Community Change – Chapter 21Community ChangeTwo Types of SuccessionMount St. Helens – Primary SuccessionSlide 5Concepts of SuccessionSlide 7Slide 8PowerPoint PresentationThe Climax StateSlide 11Patch (Gap) DynamicsCommunity Change – Chapter 21Community Change•Sit in an open field or wooded lot, and you will see the community change•If we designate a prairie as a protected area and keep out grazers and fire, the grassland will go from prairie  shrubland  forest•Succession – the development of the community by the action of the vegetation on the environment, which leads to additional species being establishedTwo Types of Succession•Primary succession – occurs on new sterile land, such as that uncovered by a retreating glacier or created by an erupting volcano•Secondary succession – the recovery of disturbed sitesMount St. Helens – Primary SuccessionMount St. Helens – Primary SuccessionChance events tend to drive early primary succession – little biological interactionConcepts of Succession•Relay floristics – an orderly hierarchical system of change in the communityMonoclimax hypothesis – the development of the community is a gradual and progressive change from pioneer species to the climatic climax (community determined by the climate).Subclimax community – results from particular soil types, fire, or grazing (refers to the climatic climax)Facilitation model – early species facilitates the arrival of the later species.Concepts of Succession•Initial floristic composition – development at any one site depends on who gets there firstFirst species there either inhibits or has no effect on the next species. Eventually, longer lived species will become the stable community.Concepts of Succession•Random Colonization Model – succession only involves the chance survival of different species and the random colonization of new speciesNo facilitation or inhibition. Succession can move in any directionThe Climax State•The final or stable community in a successional series–Self-perpetuating and in equilibrium with the physical and biotic environment•Monoclimax – only one possible climax state in each region–Take away time and disturbance, will always end up with the same community•Polyclimax – many different climax states can be found in the same area–Climaxes controlled by soil moisture, nutrients, animal activity, or some other factorThe Climax State•Criteria is a steady state over time–Abstract idea, climate is always changing on a geologic time scalePatch (Gap) Dynamics•Space in a forest = light–A large tree falls in the forest and a ‘gap’ in the canopy opens up and light floods the floor (Even if no one hears it!)•A stable community at a regional level may be a mosaic of patches at a local