Stressors are those activities or phenomena that place stress on an
organism or its natural habitat (community), threatening its viability.
Most of the stressors described below are connected to human activities,
but some are due to natural causes. Some human activities can increase
the likelihood of natural stressors, such as allowing dead vegetation
to build up, which can increase the likelihood of wildfire. Another example
is the increase loadings of greenhouse gases, which has been attributed
to global climate change and the attendant changes in the frequency and
intensity of storms, melting of glaciers and changes in heating and cooling
days, as well as changes in rates of precipitation and evaporation. Although
natural disturbances are an integral part of healthy ecosystem dynamics,
exacerbation of the frequency or intensity of those disturbances can threaten
ecosystem integrity as much as human stressors.