The effects of mowing

Many grassy areas in towns and cities are mown. The effects of mowing are similar to the effects of trampling (by human and animal feet). Trampling crushes and flattens the plants. Mowing cuts the plants, and the cut material is often removed. Mowing may also have a crushing effect if heavy machinery and rollers are used. As a result of trampling and mowing it is often easy to see a change in the height of the vegetation and both can result in changes to soil conditions as a result of compaction.

What could you investigate by fieldwork?

Apart from mowing, grassland can be managed in many ways.

• selection of grass species
• mechanical removal of weeds
• replacement of damaged turf
• artificial irrigation
• improved drainage
• soil compaction by rolling
• application of chemicals (e.g. fertilisers, weed killers, line paint)
• rotation of playing pitches

The effects are likely to be spread more evenly in mowing than in trampling and extreme damage e.g. the creation of bare ground is less likely. Therefore it is usually best in a mowing study to compare directly two areas cut for example:

• by different types of machine e.g. strimmers, hover mowers, rotary mowers, ride-on mowers
• at different time intervals
• at different heights

In a trampling study it is often possible to see different degrees of trampling and a good way of investigating this is to look at changes along a transect line.

What should you look for?

Apart from the obvious immediate effects of cutting and flattening the vegetation these differences in height may also be due to a change

• in the species present - species composition
• the number of different species present - species richness
• the types of growth form present
• changes in the growth form of individual species

Warnings - before you start...

• Make sure that any factor you are investigating has had time to produce an effect:
  changes in the growth form (morphology) of a species are unlikely to be visible for 2-3 weeks
  changes in species composition may not be significant for 2 or more growing seasons
  
• Mown grassland whether it is kept for recreation or its pleasing appearance (aesthetic value) will often be subjected to other management techniques. Whether you are just looking at the effects of mowing or doing a trampling study find out what is going on before you start your investigation to try and make sure that only the factor that you are investigating varies.
  
• NOTE ongoing management can be bad for your field work!

Fieldwork techniques

In this section differences in growth form (morphology) of plants growing in grassland kept at different heights by mowing are considered.

1. Species composition and species richness

Differences in species composition and species richness are described under the effects of trampling.

2. Soil conditions

More information about soil conditions and how to measure them are described in the Introduction to grassy areas.

3. Measuring the height of the grass

This can be done in a number of different ways. Measurements can be made directly with a ruler or by methods that involve measuring distance from the ground of a plate resting surface of the grass. (see photograph below).

Explaining the effects of mowing

For convenience, plants other than grasses and sedges are referred to as broad-leaved species.

(a) Surviving in short grass

Amongst broad-leaved plants the rosette plant form is often the most abundant. Here the leaves are flattened close to the ground and the main growing point, situated low down amongst the leaves is protected. Rhizomes or stolons may also be present.
	Grasses are able to survive regular cutting as their growing points are situated at the base of the plant. Many perennial grasses do not need to rely on the production of flowers and seeds for reproduction as they have extensive creeping stolons (runners) or underground stems (rhizomes) which allow the plants to spread vegetatively.

(b) Surviving in long grass

In long grass there will be strong competition for light and many small low growing broad leaved plants disappear. Some plants however, however are able to vary their morphology in grassland of different heights.

The ribwort plantain Plantago lanceolata is a good example. In short regularly cut grass the plant forms small neat rosettes. In long grass the leaves become larger, longer and narrow and also stand upright at an angle from the ground. These long upright leaves help the plant to receive more light.

Ribwort plantain growing in long grass

Ribwort plantain growing in short grass