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How Plants Grow & Respond to Disturbance

How Plants Grow & Respond to Disturbance. Succession & Disturbance. Community change is driven by successional forces: Immigration and establishment of plants Competition between plants Site modification Stabilization. Succession & Disturbance. Disturbances affect succession: Fire

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How Plants Grow & Respond to Disturbance

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  1. How Plants Grow & Respond to Disturbance

  2. Succession & Disturbance • Community change is driven by successional forces: • Immigration and establishment of plants • Competition between plants • Site modification • Stabilization

  3. Succession & Disturbance • Disturbances affect succession: • Fire • Grazing • Drought (climate/weather) • Human activity To understand how disturbances affect community change, must understand how these disturbances affect plant growth.

  4. Functional Categories of Plants Annual (grass, forb) Perennial (grass, forb) Woody Deciduous or evergreen Sprouting or non-sprouting (basal) Cool season or warm season Anti-herbivory Chemical Physical These factors affect how plants respond to disturbance

  5. Major Plant Groups on Rangelands Tree Dicots Monocots Shrub • Grass • Grasslike Forb These factors affect how plants respond to disturbance

  6. Key Points of Plant Response • Location of Growth Points • Growth Limiting Factors • Importance of Roots • Carbohydrates – Energy for Growth

  7. Location of Growing Points Keep meristems out of reach Keep meristems out of reach

  8. Location of Growing Points • Location depends on season • Early in the growing season - close to the ground and protected. • As the season progresses - elevates and subject to removal. Apical Meristem Axillary Buds

  9. Factors Limiting Plant Growth Environment Heat - optimal temperature Humidity Belowground (i.e., roots) Water Nitrogen and other nutrients Aboveground (i.e. shoots) Light CO2 Growing points (i.e., meristems)

  10. Allocation of Plant Resources Carbon Allocation Patterns • CHOs Needed: • To reestablish photosyn material • For seed production • For root growth • Excess stored in roots & crowns

  11. Allocation of Plant Resources Plants allocate resources (i.e., phytosynthate) with the priority towards acquiring the most limiting resource(s). • If water is limiting, allocation shifts to roots • If leaf area is limiting, allocation shifts to leaf growth

  12. Key Concepts Nitrogen uptake is with water If water is limiting, N will be limiting Fertilizer application not usually effective in dry environments Level of available N in the soil affects plant species composition Weeds require higher levels of N than late seral grasses

  13. Importance of roots Remove the Leaves ----- Affect the Roots

  14. Root Responses to Defoliation 50% 70% 90% Level of Removal

  15. Root Responses to Defoliation Root growth decreases as > 50% of the plant leaf area is removed. Frequency of defoliation also affects root growth. The more intense the defoliation, the greater the effect of frequency of defoliation.

  16. Consequences of Reduced Root Growth The net effect of severe grazing is to reduce: Total absorptive area of roots. Soil volume explored for soil resources e.g. water and nitrogen. How may this alter competitive interactions?

  17. Carbohydrates – Energy for Growth Current photosynthesis is the primary source for growth of new shoots. Carbohydrate reserves exist and they provide a small amount of energy to contribute to initial leaf growth following fire, grazing, or other disturbance.

  18. What we now know makes this untrue FALSE

  19. Season is Important • Effect of grazing, fire, or mowing varies according to: • Season of use & Phenological stage -- Plants are more resistant to intense herbivory during dormancy than in active growth. • Opportunity for re-growth – Will plants be able to produce new leaves and develop strong root systems prior to entering dormancy following defoliation?

  20. Season is Important Potential Damage to Herbaceous Plants from Defoliation Potential Damage Green-upGrowth Initiation Dormancy Flowering/Seed Set • High Demand for energy and nutrients • Limited Resources for recovery • Low Demand Low biomass & low need for CHOs • Abundant Resources for recovery • time, moisture, nutrients temperature • Very Low Demand

  21. Season is Important http://www.youtube.com/watch?v=YR-mowuYcCA

  22. Take home message Leaf material provides resources to recover after disturbance. Amount of roots is important to provide resources for recover. Climate favors or hinders recover from disturbance.

  23. Key Points of Plant Response • Location of Growth Points • Growth Limiting Factors • Importance of Roots • Carbohydrates – Energy for Growth • Season

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