The document summarizes different types of ecological succession that occur in ecosystems. It describes how succession leads to increases in ecosystem complexity over time through changes in species composition and interactions. Succession can be driven by external environmental changes (allogenic) or internal biological processes (autogenic). Primary succession occurs on new, undeveloped habitats while secondary succession follows disturbances to existing habitats. Intensive human activities like agriculture, pollution, and development can reduce ecosystem complexity by simplifying species interactions and food webs.

7. In 1850, Connecticut was almost entirely open land cleared for farming or timber. Today, Connecticut has been mostly reforested through the process of secondary succession as farming has left the state since the 1800's This area has not been cleared in over fifty years. These trees represent the CLIMAX COMMUNITY for the rainfall, temperature and soil of this area This area has not been has not been mowed in about ten years. Shrubs and evergreen trees have moved in. These are the INTERMEDIATE species This area has been mowed within the last year. The plants are all annuals or herbaceous perennials. These are the PIONEER species

12. CHANGES IN ECOSYSTEM COMPLEXITY Increase in complexity shown by:  Number of species  Population size  Biological Productivity  Habitat/Niche Variety  Complexity of Food Webs Loss of complexity caused by: Monoculture Eutrophication Toxic Pollution Oxygen depletion AUTOGENIC SUCCESSION ALLOGENIC SUCCESSION DEGRADATIVE SUCCESSION Geophysical Forces (e.g. Climatic Extremes) Associated with Decomposition Primary Secondary Barren Land Colonisation by Pioneer Species e.g. moss, microbes Disturbance of Existing Community

26. BOD of a river