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Deserts, Prairies, and Forests

Deserts, Prairies, and Forests






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    Deserts, Prairies, and Forests Deserts, Prairies, and Forests Presentation Transcript

    • Where Are Plants?
    • The Importance of Abiotic Factors
      Dr. Mark McGinley
      Fulbright Visiting Scholar
      Institute of Biological Sciences
      University of Malaya
    • Let’s Start By Trying to Understand the Plants
      Because the growth form and species identities of plants are diagnostic characteristics of biomes, ecoregions, and communities we will begin by trying to understand the factors that affect the distrubution and growth form of plants.
    • Where Are Plants?
    • Primary Production
      The rate at which carbon dioxide is turned into sugar by photosynthesis
      Typically measured as mass/area/time
      Primary production is important because it is the energy converted from sunlight to sugar by photosynthesis that is available for use by the rest of the food chain.
    • Primary Production
      Units- g C/m2/yr
    • What Limits Primary Production?
      All of the factors that can limit the rate of photosynthesis
    • What Limits Primary Production?
    • Effect of Temperature and Precipitation on Biome Type
    • Patterns We Can Observe
      The rate of photosynthesis varies across the globe
      The number of days per year that plants can conduct photsynthesis varies across the globe
      Primary Productivity varies across the globe
      Primary productivity limited by different factors across the globe
    • Pattens
      Biome type determined by precipitation and temperature (both factors that affect productivity)
      Biomes often defined by dominant plant type
    • Dominant Plant Types
      Deserts- shrubs
      Prairies- grasses
      Forests- trees
      Couple of questions
      1. What are the causes for the differences in dominant plant types among biomes?
      2. What are the ecological implications of these differences?
    • Causes
      All organisms are affected by both abiotic (non-living) and biotic aspects of the environment.
      Temperature, soil moisture, pH, humidity, soil N content, etc.
      Competition, predation, mutualism, etc.
    • Photosynthesis
      I think that it makes the most sense to start with the plants
      Plants get useable energy via photosynthesis
      Photosynthetic rates can be limited by light, soil moisture, and soil nutrient content.
      Let’s start focusing on water and light
    • Water
      Plants pick up water from the soil and lose water to the atmosphere via transpiration
      Transpiration occurs when the plants open their stomata to take up the carbon dioxide they need for photosynthesis
      Water is important to plants because it provides structure (hydrostatic skeleton)
      That’s why you know your house plant needs watering when it starts to wilt
    • How Does Water Get Into the Soil?
      in the areas we are talking about usually rain (any snow in Malaysia?)
      When precipitation strikes the earth three things can happen
      Runs off into streams, rivers, lakes, and ocean
      Infiltrates into the soil
      Water enters the soil as the surface and percolates down
      Sometimes there is permanent “ground water”
    • Desert Plants Live Where There is Very Low Precipitation
      Possible strategies for desert plants to pick up water from the soil
      1. Capture the water as soon as it reaches the soil and the store the water until it rains again
      Shallow, widespread root system
      Protect the water while it is stored
      2. Capture water stored in aquifers
      3. Only live when there is water.
    • Xerophytes
      • Capture water after rainfall
      • Generally have shallow, but far spread root system
      • Greatly reduced leaf size
      • Leaves become spine
      • Reduces transpiration
      • Store water
      • Protected by spines
      Prickly pear Cactus
      Optuntia sp.
      Barrel Cactus
      Ferrocactus sp.
    • Cactus Root Systems
    • Store Water in Their Stems
    • Protect Water- Leaves are modified to spines
    • Cactus “wood”
    • Ground Water
      Water stored beneath the ground in “aquifers”
      Water infiltrates into the soil until it hits an impermeable layer
      The permeable layers are usually gravel and sand
      The impermeable layers are usually clay
      The top of the saturated zone is known as the “water table”
      Plants with roots deep enough to reach the water table have access to a permanent water source.
    • Phreatophytes
      • Produce long root systems that reach permanent ground water
      • often protected by chemical or physical means
      • Also have small leaves to reduce transpiration
      Larrea tridentata
    • Mesquite (Prosopis sp.)
      Mesquite roots can reach up to 50 m below the surface!!
    • Ephemerals
      • Annual plants that germinate, grow, and reproduce when moisture is available
      • Seeds may live for many years in the seed bank until suitable germination conditions occur
      • Seeds are an important food source for desert granivores
      • Rodents, ants, birds
      Desert Poppies
    • Chihuahauan Desert
    • Desert Annual Blooms
    • Interesting Points
      The dominant plant types in deserts, the biome type with the lowest primary productivity are woody (cactii and shrubs)
    • Let’s think about prairies (grasslands)
      Prairies are dominated by grasses
      Family Poaceae
      Grasslands in North America are in the central part of the country where precipitation is higher than in deserts but lower than in forests
      Central US falls within the temperate zone
      Warm summers, cold winters
      Large seasonal changes in temperature and sometimes precipitation
    • Climate Graphs for Wichita, Kansas(Kansas was covered with prairie before farming started)
    • Konza PrairieNear Manhattan, KS
      Warm and wet in the summer. Good for plant growth!
    • Prairies
      Conditions are good for plant growth during the summer when it is warm and wet.
      What happens during the winter when it is cold and potentially freezing?
    • How do plants deal with cold weather?
      Stay alive and active during the winter
      In the US, most evergreen trees are Gymnosperms
      Go dormant during the cold season
      These plants typically lose their leaves before the winter comes - deciduous
      That’s why we call the season that comes between summer and winter fall
      Many angiosperms are deciduous
    • Winter-Deciduous Trees
      If leaves die in the winter, the plants lose all of the resources in the leaves
      Thus, in the fall many species of plants translocate nutrients from the leaves to the roots where it is stored during the winter
      Because chlorophyll, the pigment that makes leaves green, is broken down leaves change color in the fall before they are dropped by the tree.
    • “Fall colors” in the Eastern Deciduous Forest
    • Deciduous trees have no leaves during the winter.
    • Back to Prairies
      Prairie grasses die during the winter. Here is summer…
    • Here is Konza Prairie in the Winter!
    • Grasses are Not Deciduous
      In the fall, grasses translocatenutrients to the roots and eventually the leaves die
      In the spring, new leaves are formed
      Dead leaves (litter) can build up in the prairie!!!!
    • Prairie Fires!!
    • Some Basic Botany
      Not all plant cells are capable of cell division.
      Once cells have differentiated into a certain cell type the can not divide.
      Areas of plants with cells that are capable of active cell division are called “meristems”
    • Apical Meristems
      “Apical meristems” are located at the end of branches and roots.
      If an apical meristem is damaged in some way then that branch or root can no longer grow.
    • Intercalary Meristems
      Intercalary meristems are areas of actively dividing cells located within the stems
      Only found in monocots
      Thus, if the tip of a branch is damaged a plant with an intercalary meristem can still grow.
    • Important Adaptation for Prairie Plants
      Intercalary meristems are very important adaptations to allow plants to survive in the grassland biome.
      Suggest that dicot plants with only apical meristems could not survive well in the prairie environment.
      To understand why we need to think about what can damage the tips of plants in the prairie/grassland?
    • What Can Damage the Tips of Branches in Grasslands/Prairies?
      Abiotic factors
      Biotic factors
    • Abiotic Factors- Fire
      Prairie fires commonly occur in the summer when plants are actively growing
      Warm temperatures
      Fires started by lightning strikes from summer thunderstorms
    • Biotic Factors- GrazersAmerican Prairies used to be covered with huge bison herds!
    • African Grazers
    • Fire and Grazers Can Damage the End of Branches
      How do grasses survive?
      Intercalary meristems are located near or below ground level
      Not damaged by fire or grazing
      Simply regrow after burned our eaten
      Intercalary meristem
    • Grasses appear to be best adapted to living in conditions found in “prairie” biomes
      In slightly more productive environments grasses are the dominant growth form
    • Can’t see the forest for the trees
      As precipitation increases, then it becomes less likely that soil moisture will become the major factor limiting the rate of photosynthesis.
      In these cases, light might become a limiting factor.
    • Light
      Light energy is part of the electromagnetic spectrum that is released by fusion reactions on the sun.
    • Light
      For our purpose, a very important thing to know about light is the seemingly trivial fact that light “shines down”.
    • Competition for Light
      Because light shines “down”, if two plants are competing for light, then the taller plant will win.
      However, there is a limit to how tall a plant can grow without adaptations to help it grow taller.
    • How to plants get “taller”?
      Produce tissues that support tall growth
      Wood => trees
      Grow on top of other plants
    • Wood expensive and non photosyntheitic
      Carbon that is invested in cellulose in wood can not be used to make leaves or roots
      Therefore, in order for natural selection to favor large investment in wood, there must be a big advantage to growing taller.
    • Forests
      Competition for light selections for large investment in wood
      Tall trees
      Canopy layers
    • Tropical ForestsLots of Opportunities for Epiphytes
    • Tropical Rainforests
      Wet and Warm
      Some of the highest productivity of any terrestrial ecosystems.
    • Patterns
      Possible interesting relationship between productivity and dominant plant type
      Lowest- deserts-shrubs (little trees)
      Next lowest- prairies- grasses
      Next highest- forests- trees
      Highest-marshes- grasses (????)