A Brief Discussion of the Ecological Effects of Fire on Bees (Apoidea)

In recent years, factors such as climate change and shifts in land-use practices have caused fires to occur with unprecedented frequency and intensity across many regions of the world. Under such conditions, fire is no longer merely a short-lived natural disturbance. Instead, it increasingly acts as a long-term ecological force capable of reshaping ecosystem structure. Bees of the superfamily Apoidea are among the most important pollinators of plants globally, and understanding how they respond to fire has therefore become an important ecological question.

Research investigating the effects of fire on bees has revealed highly variable outcomes. Some studies report that the abundance of Apoidea increases after fire, others report declines, and many detect no significant change. A similar lack of consistency appears in species richness. However, although overall abundance or species number may not show a clear directional pattern, fire consistently alters community composition. Burned and unburned habitats often host distinctly different assemblages of bee species. Even when total abundance or species richness remains similar, the identities of the species present can differ markedly. In other words, fire reshuffles bee communities: certain species thrive under post-fire conditions while others decline or disappear. These contrasting responses are closely tied to differences in life-history traits among bee species.

How fire influences bees. The figure highlights how different life-history traits — nesting strategy, pollen specialization, sociality, and body size — tend to respond to fire according to the studies reviewed. A plus sign indicates a generally positive response across most studies, a minus sign indicates a generally negative response, and a question mark indicates inconsistent outcomes where responses vary depending on ecological context（Image source：Prendergast KS et al. (2025)， CC BY-NC-ND 4.0 ）

One major factor shaping these responses is nesting strategy. Bees that construct nests in the ground often recover relatively well after fires. Species belonging to genera such as Lasioglossum may even increase in abundance following fire. Soil can act as an insulating barrier that limits the penetration of heat, preventing direct mortality in nests located at sufficient depth. Moreover, fires often reduce vegetation cover and expose bare ground, conditions that may create additional suitable nesting sites for ground-nesting bees.

In contrast, species that rely on above-ground structures such as tree cavities or plant stems for nesting tend to be more vulnerable. Bees that nest in hollow stems, for instance those in the genus Hylaeus, are particularly susceptible. These plant structures provide little insulation against heat, meaning that even relatively low-intensity fires may destroy entire nests. In addition, the burning of trees can remove critical nesting substrates, making it difficult for such species to re-establish populations in the short term after a fire.

Another key ecological trait influencing vulnerability is pollen specialization. Some bees rely on pollen from a narrow range of plant species. These specialist bees, including certain species of Andrena, face elevated risks following fire if the plants on which they depend require several years to recover and produce flowers again. By contrast, bees capable of collecting pollen from a wide variety of plants are better positioned to exploit the flush of herbaceous flowers that often appears soon after fires. Such generalist species can rapidly expand their populations by utilizing these temporary but abundant floral resources.

Comparison of bee taxa that are favoured and disfavoured by fire. The upper panel shows the proportional representation of favoured and disfavoured taxa across different bee families. In the middle panel, the left image shows the polylectic, ground-nesting species Lasioglossum castor, while the right image shows the pollen-specialist, cavity-nesting species Hylaeus violaceus, which nests in hollow stems. The lower panel illustrates the proportion of genera that benefit from or are negatively affected by fire（Image source：Prendergast KS et al. (2025)， CC BY-NC-ND 4.0 ）

These patterns are also reflected at the level of bee families. Members of the family Halictidae—many of which nest underground and display generalist foraging behavior—frequently increase in abundance after fires and may become dominant in burned habitats. Conversely, families such as Andrenidae and Colletidae, which contain many solitary and pollen-specialized species, often decline in response to fire and may even disappear locally. Nonetheless, even within a single genus, small ecological differences among species can produce contrasting responses, making it difficult to predict outcomes solely based on taxonomic position.

Body size and social behavior introduce additional complexity. Larger bees can fly longer distances, which in principle allows them to escape fires or forage across fragmented landscapes created by burning. However, large body size also entails higher energetic demands and greater dependence on abundant floral resources. In post-fire environments where flowers may be temporarily scarce and canopy cover reduced—leading to higher ground temperatures—large bees may experience greater physiological stress. Because these positive and negative influences operate simultaneously, empirical studies have not detected a clear overall pattern linking body size to fire responses.

Sociality may also shape resilience in complicated ways. Social bees are often considered robust because colonies contain many individuals and frequently exploit diverse floral resources. Yet colonies also require sustained and stable resource supplies to maintain brood, workers, and the nest structure itself. In certain fire scenarios, these requirements may render social species more vulnerable. Kleptoparasitic bees face another challenge: because they depend on host species to reproduce, their persistence after fire is contingent on whether their hosts survive or recolonize the burned habitat. As a result, studies often suggest that parasitic bees struggle to maintain populations after fire events.

Beyond the biological traits of bees themselves, the characteristics of the fire strongly influence ecological outcomes. Fire frequency, intensity, burned area, and seasonal timing can all alter how bee communities respond. Moderate burning may help maintain open habitats rich in herbaceous flowering plants, conditions favorable to many bees. However, excessively frequent fires can damage soil structure and reduce the availability of suitable nesting substrates for ground-nesting species. Some studies suggest that high-severity fires may promote certain bee species or flowering plants, while others indicate that landscapes containing a mixture of fire intensities may support more stable pollination networks. Seasonal timing also matters: fires that occur during periods when bees are dormant may have weaker direct effects on populations.

Despite the growing body of research, significant knowledge gaps remain. More than half of the existing studies have been conducted in the United States, and most focus on ecosystems where fire is historically common, such as pine forests and grasslands. Tropical regions, the Southern Hemisphere, and ecosystems dominated by flowering trees remain poorly studied. Consequently, our understanding of how bees respond to fire in habitats that rarely experienced fire during their evolutionary history remains limited. In a future characterized by intensifying climate change and increasingly extreme fire events, these poorly studied bee communities may face particularly high risks. At present, the ecological consequences of such disturbances remain difficult to predict.

Author: Shui-Ye You

Reference:

Prendergast KS et al. (2025). Bees feeling the burn. Biological Reviews.