High Forest Hypothesis

A traditional view of European primeval forest is high closed forest with regeneration in canopy gaps created by the death of small groups of trees. This implies forests are mainly drived by vegetation growth, including plant growth, death, interspecific and intraspecific competition, etc. Large herbivores have no significant influence on the composition or succession of the vegetation (Bottom-Up control).

Wood Pasture Hypothesis

However, Frans Vera (2003) challenged this view by a new pothesis: it was large herbivores that not only created larger openess in the canopy by browsing, grazing and trampling, but also drove the whole forest through a cycling regeneration process (Top-Down control):open land - scrub dominated - high forest - break-up.

• Why is this intesreting ?
• How to test ? 
• The conclusion ?