ForestClim-Bioclimatic variables for microclimate temperatures of European forests.

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.

ForestTemp - Sub-canopy microclimate temperatures of European forests.

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.

Meta-analysis of multidecadal biodiversity trends in Europe.

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.

Effect of altitude and season on microbial activity, abundance and community structure in Alpine forest soils.

In the current context of climate change, the study of microbial communities along altitudinal gradients is especially useful. Only few studies considered altitude and season at the same time. We characterized four forest sites located in the Italian Alps, along an altitude gradient (545-2000 m a.s.l.), to evaluate the effect of altitude in spring and autumn on soil microbial properties. Each site in each season was characterized with regard to soil temperature, physicochemical properties, microbial activities (respiration, enzymes), community level physiological profiles (CLPP), microbial abundance and community structure (PLFA). Increased levels of soil organic matter (SOM) and nutrients were found at higher altitudes and in autumn, resulting in a significant increase of (soil dry-mass related) microbial activities and abundance at higher altitudes. Significant site- and season-specific effects were found for enzyme production. The significant interaction of the factors site and incubation temperature for soil microbial activities indicated differences in microbial communities and their responses to temperature among sites. CLPP revealed site-specific effects. Microbial community structure was influenced by altitudinal, seasonal and/or site-specific effects. Correlations demonstrated that altitude, and not season, was the main factor determining the changes in abiotic and biotic characteristics at the sites investigated.

Potential and limitations of inferring ecosystem photosynthetic capacity from leaf functional traits.

The aim of this study was to systematically analyze the potential and limitations of using plant functional trait observations from global databases versus in situ data to improve our understanding of vegetation impacts on ecosystem functional properties (EFPs). Using ecosystem photosynthetic capacity as an example, we first provide an objective approach to derive robust EFP estimates from gross primary productivity (GPP) obtained from eddy covariance flux measurements. Second, we investigate the impact of synchronizing EFPs and plant functional traits in time and space to evaluate their relationships, and the extent to which we can benefit from global plant trait databases to explain the variability of ecosystem photosynthetic capacity. Finally, we identify a set of plant functional traits controlling ecosystem photosynthetic capacity at selected sites. Suitable estimates of the ecosystem photosynthetic capacity can be derived from light response curve of GPP responding to radiation (photosynthetically active radiation or absorbed photosynthetically active radiation). Although the effect of climate is minimized in these calculations, the estimates indicate substantial interannual variation of the photosynthetic capacity, even after removing site-years with confounding factors like disturbance such as fire events. The relationships between foliar nitrogen concentration and ecosystem photosynthetic capacity are tighter when both of the measurements are synchronized in space and time. When using multiple plant traits simultaneously as predictors for ecosystem photosynthetic capacity variation, the combination of leaf carbon to nitrogen ratio with leaf phosphorus content explains the variance of ecosystem photosynthetic capacity best (adjusted R2 = 0.55). Overall, this study provides an objective approach to identify links between leaf level traits and canopy level processes and highlights the relevance of the dynamic nature of ecosystems. Synchronizing measurements of eddy covariance fluxes and plant traits in time and space is shown to be highly relevant to better understand the importance of intra- and interspecific trait variation on ecosystem functioning.

Long-term monitoring of soil microbiological activities in two forest sites in South tyrol in the italian alps.

We monitored microbiological properties in two forest sites over a period of 17 years (1993-2010) within the International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM). The two study sites were located in South Tyrol in the Italian Alps at altitudes of 1,737 m a.s.l. (subalpine site IT01) and 570 m a.s.l. (submontane site IT02). Soil samples were collected in the late spring and autumn of 1993, 2000, and 2010, and were characterized by measuring respiration, key enzyme activities involved in the C, N, P, and S cycles and litter degradation, and the abundance of viable bacterial and fungal populations. Over the study period, an increase in mean annual air temperatures at both sites (+0.6°C and +0.8°C at IT01 and IT02, respectively) was calculated from trendlines. Significantly lower mean annual air temperatures, higher temperature fluctuations, and higher annual precipitation rates were observed at site IT01 than at site IT02. Subalpine site IT01 was characterized by significantly lower microbial activity (respiration, enzymes) and abundance than those at submontane site IT02. The year of sampling had a significant effect on all the parameters investigated, except for nitrification. Fungal abundance decreased consistently over the study period, while no consistent trend was noted among the other parameters investigated. Season only affected a few of the measured microbiological parameters: respiration and bacterial numbers were significantly higher in the spring than in the autumn, while the opposite was noted for xylanase and phosphatase activities. Soil fungi contributed essentially to xylanase and protease activities, while soil bacteria were mainly involved in degradation processes that required the activity of sulfatase.