Cropping Systems and Agroecosystems in the Landscape

1
Cropping Systems and Agroecosystems in the
Landscape
2
Cropping System

• cropping patterns and practices (tillage,
  mulches, etc.) used on a site (or farm).
• Monoculture vs polyculture

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Multiple Cropping

• growing two or more crops on the same field (in
  a year) vs monoculture
• Multiple crops can be separated
• In time sequential cropping crop rotation
• In space two or more crops grown on same land
  at same time intercropping polyculture
  mixed cropping

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Landscape Ecology

• Landscape all ecosystems bordering on the
  particular ecosystem of study
• Agroecosystem in the landscape ag field
  embedded in its surrounding environment

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Overview of an Agricultural LandscapeSmith
McSorley, 2000. Amer. Entomol.
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Genetic Diversity in Field vs Genetic Diversity
in Landscape
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Agroecosystem in the Landscape

• Neighboring agricultural fields
• Natural areas
• Urban ecosystems

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Neighboring Agricultural Fields

• Source of agricultural pests (important in
  regional IPM)
• Possible source of beneficial organisms

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Natural Areas Effects on Agriculture

• Watersheds could reduce floods, erosion, remove
  pesticides, fertilizers, etc.
• Source of ag products and genetic resources
• Source of pests (usually not) or beneficial
  species

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Natural Areas Effects on Agriculture

• Watersheds could reduce floods, erosion, remove
  pesticides, fertilizers, etc.
• Source of ag products and genetic resources
• Source of pests (usually not) or beneficial
  species
• Buffer strips can ease transition from ag to
  natural and provide some of these advantages

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Agriculture Effects on Natural Areas

• Direct Habitat Modification
• Loss of area as agriculture expands
• Fragmentation of natural areas into smaller
  patches, which may be distant from one another
• Erosion of soil from ag into natural areas,
  including aquatic systems

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Agriculture Effects on Natural Areas

• Indirect Habitat Modification
• Habitat degradation from pesticide contamination
  and runoff
• Source of pests that may invade or colonize
  natural areas, including exotic species imported
  from distant regions (e.g., kudzu, melaleuca,
  cane toad)

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Melaleuca Invasive Species in South Florida
Langeland, 2009. EDIS
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Urban Ecosystems

• Nearby market for ag products
• - - Environmental concerns from sprays, etc.
• - - High land value loss of farm

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Interactions Among Ecosystems

• Destruction of ecosystems
• Natural to agricultural to urban succession.
• Agricultural vs. natural farmers concerned
  pests will come out of the woods (not true).
• Urban vs. natural environmental losses
• Urban vs. agricultural concerned about
  pesticide issues.

Nat.
Urban
Ag
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Ecotone transition zone between two ecosystems

• Ecotones are often overlooked
• roads, fences, old fences, wind breaks.
• Ecotone (boundary) more diverse than either
  ecosystem
• numbers of species often greater in ecotone than
  in neighboring habitats.
• Edge effect
• in agroecosystem, edges of fields (near ecotone)
  often most diverse, highest number of species
  (natural enemies).

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Species Diversity at Ecotone
Ecotone
of species
Ecosystem A
Ecosystem B
Distance
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Ecotones

• Ecotones as sources of natural enemies
• U.K. - hedgerows maintained in agricultural
  landscape
• insect predator abundance in field greatest near
  edges (Altieri, 1994)

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Ecotones
Carabid beetle movement into soybean field over
time
Altieri, 1994.
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Ecotones
Altieri, 1994
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Ecotones

• Ecotones as sources of pests
• a) boll weevils overwinter in litter at field
  margin (part of management program was to reduce
  weedy refuges).
• b) weeds at field margin as source of pests --
  difficulty increases with weeds more closely
  related to crop plant (e.g., source of plant
  virus inoculum, similar hosts for herbivores).
• In general, if weedy plants in ecotones are
  related to crop, reduce weeds.

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Ecotones

• Manipulation of field borders to maximize
  benefits of edge effects.
• Altieri suggests long thin fields with plenty of
  borders or add windbreaks and other within-field
  ecotones.

Windbreaks
Long borders
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Diversity

• Biodiversity number of species richness
• Diversity idea is that it is easy to find many
  different species -- so
• 1 there must be many species present
• 2 many species must be reasonably common
• Definitions

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Diversity

• Diversity many species in community of equal
  abundance vs. community dominated by one species.
• Diversity measures of diversity take into
  account richness (many species) and evenness (all
  reasonably common).
• many species in community of equal abundance
  (diverse) vs. community dominated by one species
  (not diverse).

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Diversity evenness example
Abundance of each species in two communities
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Diversity

• Shannon Index
• s total number of species
• pi proportion of species i in total sample
• Diversity increases as
• Species become more evenly distributed in
  abundance
• Species are added to the community (max. value
  for
• H' In s)

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Diversity
If there are 20 individuals of species 1 out of
a total of 100 total individuals in the
community, then p1 20/100

• Shannon Index
• s total number of species
• pi proportion of species i in total sample
• Diversity increases as
• Species become more evenly distributed in
  abundance
• Species are added to the community (max. value
  for
• H' In s)

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Diversity
Do this for every species, up to s total no. of
species
If there are 20 individuals of species 1 out of
a total of 100 total individuals in the
community, then p1 20/100

• Shannon Index
• s total number of species
• pi proportion of species i in total sample
• Diversity increases as
• Species become more evenly distributed in
  abundance
• Species are added to the community (max. value
  for
• H' In s)

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Diversity

• Shannon Index
• s total number of species
• pi proportion of species i in total sample
• Diversity increases as
• Species become more evenly distributed in
  abundance
• Species are added to the community (max. value
  for
• H' In s)

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Sample Data Set for Shannon Index

• Species 1 90 Pi P1 90/100
• Species 2 10 Pi P2 10/100
• -((90/100ln90/100) (10/100ln10/100))
  0.324
• If species 1 0.5 and species 2 0.5, H
  0.693.
• Note max value for a 2 species community is ln s
  ln 2 0.693

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Shannon Index sample calculation from book
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Diversity - Evenness

• Evenness (standardizes diversity on 0 to 1 scale)
• 0.324/0.693 0.468.
• 0.693/0.693 1.00

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Diversity

• Simpsons index
• This is an index of dominance, on 0 to 1 scale.
  Simpsons index of diversity is given by 1/?.
• Example Sp. 1 90, Sp. 2 10
• (0.9)2(0.1)2 0.82

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Diversity Indices

• Many indices are possible see various ecology
  texts.
• Shannon and Simpson are the oldest and most
  commonly used diversity indices.
• Diversity indices evaluate only richness and
  evenness

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References

• Text, Ch. 12, pp. 243-252.
• Altieri, 1994. Biodiversity and Pest Management
  in Agroecosystems. Food Products Press, New York.
• Begon et al., 1990. Ch. 17.
• Carroll et al. 1990. Chs. 13, 18.
• Odum, 1983. Ch. 7.