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factors that determine the nature of the ecosystem that develops on a given site
- - climate
- - topograhy
- - soils
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temperature and precipitation regimes determined by
- - latitude
- - elevation
- - maritime influence
- - relief - orgraphic precipitation
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what factors affect topography
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what factor does slope position influences, and how?
- moisture
- higher position of the slope more rapid drainage
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what is disturbance
any relatively discrete event in time that disrupts ecosystem, community or population structure, and changes resources, substrate availability or the physical environment
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examples of forest disturbances
- fire
- logging
- land slide
- pathogens
- flooding
- wind
- etc.
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what is stand
spatially contiguous group of trees and associated vegetation having similar structures and growing under similar soil and climatic conditions
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spatially contiguous group of trees and associated vegetation having similar structures and growing under similar soil and climatic conditions
stand
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what is forest?
a heterogeneous mosaic of forest stands
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a heterogeneous mosaic of forest stands
forest
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what is landscape
a heterogeneous mosaic of forest stands and non-forest ecosystems
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a heterogeneous mosaic of forest stands and non-forest ecosystems
lanscape
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what is cohort
a group of trees regenerating after a single disturbance until growing space is filled
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what are the stages of stand development
- 1. stand initiation
- 2. stem exclusion
- 3. understory re-initiation
- 4. old growth
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what happen in stand initiation stage
- Re-colonizing the site
- •Available growing space and resources
- •Open growth
- •Single cohort
- • Many species invade
- • Competition with non-tree species
- • Foliage to the ground
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what happen in stem exclusion stage
- – no available growing space
- – increasing competition among trees
- – above ground (light)
- – below ground (water, nutrients)
- •crown closure
- •mortality of smaller trees
- •self-thinning
- •no regeneration
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what happen in understory re-initiation stage?
- •Canopy begins to open
- –some overstory trees die
- –crowns thin as trees get older
- –branches die, ripped off by wind
- •more light reaches the understory
- •understory trees often different species
- •advanced regeneration
- •at least two cohorts
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what happen in old-growth stage
- •trees of all ages and sizes
- •diversity of tree and non-tree species
- •gaps, clumps
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what are the different types of crown classes?
- •Dominant
- •Co-dominant
- •Intermediate
- •Suppressed
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why there are different crown classes?
- •age
- •micro-sites
- •competition
- •genetically superior
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what happens in gaps in forest?
- •openings of any size in the overstory
- •death of one or several trees
- •late-successional species perpetuate themselves
- •usually little disturbance of forest floor
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what happen when there is a stand-replacing disturbance?
stem exclusion, understory re-initiation and old-growth stages will return to stand initiation stage.
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macronutrients
N P S Ca Mg K
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Micronutrients
Mn Zn Bo Fe Cu Mo
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Nutrient Availability
Concentration of nutrients accessible to roots
• dissolved in soil solution
In forms that can be taken up by roots
• ionic forms
• nitrate NO3-, ammonium NH4+, phosphate PO42-
• or simple organic forms e.g. amino acids
Small proportion of total soil nutrient pool
Can limit primary productivity
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how are nutrients available to plants?
- - dissolved in soil solution
- - in ionic forms or simple organic forms
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inputs to ecosystem (nutrient cycling)
- - fixation of gaseous N2, CO2
- - dry deposition
- - wet deposition
- - weathering
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outputs to ecosystem (nutrient cycling)
- - leaching, erosion
- - volatilization
- - denitrification, respiration
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soil -> tree (nutrient cycling within ecosystem)
uptake:absorbed by plant roots and associated mycorrhizae
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within tree (nutrient cycling within ecosystem)
- *Assimilated
- – incorporation into organic forms
- - used as needed for metabolism and growth
*Remobilized – converted back into mobile forms
*Redistributed – moved throughout plant as needed
*Reassimilated – converted into new forms
*Resorbed – remobilized and removed from tissue prior to tissue death
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Resorption within-tree cycling
remobilized and removed from tissue prior to tissue senescence and abscision
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Senescence
aging and death
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Abscision
separation from tree
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tree -> soil (nutrient cycling within ecosystem)
- - litterfall
- - consumption
- - throughfall and stemflow
- - root exudates
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within soil (nutrient cycling within ecosystem)
- - litter decomposition
- - mineralization
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site nutrient supply depends on:
- nutrient capital
- nutrient availability
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decomposition measured as:
- - mass loss in litterbags
- - CO2 release
- - residence time
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Decomposition
primarily a consequence of extracellular enzyme activity of soil microorganisms (fungi and bacteria)
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rate and completeness of decomposition is influenced by
- - any factors that affects microbial activity
- - leaching of water
- - soil fauna
- - sunlight
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Amount of nutrient mineralized depends on ...
rate of decomposition and concentration of the nutrient in the material
Rates of net N mineralization are positively correlated with rates of net primary production in forests
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Site nutrient management entails
- • minimizing losses of nutrients or disruptions of nutrient cycling
- • ameliorating low nutrient supply to increase productivity
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