|MadSci Network: Botany|
You are correct that grasses are well adapted to stand up to trampling because of their intercalary meristems. Trampling can cause a direct effect on plants by physically damaging the meristems as you indicate, and can also damage stems, leaves, flowers and fruits. However, trampling can also damage the soil in more long term ways. Soil compaction can reduce air and water availablity to the plants. A compacted soil surface can cause rain to run off rather than penetrate the soil, thereby causing drought. If the rain does not run off, it may pond on the surface and cause root aeration problems. Compaction also often increases the mechanical resistance to root growth, termed soil strength. Soil strength can be measured with a penetrometer, which uses pressure units. The soil bulk density is another method of expressing compaction. Some types of soils naturally tend to form a hard pan or impenetrable layer at a certain depth. Trampling may promote the formation of a hardpan. The soil compaction can have very dramatic and long lasting effects so they are often more important than the direct effect of trampling on plants. For example, soil compaction can also greatly reduce seed germination, which could have a long term, if not permanent, effect on species distribution. High traffic turfgrass areas such as football fields and golf greens are often grown in a layer of pure sand rather than regular soil. The sand basically eliminates the possibility of soil compaction and greatly reduces problems of high traffic. However, even without soil compaction, turfgrass will eventually be killed if trampling or traffic is high enough. Soil compaction is a major concern in agricultural crops, and there are lots of websites discussing it. References Response of five native plant communities to trampling in the Wind River Range, Wyoming, USA Addressing soil strength problems on restoration projects Soil Strength Soil strength and plant roots Soil Hardpan Soil Compaction And Drainage Prescription Athletic Turf Construction Overview
Try the links in the MadSci Library for more information on Botany.