1958: Bryce Canyon National Park

1970

1991

Vegetation dynamics Also known as plant succession –Sequence of compositional and structural vegetation changes through time Why study succession?

Succession Pragmatic reasons: forest management and restoration

Succession Study of succession raises other questions: –How is nature organized? –Are communities highly integrated or are they more individualistic?

Succession Two types of succession –Primary –Secondary

Recovery following eruption on Mount St. Helens--- primary or secondary? Or is this an overly simplistic dualism?

Early views on ecological change Pervasive order, nature as clockwork of God Nature has telos, a guiding hand to development Change is to admit imperfection Succession (and evolution) runs counter to religious doctrine Nature as a cathedral, holy and timeless, without change, a static view of nature

Early views on ecological change Darwin (1859, On the Origin of Species) –Originally held religious, static views of nature –Observation of competition in nature contradicted the perfection of holy design –Competition, natural selection drives change –Change and flux in nature accepted –No telos: there is no external, god-like entity orchestrating natural selection towards an endpoint in a rigid, predetermined way.

History of plant succession Holistic, equilibrial, organismal views (Clements) Individualistic views (Gleason, Whittaker, Watt, Egler) Ecosystem ecology and resurgence of holistic, organismal views (Odum) Disturbance and non-equilibrium ecology Synthesis views that combine holistic and individualistic perspectives

Frederic Clements ( ) Key terms associated with his facilitation model of succession: immutable deterministic equilibrial organismal holistic superorganismal orderly integrated

Contributions of Clements Defined primary and secondary succession Popularized a misleading concept often abused: nature will always grow back to its climax state Immutable pioneer-to-climax sequence brought out critics who saw natural disturbance as overlooked phenomena Introduced idea that evolution works at higher levels than the individual Superorganismal concept has been discredited, but he still receives undue criticism---he had a much more nuanced conception of a climax

Henry Allen Gleason ( ) Key terms associated with his continuum concept: individualistic reductionist random contingent non-equilibrial disorganized

Contributions of Gleason Major works published in mid 1920’s, but not acknowledged for 30 years because of the shadow of Clements Contributed to development of non-equilibrium ecology His work allowed for a much richer possibility of new and novel plant communities Idea of loosely organized plant communities has been abused: if nature is unorganized, then why worry about human impacts, right?

The decline of Clementsian dominance and the turn toward Gleasonian individualism Dust Bowl (1930’s) Chestnut blight (1950’s) Scholars –R.H. Whittaker –Frank Egler –A.S. Watt

American chestnut (Castanea dentata)

R.H. Whittaker (1920–1980) Individualistic Gleasonian Mathematical Gradient analysis Smoky Mountains

Individual species, not entire populations, replace each other during succession (time) and across space (ecotone). In absence of disturbance or environmental discontinuities (a sudden change in soil type or topography) boundaries between plant communities are not sharp.

A.S. Watt (1947) Gap phase dynamics Endogenous disturbance Stability through constant change Dynamic equilibrium Space time substitution

Gap phase dynamics

Space-time substitution in a chronosequence

F. Egler’s (1954) Initial relay floristics model of succession Individualistic Contingent Novelty Life history traits

Initial relay floristics (Egler) Grasses and forbs (A) –r-selected, efficient long-distance dispersal, fast- growing, shade intolerant Pines (B) –Shade intolerant, intermediate growth rate Oaks,hickories (C) –C: k-selected, more local dispersal, slow growing, shade tolerant

The rise of ecosystem approaches to the study of succession: revising Clementsian ideas of development and equilibrium Eugene Odum ( ) Systems ecology Ecosystems Holistic Community controlled Equilibrium Biomass Mutualisms Zero growth economy Homeostasis Scale

Odum: the strategy of ecosystem development (1969) Succession is orderly, directional, and predictable Succession is community-controlled, though physical environment often sets limits Culminates in a stabilized ecosystem in which a maximum in biomass and mutualisms are maintained for the available energy flow. Strategy of succession is increased control of, or homeostasis with, the physical environment to achieve maximum protection from its perturbations.

Rejection of equilibrium views and questions about how to incorporate exogenous disturbance

Inhibition model of succession

Connell and Slatyer (1977)

Did the Gleasonian individualistic paradigm go to far?

Tom Vale (Plants and People,1982)