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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Ecological succession | 3/6 | https://en.wikipedia.org/wiki/Ecological_succession | reference | science, encyclopedia | 2026-05-05T07:17:58.613092+00:00 | kb-cron |
=== Disruptions === Two important perturbation factors today are human actions and climatic change. Additions to available species pools through range expansions and introductions can also continually reshape communities.
== Types of succession ==
=== Primary succession ===
The successional dynamics beginning with colonization of an area with little to no biotic factors is referred to as primary succession. This includes newly exposed rock or sand surfaces, lava flows, and newly exposed glacial tills. The stages of primary succession include pioneer species such as microorganisms, plants (lichens and mosses), grasses, smaller shrubs, and trees. Small animals move into the area when enough suitable habitat has been established. When it is a fully functioning ecosystem, it has reached the climax community stage.
=== Secondary succession ===
Secondary succession follows severe disturbance or removal of a preexisting community that has remnants of the previous ecosystem. Secondary succession is strongly influenced by pre-disturbance conditions such as soil development, seed banks, remaining organic matter, and residual living organisms. Because of residual fertility and preexisting organisms, community change in early stages of secondary succession can be relatively rapid. Secondary succession is much more commonly observed and studied than primary succession. Particularly common types of secondary succession include responses to natural disturbances such as fire, flood, and severe winds, and to human-caused disturbances such as logging and agriculture. In secondary succession, the soils and organisms need to be left unharmed so there is a way for the new material to rebuild. As an example, in a fragmented old field habitat created in eastern Kansas, woody plants "colonized more rapidly (per unit area) on large and nearby patches".
Secondary succession can quickly change a landscape. In the 1900s, Acadia National Park had a wildfire that destroyed much of the landscape. Originally evergreen trees grew in the landscape. After the fire, the area took at least a year to grow shrubs. Eventually, deciduous trees started to grow instead of evergreens. Secondary succession has been occurring in Shenandoah National Park following the 1995 flood of the Moorman's and Rapidan rivers, which destroyed plant and animal life.
=== Seasonal and cyclic dynamics ===
Unlike secondary succession, these types of vegetation change are not dependent on disturbance but are periodic changes arising from fluctuating species interactions or recurring events. These models modify the climax concept towards one of dynamic states.
=== Causes of plant succession === Autogenic succession can be brought by changes in the soil caused by the organisms there. These changes include accumulation of organic matter in litter or humic layer, alteration of soil nutrients, or change in the pH of soil due to the plants growing there. The structure of the plants themselves can also alter the community. For example, when larger species like trees mature, they produce shade on to the developing forest floor that tends to exclude light-requiring species. Shade-tolerant species will invade the area. Allogenic succession is caused by external environmental influences and not by the vegetation. For example, soil changes due to erosion, leaching or the deposition of silt and clays can alter the nutrient content and water relationships in the ecosystems. Animals also play an important role in allogenic changes as they are pollinators, seed dispersers and herbivores. They can also increase nutrient content of the soil in certain areas, or shift soil about (as termites, ants, and moles do) creating patches in the habitat. This may create regeneration sites that favor certain species. Climatic factors may be very important, but on a much longer time-scale than any other. Changes in temperature and rainfall patterns will promote changes in communities. As the climate warmed at the end of each ice age, great successional changes took place. The tundra vegetation and bare glacial till deposits underwent succession to mixed deciduous forest. The greenhouse effect resulting in increase in temperature is likely to bring profound Allogenic changes in the next century. Geological and climatic catastrophes such as volcanic eruptions, earthquakes, avalanches, meteors, floods, fires, and high wind also bring allogenic changes.
== Changes in animal life == Succession theory was developed primarily by botanists. The study of succession applied to whole ecosystems initiated in the writings of Ramon Margalef, while Eugene Odum's publication of The Strategy of Ecosystem Development is considered its formal starting point. Animal life also exhibits changes with changing communities. In the lichen stage, fauna is sparse. It comprises a few mites, ants, and spiders living in cracks and crevices. The fauna undergoes a qualitative increase during the herb grass stage. The animals found during this stage include nematodes, insect larvae, ants, spiders, mites, etc. The animal population increases and diversifies with the development of the forest climax community. The fauna consists of invertebrates like slugs, snails, worms, millipedes, centipedes, ants, bugs; and vertebrates such as squirrels, foxes, mice, moles, snakes, various birds, salamanders and frogs. A review of succession research by Hodkinson et al. (2002) documented what was likely first noted by Darwin during his voyage on the H.M.S. Beagle:
The often repeated description of the stately palm and other nobel plants, then birds, and lastly man, taking possession of the coral islets as soon as formed in the Pacific, is probably not quite correct; I fear it destroys the poetry of this story, that feather and dirt-feeding and parasitic insects and spiders should be the first inhabitants of newly-formed oceanic land. These naturalists note that prior to the establishment of autotrophs, there is a foodweb formed by heterotrophs built on allochthonous inputs of dead organic matter (necromass). Work on volcanic systems such as Kasatochi Volcano in the Aleutians by Sikes and Slowik (2010) supports this idea.
== Microsuccession ==