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Understanding Community Properties and Mechanisms

Explore the various concepts and characteristics of plant communities, including associations, assembly rules, and interdependence. Discover the significance of keystone species and the role they play in ecosystems. Delve into the unique traits of different community types like chaparral and fynbos.

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Understanding Community Properties and Mechanisms

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  1. Ch. 9: Community Properties and Mechanisms

  2. Communities • Community: general term for plant cover

  3. Communities • Community: general term for plant cover • Association: formal/

  4. Association • Stands comprising association have: • 1) consistent • 2) uniform • 3) consistent

  5. Association Concept • 1) Organismic View (Clements, 1920s): Along environmental gradient, widespread sp. (B) • Also sp. characteristic associations (C, D, E):

  6. Association Concept • 1) Organismic View (Clements, 1920s) • Node: • Ecotone: assocs.

  7. Association Concept • 1) Organismic View (Clements, 1920s) • Concept: interdependence strong

  8. Association Concept • 1) Organismic View (Clements, 1920s) • Assembly rules: • Assembly rules may operate on guilds

  9. Association Concept • 2) Continuum View (Gleason, 1920s) • Spp. reception

  10. Association Concept • Studies: spp. respond individualistically • b=Siskiyou Mtns CA forests • c=Catalina Mtns AZ forests

  11. Association Concept • Sampling scale/technique matter! • Scale: communities change

  12. How great is interdependence? • Not as strong as Clements proposed • Ex: American chestnut (Castanea dentata)

  13. How great is interdependence? • Major overstory tree Large chestnut trees Mature chestnut 1912

  14. How great is interdependence? • Important food

  15. Blight introduced 1904 • 1950, adults wiped out (“all of them”) Dead chestnuts along Blue Ridge Parkway in 1950s Darth Sidious: 1999

  16. How great is interdependence? • Some still

  17. Reconciliation • Interactions often weak, but can be strong….

  18. Keystone species/guilds • Keystone: sp./guild that Monty Python: Spanish Inquisition Sketch

  19. The Keystone Concept Keystone Dominant Relativeimpact of sp./guild Common but low impact Rare species Relative biomass

  20. Keystone example: sea otters • Top carnivores (almost): eat mussels, abalone, sea urchins

  21. Keystone example: sea otters • Urchins Purple sea urchin

  22. Plant keystone species Hint: Golden dots on leaf • 1) N fixers Granite outcrop

  23. Plant keystone species • 2) Generalist parasites/predators

  24. Plant keystone species • 3) Some nonnative invasive weeds

  25. Community Characteristics • Many!

  26. Physiognomy • Physiognomy: Growth

  27. Sclerophyll scrubland • Growth form: dominated sclerophyll shrubs • Architecture: 1-2 m high, dense interlocking canopy • Chaparral – • Maquis – • Fynbos–

  28. Sclerophyll scrubland Tony Danza as scale! • Chaparral - Western U.S. Arctostaphylos (manzanita) in California chaparral

  29. Sclerophyll scrubland • Fynbos (South Africa) • Plants: floristic • 70% endemic

  30. Community Characteristics • Many!

  31. Leaf Area Index (LAI) • Area

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