Mapping the microclimate effect of forest canopies on understory temperature requires spatially explicit predictors at very fine spatial resolutions. Light Detection And Ranging (LiDAR) offers ...promising prospects in that regard, as it allows capturing the vertical dimension of vegetation structure at a very high resolution over large areas.
To explore the potential of airborne LiDAR-derived metrics to predict understory temperature, we focused on the forest of Blois (France), a 2740-ha lowland managed forest dominated by oak (Quercus petraea). We installed HOBO sensors measuring microclimate air temperature at one-metre height in 53 stands of contrasting vegetation structure, from open to very dense and from young regeneration to mature stages. Using a nearby weather station as the macroclimate temperature reference, we calculated the slope (log scale) coefficient of the linear regression between microclimate and macroclimate, as a simple parameter describing the microclimatic buffering (log(slope) < 0) or amplification (log(slope) > 0) capacity of the habitat.
An airborne LiDAR flight was conducted during summer 2021, matching the timing of our temperature measurements. From the resulting 3D point cloud, three complementary metrics of forest structure were derived: the maximum height, the Plant Area Index and the Vertical Complexity Index. They were calculated for circular buffers of different radii (1 m to 100 m) centred on each HOBO sensor.
We found that the 5-m radius combining the three metrics into a single multivariate model explained the greatest proportion of variance in the microclimate effect of each stand (R2 = 0.91). We mapped the buffering or amplification effect of vegetation structure on understory temperatures over the entire forest of Blois at a 10-m resolution. 91.4% of the surface of the forest was significantly buffered relative to macroclimate temperature, while 2.7% was amplified, especially in road verges, clear-cut and regeneration areas. Based on our simple linear model, we were able to derive understory air temperature maps for any temporal resolution (i.e. hourly, daily, or seasonal). The results highlight the great capacity of airborne LiDAR to retrieve forest structure parameters and generate high-resolution maps of the thermal environment.
Applications for mapping the buffering or amplification of microclimate temperature are plentiful, especially in the context of climate change. They include improving the understanding of physiological processes such as thermoregulation or phenology, modelling the thermal connectivity of the landscape, improving species redistribution models, spotting microrefugia for conservation, informing forest management for tree regeneration or wildfire control, or even prioritising cooling recreational areas for humans to escape heatwaves in urban forests.
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•Airborne LiDAR is ideal to predict forest thermal environment at a high resolution.•We used Maximum height, Plant Area & Vertical Complexity Index as structure metrics.•Forest structure explained 91% of microclimate variability at a 10-m resolution.•We mapped the buffering or amplification effect of forest on microclimate temperature.•Ecologists, conservationists and forest managers would highly benefit from such maps.
On the measurement of microclimate Maclean, Ilya M. D.; Duffy, James P.; Haesen, Stef ...
Methods in ecology and evolution,
August 2021, 2021-08-00, 20210801, 2021-08, Letnik:
12, Številka:
8
Journal Article
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Many organisms live in environments in which temperatures differ substantially from those measured by standard weather stations. The last decade has witnessed a paradigm shift in efforts to quantify ...these differences and to understand their ecological, functional and evolutionary implications. This renewed interest in microclimate ecology has been accompanied by the development of various compact temperature sensors and radiation shields. However, it is clear that there are many pitfalls when measuring temperature using these devices.
Here we address the problem of measuring temperatures in these microenvironments accurately. We first discuss the theory of measuring surface, ground and air temperatures with reference to energy fluxes and how these are modified by material, reflective properties and size of the device. We highlight the particular difficulties associated with measuring air temperature. We then report on the results of a series of experiments in which air temperatures recorded by various commonly used microclimate temperature loggers are compared to those obtained using research‐grade instruments and synoptic weather stations.
While accurate measurements of surface and ground temperatures and air temperatures at night and in shaded environments can be relatively easily obtained, we show substantial errors are to be expected when measuring air temperatures in environments exposed to sunlight. Most standard sensors yield large errors, which can reach 25°C due to radiative fluxes operating on the thermometer. This problem cannot be wholly overcome by shielding the thermometer from sunlight, as the shield itself will influence both the temperatures being measured and the accuracy of measurement.
We demonstrate that reasonably accurate estimates of air temperature can be obtained with low‐cost and unshielded ultrafine‐wire thermocouples that possess low thermal emissivity and a highly reflective surface. As the processes that create microclimatic temperature variation are the same as those that cause errors, other logger types should be used with care, and generally avoided in environments exposed to sunlight and close to the ground where wind speeds are lower. We urge researchers interested in microclimates and their effects to pay greater heed to the physics of heat exchange when attempting to measure microclimate temperatures and to understand the trade‐offs that exist in doing so.
Abstract
Species distributions are conventionally modelled using coarse‐grained macroclimate data measured in open areas, potentially leading to biased predictions since most terrestrial species ...reside in the shade of trees. For forest plant species across Europe, we compared conventional macroclimate‐based species distribution models (SDMs) with models corrected for forest microclimate buffering. We show that microclimate‐based SDMs at high spatial resolution outperformed models using macroclimate and microclimate data at coarser resolution. Additionally, macroclimate‐based models introduced a systematic bias in modelled species response curves, which could result in erroneous range shift predictions. Critically important for conservation science, these models were unable to identify warm and cold refugia at the range edges of species distributions. Our study emphasizes the crucial role of microclimate data when SDMs are used to gain insights into biodiversity conservation in the face of climate change, particularly given the growing policy and management focus on the conservation of refugia worldwide.
Forest canopies buffer macroclimatic temperature fluctuations. However, we do not know if and how the capacity of canopies to buffer understorey temperature will change with accelerating climate ...change. Here we map the difference (offset) between temperatures inside and outside forests in the recent past and project these into the future in boreal, temperate and tropical forests. Using linear mixed-effect models, we combined a global database of 714 paired time series of temperatures (mean, minimum and maximum) measured inside forests vs. in nearby open habitats with maps of macroclimate, topography and forest cover to hindcast past (1970–2000) and to project future (2060–2080) temperature differences between free-air temperatures and sub-canopy microclimates. For all tested future climate scenarios, we project that the difference between maximum temperatures inside and outside forests across the globe will increase (i.e. result in stronger cooling in forests), on average during 2060–2080, by 0.27 ± 0.16 °C (RCP2.6) and 0.60 ± 0.14 °C (RCP8.5) due to macroclimate changes. This suggests that extremely hot temperatures under forest canopies will, on average, warm less than outside forests as macroclimate warms. This knowledge is of utmost importance as it suggests that forest microclimates will warm at a slower rate than non-forested areas, assuming that forest cover is maintained. Species adapted to colder growing conditions may thus find shelter and survive longer than anticipated at a given forest site. This highlights the potential role of forests as a whole as microrefugia for biodiversity under future climate change.
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•Temperature differences inside vs. outside forests were mapped across the globe.•Forest canopies buffer minimum (Tmin), mean (Tmean) and maximum (Tmax) temperatures.•In the future, buffering for Tmean and Tmax may increase, but may decrease for Tmin.•Refugial capacity of forests might last longer than anticipated in a warming world.
Ecological research heavily relies on coarse‐gridded climate data based on standardized temperature measurements recorded at 2 m height in open landscapes. However, many organisms experience ...environmental conditions that differ substantially from those captured by these macroclimatic (i.e. free air) temperature grids. In forests, the tree canopy functions as a thermal insulator and buffers sub‐canopy microclimatic conditions, thereby affecting biological and ecological processes. To improve the assessment of climatic conditions and climate‐change‐related impacts on forest‐floor biodiversity and functioning, high‐resolution temperature grids reflecting forest microclimates are thus urgently needed. Combining more than 1200 time series of in situ near‐surface forest temperature with topographical, biological and macroclimatic variables in a machine learning model, we predicted the mean monthly offset between sub‐canopy temperature at 15 cm above the surface and free‐air temperature over the period 2000–2020 at a spatial resolution of 25 m across Europe. This offset was used to evaluate the difference between microclimate and macroclimate across space and seasons and finally enabled us to calculate mean annual and monthly temperatures for European forest understories. We found that sub‐canopy air temperatures differ substantially from free‐air temperatures, being on average 2.1°C (standard deviation ± 1.6°C) lower in summer and 2.0°C higher (±0.7°C) in winter across Europe. Additionally, our high‐resolution maps expose considerable microclimatic variation within landscapes, not captured by the gridded macroclimatic products. The provided forest sub‐canopy temperature maps will enable future research to model below‐canopy biological processes and patterns, as well as species distributions more accurately.
Combining more than 1200 time series of in situ near‐surface forest temperatures with topographical, biological and macroclimatic variables in a machine learning model, we predicted the mean monthly offset between sub‐canopy temperature at 15 cm above the surface and free‐air temperature over the period 2000–2020 at a spatial resolution of 25 m across Europe. This offset was used to evaluate the difference between microclimate and macroclimate across space and seasons and finally enabled us to calculate mean annual and monthly temperatures for European forest understories.
Biological communities are reshuffling owing to species range shifts in response to climate change. This process inherently leads to novel assemblages of interacting species. Yet, how climatic change ...and local dynamics in biotic interactions jointly affect range shifts is still poorly understood.
We combine a unique long‐term transplant competition‐exclusion experiment with species distribution models (SDMs) to test the effects of biotic interactions on understorey species range shifts under climate change in European temperate forests. Using a time series of 18 years of individual‐level demographic data of four common understorey plant species transplanted beyond their cold range edge to plots with and without interspecific competition, we built integral projection models (IPMs) and analysed the effects of competition on five key vital rates and population growth (λ). We assessed the results of the transplant experiment in the context of the modelled species' current and future potential distributions.
We find that species' population performances in the transplant experiment decreased with lower predicted habitat suitability from the SDMs. The population performance at the transplant sites was mediated by biotic interactions with the local plant community: for two species with intermediate levels of predicted habitat suitability at the transplant sites, competition effects could explicitly differentiate between net population growth (λ > 1) or shrinkage (λ < 1).
Synthesis. Our findings contest the long‐standing idea that at cold range edges, mainly abiotic factors structure species' distributions. We conclude that biotic interactions, through acting on local population dynamics, may impact species distributions at the continental scale. Hence, predicting climate‐change impacts on biodiversity redistributions ultimately requires us to also integrate dynamics in biotic interactions.
Overzicht
Veel plantsoorten volgen het opwarmende klimaat en verplaatsen daarbij hun verspreidingsgebied richting de polen of hoger gelegen gebieden. Dit proces leidt onvermijdelijk tot nieuwe assemblages van soorten die interageren binnen een nieuwe natuurlijke gemeenschap. Echter, hoe klimaatverandering en lokale dynamieken in biotische interacties samen toekomstige verspreidingsgebieden van soorten bepalen, is niet duidelijk.
We combineerde een lange‐termijn transplantatie competitie‐exclusie experiment met soortverspreidingsmodellen om te onderzoeken wat de effecten zijn van biotische interacties op de verplaatsing van het verspreidingsgebied van Europese bosplanten tijdens klimaatverandering. Op basis van demografische data van vier algemene bosplantensoorten overheen een tijdreeks van 18 jaar, onderzochten we de effecten van competitie op hun populatiegroeisnelheid. De resultaten van het experiment werden beoordeeld in de context van de huidige en toekomstige potentiële verspreidingsgebieden.
We vonden dat de populatiegroeisnelheid in het transplantatie experiment lager was bij een lagere gemodelleerde habitat geschiktheid. Op plot niveau, vonden we dat de populatie groeisnelheid ook bepaald werd door biotische interacties met de natuurlijke plantgemeenschap: voor twee soorten kon de aanwezigheid van competitie expliciet het verschil maken tussen een toename (λ > 1) of afname (λ < 1) van de populatiegrootte.
Synthese. Onze resultaten spreken Darwin's idee, dat bij de noordelijke grenzen van soort verspreidingsgebieden, vooral abiotische factor de grens bepalen, tegen. We besluiten dat biotische interacties, door hun effect op lokale populatie dynamieken, het verspreidingsgebied van soorten op continentale schaal kunnen beïnvloeden. Om accuraat het effect van klimaatverandering op de verschuiving van soort verspreidingsgebieden in te schatten, dienen we biotische interacties mee in rekening te brengen.
Based on a dual approach that combines an 18‐year transplant experiment and species distribution modelling, we show that biotic interactions mediate population growth beyond cold range margins, and may hereby impact species distributions at the continental scale. Hence, biodiversity redistributions cannot be predicted from abiotic predictors alone, but ultimately requires us to also integrate biotic interactions.
Aim
Climate change causes species to shift their distributions. Individual species, however, greatly vary in their capacity to track the macroclimatic temperature increase due to differences in ...demography and dispersal. To better predict range shifts to climate change we need a complementary integration of long‐term empirical data and predictive modelling.
Location
Belgium and North‐West Europe.
Taxon
Hyacinthoides non‐scripta¸ forest understorey plants.
Methods
Complementing species distribution models with demographic data from an exceptional 60‐year‐old over‐the‐range‐edge transplant experiment measured not less than 45 and 60 years after installation, we evaluated the long‐term consequences of climate change on one of the most emblematic but also among the slowest colonizing plant species of European forests, bluebell Hyacinthoides non‐scripta.
Results
We found bluebell able to establish viable populations beyond its natural range. These results were confirmed by the SDM, showing that bluebell’s potential range is considerably larger than its current range. Colonization rates of only 2 m century−1 were observed in the transplanted populations. Beyond bluebell’s current range, we observed decreasing trends in population growth rates over the past 15 years. By the end of the 21st century, substantial decreases in the southern parts of bluebell’s range were predicted.
Main conclusions
Based on empirical and modelling results, we expect serious population declines in large parts of its current natural distribution of bluebell. Although the species is able to establish viable populations beyond the natural range edge, slow demography and local colonization rates four orders of magnitude lower than the velocity of climate change make fast enough range shifts virtually impossible in this species.
Forests play a key role in global carbon cycling and sequestration. However, the potential for carbon drawdown is affected by forest fragmentation and resulting changes in microclimate, nutrient ...inputs, disturbance and productivity near edges. Up to 20% of the global forested area lies within 100 m of an edge and, even in temperate forests, knowledge on how edge conditions affect carbon stocks and how far this influence penetrates into forest interiors is scarce. Here we studied carbon stocks in the aboveground biomass, forest floor and the mineral topsoil in 225 plots in deciduous forest edges across Europe and tested the impact of macroclimate, nitrogen deposition and smaller-grained drivers (e.g. microclimate) on these stocks. Total carbon and carbon in the aboveground biomass stock were on average 39% and 95% higher at the forest edge than 100 m into the interior. The increase in the aboveground biomass stock close to the edge was mainly related to enhanced nitrogen deposition. No edge influence was found for stocks in the mineral topsoil. Edge-to-interior gradients in forest floor carbon changed across latitude: carbon stocks in the forest floor were higher near the edge in southern Europe. Forest floor carbon decreased with increasing litter quality (i.e. high decomposition rate) and decreasing plant area index, whereas higher soil temperatures negatively affected the mineral topsoil carbon. Based on high-resolution forest fragmentation maps, we estimate that the additional carbon stored in deciduous forest edges across Europe amounts to not less than 183 Tg carbon, which is equivalent to the storage capacity of 1 million ha of additional forest. This study underpins the importance of including edge influences when quantifying the carbon stocks in temperate forests and stresses the importance of preserving natural forest edges and small forest patches with a high edge-to-interior surface area.
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•Carbon stocks were studied in temperate deciduous forest edges across Europe.•Total and aboveground biomass C-stocks were higher near forest edges.•N-deposition was an important driver of the increase in C near the edge.•The additional C stored in deciduous forest edges across Europe amounts to 183 Tg C.•Small forest patches and natural forest edges should be preserved.
Microclimate research gained renewed interest over the last decade and its importance for many ecological processes is increasingly being recognized. Consequently, the call for high‐resolution ...microclimatic temperature grids across broad spatial extents is becoming more pressing to improve ecological models. Here, we provide a new set of open‐access bioclimatic variables for microclimate temperatures of European forests at 25 × 25 m2 resolution.
We present a set of high‐resolution bioclimatic variables of forest microclimate temperature variables based upon the ForestTemp model, where we provided the proof of concept for the derivation of monthly mean temperature offset values at a spatial resolution of 25 m × 25 m across Europe.
Global maps of soil temperature Lembrechts, Jonas J; van den Hoogen, Johan; Aalto, Juha ...
Global change biology,
2021
Journal Article
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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.
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