Ecological Succession in Mississippi
Patterns & Processes
By Samuel P. Faulkner,
Delta State University
Ecological succession is defined as change in the composition of species in the landscape over time. The process shows us how dynamic "communities" are as they undergo species compositional changes and shift in physiognomy as new species aggregations form. Generally, as environmental conditions shift (changes in soils, moisture, hydrology, light, nutrients, etc.), one species is gradually replaced by another species, and so on. Although this is strictly a generalization, as succession progresses, the number of species in a community (species diversity) and the total biomass tend to increase. Eventually a relatively persistent stage of successional species composition is achieved. Frederick Clements termed this "end" community, the "climax" community. Today, many ecologists are more comfortable with the notion of the "equilbrium" community or something similar.

Contrary to the theories of "directionalists" such as Clements,, we now know that generally, most succession is not very predictable. Theoretical stages might not always occur in the anticipated order; and the establishment of species can be altered by various influential conditions. The 20th century American plant ecologist, Henry Gleason, noted that the establishment of some species, most in fact, is somewhat random. Succession can be influenced by such factors as season, climatic conditions, or by which species happen to arrive first. And, the establishment and success of such species can be altered by various influential conditions that exist at the time of arrival, or develop later. Thus, a habitat can become unsatisfactory for the resident species because the conditions that first attracted the species no longer exist.

Can organisms alter their environment? We certainly see this in the activities of the human species. Actually, all organisms exert influences on their environment and some effects are profound. Some of the changes induced by organisms include: (1) Soil changes - Due to erosion and action of bacteria and humic substances, a substrate may weather from solid rock to sand to loamy soil; (2) Soil pH often decreases due to the decomposition of organic matter and release of carbon dioxide and organic acids; (3) The ability of a soil to hold moisture changes as the soil texture changes; (5) Plants extract moisture and alter local soil moisture and hydrologic patterns; (4) Light availability can change from full sunlight to shade as plant physiognomy changes and leaf area index (LAI) increases; (6) Competition for space, light, nutrients and moisture may prove unsuitable for some species and these die out or diminish.

So, as I've already mentioned, most succession (not all!) leads to a “final” successional stage is typified by relatively constant species composition. Let’s use the modern convention and call these assemblages equilibrium communities. Once established, such landscape elements may remain relatively unchanged for hundreds of years until destroyed by some catastrophic event, or until the climate shifts, forcing shifts in community structure.

In some cases, a stable "end" community is never attained because fires and other disturbances occur so frequently. The late University of Georgia ecologist E.P. Odum termed this phenomenon "pulse stabilization." For example, coastal marsh is maintained in part due to daily tidal inundation. Also, succession can be held "in check" by certain edaphic conditions - for example, dry or wet hydrology, or soil chemistry (e.g., calcareous cedar glades in Mississippi; serpentine barrens in New Jersey & northern California).

Long-term longitudinal succession occurs in some regions where the climates change over thousands of years. For example, northern Mississippi during and at the conclusion of the last glaciations, was essentially cool temperate and possibly even boreal. As global warming followed the glacial period, the climate has shifted to warm temperate for most of the state, and coastal temperate (subtropical) in the southern end of the state.

Over shorter periods of time, succession occurs because the species of the community can alter the habitat through their presence. In a process called facilitation, the habitat can become more favorable to new species because it can no longer provide the conditions that originally attracted the species. Animals also affect the succession of their habitat.

The first plants and animals to inhabit an area are called the "pioneer species." We generally recognize two modes of succession:

1. Primary Succession: Begins in areas barren of life because of an absence of soil. In Mississippi, we only see this in special situations, on bare limestone or sandstone outcrops, on aging shingles on old houses and other buildings, and arguably, in sand dune ecosystems in the barrier islands of the Gulf of Mexico.

2. Secondary Succession: By far, the most prevalent mode of succession in Mississippi, this process occurs when an existing community has been cleared by a natural disaster or other disturbance such as farming, mowing, deforestation, etc. (but, leaving the soil intact). The area in the post-disturbance period begins to return to a natural community.

Successional Patterns in Mississippi
As I've indicated, what first colonizes a disturbed area, depends upon many factors, including soil type, drainage and hydrology, proximity to propagules, and so on. Not surprisingly, different areas of Mississippi generally have unique successional patterns.

Yazoo-Mississippi Floodplain Forests - Typically, the first several years are dominated by foxtail grass, johnsongrass, giant ragweed, horseweed, fireweed, goldenrod. Goldenrod, Johnsongrass, Ironweed give way after 3-5 years to brambles (dewberry and blackberry), Japanese honeysuckle. Cottonwood, sycamore, sweetgum and ash (light-seeded trees) are often the first colonizers of the developing forest communities. Bottomland hickories, hackberry and oak (heavy-seeded trees) usually follow.

Loess Bluffs - Typically, the first several years are dominated by bluestem grasses, goldenrod, etc. Goldenrod, Johnsongrass, Ironweed give way after 3-5 years to brambles (dewberry and blackberry), Japanese honeysuckle. Boxelder, sweetgum, cottonwood, sycamore and yellow poplar are the first woody plants to colonize. Upland hardwood forests usually develop on these landscapes. Sycamores and sweetgums often persist in the forests for many years, even after oak, beech, hickory and other trees begin to dominate.

Northeastern Hills - Typically, the first several years are dominated by bluestem grasses, goldenrod, etc. Goldenrod, bluestem grass species, tickseed, Ironweed give way after 3-5 years to brambles (dewberry and blackberry), Japanese honeysuckle. Shortleaf pine and sweetgum are common initial woody colonizers on acidic soils. Eastern red cedar is a common primary colonizer of more basic soils. Mixed hardwood and shortleaf pine forests develop in these landscapes, ultimately leading to mixed oak-hickory dominated forests.

Lower Coastal Plains – Early succession is similar to hilly areas elsewhere in the state. The first woody plants include most of the pines, especially loblolly and slash pine, sweetgum, tallow tree, yaupon, wax myrtle, bay magnolia. Live oaks, hickories and other heavy-seeded hardwoods follow. The pines will persist for years in mixed forests.

Please cite this document as:

Faulkner, S.P. 2003. Ecological succession in Mississippi - patterns
and processes. Handout, Department of Biological Sciences, Delta State University, 3 pp.


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