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- Ogana, Friday Nwabueze, et al.
(författare)
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Optimizing height measurement for the long-term forest experiments in Sweden
- 2023
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 532
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Tidskriftsartikel (refereegranskat)abstract
- Information on tree height is useful for volume estimation and site productivity assessment and as such, remains one of the most important variables often measured in forest inventories. Measuring a sufficient number of sample trees requires considerable sampling effort and cost. In this study, we developed height functions for optimizing tree height measurement in the Swedish long-term forest experiments (LTFEs). Two large datasets from the LTFE databases: fitting data (from thinning, fertilisation and mixed species experiments) and validation data (tree species and spacing experiments) collected over several decades were used. The fitting and validation data comprise 133,788 and 68,440 observations, respectively, each covering a large range of growth and environmental conditions across Sweden. A multilevel nonlinear mixed-effects modelling approach was used to build the generalised height functions for Scots pine, Norway spruce, birch (Silver and Downy birch united), other conifers and other broadleaves, considering variations in heights and other stand characteristics at sample plot-level and revision-level. The response calibration of the functions was first carried out with all measured heights of the validation data, and second, using heights of one to six sample trees obtained from different tree selection strategies (diameter extremes, largest diameters, and smallest diameters). The mixed-effects height functions explained most of the height variations in the fitting dataset (pseudo R2: 0.938 - 0.970; RMSE: 0.957 - 1.363 m) without any residual trends. The validation showed that the functions accounted for 95 - 98 % of the height variation in the validation dataset, with RMSE ranging between 0.770 and 1.040 m, confirming the functions' high accuracy. We recommend the measurement of four sample tree heights based on diameter ex-tremes as the ideal threshold for response calibration. These functions and the suggested sampling technique would reduce sampling effort and inventory cost of height measurements for subsequent inventories of the LTFEs.
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| 2. |
- Ogana, Friday Nwabueze
(författare)
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Vessel characterization and ring-width of a multipurpose agroforestry tree species (Garcinia kola.(Heckel)) and its relationship with climate in Nigeria
- 2024
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Ingår i: Trees - Structure and Function. - 0931-1890 .- 1432-2285. ; 38, s. 139-150
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Tidskriftsartikel (refereegranskat)abstract
- Tropical agroforestry species are characterized by irregular growth and fruiting pattern, this is because of seasonal differences in the region and unanticipated environmental changes. Tree-ring width features and vessel variables could have a direct relationship with environmental conditions and factors such as precipitation and temperature could impact the growth of the species. This is because, during stressful environmental conditions, tree species record environmental changes through their physiological adjustment. Therefore, wood anatomical and tree-ring width time series was developed for Garcinia kola, a multipurpose tropical species, from a humid forest zone and derived savannah, along two vegetation zones in Nigeria. The species forms rings characterized by marginal parenchyma. The mean tree-ring width (TRW) ranges from 2.63 and 2.30 mm in the humid forest zone and derived savannah, respectively while the vessel number (VN) and vessel density (VD) are 95, 93, and 9.46, and 10.28 N/mm(2) respectively. The results revealed that the radial growth of G. kola showed a positive relationship with the precipitation and the minimum temperature during the peak of the rainy season in derived savannah areas. The VN, RW, and TVA show a significant relationship with the mean annual maximum temperature in the Rainforest and derived savannah area. The vessels are more abundant in samples from the rainforest area than in the derived savannah area, the results revealed that the wood anatomical variables and TRW were sensitive to climatic variables. Hence, they could be good indicators for evaluating tropical tree responses to environmental changes in tropical agroforestry species.
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