Chapter 5: More Disturbance January 31

Disturbance Disturbance events make resources available that were formerly in use by other organisms Fires clear litter layer and return nutrients to the soil as ash Wind adds undecomposed organic matter to the litter layer

Wind Fire impact surface vegetation, wind impacts canopy Important in temperate forests, tropical forest, high-elevation forests, at forest edge, and trees on shallow soil Fell old and senescent trees Tree-fall gaps (aka canopy gaps) – when one or more trees fall from the canopy due to senescence, disease, lightning, wind)

Tree Gaps Gaps in the canopy create very different microhabitats than those under a canopy –More light –Warmer soil and air temperatures –Lower humidity Frequency of gaps depends on species, local disturbances, topography, soil

Gap Dynamics Gap Dynamics – cyclic changes in plant distributions involving tree falls and subsequent filling in of gaps in the forest canopy that tree falls create What happens when a gap forms? –Proliferation of herbaceous growth –Reproduction by suckers –Germinations of seeds in soil –Germination of seeds entering the gap –Release of juvenile suppressed trees

Flood Flood – high flow of water that overtops the normal confinements and covers land that is normally dry River and lake flooding Flash floods Coastal floods

Pathogens Pathogen - a biological agent that causes disease or illness to its host Hemlock wooly adelgid Introduced from east Asia in 1920s