Question

In plant life histories, what is the difference between a disturbance and a stress?

Answer 1

Ans. Stress is defined according to Grime (1979) as the external constraints which limit the dry matter production rate of all or a part of vegetation, whereas disturbance consists of the mechanisms limiting plant biomass by causing its destruction.

• According to Pickett and White (1985),disturbance means any relatively discrete event in time that disrupts an ecosystem, its community and population structure, and changes substrate availability or the physical environment.
• Disturbance is often considered as an
  unpredictable event. These two processes structure habitats and can explain the distribution and dynamics of plants.
• Disturbance by floods creates a mosaic of aquatic habitats and thus heterogeneity within channel and floodplain.
  It is an important parameter which structures the aquatic systems and maintains their dynamics. As a consequence, this patchy mosaic changes both temporarily and spatially, which explains the high community richness and specific richness at different spatial scales. The recolonization of a disturbed habitat depends on propagule inputs and/or
  seed banks in a place, the biological capacity of species to settle and grow, and environmental factors such as sub-
  strate granulometry and water nutrient supply.
• Factors like salinity, light, nutrient content is stress and ephemeral inundation is disturbance for an aquatic ecosystem.

Grime(1979) on the basis of disturbanc, stress and competition recognized 3 categories of plants-

1. Ruderals(R)
2. Competitors(C)
3. Stress tolerant(S)

Stress factors-Reduces biomass production like low light,low moisture, low nutrients etc.

Disturbance factors- remove part or whole of biomass like grazing etc.

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