Plant-animal interactions deal with wildfires in unexpected ways

A guest post by Yedra García, María Clara Castellanos and Juli G. Pausas

Wildfires might seem like dramatic events, even in ecosystems where they are fully natural. Yet plants and animals have evolved all sorts of strategies to cope with them. But what happens to sensitive animal-plant interactions after a fire? Our recent studies show that fire-adapted Mediterranean plants can quickly adjust to post-fire losses of beneficial insects, and even benefit from the loss of antagonistic ones.

Some insects show a strong dependence on one or a few plant species on which they feed or breed. After a fire, as their host plant recovers, specialist insects can be slow at recolonizing the burnt area. This means that antagonistic interactions such as seed predation and herbivory are disrupted. Plants temporarily benefit from the post-fire reduction in predators. This is what we observed in two fire-loving plants with specialist seed predators in Spain (García et al., 2016). Both the branched asphodel (Asphodelus ramosus) and the Mediterranean gorse (Ulex parviflorus) quickly recover after fires. Asphodel has underground tubers, and gorse germination even improves after exposure to fire. But luckily for the plants, their specialist predators take longer to catch up.

Does this mean that mutualistic (=beneficial) interactions will also be disrupted by fires with negative consequences for the plants? In a new study, we investigated the consequences of a fire on a mutualistic interaction: the pollination by a specialist insect.

The Mediterranean dwarf palm Chamaerops humilis is a native plant from the Mediterranean Basin. After a fire it resprouts quickly, and flowers again in the spring after the fire. This palm is pollinated by the specialist weevil Derelomus chamaeropis, which feeds and breeds inside the palm inflorescences. What happens to this system after a fire? 

We studied the palm-weevil interaction in palms from four different sites after wildfires during two years. For this, we counted the number of weevils on the palm, and then the number of fruits produced. At each fire site we studied the interaction inside the burnt area and in nearby unburnt areas. This helped us to determine the effects of fire on pollinator abundance and on plant reproduction.

After the fires, the specialist weevil pollinator declined considerably. Surprisingly, the negative effects on fruit set by the palm were very weak and short-term. Why did palm reproduction recover so quickly? Thanks to the action of a new pollinator, previously gone unnoticed, the minuscule sap beetle Meligethinus pallidulus. Our study shows that a pollinator can replace another pollinator inside the burnt area, and this counterbalances the negative effects of fire on the main pollinator. This replacement by secondary pollinators may provide resilience to plant pollination systems, even if they are specialised.

Our work shows ways in which plant-animal interactions from fire-prone ecosystems cope with natural disturbances, and provide a mechanism for the maintenance of biodiversity. Given that humans are changing the frequency, intensity and size of fires even in ecosystems with a long fire history, more studies on this topic are needed to better understand the effects of new fire regimes on biodiversity.

About the authors

Yedra García is a Spanish PhD student who studies the effects of wildfires on plant-insect interactions from fire-prone ecosystems. She is supervised by María Clara Castellanos (@calacastellanos), who works on plant and floral evolution, and Juli Pausas who studies fire from all perspectives (@jgpausas).