Test_4_Notes

1923 shows impact of man on environment clear cutting

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Unformatted text preview: vironment Clear cutting entire water shed Nutrient losses were 10x higher in clear cut water shed relative to water shed number 6 Doubled nitrogen fixation rates globally, all not beneficial Disturbance has a negative impact on nutrient cycles Aldo Leopold (1887-1948) A Sand County Almanac “The Odyssey of X” describes how man influences nutrient cycles Succession (Chp 20) primary vs secondary mechanisms stability an integrated summary Bacteria fungi and lichens create weathering of rocks to facilitate the initial production of an area – EX: Glacier Bay Alaska (took 1500 to 2000 years for final stable climax community to form) Community organization in space Smaller spaces create more dense communities and inhibit development of the area Look at composition and growth form Special composition based on physionomy Community organization through time (temporal changes) Herbaceous species give rise to an area that can hold shrubs, which then gives rise to trees New ground usually have pioneer species, change with site location, but process remains the same Alaska ecosedum, willowards species then other organisms come in New species modify the environment Suga are in steep slopes Muskegs on shallow slopes Example of ecological succession in an old field weeds changing to a pine forest then a pine forest then an oak hickory forest Your text describes ecological succession for: Glacier Bay, Alaska A rocky intertidal community Sycamore Creek, Arizona Do species composition, community structure, and associated ecological processes change in a predictable, directional way over time in ecological communities? Succession – a change in species composition and community structure over time Sere – series of communities Seral stage – each community Climax – final “stable” community Most studies of succession focus on plants because plants influence animals Secondary Succession in Virginia Pgs 487-488 100-150 years Old field Grasses and weeds Loblolly pine forest Oak forest Loblolly pine forest - No hardwoods - Recurring fires - Poor soils Animal succession? Yes Primary Succession Succession in environments that have not been influenced by organisms. A slow process. Examples: Receding glaciers, colcanoes, talus slopes In Virginia? Accreting coastlines Secondary Succession Succession after a disturbance in environments where organisms once thrived Examples: Fire, floods, avalanches, hurricanes, tornadoes, etc. Human related disturbances? Agriculture, clearcutting, roadcuts, mining? TIME! New land (1^0 Succession) Pioneer seral stage Seral stages CLIMAX Disturbance (2^0 Succession) (Successional Mechanisms) Fig. 20.20 Relate these mechanisms to the data presented in Figures 21, 23, 24 and 25 Succession may include a combination of all three of these mechanisms Stability – the persistence of, or rapid return to, a given state after a temporary disturbance Resistance – to remain unchanged Resilience – to absorb changes and rapidly return to an original state STABILITY = RESISTANCE + RESILIENCE System parameter Disturbance or perturbation...
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