Lecture 9: spatial eco, plant communities, and disturbance ...
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; 6shrub layers thin, shad-tolerant understory only; 7 – only shade-tolerant spp remain, including canopy tree spp that are now replacing themselves - species turnover minimal It happens spontaneously Drivers of terrestrial succession -
Soil development; accumulation of organic matter, N content, pH buffering, water retain capacity Shading; Shade-tolerant replace shade-intolerant ones Stable climax; may reach it, configuration f dark shade, organic-rich soils
Succession where no climax-type equilibrium -
Boreal forest: successional stages lead to spruce-fir forest, but it does not replace itself Acid, sandy soils: pine-oak leaf litter slows down succession, because it make the soil more acid, therefore, less rich Fire-prone ecosystems and biomes Systems driven by seasonality Cycling of dominants, A replaces B, then B replaces A Transient substrates
Tropical rainforest, very unlikely to burn, never get dry enough for fire; succession happens on the individual level, gap-phase – pioneer species come after major tree falls down, which creates a big gap hen it falls. Not the whole patch gets reset, but as a mosaic. Fire-dominated communities: pine trees make a lot of flammable compound, if a fire comes there, everything will go up in a fire, and leaf litter is flammable too. Same for eucalyptus; fire in southern California, chaparral 2007, every august, have to clean space for houses to protect them from fire; 3 – ground fire, big trees will survive, 4- crown fire, ground fire can jump to make crown fire, nothing will survive Adaptations to fire: serotinous cones as an adaptation to seeding in after a fire: Fire-opened cones of pitch pine. Open up to reproduce when trees are on fire – serotony. Good time to put seeds because there is no competition anymore. Modern understanding of patterns -
Climax = old-growth forest Characteristic disturbance regimes -> quasi-equilibrium Gap-phase succession – little patches that sum up Intermediate disturbance hypothesis for max species diversity:
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; 6shrub layers thin, shad-tolerant understory only; 7 – only shade-tolerant spp remain, including canopy tree spp that are now replacing themselves - species turnover minimal It happens spontaneously Drivers of terrestrial succession -
Soil development; accumulation of organic matter, N content, pH buffering, water retain capacity Shading; Shade-tolerant replace shade-intolerant ones Stable climax; may reach it, configuration f dark shade, organic-rich soils
Succession where no climax-type equilibrium -
Boreal forest: successional stages lead to spruce-fir forest, but it does not replace itself Acid, sandy soils: pine-oak leaf litter slows down succession, because it make the soil more acid, therefore, less rich Fire-prone ecosystems and biomes Systems driven by seasonality Cycling of dominants, A replaces B, then B replaces A Transient substrates
Tropical rainforest, very unlikely to burn, never get dry enough for fire; succession happens on the individual level, gap-phase – pioneer species come after major tree falls down, which creates a big gap hen it falls. Not the whole patch gets reset, but as a mosaic. Fire-dominated communities: pine trees make a lot of flammable compound, if a fire comes there, everything will go up in a fire, and leaf litter is flammable too. Same for eucalyptus; fire in southern California, chaparral 2007, every august, have to clean space for houses to protect them from fire; 3 – ground fire, big trees will survive, 4- crown fire, ground fire can jump to make crown fire, nothing will survive Adaptations to fire: serotinous cones as an adaptation to seeding in after a fire: Fire-opened cones of pitch pine. Open up to reproduce when trees are on fire – serotony. Good time to put seeds because there is no competition anymore. Modern understanding of patterns -
Climax = old-growth forest Characteristic disturbance regimes -> quasi-equilibrium Gap-phase succession – little patches that sum up Intermediate disturbance hypothesis for max species diversity:
