Plant Succession

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Plant Succession

• Lauren Fins, Ph.D
• Professor of Forestry
• University of Idaho

Photo Willamette National Forest Old Growth
americanlands.org
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Plant Succession

• Definition
• Stages
• Tolerance

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Plant Succession - Definition

• The orderly process of one plant community
  gradually or rapidly replacing another
• Can result from the developmental changes in the
  ecosystem itself
• Or from disturbances such as wind, fire, volcanic
  activity, insects and disease or harvesting
• In a particular environment, there is a
  characteristic sequence of biotic communities
  that successively occupy and replace each other
  over time following disturbance

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Plant Succession

• Assumptions
• no change in regional climate
• no catastrophic events
• long time frame (hundreds of years)
• Some stages of the characteristic sequence may be
  skipped
• Disturbance moves the community to a different,
  usually earlier, successional stage.

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Stages of Succession

• Primary succession
• Initiated by disturbances that expose substrates
  and are left with essentially no plant growth at
  the beginning
• Examples glacial retreat volcanic ash
  deposition

Mt. St. HelensMay 18, 1980
Gilkey Glacier, Alaska from www.geophot.de

• Secondary succession
• Established plant community has been destroyed
  but without severe disturbance of the soil
• Example forest succession following wildfire -
  pioneer forest re-establishes and is eventually
  replaced with climax forest

wildfirefrom www.us.gov
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Plant Succession

• Seral stages
• Climax stage

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Stages of Succession

• Seral communities The various temporary
  communities in the succession
• Seral species - those that will ultimately be
  replaced
• examples annual plants, shrubs, intolerant trees

eastern white pine invading old fieldHarvard
Forest diorama slide collection
shrub species at Mt. St. Helensphoto by John
Donohue 1995 or 1996
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Stages of Succession

• Climax community The final stage of the
  succession - consists of those plants that can
  reproduce successfully beneath their own shade
  and therefore maintain the community indefinitely
  under the prevailing conditions
• Climax species Those species that will occupy
  the site at the climax stage of succession
• Examples tolerant tree species such as cedar
  and hemlock

eastern white pine replaced by eastern
hemlockHarvard Forest diorama slide collection
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Why do some species replace others in the
successional progression?
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Shade Tolerance

• Refers to the ability of a tree to grow in the
  shade of other trees
• Tolerant species (T) can grow comparatively well
  when little light is available and do not show
  large increases in growth with increasing light
  levels. Climax species
• Intolerant species (I) cannot grow well in low
  light levels but grow very well at light levels
  approaching full sunlight. Pioneer species
• Some species are intermediate (N) in their
  ability to grow in shade

a before disturbance b immediately after
disturbance (5 years) c midpoint of succession
(50-75 years) d full recovery and return to
pre-disturbance conditions
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Relative Shade Tolerance of Some North American
Species

• Very intolerant
• western larch
• subalpine larch
• whitebark pine

Whitebark pine Oregonwww.orst.edu/instruc/for24
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Western larch in mixed conifer stand
Photo - http//forestry.about.com
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Relative Shade Tolerance of Some North American
Species

• Intolerant
• lodgepole pine
• ponderosa pine
• juniper species

ponderosa pine - Oregonwww.orst.edu/instruc/for24
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lodgepole pine Oregonwww.orst.edu/instruc/for24
1
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Relative Shade Tolerance of Some North American
Species

• Intermediate
• Douglas-fir
• western white pine
• giant sequoia

western white pine
Douglas-fir Oregonwww.orst.edu/instruc/for241
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Relative Shade Tolerance of Some North American
Species

• Tolerant
• grand fir
• subalpine fir
• Engelmann spruce

grand fir needles www.geocities.com
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Relative Shade Tolerance of Some North American
Species

• Very tolerant
• western redcedar
• western hemlock
• Pacific yew

Western redcedar at Ross Creek, Montana Photo by
John R. Pierce
western redcedar, western hemlock and others at
Ross Creek, MTphoto by John R. Pierce
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Classic Forest Succession

• Grass-forb
• Forbs, grasses and shrubs dominate the site
• Shrub-seedling
• Trees tend to share and then begin to dominate
  the site. The shade intolerant species grow
  rapidly and dominate over shade tolerant species
• Sapling-pole
• Trees eventually overtop and out-compete the
  forb and shrubs. The intolerant trees continue
  rapid height growth while the shade-tolerant
  trees occupy their respective niche

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Classic Forest Succession

• Young
• Growth is still rapid. Tree-to-tree competition
  may be severe resulting in competition-caused
  mortality. Any intolerant individuals that drop
  behind may die and their growing space may be
  occupied by the tolerant trees.
• Mature
• Competition-caused mortality continues. Both
  intolerant and tolerant trees may share the main
  canopy. In mixed conifer stands, there may be
  distinct layering of intolerants and tolerants.

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Classic Forest Succession

• Climax
• Shade-tolerant trees dominate the site and the
  climax species will reproduce.
• Shade-intolerant trees cannot replace themselves.
  
• Most climax stands (old growth) are set back to
  the early seral grass-forb or shrub-seedling
  stage by fire in the Northern Rockies.

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Buell-Small Successional StudyHutcheson Memorial
Forest Somerset County, New Jersey
First year field dominated by annuals
Fifth year field dominated by goldenrod
Year 10 field dominated by goldenrod, asters,
yarrow, daisies eastern redcedar invading
Year 28 red maple dominates
Year 20 dogwood, oaks and maples invading along
with redcedar
Photos from www.ecostudies.org
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Forest Succession - Summary

• Plant communities continually change
• The community is a continuum in time and space
• New species invade the site
• Existing species continue to reproduce or they
  eventually disappear
• Succession results in a rich dynamic tapestry of
  vegetation, providing an array of habitats for
  animals and microbes. (Perry 1994)

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Distribution of forest species along
environmental gradients in eastern
Washington/northern Idaho
(whitebark pine)
(mountain hemlock)
(subalpine fir)
(Engelmann spruce)
(western hemlock)
(western redcedar)
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Forest Classification

• Cover type refers to species that are currently
  present on the site
• Habitat types indicate the potential climax
  vegetation on a site if left undisturbed
• Habitat types are named for the climax tree
  species and an understory indicator species -
  example Pinus ponderosa/Physocarpus malvaceus
  (ponderosa pine/ninebark)

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Comparison of the distributions of habitat series
in northern Idaho
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Misconceptions about Habitat Types

• An abundance of climax vegetation is present in
  the current landscape
• We should manage the resource to promote climax
  vegetation
• To apply the habitat type classification system
  requires climax vegetation to be present