stand dynamics sept 9 cp
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Disturbance and Stand Development
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Disturbance
any relatively discrete event in time that
disrupts ecosystem, community or population
structure, and changes resources, substrate
availability or the physical environment
White and Pickett 1985
biotic or abiotic
human-caused or natural
single-tree, gap-forming or stand-replacing
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Examples of forest disturbances
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Recognizing forest disturbances
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Stand Development
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landscape
Stand spatially contiguous group of trees and associated vegetation having
similar structures and growing under similar soil and climatic conditions
- relatively homogeneous
Forest a heterogeneous mosaic of forest stands
Landscape a heterogeneous mosaic of forest stands and non-forest ecosystems
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Stand Development
4 main stages of development of even-aged
stands following stand-replacing disturbance
Cohort: a group of trees regenerating after a
single disturbance until growing space is filled
Cohorts may range in age from years to
decades
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Stand initiation
Stem exclusionUnderstory re-initiation
Old growth
Stages of stand development
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Stand Initiation Stage
Re-colonizing the site
Available growing space and resources
Open growth
Single cohort
Many species invade
Competition with non-tree species
Foliage to the ground
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Stem Exclusion Stage
no available growing space
increasing competition among trees
above ground (light)
below ground (water, nutrients)
crown closure
mortality of smaller trees
self-thinning no regeneration
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Understory Re-initiation Stage
Canopy begins to open
some overstory trees die
crowns thin as trees get older
branches die, ripped off by wind
more light reaches the understory
understory trees often different species
advanced regeneration
at least two cohorts
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Old-growth Stage
trees of all ages and sizes
diversity of tree and non-tree species
gaps, clumps
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Crown classes
Dominant
Co-dominant
Intermediate
Suppressed
Why differentiation?
age
micro-sites
competition
genetically superior
http://www.dnr.state.md.us/education/envirothon/forestry/silviculture.html
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Gap Dynamics
Gaps:
openings of any size in the overstory
death of one or several trees
late-successional species perpetuatethemselves
usually little disturbance of forest floor
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Stand initiation
Stem exclusionUnderstory re-initiation
Old growth
Stages of stand development
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Stand initiation
Stem exclusionUnderstory re-initiation
Old growth
Stand-replacing disturbance
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Stand initiation
Stem exclusionUnderstory re-initiation
Old growth
Hastening stand development