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Query: "author" (Mitja Skudnik) .

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21.
Artificial neural networks as an alternative method to nonlinear mixed-effects models for tree height predictions
Mitja Skudnik, Jernej Jevšenak, 2022, original scientific article

Abstract: Tree heights are one of the most important aspects of forest mensuration, but data are often unavailable due to costly and time-consuming field measurements. Therefore, various types of models have been developed for the imputation of tree heights for unmeasured trees, with mixed-effects models being one of the most commonly applied approaches. The disadvantage here is the need of sufficient sample size per tree species for each plot, which is often not met, especially in mixed forests. To avoid this limitation, we used principal component analysis (PCA) for the grouping of similar plots based on the most relevant site descriptors. Next, we compared mixed-effects models with height-diameter models based on artificial neural networks (ANN). In terms of root mean square error (RMSE), mixed-effects models provided the most accurate tree height predictions at the plot level, especially for tree species with a smaller number of tree height measurements. When plots were grouped using the PCA and the number of observations per category increased, ANN predictions improved and became more accurate than those provided by mixed-effects models. The performance of ANN also increased when the competition index was included as an additional explanatory variable. Our results show that in the pursuit of the most accurate modelling approach for tree height predictions, ANN should be seriously considered, especially when the number of tree measurements and their distribution is sufficient.
Keywords: height-diameter models, national forest inventory, permanent sample plot, mixed forests, model comparison, principal component analysis
Published in DiRROS: 08.06.2022; Views: 495; Downloads: 205
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Trajnostno gospodarjenje z gozdovi in trajnostna oskrba lesnopredelovalnih podjetij z lesom
Mitja Skudnik, Polona Hafner, 2021, preface, editorial, afterword

Published in DiRROS: 18.12.2021; Views: 786; Downloads: 232
.pdf Full text (46,36 KB)

28.
Growing stock monitoring by European National Forest Inventories : historical origins, current methods and harmonisation
Thomas Gschwantner, Iciar Alberdi, Sébastien Bauwens, Susann Bender, Dragan Borota, Michal Bošela, Olivier Bouriaud, Johannes Breidenbach, Janis Donis, Christoph Fischer, Mitja Skudnik, 2022, original scientific article

Abstract: Wood resources have been essential for human welfare throughout history. Also nowadays, the volume of growing stock (GS) is considered one of the most important forest attributes monitored by National Forest Inventories (NFIs) to inform policy decisions and forest management planning. The origins of forest inventories closely relate to times of early wood shortage in Europe causing the need to explore and plan the utilisation of GS in the catchment areas of mines, saltworks and settlements. Over time, forest surveys became more detailed and their scope turned to larger areas, although they were still conceived as stand-wise inventories. In the 1920s, the first sample-based NFIs were introduced in the northern European countries. Since the earliest beginnings, GS monitoring approaches have considerably evolved. Current NFI methods differ due to country-specific conditions, inventory traditions, and information needs. Consequently, GS estimates were lacking international comparability and were therefore subject to recent harmonisation efforts to meet the increasing demand for consistent forest resource information at European level. As primary large-area monitoring programmes in most European countries, NFIs assess a multitude of variables, describing various aspects of sustainable forest management, including for example wood supply, carbon sequestration, and biodiversity. Many of these contemporary subject matters involve considerations about GS and its changes, at different geographic levels and time frames from past to future developments according to scenario simulations. Due to its historical, continued and currently increasing importance, we provide an up-to-date review focussing on large-area GS monitoring where we i) describe the origins and historical development of European NFIs, ii) address the terminology and present GS definitions of NFIs, iii) summarise the current methods of 23 European NFIs including sampling methods, tree measurements, volume models, estimators, uncertainty components, and the use of air- and space-borne data sources, iv) present the recent progress in NFI harmonisation in Europe, and v) provide an outlook under changing climate and forest-based bioeconomy objectives.
Keywords: forest history, natural resources, sustainability, timber volume, sampling, remote sensing, bioeconomy, climate change
Published in DiRROS: 14.12.2021; Views: 753; Downloads: 535
.pdf Full text (17,73 MB)
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29.
Environmental signals in Quercus robur L. tree-ring widths and [delta]13C
Polona Hafner, Jožica Gričar, Mitja Skudnik, Tom Levanič, 2015, published scientific conference contribution abstract

Published in DiRROS: 03.11.2021; Views: 517; Downloads: 181
.pdf Full text (1,05 MB)

30.
Aktivni lastniki gozdov in njihov prispevek k prehodu v brezogljično družbo
Mitja Skudnik, Polona Hafner, 2021, preface, editorial, afterword

Published in DiRROS: 26.10.2021; Views: 792; Downloads: 237
.pdf Full text (423,00 KB)

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