Syllabus Edition
First teaching 2015
Last exams 2025
Human Impact on Succession (DP IB Environmental Systems & Societies (ESS))
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Human Impact on Succession
Human activities can divert the progression of succession to an alternative stable state by modifying the ecosystem through various activities, such as:
Burning
Agriculture
Grazing pressure
Resource use (such as deforestation)
These activities can have both direct and indirect impacts on the ecosystem, leading to changes in the biotic and abiotic components, and ultimately altering the course of ecological succession within the ecosystem
For instance, controlled fires are often used to clear land for agricultural purposes or to manage the spread of wildfires
However, fire can have serious negative effects on the ecosystem by killing off plants, reducing soil fertility, and altering nutrient cycles
Similarly, agriculture and grazing can cause soil erosion, loss of vegetation cover, and changes in nutrient cycling, which can in turn affect the composition of the species in the ecosystem
Photo by Randy Fath on Unsplash
Human activities often simplify ecosystems, rendering them unstable
These activities, which divert the progression of succession, may be temporary or permanent depending upon the resilience of the ecosystem
Resilience refers to the ability of an ecosystem to recover from a disturbance and return to its original state
If the human disturbance is mild and the ecosystem is highly resilient, then it may be able to recover from the diversion to the process of succession and return to its original state
However, if the disturbance is severe and the ecosystem is less resilient, the diversion may be permanent, leading to a new stable state with a different set of species and ecological interactions
This is one reason why it is so important to carefully consider the environmental impacts of human activities and strive to minimise their negative effects on the ecosystem, to protect natural ecological processes, such as succession
Worked Example
Giving a specific example of an ecosystem, discuss the human activities and factors which could disrupt the process of succession and lead to an alternative stable state in that ecosystem.
Answer
Tropical rainforests are being affected by human activities, resulting in alternative stable states. Human activities such as deforestation, mining, and agriculture can disrupt the natural progression of succession in rainforests and lead to alternative stable states.
Deforestation and agriculture is the most significant human activity that can disrupt the succession process. The removal of trees from the system to create grazing land reduces the complexity of the habitat, resulting in the loss of biodiversity, decreased nutrient cycling, and changes in the hydrological cycle. Deforestation leads to soil erosion and loss of topsoil, which can result in lower soil fertility, decreased primary productivity and can allow the process of desertification to begin.
Mining is another human activity that can disrupt the natural succession process. Mining results in the removal of topsoil and vegetation, which can lead to soil erosion and landslides. The use of chemicals in mining can also result in water pollution, which can negatively impact aquatic life within the ecosystem.
These human activities can lead to alternative stable states in the tropical rainforest. For example, deforestation can lead to the formation of savannas or grasslands instead of the original forest ecosystem. These alternative stable states have lower resilience compared to rainforests, as they have lower biodiversity, decreased productivity, and different abiotic and biotic factors compared to the original ecosystem. The ability of the rainforest ecosystem to recover depends on the resilience of the ecosystem - even naturally ecologically resilient systems like rainforests can shift to an alternative stable state given enough pressure from human activities.
Human activities can divert the process of ecological succession and push the ecosystem towards an alternative stable state
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