What is vertical woodland structure?
Vertical woodland structure refers to the differences found at different heights in the woodland. Woodland is usually referred to as having four distinct layer.
The Ground layer refers to the plants growing on the floor of the woodland. Towards the edge of the woodland this may well be very green and made up of grasses, mosses, lichens and fungi. Under the canopy of trees this will consists predominantly of leaf litter – rotting vegetation and leaves that were shed the previous autumn. Many creatures will 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 Field layer is made up of grasses, ferns and flowering plants. The amount of growth at this layer will vary hugely depending on how much light reaches it through the canopy above. The species of plants you find at this layer will also vary but plants such Bramble and Nettle are often abundant.
The Understorey (or Shrub) layer is comprised of younger smaller trees and shrubs which have evolved to grow with less light. Young trees you find in this layer will very likely be the same species as the larger more dominant trees that make up the canopy. If the woodland is very dense then little light will get through and little will grow at this layer. 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 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. The trees that form the majority of the canopy tend to be considered the dominant species of the woodland, for example if the majority of the canopy is comprised of Oak trees it would be considered an Oak woodland.
What is horizontal woodland structure?
The horizontal woodland structure refers to the differences found at different points, or 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. Plant disease and the presence of other plants will also affect which species grow at different stands. Generally you will find a wider variety of plants towards the outer edge of a woodland where the canopy is less dense. The plants you find towards the edge will likely be younger or have a shorter life cycle. As you move deeper into the woodland you will probably find the number of different species decreases but the age and height of the plants and trees increase.
The photo above shows the impact of environmental features on plant growth. In this case the buffer between the stream and the land, known as a riparian area, shows very different plant life. As well as the extra water provided to the plants in this area the break in the canopy caused by the stream allows more light to reach the woodland floor.
Survey the structure of your Forest School site
One of the best ways of demonstrating an understanding of vertical and horizontal woodland structure is to survey your own Forest School site. As you complete your survey:
- Record the name of the trees or plants you find.
- Take a photo of each tree or plant – this will be invaluable if you need help identifying it.
- Record any significant features of the plant, such as whether it is native or not or if it is growing near a specific environmental feature such as rocks or a body of water.
To survey the horizontal structure of your site start at the edge of the woodland and walk into the centre. At intervals record the different plants and trees you can see. Mark the location of any significant changes in plant life on a plan or map of your site or record the approximate distance from the edge or center of the woodland.
To survey the vertical structure of your site walk into the centre of the your woodland. Take a look at the plants and trees that your find at the four different woodland layers. Estimate the height of the plant or tree and record the layer you consider it to belong to.
If you need help identifying the trees in your site then the Collins British Tree Guide is a great companion, the full colour pictures of leaves, bark and twigs will aid identification in any season. If you prefer photographs you can’t go wrong with the Complete Guide to British Trees. Both books feature plenty of additional information on the ecology of trees and woodland. For help with identifying other common woodland plants then the Field Studies Council’s fold out Guide to Woodland Plants is a very handy and affordable guide,