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2021. március 8.

Variability: The X Factor

Understanding the need for protecting ecosystemic variability is critical: it brings a much needed functional diversity to handle ecosystem shocks.

Resilience is not stillness or rigidity. When C. S. Holling first described the term, his main finding was how variability is present in all ecosystems. His example case was how unexpected outbreaks of the spruce budworm (Choristoneura freemani) maintains the spruce-fir balance in the forests of eastern Canada.

The arrival of the budworm is hardly predictable and is disastrous for foresters. The outbreak happens suddenly, large masses of worms emerge, and in a few years’ time defoliate most of the forest in a huge area. Normally, predators control the population of the worm, but when the forest gets older, they find abundant food that creates a very favourable condition for rapid population growth. If a few dry years follow each other, the balance between the budworm and its predators tips toward the worm and an outbreak happens.

It turns out, the forest needs these outbreaks. Without them, fir would dominate spruce that would eventually disappear from the forest. Since the budworm prefers fir as its food, after each outbreak, the population of spruce becomes stronger; thus, the diversity of the forest is strengthened. Worms also prefer older trees, thus younger stands survive better that is also useful for the renewal of the forest in the longer term.

Variability is part of the normal in ecological systems — in fact, in all complex adaptive systems. This is true for rivers and floods, forests and pests, game and diseases, forests and wind, temperature and agriculture, etc.

Even sustainability-oriented management is often aspiring to control the system, producing maximum sustainable yield, defining carrying capacity for various pressures, etc. The problem with this approach is that it leads to over-optimization of the system, which is highly efficient but usually also aims to control disturbances and thus reduces biodiversity. Without disturbances and sub-optimal events in the system, the only ecological process is competition; thus, the most efficient species will take all place and resources. The problem is that these kinds of systems become highly vulnerable to more and more shocks as they lack the functional diversity to handle shocks that would be normal in that specific ecological context. This high vulnerability is leading to one of the two outcomes: collapse or rigidity trap. 

When a system collapses, a shock or disturbance is causing major disruption, many of the capital that was accumulated during the prolonged and highly efficient production phase will be released and the system has to rebuild itself. The other option is to control and monitor the system with ever greater effort, using more and more technology to keep out disturbances and continue the optimization for a single ecosystem service. While in theory this is a viable strategy, usually, sooner or later, these systems also collapse.

Variability is necessary for ecosystem resilience.

Variability is part of the normal in ecological systems — in fact, in all complex adaptive systems. This is true for rivers and floods, forests and pests, game and diseases, forests and wind, temperature and agriculture, etc.