1,721,671 research outputs found
Veranderingen in populaties van soorten in functie van de tijd en de mechanismen die deze veranderingen sturen
No full textsponsorship: Agentschap voor Natuur en Bosstatus: Publishe
Implications of Country-Level Decisions on the Specification of Crown Cover in the Definition of Forests for Land Area Eligible for Afforestation and Reforestation Activities in the CDM
No full text
Effectiveness of exclosures to control soil erosion and local community perception on soil erosion in Tigray, Ethiopia
No full textThe study investigated how effective exclosures are in the fight against soil erosion and how they are perceived as a means to control soil erosion by the local community (farmers and local experts). The universal soil loss equation (USLE) used to estimate potential soil erosion. Data on local community perception obtained from a survey of 62 farm households and five local experts. In-depth interview, group discussion and non-participant field observation also carried out to obtain additional information. The USLE results agreed with the farmers’ (67%) and local experts’ opinion that erosion at study area is severe and affects the quality of lives of residents. Insignificant difference (p > 0.05) was observed in the estimated soil loss among treatments. However, the estimated soil loss from free grazing lands was higher by 47% than soil loss from exclosures which illustrated that exclosures are effective to control soil erosion. The majority of farmers (70%) also rated exclosures effectiveness to control soil erosion as high. Local communities were optimistic about the chances to rehabilitate degraded lands and make them productive. The majority of farmers (60%) did not consider population growth as a cause of soil erosion. For the majority of interviewed farmers, poor land management is more important. Efforts to create awareness within the rural communities should focus on the link between high population growth, environmental degradation and poverty. The optimistic view of local communities can be considered as an asset for the planning and development of degraded lands rehabilitation efforts
Improving the knowledge base for tropical dry forest management in southern Africa: Regional volume models for <i>Pterocarpus angolensis</i>
No full textThe development of site-specific allometric models for tree species of natural tropical forests is hampered by limited resources while there is little quality control of the models developed. This study compares site- and species-specific models with generic and regional or pantropical models for Pterocarpus angolensis, the most widely exploited timber tree of southern Africa. We developed regional models with diameter at breast height (DBH) and tree height for the total and merchantable wood volume of P. angolensis with a dataset of 415 trees collected by destructive and non-destructive methods at 14 different sites in the Baikiaea – Pterocarpus woodlands of Namibia and southern Angola. Sources of data heterogeneity, such as site, collector and method, were investigated using mixed models and climate variables as model predictors. The study compared the ability of the new models with ten other site and species-specific volume models and nine generic volume and biomass models to estimate wood volume at tree and stand level. Stand data of 129 sample plots, representing a rainfall gradient from 480 mm to 750 mm, were used. Results showed that the three best performing models with DBH as single predictor (error 28% − 30%), including our new model, were developed for Namibia and Zambia. Adding tree height as predictor to our model removed the heterogeneity caused by site and reduced the error to 22%. One regional generic and one pantropical generic model, both with tree height, performed as well and outperformed other Pterocarpus specific models. Our models showed that the mean portion of merchantable wood was 35% of the total wood volume, of which 58% was heartwood. Although addition of climate variables improved our models, they did not perform well at stand level. Estimated merchantable volume of P. angolensis at stand level varied from 1.9 to 2.7 m³ ha⁻¹, depending on the models employed. Total growing stock is estimated between 36 and 52 m³ ha⁻¹ in our study area, depending on the model, with the contribution of P. angolensis approximately 13%. Our results suggest that site-specificity of models is needed when they only include DBH. The use of pantropical and regional DBH-height based models that are adapted to site conditions through the collection of accurate height and wood density data for biomass conversion factors, is advised rather than developing site-specific DBH based allometric models.sponsorship: We acknowledge the support and data of the Namibian Directorate of Forestry (DoF) and especially would like to mention the assistance of the late Dr Alex Verlinden and Dr Jonathan Kamwi. We are thankful to Cori Ham, Miya Kabajani and Jolien De Ruytter for their contributions to fieldwork. We thank two reviewers for their valuable comments. Some of the fieldwork was part of The Future Okavango (TFO) project or the SASSCAL project, funded by the German Federal Ministry of Education and Research under promotion numbers 01 LL 0912 A and 01 LG 1201M respectively. The Hans Merensky Stipendienstiftung of Germany funded a field trip that also contributed data to this study. (German Federal Ministry of Education and Research|01 LL 0912 A, German Federal Ministry of Education and Research|01 LG 1201M, Hans Merensky Stipendienstiftung of Germany, Namibian Directorate of Forestry (DoF))status: Publishe
- …
