Fire in ecosystems - a natural disturbance or an anthropogenic threat?
In the context of ecosystems, natural disturbances can be defined as a process that removes biomass from its environment. Such events can be storms, fires, floods and volcanic eruptions. From a human perspective, they are usually seen as unnecessary catastrophes that we try to avoid. Unlike anthropogenic disturbances, however, natural disturbances are an important part of ecosystems' dynamics and for maintaining biodiversity, as long as the disruption they cause is within the boundaries of what the ecosystem can cope with without deteriorating. According to the intermediate disturbance hypothesis, species diversity is higher when the frequency of disturbances is intermediate.
Depending on the ecosystem in question, fire can either be a serious and unnatural threat, or a natural and essential part for the long-term functioning of ecosystems. For instance, in Indonesia the tropical forest is often burnt to give way to alternative land-use such as palm-oil plantations. The peat soil, which is a significant sink of carbon, is even drained to speed up the process land conversion. Such disturbances have a catastrophic effect on the ecosystem and its biodiversity.
In the boreal forest that covers a significant part of the northern hemisphere (the Taiga), fire is a natural source of regeneration. Due to contemporary forest and land management policies, fires are nowadays suppressed, which has implication for the fire regime and for forest ecosystems as a whole. By suppressing frequent, small, short-lived fires that burn quickly with a high intensity, the fuel load is allowed to build up. The next fire will be greater and different. Once a fire occurs, it will burn with an altered fire regime. The accumulated fuel load allows the fire to burn for longer and to reach higher, and so cause damage to the species and the soil beyond an ecosystem's natural range of variability.
In intensively managed forests, the felling of trees removes some of the potential fuel load and aims to mimic the regeneration created by fires. Unfortunately it does little to help the species and ecosystem process that depend on real forest fires. In some cases, forest is intentionally burnt for conservation purposes. The challenge is to mimic the natural fire regime in forests that have been managed for centuries. Other attempts to copy natural disturbances include the planting and burning of foreign species of trees (such as non-native species of Eucalyptus) within tree plantations for management purposes, and the use of dynamite to imitate lightning and create dead standing trees.
Written by Tina Sommarstorm
Provita Oct 31, 2017