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Lecture 9 Study Notes.docx

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University of Toronto St. George
James Thomson

Lecture 9 Study Notes: Spatial ecology, plant communities, and disturbance Predictable successional change in plant communities: -pioneer species get in first from either dispersal or seed bank -important factors that drive species replacement: soil-building processes and shade (taller plants out-shade shorter plants) -most heavily studied in human-impacted landscapes in eastern North America, especially “old- field succession” from abandoned land to forest -Vegetation changes spontaneously as vegetation itself modifies environment Classic View of Successional Change -Starts with pioneer speciesweedy type plants, r-strategists, short-lived, annuals, good at dispersing -Then go through temporary, non-equilibrium stages -Ends at stable climax stage-no new species introduced, animals adapted to climax environment, k-strategists, good at competition for resources, make bigger seeds, no large investments in dispersal, tolerant in dense shade, unlike pioneer species Two categories of Succession -Primary: new substrate created, no pre-existing vegetation, rare but does happen eg. Formation of new sand dunes on seashores, retreat of glacier opens up habitat that didn't have any habitat 2000 years ago, lava flow -Secondary: Places where there has been developed plant community of some kind, but has been destroyed or extremely modified by disturbance event, most common are logging and clearing for agriculture; short-lived; pioneer species arrive, eg. old field succession -Disturbance: discrete event that causes abrupt change in ecosystem, community, population, eg. fire, bad weather, logging, agriculture; sets back succession Primary succession on new lava flows in Kilauea Volcano, Hawaii -Seeds and spores blow in, hardy pioneer plants can establish themselves; fern is pioneer species -Plants attract birds; birds bring in more seeds -Herbaceous plants cover ground, trees grow -Tree canopy closes in, soil is well developed, shade becomes more important Secondary succession in temperate deciduous forest biome: Joker’s Hill or Koffler Scientific Reserve Old-field succession stage 1: Annual weeds (semelparous) Old-field succession stage 2: Perennial weeds for several years (iteroperous) Old-field succession, stage 3: Woody shrubs move in Old-field succession, stage 4: Tree saplings (aspen, cloning) Old-field succession, stage 5: Tree canopy closes in, foliage down lowlight still penetrating into lower forest, shade becomes main factor, becomes shadier Old-field succession, stage 6: Shrub layer thins, shade-tolerant understory only either shade- tolerant plants or spring ephemerals (come early in spring, do photosynthesis before leaves grow back) Old-field succession, stage 7: Climax—Only shade-tolerant spp. remain, including canopy tree spp. that are now replacing themselves— species turnover minimal Primary Succession Secondary Succession • weedy-type plants; r strategists • good at competition; k- • short-lived, annuals strategists • produces many seeds; good at • lo
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