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.
2013
Authors
Grete H. M. JørgensenAbstract
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Tore SkrøppaAbstract
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Christian Brischke Linda Meyer Gry Alfredsen Per Otto Flæte Lesley Francis Mattias Hansson Pia Larsson-Brelid Jöran Jermer Christian Welzbacher Andreas Otto Rapp Karin Brandt Eckhard MelcherAbstract
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Abstract
Syngenta’s GREENCAST model was used to predict timing of fungicide application against microdochium patch and pink snow mold caused by Microdochium nivale on an experimental golf green with annual bluegrass (Poa annua) at Bioforsk Landvik, Southern Norway from 5 Oct. 2012 until 1 June 2013. From 5 Oct. until snow covered the green on 2 Dec. 2012, application of the fungicides Headway (azoxystrobin + propiconazole) or Medallion (fludioxonil) only at GREENCAST high risk warnings resulted in equal control of microdohium patch with one less fungicide application than prophylactic application every third week, application at first sign of disease or application at GREENCAST medium risk warnings. The consequences for pinks snow mold in spring could not be evaluated as the turf was killed by the combination of ice encasement and low freezing temperatures during winter.
Abstract
Modelling stem taper and volume is crucial in many forest management and planning systems. Taper models are used for diameter prediction at any location along the stem of a sample tree. Furthermore, taper models are flexible means to provide information on the stem volume and assortment structure of a forest stand or other management units. Usually, taper functions are mean functions of multiple linear or nonlinear regression models with diameter at breast height and tree height as predictor variables. In large-scale inventories, an upper diameter is often considered as an additional predictor variable to improve the reliability of taper and volume predictions. Most studies on stem taper focus on accurately modelling the mean function; the error structure of the regression model is neglected or treated as secondary. We present a semi-parametric linear mixed model where the population mean diameter at an arbitrary stem location is a smooth function of relative height. Observed tree-individual diameter deviations from the population mean are assumed to be realizations of a smooth Gaussian process with the covariance depending on the sampled diameter locations. In addition to the smooth random deviation from the population average, we consider independent zero mean residual errors in order to describe the deviations of the observed diameter measurements from the tree-individual smooth stem taper. The smooth model components are approximated by cubic spline functions with a B-spline basis and a small number of knots. The B-spline coefficients of the population mean function are treated as fixed effects, whereas coefficients of the smooth tree-individual deviation are modelled as random effects with zero mean and a symmetric positive definite covariance matrix. The taper of a tree is predicted using an arbitrary number of diameter and corresponding height measurements at arbitrary positions along the stem to calibrate the tree-individual random deviation from the population mean estimated by the fixed effects. This allows a flexible application of the method in practice. Volume predictions are calculated as the integral over cross-sectional areas estimated from the calibrated taper curve. Approximate estimators for the mean squared errors of volume estimates are provided. If the tree height is estimated or measured with error, we use the “law of total expectation and variance” to derive approximate diameter and volume predictions with associated confidence and prediction intervals. All methods presented in this study are implemented in the R-package TapeR.
Authors
Ievina SturiteAbstract
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Authors
Belen Cotes Linda-Marie Rännbäck Peter Andersson Nicolai Vitt Meyling Maria Björkman Birgitta RämertAbstract
No abstract has been registered