The Effects of Frost and Fire on the Traits, Resources, and Floral Visitors of a Cerrado Plant, and Their Impact on the Plant-Visitor Interaction Network and Fruit Formation

Abstract

The Cerrado, the world's most diverse savanna, has several adaptations to fire. However, intense and frequent fires, especially after frosts, can severely impact this ecosystem. Despite this, few studies have evaluated the combined effects of frost followed by fire. We investigated how these disturbances affect plant traits, floral resources, floral visitor richness, and the structures of plant-pollinator interaction networks by using Byrsonima intermedia, a common Malpighiaceae shrub, as a model. We compared areas affected by frost alone and frost followed by fire and the same fire-affected area two years later. We examined pollen, oil volume, buds, and racemes and recorded floral visitors. Our main hypothesis was that fire-affected areas would exhibit higher floral visitor richness, more conspicuous plant traits, and greater fruit production than areas affected by frost only, which would show higher interaction generalization due to stronger negative impacts. The results confirmed that frost drastically reduced floral traits, visitor richness, and reproductive success. In contrast, fire facilitated faster recovery, triggering increased floral resource quantities, richer pollinator communities, more specialized interactions, and greater fruit production. Our findings highlight that fire, despite its impact, promotes faster ecosystem recovery compared to frost, reinforcing its ecological role in the Cerrado's resilience.

Keywords: mutualism; plant–insect interactions; pollination; tropical savanna.

Figure 1

A typical shrub of Byrsonima intermedia (A), with flowers being visited by Centridini bees (Apidae): Epicharis bicolor (B) and Centris aenea (C).

Figure 2

Effects of disturbances on B. intermedia two years after frost and fire (2023), after frost followed by fire (2021), and after frost only (2021). Variables analyzed: (a) floral visitor richness, (b) floral visitor abundance, (c) number of racemes, (d) oil volume, (e) number of floral buds, and (f) pollen quantity. Different letters indicate statistically significant differences between treatments. * p < 0.05; ** p < 0.01; *** p< 0.001.

Figure 3

Frequency of floral visitors in B. intermediates two years after frost and fire (2023), under the influence of frost and fire (2021), and under the influence of frost only (2021).

Figure 4

Difference in the number of fruits formed between pollination treatments (SSP—spontaneous self-pollination, SP—self-pollination, and NP—Natural pollination) two years after frost and fire (2023), under the influence of frost and fire (2021), and under the influence of frost only (2021). The symbols *** and n.s. indicate significant and non-significant differences, respectively.

Figure 5

Interaction networks between individuals of Byrsonima intermedia and their floral visitors (a) after being subjected to frost only, (b) under the influence of frost and fire (2021), and (c) two years after frost and fire (2023). In the networks, the pink circles represent the floral visitors, and the gray squares signify the B. intermedia specimens.

Figure 6

Average of the d’ specialization (a) and degree (b) values for floral visitors of Byrsonima intermedia two years after frost and fire (2023), under the influence of frost and fire (2021), and under the influence of frost only (2021). The ANOVA did not show significant differences (p > 0.05). n.s. indicates non-significant differences.