Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids thus fail to reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions are controlled and most terrestrial species reside. Here we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0-5 and 5-15 cm depth. These maps were created by calculating the difference (i.e., offset) between in-situ soil temperature measurements, based on time series from over 1200 1-km² pixels (summarized from 8500 unique temperature sensors) across all of the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding 2 m gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (3.6 ± 2.3°C warmer than gridded air temperature), whereas soils in warm and humid environments are on average slightly cooler (0.7 ± 2.3°C cooler). The observed substantial and biome-specific offsets underpin that the projected impacts of climate and climate change on biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining global gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.

Research in environmental science relies heavily on global climatic grids derived from estimates of air temperature at around 2 meter above ground1-3. These climatic grids however fail to reflect conditions near and below the soil surface, where critical ecosystem functions such as soil carbon storage are controlled and most biodiversity resides4-8. By using soil temperature time series from over 8500 locations across all of the world’s terrestrial biomes4, we derived global maps of soil temperature-related variables at 1 km resolution for the 0–5 and 5–15 cm depth horizons. Based on these maps, we show that mean annual soil temperature differs markedly from the corresponding 2 m gridded air temperature, by up to 10°C, with substantial variation across biomes and seasons. Soils in cold and/or dry biomes are annually substantially warmer (3.6°C ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are slightly cooler (0.7 ± 2.3°C). As a result, annual soil temperature varies less (by 17%) across the globe than air temperature. The effect of macroclimatic conditions on the difference between soil and air temperature highlights the importance of considering that macroclimate warming may not result in the same level of soil temperature warming. Similarly, changes in precipitation could alter the relationship between soil and air temperature, with implications for soil-atmosphere feedbacks9. Our results underpin that the impacts of climate and climate change on biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments.

The black locust (Robinia pseudoacaciaL.) has been present in Poland for more than 200 years now, its range coming to encompass the entire country, albeit with a particular concentration of occurrence in the west. Overall, it is present in 3.4% of the stands making up Poland’s “State Forests National Forest Holding” (Państwowe Gospodarstwo Leśne Lasy Państwowe), and is the dominant species in 0.1% of stands. Thanks to its producing durable wood of favourable energetic properties, this species is used in medium-rotation (≤ 40-year) plantations as well as in biomass energy plantations (where there is a 5–7-year rotation). In terms of its nectar production, the black locust is second only to lime as the Polish tree best serving the production of honey. While the species shows marked expansiveness in Poland, it has not thus far been placed on the list of aliens capable of threatening native species or natural habitats. Breeding of the species has been engaged in – if to only a limited extent – in Poland for some 20 years now, and 2 selected seed stands have been registered, as well as 34 plus trees and 2 seed orchards.

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Winter underpins key ecological processes, such as dormancy loss and seedling emergence. Enhanced warm spells, together with warming are occurring and will continue in the future. The consequences of these climate phenomena on germination were investigated among co‐occurring woody plants, whose seeds are bird‐dispersed in autumn and require cold stratification for spring emergence. Seeds from nine common southeastern USA plants were collected in autumn. We verified that seeds of the study species required cold stratification for dormancy loss. We then examined the following aspects in the laboratory or field: effect of warm spells during cold stratification on germination, effect of a warm spell during winter on seed survival and germination phenology, and effect of warming from autumn dispersal through winter dormancy loss on timing of germination. While no consistent effects of warm spells were found in the laboratory on quantity of germination, warm spells advanced spring field germination for several species. Some species germinated during cold stratification and during warm spells, especially extreme spells, in the laboratory. In the field, about half of Lonicera maackii seedlings that emerged with a warm spell died by late winter. With warming from autumn through spring, laboratory germination shifted from spring to predominately autumn for some species. With precocious germination during warm spells or germination phenology shifts, two scenarios are possible. Seedlings may die during winter, reducing the size of the soil seed bank and number of emergents, or they would survive in warmer winters, which would give them a competitive advantage over spring‐emerging seedlings.