Fuel buildup shapes post-fire fuel decomposition through soil heating effects on plants, fungi, and soil chemistry

Abstract

Forty percent of terrestrial ecosystems require recurrent fires engineered by feedbacks between fire and plant fuels. Fuel loads control fire intensity which alters soil nutrients and shapes soil microbial and plant community responses to fire. Changes to post-fire plant fuel production are well known to feed back to future fires, but post-fire decomposition of new fuels is poorly understood. Our study sought to quantify how pre-fire fuel loading impacted post-fire fuel decomposition through soil abiotic properties, plant and soil fungal communities. In a longleaf pine savanna, both near and away from overstory pines, we manipulated pre-fire plot fuel loads to modify soil heating. We then assessed how fuel load and soil heating influenced post-fire plant fuel decomposition through changes to soil chemistry, vegetation, and fungi. Larger fuel loads, particularly beneath pines, increased soil heating and reduced decomposition of newly deposited fuels during the eight months following fire. Fire intensity effects on soil nutrients had the most consistent effects on decomposition with plant and fungal communities playing secondary roles. This demonstrates how fuel load and soil heating influence post-fire decomposition through fire-driven changes to soil abiotic properties, plant communities, and soil fungi. Further, since fire effects on decomposition and fire-fuel feedbacks were temporally dynamic this illustrates the importance of considering fire-fuel feedbacks across time. Understanding the importance of these feedbacks among ecosystems can help increase our predictive ability to manage fuels and the effects of repeated fires.