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The effects of human disturbances on the productivity of ecosystems

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					The effects of human disturbances
on the productivity of ecosystems




 Lisa Orman
 February 28,
 EEES 4760
               Energy flow

 Light converted by plants
 Into organic matter
 Transferred into other organisms
 Nutrients (N, P) cycle between living and
  non living parts of ecosystem
 These nutrients flow between many
  different levels, from cells to ecosystems
        Healthy ecosystems
 Healthy ecosystems are able to sustain
  functionality and services
 Healthy ecosystems retain soil, water,
  nutrients and organic matter
 Landscapes are composed of two or more
  land units positioned so they are linked by
  processes
The connection between landscape
  heterogeneity and disturbance
   dynamics is one of the most
   important challenges facing
         ecologists today
            Turner et al, 2001
Disturbances
             Disturbances
 Produce a series of successional stages
  that maintain structure and function
 The degree of impact is important in the
  flow of energy
 Minor disturbances can occur at regular
  intervals
 Large disturbances can completely
  change the nutrient flow
    The ecosystem process is
   ultimately determined by the
interaction between the biological
  community and environmental
              factors
              Zhang, 2007
 Ways to study ecosystem function
   Sapling density
   Leaf area
   Aboveground net primary production
   Aboveground biomass
   Carbon cycle
   Percent of ground cover
   Net primary production
     Amount of solar energy converted to chemical energy
 Net ecosystem productivity
     Balance of gross primary production minus ecosystem respiration
                         NPP
 Primary source of food for heterotrophic
  organisms
 Influenced by
   Regional prevailing climate
   Variation in fractional vegetation cover
   Degree to which an ecosystem is altered relative to
    nearby non urban areas, fertilization, irrigation, and
    invasive species
   Seasonal patterns of photosynthetic activity in line
    with urban heat island hypothesis
   Imhoff et al, 2004
  Carbon storage and budgets
 Net ecosystem carbon balance represents
  the net flux of C entering or leaving an
  ecosystem
 Typically after a disturbance, NECB will be
  negative due to decomposition
 Over time, growth rate become greater
  than decomposition rates
             Case studies
 Urban sprawl
 Drylands
 Forests
 Spatial resolution
Urban sprawl
             Urban sprawl
 One third to one half of the planet’s
  surface has been transformed by humans
  (Imhoff et al, 2004)
 In 1992, urban landscape increased by
  25% in the U.S. (Golubiewski, 2006)
 Typically urban sprawl takes over highly
  productive lands--lands with high NPP
                Urban sprawl
 Replaces native vegetation with suburban
    turfgrass, shrubs, and the occasional tree
   Requires irrigation and fertilization
   Non-native species are often bred to out-
    compete native species
   Urbanization accounts for a loss of 4.15 x 10^-2
    Pg of photosynthetically fixed carbon
   Global NPP decrease of 5% (Imhoff et al, 2004)
Drylands
                   Drylands
 40% of the land surface of the globe is
  drylands
 In Australia, they cover 5 million sq km
 Used for rangelands for domestic livestock
                  Wheatbelt
 180,000 sq km
 90% cleared
 Fragmented
  landscape
 Remaining vegetation
  plays an important
  goal in the
  conservation of the
  region
Chequamegon National Forest
   Chequamegon National Forest
            (CNF)
 Management dominated by timber
  production and silvicultural techniques
 AGB used to study productivity, C cycles,
  nutrient allocation, and fuel accumulation
 Remote sensing failed to estimate
  biomass levels at landscape level
 Field observations are necessary to
  understand landscape levels
Pacific Northwest
           Pacific Northwest
 Accumulation of biomass in PNW coniferous
  forests among highest in the world
 Logging of the PNW creates a large C source
  (burning and decomposition) and C sink (long-
  lived forest products)
 Estimates of NPP and NEP greatly affected by
  satellite resolution
 As land use becomes more intensive and
  extensive, scale dependent errors may become
  potentially large
            In conclusion
 The function of an ecosystem can be
  measured by the biomass and production
  of the ecosystem
 The health of an ecosystem is not always
  so straight forward
 Landscape ecology needs continuous
  studies to learn how patterns and their
  dynamics influence ecological processes
  (Turner, 2001)

				
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posted:5/5/2012
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