Fundamental Considerations

The Plant Layers.

  • The Overstory - the plant growth above ground furthest from the soil

    • The overstory is considered a canopy when it exceeds the 12-50ft [or 4-15m] threshold.

  • The Understory - the plant growth above ground closest to the soil

  • The Roots - the plant growth underground into the soil

The Soil Horizons.

  • Topsoils.

    • The Organic Horizon - the litter of organic matter that has yet to be decomposed

    • The Assimilation Horizon - the decomposers of organic matter and the products of decomposition

  • Subsoils.

    • The Eluviation Horizon - where the leaching of the products of decomposition takes place

    • The Banking Horizon - where the leached products of decomposition are deposited

  • Substrates.

    • The Material Horizon - the parent material from which soils have been formed

    • The Durable Horizon - the bedrock upon which soils rest

The Coverage.

  • The Crown-cover - the coverage with respect to the above ground competition for sunlight

  • The Ground-cover - the coverage with respect to the on the ground competition for room to grow

  • The Deep-cover - the coverage with respect to the below ground competition for soil nutrients

The Prevailing Vegetation Regime.

  • Forest - a regime in which a developed canopy prevails — trees growing at the top end or well above the canopy threshold provide the greater part of the crown-cover

  • Woodland - a regime in which a nascent canopy prevails — trees and shrubs growing at the lower end of the canopy threshold provide the greater part of the crown-cover.

  • Scrub  - a regime in which a canopy is lacking and shrubs, growing well-above the ground-cover but well-beneath the canopy threshold, form the crown-cover.

  • Field - a regime in which a canopy is lacking and the crown-cover is more or less equivalent to the ground-cover. The different types of field include:

    • Grassland (temperate or subtropical)

    • Steppe (semi-arid)

    • Savannah (tropical) 

    • Tundra (alpine & polar)

  • Desert - a regime in which the area without vegetation exceeds the area with vegetation. The different types of desert include:

    • Alpine desert

    • Polar desert

    • Temperate desert

    • Tropical desert

    • Anthropogenic desert (e.g., urban sprawl, industrial wastes)

The Life Zone.