): mostly conifers.|
|(b)||Canopy trees (20-25 m).|
|(c)||Subcanopy trees (10-15 m): including our only native palm, the nikau (Rhopalostylis sapida) and Cyathea and Dicksonia tree ferns.|
|(d)||Shrubs and small trees (3-8 m).|
|(e)||Ground plants (0-1 m): mostly ferns, but some flowering plants particularly in the north.|