Temporal changes

Ecological succession is the gradual process by which ecosystems change and develop over time, nothing remains the same and habitats are constantly changing.

There are two main types of succession, primary and secondary. Ecological succession provides diversity and depth to a biotic community and without it, life cannot grow or progress. Succession is the gateway to evolution, there are five main elements to ecological succession: primary succession, secondary succession, pioneer and niche species, climax communities and sub-climax communities. (Ehow, 2014). Immature communities tend to have high populations of a few species that are relatively small and simple, food chains are short, and available energy is shared by few species. Community structure is simple and easily disrupted by external forces as communities mature larger and more complex organisms appear therefore resulting in a higher species diversity (number of different species) (Ehow,2014).

A Climax community

A climax community is one that has reached the stable stage, when extensive and well defined, the climax community is called a biome, examples of this are tundra, grassland,coniferous, desert and tropical rain forests. Stability is attained through a process known as succession, whereby relatively simple communities are replaced by those more complex. On a lakefront, grass may invade a build-up of sand, humus (a dark brown or black mass of partially decomposed organic matter in the soil. It improves the fertility of the soil therefore important for plant growth) (free dictionary, 2014) formed by the grass then gives root to oaks and pines and lesser vegetate on which displaces the grass and forms a further altered humus. That soil eventually nourishes maple and beech trees, which gradually crowd out the pines and oaks and form a climax community. In addition to trees, each successive community harbours many other life forms, with the greatest diversity populating the climax community (Info please, 2014).

A sub climax community

Sub-climax communities are communities that are not yet in a state of equilibrium, these communities can both precede and follow climax communities. Sub-climax communities can follow climax communities for many reasons. Sometimes the biotic landscape is invaded and occupied for a brief time by an invasive species. The invasive species alters the equilibrium, opening the landscape up to pioneer species. Biological niches are altered and the landscape begins to change (ehow, 2014).

Primary Succession

Primary succession is a long and drawn out process, primary succession takes many thousands of years but it can occur in a few centuries preparing it for larger more complex organisms. Once the landscape begins to accept more complex life, succession continues until a climax or general equilibrium is reached. Primary succession is the process by which an area, void of life becomes populated by simple, hardy species known as pioneers that gradually spread through the landscape (ehow, 2014).

Secondary Succession

Secondary succession is similar to primary succession in that pioneer species populate and prepare an area or landscape for more complex life however it occurs much more rapidly. Secondary succession occurs in a single century or less and is the result of a damaged landscape re-establishing itself or changing all together into a new kind of biotic landscape. In secondary succession, the recently occupied landscape has been dramatically changed by disaster or environmental invasion, examples of this are forest fires (ehow, 2014).

Pioneer and Niche Species

Pioneer species are generally small hardy species that spread into un-colonized areas and are often species that spread quickly, die off each season and leave behind a large amount of seeds for the next season. Niche species are larger more complex organisms that live longer and interact with the surrounding environment more they fill a biological gap where their specific traits suit their needs for survival (ehow, 2014).

Rainforest succession

Nearly every forest has to go through succession in order to reach its full potential.
 

Figure 21 showing rainforest succession.Source: http://www.teara.govt.nz/en/diagram/11898/stages-of-forest-succession

Natural disturbances play a great role in forest succession, trees die of old age, blown over by wind or are knocked down by other falling trees. When this occurs, gaps appear in the forest canopy, which alters the environment for all of the plants surrounding the open area. Tropical rainforests go through several stages during regeneration, a small gap, caused by the death of a small tree, will not alter much in the forest, limbs from other trees will fill in a gap and their shade will prevent the growth of most seedlings on the forest floor, except for those which do not require much light (Rainforest conservation, 2015).However a larger gap changes the physical state of that area of the forest, there will be more light, heat and wind on the forest floor where a gap forms resulting in the forest floor of the gap will become hotter and drier than previously, although more rain will reach the ground (but it will be dried quickly by the sun). Under these circumstances the slower-growing and shade-tolerant seedlings in the understory cannot survive, and are gradually replaced by seedlings of fast-growing and light-tolerant species known as the pioneer species (Rainforest conservation, 2015). Pioneer species are characterized most importantly by a requirement for strong light for seed germination and seedling establishment, when a gap forms and light hits the forest floor, their seeds are able to sprout and grow rapidly to fill in the gap. At this early successional stage the extent of the seedling sprouting and survival is determined mainly by factors in the environment such as competition, temperature, nutrient availability and degree of shade. The seedlings which survive begin to influence their own environment as they grow producing shade, using soil matter, and producing new types of habitats. The early pioneer trees however are often low and short-lived, and may be replaced by longer-lived taller pioneer species which then form a higher canopy forest.

Meanwhile, the seedlings of climax species remain undeveloped in the shade of the pioneer trees, as they do not do well under gap conditions of high temperatures and strong light. Climax species in general have large seeds with substantial nutrient reserves, have shade-tolerant seedlings and are a slow-growing relative to the pioneer species, since once the pioneer trees form a canopy, the climax species’ shade-tolerant seedlings can grow in their shade. Once the large pioneer trees die conditions are suitable for the small trees of the climax species to grow rapidly and take their place. Once established, a climax forest can reproduce itself endlessly, since it provides shade for its seedlings, and the large trees have attained the canopy (Rainforest conservation, 2015). There is a very large genetic pool, and incredible diversity among the organisms in rainforests, there are species which are adapted to almost every condition, there are fast-growing species, species which require sun, those which require shade, in short, whatever happens in a forest, there will be species which can exploit the given situation and thrive. However, diversity in a secondary (successional) forest tends to be lower, at least at first, than in a primary forest. Rainforests are ecosystems, the seeds of the woody species are fragile, many forest plant seeds cannot tolerate sun meaning they cannot disperse across cleared land, the soil is fragile and easily eroded by heavy rainfall, and many species have a limited distribution and will be destroyed by removal of even small areas of forest. Rainforest regeneration is slow and the forest may never regenerate, at least not to its original condition (Rainforest conservation, 2015).
 

Table 2 showing factors of primary and secondary succession. Source: http://www.picstopin.com/548/primary-succession-vs-secondary/http:%7C%7Cpeople*eku*edu%7Critchisong%7Cprimarysuccession*jpg/

Wetlands

According to the Ramsar Convention on Wetlands; “Wetlands are areas of marsh,peat land or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres” (Ramser.org, 2014)

A wetland is defined as an area in which water covers the soil. The presence of water in surface soils is a primary factor in determining soil development and the types of flora and fauna that inhabit that particular region. Wetlands are often identified by the presence of hydrophytes, which are types of plants which are adapted to flooded or saturated soil conditions (Ramsar.org, 2014).

Figure 22 showing various hydrophyte plants. Source: http://www.nckansil.com/hydrophytes-charts-1029364.html

There are many different types of wetlands including including marshes, estuaries, mudflats, ponds, swamps, coral reefs, lagoons, shallow seas, bogs, lakes, and floodplains. Peat lands are wetlands with a thick water-logged organic soil layer (peat) made up of dead and decaying plant material. They are critical for water regulation, a volume of peat soil consists of 90% of water and are generally meters deep and store and maintain large quantities of water. As a result of this peat lands play an important role in protection against floods after heavy rainfall and in ensuring a supply of clean water throughout the year (about news, 2015).

Wetlands are essential ecological features in any landscape, they are primary habitat for hundreds of species of birds, fish, mammals and insects. Other important aspects of wetlands is they naturally filter and recharge the water that later comes out of our faucets downstream. They also act like giant sponges, slowing the flow of surface water and reducing the impact of flooding. Wetlands also prevent soil erosion, they can remove and store greenhouse gases from the Earth’s atmosphere, this results in slowing down the onset of global warming (about news, 2015).
 

Figure 23 showing benefits of wetlands. Source: http://www.earthgauge.net/2012/wetlandsmonth

Figure 24 showing wetlands in Africa.Source: http://www.plexuseco.com/EPOW/EPOW-Archive/archive_2009/EPOW-090119.htm

Africa’s wetland ecosystems are estimated to cover more than 131 million hectares and deliver a wide range of ecosystem services that contribute to human well-being such as water supply and purification, nutrition, climate regulation, coastal protection, feeding and nesting sites. African wetlands are among the most biologically diverse on the planet (Epow, 2009).

Animal adaptations to wetlands
 
Wetlands are home to many interesting animals. Some have unusual adaptations that enable them to survive even when the wetland dries up during drought.

Walking Catfish 

Figure 25 illustrating a walking catfish, Source: http://www.mbgnet.net/fresh/wetlands/animals/index.htm

The walking catfish is capable of moving on land and and is able to breathe air when itdoes. If necessary, the walking catfish can bury itself in mud at the bottom of a pond and remain dormant throughout a dry season until the rains return. It feeds on aquatic invertebrates and fish (wetland animals, 2002).

Two-toed Amphiuma

Figure 26 illustrating a two-towed Amphiuma. Source: http://www.mbgnet.net/fresh/wetlands/animals/index.htm

This aquatic salamander has tiny, virtually useless limbs, each with two toes

Mainly active at night, it hunts in water for crayfish, frogs, small snakes and fish and may come onto land in extremely wet weather (wetland animals, 2002).

South American Lungfish 

Figure 27 illustrating a South American lungfish. Source: http://www.mbgnet.net/fresh/wetlands/animals/index.htm

The South American lungfish has a pair of lung like organs connected with its oesophagus. This fish usually lives in oxygen-poor, swampy areas, but because of its lungs it is able to supplement the oxygen obtained from the water by breathing air at the surface. The fish survives dry periods by digging itself a burrow in which it lives, breathing air, while the swamp dries out, the fish closes the burrow entrance with mud, curls up and covers itself with a protective covering of mucus secretion to conserve moisture. Its body slows down to a state of dormancy, but it continues to breathe air. When the rains return, the lungfish emerges from its burrow (wetland animals, 2002).

Dwarf Siren 

Figure 28 illustrating a dwarf siren. Source: http://www.mbgnet.net/fresh/wetlands/animals/index.htm

If its habitat is in danger of drying up, as in a drought, the siren can burrow into the mud and remain there, dormant, for up to 2 months, mucus produced by skin glands prevents the body drying out during such a period (wetland animals, 2002).

Cape Lopez Lyretail 

 

Figure 29 illustrating a Cape lopez lyretail. Source: http://www.mbgnet.net/fresh/wetlands/animals/index.htm

The lyretail deposits its eggs among the mud and detritus at the bottom of its habitat. If there is then a prolonged dry season, the embryos cease their development and lie dormant in the mud, protected by their drought-resistant egg membrane. Although the parent fishes die in the drought, the eggs resume development with the arrival of rain and hatch shortly afterward (wetland animals, 2002).

Glaciers were responsible for forming wetlands in two ways by leaving behind chunks of ice to melt and cover the surroundings, and by leaving glacial run-off water in depressions in which the bottom was sealed by organic material and fine clays. Primary succession in wetlands is effected by both environmental conditions in the wetland region and the distance from surrounding ecosystems. Early colonizers of the particular area usually arrive by wind or are transported by migratory or wandering species.
In the self-generating view of wetland primary succession early biotic colonizers such as plankton, live, reproduce and then die, this creates an accumulation of organic material which in turn builds up to the surface until the region is no longer flooded.

An environment may progress from the open-water stage, where plants are submerged into a wetland primary succession stage where floating plant species are present. The following stage is a  swamp state where flood tolerant plants are present, to a grass stage then onto a shrub stage where the ecosystem is no longer classified as a wetland, and finally to a tree stage (as shown in figure 25) . In the early stages of wetland primary succession, initial colonizers are often microscopic organisms and biodiversity is very low. However as succession continues larger and more complex organisms appear therefore biodiversity increases (Ehow, 2009).

Figure 25 showing aquatic succession.Source: http://sandovalawesomescience.blogspot.co.uk/

Figure 26 showing succession of a pond Source:http://kilby.sac.on.ca/faculty/dgalajda/enviro/eco_review_2000.htm

During succession changes in the plant species present in a particular area is one of the main factors behind changes in animal species. This is because each plant species will have associated animal species which feed on it, the presence of these herbivore species in turn dictate which particular carnivores are present. A hydrosphere is simply a succession which starts in water, wetlands, which is a transitional area between open freshwater and dry land, provides a good example of this and is an excellent place to see several stages of a hydrosphere at the same time.

In time, an area of open freshwater such as a lake, will naturally dry out, ultimately becoming woodland. During this process, a range of different habitats such as swamp and marsh will succeed each other. This succession from open water to climax woodland is likely to take at least two hundred years (probably much longer) (Countryside info, 2015).

For a freshwater ecosystem, the climax community can actually be the terrestrial ecosystem that ultimately remains after the water is gone, throughout the process of the water filling in with sediment some aquatic species die off such as fish and plants near the shore, other species such as frogs may flourish in their new environment (Countryside info, 2015)

Wetland management

Wetlands are dynamic areas, influenced by both natural and human factors. In order to maintain their biological diversity and productivity there is an urgent need to conserve them. Wetlands are called the sponge of the natural world, they absorb much of the pollution we produce and filter out pollutants then slowly release clean water and oxygen back into the ecosystem.

In wetland restoration the purpose is to replace the natural functions of any given wetland in regards to habitat for wildlife, nutrient cycling, and erosion control. Restoration starts at either a primary or in the early stages of secondary succession as a result there biotic and environmental factors should be the same as a natural system at the very same stage of succession (wetlands.org, 2014).

Wetland management generally involves activities that can be conducted in and around wetlands, both natural and man-made, to protect, manipulate restore, or provide for their functions and values. Despite their importance, human activities and the changing climate are degrading wetlands faster than any other ecosystem, increasing population in conjunction with efforts to increase food security is escalating pressure to expand agriculture within wetlands. Additionally climate changed related events, such as unpredictable and decreasing rainfall, are expected to reduce the water stored in wetlands and exacerbate their overexploitation (wetlands.org, 2014).

A study by Erwin (2009) recognizes that Global climate change is recognized as a threat to species survival and the health of natural systems, scientists are looking at the ecological impacts from climate change. Ultimately climax change will make any future efforts to both restore and manage wetlands more complex. Wetland systems are vulnerable to changes in both quantity and quality of water supply and it is expected that climate change will have a pronounced effect on wetlands through alterations in hydrological regimes which is changes over time in the rates of flows of rivers and the levels and volumes of water in rivers and lakes.

The hydrological regime is closely related to seasonal changes in climate. In regions with a warm climate, the hydrologic regime is mainly affected by atmospheric precipitation and evaporation which ultimately reduces the water level making it easier for succession to happen.

 

.figure 27 illustrating buffers. Source: http://www.gov.pe.ca/environment/buffer-zones

One method used for protecting wetlands is the use of buffers. Wetland buffers are areas that surround a wetland and reduce adverse impacts to wetland functions from adjacent development. They reduce wetland impacts by moderating the effects of storm water runoff including stabilizing soil to prevent erosion, filtering suspended solids, nutrients, and harmful or toxic substances; and moderating water level fluctuations. Buffers also provide essential habitat for wetland-associated species for use in feeding, roosting, breeding and rearing of young, and cover for safety, mobility, and thermal protection (Prince Edward Island,2015).

Dredging is another method used in wetland conservation, it involves the removal of sediments and debris from the bottom of wetlands, without this measure being taken the natural process of sediment build up the wetland would gradually fill allowing for succesion to take place and move from a wetland to a marsh to a forest.

Figure 28 illustrating dredging. Source :http://www.dredgingsystems.com.au/service/environmental-dredging-wetlands-lagoons






 Another method for wetland conservation is fencing, in areas where excessive human use is degrading wetlands, fencing is one of the simplest ways to protect wetlands. This is especially critical in wetlands along streams and lakes where the degradation is directly impacting water quality through erosion and sedimentation. Fencing should be placed as far from the wetland as is possible by doing this the fenced area also includes a protective buffer between the activity and the wetland (Hillsdale county, 2015). Although it could be argued that fencing off wetlands actually prevents animals from grazing which is another form of wetland management, allowing the animals to graze reduces the amount of vegetation which prevents overgrowth and in turn helps to prevent succession!!!!


Reducing pollution of wetlands is another major factor in wetland conservation, nutrients like nitrate and phosphate polutants that will increase the growth of algae which will add to the debris that sinks to the bottom of the pond or wetland when it dies this will help to fill the wetland and therefore aids succession .


It is clear that the biggest threats to wetlands are humans, luckily we can reduce the damage and be a driving force in their conservation!!!