Grasslands Study Notes

Terrestrial Ecosystems: Grasslands

Defining Grasslands

  • Natural grasslands: Rainfall 25-80 cm/year.

  • Shrunk to <12% of original size.

  • Occur in midcontinental regions with reduced annual precipitation.

  • Temperate grasslands experience recurring drought; productivity influenced by precipitation and temperature.

  • Evolved under selective pressure of grazing; major consumers include invertebrates, particularly nematodes.

Types of North American Grasslands

  • Six Major Types:

    1. Mixed grass prairie

    2. Tall grass prairie

    3. Short grass prairie

    4. Desert grassland

    5. Palouse grassland

    6. California annual grassland

  • Types reflect height of dominant species, linked to precipitation and temperature.

Grassland Structure

  • Herbaceous Layer:

    • Upper: Tall grasses, flowering stems of forbs.

    • Middle: Shorter grasses and forbs.

    • Lower: Ground-hugging plants.

  • Ground Layer:

    • Thick mulch layer aiding in decomposition, soil moisture, and stabilization.

  • Root Layer:

    • More developed than in other vegetation types; stores food, supports vegetative reproduction.

Human Impacts

  • Cultivation and agriculture.

  • Fire suppression.

  • Invasive alien plant species.

  • Replacing natural grazers with domestic stock, leading to overgrazing.

Key Points

  • Grasslands play critical roles in ecosystem function influenced by disturbance mechanisms.

  • Grazing and fire are essential for maintaining grassland health.

  • Human activities have significantly diminished grassland areas, affecting ecosystem resilience.