Transcript Deciduous Forest Ecosystems

Deciduous Forest Ecosystems
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Global Distribution
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Climate (1)
• Seasonal climate promotes deciduousness
– Tropics: drought deciduous
– Temperate: cold deciduous
• Roughly 50-150 cm precipitation annually
• As in coniferous forests, P/E > 1, but deciduous
forests have higher AET than coniferous
• More moisture is available during the growing
season
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Climate (2)
• Climate is more moderate (warmer) than
where coniferous forests grow
– growing season is 5-6 months
– trees don’t require evergreen leaves to
maintain positive C balance
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Biodiversity
• Biodiversity of tree
species increases
at lower latitudes
• More conifers are
mixed in at higher
latitudes and in
sandy or nutrientpoor soils
• Much biodiversity
provided by spring
“ephemerals”
– Herbaceous
geophytes that
sprout in April and
die back by July
when light
becomes limiting
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NA deciduous forests
• These forests are
very diverse!
• Forest land is still
increasing in many
areas
• Map by E. Lucy Braun
– PhD in 1914
– Hiked 65,000 miles in
eastern forests
– Advocated for
conservation
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Deciduous forest types of NA
• Mixed mesophytic forest (Great Smokies figs)
– Southern Appalachians
– High species richness (25 tree species/ha)
– Coves may harbor relict species
• Maple-basswood-beech forest
– Shade-tolerant trees
– Moist sites with fertile soils
– Dense canopy
• Oak-hickory forest
– Drier sites with less fertile soils than MBB
– Oaks relatively shade intolerant
– Canopy is more open
– Fire frequency higher than other deciduous forest types
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Deciduous forest types (2)
• Floodplain forest
– Disturbances are common; early seral stage species
are favored
– Bald Cyprus found on wet soils in riparian zone
• Mixed conifer-hardwood forests
– Oak-pine associations in SE (several species of each)
– White pine – red pine – birch – maple in NE
• Some of these forests are likely still undergoing
succession following logging or farming in the
last century
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Visit Bioimages web page to learn more
details about deciduous forest types
http://www.cas.vanderbilt.edu/bioimages/frame.htm
• Chestnut oak
(Q. prinus) is an
important
canopy tree
• Has largely
replaced
American
chestnut
(Castanea
dentata)
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(c) 2002 Steve Baskauf
Tulip poplar flowers
and fruits
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Sugar maple
Sweetgum ranges from midAtlantic states to southern
Mexico
Black oak
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Whittaker’s classic study in Tennessee
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More complex environmental gradients
• Moisture status plays an
important role in species
distributions in coniferous
and deciduous forests
• Concave slopes in
ravines are the moistest
sites; convex, south
facing slopes are the
driest
• Biodiversity is high and
relic species are found in
cove forests
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Spruce-fir
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Structural and
floristic diversity
in cove forests
Silverbell
Yellow buckeye
rhododendron
sweetshrub
Charles Wilder photos
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http://www.dlia.org/atbi/grsmnp_habitats
/forest/deciduous/CEGL007710.shtml
Deciduous forest soils
• Tend to have clay-rich argillic horizons
• Litterfall abundant (~300-650 g m-2 y-1) and less
acidic than conifer litter; maintains soil fertility
• In NE, soils are young, basic cations have not
been leached and so Alfisols are present
• In SE, older soils have lower nutrient status and
basic cations have been leached, so Ultisols are
present
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Nutrient cycling in deciduous forests
• Generally nutrients are less limiting than under
coniferous forests
• Some areas are prone to nitrogen deposition
(acid rain), which may stimulate plant growth up
to a point; becomes detrimental when soils are
acidified and Al is mobilized
• Nutrients are resorbed from leaves before
litterfall
• Relatively fertile soils and long growing season
made eastern deciduous forests ideal for
cropping by early white settlers (well, except for
those darned big trees!)
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Succession (1)
• Large scale disturbances
– Wind, hurricanes, fire, insects (introduced
gypsy moths)
• How does topography affect disturbance?
– Diseases such as Dutch elm and chestnut
blight have caused large scale disturbances
and loss of dominant species
– Chestnuts have been replaced by oak and
hickory
– Some trees can resprout following logging or
fire
– Largest disturbance has been agriculture
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Succession (2)
• Small scale disturbances (Gap dynamics)
– Much more important than in coniferous
forests
– About 9% of deciduous forest area is in gaps
at any point in time
– Old gaps fill at roughly the same rate new
gaps are created; rough steady-state
– Larger gaps favor greater tree diversity
– “Cyclic microsuccession”
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Old field succession: Shade-intolerant
species are replaced by shade-tolerant ones
• Rubus spp. (e.g., blackberries)
establish soon after a cropped
field is abandoned
• Pin cherry seeds last up to 50
years in seed bank and play
important role in early
succession
• Maples are very shade tolerant
but have short-lived seeds, so
grow from seeds that are
dispersed to shady areas
• Yellow birch and quaking
aspen are early successional
species that can persist for a
century or more
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Old-field succession in the Southeast
Topography (moisture status)
influences successional pathways
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