What is rewilding?

damselfly

The term rewilding has been thrown about a lot quite recently but in many cases, the term has been misused to just be about planting trees. Here I explain how ecologists view rewilding, as well as important concepts required to understand rewilding. This is somewhat a summary of a review paper by Perino et al. (2019). If you want to read something more technical you can find the details of that paper in the references below.

Rewilding is not only about introducing wild things to where they can’t be found anymore. To quote Dave Foreman:

“I meant rewilding to instead be about wilderness restoration – restoring wildness with native species and processes. So, let us all remember that rewilding comes from wilderness recovery (or restoration).”

In other words, the goal of rewilding is to restore functions to ecosystems through the reintroduction of native species. This is the main difference between rewilding and ecological restoration, which focuses on the restoration of ecosystem functions without the emphasis on reintroducing native species. This does not mean that ecological restoration is worse; in locations where invasive species are impossible to eliminate or native species cannot be reintroduced, ecological restoration is a more viable option.

What is an ecological function? An example would be a butterfly, which as an adult serves as a pollinator for flowering plants, while, as a caterpillar, it functions as prey for insect-eating birds and a host for parasitoid wasps.

Restoring ecological functions drives 3 processes (simple terms are in bold, scientific terms are in brackets):

  • Food chains (Trophic complexity)
  • Disturbance (Stochastic disturbance)
  • Movement (Dispersal)

Plants, fungi and animals with a lot of ecological functions create a complex web of interactions. Among these interactions are food chains. This is the process in which energy is stored and moved throughout the ecosystem. The more complex the food chains or food webs, the more stable and resilient the ecosystem will be. This is why rewilding efforts can start with first reintroducing predators back into ecosystems. For example, in Yellowstone National Park in the United States, wolves were reintroduced back into the park first, to regain ecosystem balance.  By doing so, you add another level to the food chain and the lower levels of the food chain are regulated by the predators on the upper levels.

We tend to think of disturbance as a bad thing, but that is not always the case in a dynamic system. Random disturbance events help to make ecosystems more diverse and stable by ensuring that no one organism can dominate. For example, in rainforests, large trees will grow and block sunlight from reaching the understory. If the large trees do not die – through falling over, disease, lightning strikes or fire – then there will not be any new space for younger trees to grow. So a forest is not a permanent collection of trees, but it is in a constant state of change in which large trees fall and new trees fill the gaps. This prevents a single tree species from taking over in a rainforest, as many different species fill the niches that become available after a tree fall.

Random disturbance events help to make ecosystems more diverse and stable by ensuring that no one organism can dominate.

Movement is crucial for maintaining the food chains when disturbance happens. Ecosystems are often patches of resources that animals, fungi and plants can use. Usually, this results in patches with different compositions of species. For example, if there are many species in a single large patch, it can help to rescue populations in other smaller patches through the movement of organisms between patches.

This is why creating networks of patches that enable movement between patches is important. It helps to maintain the food chains in all the connected patches by buffering the random disturbance.

On a large scale, preserving ecological functions pays humans back in the form of ecological services. The previous example of a butterfly supplies the supporting service of pollination. This is necessary for the provisioning services which create food and raw materials for people.

Overall ecological services can be categorised into 3 benefits:

  1. Non-material
  2. Material
  3. Regulating

Non-material benefits are things like improvements to human health and wellbeing that can be gained through interactions with nature. Non-material benefits also extend to profits from services such as tourism.

Material benefits are things that you can harvest from nature, such as wood or food. Malaysians have a very close relationship with many species of plants that are used in our culture and cuisine.

Regulating benefits are things that are controlled by having nature around. These include natural disasters like floods and landslides, regulation of heat and climate, and reduction of dust and pollution.

When you have many ecological functions, all these interactions create an ecosystem. Ecosystems, by definition, are living and non-living components interacting in a shared space. The goal of rewilding should always be to restore ecosystems, and that is why we have to be careful about how we use this term and not use it as a buzzword that means only planting trees.

In the next article, I give an example of a successful case of urban rewilding in relation to food chains and interactions, and the lessons we can learn from it, especially from a functional ecology perspective.

References:

  1. https://rewilding.org/what-is-rewilding/
  2. Perino, A., Pereira, H. M., Navarro, L. M., Fernández, N., Bullock, J. M., Ceaușu, S., … & Pe’er, G. (2019). Rewilding complex ecosystems. Science, 364(6438), eaav5570.

This article is supported by The Habitat Foundation Conservation Grant

See also

Gliding lizards and how disturbance helps biodiversity

gliding lizard

Draco gliding lizards are interesting tropical animals. They have ‘wings’ that fold out from their ribs and allow them to glide from tree to tree. They also have a small flap under their chins that acts as both a flag to communicate and like the tail of a plane to stabilise their flight. When I read about them as a kid, they always struck me as incredibly exotic animals that would be really hard to find.  It turns out that they are quite well adapted to living in our cities.

There are 11 species of Draco in Peninsular Malaysia. In the natural world, they tend to be found in forest clearings where there is space between trees and not too much dense vegetation. These gaps between trees are usually created by tree fall events. In a mature rainforest, trees fall very often, either due to old age, disease, or unstable soil. Rainforest trees are often connected to other trees by vines or lianas, so when one tree goes down, it can pull down others and crush anything smaller in its path. This is a natural disturbance that creates gaps in the otherwise dense canopies of the rainforest. Young trees and saplings use this opportunity to fill the gap and start the cycle over again.

Liana have long, woody winding stems that climb up vertical structures like trees, thus extending from the ground to high canopies

Many species are known to take advantage of these forest gaps, including gliding lizards. The constant disturbance of tree falls creates more diverse patches of forest, where trees of different species and ages are always going through tree falls and regrowth, nothing staying permanent. This, in turn, creates space for all sorts of gap species that are adapted to these environments. The layperson may view change and disturbance as something undesirable or negative, but these are necessary processes to keep the ecosystem in balance.

In cities, humans are the main force of disturbance. We cut weeds and shrubs and maintain clear gaps between trees. While this may not be good for animals that prefer some shelter, the lack of dense vegetation seems to be a boon for gliding lizards. They can bask in the sunlight created by our sparsely planted trees and glide in between them with ease. Scientists call this pre-adaptation – an organism is predisposed to survive in certain habitat structures, allowing it to take advantage of new habitats with similar features.

A lot of our urban species have, by luck of the draw, found a place for themselves in our urban spaces. So perhaps we should ask the question of how we should use disturbance as a tool for biodiversity and healthier ecosystems, instead of maintaining landscapes just for the sake of maintaining aesthetic practices.

References:

Whitmore, T. C. (1984). Tropical rain forests of the Far East. Oxford University Press, Oxford.

Grismer, L. L. (2008). A revised and updated checklist of the lizards of Peninsular Malaysia. Zootaxa, 1860(1), 28-34.