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Disturbance and Succession. 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)
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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…
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 competition2) Altering seed bed characteristics3) Changing soil nutrient environment4) 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
Summer - 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 Winter
One year Winter 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.
A) A) C) C) B) B) D) D)
Early successional species vs.Late successional species
Some theories of succession… equilibrium forces, facilitation, inhibition and tolerance…
Equilibrium forces (succession) Non-equilibrium forces (disturbance)
Question: Why to later species replace earlier species?
Some theories of succession- • 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. • Inhibition- Species hold onto the site via competition (and other negative interactions) and only give way to other species due to disturbance or death. • 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
