Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.
The Northeast German Lowland Observatory (TERENO-NE) was established to investigate the regional impact of climate and land use change. TERENO-NE focuses on the Northeast German lowlands, for which a high vulnerability has been determined due to increasing temperatures and decreasing amounts of precipitation projected for the coming decades. To facilitate in-depth evaluations of the effects of climate and land use changes and to separate the effects of natural and anthropogenic drivers in the region, six sites were chosen for comprehensive monitoring. In addition, at selected sites, geoarchives were used to substantially extend the instrumental records back in time. It is this combination of diverse disciplines working across different time scales that makes the observatory TERENO-NE a unique observation platform. We provide information about the general characteristics of the observatory and its six monitoring sites and present examples of interdisciplinary research activities at some of these sites. We also illustrate how monitoring improves process understanding, how remote sensing techniques are fine-tuned by the most comprehensive ground-truthing site DEMMIN, how soil erosion dynamics have evolved, how greenhouse gas monitoring of rewetted peatlands can reveal unexpected mechanisms, and how proxy data provides a long-term perspective of current ongoing changes.
Mechanistic understanding of tree-ring formation and its modelling requires a cellularbased and spatially organized characterization of a tree ring, moving from whole rings, to intraannual growth zones and individual cells. A tracheidogram is a radial profile of conifer anatomical features, such as lumen area and cell wall thickness, of sequentially-and positionally-ranked tracheids. However, its construction is tedious and time-consuming since image-analysis-based measurements do not recognize the position of cells within a radial file, and present-day tracheidograms must be constructed manually.Here we present the R-program library RAPTOR that complements tracheid anatomical data obtained from quantitative wood anatomy software (e.g., ROXAS, WinCELL, ImageJ), with the specific positional information necessary for the automatic construction of tracheidograms. The package includes functions to read and visualize tracheid anatomical data, and uses local search algorithms to ascribe a ranked position to each tracheid in identified radial files. The package also provides functions to ensure that tracheids are adequately aligned for identifying the first tracheid in each radial file, and obtaining the correct ranking of tracheids along each radial file. Additional functions allow automating the analyses for multiple samples and rings (batch mode) and exporting data and plots for quality control.RAPTOR allows tracheidogram users to take advantage of the latest generation of cell anatomical measuring systems. With this R-package we aim at facilitating the construction of more robust and versatile tracheidograms for the benefit of the research community.
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