Download Dynamics

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
(1874-1945)
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
(1882-1975)
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
Life history traits
Initial relay floristics (Egler)
• Grasses and forbs (A)
– r-selected, efficient long-distance dispersal, fastgrowing, 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
(1913-2002)
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)