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Lecture 5

EESC 3310 Lecture 5: Week 5 (9/27)

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Earth & Environmental Sciences
EESC 3310

Exam: focus on lectures, use learning objectives as a guide, use EXAMPLES to illustrate points NITROGEN CYCLE *** The Role of Fire in Agroecosystems and the Environmental Complex ➢ Fire in Natural Ecosystems ○ Surface fire: shallow, not too hot, quick, burns surface litter and vegetation ○ Crown fire: canopy is consumed, mature plant species are killed ○ Ground or subsoil fire: slow and destructive occurring in soil with high OM ➢ Fire’s Effect on Soil ○ Increases surface temp (100-700 C) ○ Subsurface also increases but more moderately and temporary (50-100 C) ○ Nitrogen and organic acids are burned off returning inorganic cations (K, Ca, Mg) -- little flush of availability after a fire -- allows quick access to nutrients for growth ○ Ash adds Phosphorus ○ Nitrogen becomes more available immediately, but long term availability declines ○ Increase in pH ○ Charred soil absorb soil radiation ○ Bulk density increases (decrease in porosity) ○ Decrease water infiltration/percolation ○ Increase risk soil erosion/nutrient leaching ➢ Fire’s Effect on Flora ○ Mortality on non-fired adapted species ○ Loss of above-ground vegetation ○ Some plants can regenerate from underground reserves ○ Some seeds die or break dormancy or germinate under new soil conditions ○ Higher patchiness in landscape (Which can increase plant diversity) ➢ Fire-Adaptive Plant Traits ○ Serotiny - allows release of seeds triggered by fire because fire melts resin in pine cone and opens it up ○ Hard seed coats ○ Tuber/bulb seeds protected in the soil ○ Varying locations of seeds on plant - some above, some below, some outside, some inside ○ Thick bark ➢ Adaptations to Fire ○ Fire resistance ■ Redwoods - super thick bark, sprout from the bottom, regeneration ○ Fire tolerance ■ Redwoods - super thick bark ■ Many ecosystems have adapted to frequent fires as result of low precip ○ Fire dependance ■ Ecosystems can have natural fire disturbance ● I.e. shrubland, grassland, pine forest, peat bogs, chaparral, african savannah ➢ Benefits of Fire to Natural Systems ○ Helps weed out old and weak individuals ○ Returns nutrients to the soil ○ Rejuvenate vegetation ○ Increase or maintain plant biodiversity ○ Increase habitat heterogeneity ○ Catalyst/trigger for succession ○ Lodgepole Pine Ecology ■ Cones remain on mature trees for years and require v high tempers for release ■ Ecological Succession ➢ Role of Fire in Agroecosystems
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