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61-577: One of the most reliable indicators of highway condition in Africa are the Michelin maps which grade highway condition, in part from traveller's reports. The 2000 edition for 'Africa Central and South' indicates three 'transcontinental routes' between Kinshasa and Kisangani or Bukavu, all of them with very long stretches of road in the lowest category of highway condition, described as 'earth tracks likely to become impassable in bad weather'. The area has some of

122-441: A climatically determined stable climax community regardless of starting conditions. Clements explicitly analogized the successional development of ecological communities with ontogenetic development of individual organisms, and his model is often referred to as the pseudo-organismic theory of community ecology. Clements and his followers developed a complex taxonomy of communities and successional pathways. Henry Gleason offered

183-431: A climax community. Depending on the substratum and climate, different seres are found. 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

244-512: A climax community. The annual production and use of energy is balanced in such a community. There are three schools of interpretations explaining the climax concept: The theory of alternative stable states suggests there is not one end point but many which transition between each other over ecological time. Forests, being an ecological system, are subject to the species succession process. There are "opportunistic" or "pioneer" species that produce great quantities of seed that are disseminated by

305-444: A codification of successional processes by mechanism. Among British and North American ecologists, the notion of a stable climax vegetation has been largely abandoned, and successional processes have come to be seen as much less deterministic, with important roles for historical contingency and for alternate pathways in the actual development of communities. Debates continue as to the general predictability of successional dynamics and

366-528: A contrasting framework as early as the 1920s. The Gleasonian model was more complex and much less deterministic than the Clementsian. It differs most fundamentally from the Clementsian view in suggesting a much greater role of chance factors and in denying the existence of coherent, sharply bounded community types. Gleason argued that species distributions responded individualistically to environmental factors, and communities were best regarded as artifacts of

427-626: 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

488-478: A lack of sunlight, and hence relatively easy to traverse. Jungles may exist within, or at the borders of, tropical forests in areas where the woodland has been opened through natural disturbance such as hurricanes, or through human activity such as logging. The successional vegetation that springs up following such disturbance, is dense and tangled and is a "typical" jungle. Jungle also typically forms along rainforest margins such as stream banks, once again due to

549-429: A lawless chaos. The word "jungle" carries connotations of untamed and uncontrollable nature and isolation from civilisation, along with the emotions that evokes: threat, confusion, powerlessness, disorientation and immobilisation. The change from "jungle" to "rainforest" as the preferred term for describing tropical forests has been a response to an increasing perception of these forests as fragile and spiritual places,

610-826: A microhabitat is known as microsuccession or serule. In artificial bacterial meta-communities of motile strains on-chip it has been shown that ecological succession is based on a trade-off between colonization and competition abilities. To exploit locations or explore the landscape? Escherichia coli is a fugitive species, whereas Pseudomonas aeruginosa is a slower colonizer but superior competitor. Like in plants, microbial succession can occur in newly available habitats ( primary succession ) such as surfaces of plant leaves, recently exposed rock surfaces (i.e., glacial till) or animal infant guts, and also on disturbed communities ( secondary succession ) like those growing in recently dead trees, decaying fruits, or animal droppings. Microbial communities may also change due to products secreted by

671-483: A much greater extent than road transport in the country. It was said that the route of the Kinshasa Highway had to be carved out from thick jungle , and that after it was paved, AIDS spread quicker, as carriers of the disease travelled along its length on board cars and trucks , from populated areas to more isolated rural areas. Prostitutes at truck stops helped spread the disease even faster, and it

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732-405: A newly created habitat, or after a disturbance substantially alters a pre-existing habitat. Succession that begins in new habitats, uninfluenced by pre-existing communities, is called primary succession , whereas succession that follows disruption of a pre-existing community is called secondary succession . Primary succession may happen after a lava flow or the emergence of a new island from

793-560: A rate that makes a "climax" community unattainable. Climate change often occurs at a rate and frequency sufficient to prevent arrival at a climax state. Additions to available species pools through range expansions and introductions can also continually reshape communities. The development of some ecosystem attributes, such as soil properties and nutrient cycles , are both influenced by community properties, and, in turn, influence further successional development. This feed-back process may occur only over centuries or millennia. Coupled with

854-414: A resident of the jungle representing the savage, untamed and wild, yet still a white master of it; and in his essay " An Image of Africa " about Heart of Darkness Nigerian novelist and theorist Chinua Achebe notes how the jungle and Africa become the source of temptation for white European characters like Marlowe and Kurtz. Former Israeli Prime Minister Ehud Barak compared Israel to "a villa in

915-451: A viewpoint not in keeping with the darker connotations of "jungle". Cultural scholars , especially post-colonial critics, often analyse the jungle within the concept of hierarchical domination and the demand western cultures often places on other cultures to conform to their standards of civilisation. For example: Edward Said notes that the Tarzan depicted by Johnny Weissmuller was

976-647: Is able to reproduce itself, repeating with essential fidelity the stages of its development. while Gleason, in his 1926 paper, said: An association is not an organism, scarcely even a vegetational unit, but merely a coincidence. Gleason's ideas were, in fact, more consistent with Cowles' original thinking about succession. About Clements' distinction between primary succession and secondary succession , Cowles wrote (1911): This classification seems not to be of fundamental value, since it separates such closely related phenomena as those of erosion and deposition, and it places together such unlike things as human agencies and

1037-585: Is food there for them to eat. When it is a fully functioning ecosystem, it has reached the climax community stage. 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

1098-441: 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. In 1916, Frederic Clements published a descriptive theory of succession and advanced it as a general ecological concept. His theory of succession had a powerful influence on ecological thought. Clements' concept

1159-410: 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

1220-570: Is prevalent in many languages of the Indian subcontinent , and the Iranian Plateau , where it is commonly used to refer to the plant growth replacing primeval forest or to the unkempt tropical vegetation that takes over abandoned areas. Because jungles occur on all inhabited landmasses and may incorporate numerous vegetation and land types in different climatic zones , the wildlife of jungles cannot be straightforwardly defined. One of

1281-427: Is usually termed classical ecological theory . According to Clements, succession is a process involving several phases: A seral community is an intermediate stage found in an ecosystem advancing towards its climax community . In many cases more than one seral stage evolves until climax conditions are attained. A prisere is a collection of seres making up the development of an area from non-vegetated surfaces to

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1342-564: The Indiana Dunes of Northwest Indiana and remains an important ecological topic of study. Over time, the understanding of succession has changed from a linear progression to a stable climax state, to a more complex, cyclical model that de-emphasizes the idea of organisms having fixed roles or relationships. Precursors of the idea of ecological succession go back to the beginning of the 19th century. As early as 1742 French naturalist Buffon noted that poplars precede oaks and beeches in

1403-602: The Sanskrit word jaṅgala ( जङ्गल ), meaning rough and arid. It came into the English language in the 18th century via the Hindustani word for forest ( Hindi/Urdu : जङ्गल / جنگل ) (Jangal). Jāṅgala has also been variously transcribed in English as jangal , jangla , jungal , and juṅgala . It has been suggested that an Anglo-Indian interpretation led to its connotation as a dense "tangled thicket". The term

1464-507: The stochastic nature of disturbance events and other long-term (e.g., climatic) changes, such dynamics make it doubtful whether the 'climax' concept ever applies or is particularly useful in considering actual vegetation. The trajectory of successional change can be influenced by initial site conditions, by the type of disturbance that triggers succession, by the interactions of the species present, and by more random factors such as availability of colonists or seeds or weather conditions at

1525-454: The 1970s; since then it has been steadily replaced by "rainforest", although "jungle" still remains in common use when referring to tropical rainforests. As a metaphor, jungle often refers to situations that are unruly or lawless, or where the only law is perceived to be "survival of the fittest". This reflects the view of "city people" that forests are such places. Upton Sinclair gave the title The Jungle (1906) to his famous book about

1586-464: The 1995 flood of the Moorman's and Rapidan rivers, which destroyed plant and animal life. 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. Autogenic succession can be brought by changes in

1647-482: The Kinshasa of the 1920s and spread through the railroad into Brazzaville and the mining province, Katanga long before AIDS was recognized in the early 80s. Trans-African Highway network Jungle A jungle is land covered with dense forest and tangled vegetation, usually in tropical climates . Application of the term has varied greatly during the past century. The word jungle originates from

1708-410: The absence of disturbances that create such gaps. In the tropics, well known pioneer forest species can be found among the genera Cecropia , Ochroma and Trema . Things in nature are not black and white, and there are intermediate stages. It is therefore normal that between the two extremes of light and shade there is a gradient, and there are species that may act as pioneer or tolerant, depending on

1769-426: 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

1830-524: The bacteria present. Changes of pH in a habitat could provide ideal conditions for a new species to inhabit the area. In some cases the new species may outcompete the present ones for nutrients leading to the primary species demise. Changes can also occur by microbial succession with variations in water availability and temperature. Theories of macroecology have only recently been applied to microbiology and so much remains to be understood about this growing field. A recent study of microbial succession evaluated

1891-455: The balances between stochastic and deterministic processes in the bacterial colonization of a salt marsh chronosequence . The results of this study show that, much like in macro succession, early colonization ( primary succession ) is mostly influenced by stochasticity while secondary succession of these bacterial communities was more strongly influenced by deterministic factors. According to classical ecological theory , succession stops when

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1952-563: The central characteristic. New research techniques are greatly enhancing contemporary scientists' ability to study succession, which is now seen as neither entirely random nor entirely predictable. Ecological succession was formerly seen as having a stable end-stage called the climax , sometimes referred to as the 'potential vegetation' of a site, and shaped primarily by the local climate. This idea has been largely abandoned by modern ecologists in favor of nonequilibrium ideas of ecosystems dynamics. Most natural ecosystems experience disturbance at

2013-1114: The classical model are accurate. Species diversity, overall plant biomass, plant lifespans, the importance of decomposer organisms, and overall stability all increase as a community approaches a climax state, while the rate at which soil nutrients are consumed, rate of biogeochemical cycling, and rate of net primary productivity all decrease as a community approaches a climax state. Communities in early succession will be dominated by fast-growing, well- dispersed species ( opportunist , fugitive , or r-selected life-histories). These are also called pioneer species . As succession proceeds, these species will tend to be replaced by more competitive ( k-selected ) species. Some of these trends do not apply in all cases. For example, species diversity almost necessarily increases during early succession as new species arrive, but may decline in later succession as competition eliminates opportunistic species and leads to dominance by locally superior competitors . Net Primary Productivity , biomass , and trophic properties all show variable patterns over succession, depending on

2074-528: The dense tangled vegetation lining the stream banks gave a misleading impression that such jungle conditions existed throughout the entire forest. As a result, it was wrongly assumed that the entire forest was impenetrable jungle. This in turn appears to have given rise to the second popular usage of jungle as virtually any humid tropical forest . Jungle in this context is particularly associated with tropical rain forest , but may extend to cloud forest , temperate rainforest, and mangroves with no reference to

2135-566: The early stages of forest development, then pine (on dry soil) and spruce (on wet soil). If the birch is replaced by oak it eventually develops to beechwood . Swamps proceed from moss to sedges to moor vegetation followed by birch and finally spruce. Between 1899 and 1910, Henry Chandler Cowles , at the University of Chicago , developed a more formal concept of succession. Inspired by studies of Danish dunes by Eugen Warming , Cowles studied vegetation development on sand dunes on

2196-492: 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. Succession of micro-organisms including fungi and bacteria occurring within

2257-466: The greater available light at ground level. Monsoon forests and mangroves are commonly referred to as jungles of this type. Having a more open canopy than rainforests, monsoon forests typically have dense understoreys with numerous lianas and shrubs making movement difficult, while the prop roots and low canopies of mangroves produce similar difficulties. Because European explorers initially travelled through tropical forests largely by river,

2318-509: The ground, but I am not aware that any one has thus accounted for the regular succession of forests." The Austrian botanist Anton Kerner published a study about the succession of plants in the Danube river basin in 1863. Ragnar Hult 's 1885 study on the stages of forest development in Blekinge noted that grassland becomes heath before the heath develops into forest. Birch dominated

2379-408: The highest rainfall in Africa. The editions published in the 1980s and 1990s indicate the same, an absence of paved roads through 750 km of rainforest from central to eastern DR Congo. One reason for the absence of highways through the rain forests and swamps of the central Congo, in addition to the difficulty of building and maintaining them, is that river transport has traditionally been used to

2440-457: The jungle", a comparison which had been often quoted in Israeli political debates. Barak's critics on the left side of Israeli politics strongly criticised the comparison. Ecological succession Ecological succession is the process of change in the species that make up an ecological community over time. The process of succession occurs either after the initial colonization of

2501-455: The juxtaposition of species distributions. Gleason's ideas, first published in 1926, were largely ignored until the late 1950s. Two quotes illustrate the contrasting views of Clements and Gleason. Clements wrote in 1916: The developmental study of vegetation necessarily rests upon the assumption that the unit or climax formation is an organic entity. As an organism the formation arises, grows, matures, and dies. Furthermore, each climax formation

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2562-657: 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

2623-612: The life of workers at the Chicago Stockyards, portraying the workers as being mercilessly exploited with no legal or other lawful recourse. The term " The Law of the Jungle " is also used in a similar context, drawn from Rudyard Kipling's The Jungle Book (1894)—though in the society of jungle animals portrayed in that book and obviously meant as a metaphor for human society, that phrase referred to an intricate code of laws which Kipling describes in detail, and not at all to

2684-399: The most common meanings of jungle is land overgrown with tangled vegetation at ground level, especially in the tropics . Typically such vegetation is sufficiently dense to hinder movement by humans, requiring that travellers cut their way through. This definition draws a distinction between rainforest and jungle, since the understorey of rainforests is typically open of vegetation due to

2745-634: The natural evolution of a forest. Buffon was later forced by the theological committee at the University of Paris to recant many of his ideas because they contradicted the biblical narrative of Creation. Swiss geologist Jean-André Deluc and the later French naturalist Adolphe Dureau de la Malle were the first to make use of the word succession concerning the vegetation development after forest clear-cutting. In 1859 Henry David Thoreau wrote an address called "The Succession of Forest Trees" in which he described succession in an oak-pine forest. "It has long been known to observers that squirrels bury nuts in

2806-409: The ocean. Surtsey , a volcanic island off the southern coast of Iceland , is an important example of a place where primary succession has been observed. On the other hand, secondary succession happens after disturbance of a community, such as from a fire , severe windthrow , or logging . Succession was among the first theories advanced in ecology . Ecological succession was first documented in

2867-467: The particular system and site. Successional dynamics beginning with colonization of an area that has not been previously occupied by an ecological community are 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 microorganisms, plants (lichens and mosses), grassy stage, smaller shrubs, and trees. Animals begin to return when there

2928-411: The relative importance of equilibrial vs. non-equilibrial processes. Former Harvard professor Fakhri A. Bazzaz introduced the notion of scale into the discussion, as he considered that at local or small area scale the processes are stochastic and patchy, but taking bigger regional areas into consideration, certain tendencies can not be denied. More recent definitions of succession highlight change as

2989-424: The sere has arrived at an equilibrium or steady state with the physical and biotic environment. Barring major disturbances, it will persist indefinitely. This end point of succession is called climax. The final or stable community in a sere is the climax community or climatic vegetation . It is self-perpetuating and in equilibrium with the physical habitat. There is no net annual accumulation of organic matter in

3050-679: The shade-tolerant species replace them. These species are capable of growing beneath the canopy, and therefore, in the absence of disturbances, will stay. For this reason it is then said the stand has reached its climax. When a disturbance occurs, the opportunity for the pioneers opens up again, provided they are present or within a reasonable range. An example of pioneer species, in forests of northeastern North America are Betula papyrifera ( White birch ) and Prunus serotina ( Black cherry ), that are particularly well-adapted to exploit large gaps in forest canopies, but are intolerant of shade and are eventually replaced by other shade-tolerant species in

3111-495: The shores of Lake Michigan (the Indiana Dunes ). He recognized that vegetation on dunes of different ages might be interpreted as different stages of a general trend of vegetation development on dunes (an approach to the study of vegetation change later termed space-for-time substitution, or chronosequence studies). He first published this work as a paper in the Botanical Gazette in 1899 ("The ecological relations of

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3172-468: 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

3233-599: 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

3294-402: The subsidence of land. In 1969, Eugene Odum published The Strategy of Ecosystem Development , a paper that was highly influential to conservation and environmental restoration. Odum argued that ecological succession was an orderly progression toward a climax state where “maximum biomass and symbiotic function between organisms are maintained per unit energy flow." Odum highlighted how succession

3355-409: The time of disturbance. Some aspects of succession are broadly predictable; others may proceed more unpredictably than in the classical view of ecological succession. Two important perturbation factors today are human actions and climatic change . Though the idea of a fixed, predictable process of succession with a single well-defined climax is an overly simplified model, several predictions made by

3416-498: The vegetation of the sand dunes of Lake Michigan"). In this classic publication and subsequent papers, he formulated the idea of primary succession and the notion of a sere —a repeatable sequence of community changes specific to particular environmental circumstances. From about 1900 to 1960, however, understanding of succession was dominated by the theories of Frederic Clements , a contemporary of Cowles, who held that seres were highly predictable and deterministic and converged on

3477-421: The vegetation structure or the ease of travel. The terms "tropical forest" and "rainforest" have largely replaced "jungle" as the descriptor of humid tropical forests, a linguistic transition that has occurred since the 1970s. "Rainforest" itself did not appear in English dictionaries prior to the 1970s. The word "jungle" accounted for over 80% of the terms used to refer to tropical forests in print media prior to

3538-407: The wind, and therefore can colonize big empty extensions. They are capable of germinating and growing in direct sunlight. Once they have produced a closed canopy , the lack of direct sun radiation at the soil makes it difficult for their own seedlings to develop. It is then the opportunity for shade-tolerant species to become established under the protection of the pioneers. When the pioneers die,

3599-478: Was also referred to as the 'AIDS Highway'. This description may apply to a few highways which have been paved in the eastern Congo, such as the Kisangani-Bukavu road. It applies to an extent to the road across Uganda and into Kenya but this road was constructed and paved several decades before the emergence of AIDS. It has been established from analysing archived samples of HIV, that HIV-1 originated in

3660-454: 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

3721-463: Was not merely a change in the species composition of an ecosystem, but also created change in more complex attributes of the ecosystem, such as structure and nutrient cycling . A more rigorous, data-driven testing of successional models and community theory generally began with the work of Robert Whittaker and John Curtis in the 1950s and 1960s. Succession theory has since become less monolithic and more complex. J. Connell and R. Slatyer attempted

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