Fire and Periodical Cicadas: their effect on soil composition and seed germination

Background/Question/Methods

Environmental disturbances come in a wide range of forms and can have cascading effects on ecosystems. During the summer of 2021, two disturbances occurred during the same time period, a periodical cicada emergence and prescribed burnings. These two events have unique impacts on the soils of the area, cicadas through their bioturbation and the prescribed fire through modifying the chemical and physical properties of the soil. This research aims to explore the impact these events have on soil and indirectly on the understory flora. To represent the cicada's impact on soils, we collected turrets (mounds of soil sometimes produced by cicadas before emergence) and soil from burned and control (unburned) sites. Collected soils from burned and control sites, and gathered turrets, and were analyzed for their pH level, carbon, nitrogen, and nutrient composition (Ca, K, Mg, Mn, P, and Zn). Burned or unburned soils were combined with either turrets or no turrets to create a 2-factorial study looking at the germination of seeds from the natural seed bank. We hypothesize that the combination of burned soil and the addition of turrets will result in a higher number of seeds germinating due to a resource pulse associated with fire cicada disturbances.

Results/Conclusions

There were significantly higher averages in the majority of nutrients in the turret samples compared to fire only and control samples, especially calcium (54% and 91% increase compared to fire and control, respectively) and phosphorus (61% and 76% increase compared to fire and control, respectively). A Poisson regression analysis of the germination data showed that there was a significant difference between the burned and control samples. Contrary to what we hypothesized, the majority of seeds germinated in the control soil, suggesting that increased nutrient content has no effect on seed germination. However, additional nutrients may impact growth and survival rates after the seeds have broken dormancy and germinated.