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.
Climatically controlled allocation to reproduction is a key mechanism by which climate influences tree growth and may explain lagged correlations between climate and growth. We used continent‐wide ...datasets of tree‐ring chronologies and annual reproductive effort in Fagus sylvatica from 1901 to 2015 to characterise relationships between climate, reproduction and growth. Results highlight that variable allocation to reproduction is a key factor for growth in this species, and that high reproductive effort (‘mast years’) is associated with stem growth reduction. Additionally, high reproductive effort is associated with previous summer temperature, creating lagged climate effects on growth. Consequently, understanding growth variability in forest ecosystems requires the incorporation of reproduction, which can be highly variable. Our results suggest that future response of growth dynamics to climate change in this species will be strongly influenced by the response of reproduction.
The growth of past, present, and future forests was, is and will be affected by climate variability. This multifaceted relationship has been assessed in several regional studies, but spatially ...resolved, large-scale analyses are largely missing so far. Here we estimate recent changes in growth of 5800 beech trees (Fagus sylvatica L.) from 324 sites, representing the full geographic and climatic range of species. Future growth trends were predicted considering state-of-the-art climate scenarios. The validated models indicate growth declines across large region of the distribution in recent decades, and project severe future growth declines ranging from -20% to more than -50% by 2090, depending on the region and climate change scenario (i.e. CMIP6 SSP1-2.6 and SSP5-8.5). Forecasted forest productivity losses are most striking towards the southern distribution limit of Fagus sylvatica, in regions where persisting atmospheric high-pressure systems are expected to increase drought severity. The projected 21
century growth changes across Europe indicate serious ecological and economic consequences that require immediate forest adaptation.
Aim: Cold events determine the distributional range limits of woody species. Despite global warming, the magnitude of late frost events in boreal and temperate regions is not expected to change. ...Hence, the risk for late spring frost damage of woody species may increase with an earlier onset of the growing season. Here, we investigated biogeographical, phenological and phylogenetic effects on late frost sensitivity. Location: Ecological-Botanical Gardens Bayreuth, Germany (49°55'45"N,11°35'10"E). Methods: We inspected 170 woody species in the Ecological-Botanical Gardens from across the entire Northern Hemisphere for frost damage after an extreme late frost event in May 2011 (air temperature —4.3°C after leaf unfolding of all species). Distribution range characteristics, climatic parameters of place of origin and phenological strategy were linked to sensitivity to the late frost event. Results: The northern distribution limit and the range in continentality across the distributional ranges correlated negatively with a taxor's late frost sensitivity (pseudo-R² = 0.42, pseudo-R² = 0.33, respectively). Sensitivity to the late frost event was well explained by the climatic conditions within species' native ranges (boosted regression trees; receiver operating characteristic 0.737). Average (1950–2000) May minimum temperature in species' native ranges was the main explanatory variable of late frost sensitivity (51.7% of explained variance). Phylogenetic relatedness explained additional variance in sensitivity to the late frost event Sensitivity to the late frost event further correlates well with species phenological strategy. Frosttolerant species flushed on average 2 weeks earlier than frost-sensitive species. Main conclusions: Range characteristics and the prevalent climatic parameters across species native ranges are strongly related to their susceptibility to late spring frost damage. Further, more late frost-sensitive species unfolded their leaves later than more tolerant species and late frost tolerance is phylogenetically conserved. Thus, late frost sensitivity may challenge natural and human-assisted migration of woody species under global warming.
The magnitude and frequency of soil frost events might increase in northern temperate regions in response to climate warming due to reduced insulation caused by declining snow cover. In temperate ...deciduous forests, increased soil frost severity can hamper tree growth and increase the mortality of fine roots, soil fauna and microorganisms, thus altering carbon and nutrient cycling. From single-site studies, however, it is unclear how the sensitivities of these responses change along continental gradients from regions with low to high snowfall. We conducted a gradient design snow cover and soil temperature manipulation experiment across a range of lowland beech forest sites to assess the site-specific sensitivity of tree growth and biogeochemical cycling to soil cooling. Even mild and inconsistent soil frost affected tree increment, germination, litter decomposition and the retention of added
15
N. However, the sensitivity of response (treatment effect size per degree of warming or cooling) was not related to prevailing winter climate and snow cover conditions. Our results support that it may be valid to scale these responses to simulated winter climate change up from local studies to regional scales. This upscaling, however, needs to account for the fact that cold regions with historically high snowfall may experience increasingly harsh soil frost conditions, whereas in warmer regions with historically low snowfall, soil frost may diminish. Thus, despite the uniform biotic sensitivity of response, there may be opposing directions of winter climate change effects on temperate forests along continental temperature gradients due to different trends of winter soil temperature.
Assessing the genetic adaptive potential of populations and species is essential for better understanding evolutionary processes. However, the expression of genetic variation may depend on ...environmental conditions, which may speed up or slow down evolutionary responses. Thus, the same selection pressure may lead to different responses. Against this background, we here investigate the effects of thermal stress on genetic variation, mainly under controlled laboratory conditions. We estimated additive genetic variance (V
), narrow-sense heritability (h
) and the coefficient of genetic variation (CV
) under both benign control and stressful thermal conditions. We included six species spanning a diverse range of plant and animal taxa, and a total of 25 morphological and life-history traits. Our results show that (1) thermal stress reduced fitness components, (2) the majority of traits showed significant genetic variation and that (3) thermal stress affected the expression of genetic variation (V
, h
or CV
) in only one-third of the cases (25 of 75 analyses, mostly in one clonal species). Moreover, the effects were highly species-specific, with genetic variation increasing in 11 and decreasing in 14 cases under stress. Our results hence indicate that thermal stress does not generally affect the expression of genetic variation under laboratory conditions but, nevertheless, increases or decreases genetic variation in specific cases. Consequently, predicting the rate of genetic adaptation might not be generally complicated by environmental variation, but requires a careful case-by-case consideration.
Recent hot droughts have caused tree vitality decline and increased mortality in many forest regions on earth. Most of Central Europe's important timber species have suffered from the extreme ...2018/2019 hot drought, confronting foresters with difficult questions about the choice of more drought- and heat-resistant tree species. We compared the growth dynamics of European beech, sessile oak, Scots pine and Douglas fir in a warmer and a cooler lowland region of Germany to explore the adaptive potential of the four species to climate warming (24 forest stands). The basal area increment (BAI) of the two conifers has declined since about 1990–2010 in both regions, and that of beech in the warmer region, while oak showed positive BAI trends. A 2 °C difference in mean temperatures and a higher frequency of hot days (temperature maximum >30 °C) resulted in greater sensitivity to a negative climatic water balance in beech and oak, and elevated sensitivity to summer heat in Douglas fir and pine. This suggests to include hot days in climate-growth analyses. Negative pointer years were closely related to dry years. Nevertheless, all species showed growth recovery within one to three years. We conclude that all four species are sensitive to a deteriorating climatic water balance and hot temperatures, and have so far not been able to successfully acclimate to the warmer climate, with especially Douglas and beech, but also Scots pine, being vulnerable to a warming and drying climate.
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•All species except sessile oak show growth declines, especially less vital trees.•Trees in the warmer region show higher climate sensitivity.•Conifers display higher heat sensitivity than broadleaf trees.•All species showed fast recovery after hot and dry years.
Most of Central Europe’s economically important tree species have suffered vitality losses, growth decline and locally increased mortality during recent hot droughts. Foresters thus require ...comparative assessments of the major timber species’ climate vulnerability.
This dendroecological study compares long-term radial growth trends (basal area increment; BAI) and climate-growth relationships of (co-)dominant trees of the major timbers European beech (Fagus sylvatica L.), sessile oak (Quercus petraea (Matt.) Liebl.), Scots pine (Pinus sylvestris L.) and Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) along a precipitation gradient (834 − 570 mm yr−1) in the lowlands of Northern Germany on deep sandy to sandy-loamy soils with the aim to explore the species’ climate vulnerability and to assess the adaptive potential to reduced precipitation. The BAI of Douglas fir and beech has decreased in recent decades at most sites, while pine and oak growth was predominantly stable or has increased. Yet, the growth synchrony of all species has recently increased at some (or all) stands, hinting at the impact of increasing climatic stress. Increasing BAI at drier sites may indicate successful acclimation to reduced precipitation in oak and pine. The conifers profited primarily from sufficient moisture in late-summer and a warmer February and March, the broadleaf trees from a moister and cooler previous summer. Winter temperature emerged as a new driver of growth in pine, Douglas fir and oak, which may promote pine and oak growth at some sites through reduced winter cold stress. We conclude that all four species, but especially Douglas fir and beech, are vulnerable to climate warming in the Northern German lowlands.
•Stem growth declined in all species, especially in Douglas fir and European beech.•Growth decline was accompanied by rising growth synchrony and crown vitality loss.•Water availability in summer and warm winters are main drivers of growth.•Acclimation to increasing aridity was often insufficient, especially at moist sites.•We recommend planting alternative timber species together with sessile oak.
Increasing exposure to climate warming‐related drought and heat threatens forest vitality in many regions on earth, with the trees' vulnerability likely depending on local climatic aridity, recent ...climate trends, edaphic conditions, and the drought acclimatization and adaptation of populations. Studies exploring tree species' vulnerability to climate change often have a local focus or model the species' entire distribution range, which hampers the separation of climatic and edaphic drivers of drought and heat vulnerability. We compared recent radial growth trends and the sensitivity of growth to drought and heat in central populations of a widespread and naturally dominant tree species in Europe, European beech (Fagus sylvatica), at 30 forest sites across a steep precipitation gradient (500–850 mm year−1) of short length to assess the species' adaptive potential. Size‐standardized basal area increment remained more constant during the period of accelerated warming since the early 1980s in populations with >360 mm growing season precipitation (April–September), while growth trends were negative at sites with <360 mm. Climatic drought in June appeared as the most influential climatic factor affecting radial growth, with a stronger effect at drier sites. A decadal decrease in the climatic water balance of the summer was identified as the most important factor leading to growth decline, which is amplified by higher stem densities. Inter‐annual growth variability has increased since the early 1980s, and variability is generally higher at drier and sandier sites. Similarly, within‐population growth synchrony is higher at sandier sites and has increased with a decrease in the June climatic water balance. Our results caution against predicting the drought vulnerability of trees solely from climate projections, as soil properties emerged as an important modulating factor. We conclude that beech is facing recent growth decline at drier sites in the centre of its distribution range, driven by climate change‐related climate aridification.
Zusammenfassung
Die zunehmende Gefährdung durch Trockenheit und Hitze im Zusammenhang mit der Klimaerwärmung bedroht die Vitalität der Wälder in vielen Regionen der Erde, wobei die Anfälligkeit der Bäume wahrscheinlich von der lokalen Aridität, den jüngsten Klimatrends, den edaphischen Bedingungen und der Trockenheitsakklimatisierung und ‐anpassung der Populationen abhängt. Studien, die sich mit der Anfälligkeit von Baumarten für den Klimawandel befassen, sind häufig lokal ausgerichtet oder modellieren das gesamte Verbreitungsgebiet der Art, was die Trennung der Bedeutung von klimatischen und edaphischen Faktoren für die Anfälligkeit für Trockenheit und Hitze erschwert. Wir haben die aktuellen radialen Wachstumstrends und die Trockenheits‐ und Hitzesensitivität in zentralen Populationen einer in Europa weit verbreiteten und von Natur aus dominanten Baumart, der Rotbuche (Fagus sylvatica), an 30 Waldstandorten über einen steilen Niederschlagsgradienten (500–850 mm pro Jahr) von kurzer geographischer Länge verglichen, um das Anpassungspotenzial der Art zu bewerten. Der größenstandardisierte Grundflächenzuwachs war während des Zeitraums der rasanten Klimaerwärmung seit den frühen 1980er Jahren in Populationen mit mehr als 360 mm Niederschlag in der Vegetationsperiode (April–September) konstanter, während die Trends an Standorten mit weniger als 360 mm Niederschlag deutlich negativer waren. Klimatische Trockenheit im Juni erwies sich als der einflussreichste Klimafaktor, der das radiale Wachstum beeinflusste, wobei die Auswirkungen an trockeneren Standorten stärker waren. Eine jahrzehntelange Verschlechterung der klimatischen Wasserbilanz des Sommers wurde als wichtigster Faktor identifiziert, der zu einem Wachstumsrückgang führt, der durch höhere Stammdichten noch verstärkt wird. Die interannuelle Wachstumsvariabilität hat seit Anfang der 1980er Jahre zugenommen, und die Variabilität ist an trockeneren und sandigeren Standorten generell höher. Auch die Synchronität des Wachstums innerhalb der Populationen ist an sandigeren Standorten höher und hat mit einer Abnahme der klimatischen Wasserbilanz im Juni zugenommen. Wir kommen zu dem Schluss, dass die Buche in letzter Zeit an trockeneren Standorten im Zentrum ihres Verbreitungsgebiets mit einem Wachstumsrückgang konfrontiert ist, der auf die mit dem Klimawandel verbundene Aridifizierung zurückzuführen ist. Unsere Ergebnisse warnen davor, die Trockenheitsanfälligkeit von Bäumen allein anhand von Klimaprojektionen vorherzusagen, da sich die Bodeneigenschaften als wichtiger Einflussfaktor erwiesen haben.
Global change threatens forest vitality and productivity. We compared recent radial growth trends and the sensitivity of growth to drought and heat in central populations of a widespread and naturally dominant tree species in Europe, European beech (Fagus sylvatica), at 30 forest sites across a steep precipitation gradient. A decadal increase in evaporative demand was identified as the most important factor leading to growth decline, more so toward drier sites, which is amplified by higher stem densities. Our results caution against predicting the drought vulnerability of trees solely from climate projections, as local habitat factors emerged as important modulating factors.
The role of future forests in global biogeochemical cycles will depend on how different tree species respond to climate. Interpreting the response of forest growth to climate change requires an ...understanding of the temporal and spatial patterns of seasonal climatic influences on the growth of common tree species. We constructed a new network of 310 tree‐ring width chronologies from three common tree species (Quercus robur, Pinus sylvestris and Fagus sylvatica) collected for different ecological, management and climate purposes in the south Baltic Sea region at the border of three bioclimatic zones (temperate continental, oceanic, southern boreal). The major climate factors (temperature, precipitation, drought) affecting tree growth at monthly and seasonal scales were identified. Our analysis documents that 20th century Scots pine and deciduous species growth is generally controlled by different climate parameters, and that summer moisture availability is increasingly important for the growth of deciduous species examined. We report changes in the influence of winter climate variables over the last decades, where a decreasing influence of late winter temperature on deciduous tree growth and an increasing influence of winter temperature on Scots pine growth was found. By comparing climate–growth responses for the 1943–1972 and 1973–2002 periods and characterizing site‐level growth response stability, a descriptive application of spatial segregation analysis distinguished sites with stable responses to dominant climate parameters (northeast of the study region), and sites that collectively showed unstable responses to winter climate (southeast of the study region). The findings presented here highlight the temporally unstable and nonuniform responses of tree growth to climate variability, and that there are geographical coherent regions where these changes are similar. Considering continued climate change in the future, our results provide important regional perspectives on recent broad‐scale climate–growth relationships for trees across the temperate to boreal forest transition around the south Baltic Sea.
A tree‐ring network from European beech, Scots pine and oak trees from around the south Baltic Sea was compiled to examine the relationship between tree growth and climate. Our findings indicate tree growth is influenced by warming winter climate and summer moisture availability in northern temperate forests. Furthermore, spatial analysis suggests that there are geographical patterns in similar growth responses to climate and that these responses can be unstable through time.
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