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COMMUNITY CHANGE (SUCCESSION)

COMMUNITY CHANGE (SUCCESSION). Krebs cpt. 21; pages 403-424; 431. SUCCESSION …. Is the non-seasonal, directional and continuous pattern of colonization and extinction on a site by populations.

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COMMUNITY CHANGE (SUCCESSION)

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  1. COMMUNITY CHANGE (SUCCESSION) Krebs cpt. 21; pages 403-424; 431

  2. SUCCESSION…. Is the non-seasonal, directional and continuous pattern of colonization and extinction on a site by populations. Is the replacement of one kind of community by another kind; the progressive changes in vegetation and animal life that may culminate in the climax community (Krebs 622)

  3. PRIMARY SUCCESSION…. … recovery from a new sterile area that has been uncovered by a retreating glacier, or created by an erupting volcano. SECONDARY SUCCESSION …. … recovery of a disturbed site.

  4. PRIMARY SUCCESSION Mt. St. Helens pp403-405 Lake Michigan dunes pp416-419 Glacier Bay pp413-416

  5. SECONDARY SUCCESSION Krebs pp419-422

  6. Connell and Slatyer1977 • Succession driven by interactions between species: • FACILITATION • TOLERANCE (COMPETITION) • INHIBITION

  7. FACILITATION …only certain pioneer species can establish after disturbance. Early species enhance the ability of later species to establish. TOLERANCE …any species can invade. Early species have little or no effect on abilities of later species to invade. Later species can displace early species by reducing resources to levels below those tolerated by earlier occupants. INHIBITION …any species can invade. Once established, species resist further invasion and are displaced only by death or further disturbance.

  8. SUCCESSION PATHWAYS A B C D Facilitation Tolerance & Inhibition A B D C

  9. FACILITATION TOLERANCE INHIBITION

  10. A study from abandoned farmland illustrates some aspects of Facilitation, Tolerance and Inhibition (see Krebs pp 419-422) • FIELD ABANDONED IN FALL • 1. INITIAL INVASION: • Horseweed • a winter annual • produces abundant seed • self-allelopathic Conyza canadensis

  11. 2. NEXT SEASON: • Asters • More susceptible to decaying roots of horseweed, than horseweed • Tolerant of dry conditions

  12. 3. SECOND AND THIRD SEASONS: • Bluestem • Seedlings invading since initial abandonment • Broomsedge • Seedlings invading since initial abandonment • More tolerant of dry conditions than Asters • Decaying roots of Horseweed promote growth

  13. Bluestem Broomsedge

  14. SUMMARY • FACILITATION: • Broomsedge is promoted by decaying roots of horseweed & aster • TOLERANCE: • Broomsedge displaces aster through competition for water • INHIBITION: • Horseweed litter prevents aster from persisting

  15. FORCIER 1975 Succession driven by interaction of disturbance & life history traits of species • Studied trees in a New Hampshire forest • Trees with dbh >2 cm (400 plots) • 90% of canopy: • Sugar maple • American beech • Yellow birch

  16. Eastern deciduous hardwood forests Several tree species

  17. Grey Birch, Betula populifera Black Gum, Nyssa sylvatica

  18. Beech, Fagus sylvatica Red Maple, Acer rubrum

  19. SUGAR MAPLE YELLOW BIRCH BEECH r K

  20. CLIMAX MICROSUCCESSION Beech (sprouts) Beech (seed) MINOR DISTURBANCE Sugar Maple Yellow birch CATASTROPHIC DISTURBANCE Successional communities

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