The effects of trampling

Trampling has some similar effects to mowing. See here for a discussion about the biotic differences that might be found in long and short grass caused by trampling or mowing and also for advice about tackling this kind of investigation. You will also find information about how the plant growth form is affected by the height of the vegetation.

Here we look at how the degree of trampling affects the species composition of the plant community and the species richness (the number of species present).

Plants growing on trampled areas have to be tolerant to soil compaction and its effects on soil conditions. However, the species composition of the plant community, will also be influenced by a number of other interacting factors.

1. Physical damage to plants by removal of growing tips and crushing occurs, so having the right growth form is important. Species able to form rosettes (e.g. plantains, daisies and dandelions) are often common.

2. Damage may also reduce flowering so the ability to reproduce vegetatively is another advantage. In white clover the leaves are carried up to the light on long leaf stalks. The main stem forms a horizontal runner (stolon) which keeps the growing point close to the soil surface and provides a means of vegetative reproduction.

White clover (Trifolium repens)

3. Trampling, like mowing, results in different heights of vegetation so competition for light might be a factor (see here).

4. Extreme trampling can result in removal of parts of the turf and the creation of bare ground. This may allow new species to colonise particularly less vigorous species which are not good competitors.

5. On bare ground and in short turf plants are more likely to have to be able to survive extremes of relative humidity and temperature. Particular growth forms of mosses, for example, can often be linked to the humidity of their habitat. Species with turf and cushion forms appear to be better able to resist drying out than the weft and mat forms which most often occur in taller vegetation. This is also important when considering the ecology of walls.

Turf-forming moss on bare ground	Mat-forming moss in long grass

6. Deposition of litter and dog fouling may cause changes in the soil mineral content though any change is difficult to measure without sophisticated equipment.

The plantain case study shows how the interaction of a number of factors determines the distribution of two closely related plantain species on trample ground

Fieldwork: measuring the amount of trampling

It is difficult to measure the amount of trampling directly. Since however a major effect of trampling is compaction of the soil, measuring soil infiltration rate (see here) can often be a good indicator of the degree of trampling.

Soil compaction reduces the size of spaces between the soil particles and affects soil conditions in a number of ways, as shown below.

Explaining the effects of trampling on species richness

Relatively few species are likely to be able to survive when environmental conditions are extreme for example

• in most trampled areas where the chance of physical damage is high and the soil is very compacted
• in non trampled areas where the vegetation is tall and there is strong competition for light

It is at the boundary between the two extremes that the greatest number of species is usually found. At the edge of a trampled areas species are least affected by trampling but avoid too much competition with the more vigorously growing species. The following 3 photographs show a transect from the centre of a heavily used footpath to the edges.

	most trampled area in centre of path number of species = 6
	boundary between trampled and least trampled area number of species = 12
	least trampled area number of species = 3

Case study: distribution of ribwort plantain and greater plantain in trampled areas

Two species of plantain, ribwort plantain (Plantago lanceolata) and greater plantain (Plantago major), are very common in grassy areas in Britain.

If you carry out a transect of a moderately trampled footpath (i.e. where there is more than just bare soil in the centre of the path), you are likely to find that there is a higher abundance of greater plantain in the more trampled centre of the path, and a higher abundance of ribwort plantain in the less trampled edges of the path.

Ribwort plantain is less well adapted to heavily trampled sites. It is less tolerant to physical damage and is less likely to grow in waterlogged soil.

By contrast, greater plantain is most abundant on heavily trampled ground. It is very tolerant of waterlogging and physical damage due to trampling. Itsseeds which germinate best on open ground.

Ribwort plantain can readily vary its growth form in response to environmental conditions. In shorter grass, it grows in the rosette form with short leaves held flat to the ground, while in longer grass its leaves are longer and more angled off the ground. Its seeds can germinate amongst other plants. These factors help it to grow in less trampled areas with taller vegetation, where there is more competition to reach the light.

Both plantain species are frequently found on trampled ground. The table shows how the characteristics of these two species are suited to this habitat.

Feature	Greater plantain	Ribwort plantain
Main growth form	rosette	rosette
Drought	tolerant	not tolerant
Physical damage by trampling	very resistant	moderately resistant
Ability to vary growth form under different conditions	can vary	varies readily
Vegetative reproduction	limited but can form daughter rosettes from lateral buds	limited but can form short thick rhizomes
Seed dispersal	mucilage on seed coat becomes very sticky when wet allowing seeds to stick to animals including humans and also machinery helping to disperse seeds along track ways	mucilage on seed coat becomes very sticky when wet allowing seeds to stick to animals including humans and also machinery helping to disperse seeds along track ways
Seed germination	best near soil surface on open disturbed ground	best on lightly compacted soil either in open or amongst vegetation
Overwintering	as small rosettes or underground	as small rosettes