Articles, Conference and Workshop Papers Collection
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Browsing Articles, Conference and Workshop Papers Collection by Author "Bollandsås, O. M."
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Item Allometric models for prediction of above- and belowground biomass of trees in the miombo woodlands of Tanzania(Elservier, 2013-08-02) Mugasha, W. A.; Mugasha, W. A.; Eid, T.; Bollandsås, O. M.; Malimbwi, R. E.; Chamshama, S. A. O.; Zahabu, E.; Katani, J. Z.Miombo woodland is a significant forest type occupying about 9% of the African land area and forms a dominant vegetation type in many southeastern African countries including Tanzania. Quantification of the amount of carbon stored in forests presently is an important component in the implementation of the emerging carbon credit market mechanisms. This calls for appropriate allometric models predicting biomass which currently are scarce. The aim of this study was to develop above- and belowground allometric general and site-specific models for trees in miombo woodland. The data were collected from four sites in Tanzania and covers a wide range of conditions and tree sizes (diameters at breast height from 1.1 to 110 cm). Above- and belowground biomass models were developed from 167 and 80 sample trees, respectively. The model fitting showed that large parts of the variation (up to 97%) in biomass were explained by diameter at breast height and tree height. Since including tree height only marginally increased the explanation of the biomass variation (from 95% to 96–97% for aboveground biomass), the general recommendation is to apply the models with diameter at breast height only as an independent variable. The results also showed that the general models can be applied over a wide range of conditions in Tanzania. The comparison with previously developed models revealed that these models can probably also be applied for miombo woodland elsewhere in southeastern Africa if not used beyond the tree size range of the model data.Item Background on the Development of Biomass and Volume Models(E&D Vision Publishing Ltd, 2018-05-12) Bollandsås, O. M.; Zahabu, E.; Katani, J. Z.Item Biomass and volume models for different vegetation types of Tanzania(E&D Vision Publishing Ltd, 2016) Malimbwi, R. E.; Mauya, E. W.; Zahabu, E.; Katani, J. Z.; Chamshama, S. A. O.; Eid, T.; Bollandsås, O. M.; Maliondo, S. M. S.; Mugasha, W. A.; Masota, A. M.; Njana, M.; Makero, J. S.; Mshana, J. S.; Luganga, H.; Mathias, A.; Msalika, P.; Mwangi, J.; Mlagalila, H. E.Climate change and high rates of global carbon dioxide (CO2) emissions have increased the attention paid to the need for high-quality monitoring systems to assess how much carbon (C) is present in terrestrial systems and how these change over time. The choice of a system to adopt relies heavily on the accuracy of the method for quantifying biomass and volume as important primary variables for computing C stock and changes over time. Methods based on ground forest inventory and remote sensing data have commonly been applied in the recent decade to estimate biomass and volume in the tropical forests. However, regardless of the method, accurate tree level biomass and volume models are needed to translate field or remotely sensed data into estimates of forest biomass and volume. Therefore, the main goal of this study was to develop biomass and volume models for the forests, woodlands, thickets, agroforestry systems and some selected tree species in Tanzania. Data from destructively sampled trees were used to develop volume and above- and below-ground biomass models. Different statistical criteria, including coefficient of determination (R2), relative root mean square error (RMSE %) and Akaike Information Criterion (AIC), were used to assess the quality of the model fits. The models selected showed good prediction accuracy and, therefore, are recommended not only to support the ongoing initiatives on forest C Measurement, Reporting and Verificatio (MRV) processes but also for general forest management in Tanzania.Item Decision-support tool for management of miombo woodlands: a matrix model approach(SOUTHERN FORESTS, 2017-03-06) Mugasha, W. A.; Bollandsås, O. M.; Gobakken, T.; Zahabu, E.; Katani, J. Z.; Eid, T.Rational forest management planning requires information on the present forest state and on future development. However, forest management planning in Tanzania has often been done without any information on forest development because appropriate tools are lacking. This study presents a matrix model that combines distance-independent growth and mortality models, area-based recruitment models, and allometric models for prediction of volume and biomass. In this way forest development can be simulated according to different treatment options. A shortterm (seven years) test of the matrix model using independent data from permanent sample plots showed that the overall difference between predicted and observed basal area was small (6.5%). Long-term simulations (1 000 years) with the model showed that it was able to attain, irrespective of initial conditions, similar steady-state conditions (i.e. basal area, volume and biomass of 13 m2 ha−1, 130 m3 ha−1 and 90 t ha−1, respectively), which also correspond well to biological expectations in the ‘real’ miombo woodlands of the country. The flexibility of the model as a decision-support tool was demonstrated by simulating three harvesting options aiming at different combinations of charcoal and timber production. The model complexity is well adapted to the data quality and abundance, and it is dependent on proxies of some main drivers of the dynamic processes. The development of the matrix model is a step forward facilitating better decisions in the management of miombo woodlands. However, data ranges used for calibrating the submodels are limited in time and space, and future efforts should focus on tests and recalibrations based on extended data ranges. Presently, therefore, applications of the matrix model should be limited to the data ranges of the modelling data from the Iringa and Manyara regions.Item Modelling diameter growth, mortality and recruitment of trees in miombo woodlands of Tanzania(Southern Forests, 2016-11-24) Tron, E.; Mugasha, W. A.; Bollandsås, O. M.; Mbwambo, L.Miombo woodlands cover large areas in Tanzania but very little reliable data on forest dynamics for the woodlands exist. The main objective of this study was to develop a model system describing such dynamics based on easily measurable tree variables. Individual tree diameter growth and mortality models and area-based recruitment models were developed. The modelling was based on data from 117 permanent sample plots established between 1997 and 2009 on seven sites in the Iringa and Manyara regions. The data set comprised 2 314 trees at establishment and 4 758 observations of individual tree growth, and covered a large number of species (141). Based on diameter growth and by using a model-based clustering procedure, three tree species groups were developed. Several model forms with different independent variables were tested. Simple and robust models with few independent variables, which agreed with expected biological behaviour, were finally selected. Although biological behaviour was the principal model selection criterion, the models also performed well statistically. The developed model system, which is the first of its kind for miombo woodlands in Africa, may be used to develop a decision-support tool for practical forest management planning in the country.