Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2011
Authors
Bruce Talbot Morten NittebergAbstract
In the coastal region of Norway, large volumes of relatively inaccessible plantation timber are maturing for harvest. The economic feasibility of accessing much of this timber has limited the level of harvesting activity considerably. Harvesting planners are faced with the classic dilemma of finding the appropriate level of investment in infrastructure, as against inoptimal transportation. In this paper, we present results from a simple deterministic simulation carried out to illustrate the efficiency frontiers of three transport methods, one of which requires a substantial investment in road upgrading. Results depend on assumptions made, but clearly show that in these conditions, upgrading roads for truck+trailer transport should be evaluated on a cases by case basis. Forest road length and condition, public road distance to conversion site, and investment level all play important roles in the decision structure. In the coastal regions, road upgrades would generally need to be justified by benefits other than timber harvesting alone.
Abstract
No abstract has been registered
Abstract
1. In the face of a rapidly changing environment, long-term studies provide important insights into patterns of vegetation and processes of change, but long-term studies are rare for many ecosystems.2. We studied recent vegetation changes at a fine scale in a Sphagnum-dominated bog in south Sweden by resurveying part of the bog 54 years after the original phytosociological survey. We used an indirect approach to identify changes in vegetation composition in relation to environment because of a lack of permanent sampling units. By applying a weighted averaging technique, we calculated relative changes in species optimum values for different environmental gradients as represented by indicator values for light, temperature, pH, moisture and nutrients.3. Species composition of the mire vegetation has changed significantly over the past five decades, as indicated by significant changes in species frequencies and species optima for the gradients examined. Species with lower indicator values for moisture and light and higher indicator values for nutrients have become more frequent on the mire. In particular, species of trees and dwarf shrubs increased in frequency, whereas typical mire species decreased (e.g. Trichophorum cespitosum (L.) Hartm.) or disappeared fromthe study site (e.g. Scheuchzeria palustris L.).4. Synthesis. Composition of the mire vegetation is found to be dynamic at different temporal and spatial scales. Increased air temperature and nutrient availability in south Sweden over the past few decades may have augmented productivity (e.g. tree growth), resulting in drier and shadier conditions for several species. This study successfully demonstrated the applicability of an indirect approach for detecting long-term vegetation change at a fine scale. This approach is an effective way of using historic and modern phytosociological data sets to detect vegetation and environmental change through time.
Abstract
Understanding the driving forces affecting species occurrences is a prerequisite for determining the indicator suitability of crenic plants. We analysed 18 environmental variables in a two-step approach, evaluating their ability to explain the species composition of 222 springs on five siliceous mountain ranges, in central Germany and north-west Czech Republic (49.9°–50.8°N, 10.6°–12.8°E). First, we identified the significant environmental variables in three subsets of spatial, hydrophysical and hydrochemical variables using a forward-selection procedure. We then performed a partial canonical correspondence analysis (pCCA) to estimate the influence of each subset alone, as well as in combinations. We also used a multiple response permutation procedure (MRPP) to compare the five regions with respect to the dissimilarity of their vegetation composition and environmental variables. Hydrochemical factors played a fundamental role in determining the plant community of the investigated springs. Spatial factors, in particular altitude, were correlated with the hydrochemical factors, but were less important. Hydrophysical factors played only a marginal role. More precisely, species occurrence was mainly driven by a gradient of nutrient availability, which in turn reflected the acidity status. This gradient was primarily represented by high Al, Cd, and Mn concentrations in acidic crenic waters, high Ca and Mg concentrations were encountered in circumneutral springs. By comparing the five regions we could show that there are spatial patterns in the vegetation of springs, which provide valuable ecological information on the water quality. We therefore suggest that biomonitoring approaches to vegetation are suitable for revealing the acidity status of springs and their forested catchments.
Authors
Holger LangeAbstract
Spatial dependencies among environmental variables are often quantified by spatial autocorrelation functions. The latter basically assume linearity and isotropy, requirements usually not satisfied for measured data. Typical symptoms of violated assumptions are biased parameter estimations. Relaxing the assumptions of linear dependencies and isotropy, we present a conceptual generalization of spatial analysis where locally varying anisotropies in the geographical space are uncovered by investigating nonlinear dependencies among observations. The framework is illustrated by generalizing two examples: distance decay relations and spatial filtering. The proposed alternative is based on geodesic ecological and anisotropic spatial distances.
Abstract
Long-term monitoring of headwater semi-natural catchments is used to document persistence and changes in ecosystems. At three headwater catchments in the Bramke basin in Northern Germany, physical and chemical variables in rainfall, soil solution from various depths (20–300 cm) and streamwater have been monitored. The Lange Bramke catchment is largely covered by a Norway spruce (Picea abies, Karst.) stand planted in the 1950ies. Over 29 years, 4310 water samples from streamwater and 5475 soil water samples were analysed for major constituents. Both linear methods (principal component analysis (PCA) and cross correlation (CC)) as well as non-linear methods (isometric feature mapping (ISOMAP) and maximum variance unfolding (MVU)) were used to analyze the spatiotemporal patterns of dissolved major ion concentrations in soil solution and streamwater. This approach provides a multiscale characterisation of links between soil water and streamwater at the catchment scale. Pattern identification augments the interpretation of processes in terms of transport and storage. The long time scales were dominated by trends in ions implicated in soil acidification. This reflects the decreasing input of acid deposition. At the annual scale, where hydrological effects dominate, each of the three adjacent catchments showed different patterns. Various empirical and process-based models have been applied in the past to the Bramke catchments. Results of the data-oriented approach can be used to indicate the potential and limits of process-oriented models for this data set.
Abstract
Remote sensing of the activity of vegetation in relation to environmental conditions provides an invaluable basis for investigating the spatiotemporal dynamics and patterns of variability for ecosystem processes. We investigate the fraction of Absorbed Photosynthetically Active Radiation (fAPAR) using SeaWiFS satellite observations from 1998 to 2005 and ancillary meteorological variables from the CRU-PIK dataset with a global coverage at a spatial resolution of 0.5o x 0.5o. A pixel-by-pixel spectral decomposition using Singular System Analysis leads to a global “classification” of the terrestrial biosphere according to prevalent time-scale dependent dynamics of fAPAR and its relation to meteorology. A complexity analysis and a combined subsignal extraction and dimensionality reduction reveals a series of dominant geographical gradients, separately for different time scales. At the annual scale, which explains around 50% of the fAPAR variability as a global average, patterns largely resemble the biomes of the world as mapped by biogeographical methods, and are driven by temperature and by pronounced rain seasons in the tropics. On shorter time scales, fAPAR fluctuations are exclusively driven by water supply, inducing, e.g., semiannual cycles in the equatorial belt of Africa or the Indo-Gangetic Plain. For some regions however, in particular South America, altitude, mean temperature, drought probability and fire occurrences are parameters that seem to shape the spatial patterns of fAPAR across time scales. Overall, we provide a first global multiscale characterization of fAPAR and highlight different mechanisms in land-surface-climate couplings.
Abstract
There is a great demand for involving rapid, non destructive and less time consuming methods for quick control and prediction of soil quality, environmental monitoring, and other precision measurements in agriculture. Near infrared reflectance spectroscopy (NIRS) is considered as an appropriate alternative method to conventional analytical methods for large scale measurements. The objective of this study was to investigate the possibilities of NIRS for prediction of some chemical properties of soil samples. A total of 97 samples from Stara Zagora, Kazanlak and Gurkovo region taken from the 0-40 cm layer were collected. Soil types were Luvisols, Vertisols, Fluvisols and Rankers. The samples were analyzed for total phosphorus by spectrometric determination of phosphorus soluble in sodium hydrogen carbonate solution, total nitrogen by Kjeldahl method, pH (H O)-potentiometrically and electrical conductivity (EC). 2 The spectral data of all air dried samples were measured using an Perkin Elmer Spectrum One NTS, FT-NIR Spectrometer, within the range from 700 to 2500 nm. Partial Least Squares (PLS) regression was used to built models to determine soil chemical parameters from the NIR spectra. Two-third of the samples were used as a calibration set and the remaining samples as independent validation test set. The best model was obtained for total nitrogen with a coefficient of determination r=0,91, standard error of calibration SEP=336 mg/kg, and the ratio of the standard variation of the reference data to the SEP, indicating the performance of the calibration, of RPD=2,3. The accuracy of prediction was poor for electrical conductivity. The results obtained clearly indicated that NIRS had the potential to predict some soil components rapidly and without sample preparation.
Abstract
A changing climate will likely influence the selection of tree species in the future, and this may in turn affect the size of the pools and fluxes of carbon. Tree species differ in growth rate, fine-root turnover and quality of litter and tend to produce different types of understory vegetation. In Sweden three tree species (Norway spruce [Picea abies] 43%, Scots pine [Pinus sylvestris] 39% and birch [Betula spp.] 11%) dominate. In the present study we used field experiments in southern Sweden to test if these tree species differed in root distribution and turnover.
Abstract
For tracer studies at the catchment scale, travel times are often assumed to be stationary. We question the validity of this assumption. We analyzed a series of tracer experiments conducted under exceptionally controlled conditions at Gårdsjön, Sweden. The Gårdsjön G1 catchment was covered by a roof underneath which natural throughfall has been replaced by artificial irrigation with a pre-defined chemical composition. This unique setup was used to perform replicated catchment scale Br tracer experiments under steady state storm flow conditions in five different years. A log-normal distribution function was fitted to all Br breakthrough curves. Fitted parameter values differed significantly for some of the experiments. These differences were not only related to the slightly different hydrologic boundary and initial conditions for the experiments, but also to seasonal changes in catchment properties that may explain the different flow paths during the experiments. We conclude that the travel time distribution is not only linked to discharge but also explicitly related to other water fluxes such as evapotranspiration, and that it is not stationary even under steady-state flow conditions. Since the attenuation of soluble pollutants is fundamentally linked to the travel times of water through the subsurface of a catchment, it is of crucial importance to understand the latter in detail. However, it is still unclear which are the dominant processes controlling their distribution.