Introduction to Vegetation Classification and the Biogeoclimatic by thejokerishere

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									FRST 211: Forest Classification and Silvics




  Introduction to Vegetation Classification and the
      Biogeoclimatic Ecosystem Classification
                      System
    Purpose of Lecture Module
• Understand the basic principals of classification
• Introduce examples of classification across a
  range of spatial scales
• Understand the basic concepts of the
  Biogeoclimatic Ecosystem Classification (BEC)
  system
• Become familiar with the BEC framework
        What is classification?
• Grouping together of a set observational units
  on the basis of common attributes

• Vegetation classification: unit of observation
  is the ‘stand’ or ‘community unit’, which is
  homogenous in species composition, structure
  and function
• Ecosystem classification, unit of observation
  is the ‘ecosystem unit’
              Why classify?
• increase our knowledge of ecological units of
  ecosystems being managed
• increase our ability to communicate about
  ecosystems
• provides a framework for planning and
  management
• improves our ability to predict outcome of
  management practices on specific sites
 Practical examples of Ecosystem
   Classification use in forestry

• Foundation for Forest Practices Code
• Ecosystem mapping
• Vegetation inventories (e.g., AAC)
• Silviculture prescriptions
• Silviculture surveys
           Community Units

• To understand ‘community unit’ concept, need to
  understand basic community and succession
  models

• Clements versus Gleason dissent: community
  unit concept versus individualistic concept
     Clements view of ecosystems
• Pioneered holistic view of ecosystems:
  The Development and Structure of Vegetation (1904)
• Ecosystems develop and behave as ‘super-
  organisms

                                                       Frederic E. Clements
• Also interested in Communities and Succession         American Botanist
• Communities replace one another                          (1874-1945)

• There are physiological processes involved in
  succession.

• Succession moves toward climatic climax
  Clements view is similar to Relay
   Floristics model of succession

• Communities represent different seral stages
  over time since disturbance.
• Each seral stage prepares for the next stage.
• Fits well with primary succession.
• Bare rock > Lichens, mosses > herbs > shrubs >
  trees > climax
Clements:
  Abundance




                                                                           Climax
                                                              Shade        shade
                                                              Intolerant   tolerant
              lichens   herbs     herbs      tall     Decid   conifer      conifer
              mosses    grasses   shrubs     shrubs   trees   trees        trees

                                      Time

 Processes: disturbance, migration, reaction, germination, competition, stabilization

 Assumptions:
 •Species differ in dispersal abilities
 •Species differ in physiognomic requirements
 •Pioneers modify the site
 •Later successional species outcompete earlier successional species
 •A stage is reached where the environment is steady
 •All ecosystems progress toward climatic climax
     Gleason’s and Egler’s view of
             ecosystems
            Henry Gleason         Frank Egler
             (1882-1975)         (1911–1996)
           American botanist   American Ecologist



• Individualistic view: communities are merely functions
  of populations, and are not organized in any way
• Distribution of species independent of one another

• Don’t require pioneer species for second species to
  invade bare rock (e.g., spruce on terminal moraine)

• Both primary and secondary succession species co-
  occur
     Gleason’s and Egler’s view of
          ecosystems (cont..)
• All species except a few are present after a disturbance
• Not a turn-over in species but a change in dominance
  over time
• Presence or absence of species is more accidental
• Views more in line with the Initial Floristics model of
  succession (Egler, 1954)
 Despite polarized view, there are widely
  recognized features of communities:

• Similar species combinations often recur
• Species combinations are correlated with their
  environment
• Species are continuously distributed (barring
  shopping malls etc..)
• Species combinations (assemblages) tend to
  change continuously over a wide area
  Terrestrial Ecosystem Classifications

• Vegetation classifications require predetermined
  consistency that never does justice to the
  complexity and variability of the units.

• Terrestrial ecosystems have geographical
  bounds that are gradual, therefore there is
  variation

• Terrestrial classification schemes deal mainly
  with climate, plant communities and soils for
  simplicity
                    Climate
• Most important determinant of nature of
  terrestrial ecosystems (regional climate)
• Best represented by temperature and
  precipitation
• Climate data is scarce for the range of
  ecosystems, so zonal ecosystem concept links
  climate and ecosystem (concept of zonal
  ecosystems)
                Zonal ecosystem
• Best reflects regional climate of an area
• Integrated influence of climate on an ecosystem is most
  strongly expressed in ecosystems least influenced by
  local relief and soil parent material
   – Middle slope position in meso-slope
   – Slope position, gradient, aspect, location that does not result in
     strong modifying influence of climate
   – Gentle slope (5-30%)
   – Soils deep, loamy, freely drained, no restricting horizon
• Because zonal ecosystems are characteristic of regional
  climate, they are used to characterize biogeoclimatic
  units
       Climax and Succession
• Succession: Progressive development of ecosystems
  through time following a disturbance

• Sere/seral stage: One in a sequence of successional
  stages

• Climatic Climax: dynamic equilibrium with climate;
  members are in dynamic balance; pant species self-
  perpetuating (shade tolerant) and in all stages of
  development

• Many of BC forests have escaped large-scale
  disturbances and therefore are at climatic climax

• Some frequently disturbed and never reach climax
       Ecological Equivalence
• The same climax vegetation can occur over a
  range of sites because of the compensating
  effects of environmental factors on plants

• Therefore, a climax plant association may
  represent ecosystems in different regional
  climates with different soils

• Also, plant communities within an ecosystem
  can vary due to chance, site, disturbance, time

								
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