Agriculture – especially slash-and-burn agriculture – can have devastating effects on the natural environment. During fallow periods immediately after agricultural use, secondary succession occurs when remaining seeds, root systems, weeds and other pioneer species begin to repopulate the land. This process is similar to what happens during deforestation and other deforestation. Community behaviour after a disturbance depends on a number of factors, but especially on the type of ecosystem before the disturbance. However, since secondary succession begins with a few remnants of the original community, change usually occurs much more quickly than primary succession. Alder, birch and grasses are common pioneer species in these environments, as they thrive in sunny conditions. The use of a natural enemy or parasite to control the number of pest species is known as: Recently, species of microbial and invertebrate taxa have been added to the list of pioneer species. These species can be photo/chemo, auto/straight, litho/organotrophic. This means a very important point here that secondary succession takes place in places where certain nutrient sources are present in the substrate. Areas such as deforestation, deforested forests, areas affected by storms, etc. are subject to secondary succession. Thus, many species of microbial species (bacteria, archaea), invertebrates and tree species such as Betula spp. (birch species) and Alnus spp.
(alder species) are examples of pioneer species that cause secondary succession. Seeds that have a specific need for light for germination are called photoblastic seeds. The phenomenon often occurs in herbaceous and pioneer species, which produce a large number of small seeds with relatively low food reserves. Many of these photoblastic seeds require brief exposure to red light (660 nm) in the wet state. The photoreceptor in this case is phytochrome, and the reaction has been well studied in the seeds of Datura ferox (a tropical weed) and lettuce (Lactuca sativa). In fact, phytochrome was discovered after remarkable observations of the far red/red reversal of lettuce seed germination (see Chapter 26). Seeds that need light also show sensitivity to cold temperatures and gibberellins, and in some cases the need for light can be bypassed by exposing the seeds to cooling (2-5°C) or GA. In lettuce and Arabidopsis seeds, red light has been shown to induce the transcription of genes encoding specific isoforms of 3β-hydroxylase, the enzyme that catalyzes the conversion of GA20 to biologically active GA1. Thus, the roles of phytochrome and gibberellin in seed germination requiring red light have been partially clarified. The niche of tropical forest species is usually large because sexual reproduction requires more energy and takes time, pioneer species may not be best suited for this. However, there are cases where pioneer species are involved in sexual reproduction. However, the asexual mode is more widely used because of its many advantages.
Fungi and lichens are the most common pioneer species in primary succession because they have the ability to break down minerals to form soil and subsequently develop organic matter. Once pioneer species colonize the area and begin to build the soil, other species such as grasses begin to grow. The complexity of the new community increases as new species, including small shrubs and eventually trees, arrive. Unlike arid and previously uninhabited areas, some areas need to be restored after a disturbance that “wiped out” an entire ecological community. This new foundation is the secondary succession. In these areas, parts of the soil and vegetation previously present are remains. In these areas, there are fewer battles for resources and pioneer species are more privileged here. If we are asked what a pioneer species is in secondary succession, we can list angiosperm trees and shrubs.
These have exceptionally high rates of growth and community development. Pioneer species in secondary succession do not need to be photo-autolithotrophic by constraint. The seeds of pioneer species are extremely viable and are produced geometrically, which has high dispersal rates. In order to colonize land that lacks nutrients, it is imperative to have this rate of dispersal. Mangrove forest develops where there is coastal sedimentation of mud; Mangroves are the usual initial colonizers. The mud is penetrated by the tide twice a day, but the shoots of pneumatophore of the pioneer species of Avicennia, followed later by the multi-stemmed feces of Rhizophora, trap the sediment very effectively (sometimes up to several meters per year). The vegetation is simple, according to the municipality from 5 to 25 m high, with a relatively flat and uninterrupted canopy, a layer of undergrowth very poor, often missing, and poor in species. The main tree species are limited to these habitats and are often characterized by special root formations such as roots on stilts (Rhizophora) and pneumatophores (Avicennia, Bruguiera, Sonneratia and Xylocarpus). The vegetation is often very simple, with few species dominating the entire stock. There is also a separate sequence from the waterfront to the land side.
The mangrove forest is found in the tropics. The mangroves of Madagascar and the east coast of Africa have a strong Asian affinity, while those of the Atlantic coasts of the United States and West Africa have similar floristic affinities. In the Far East, bordering mangroves and at the upper limit of estuaries, there is a forest with a number of characteristic species, among which Nypa fruticans is important and forms large pure stands, mainly along streams in estuaries. Pioneer species are an important part of the natural selection process. Greening projects typically introduce pioneer species to allow the disturbed area to be repopulated by vegetation and other life forms it would otherwise have supported. The succession process begins with primitive lichens giving way to herbaceous plants, fast-growing trees and shrubs, and later the type of vegetation that would have been present had the area not been disturbed.
