Explaining the large-scale diversity of soil organisms that drive biogeochemical processes-and their responses to environmental change-is critical. However, identifying consistent drivers of ...belowground diversity and abundance for some soil organisms at large spatial scales remains problematic. Here we investigate a major guild, the ectomycorrhizal fungi, across European forests at a spatial scale and resolution that is-to our knowledge-unprecedented, to explore key biotic and abiotic predictors of ectomycorrhizal diversity and to identify dominant responses and thresholds for change across complex environmental gradients. We show the effect of 38 host, environment, climate and geographical variables on ectomycorrhizal diversity, and define thresholds of community change for key variables. We quantify host specificity and reveal plasticity in functional traits involved in soil foraging across gradients. We conclude that environmental and host factors explain most of the variation in ectomycorrhizal diversity, that the environmental thresholds used as major ecosystem assessment tools need adjustment and that the importance of belowground specificity and plasticity has previously been underappreciated.
Abstract
Local biodiversity trends over time are likely to be decoupled from global trends, as local processes may compensate or counteract global change. We analyze 161 long-term biological ...time series (15–91 years) collected across Europe, using a comprehensive dataset comprising ~6,200 marine, freshwater and terrestrial taxa. We test whether (i) local long-term biodiversity trends are consistent among biogeoregions, realms and taxonomic groups, and (ii) changes in biodiversity correlate with regional climate and local conditions. Our results reveal that local trends of abundance, richness and diversity differ among biogeoregions, realms and taxonomic groups, demonstrating that biodiversity changes at local scale are often complex and cannot be easily generalized. However, we find increases in richness and abundance with increasing temperature and naturalness as well as a clear spatial pattern in changes in community composition (i.e. temporal taxonomic turnover) in most biogeoregions of Northern and Eastern Europe.
The response of forest ecosystems to increased atmospheric CO₂is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to ...climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.
Years with high fruit production, known as mast years, are the usual reproduction strategy of European beech. Harsh weather conditions such as frost during flowering can lead to pollination failure ...in spring. It has been assumed that mast is controlled by flowering, and that after successful pollination, high amounts of fruits and seeds would be produced. However, the extremely hot and dry European summer of 2018 showed that despite successful pollination, beechnuts did not develop or were only abundant in a few forest stands. An in-depth analysis of three forest sites of European beech from the Swiss Long-Term Forest Ecosystem Research Programme over the last 15-19 years revealed for the first time that extreme summer heat and drought can act as an "environmental veto", leading to early fruit abortion. Within the forest stands in years with fruit abortion, summer mean temperatures were 1.5 °C higher and precipitation sums were 45% lower than the long-term average. Extreme summer heat and drought, together with frost during flowering, are therefore disrupting events of the assumed biennial fruiting cycle in European beech.
•Stand density and age were strong predictors of European forest growth.•We found direct and indirect impacts of N deposition on forest growth.•Forest growth showed a positive, but in some cases ...quadratic response to N deposition.•Beech forest growth was significantly reduced at high N deposition levels.•Climate predictors were species-specifically related to European forest growth.•There was limited evidence of an ozone impact on European forest growth.
Changing environmental conditions may substantially interact with site quality and forest stand characteristics, and impact forest growth and carbon sequestration. Understanding the impact of the various drivers of forest growth is therefore critical to predict how forest ecosystems can respond to climate change. We conducted a continental-scale analysis of recent (1995–2010) forest volume increment data (ΔVol, m3 ha−1 yr−1), obtained from ca. 100,000 coniferous and broadleaved trees in 442 even-aged, single-species stands across 23 European countries. We used multivariate statistical approaches, such as mixed effects models and structural equation modelling to investigate how European forest growth respond to changes in 11 predictors, including stand characteristics, climate conditions, air and site quality, as well as their interactions. We found that, despite the large environmental gradients encompassed by the forests examined, stand density and age were key drivers of forest growth. We further detected a positive, in some cases non-linear effect of N deposition, most pronounced for beech forests, with a tipping point at ca. 30 kg N ha−1 yr−1. With the exception of a consistent temperature signal on Norway spruce, climate-related predictors and ground-level ozone showed much less generalized relationships with ΔVol. Our results show that, together with the driving forces exerted by stand density and age, N deposition is at least as important as climate to modulate forest growth at continental scale in Europe, with a potential negative effect at sites with high N deposition.
Atmospheric nitrogen (N) deposition in terrestrial ecosystems is difficult to quantify, especially in forests. In this study, we compared three approaches for determining the wet and dry deposition ...of nitrogen (total deposition) at 17 intensively monitored forest sites in Switzerland. Specifically, we considered approaches based on: 1) measurements of bulk deposition and throughfall in 2014 (throughfall method); 2) measurements of bulk deposition and measurements of air concentrations of ammonia (NH3) and nitrogen dioxide (NO2), to which deposition velocities were applied, also in 2014 (inferential method); and 3) a model developed for Switzerland at a high spatial resolution, run for the five-year period 2013–2017 (emission based model). In addition, changes over two decades were assessed using continuous measurements of throughfall and bulk deposition. Further, air concentrations of NH3 and NO2 measured in 2014 were compared with concentrations measured in 2000 at 10 of the sites. The three approaches generally yielded comparable estimates of total deposition, with some notable differences at some sites. For both the model and the inferential method, uncertainties were related to the deposition velocities that were applied to air concentrations of N compounds, especially for NH3. The throughfall method provided a minimum estimate of the total N deposition in the forest, but the fraction of the deposited N that is directly taken up by the canopy remained difficult to quantify. Nitrogen deposition has decreased since the mid-1990s at the majority of the sites. However, deposition of the reduced forms of N seems to have stagnated at the local level. Furthermore, N deposition is still too high in comparison with the range of empirical critical loads of N (CLN). The minimum deposition estimated from throughfall exceeds the lower limit of CLN at all sites except those in the Central Alps. Deposition estimated with the model and the inferential method exceeds the lower limit of CLN at all sites and even exceeds the upper limit at several locations.
•Throughfall and inferential methods and an emission based model were compared.•Deposition estimates were consistent overall but showed large local differences.•The uncertainties related to each method are difficult to reduce.•The deposition of oxidised nitrogen compounds decreased from 1995 to 2015.•Nitrogen deposition is still too high in comparison with critical loads.
▶ Leaf area index (LAI) was measured by hemispherical photography at 91 Swiss forests. ▶ Regressions on stand parameters from vegetation surveys could predict well LAI. ▶ Applied to 981 sites, these ...regressions produced plausible values and patterns. ▶ Limitation of LAI by altitude and by water availability appeared clearly. ▶ The regression method appears reliable and robust across forest types.
Canopy gap fraction and leaf area index (LAI) were measured using hemispherical photography in 91 mature forests across Switzerland, including coniferous, broadleaved and mixed stands. The gap fraction and LAI derived from five photographs per site could be reproduced with a high coefficient of determination (R2>0.7) by regression against simple stand parameters obtained from vegetation surveys: coverages of the tree, shrub and herb layers, and tree height. The method appeared to be robust across the different types of forests. Applied to 981 sites across Switzerland, the regression model produced LAI values ranging from 1.4 to 6.7. These predictions were compared with site variables not included in the regression. LAI appeared limited by the altitude, with maximal values decreasing by one third from 400 to 2000m above see level. Water availability was also clearly a limitation at sites with a negative water balance, i.e. where the yearly potential evapotranspiration exceeded the precipitation. High or low values of a humidity index based on the ground vegetation also corresponded to a limitation of the LAI, with shorter trees at dry sites and more open canopies at wet sites. Compared to optical measurements (including hemispherical photography), our regression method is fast and inexpensive. Such an approach appears very promising for obtaining reliable estimates of LAI for many sites with low costs. These estimates can then be fed into process models at the stand level.
KEY MESSAGE : Throughfall nutrient fluxes were generally higher in a mixed stand than in a pure stand of Oriental beech. Throughfall fluxes were higher than bulk precipitation fluxes except for ...nitrogen and indicate higher canopy uptake of this element in the pure stand compared to the mixed stand. CONTEXT : Oriental beech is an economically relevant tree species for Iran and adjacent countries. Yet little is known about nutrient cycling in Oriental beech stands and the influence of the degree of mixture with other species. AIM S : We assessed the effect of seasons on nutrient fluxes in precipitation and whether throughfall chemistry differed between pure and mixed stands. METHODS : Bulk precipitation in the open field and throughfall were sampled during one whole month within each season from August 2013 to May 2014 in a pure (81 % of beech trees on average) and a mixed stand (57 % of beech trees) of Oriental beech. Samples were analysed for pH, nitrate (NOâ â»), ammonium (NHâ âº), phosphorus (P), calcium (Ca²âº), magnesium (Mg²âº) and potassium (Kâº). RESULTS : Nutrient concentrations were generally higher in the growing season than in the dormant season, both in bulk precipitation and in throughfall. Nutrient fluxes were higher in fall and these peaks coincided with higher amounts of precipitation. The concentrations and fluxes of NHâ âº, NOâ â», P, Ca²âº, Mg²⺠and K⺠were generally higher in the mixed stand than in the pure stand in all seasons. Compared to the open field, throughfall fluxes were usually higher, except for NOâ â» and NHâ âº, indicating direct canopy uptake of nitrogen. CONCLUSION : Canopy composition in Oriental beech stands (owing to differences in foliage chemistry) and seasons (owing to differences in precipitation regime and phenological stages) have a significant effect on throughfall nutrient fluxes.
Introduction
Nitrogen (N) gradient studies in some cases use N deposition in throughfall as measure of N deposition to forests. For evaluating critical loads of N, however, information on total N ...deposition is required, i.e., the sum of estimates of dry, wet and occult deposition.
Methods
The present paper collects a number of studies in Europe where throughfall and total N deposition were compared in different forest types. From this dataset a function was derived which allows to estimate total N deposition from throughfall N deposition.
Results
At low throughfall N deposition values, the proportion of canopy uptake is high and thus the underestimation of total deposition by throughfall N needs to be corrected. At throughfall N deposition values > 20 kg N ha
–1
yr
–1
canopy uptake is getting less important.
Conclusion
This work shows that throughfall clearly underestimates total deposition of nitrogen. With the present data set covering large parts of Europe it is possible to derive a critical load estimate from gradient studies using throughfall data.
Leaf morphological traits (LMTs) of forest trees have been observed to vary across space and species. However, long-term records of LMTs are scarce, due to a lack of measurements and systematic leaf ...archives. This leaves a large gap in our understanding of the temporal dynamics and drivers of LMT variations, which may help us understand tree acclimation strategies. In our study, we used long-term LMT measurements from foliar material collections of European beech (
Fagus sylvatica
) and Norway spruce (
Picea abies
), performed every second year from 1995 to 2019 on the same trees within the Swiss Long-term Forest Ecosystem Research Program LWF. The 11 study plots (6 beech, 4 spruce, and 1 mixed) are distributed along gradients of elevation (485–1,650 m a.s.l.), mean annual precipitation (935–2142 mm), and mean annual temperature (3.2–9.8°C). The investigated LMTs were (i) leaf or needle mass, (ii) leaf area or needle length, and (iii) leaf mass per area or needle mass per length. We combined this unique data set with plot variables and long-term data on potential temporal drivers of LMT variations, including meteorological and tree trait data. We used univariate linear regressions and linear mixed-effects models to identify the main spatial and temporal drivers of LMT variations, respectively. For beech LMTs, our temporal analysis revealed effects of mast year and crown defoliation, and legacy effects of vapor pressure deficit and temperature in summer and autumn of the preceding year, but no clear long-term trend was observed. In contrast, spruce LMTs were mainly driven by current-year spring conditions, and only needle mass per length showed a decreasing long-term trend over the study period. In temporal models, we observed that LMTs of both species were influenced by elevation and foliar nutrient concentrations, and this finding was partly confirmed by our spatial analyses. Our results demonstrate the importance of temporal analysis for determining less recognized drivers and legacy effects that influence LMTs, which are difficult to determine across space and species. The observed differences in the temporal drivers of beech and spruce LMTs suggest differences in the adaptation and acclimation potential of the two species.