Succession theory

Dominic Koch – Succession theory

Abstract

Theories are widely used throughout science, to predict or explain outcomes or events. In conservation, ecological theories are used to inform and justify actions. Succession theory is used to predict the process of change within an ecological community throughout time and can also be used to predict the trajectory of a disturbed community back to a pre-disturbed state. Succession theory although disputed over its accuracy, is widely used in restorative conservation where habitats have degraded or are recovering from a disturbance. This theory provides a framework of ideas to inform restorative practises. This essay explores the literature, seeking what succession theory is, how it’s been challenged and why this theory Is still widely used today in restoration conservation.

Intro

Theories are widely used in science, to predict or explain outcomes or events. These theoretical ideas are generally broad, abstract and do not address or acknowledge the subtle nuances in case by case situations. I will make a case for succession theory as a useful conceptual framework for ecological restoration (Choi, 2004).

 

What is succession theory?

Succession is the continuous unidirectional sequential change in the species composition of natural communities and is usually instigated by some sort of disturbance (Smith, 1995). Succession theory is used to describe the process of succession within communities regardless of whether the disturbance was natural or artificial. There are different opinions about the ubiquity of predictable successful trajectories and usefulness of succession theory (Smith, 1995). Temporal shifts within community composition can be attributed to changes in the presence and relative abundance of species within an environment. Whilst succession is often used to describe plant communities, succession theory is also applicable for shifts in populations of other organisms (Emery, 2010). The process of succession can be seen in motion in a wide range of settings, and the rate of succession can vary depending on the size (intensity and scale) of the disturbance. Disturbances can range from volcanic eruptions to abandoned parking lots, to retreating glaciers.

 

Succession theory is one of the longest studied ecological concepts. Successional patterns were first properly characterised by Henry Cowles (1899), observing a shift in community complexity from the shore of Lake Michigan inland. He observed a gradient between plant communities from the lakeshore inland. The further away from shore the plant community was, the older he believed it to be. Ecologists used succession theory to predict temporal patterns within communities and their trajectories based on a snapshot of an area which represents the various ‘stages’ of community succession.

 

Although Succession theory is commonly used, succession itself is not easy to predict, and the theory is frequently under refinement and critique. Succession is perhaps best-known thanks to Frederick Clements, proposing that communities over time will reach a climax, the end stages of succession. Climax communities are used to define an ecosystem type (Emery, 2010). Clements believed that after a disturbance the community would ultimately reach the same climax assemblage again, returning to the same pre-disturbance state. Clements’ idea of extreme predictability of succession led him to put forward the idea of the super-organism concept of succession. Super-organism concept is whereby all species work together to maintain stability, self-renewing and self-forming (Emery, 2010). This ‘superorganism’s concept is not too dissimilar to the later proposed Gaia hypothesis by James Lovelock (1968) (Lovelock, 1974).

Restoration process – succession

So how is succession theory useful for restorative conservation? To restore a site, one must initially grasp how a community grows and changes over time. Succession provides insight into those ecological community changes. Ecological restoration is a two-step process: (1) colonisation, which is the selection and immigration of adapted and adaptable species. These colonising species are typically slow growing. (2) Ecosystem development, this is the colonisation of a species and an accumulation of nutrients into the soil, changing soil structure and reducing soil toxicity. This unravelling of events enables other species to begin colonising, creating a snowball effect. Typically, those colonisers are poor competitors and can become quickly outcompeted once the habitat becomes suitable for other, more competitive species (Smith, 1995). Restorative conservation uses these principles to formulate an appropriate management plan. By introducing species at the appropriate stages, species have more chance of success, and the restorative process is more resource efficient. An example of the implementation of these practises is the restoration of Matiu/Sommes Island, in the centre of Wellington Harbour, New Zealand. Here faster-growing shrubs are first established, and late colonisers are then introduced such as the Kaori tree (DOC, 2012).

Succession and disturbances – What does it do? When does it occur?

Succession takes place when a community is disturbed, and an area is partially or completely made devoid of vegetation due to a disturbance, be it natural or artificial (human induced) (Emery, 2010). Disturbances can take many forms, and the impact of these disturbances can vary greatly. Disturbances can range from volcanic eruptions with extensive and wide-reaching impacts to small, relatively frequent disturbances like the death of a canopy tree. The type of community composition which follows after a volcanic eruption or glacial retreat is very slow and described as primary succession. The long recovery time is due to the complete loss of the community and soil profile, which needs to re-establish. Comparatively, secondary succession is large, low-intensity disturbances like ploughing an agricultural field, leading to moderate succession. This is because species survive, and the soil complex largely remains intact (Emery, 2010). Species quickly recolonise areas moderately disturbed (Emery, 2010). There are two types of successional communities, early and late. Early communities are quick to establish and are rapidly growing. Those that establish themselves much later represent late successional communities (Emery, 2010). A community will transition between the two succession types.

Critiques – What doesn’t it do? And when doesn’t it occur?

After reviewing the literature on succession theory, in particular, Clements model of succession critiques, (in the form of other models of succession) do not deviate significantly from Clements initial proposal. One of the flawed assumptions of Clements theory is that after a disturbance, communities will reach the same climax, irrespective of the type or intensity of disturbance. This is one of the critiques of this theory, that environments and communities do not change. Cairns & Heckman (1996) concluded that Clements model did not adequately represent community succession in restoration (Choi, 2004). This, of course, is incorrect; communities are inconstant and are constantly changing to the environment around them. Put simply, the theory does not account for the unpredictable nature of succession and change. Diamond (1975) proposed a revised set of rules first put forward by Clements, Diamond proposed that it is perchance the presence and abundance of species that affect the success of other species, forming local scale guilds or communities. Introduced species to these communities must initially pass through an abiotic and biotic filter before they succeed within that community. These filters change with the disturbance regime. Furthermore, most of the research conducted on succession theory has been done on plant communities, and so some mechanism has yet to be explored. For example, literature has failed to explore the effects of herbivory on plant communities in depth (Choi, 2004).

Conclusion

Succession theory is widely used in restoration conservation despite its flaws because of the effective framework of thought it provides. Succession theory is founded on the ideas of succession. This theory has enables researchers to describe and predict community structure progression throughout time through observation. Clements remains the first strong advocate for succession and whilst his model was not accurate it became the foundation for other, yet similar models of succession. Disturbance regimes disrupt community composition. All disturbance regimes are responded to the same within communities, be it attributed to natural or artificial causes.

 

References

Choi, Y. D. (2004). Theories for ecological restoration in changing environment: toward ‘futuristic’restoration. Ecological research, 19, 75-81.

Citation: Emery, S. (2010) Succession: A Closer Look. Nature Education Knowledge 3(10):45. Retrieved from https://www.nature.com/scitable/knowledge/library/succession-a-closer-look-13256638

Clements. F. E. (1919). Plant succession; an analysis of the development of vegetation. Cambridge Institution of Washington. https://archive.org/details/cu31924000531818/page/n4

Connell, J. H., & Slatyer, R. O. (1977). Mechanisms of succession in natural communities and their role in community stability and organization. The American Naturalist, 111(982), 1119-1144. http://www.columbia.edu/cu/e3bgrads/JC/Connell_1977_AmNat.pdf

Connell, J. H., & Slatyer, R. O. (1977). Mechanisms of succession in natural communities and their role in community stability and organization. The American Naturalist, 111(982), 1119-1144.

Lovelock, J. E., & Margulis, L. (1974). Atmospheric homeostasis by and for the biosphere: the Gaia hypothesis. Tellus, 26(1-2), 2-10.

McCook, L. J. (1994). Understanding ecological community succession: causal models and theories, a review. Vegetatio, 110(2), 115-147.

Smith. L. R. (1995). Ecology and Field Biology: Fifth Edition. HarperCollins College Publishers.

Wellington Harbour Islands KAITIAKI PLAN 2012-2017. (2012). Department of conservation. Retrieved from https://www.pnbst.maori.nz/assets/PDFs/Harbour-Islands-Kaitiaki-Plan.pdf

 

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