Lecture 21: Community Dynamics Flashcards
Succession
change in species composition over time
Primary succession
all life is gone, no soil at beginning
ex. lava flow, strip mine
Secondary succession
some life is still present after disturbance; soil present at the beginning
Ex. hurricane, clear cut forestry
Ex. Primary succession on sand dunes of Lake Michigan
Facilitation model
Marram grass → dominated by various grasses and forbs → dominated by various shrubs → dominated by white pine trees → dominated by deciduous broadleaved trees
Climax community
The endpoint of succession
Characteristics of old growth forests
Standing dead trees (snags), many large logs, no stumps, tree rings
High diversity
Species not found in other communities
Rare species (ex. Northern spotted owl)
Life histories of early succession species include
good dispersal, poor competitors
Life histories of late succession species
include poor dispersal, strong competitors
Connel and Slatyer
explain classic ideas of mechanisms of deterministic succession
Examinations of real successional sites show that
successional trajectories are often not marches to a single endpoint
Classic succession include
Primary and secondary succession
Alternatives to classic succession
Disturbance maintained communities
Succession proceeds, then stopped by repeated disturbances before reaching its potential ‘climax community’
Change in 2 directions
Pattern of community change: Disturbance maintained communities
communities stay stable due to regular disturbances
Ex. a tall grassland (central Us, southcentral Canada) and fire is an intrinsic part of the community
Pattern of community change: Succession proceeds, then stopped by repeated disturbances before reaching climax community
Stable cycle
Ex. Conifer forests of Northern Rockies
Post fire vegetation (tree seedlings, forbs) –> Conifer forest of Northern Rockies
Crown fire makes forest return to forest post fire vegetation
Crown Fire and adaptation of lodgepole pine
Natural
Result in patchy mosaic
Lodgepole pine regeneration is fire adapted, seeds release from serotinous cones in fire, need open sunny areas to germinate
