Holling (1973) originally defined stability as the ability of a community to withstand disturbance
with little change in structure, whereas resilience was defined as the capacity
of the community to recover following perturbation. Webster et al. (1975) subsequently
refined the definition of stability to incorporate both resistance to change and resilience
following perturbation. Succession is an expression of resilience. However, the criteria for
measuring stability remain elusive. What degree of change can be accommodated before
resistance is breached? Does resilience require the recovery of a predisturbance community
composition or of ecosystem functions that support a particular community type, and
over what scale of space or time?
ecosystems based on the lowest turnover rates, i.e., the longest time constraint, and
damping factors (factors that reduce amplitude of fluctuation) in the system. The system
has not fully recovered from displacement until the slowest component of the response
has disappeared. They concluded that ecosystems with greater structure and amounts of
resource storage were more resistant to disturbance, whereas ecosystems with greater
turnover (e.g., via consumption and succession) were more resilient. From a community
standpoint, resistance depends on the level of tolerance of the dominant species to characteristic
disturbances or other environmental changes, e.g., through protected meristems
or propagules, or resource storage; resilience is conferred by species with rapid recolonization
and growth rates. Overall, temperate forests, with high biotic and abiotic storage
and slow turnover, appear to be most resistant, but least resilient, to disturbance. Stream
systems, with low biotic and abiotic storage and high turnover, appear to be least resistant,
but most resilient. Resistance and resilience were found to be related inversely, with their
relative contributions to stability in a given ecosystem being determined by the proportions
of K- and r-specialists (see Chapter 5). Succession appears to represent a trend from
more resilient to more resistant communities.
Resistance and resilience are affected by regional species abundance and distribution.
Resistance can be compromised by fragmentation, which increases community exposure
to external factors. For example, trees in interior forest communities are typically buffered
from high temperatures and high wind speeds by surrounding trees, and they typically have
less buttressing than open-grown trees. Fragmentation increases the proportion of trees
that are exposed to high temperatures and wind speeds and thereby are more vulnerable
to moisture stress or toppling (J. Chen et al. 1995, Franklin et al. 1992). Fragmentation also interferes with the adapted abilities of species in the regional pool to recolonize disturbed
sites. Species are adapted to levels of dispersal and colonization that are sufficient to maintain
populations within the characteristic habitat matrix of the landscape. If the rate of
patch turnover is increased through fragmentation, the colonization rates for many species
may be insufficient to provide the necessary level of resilience for community recovery.
Such changes in landscape condition may bias evaluation of community stability