Herbivores and controlled fire: a necessary alliance to prevent large forest fires
Rose Mary Canals
Professor of Pasture Cultivation and Ecosystem Restoration, Public University of Navarre.
Reproduction of the article published in The Conversation on 3 September 2025 
Following the wave of fires that has shaken and shocked Spain, a shared awareness has emerged: it is necessary to manage the landscape to make it less vulnerable to high-intensity fires.
However, alongside this lesson learned many questions arise that have no simple answer. Can the original forests be restored in the areas of greatest ecological value if we apply proper management? Can we prevent fire from returning to the same place? How should we approach the management of urban–forest interfaces in an economical and sustainable way?
These are complex issues. I will try to address some of them in light of what I have learned over more than three decades of work in plant community ecology and in environmental restoration projects in which fire and herbivores have been key tools.
Alteration of the dynamics of natural disturbance
We know that the plant communities that establish themselves in a given location respond to the prevailing climatic and soil conditions, with the set of plant species best adapted to that particular environment being selected.
But that is not all. There is a third decisive factor that determines the establishment of a plant community: the historical regime of disturbances. Under this concept are encompassed natural processes that on the surface might seem destructive, but which in reality have shaped vegetation for millions of years, such as droughts, pests, avalanches, the presence of herbivores and, of course, fire. Each plant community is adapted to a specific disturbance regime and demonstrates this through the adaptive strategies of its dominant species: thorns and toxins against herbivores, insulating barks and serotinous cones against fire, etc.
The truth is that we humans have profoundly altered these natural disturbance dynamics, and have done so more intensely over the last century. For example, open ecosystems – those dominated by herbaceous vegetation, such as grasslands, sparse scrublands, dehesa woodlands and savannahs – have seen plant biomass consumption by herbivores greatly reduced and are disappearing in favour of more lignified plant communities with a higher fuel load.
Although the extinction of megafauna began at the end of the Pleistocene, in the Holocene populations of ungulate herbivores have been severely reduced, with humans playing a decisive role.
Furthermore, Neolithic domestications focused on a specific group of herbivores, the grazers, because they are gregarious animals, have predictable migratory movements and feed in open, well-visible areas. Over the past few thousand years, domestic herbivores have emulated the disturbance regime of wild grazers, helping to maintain open ecosystems. But in recent decades, the steep decline of extensive livestock farming and the rise of intensive operations have radically altered this dynamic.
Something similar has happened with the natural regimes of fire. Many plant communities, in Mediterranean environments and also in temperate and tropical regions, have a natural fire regime associated with them, with a profound ecological role linked to the recycling and regeneration of vegetation. Climate change, generating extreme conditions conducive to fire and subjecting vegetation to severe thermal and water stress, the accumulation of fuel due to a lack of management, and the so-called extinction paradox (decades of natural fire suppression that encourage fuel build-up) have completely disrupted that balance and are fuelling ever more intense and difficult-to-control fires. In this scenario, fires will be inevitable and recurrent, as long as there is vegetation to burn.
Interconnection between fire and herbivores
The herbivore and fire have always been closely interconnected and in temperate and Mediterranean latitudes they have been the two great managers and recyclers of plant matter. Decomposition, although it also fulfils that function, plays a more significant role in other environments. The herbivore consumes vegetation in a selective, slow and recurrent manner, transforming it into energy, animal growth and into nutrients that it partially returns to the soil through its excrement. Fire, on the other hand, is a rare event that acts quickly and intensely, recycling organic compounds as resistant as lignin. Thus, it generates a great mineralisation of plant matter – by reducing it to ash – which can be retained in the ecosystem or lost (volatilisation, run-off, leaching) depending on the intensity of the fire and the local conditions after the flames have passed.
While the herbivore selects what is most nutritious and digestible, fire makes no distinctions. They are distinct but complementary processes, and when managed together and in a planned way, emulating natural regimes of disturbance, they allow open, mosaic-like landscapes to be maintained at low economic cost, combining different types of vegetation, with a low fuel load and high biodiversity.
Final lessons from disturbance ecology
The plant communities we know have evolved over millions of years, adapting to specific disturbance regimes defined by their type, intensity and frequency. Thus, the dominant type of disturbance shapes the characteristics of ecosystems as much as climate and soil do. Where herbivores prevail, plant communities tend to be nutritious and attractive to the animals, seeking to be grazed to ensure their regeneration. Where fire dominates, flammable species that burn quickly and regenerate rapidly thrive, which favour the occurrence of new fires. Without herbivores and with climate change underway, it is easy to guess which types of plant communities will be favoured in the future: communities adapted to fire and that depend on it primarily to regenerate.
As various experts point out, many plant communities no longer correspond to the climate in which they originated. We can also add that they are evolving and responding to the current disturbance regime, which is different from the historical one, in which the near-total absence of herbivores leaves fire as the main natural recycler of plant biomass.
All signs point to the fact that, spurred on by climate change, fires will recur more frequently and, in many cases, it will be impossible to restore many ecosystems as we knew them. Faced with this reality, management must be geared towards reducing the stress our forests are under by lowering their density and cover to restore forest stands and mitigate the severity of fires. But it is also essential to promote mosaic landscapes and open spaces where extensive livestock farming and grazing by herbivores can fulfil the lost recycling role, so vital at this time.
Technical burns can help control woody vegetation in its early stages. However, only a combination with multi-year grazing plans will prevent the consolidation of pyrophytic communities and reduce the dangerous reliance on fire as the sole mechanism regulating plant matter. The combination of prescribed fire and environmental grazing, called pyro-grazing, offers a sustainable management approach capable of maintaining more resilient, less flammable and, at the same time, more biodiverse ecosystems. This is what we are working on.
