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Lecture 9: Soils and Forests (Soils (Good soil Properties (Transmits…
Lecture 9: Soils and Forests
Soils are complex and dynamic
Varying proportions of minerals, organic matter, void space
Soils are formed by weathering (less weathering = less soil)
Physical
Chemical
e.g. Atmospheric CO2 causes weathering and chemical reactions
CO2 Feedback System
Biological
'Coffee Model'
Soil Formation and composition
Factors Influencing Formation (Info in Textbook table 7.1)
Bedrock
Topography
organisms
Climate
Time
Soils
Good soil Properties
Transmits moisture and air
Allows excess moisture to drain
Provides adequate nutrients
Retains nutrients and water
Good soil Composition
Inorganic matter (~45%)
Organic matter ~ 5%
water ~25%
Air ~25%
'Porosity'
Void space
Organisms
Soils = Complex ecosystems
Ecosystems services
Nutrient Cycling
Soils and Biogeochemical Cycles
Nutrient Depletion
Soil Horizons
Different horizons: O,A,E,B,C,R
Soil Variability
Highly variable
Easily depleted
Easily Eroded e.g. Madagascar
Distribution of particle size determines soils texture
Soil Texture
Silt
clay
Sand
Soil Properties vs Texture
Acidity
Strogly influences productivity and nutient solubility
Soil Erosion and degradation
Occurring globally, mainly due to agriculture
Soil Problems
Erosion
Can cause loss of fertility
More fertilizer required
By water
Vegetation
By WInd
Transport magnitude
E.g. The 'Dirty 30s' (American Dust Bowl)
Drought and poor soil management practices
Topsoil loss vs yeild
Soil Salinization
Land Degradation
Desertification: Product of nutrient or soil loss
Soil Conservation
Conservation/Zero Tillage
Crop Rotation
Other methods:
Contour Plowing
Strip Cropping
Terracing
E.g. Intercropping (3 sisters) Corn, Beans, Squash
Corn grows tall, provides structure for beans
Beans puts nitrogen back into soil
Squash grows wide, preventing weeds from growing
Soil Reclamation
Shelter belts
Forests
Basic Facts
Forests cover about 31% of earth's Land surface
Trees have several basic requirements
Three Major groups of forest biomes
Boreal forest
Temperature Forest
Tropical Forest
Canada's Forests are varied and valuable
Trees Provide Ecosystem Services
Forests are Economically Valued
Plantation Forestry has increased
Timber Harvesting
Clearcutting
Seed tree and shelterwood
Selection harvest
Land Conversion and deforestation
Pest infestations have become increasingly problematic
Forestry Management Principles
Forestry
Harvesting
Public forests in canada are managed for many puposes
Mangement
Ecosystem based management = Managing the harvesting of resources to minimize impact on ecosystems and ecologocal processes
Adaptive management = Systematically testing different management approaches and aiming to improve methods
e.g controlled fires
Climate change poses new management challenges
Sustainable forestry is gaining ground