There are ecosystems that periodically have been burning due to natural causes for millions of years. Mediterranean forests are one example. Many organisms inhabiting them have been living with fire for so long that they have adapted to it. Some species even need it to survive. Sensing the heat of a fire from kilometres away and using the burnt forest to lay eggs, or attracting flames to awaken seeds from their dormancy. These are just two of the strategies used by certain plants and animals to benefit from an ecosystem that has burnt.
Animal strategies
Over time, in an ecosystem that has burnt, animals that used different tactics to avoid succumbing to the flames or even to profit from them may proliferate. The fire beetle (Melanophila acuminata) is one of the animals that have learned to take advantage of wildfires. It has infrared radiation receptors that detect the heat of flames even from 40 km away. This beetle knows well that a fire has a great advantage: the flight of predators. It goes to “black forests” to lay its eggs in freshly burnt wood or even still in the form of embers. This way, baby beetles can be born without the danger of being eaten by hungry animals.
Fires can clear the landscape, that is, where there were a large number of trees and shrubs per square kilometre, there are fewer afterwards. This benefits species typical of open natural spaces such as the red-legged partridge (Alectoris rufa) and the European rabbit (Oryctolagus cuniculus). Why? In the early stages of recovery of an ecosystem that has burnt, herbs with a high nutrient content appear. Both they and their seeds are a source of food for rabbits and partridges, respectively. But that’s not all. These species are a delicacy for a bird of prey that is also typical of open spaces: the Bonelli’s eagle (Aquila fasciata). In this way, a fire can be good news for the red-legged partridge and Bonelli’s eagle, both listed as species vulnerable to extinction in the Libro Rojo de las Aves de España 2021.
In addition to feeding, living things seek to reproduce successfully. To do this, some oviparous species, that is, those that lay eggs, make their nests in places where the eggs can be comfortable and safe. The violet carpenter bee (Xylocopa violacea) and different species of woodpeckers drill their nests in dead trees. The fact that the wood of these trees is soft makes the work easier for these animals, who find many possibilities to drill their nests after a fire. In fact, the black-backed woodpecker (Picoides arcticus), a woodpecker from the United States, adores recently burnt forests.
Plant strategies
Plants can’t walk or fly, so they’ve figured out other ways to proliferate after a fire. The two basic types of strategies consist of being reborn and producing a lot of seeds dependent on the heat of the flames. There are also plants capable of resisting fire.
The kermes oak (Quercus coccifera) is one of the plants that can be reborn, also called resprouters. It does this thanks to spots called buds where many cells specialised in generating new shoots are concentrated. The buds have a coating that protects them from fire. In addition, they contain all the energy that the bud-generating cells need to be able to do their job. It is curious to see in this type of burnt plants, when they are being reborn, the contrast between the jet black of the burnt parts and the intense green of the new shoots.
Plants that produce a lot of seeds, or seeders, accumulate them in the soil or higher up. The Mediterranean gorse (Ulex parviflorus) is a shrub of the first group. Their seeds lie dormant in the ground, and do not emerge from their dormancy until the flames arrive and awaken them. Then, they can then germinate and generate new shrubs. Also, to make sure that enough heat reaches the seeds, gorse is made to burn. How? They have very thin branches and leaves and many of both, which makes them catch on fire easily.
The Aleppo pine (Pinus halepensis) accumulates its seeds in pine cones that hang from the branches of the treetop. These cones are tightly closed and only open with the heat of the flames. For this reason, they are called serotine pine cones. In a forest of Aleppo pines, fires cause a rain of seeds that fall to the ground. There they will be available to germinate.
The cork oak (Quercus suber) has done the opposite to the gorse. It has a thick, insulating bark that allows it to withstand relatively intense fires. But that’s not all: its crown recovers relatively easily because it contains buds from which new shoots can emerge.
Finally, it seems that fires help some herbs and plants in the lily group to blossom. Not much is yet known about this phenomenon, but it is believed that it is due to the use of the nutrients present in the ashes.
Thank to these strategies, ecosystems have the potential to recover after a fire. Over the years, the grey and glooby landscape can be transformed into a green and renewed one, and with the potential to be better prepared for the next fire.
So, we shouldn’t be concerned when an ecosystem burns?
On the one hand, not all living things are adapted to fire. We only find adapted species in ecosystems that have naturally burnt from time to time and steadily for thousands of years. This is the case, for example, of the Cap de Creus Natural Park, in the northeast of the Iberian Peninsula.
On the other hand, living things with adaptations are not adapted to any type of fire. These organisms have learned to live with something called a fire regime, that is, a specific pattern of fires: occurring at a particular time of the year and every certain period of time that lasts more or less the same, with a certain intensity, and spreading in a certain way that can be, for example, through the ground or through the treetops.
So, in order to stay alive, these species need their fire regime not to change. The problem is that fire regimes are changing on a global scale. We are seeing more and more wildfires with more destructive capacity and more fires in places where they have not occurred before. Why? Because of climate change and insufficient forest management. If a forest is left unmanaged, vegetation can proliferate so much that when a fire comes, the flames find so much material available to burn that they become larger and more intense. This is what is happening in many rural areas where extensive agriculture and livestock farming are becoming less and less common.
So yes, we should be concerned, as alterations to fire regimes pose a threat to the biodiversity of ecosystems. The serotine cones of the Aleppo pine, the buds of the kermes oak and the bark of the cork oak do not resist too intense flames. The seeds of the gorse do not have time to germinate if the fires are too close together. Fire beetles, rabbits, partridges, Bonelli’s eagles, and woodpeckers can all perish from devastating fires.
Conserving fire regimes through forest management, the development of a sustainable rural economy, and measures to curb climate change is key to ensuring biodiversity conservation and maintaining the life cycle of ecosystems.
Find out more
- Article by Andrew Stillman and collaborators in The Condor: Nest site selection and nest survival of Black-backed Woodpeckers after wildfire.
- Article by Helmut Schmitz and collaborators in Proceedings of SPIE – The International Society for Optical Engineering: The Infrared Sensilla in the Beetle Melanophila acuminata as model for new infrared sensors.
- Article by Jorge Poveda in The Conversation: De crecer bajo tierra a autopodarse: los secretos de las plantas para sobrevivir a las llamas.
- Article by Luke Kelly and Lluís Brotons in the journal Science: Using fire to promote biodiversity.
- Article by Juli Pausas in The Conversation: Beneficios de no cortar los árboles después de un incendio.
- Article by Pere Pons in The Conversation: Así cambia un bosque quemado a lo largo de 10 años.
- Chapter by Filipe X. Catry and collaborators in the book Post-Fire Management and Restoration of Southern European Forests: Post-Fire Management of Cork Oak Forestes
- Talk by Juli Pausas at the Institut Valencià d’Investigacions Agràries (IVIA): Incendios forestales y biodiversidad.
- Post by Sandra Saura Mason the CREAF blog: De la impotencia a la acción: después de un incendio forestal, ¿qué?
- Post by Anna Ramón on the CREAF blog: Las especies omnívoras resisten mejor los efectos del fuego.
- Post on the website of the Conservation Biology Team of the University of Barcelona: Mejorar la gestión forestal tras un incendio para favorecer la biodiversidad y las especies clave mediterráneas.
- Final Bachelor´s degree project by Antoni A. Ruiz Vicaría: Efecto del fuego sobre las comunidades de escarabajos xilófagos y saproxílicos de un sistema de coníferas de Salo (Cataluña, España).
