Presentation on theme: "Disturbance and Succession. Primary succession is a process that generally involves: 1) the accumulation of organic matter- wind blown debris, insects."— Presentation transcript:
Primary succession is a process that generally involves: 1) the accumulation of organic matter- wind blown debris, insects migrating in, etc. 2) Small plants (long-distance dispersal, small seeds) 3) Accumulation of more material, deeper rooted species- more habitats for wildlife 4) Continued increase in organic matter, the formation of rudimentary soil, eventually “real” soil, vegetation and the accompanying animal species.
A sequence of species colonize the blocks, replacing each other in an apparently predictable way…
Henry Chandler Cowles- Lake Michigan Dunes, 1899
Fire is a spectacular, and sometimes scary process, but ecologically this is very often essential to the functioning of the system. It is almost never a “disaster” from an ecological perspective
Fire influences ecosystems by: 1) Reducing competition 2) Altering seed bed characteristics 3) Changing soil nutrient environment 4) Creating/Perpetuating a mosaic 5) Reducing forest floor mass (fuels) 6) Many others
Dendroecological reconstruction of fire history First- what is a tree ring? -A record of tree growth, created by a tree’s seasonal access to resources and/or by cold weather.
Temperature-derived tree rings: -In the summer, it is warm and wet, the trees grow rapidly. -In the autumn, temps drop, trees lose their leaves. -In the winter, in freezing temps, the trees are “dormant”. Summer Winter
- This process is recorded in the wood as an “annual ring” - “Annual”- because it happens every year. - This means we can date the trees with great accuracy Summer Winter
Tree-ring analysis can be used to reconstruct fire history: - When fire passes near a tree the heat kills the cambium. - The tree closes the wound and therefore, encapsulates that injury in the wood. - The wounds are found in a tree-ring series, so they can be dated. -Fire scars give information about the frequency of fires in the forest. -If you collect many samples in a forest you can also reconstruct spatial patterns of fire. -If have old trees, you can develop long histories.
Early successional species vs. Late successional species
Some theories of succession… equilibrium forces, facilitation, inhibition and tolerance…
E quilibrium forces (succession) Non-equilibrium forces (disturbance)
Question: Why to later species replace earlier species?
Some theories of succession- 1)Facilitation- Each species creates opportunities for the next species. The system cycles through species until a species no longer provides this opportunity and become dominant. 2)Inhibition- Species hold onto the site via competition (and other negative interactions) and only give way to other species due to disturbance or death. 3)Tolerance- Species that make up the final composition of the community are those best able to tolerate environmental conditions. They are neither hindered (inhibition) or helped (facilitation) by other species