In situations where advance regeneration dominates gaps, the most important factor affecting tree species diversity and initial stem density within the gap is the relative ability of species to regenerate under a closed canopy. Gap size and the provision of suitable microclimate at any particular location within the gap affect subsequent opportunities for each individual to become a canopy tree (Canham, 1988).
We infer from the gap regeneration literature that the size-class distribution of gaps within a forested area after the first harvesting entry and the proportion of each size class characterized by a given type of microenvironment directly affects colonization by individuals, their persistence and growth and the number of species in an area. The subsequent frequency
of gap creation or gap expansion by silvicultural intervention will probably play a more important role than initial gap size for many specie (particularly the more shade-tolerant species; e.g., Canham, 1985, 1990). Future timing of silvicultural
treatments will have an important influence on population dynamics.
Another lesson to be drawn from gap ecology studies is the importance of determining the origin of regeneration found within gaps. When gaps are dominated by colonists established from seed after gap formation, studies that examine the factors that influence successful establishment, survival, and growth of new seedlings (e.g. gap size, gap microclimate,
substrate diversity; Table 2 are needed. When advance regeneration is abundant, regeneration (i.e. germination and emergence) studies can be estricted to closed canopy conditions (e.g., Harmon and Franklin, 1989) and subsequent growth can be examined over a range of gap sizes and various positions within gaps to determine how the advance regeneratio responds to changes in resource availability (e.g., Pacala et al., 1994). The latter also applies to coppice regeneration. Contrasting the success of natural regeneration and planting over the range of gap attributes provides an opportunity to distinguish the ‘regeneration niche’ (Grubb, 1977) from the ‘growth niche’.