Gabriele Broll

Bio: Gabriele Broll is an academic researcher from University of Osnabrück. The author has contributed to research in topics: Ecotone & Humus. The author has an hindex of 26, co-authored 86 publications receiving 3087 citations. Previous affiliations of Gabriele Broll include International Sleep Products Association & University of Vechta.

Sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change at landscape and local scales

Abstract: The sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change are increasingly discussed in terms of climate change, often forgetting that climate is only one aspect of environmental variation. As treeline heterogeneity increases from global to regional and smaller scales, assessment of treeline sensitivity at the landscape and local scales requires a more complex approach than at the global scale. The time scale (short-, medium-, long-term) also plays an important role when considering treeline sensitivity. The sensitivity of the treeline to a changing environment varies among different types of treeline. Treelines controlled mainly by orographic influences are not very susceptible to the effects of warming climates. Greatest sensitivity can be expected in anthropogenic treelines after the cessation of human activity. However, tree invasion into former forested areas above the anthropogenic forest limit is controlled by site conditions, and in particular, by microclimates and soils. Apart from changes in tree physiognomy, the spontaneous advance of young growth of forest-forming tree species into present treeless areas within the treeline ecotone and beyond the tree limit is considered to be the best indicator of treeline sensitivity to environmental change. The sensitivity of climatic treelines to climate warming varies both in the local and regional topographical conditions. Furthermore, treeline history and its after-effects also play an important role. The sensitivity of treelines to changes in given factors (e.g. winter snow pack, soil moisture, temperature, evaporation, etc.) may vary among areas with differing climatic characteristics. In general, forest will not advance in a closed front but will follow sites that became more favourable to tree establishment under the changed climatic conditions.

The Northern Circumpolar Soil Carbon Database: spatially distributed datasets of soil coverage and soil carbon storage in the northern permafrost regions

Abstract: . High-latitude terrestrial ecosystems are key components in the global carbon (C) cycle. Estimates of global soil organic carbon (SOC), however, do not include updated estimates of SOC storage in permafrost-affected soils or representation of the unique pedogenic processes that affect these soils. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify the SOC stocks in the circumpolar permafrost region (18.7 × 106 km2). The NCSCD is a polygon-based digital database compiled from harmonized regional soil classification maps in which data on soil order coverage have been linked to pedon data (n = 1778) from the northern permafrost regions to calculate SOC content and mass. In addition, new gridded datasets at different spatial resolutions have been generated to facilitate research applications using the NCSCD (standard raster formats for use in geographic information systems and Network Common Data Form files common for applications in numerical models). This paper describes the compilation of the NCSCD spatial framework, the soil sampling and soil analytical procedures used to derive SOC content in pedons from North America and Eurasia and the formatting of the digital files that are available online. The potential applications and limitations of the NCSCD in spatial analyses are also discussed. The database has the doi:10.5879/ecds/00000001 . An open access data portal with all the described GIS-datasets is available online at: http://www.bbcc.su.se/data/ncscd/ .

Treeline advance - driving processes and adverse factors

Abstract: The general trend of climatically-driven treeline advance is modified by regional, local and temporal variations. Treelines will not advance in a closed front parallel to the shift of any isotherm to higher elevations and more northern latitudes. The effects of varying topography on site conditions and the after-effects of historical disturbances by natural and anthropogenic factors may override the effects of slightly higher average temperatures. Moreover, the varying treeline-forming species respond in different ways to a changing climate. Forest advance upwards and northwards primarily depends on successful regeneration and survival of young growth rather than on increasing growth rates of mature trees. Every assessment of treeline response to future climate change must consider the effects of local site conditions and feedbacks of increasing tree population in modulating the climatically-driven change. Treeline-shift will influence regional and local climates, pedogenesis, plant communities, animal populations and biodiversity as well as having a considerable effect on economic changes in primary production. A better understanding of the functional relationships between the many treeline-relevant factors and treeline dynamics can be achieved only by extensive research at different scales within different climatic regions supported by as many as possible experimental studies in the field together with laboratory and remote sensing techniques.

Temperature dependence of carbon mineralisation: conclusions from a long-term incubation of subalpine soil samples

Abstract: Carbon mineralisation from soil samples was analysed during a 104-day laboratory incubation at 5, 15 and 258C. The samples were taken from the upper horizon of each of two topographically diAerent micro-sites (gully: A-horizon; ridge: Oe/Oa-layer) at the Stillberg Alp close to Davos in the Swiss Central Alps. On both the soils, carbon mineralisation rates decreased substantially with incubation time (e.g. from 0.3 to 0.18 mg CO2‐C d ˇ1 g ˇ1 organic carbon in the Oe‐Oa-layer and from 0.6 to 0.2 mg CO2‐ Cd ˇ1 g ˇ1 organic carbon at 258C in the A-horizon). Carbon mineralisation was well described by a first-order kinetic twocompartment model and a functional temperature dependence of the rate constants. Both temperature models, the exponential Q10-function and a quadratic function described the cumulative C-mineralisation correctly within one standard error of estimate (SE) of the measured values. However, the Q10 model gave a slightly better fit to the data, and Q10-values of 2.5 and 2.8 were computed for the rate constants of the organic layer and the A-horizon, respectively. While the temperature dependence of the (time independent) rate constants of mineralisation appeared to be well-defined, this was not the case for Q10 of the instantaneous respiration rates, which were a non-linear function of incubation time. The general pattern of fluctuation of the instantaneous Q10-values was in accordance with the results computed by the models, and can be explained by the parallel decomposition of two diAerent soil organic matter pools. To avoid the eAects of the time of the respiration measurement on the calculated Q10, it is recommended to analyse the whole time series in order to infer the temperature dependence of respiration, or at least to standardise the time at which soil respiration is measured. In a second part of the study, our laboratory results temperature eAects were extrapolated to the field, using measurements of soil temperature as driving variables to a recently developed carbon balance model. Carbon mineralisation was roughly estimated to be 52‐84 g C m ˇ2 year ˇ1 for the gullies and 70‐125 g C m ˇ2 year ˇ1 for the ridges. Unexpectedly, the choice of the temperature model had a great influence on the estimate of annual carbon mineralisation, even though models diAered only little concerning the fit to the laboratory incubation data. However, it could be shown that winter-time mineralisation probably accounted for at least 22 and 40% of the whole-year mineralisation on the ridges and the gullies, respectively, and therefore, should not be neglected in carbon-balance studies. 7 2000 Elsevier Science Ltd. All rights reserved.

World Reference Base for Soil Resources 2006

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Climate change and the permafrost carbon feedback

Abstract: Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.

SoilGrids250m: Global gridded soil information based on machine learning

Abstract: This paper describes the technical development and accuracy assessment of the most recent and improved version of the SoilGrids system at 250m resolution (June 2016 update). SoilGrids provides global predictions for standard numeric soil properties (organic carbon, bulk density, Cation Exchange Capacity (CEC), pH, soil texture fractions and coarse fragments) at seven standard depths (0, 5, 15, 30, 60, 100 and 200 cm), in addition to predictions of depth to bedrock and distribution of soil classes based on the World Reference Base (WRB) and USDA classification systems (ca. 280 raster layers in total). Predictions were based on ca. 150,000 soil profiles used for training and a stack of 158 remote sensing-based soil covariates (primarily derived from MODIS land products, SRTM DEM derivatives, climatic images and global landform and lithology maps), which were used to fit an ensemble of machine learning methods-random forest and gradient boosting and/or multinomial logistic regression-as implemented in the R packages ranger, xgboost, nnet and caret. The results of 10-fold cross-validation show that the ensemble models explain between 56% (coarse fragments) and 83% (pH) of variation with an overall average of 61%. Improvements in the relative accuracy considering the amount of variation explained, in comparison to the previous version of SoilGrids at 1 km spatial resolution, range from 60 to 230%. Improvements can be attributed to: (1) the use of machine learning instead of linear regression, (2) to considerable investments in preparing finer resolution covariate layers and (3) to insertion of additional soil profiles. Further development of SoilGrids could include refinement of methods to incorporate input uncertainties and derivation of posterior probability distributions (per pixel), and further automation of spatial modeling so that soil maps can be generated for potentially hundreds of soil variables. Another area of future research is the development of methods for multiscale merging of SoilGrids predictions with local and/or national gridded soil products (e.g. up to 50 m spatial resolution) so that increasingly more accurate, complete and consistent global soil information can be produced. SoilGrids are available under the Open Data Base License.