However, it is not broadly recognized that the birth, growth, death, and renewal cycle transforms hierarchies from fixed static structures to dynamic entities whose levels are vulnerable to small disturbances at certain critical times in the cycle. That represents a transient but important bottom-up asymmetry. There are two key phases in which slower and larger ecosystems components become briefly vulnerable to dramatic transformation because of small events and fast processes. One occurs as the system slowly moves toward maturity, when it becomes overconnected and brittle . There are tight competitive relations among the plant species.
Vulnerability comes from such loss of resilience.
The system becomes an accident waiting to happen. In the boreal forest, for example, the accident might be a contagious fire that becomes increasingly likely as the amount, extent, and flammability of fuel accumulate. Or it could be a spreading insect outbreak triggered as increasing amounts of foliage both increase food and habitat for defoliating insects and decrease the efficiency of search by their vertebrate predators. It is also the phase where, in human organizations, the rebellion of aggressive interest groups can precipitate an inexorable demand for change. During the reorganization phase, small and fast variables can also dominate slow and large ones.