Community Ecology

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Community Ecology

• The Community as an Ecological Unit
• Community Development

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Plant Communities

• Communities are composed of populations of many
  species living together in the same location at
  the same time.
• Similar communities tend to occur under similar
  environmental conditions.
• Associations have a consistent species
  composition and habitat
• But, composition can vary considerably from one
  location to another.

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Examples of Communities

• Dune plant community includes beach grass,
  seaside golden rod, beach heather, sea rocket,
  beach plum, pine trees, (and many other species).

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Some Characteristics of Plant Communities

• Architecture (forest layers)
• Species diversity
• Density how many individuals, regardless of
  species occupy a given area
• Nutrient cycling (demand, storage capacity)
• Development over time (succession)
• Productivity (Biomass)
• Microenvironments

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Plant Communities The Piedmont Forest

• Part of the temperate deciduous biome
• Precipitation relatively high
• Soils rich in organic matter
• Broad-leaf trees that lose their leaves
  seasonally dominate
• The piedmont is defined as the plateau between
  the coastal plain and the Appalachian mountains.
• The foothills of the Appalachian Mountains

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Maryland Biogeography

• Coastal Plain
• Piedmont Province
• Upland
• Lowland
• Ridge/Valley Province Middle
• Appalachian Plateau Province
• Allegheny Mountain section

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The Piedmont Forest

• How old is the Piedmont region?
• Underlying geology dates billions of years old.
• Granite, gneiss, mica-schist, gabbro, marble, and
  serpentine
• Soil types loams and clay
• Loamy soils contain sand, silt, and clay
• Holds water, but also drains well
• Good aeration
• Clay packs tightly, little water retention,
  little aeration
• Land-use history
• Deforestation beginning in the colonial period
• Primarily agricultural until the late 20th
  century
• Chestnut-Oak forests until 1930s chestnut blight
• Oak-Pine or Oak-Hickory forests

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Layers of the Forest
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Layers of the Forest
1. Canopy
2. Understory
3.Shrubs
4. Herbaceous plants
5. Forest Floor
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The Forest Community

• The Canopy
• the leafy crowns of the trees
• most of the forests food is made here
  (photosynthesis)
• feeding ground for many animals
• just below the surface of the upper most layer of
  leaves
• leaf eaters beetles, bugs and caterpillars, leaf
  hoppers, aphids etc.
• Song birds and predatory insects (spiders) feed
  on the insects
• Squirrels (eastern gray squirrel)
• protection for the forest below

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Canopy Trees of the Piedmont Forest

• Several species of Oak
• Bitternut Hickory
• Buckeye
• Red Maple
• Beech

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The Understory

• Smaller trees make up the understory
• Young trees (same species as canopy trees)
• Low-growing trees (dogwoods)
• Many birds and animals spend most of their lives
  in the understory.
• Good for nesting, protection from hawks, owls,
  and stormy weather

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Understory Trees of the Piedmont Forest

• Dogwood
• Redbud
• Paw-Paw
• Service Berry
• Musclewood

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Shrub Community

• Shrubs are woody plants with many stems
• A characteristic canopy will harbor a
  characteristic shrub community
• Oak-Hickory forest
• Spicebush
• Blueberry
• Witchhazel
• Huckleberry (Dangle berry)
• Rarely greater than 7 feet in height

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Blueberry
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Shrub Community

• Protective cover for small mammals
• shrews
• mice
• chipmunks
• Nesting sites for Robins (in shrubs)
• Berries and seeds for many mammals and birds

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Herbaceous Layer

• Emerges during the spring before the canopy is
  fully leafed-out
• Ferns and mosses
• Lichens
• Wild flowers
• Spring Beauties
• Violets
• Orchids
• Lilies
• The herbaceous layer dies out by mid-summer,
  existing underground as bulbs rhizomes

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Northern VioletViola sp.
Spring BeautyClaytonia virginica
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Lichens and Mosses
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Forest Floor

• The wastebasket for all the layers of the forest
  above
• Leaves, petals, fruits, seeds, twigs, limbs,
  whole tree trunks, feathers, fur, feces, animal
  carcasses
• estimated 2000-3000 lbs/acre in the fall
• in various stages of decay

Yellow coral mushroom
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• A handful of dirt viewed with a magnifying glass
  reveals
• earthworms, other nematodes
• mites, spiders, black ants, and many other
  insects
• Many more organisms are microscopic
• The plants and animals on one acre may out number
  the entire human population by 106 to one!
• Decomposers of the forest ecosystem break down
  the organic matter and release inorganic matter
  (Nitrogen, O2, etc)

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Forest Dynamics

• How does the canopy affect the other layers of
  the forest?
• The amount of sunlight entering the lower layers,
  which controls photosynthesis temperature.
• Influences shading and temperature,
• Important sources of organic material for
  decomposers, invertebrates and aquatic (stream)
  organisms.

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Assessing Forest Communities

• Density how many individuals, regardless of
  species occupy a given area
• Age class
• Basal Area
• Canopy cover
• Species Diversity

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Measuring the size of trees

• Diameter breast height (dbh)
• Measures the girth of a tree
• Estimates age of the tree
• Saplings vs. Mature
• The larger trees (older trees) have the greatest
  impact on the other trees in the forest

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Estimating Tree Basal Area

• Basal area measures the area occupied by a tree.
• It is reported in ft2 per acre or
  meters2/hectare
• Measure of biomass and productivity and

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Dynamics of the tree community in an area of
tropical semi-deciduous forest.
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Measuring Canopy Closure

• How much light is hitting the forest floor?
• The amount of shading influences the temperature
  of habitats under the canopy
• Using a densitometer

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Measuring Diversity in Plant Communities
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Levels of Biodiversity

• Genetic diversity the gene pool within a
  population
• Species diversity the number and types of
  species in an area
• Higher taxonomic diversity (Families, Genera)
• Community Diversity
• Ecosystem diversity (Habitat diversity)

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Species diversity has two components

• Species richness how many different species are
  present in a habitat
• Species abundance total number of individuals of
  each species present. Usually expressed as

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Defining Biodiversity

• Old growth forest in the Shenandoah Mountains of
  Virginia
• 50,000 trees represented by 10 species.
• Managed forest, recently clear cut
• 45,000 trees are maple and birch
• Only 1/10th of the forest is represented by the
  remaining 8 species

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• Species diversity has two components
• Species richness how many different species are
  present in a habitat
• Relative abundance total number of individuals
  of each species present
• Which area is more diverse?
• There are many diversity indices used by
  ecologists
• Shannon-Weiner Diversity Index

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Community DevelopmentEcological succession

• Defined as the transition in species composition
  over ecological time
• Plants and animals appear and gradually alter
  their environment as they carry on their normal
  activities.
• The accumulation of waste, dead organic matter,
  and abiotic factors such as light and water
  availability further alters the community.

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Community DevelopmentEcological succession

• Primary succession
• Occurs in an area not previously inhabited
• Areas that have been completely devastated by
  disturbance
• Secondary succession
• Occurs where there is a pre-existing community
  and well-formed soil

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Mount St. Helens Eruption in 1980

• Five explosive eruptions of Mount St Helens in
  1980 sent pumice and ash 6-10 miles into the air.

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The Aftermath of Mount St. Helens Eruption

• These trees were blown down by a lateral blast.
  This is an example of where the process of
  primary succession will begin to bring new life

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Primary Succession

• Occurs on essentially lifeless terrain
• Volcanic eruptions
• Retreat of glaciers
• May take hundreds to thousands of years
• The first group of organisms to appear
• Autotrophic bacteria
• Lichens
• Mosses (organisms that reproduce by spores)
• Grasses, ferns, shrubs, pine trees

• Lichens are a symbiotic relationship between
  Algae and Fungi. They secrete acid that turns
  rock into soil. Once the soil is established,
  plants can colonize

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Primary Succession

• Iceland is a new country emerging from both the
  recent ice age and frequent volcanic eruptions

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Primary Succession in Ponds and Lakes

• Bogs

• Algae carried in by birds and the wind
• They die and fall to the bottom contributing to
  the organic matter.
• Duckweeds form at the edges
• When nutrients, oxygen, pH, and temperatures are
  low
• Peat mosses take over, forming a thick mat.
• Woody shrubs and carnivorous plants grow on this
  substrate

• In the Northern US, many ponds and lakes are were
  left behind by the receding glaciers (10,000ybp)
• Many ponds become bogs.
• have no streams drainage, so they are filled by
  precipitation
• Grow smaller every year because of succession

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Bogs are an example of Primary Succession

• Peat moss

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Duckweeds occur early in succession

• Under less acidic conditions, duckweeds are one
  of the 1st plants to grow
• Grass-like sedges become established and form a
  mat
• Once a mat is formed, bushes, shrubs and trees
  become established

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Secondary Succession

• Existing community has been disturbed
• Soil is intact
• Abandoned Agricultural fields
• Old field succession
• Climax community can become established after
  only decades
• Disturbance colonizers weedy plant species
• a high reproductive rate,
• good at dispersal

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Old Field Succession
70th-100th Pine to Hardwood transition
3rd-18th year Young Pine forest
1st year Horseweed Crabgrass pigweed
19th-30th year Mature pine Forest Understory of
Young hardwoods
100th year plus Climax Oak-hickory forest
2nd year Asters Crab grass
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Disturbance

• Disturbance is a natural part of the life of a
  community
• Most communities are always in recovery from
  disturbance
• Humans, too, are agents of disturbance

Tsunamis Hurricanes Storms
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The Nature of Disturbance

• Damage communities
• Alter the resources available to organisms
• Disrupt the food chain
• Removing organisms!!
• Opportunity for secondary succession to rebuild
  community
• Examples of Disturbance
• Storms, Hurricanes, Tsunamis
• Ice storms
• Flooding
• Tornados
• Fire

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Fire Ecology Yellowstone fires of 1988 Fire is
being used to manage marshes and forests
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