Effects of environmental factors on terrestrial species
In grasslands trampling by people and animals can affect both species richness and the distribution of each species. The morphology of individual plants within the same species may also be influenced by trampling.
Impact of trampling on species richness
- 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.
most trampled area in center of path number of species = 6
boundary between trampled and least trampled area number of species = 12
least trampled area number of species = 3
Impact of trampling on the distribution of a particular species
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 sampling on trampled footpath (i.e. where there is more than just bare soil in the center of the path), you are likely to find that there is a higher abundance of greater plantain in the more trampled center 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. Its seeds which germinate best on open ground.
Impact of trampling on the morphology of a particular species
Trampling can also affect the morphology of certain species that show phenotypic plasticity. 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.
Investigation comparing different woodland areas e.g type of woodland or woodland management, are usually a comparison of the effect of light available to the ground layer plants. Therefore this impacts on the type or abundance of plants in the two sample areas.
Impact of light availability on distribution of an individual woodland species
The bluebell (Hyacinthoides non-scripta) needs a lot of light to grow and flower successfully, but does not compete well with other species. It avoids competition by growing under the dense canopies of deciduous trees such as oak and beech where most species are excluded by lack of light. The bluebell is able to tolerate these conditions by using food reserves stored in its bulb. It grows rapidly in spring and is in flower by early summer before the trees come into leaf and lack of light becomes a problem.
In recently cleared or coppiced areas where light levels are high throughout the summer bluebells may initially do particularly well but eventually succumb to competition as other species invade.
The bluebell grows best on slightly acidic soils. On alkaline soils it may be replaced by species such as dog's mercury which occupy the same niche.