Community Ecology

1. Community Ecology • The concept of a ‘climax’ system – a stable and self-replacing vegetational association that could be determined over large regions using climatic variables • ‘Climax’ system – Clements (1916). Plant Succession: An Analysis of the development of vegetation. • Today, Clement’s ‘climax’ system is known not to exist – • The concept of ‘arrested succession’ – vegetative community may dominate a site long – ultimately, given the right condition, vegetation will shift to another state.

2. Egler’s modification of Clements’ ideas • Mechanisms that controlled why species replaced one another with time • Contrasted Clement’s successive replacement of species (assumed that succession was the orderly and unidirectional replaement of species (or group of species) by other species, as each in turn made conditions less favorable for itself and more favorable for the succeeding species. • Egler’s view: plant species have physiological attributes that determine when they will be present at different successional stages.

3. Egler’s theory of succession • Early successional species are fast growing but shade intolerant • Early successional species are replaced by late successional species when they become shaded • Late successional species grow slower but can survive in the shade of the early successional species, and eventually replce them after small disturbances • Paved the way for the development of predictive’ tools for explaining successional changes in species. Egler. 1954. Vegetation science concepts. Vegetatio. 4:412-417.

4. Oliver’s Four stage-stand development model • Stand initiation stage • Stem exclusion stage • Understory re-initiation • Old growth Oliver, C. 1981. Forest development in North America following major disturbances. Forest Ecology and Management. 3:153-168.