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A large-scale re-inventory of red wood ant (RWA; Formica rufa-group) nests and a comparative analysis of their presence/absence data was carried out for the first time in 2023 at two study sites in the Oberpfalz, NE Bavaria, Germany, to investigate the suspected decline of nests, their relationship with forestry aspects, and possible changes in spatial distribution due to tectonic activity (GeoBio-Interactions). We inventoried, in two sustainably managed forests, outstanding nest occurrences (5393 nests including 5276 active nests) and an increase of ≈8% over 4–7 years. Our results do not support claims that the number of nests in the Oberpfalz is in sharp decline. RWA preferred mature and medium–mature pine-dominated forests. Standing and downed dead wood did not negatively affect nests. The number of nests with woodpecker cavities and the diversity of the herb layer increased. Nests clusters in NW–SE direction suggest a strong interaction between nest distribution and active tectonics. Our (re-)inventory approach combined with the extensive photo database is a valuable tool for (a) monitoring the entire forest habitat including natural restocking, herb biodiversity, woodpecker cavities, and dead wood in, at, and around nests, and (b) identifying GeoBio-Interactions. Such an approach will lead to more realistic counts of RWA nests and provide scientific evidence of the current situation of nests occurrence. We suggest seven to eight years as an appropriate time interval for re-inventories. [ABSTRACT FROM AUTHOR]

We used presence/absence data of 5,160 red wood ant nests (RWA; Formica polyctena) acquired in a systematic large-scale area-wide survey in two study areas (â350 ha) in the Oberpfalz, NE Bavaria, Germany to explore for the first time the influence of variable (e.g., forest type, tree age) and quasi-invariant factors (e.g., tectonics, geochemical composition of the bedrock) on nest size and spatial distribution for Variscan granites. A combination of the forest type (mature pine-dominated forests (â80-140 years) as main variable factor and the geochemical property of the Variscan granites with their high natural Radon potential and moderate heat production as main quasi-invariant factor could explain the high nest numbers in both study areas. In addition, the spatially clustered distribution patterns of the observed nests suggest a strong interaction between nests and their quasi-invariant environment, especially the directionality of the present-day stress field and the direction of the tectonically formed "Erbendorfer Line". In general, such a combination of variable and quasi-invariant factors can be addressed as particularly favorable RWA habitats. [ABSTRACT FROM AUTHOR]

Simple Summary: Methane (CH4) is common on Earth but its natural sources are not well-characterized. We investigated concentrations of CH4 and its stable carbon isotope (δ13C-CH4) within a red wood-ant (RWA; Formica polyctena) nest in the Neuwied Basin, a part of the East Eifel Volcanic Field (EEVF), and tested for associations between methane concentration and RWA activity patterns, earthquakes, and earth tides. Methane degassing was not synchronized with earth tides, nor was it influenced by a micro-earthquake or RWA activity. Elevated CH4 concentrations in nest gas appear to result from a combination of microbial activity and fault-related emissions. The latter could result from micro-seepage of methane derived from low-temperature gas-water-rock reactions that subsequently moves via fault networks through the RWA nest or from overlapping micro-seepage of magmatic CH4 from the Eifel plume. Given the abundance of RWA nests on the landscape, their role as sources of microbial CH4 and biological indicators for abiotically-derived CH4 should be included in estimations of methane emissions that are contributing to climatic change. We measured methane (CH4) and stable carbon isotope of methane (δ13C-CH4) concentrations in ambient air and within a red wood-ant (RWA; Formica polyctena) nest in the Neuwied Basin (Germany) using high-resolution in-situ sampling to detect microbial, thermogenic, and abiotic fault-related micro-seepage of CH4. Methane degassing from RWA nests was not synchronized with earth tides, nor was it influenced by micro-earthquake degassing or concomitantly measured RWA activity. Two δ13C-CH4 signatures were identified in nest gas: −69‰ and −37‰. The lower peak was attributed to microbial decomposition of organic matter within the RWA nest, in line with previous observations that RWA nests are hot-spots of microbial CH4. The higher peak has not been reported in previous studies. We attribute this peak to fault-related CH4 emissions moving via fault networks into the RWA nest, which could originate either from thermogenic or abiotic CH4 formation. Sources of these micro-seepages could be Devonian schists, iron-bearing “Klerf Schichten”, or overlapping micro-seepage of magmatic CH4 from the Eifel plume. Given the abundance of RWA nests on the landscape, their role as sources of microbial CH4 and biological indicators for abiotically-derived CH4 should be included in estimation of methane emissions that are contributing to climatic change. [ABSTRACT FROM AUTHOR]