Intermediate Disturbance Hypothesis and the Spatial Mosaic

Intermediate disturbance hypothesis:

These disturbances don't impact the entire ecosystem, but just a section

Examples of intermediate disturbances in a temporal forest might be:

• lightening strikes and other small fires
• blowdown of trees
• river meander or flooding
• landslides
• small patches of logging

These occur occassionally throughout the landscape allow the ecosystem to:

• maintain a full range of age classes and successional stages
• increases internal niche diversity
• provides continual interal sources for replacement species

The mosaic of patches of different ages and successional stages breaks up the over-connectivity* that can lead to large scale, catastrophic events.

• whole basin forest fires
• insect outbreaks

* see Chapter 7 Networks part B: connectivity

low connectivity - parts of the whole system are functioning independently
medium connectivity - some interaction that preserves a wider range of functions
over-connectivity - all of the system is so connected that it acts as one simple unit, loosing a diversity of functions and scales

 

Landscape Mosaic

The continual creation of new patches results in a wide range of ages and stages. Each of them has a date of origin. For example, there could have been a small fire that left exposed soil behind, and this is recovering

This may overlay the soil and slope conditions that also determine plant communities and growth success. For example, a stream with sand bar and differing vegetation types as you move away from the stream.