Not in Isolation
The effects of natural disturbances cannot be considered in isolation. Disturbances
may interact with one another, such that effects of an initial disturbance alter characteristics
and effects of subsequent disturbances (Paine et al. 1998 Robertson and
Platt 2001, Platt et al. 2002, Suding et al. 2004, Schroder et al. 2005). As a result,
species may invade following sequences of disturbances, especially when de novo
disturbances are involved (Kercher and Zedler 2004, Zedler and Kercher 2004).
Natural landscapes can be greatly affected by human-caused alterations of natural
disturbance regimes and by de novo anthropogenic disturbances. Altering
disturbance regimes changes the environments to which species may have become
adapted. Habitat fragmentation as a result of human activity is a major cause of
indirect alteration of disturbance regimes, especially those of large-scale disturbances.
Fires that otherwise might have swept across large regions of the southeastern
U.S., for instance, are contained in much smaller areas by a fragmented
landscape (Gilliam and Platt 2006). The result may be less frequent, but more intense
fires that are now less dependent on global climate patterns and more dependent
on fuel accumulation (Slocum et al. 2007). Similarly, floodplain communities
once linked to natural flooding cycles are in altered hydrologic regimes
(Sparks 1998, Sparks et al. 1990).
Human disturbances of ecological communities may reduce standing biomass
and simplify community structure and composition (Menges and Quintana-Ascencio
2003) or, on other occasions, they may actually increase biomass by interrupting
normal burning cycles. Most significantly, human disturbance regimes
typically deviate from historic ecological disturbance regimes and oftentimes result
in radical shifts in the ecosystem, such as the introduction of exotic species
(Menges and Quintana-Ascencio 2003).
Proceed to Next Section: Military Disturbances and Associated Ecosystem Consequences