Leaf‐cutter ants are a prominent feature in Neotropical ecosystems, but a comprehensive assessment of their effects on ecosystem functions is lacking. We reviewed the literature and used our own recent findings to identify knowledge gaps and develop a framework to quantify the effects of leaf‐cutter ants on ecosystem processes. Leaf‐cutter ants disturb the soil structure during nest excavation changing soil aeration and temperature. They mix relatively nutrient‐poor soil from deeper layers with the upper organic‐rich layers increasing the heterogeneity of carbon and nutrients within nest soils. Leaf‐cutter ants account for about 25% of all herbivory in Neotropical forest ecosystems, moving 10%–15% of leaves in their foraging range to their nests. Fungal symbionts transform the fresh, nutrient‐rich vegetative material to produce hyphal nodules to feed the ants. Organic material from roots and arbuscular mycorrhizal fungi enhances carbon and nutrient turnover in nest soils and creates biogeochemical hot spots. Breakdown of organic matter, microbial and ant respiration, and nest waste material decomposition result in increased CO2, CH4, and N2O production, but the build‐up of gases and heat within the nest is mitigated by the tunnel network ventilation system. Nest ventilation dynamics are challenging to measure without bias, and improved sensor systems would likely solve this problem. Canopy gaps above leaf‐cutter ant nests change the light, wind and temperature regimes, which affects ecosystem processes. Nests differ in density and size depending on colony age, forest type and disturbance level and change over time resulting in spatial and temporal changes of ecosystem processes. These characteristics remain a challenge to evaluate rapidly and non‐destructively. Addressing the knowledge gaps identified in this synthesis will bring insights into physical and biological processes driving biogeochemical cycles at the nest and ecosystem scale and will improve our understanding of ecosystem biogeochemical heterogeneity and larger scale ecological phenomena. A plain language summary is available for this article.

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Renewable energy development is an arena where ecological, political, and socioeconomic values collide. Advances in renewable energy will incur steep environmental costs to landscapes in which facilities are constructed and operated. Scientists – including those from academia, industry, and government agencies – have only recently begun to quantify trade‐offs in this arena, often using ground‐mounted, utility‐scale solar energy facilities (USSE, ≥1 megawatt) as a model. Here, we discuss five critical ecological concepts applicable to the development of more sustainable USSE with benefits over fossil‐fuel‐generated energy: (1) more sustainable USSE development requires careful evaluation of trade‐offs between land, energy, and ecology; (2) species responses to habitat modification by USSE vary; (3) cumulative and large‐scale ecological impacts are complex and challenging to mitigate; (4) USSE development affects different types of ecosystems and requires customized design and management strategies; and (5) long‐term ecological consequences associated with USSE sites must be carefully considered. These critical concepts provide a framework for reducing adverse environmental impacts, informing policy to establish and address conservation priorities, and improving energy production sustainability.

Leaf-cutter ants are dominant herbivores that disturb the soil and create biogeochemical hot spots. We studied how leaf-cutter ant Atta cephalotes impacts soil CO 2 dynamics in a wet Neotropical forest. We measured soil CO 2 concentration monthly over 2.5 years at multiple depths in nonnest and nest soils (some of which were abandoned during the study) and assessed CO 2 production. We also measured nest and nonnest soil efflux, nest vent efflux, and vent concentration. Nest soils exhibited lower CO 2 accumulation than nonnest soils for the same precipitation amounts. During wet periods, soil CO 2 concentrations increased across all depths, but were significantly less in nest than in nonnest soils. Differences were nonsignificant during drier periods. Surface efflux was equal across nest and nonnest plots (5 μmol CO 2 m À2 s À1 ), while vent efflux was substantially (10 3 to 10 5 times) greater, a finding attributed to free convection and sporadic forced convection. Vent CO 2 concentrations were less than in soil, suggesting CO 2 efflux from the soil matrix into the nest. Legacy effects in abandoned nests were still observable after more than two years. These findings indicate that leaf-cutter ant nests provide alternative transport pathways to soil CO 2 that increase total emissions and decrease soil CO 2 concentrations, and have a lasting impact. Estimated total nest-soil CO 2 emissions were 15 to 60% more than in nonnest soils, contributing 0.2 to 0.7% to ecosystem-scale soil emissions. The observed CO 2 dynamics illuminate the significant carbon footprint of ecosystem engineer Atta cephalotes and have biogeochemical implications for rainforest ecosystems.Plain Language Summary Leaf-cutter ants modify their habitat to the extent that they are called ecosystem engineers. Living throughout the Americas, they construct massive nests to which they import the vegetation they harvest to feed a fungus they cultivate as their main food source. We studied the most common leaf-cutter ant in Costa Rica to assess the impact of its nests on carbon dioxide (CO 2 ) levels in surrounding soils and on soil CO 2 emissions. In the Costa Rican rainforest, heavy rains easily clog the clayey soils, accumulating CO 2 from microbial and root respiration. During wet periods, we observed lower CO 2 concentrations in nest soils relative to nonnest soils. We attribute this difference to the nest structure, which provides ventilation for both nest CO 2 and the CO 2 originated in the surrounding soil. We also found that soil CO 2 emissions were the same in nest and nonnest soils, but nest openings had emissions 100,000 times greater. Consequently, nests and their surrounding soils emit 15 to 60% more CO 2 than the equivalent nonnest soil areas. This difference, together with the expanding range of leaf-cutter ants, favored by human activities and warmer climate, has implications with respect to the global carbon cycle.

Global atmospheric methane growth rates have wildly fluctuated over the past three decades, which may be driven by the proportion of tropical land surface saturated by water. The El Niño/Southern Oscillation Event (ENSO) cycle drives large‐scale climatic trends globally, with El Niño events typically bringing drier weather than La Niña. In a lowland tropical wet forest in Costa Rica, we measured methane flux bimonthly from March 2016 to June 2017 and using an automated chamber system. We observed a strong drying trend for several weeks during the El Niño in 2016, reducing soil moisture below normal levels. In contrast, soil conditions had high water content prior to the drought and during the moderate La Niña that followed. Soil moisture varied across the period studied and significantly impacted methane flux. Methane consumption was greater during the driest part of the El Niño period, while during La Niña and other time periods, soils had lower methane consumption. The mean methane flux observed was −0.022 mg CH4‐C m−2 hr−1, and methane was consumed at all timepoints, with lower consumption in saturated soils. Our data show that month studied, and the correlation between soil type and month significantly drove methane flux trends. Our data indicate that ENSO cycles may impact biogenic methane fluxes, mediated by soil moisture conditions. Climate projections for Central America show dryer conditions and increased El Niño frequency, further exacerbating predicted drought. These trends may lead to negative climate feedbacks, with drier conditions increasing soil methane consumption from the atmosphere.