Monitoring climate change, and its impacts on ecological, agricultural, and other societal systems, is often based on temperature data derived from official weather stations. Yet, these data do not ...capture most microclimates, influenced by soil, vegetation and topography, operating at spatial scales relevant to the majority of organisms on Earth. Detecting and attributing climate change impacts with confidence and certainty will only be possible by a better quantification of temperature changes in forests, croplands, mountains, shrublands, and other remote habitats. There is an urgent need for a novel, miniature and simple device filling the gap between low-cost devices with manual data download (no instantaneous data) and high-end, expensive weather stations with real-time data access. Here, we develop an integrative real-time monitoring system for microclimate measurements: MIRRA (Microclimate Instrument for Real-time Remote Applications) to tackle this problem. The goal of this platform is the design of a miniature and simple instrument for near instantaneous, long-term and remote measurements of microclimates. To that end, we optimised power consumption and transfer data using a cellular uplink. MIRRA is modular, enabling the use of different sensors (e.g., air and soil temperature, soil moisture and radiation) depending upon the application, and uses an innovative node system highly suitable for remote locations. Data from separate sensor modules are wirelessly sent to a gateway, thus avoiding the drawbacks of cables. With this sensor technology for the long-term, low-cost, real-time and remote sensing of microclimates, we lay the foundation and open a wide range of possibilities to map microclimates in different ecosystems, feeding a next generation of models. MIRRA is, however, not limited to microclimate monitoring thanks to its modular and wireless design. Within limits, it is suitable or any application requiring real-time data logging of power-efficient sensors over long periods of time. We compare the performance of this system to a reference system in real-world conditions in the field, indicating excellent correlation with data collected by established data loggers. This proof-of-concept forms an important foundation to creating the next version of MIRRA, fit for large scale deployment and possible commercialisation. In conclusion, we developed a novel wireless cost-effective sensor system for microclimates.
Forest microclimatic variation can result in substantial temperature differences at local scales with concomitant impacts on plant defences and herbivory. Such microclimatic effects, however, may ...differ across abiotically contrasting sites depending on background environmental differences. To test these cross‐scale effects shaping species ecological and evolutionary responses, we experimentally tested the effects of aboveground microhabitat warming on insect leaf herbivory and leaf defences (toughness, phenolic compounds) for saplings of sessile oak Quercus petraea across two abiotically contrasting sites spanning 9° latitude. We found higher levels of herbivory at the low‐latitude site, but leaf traits showed mixed patterns across sites. Toughness and condensed tannins were higher at the high‐latitude site, whereas hydrolysable tannins and hydroxycinnamic acids were higher at the low‐latitude site. At the microhabitat scale, experimental warming increased herbivory, but did not affect any of the measured leaf traits. Condensed tannins were negatively correlated with herbivory, suggesting that they drive variation in leaf damage at both scales. Moreover, the effects of microhabitat warming on herbivory and leaf traits were consistent across sites, i.e. effects at the microhabitat scale play out similarly despite variation in factors acting at broader scales. These findings together suggest that herbivory responds to both microhabitat (warming) and broad‐scale environmental factors, whereas leaf traits appear to respond more to environmental factors operating at broad scales (e.g. macroclimatic factors) than to warming at the microhabitat scale. In turn, leaf secondary chemistry (tannins) appears to drive both broad‐scale and microhabitat‐scale variation in herbivory. Further studies are needed using reciprocal transplants with more populations across a greater number of sites to tease apart plant plasticity from genetic differences contributing to leaf trait and associated herbivory responses across scales and, in doing so, better understand the potential for dynamics such as local adaptation and range expansion or contraction under shifting climatic regimes.
Summary
Species are altering their phenology to track warming temperatures. In forests, understorey plants experience tree canopy shading resulting in light and temperature conditions, which strongly ...deviate from open habitats. Yet, little is known about understorey phenology responses to forest microclimates.
We recorded flowering onset, peak, end and duration of 10 temperate forest understorey plant species in two mesocosm experiments to understand how phenology is affected by sub‐canopy warming and how this response is modulated by illumination, which is related to canopy change. Furthermore, we investigated whether phenological sensitivities can be explained by species' characteristics, such as thermal niche.
We found a mean advance of flowering onset of 7.1 d per 1°C warming, more than previously reported in studies not accounting for microclimatic buffering. Warm‐adapted species exhibited greater advances. Temperature sensitivity did not differ between early‐ and later‐flowering species. Experimental illumination did not significantly affect species' phenological temperature sensitivities, but slightly delayed flowering phenology independent from warming.
Our study suggests that integrating sub‐canopy temperature and light availability will help us better understand future understorey phenology responses. Climate warming together with intensifying canopy disturbances will continue to drive phenological shifts and potentially disrupt understorey communities, thereby affecting forest biodiversity and functioning.
Understanding the distinct impacts of temperature and light on seedling growth is crucial for predicting forest regeneration trajectories under future climate change and forest disturbance. This is ...because temperature and light can change independently or together, influencing the competitive status of tree seedlings and forest herbs. However, most prior studies tend to explore temperature and light effects either separately or in combination, lacking comprehensive full-factorial designs. Here, we utilized two large-scale full-factorial experiments to explore warming and light effects on tree seedlings growing in mesocosms with herbaceous plants. We found that light increased seedling height, diameter, and biomass, while warming alone had no significant effects. Moreover, we observed that there was an interaction effect between light and warming, where warming increased seedling height, diameter, and biomass under illumination. Understory herbaceous plant cover alone did not affect seedling height, diameter, and biomass, but it decreased seedling biomass when mesocosms were warmed or illuminated. This highlights the importance of considering the indirect negative effects induced by the interaction between forest opening and understory herbaceous plants. By disentangling the effects of increased temperature and light availability on understory seedling height, diameter, and biomass, our results contribute valuable knowledge for future forest management. It is imperative to carefully control the size of the gaps artificially created to facilitate the understory regeneration. Small gaps are recommended considering that the herbaceous plants may interact with both warming and light to negatively affect seedlings.
The climate is changing rapidly, provoking species to shift their ranges poleward and upslope. We currently lack a mechanistic understanding of the effect of warmer temperatures on plants, especially ...for seasonally distinct patterns. Spring geophytes are emblematic forest plants that have a short aboveground lifecycle in the first half of the year and are thus particularly sensitive to winter and spring warming.
We set up a warming experiment with separate and combined winter and spring warming on seedlings of three European spring geophytes: Anemone nemorosa, Hyacinthoides non‐scripta and Ornithogalum pyrenaicum. Seedling emergence and plant height were recorded at the end of winter and spring treatment, when also biomass of the root, shoot and storage organ was determined.
We found negative effects of combined winter and spring warming on seedling emergence. The weight of the storage organ proved to be the best indicator of seedling performance and was negatively affected by separate winter warming in Anemone and by spring warming in Hyacinthoides.
Successful seedling emergence was jeopardized by the absence of a cold period, while seedling performance seemed to be negatively influenced directly by higher temperatures through a phenological shift. Our findings confirm that warmer winter and spring temperatures could hamper regeneration of spring geophytes.
We found negative effects of both experimental winter and spring warming on seedling emergence and performance in three spring geophytes of temperate forests, indicating that climate change could directly threaten plant populations at the warm edge of the distribution range.
Despite the crucial role of the seed bank in forest conservation and dynamics, the effects of forest edge microclimate and climate warming on germination responses from the forest seed bank are still ...almost unknown. Here, we investigated edge effects on the realised seed bank and seedling community in two types of European temperate deciduous forest, one in the Oceanic and one in the Mediterranean climatic region. Responses in terms of seedling density, diversity, species composition and functional type of the seed bank at the forest edge and interior were examined along latitudinal, elevational and stand structural gradients by means of soil translocation experiments. Moreover, we translocated soil samples from high to low elevation forests in the two regions, thus performing a warming simulation. Density, species diversity and mortality of the seedlings varied with region and elevation. Seedling density also differed between forest edge and interior position, while seedling cover mainly depended on forest structure. Both the edge and interior forest seed bank contained a high proportion of generalist species. In Belgium, a more homogeneous seed bank was found at the forest edge and interior, while in Italy compositional and ecological differences were larger: at the forest edge, more light and less moisture demanding seedling communities developed, with a higher proportion of generalists compared to the interior. In both regions, the upland-to-lowland translocation experiment revealed effects of warming on forest seed banks with thermophilization of the realised communities. Moreover, edge conditions shifted the seedling composition towards more light-demanding communities. The establishment of more light and warm-adapted species from the seed bank could in the long term alter the aboveground vegetation composition, with communities becoming progressively richer in light-demanding generalists and poorer in forest specialists.
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•Seed bank responses to different microclimates were studied in temperate forests.•Thermophilous forests showed a compositionally different edge vs interior seed bank.•Forest edges shifted the seedling community to a more light-demanding composition.•Soil translocation from up to lowland favoured the emergence of generalist plants.•Forest fragmentation should be prevented to conserve seed banks' forest specialists.
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.
Summary
Forests harbour large spatiotemporal heterogeneity in canopy structure. This variation drives the microclimate and light availability at the forest floor. So far, we do not know how light ...availability and sub‐canopy temperature interactively mediate the impact of macroclimate warming on understorey communities.
We therefore assessed the functional response of understorey plant communities to warming and light addition in a full factorial experiment installed in temperate deciduous forests across Europe along natural microclimate, light and macroclimate gradients. Furthermore, we related these functional responses to the species’ life‐history syndromes and thermal niches.
We found no significant community responses to the warming treatment. The light treatment, however, had a stronger impact on communities, mainly due to responses by fast‐colonizing generalists and not by slow‐colonizing forest specialists. The forest structure strongly mediated the response to light addition and also had a clear impact on functional traits and total plant cover.
The effects of short‐term experimental warming were small and suggest a time‐lag in the response of understorey species to climate change. Canopy disturbance, for instance due to drought, pests or logging, has a strong and immediate impact and particularly favours generalists in the understorey in structurally complex forests.
•We quantified evaporation and soil and air temperature offsets in forest edges across Europe.•Roughly 10% of European broadleaved forests are affected by altered temperature regimes.•Macroclimate ...and management affected edge-to-interior temperature offset gradients.•Forest structure and the forest-floor biomass are important drivers of temperature offsets.•Dense forest edges can help mitigate edge influences and protect forest interior microclimates.
Global forest cover is heavily fragmented. Due to high edge-to-surface ratios in small forest patches, a large proportion of forests is affected by edge influences involving steep microclimatic gradients. Although forest edges are important ecotones and account for 20% of the global forested area, it remains unclear how biotic and abiotic drivers affect forest edge microclimates at the continental scale. Here we report soil and air temperatures measured in 225 deciduous forest plots across Europe for two years. Forest stands were situated along a latitudinal gradient and subject to a varying vegetation structure as quantified by terrestrial laser scanning. In summer, the average offset of air and soil temperatures in forest edges compared to temperatures outside the forest amounted to -2.8 °C and -2.3 °C, respectively. Edge-to-interior summer temperature gradients were affected by the macroclimate and edge structure. From the edge onwards, larger offsets were observed in dense forest edges and in warmer, southern regions. In open forests and northern Europe, altered microclimatic conditions extended deeper into the forest and gradients were steeper. Canopy closure and plant area index were important drivers of summer offsets in edges, whereas in winter also the forest-floor biomass played a key role. Using high-resolution maps, we estimated that approximately 10% of the European broadleaved forests would be affected by altered temperature regimes. Gradual transition zones between forest and adjacent lands are valuable habitat types for edge species. However, if cool and moist forest interiors are desired, then (i) dense and complex forest edges, (ii) an undisturbed forested buffer zone of at least 12.5 m deep and (iii) trees with a high shade casting ability could all contribute to an increased offset. These findings provide important guidelines to mitigate edge influences, to protect typical forest microclimates and to adapt forest management to climate change.
Abstract
Via sheltering, decoupling and buffering mechanisms, tree canopies have the capacity to mitigate impacts of multiple global‐change drivers on below‐canopy processes and organisms in forests. ...As a result, canopies have an important potential as nature‐based solution.
The optimal combinations of forest canopy structural attributes to jointly mitigate the impacts of multiple global‐change drivers on below‐canopy organisms and processes have received little attention to date.
To help solving this research gap, here we review how forest canopies modulate the effects of four important global‐change drivers—climate warming, drought, air pollution and biological invasions—on below‐canopy conditions. Particular attention is paid to mitigating canopy attributes that can be influenced by forest management, including canopy cover, tree species composition and vertical and horizontal structure.
Synthesis
. We show that the potential of forest canopies to mitigate global‐change effects is highly context‐dependent and that optimal canopy‐based solutions strongly depend on the environmental context and the targeted subcanopy organisms. Hence, holistic approaches, which maximize synergies and minimize trade‐offs, are needed to optimize the solution potential of forest canopies.
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