Global maps of soil temperature

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 do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur 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 soil 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 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 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) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface 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 geographic gaps by collecting more in-situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Global maps of soil temperature.

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 do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur 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 soil 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 8519 unique temperature sensors) across all 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 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) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface 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 geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Radial tree growth dynamics and xylem anatomy along an elevational gradient in the El Sira Mountains, Peru

The explicit purpose of this study was to (1) characterize climate and vegetation along the western slope of the Cerros del Sira (Peru), (2) evaluate radial tree growth along this slope in response to seasonal rainfall anomalies, (3) reveal how the meteorological environment controls tree radial stem growth, and (4) to investigate how xylem anatomy relates to dynamics of tree growth. From May 2011 until September 2015, radial stem growth of 67 trees was monitored using point-dendrometers, and meteorological parameters were measured within five sites along an elevational gradient. Additionally, tree dimensions (stem diameter, stem height) and xylem anatomical traits (mean vessel diameter, vessel frequency, cumulative vessel area and potential hydraulic conductivity) were determined. The transect extends from lowland terra firme forests (ca. 250 m asl) over submontane forests, late and mid successional montane cloud forests up to exposed elfin forests (ca. 2200 m asl). Continuous rainfall records for remote tropical areas are extremely rare and measurements along this transect are also incomplete. Monthly rainfall estimates by the TRMM PR satellite ("product 3B42") were highly correlated with rain gauge observations, although they underestimate rainfall at high elevations. Different intra-annual tree growth patterns could be identified within each elevational forest type, showing species/individuals with seasonally independent continuous or alternating growth patterns and strictly seasonal growth. Stem growth at each site was typically higher during rainy seasons, except for in the elfin forest. The rainy season from October 2013 to March 2014 was extraordinarily dry, with only 73 % of long-term mean precipitation received, which resulted in reduced tree radial growth rates, again with the exception of the elfin forest. Different analytical approaches revealed that precipitation is the main growth-controlling factor at lower elevations, especially during rainy seasons. Growth within montane and cloud forests positively correlates to solar radiation. Tree growth within the elfin forest is only weakly correlated to meteorological parameters, but dry conditions during dry seasons promote growth. It was hypothesized that (1) individuals/species with large vessel diameters and low vessel frequencies have higher radial growth rates, but are more vulnerable to relatively dry periods. Therefore, (2) they are more likely to grow seasonally and predominantly during rainy seasons, (3) their growth during the exceptionally dry rainy season 2013/14 was more constrained, and (4) their growth is generally closer correlated to meteorological parameters. Larger trees tend to have larger vessel diameters, which positively relates to radial growth rates, and they also tend to grow more seasonal. As hypothesized, trees having large vessel diameters are more sensitive to droughts, as indicated by stronger positive correlations with rainfall and negative with solar radiation. However, in mountainous forests, relations between xylem anatomical traits and tree growth dynamics seem to be more complex. In late-successional cloud forests, growth of trees with large vessel diameter is positively, while of trees with small vessel diameter negatively related to solar radiation. Sensitivity to the dry rainy season 2013/14, expressed as relative reduction in growth compared to "normal" rainy seasons, could not be explained by xylem anatomical traits, contradicting the preceded hypothesis. Tropical lowland rainforest species, especially individuals with large vessels, will likely suffer from increasing drought frequencies and intensities. How montane forest ecosystems will react to a (globally) changing climate is rather uncertain, especially in exposed elfin forests. Results of this study suggest that species of late-successional tropical montane forests may profit from higher temperatures. While montane tropical rain forests may also suffer from prolonged droughts, exposed ridges covered by elfin forests still receive plenty of precipitation and may benefit from receiving more solar radiation for photosynthesis and, thus, grow faster.Der explizite Zweck dieser Studie bestand darin, (1) das Klima und die Vegetation entlang der westlichen Flanke des El Sira Gebirges (Peru) zu charakterisieren, (2) die Reaktion radialer Baumzuwächse auf saisonale Regenanomalien entlang des Höhengradienten zu bewerten, (3) die Abhängigkeit des radialen Stammzuwachses von Klimaparametern zu analysieren und (4) zu prüfen, inwiefern xylem-anatomische Eigenschaften des Baumes die Wachstumsdynamik beeinflussen. Von Mai 2011 bis September 2015 wurden radiale Stammzuwächse von 67 Bäumen mit vollautomatischen Punkt-Dendrometern erfasst und meteorologische Parameter an fünf Standorten entlang eines Höhengradienten gemessen. Zusätzlich wurden die Bäume vermessen (Stammdurchmesser, Stammhöhe) und xylem-anatomische Merkmale (mittlerer Gefäßdurchmesser, Gefäßfrequenz, kumulierte Gefäßfläche und potentielle hydraulische Leitfähigkeit) erfasst. Der Transsekt erstreckt sich von Terra-Firme Wälder des Tieflandes (ca. 250 m ü. NN) über submontane Wälder, montane Nebelwälder mittlerer und später Sukzessions-Stadien bis hin zu exponierten Elfenwäldern (ca. 2200 m ü. NN). Kontinuierliche Niederschlagsaufzeichnungen für entlegene tropische Regionen sind extrem selten, und auch Messungen entlang dieses Transekts sind unvollständig. Die monatlichen Niederschlagsschätzungen des TRMM PR-Satelliten (Product 3B42) ließen sich allerdings in hohem Maße mit direkten Niederschlagsmessungen korrelieren, unterschätzten jedoch den Niederschlag in höheren Lagen. Innerhalb eines jeden Waldtypes konnten unterschiedliche jährliche Baumzuwachsmuster identifiziert werden. Es gibt Arten/Individuen mit kontinuierlichen oder alternierenden Zuwachsmustern unabhängig von den Jahreszeiten und streng saison-gebundenen Wachstumsverhalten. Im Allgemeinen war das Wachstum der Bäume an allen Standorten während den Regenzeiten größer, mit Ausnahme des Elfenwaldes. Die Regenzeit von Oktober 2013 bis März 2014 war außergewöhnlich trocken. Lediglich 73% der langfristigen mittleren Niederschläge wurden ermittelt, was wiederum zu geringeren radialen Zuwächsen führte, außer im Elfenwald. Verschiedene analytische Ansätze haben gezeigt, dass Niederschlag in niedrigeren Lagen der Hauptwachstumsfaktor ist, insbesondere während den Regenzeiten. Das Wachstum in Montan- und Nebelwäldern korreliert positiv mit der Globalstrahlung. Das Baumwachstum im Elfenwald ist nur schwach mit meteorologischen Parametern korreliert, aber trockene Bedingungen während der Trockenzeit fördern das Wachstum. Es wurde die Hypothese aufgestellt, dass (1) Individuen/Arten mit großen Gefäßdurchmessern und geringer Gefäßdichte größere radiale Wachstumsraten aufweisen, jedoch anfälliger für Trockenstress sind. Daher ist es wahrscheinlich, (2) dass diese saisonal und vorwiegend während der Regenzeit wachsen, (3) das Wachstum während der außergewöhnlich trockenen Regenzeit 2013/14 geringer war, und (4) das Wachstum in der Regel enger mit meteorologischen Parametern korreliert ist. Größere Bäume weisen in der Regel größere Gefäßdurchmesser, sowie höhere Zuwachsraten auf und wachsen eher saisonal. Wie angenommen, reagieren Bäume mit großem Gefäßdurchmesser empfindlicher auf niederschlagsarme Phasen, was durch stärkere positive Korrelationen mit Niederschlag und negative mit Sonneneinstrahlung angezeigt wird. In Bergwäldern scheinen jedoch die Beziehungen zwischen den anatomischen Eigenschaften des Xylems und der Wachstumsdynamik der Bäume komplexer zu sein. In spät-sukzessionalen Nebelwäldern ist das Wachstum von Bäumen mit großem Gefäßdurchmesser positiv, und von Bäumen mit kleinen Gefäßdurchmessern negativ korreliert mit der Globalstrahlung. Die Empfindlichkeit gegenüber der trockenen Regenzeit 2013/14, ausgedrückt als relative Verringerung des Wachstums im Vergleich zu normalen Regenzeiten, konnte nicht durch xylem-anatomische Eigenschaften erklärt werden, was der vorangegangenen Hypothese widerspricht. Tropische Tieflandregenwälder, hier insbesondere Individuen mit weiten Gefäßen, werden wahrscheinlich unter zunehmenden Häufigkeiten und Intensitäten von trockenen Phasen leiden. Wie das Waldökosystem der Bergwälder auf ein sich (global) änderndes Klima reagieren wird, ist allerdings ziemlich ungewiss, vor allem in exponierten Elfenwäldern. Die Ergebnisse dieser Studie deuten jedoch darauf hin, dass tropisch montane Baumarten der späten Sukzession von höheren Temperaturen profitieren könnten. Während montane tropische Regenwälder auch unter längeren Trockenperioden leiden könnten, werden an exponierten Bergkämmen mit Elfenwäldern noch reichlich Niederschläge verzeichnet. Elfenwald-Arten könnten somit davon profitieren, dass sie mehr Sonnenstrahlung für die Photosynthese erhalten und somit auch für das Wachstum

Global maps of soil temperature

Abstract 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 do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur 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 soil 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 8519 unique temperature sensors) across all 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 gridded air temperature, by up to 10° degrees C (mean = 3.0 +/‐ 2.1° degrees 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° degrees C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (‐0.7 +/‐ 2.3° degrees C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface 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 geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications