Before you start
The ground vegetation in two contrasting areas of woodland or grassland is compared by random sampling both areas or along a transect. Vegetation can be recorded using quadrats and/or the ACFOR scale. Invertebrates can be sampled with pitfall traps on the ground, by sweep netting stems and leaves, or by using mark-release recapture.
- A quadrat (choose an appropriate size for the species present)
- 2 tape measures
- Identification guides, such as FSC woodland plants fold-out chart
- Method of generating random numbers e.g. calculator or random number table
- Equipment for measuring abiotic factors (e.g. humidity, light, soil depth, soil temperature, soil pH, soil compaction, canopy cover)
Care should be taken when working outdoors. Wear long sleeves and trousers, as woodland plants such as brambles and nettles can be prickly or stinging and in some grassland areas ticks may be a concern. Beware of branches and twigs in the eye. Wear sturdy footwear and beware of rabbit holes, roots and other uneven ground. Do not work by yourself.
Summary of procedure
- Carry out a pilot survey to identify contrasting habitats, such as oak woodland compared with beech woodland. Control as many other variables as you can, such as altitude, rock type, grazing pressure from animals and human disturbance.
- Choose a sampling strategy, such as random sampling of ground vegetation in each area.
- Identify plants or animals to the lowest taxonomic level as possible.
- Record the number of individuals of each species or use the ACFOR scale to estimate abundance.
- Take sufficient samples for your data to be statistically representative. For many statistical tests, 10-30 samples are needed in each area.
- Collect abiotic data, with sufficient repeats.
Catching invertebrates in leaf litter and soil
Pifall traps are containers, such as glass jars and plastic cups, sunk into the soil for animals to fall into. They work for running or crawling invertebrates. Place a cover, raised on stones, above the trap to keep out the rain.
To avoid predatory animals such as spiders from eating the rest of the catch, you can place a small amount of washing-up liquid in water in the bottom of the trap to kill the invertebrates. Pitfall traps can be baited - for example, beer attracts slugs and snails, while fermenting fruit attracts flies.
(b) Chemical irritants
Deep-burrowing earthworms can be brought to the surface by watering the ground with a dilute solution of potassium permanganate. A non-toxic alternative is a dilute solution of mustard powder in water.
(c) Tullgren funnel
The Tullgren funnel is used to extract invertebrates from samples of soil or leaf litter brought back from the woodland to the lab. The sample is placed in a funnel above a perforated disc and the whole apparatus placed under a low-powered electric light bulb. The rise in temperature and the drying effect encourage the animals to move away from the source of heat, downwards through the holes in the perforated disc, into the funnel and so to the collecting vessel underneath. They can be collected alive or killed by adding detergent to water in the vessel. Leave the funnel for at least 2-3 days.
Catching invertebrates from leaves
A pooter is a flexible tube that can be used to catch invertebrates directly from leaves. The user sucks one end, which draws the invertebrate upwards to a trap area. A barrier, such as a layer of muslin, prevents the user from ingesting the invertebrate. Several designs of pooter are available, but the principle is the same throughout.
Once you have finished collecting invertebrates, you will need to sort the catch, which is much easier if the animals have been anaesthetised or killed. Larger invertebrates can be temporarily stunned by placing the collecting tube in a fridge for 30 minutes. Earthworms cannot be reliably identified to species level in the field, so they will need to be killed.
(b) Kite nets and sweep nets
Kite nets are lightweight nets used for catching insects flying above the vegetation layer. In woodland, they can really only be used in open areas, such as tracks and woodland rides, or above low-growing plants. Use a figure-of-eight motion to move the net, and keep clear of any brambles and thorns that may make holes in the net.
Sweep nets are more robust nets that can be used to disturb non-woody vegetation. Use a figure-of-eight motion to move the.
(c) Beating tray
Place a white sheet on the ground below the branches of a bush. Use a strong stick to shake the leaves and branches of the bush so that invertebrates fall onto the white sheet. They can be removed from the sheet using a pooter. only the males) and that their efficiency varies with the amount of moonlight and. other environmental influences on the insects.