Deciduous Forest Ecosystems

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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 gt 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 dont 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 nutrient-poor 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)

(c) 2002 Steve Baskauf
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Tulip poplar flowers and fruits
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Sugar maple
Sweetgum ranges from mid-Atlantic states to
southern Mexico
Black oak
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Whittakers 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

Spruce-fir
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Structural and floristic diversity in cove forests
Silverbell
Yellow buckeye
rhododendron
sweetshrub
Charles Wilder photos
http//www.dlia.org/atbi/grsmnp_habitats/forest/de
ciduous/CEGL007710.shtml
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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