Bot1320 Chapter 3 The Geography of Grass
  1. The rain shadow cast by the prevailing westerlies results in a pattern of precipation that supports a diverse array of biomes.
    • • The Great Plains ecoregions can be classified into 4 types based largely on precipitation:

      • Short Grasslands occur where annual precipitation is less than 400 mm.

      • Mixed Grasslands take over where annual precipitation reaches up to 600 mm.

      • Tall Grasslands thrive where annual precipitation can accumulate up to 1000 mm.

      • Woodlands and Savannas occur in pockets of low-lying land where soil moisture supports trees.
  2. Periodic fires keep woody trees from taking hold in the grasslands.
    • • The Tall Grasslands on the eastern margin of the plains receive sufficient precipitation to support trees.

      Before European settlement, periodic fires were initiated by lightning strikes or set by Native peoples for hunting.

      Most trees were killed by the fires, while the herbaceous grasses and forbs can re-sprout from their deep roots or re-grow from seeds.

      Human suppression of fires in recent decades has contributed to the decline of prairies and other ecosystems that were historically maintained by fires.

    • Controlled (or prescribed) burning is now necessary to maintain the health of remnant prairies.

      The burns should remove many invasive plants not adapted to fires, but can also decimate animals such as this American Toad (Bufo americanus).

      A responsible burning strategy should leave unburned areas to serve as refuges for animals; the surviving animals (some may be in egg stage at the time) can then re-populate the habitat.

  3. Prairies are populated by herbaceous grasses and forbs that undergo photosynthesis to provide the base of the food chain.
    • • Prairies are dominated by grasses such as Big Bluestem.

      Grasses do have inconspicuous flowers that are apetalous and scentless.

      They do not attract insect pollinators and are pollinated by wind.

    • Big Bluestem (Andropogon gerardii) is the Illinois state grass.

      Also called Turkey Foot, this is a characteristic grass of the tallgrass prairie.

    • • Herbaceous flowering plants other than grasses are called forbs, providing vibrant diversity to the prairie landscape.

      This Prairie Sunflower (Helianthus rigidus) has bright flowers and sweet nectar that attract pollinators, initiating a complex food web.

    • • A typical plant leaf contains several layers of cells.

      An outer layer of epidermis cells is covered with a waxy, watertight cuticle that prevents dehydration.

      Embedded in the epidermis are stomata, openings formed by pairs of cells that regulate gas exchange with the atmosphere.

      A middle layer of mesophyll cells contain green chlorophyll pigments where photosynthesis occurs.

    • Photosynthesis is the process that captures light energy and converts low-energy CO2 (carbon dioxide) into high-energy sugar molecules.

      This process also requires H2O (water) and releases O2 (oxygen) as well as H2O.

      The release of water from the stomata of plants is called transpiration.

      Transpiration from plants may contribute to cloud formation; thus periods of rain may lead to a cyclical formation of more clouds due to increased photosynthesis.

  4. Prairie plants as well as animals are adapted to periods of drought.
    • • Prairie grasses and forbs possess many traits to endure cold winters and hot summers of the Great Plains.

      These adaptations to conserve water include:

      • linear leaves of grasses

      • deep roots

      • hairy surfaces

      • alternating stages of photosynthesis

    • • The Great Plains climate is influenced by the interplay of four strong winds.

      The rain shadow causes dry prevailing westerlies that sweep over the Great Plains.

      Arctic air from the north often carries severe cold to the continental interior in the winter.

      Desert air blowing in from the southwest yields hot and dry summers.

      Gulf air from the Gulf of Mexico brings seasonal moisture in spring and fall, sometimes producing violent thunderstorms.

    • Grass leaves are typically linear: the long and narrow blades reduce the surface area over which water vapor can escape through stomata.

    • • Prairie plants have long roots that penetrate deep into the soil to seek moisture and survive fires.

      A Compass Plant, (Silphium laciniatum) for example, can tower more than 5 feet above ground; its root system can be more than 10 feet deep.

      The tallgrass prairie can be considered an "upside down forest", according to Russell Kirt, with 60-80% of the biomass underground

    • Hairy stems and leaves help reduce wind velocity across plant surfaces, thus reducing water loss through evaporation.

    • Photosynthesis has 2 stages.

      • The light reactions take place in the presence of light, and uses H2O to make energy molecules ATP and NADPH, releasing O2.

        This takes place during hot daylight hours; plants can close their stomata to prevent water loss.

      • The Calvin cycle uses the energy molecules from the light reactions to convert CO2 into sugar.

        This requires CO2 from the atmosphere but not light, so can take place in the cooler night time when plants open the stomata, minimizing the loss of H2O.

    • Mormon Crickets are adapted to the arid climate of the Great Plains.

      The egg hatching rate is higher during warm, dry seasons, sometimes leading to outbreaks of large swarms.

      This female katydid has a long ovipositor for depositing eggs in vegetation.

      She has picked up a spermatophore (the white ball beneath her ovipositor: a nuptial gift from a male).

      Katydids in northern Illinois include:
      Black-legged Meadow Katydid
      Greater Angle-wing Katydid.