In most plant communities with a closed canopy, the establishment of seedlings usually requires at least some degree of disturbance to provide areas free of existing vegetation. Established plants have a clear advantage over seedlings in their ability to intercept light and monopolize other resources such as water and nutrients. Gaps that are created by any agency in vegetation can be considered ‘competitor-free spaces’ that provide opportunities for seedling establishment (Bullock, 2000). The study of gaps and their role in promoting recruitment has been an important focus of investigations into regeneration and species diversity in plant communities over the past few decades.

Gaps, patches and safe sites

A gap is an area that is at least partially free of vegetation, where there are sufficient resources available to permit the recruitment of new individuals. Gaps are not always necessary for regeneration, especially in cases where vegetation itself can ameliorate conditions in a harsh environment (see Section 8.7). The term ‘patch’ is often used in this context to mean much the same as a gap, but it is a less satisfactory term because it suggests something that is stuck on rather than removed. It is perhaps best reserved as a term to refer to the successional vegetation that comes to occupy a former gap. A useful term coined by Harper (1977) is ‘safe site’.