<P> A classic example of secondary succession occurs in oak and hickory forests cleared by wildfire . Wildfires will burn most vegetation and kill those animals unable to flee the area . Their nutrients, however, are returned to the ground in the form of ash . Thus, even when areas are devoid of life due to severe fires, the area will soon be ready for new life to take hold . Before the fire, the vegetation was dominated by tall trees with access to the major plant energy resource: sunlight . Their height gave them access to sunlight while also shading the ground and other low - lying species . After the fire, though, these trees are no longer dominant . Thus, the first plants to grow back are usually annual plants followed within a few years by quickly growing and spreading grasses and other pioneer species . Due to, at least in part, changes in the environment brought on by the growth of the grasses and other species, over many years, shrubs will emerge along with small pine, oak, and hickory trees . These organisms are called intermediate species . Eventually, over 150 years, the forest will reach its equilibrium point where species composition is no longer changing and resembles the community before the fire . This equilibrium state is referred to as the climax community, which will remain stable until the next disturbance . </P> <P> Generation of carbonates from burnt plant material following fire disturbance causes an initial increase in soil pH that can affect the rate of secondary succession, as well as what types of organisms will be able to thrive . Soil composition prior to fire disturbance also influences secondary succession, both in rate and type of dominant species growth . For example, high sand concentration was found to increase the chances of primary Pteridium over Imperata growth in Imperata grassland . The byproducts of combustion have been shown to affect secondary succession by soil microorganisms . For example, certain fungal species such as Trichoderma polysporum and Penicillium janthinellum have a significantly decreased success rate in spore germination within fire - affected areas, reducing their ability to recolonize . </P> <P> Vegetation structure is affected by fire . In some types of ecosystems this creates a process of renewal . Following a fire, early successional species disperse and establish first . This is then followed by late successional species . Species that are fire intolerant are those that are more flammable and are desolated by fire . More tolerant species are able to survive or disperse in the event of fire . The occurrence of fire leads to the establishment of deadwood and snags in forests . This creates habitat and resources for a variety of species . Fire can act as a seed dispersing stimulant . Many species require fire events to reproduce, disperse, and establish . For example, the knobcone pine ("Pinus attenuata") has closed cones that open for dispersal when exposed to heat caused by forest fires . This particular conifer grows in clusters because of this limited method of seed dispersal . A tough fire resistant outer bark and lack of low branches help the knobcone pine survive fire with minimal damage . </P>

Which of the following could result in secondary succession