Reintroducing large herbivores and using controlled fires are two of the most effective rewilding strategies

In post-war Mozambique, the reintroduction of wildebeest and buffalo has helped combat the spread of an invasive mimosa. This is one of 42 cases of renaturalization -widely known as rewilding- reviewed in a study published in the Journal of Environmental Management covering 19 countries around the world. The review, published as part of the Horizon Europe wildE project and led by CREAF researcher Miriam Selwyn, has found that 70% of the cases of renaturalization studied have improved nature's response to the effects of invasive species, droughts or fires, among other disturbances. The most effective strategies include, on the one hand, reintroducing large herbivores to reduce invasive plant populations and, on the other hand, promoting what are known as prescribed burns, controlled fires that, among other things, help more fire-resilient species to grow. The places where this strategy has been less successful are those that have suffered extreme phenomena such as prolonged droughts or large forest fires, especially in temperate or Mediterranean environments, and, according to the team, one possible explanation is that they have tried to restore ecosystems as they were in the past, without taking into account that the species of the past are no longer adapted to the new environmental conditions caused by climate change. 

“Nature is like a cog that has stopped working because we have taken many parts out of it; with rewilding we want to put it back together again and make it work more autonomously, but not necessarily as it was before, but taking into account the new climate change landscape and our cultural history, which needs to maintain and promote new landscapes such as agroforestry mosaics”, says Miriam Selwyn, lead author of the study and member of the wildE project.

According to the authors, this review study demonstrates that renaturalization strategies are very effective and the results could be useful for advising the implementation of the Nature Restoration Act, as it includes a catalogue of examples and a snapshot of what has worked best.

Among the forty or so cases and more than 300 variables they analysed, one that illustrates the benefit of recovering herbivores is in Gorongosa National Park, Mozambique. There, during the war, a large number of mammals were killed and the invasive shrub Mimosa pigra took advantage of this and expanded its territory; to reverse the situation, large herbivores such as wildebeest and buffalo were reintroduced and, after a decade, the mimosa invasion was reduced to pre-conflict levels. In the same vein, another recent initiative in India has also shown that reintroducing mega-herbivores, such as elephants and rhinos, reduces the presence of invasive plants and increases the abundance of native plants. “Although we have not analysed it in this study, in Spain there are also initiatives that are introducing grazing animals, such as horses, to prevent forest fires and promote biodiversity. These herbivores recover the function that was traditionally done with extensive livestock farming”, adds Miriam Selwyn. There are also successful examples of carnivores, such as the reintroduction of wolves in Yellowstone (USA). Specifically, the presence of wolves stopped elk from feeding in the open areas along riverbanks and this, in turn, made it easier for the vegetation on these banks to grow, because these large herbivores no longer ate them. 

With respect to fires, a prominent case is located in the Sierra Nevada (California), where excessive logging and fire suppression has made forests less resistant to fire, drought and pests. After comparing three scenarios over two decades: taking no action, prescribed burning or manually removing fuel loads, they showed that combining the latter two was the most effective strategy for reducing fuel loads. CREAF researcher Josep Maria Espelta, co-author of the study and member of the wildE project, explains that “in ecosystems used to living with fire, such as the Mediterranean, strict policies of total fire suppression are sometimes counterproductive, because they change habitat conditions and end up favouring forest structures that are more vulnerable to this disturbance”. 

Another curious example is in the UK, where wild boar have been introduced to help some plants to germinate. These animals turn the soil to find food and this, in turn, can help aerate the soil and make it easier for some plants, such as bluebells (Hyacinthoides non-scripta), to germinate.

According to the publication, unlike more traditional approaches to restoration, the new strategy of renaturalization, rewilding does not necessarily seek to replicate the past, but rather to promote living, diverse and dynamic ecosystems, “with the aim of nature adapting to uncertain scenarios such as new invasive species, extreme climatic phenomena, etc”, adds Josep Maria Espelta. This newer perspective also takes into account the interaction with people, on the one hand, because part of the landscape has evolved with our history. For example, there are species of birds and butterflies linked to agricultural areas. On the other hand, this new idea works to make socio-economic needs compatible with nature conservation in certain contexts, “for example, promoting domestic herbivores that have the same function as wild ones, so that it is positive for the ecosystem, but also for society (provision of cheese, meat, etc.)”, explains Miriam Selwyn. Another example would be to take advantage of tree mortality caused by recurrent droughts to promote forest structures that are more resistant to forest fires.  

The phrase ‘nature is wise’ hides a truth: an effective solution to protect ecosystems from the impact of climate change is to restore nature's ability to sustain itself. To do this, ecology proposes to implement land management actions focused on renaturalization. With these practices, after initial management support and some subsequent accompaniment, “nature can become more autonomous and more resilient”, adds Josep Maria Espelta. 

Specifically, the research analysed projects that addressed renaturalization from three main approaches. Firstly, those aimed at restoring complexity to the food web, for example by introducing or removing certain animals, both herbivores and carnivores, that can control populations, or facilitating the recovery of native plants. Secondly, measures that seek to adapt ecosystems to naturally occurring disturbances so that they are more prepared - for example, prescribed burning to reduce the risk of large forest fires. And finally, actions that aim to connect habitats to make it easier for species to move and expand their territory, for example, connecting a natural park with agricultural areas to facilitate seed dispersal. The expert also points out that it is important to bear in mind that rewilding aims to reduce human intervention in ecosystems, so “in some situations it can also consist of not intervening and leaving nature to evolve on its own”, explains Miriam Selwyn. To analyse the effect of rewilding initiatives on ecosystem resilience, the team compared them with control cases that had not applied any measures. To make the comparison, they included more than 300 variables, such as species richness, vegetation cover or fuel load.

“This study shows that rewilding can help ecosystems become more resilient to climate change, although its success depends on the intensity of extreme events and will sometimes require additional support measures to be implemented”, concludes Miriam Selwyn. 
 

Article: Selwyn, M., Lázaro-González, A., Lloret, F., Benayas, J. M. R., Hampe, A., Brotons, L., ... & Espelta, J. M. (2025). Quantifying the impacts of rewilding on ecosystem resilience to disturbances: A global meta-analysis. Journal of Environmental Management, 375, 124360.