Browsing by Author "Karlsson, K"

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    Height-diameter allometry for tree species in Tanzania mainland
    (Hindawi, 2019-02) Mugasha, W A; Mauya, E W; Njana, A M; Karlsson, K; Malimbwi, R E; Ernest, S
    Total tree height (H) and diameter at beast height (D) are important independent variables in predicting volume, biomass, and other forest stand attributes. However, unlike D measurement, which is easy to measure with high accuracy, H measurement is laborious. This study, therefore, developed H-D relationships for ten different forest types in Tanzania Mainland. Extents in which climate and forest stand variables explain the variation in H-D allometry were also assessed. A total of 31782 sample trees covering miombo woodlands, humid montane, lowland forests, bushlands, grasslands, mangroves, cultivated land, wetlands forests, and pines and Eucalyptus species plantations were used for model development. The H estimating model without climate and forest stand variables referred herein as “base model” was first developed followed by “generalized model” which included climate and stand variables. All the data were fitted using nonlinear mixed effect modelling approach. Results indicated that generalized H estimating models had better fit than the base models. We therefore confirm a significant contribution of climate and forest structure variables in improving H-D allometry. Among the forest structure variables, basal area (BA) was far more important explanatory variable than other variables. In addition, it was found that the mean tree H tends to increase with the increase of mean precipitation (PR A ). We therefore conclude that forest specific generalized H model is to be applied when predicting H. When forest type information is not available, generalized regional model may be applied. Base model may be applied when forest stand or climate information are missing.
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    Stump diameter : a potential predictor of removed biomass through tree cutting
    (Tanzania Journal of Forestry and Nature Conservation, 2021) Mugasha, W.A; Mauya, E; Karlsson, K; Malimbwi, R.E.
    Stump diameter (SD) has been rarely considered as an important tree parameter in forestry. It is until recently that SD has been found to be important predictor of tree diameter at breast height (D) and forest stand parameter such as volume and biomass. This study, developed D-SD relationships for nine different forest cover type in Tanzania mainland. A total of 32265 sample trees covering miombo woodlands, humid montane, lowland forests, bushlands, grasslands, mangroves, cultivated land, wetlands forests and plantations (Pines and Eucalyptus species) were used for fitting D-SD models. The findings revealed a linear relationship between D and SD for all forest covers. In addition, we found forest covers having similar D-SD allometry while others had unique D-SD allometry. This prompted fitting Generalised Linear Model where three forest cover groups were generated, i.e. group 1 (bushlands, woodlands, lowlands and grasslands); group 2 (mangroves, cultivated land, plantation and wetlands); and group 3 (humid montane). We fitted linear model to each forest cover group. Large variations in D were adequately explained by SD for each forest cover group. We further compared AGB values estimated from the measured D and estimated D from the D-SD equation. The estimated AGB from both approach did not differ significantly. We therefore, recommend the developed D-SD relationships models be applied to predict D of the missing trees for which their stumps still exist.