| 1. |
- Olsson, Jan-Ola, 1972-, et al.
(author)
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En avståndsberoende tillväxtmodell på trädnivå för gran : en preliminär modell baserad på två skiktade bestånd i Götaland
- 2019
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Reports (other academic/artistic)abstract
- The report describes parameterization and testing of a single tree growth model for simulation purposes of uneven-sized Norway spruce stands. The model includes local competition in terms of distance and size of competing trees larger than 6 cm dbh. Response variable is annual basal area growth. Parameter values are based on 101 sample trees from two uneven-sized Spruce dominated stands located in Värnamo and Östra Göinge municipalities, Sweden. The model was tested by first reconstructing stand development five years, based on growth data from sample trees. Coefficient of determination for the complete model was 0,67, compared to 0,55 for the basic model without local competition. Residual analyses revealed no visible trends.
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| 2. |
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| 3. |
- Fagerberg, Nils, 1972-, et al.
(author)
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Evaluation of individual-tree growth models for Picea abies based on a case study of an uneven-sized stand in southern Sweden
- 2022
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In: Scandinavian Journal of Forest Research. - : Taylor & Francis Group. - 0282-7581 .- 1651-1891. ; 37:1, s. 45-58
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Journal article (peer-reviewed)abstract
- To develop recommendations for tree selection in Continuous Cover Forestry (CCF), access to valid tools for simulating growth at individual tree-level is necessary. To assist efforts to develop such tools, in this study, long-term observation data from two uneven-sized Norway spruce plots in southern Sweden are used to evaluate old and new individual-tree growth models (two established Swedish models, two new preliminary models and included as a reference, a Finnish model). The plots' historical management records and site conditions are the same, but their last thinning treatment differs. Observed diameter increment at tree-level is investigated in relation to treatment. Individual tree growth residuals of tested models are evaluated in relation to tree diameter, treatment, projection length and sensitivity to the predictor mean stand age. Furthermore, the relations between displayed residuals and basal area local competition are analysed. The analyses indicate that active thinning made annual diameter increment independent of tree diameter above a threshold level, while the absence of thinning supported a concave relationship. All tested models displayed a significant linear bias leading to overestimation of small trees' growth and increasing underestimations of larger trees' growth with tree diameter. All distance-independent models displayed residual trends related to local competition.
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| 4. |
- Fagerberg, Nils, 1972-, et al.
(author)
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Individual-tree distance-dependent growth models for uneven-sized Norway spruce
- 2022
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In: Forestry (London). - : Oxford University Press. - 0015-752X .- 1464-3626. ; 95, s. 634-646
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Journal article (peer-reviewed)abstract
- Individual tree selection (ITS) is one option to manage uneven-sized forest ecosystems. However, scientifically based field guidelines adapted to ITS and economic profitability are rare, often because there is a lack of suitable tree models to use in growth and treatment simulations. The objective of this study is to develop individual-tree distance-dependent growth models focusing on Norway spruce dominated uneven-sized stands. Three models of different complexity, but with the same structural basis, are presented, followed by some examples of growth patterns for the subject trees. The data include 1456 trees (307 sample trees) collected from five sites in southern Sweden. The basic model (S) depends on subject tree size as the predictor, the second model (SD) adds distance to competitors as a predictor, and the third model (SDC) adds crown ratio as a predictor to the structure. R-Adj(2) increases with number of predictors from 0.48 to 0.58 to 0.62. The levels of RMSE improve accordingly from 5.02 cm(2) year(-1) (S) to 4.43 cm(2) year(-1) (SD) and 4.26 cm(2) year(-1) (SDC). The present calibration range and model structures primarily make the models suitable for management simulation of individual-tree selection of Norway spruce in southern Sweden. The format of the models allows for further extension with additional predictors and calibration data with greater coverage.
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| 5. |
- Fagerberg, Nils, 1972-
(author)
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Individual-tree-selection in uneven-sized Norway spruce stands in southern Sweden : Developments of tools for simulation and optimization
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Individual-tree-selection (ITS) is a continuous cover forestry method that aims to utilize the uneven-sized stand structure through optimized individual tree selections. ITS is an interesting management alternative to rotation forestry in terms of production of multiple benefits and forest owner profitability. With regard to Fennoscandia, ITS is currently only practiced to a limited extent, partly because of a scarcity in knowledge and skills among all stakeholders, but also due to the shortage of scientific guidelines for how optimized tree selections are performed in practice. Thus, the aim of the thesis is to develop tools for optimizing practical ITS recommendations for Norway spruce.Tree position data for model fitting were collected from five trial sites in southern Sweden, one of which was documented with terrestrial laser scanning to get crown shape data for knot size modelling. A method that optimizes the target diameter dependent on the discount rate and the degree of the local competition exposed to the subject tree, was developed. Technically, a defined adaptive control function was optimized with full system stochastic simulation and with expected present value as the objective function variable. Since the quality of the optimization is dependent on the quality of the models in the simulation, priority was given to the evaluation and development of the central models. Available individual tree growth models were tested and evaluated with tree data from long term uneven-sized trial plots. Furthermore, new individual-tree distance-dependent growth models were developed for uneven-sized Norway spruce. A modelling framework, for prediction of the largest knot size per stem height section, was developed to provide means of simulating log quality depending on impact from local tree competitors.The results indicated that the thinning intensity in uneven-sized stand structures may be used to actively control the transition point where smaller diameter classes are subjected to suppressed growth. The evaluation of the Swedish individual-tree growth models which are included in the HEUREKA forest simulator, showed underestimation of large trees and overestimation of small trees. The underestimation is smaller or absent in denser forests for diameter classes above 40 cm. The new distance-dependent growth models are presented in two versions, one with and one without crown ratio as a predictor. The new growth models facilitate the testing of spatial decision criteria in ITS optimization. From the results of the ITS optimization, field operators can choose either a fixed level target diameteror a flexible target diameter that is adaptive to the degree of local competition surrounding the subject tree. Optimal fixed target diameters at breast height range from 33 cm to 23 cm depending on discount rate (1–3 %). A decision support structure for ITS is proposed.
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| 7. |
- Fagerberg, Nils, 1972-
(author)
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Kontinuitetsskogsbruk
- 2010
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In: Åter. - Gudhem. - 1650-3546. ; :4, s. 14-15
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Journal article (pop. science, debate, etc.)abstract
- Det finns alternativ för skogsägare som inte vill skapa ett kalhygge inpå husknuten och som vill värna de mossor, lavar, svampar och skalbaggar som hotas av det moderna skogsbruket. Kontinuitetsskogsbruk innebär att man hela tiden behåller ett trädskikt i den skötta skogen. Genom att bedömma och styra trädens inbördes förhållanden kan man använda skogens egna mekanismer till att med små medel få mycket virke till bra kvalitet ur sin skog -samtidigt som man har den kvar.
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| 8. |
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| 9. |
- Fagerberg, Nils, 1972-, et al.
(author)
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Prediction of knot size in uneven-sized Norway spruce stands in Sweden
- 2023
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In: Forest Ecology and Management. - : Elsevier. - 0378-1127 .- 1872-7042. ; 544
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Journal article (peer-reviewed)abstract
- The size of knots is negatively correlated with bending strength in sawn timber and it is therefore used as a quality grading criterion in national roundwood grading standards. Some standards even use the size of the largest knot as the sole estimate for individual log knottiness. The size of knots is determined by crown horizontal extension, which in turn is dependent on the impact of competing trees. Thus, with knot size models that are competition-dependent, roundwood quality due to knottiness can be simulated for different management al-ternatives. However, these types of models, calibrated on uneven-sized Norway spruce in Fennoscandia, are currently not available. Therefore, the objective of this study is to develop a competition-dependent model framework for prediction of the largest knot size per stem height section, for application within uneven-sized Norway spruce stands. Data from terrestrial laser scanning of an uneven-sized stand in southern Sweden are used to calibrate a modular prediction framework, consisting of interlinked allometric statistical models. Alternative framework sub-models are presented and the preferred model combination can be selected according to context and available input data. The flexible modular format enables further development of separate sub-components for adaptation to growing conditions not covered by the current calibration range.
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