The vertical structure defines the differences typically found at different heights in the woodland. The image above shows the various vertical layers of a woodland.
- The Ground layer is made up predominantly of leaf litter – rotting vegetation and leaves shed the previous autumn. Many creatures are to be found at this layer including slugs, snails and worms and invertebrates such as spiders, centipedes and millipedes. Microscopic organisms help decompose the litter and in doing so convert it into beneficial chemicals and minerals that can be absorbed by plants. The Ground layer is also made up of mosses, lichens and fungi.
- The Field layer is made up of grasses, ferns and flowering plants. The amount of growth at this layer varies hugely depending on how much light reaches through the canopy. Bramble and Nettle are often abundant but the more open the canopy the wider the variety of plants will be found including Bluebell and Anemone.
- The Understorey (or Shrub) layer is comprised of younger smaller trees and shrubs which have evolved to grow with less light. If the woodland is very dense then little light will get through and little will grow at the layer.
- The Canopy layer is made up of the leaves of the tallest trees. These receive the most sunlight and limit the light that reaches the lower layers. Species that survive under the canopy often do so either on the edge of the woodland or because they complete their life cycle in early spring before the canopy is fully developed. The trees that form the majority of the canopy tend to be considered the dominant species of the woodland.
The horizontal structure defines the differences typically found at different stands of a woodland. These differences can be caused by a number of factors including the depth and moisture level of the soil, fire, presence of rocks, rivers or bodies of water and plant disease of the presence of other plants. Generally you will find a wider variety of plants at the outside of a woodland as the canopy is less dense. These plants will likely be younger or have a shorter life cycle. As you move deeper into the woodland you will find number of plants decreases but the age and height of them increases and they form a canopy which limits light reaching the ground.
Patchy stands with a lot of variation provide a greater range of biodiversity. In Permaculture a great emphasis is placed on edges. One of the principles of Permaculture is ‘Use Edges and Value the Marginal’. The edges of woodland is often where there is a wider variety of plant and animal to be found. A great book on permaculture principles and practice is the Earth Care Manual by Patrick Whitefield.