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Lecture 9

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Department
Biology
Course
BIO120H1
Professor
James Thomson
Semester
Fall

Description
Lecture 9: spatial eco, plant communities, and disturbance Community dynamics: predictable successional change in plant communities - Pioneer species get in first(from dispersal or seed bank soil) - Soil-building processes and shade thought to be critical - Studied in North America, esp. “old-field” – previously farm lands, succession from abandoned land to forest - Vegetation changes spontaneously as the vegetation itself modifies the environment Classification and terminology - Pioneer species – first to appear in the habitat (good at dispersing, r-strategists) - Climax stage – stable equilibrium, no more change - Primary succession – new substrate created, no pre-existing vegetation; substrate – new material that will become soil afterwards - Secondary succession – more often to occur, pre-existing vegetation undergoes a disturbance, like fire, in which it was destroyed - Disturbance = discrete event that causes abrupt change in ecosystem, community, population; sets back succession Eg of primary succession: Kilauea volcano, Hawaii, seeds and spores blow in, hardy pioneer plants can establish themselves; soil development, dead plants contribute organic matter and more complex soil starts to develop -> more plants can establish; birds attracted by plants -> birds bring in and disperse seeds; herbaceous plants cover ground, trees grow. Tree canopy closes in, shade becomes important Example of secondary succession: temperate deciduous forest biome, Joker’s Hill or Koffler Scientific Reserve, north of Toronto: Abandoned agricultural fields and pastures. 1) Annual dormant weeds require light for growth. In farm, farmers will get rid of these seeds, but not anymore, 2) perennial weeds for several years, 3) woody shrubs move in; 4 – tree saplings; 5 – tree canopy closes in, shade becomes main factor; either shade tolerant(can grow with low light levels), or early spring plants; 6- shrub layers thin, shad-toleran
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