Browsing by Author "Kilawe, Charles Joseph"

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Comparison of multi-source remote sensing data for estimating and mapping above-ground biomass in the West Usambara tropical montane forests
(Elsevier B.V., 2023-06) Madundo, Sami Dawood; Mauya, Ernest; Kilawe, Charles Joseph
Above-ground biomass (AGB) estimation is important to better understand the carbon cy- cle and improve the efficiency of forest policy and management activities. AGB estimation models, using a combination of field data and remote sensing data, can largely replace traditional survey methods for measuring AGB. There are, however, critical steps for map- ping AGB based on satellite data with an acceptable degree of accuracy, such as choice of remote sensing data, the proper statistical modelling method, and remote sensing pre- dictor variables, at known field locations. This study sought to identify the optimal op- tical and synthetic aperture radar (SAR) remote sensing imagery from five sensors (Plan- etScope, Sentinel-2, Landsat 8 OLI, ALOS-2/PALSAR-2, and Sentinel-1) to model 159 field- based AGB values from two montane forests under semiparametric (Generalized Additive Model; GAM) and non-parametric (eXtreme Gradient Boosting; XGB) approaches using in- formation from four groups of predictor variables (spectral bands/polarizations, vegetation indices, textures, and a combination of all). The study’s results showed that PlanetScope (rRMSE = 69.19%; R 2 = 0.161) was the most precise optical sensor while ALOS-2/PALSAR-2 (rRMSE = 70.76; R 2 = 0.165) was the most precise amongst the SAR sensors. XGB mod- els generally resulted in those with lower prediction errors as compared to GAMs for the five sensors. Models having textures of vegetation indices and polarization bands achieved greater accuracy than models that incorporated spectral bands/polarizations and vegeta- tion indices only. The study recommends that PlanetScope and ALOS-2/PALSAR-2 remote sensing data using the XGB-based technique is an appropriate approach for accurate lo- cal and regional estimation of tropical forest AGB particularly for complex montane forest ecosystems.
The impact of the invasive tree cedrela odorota on the electric blue gecko (Lygodactylus williamsi) and its habitat (Pandanus rabaiensis) in Kimboza forest reserve, Tanzania
(Elsevier B.V., 2022-01) Kilawe, Charles Joseph; Mchelu, Hadija Ahmad; Emily, Cosmas John
Non-native plants are a major cause of habitat loss and fragmentation that lead to biodiversity loss. Geckos are particularly vulnerable to habitat alterations due to their small range and their restricted and specific terrestrial habits. However, our understanding of how introduced plants affect geckos, is poor. In this study, we investigate the potential effects of non-native and invasive neo-tropical tree Cedrela odorata on the critically endangered electric blue gecko, Lygodactylus williamsi, and its sole habitat, Pandanus rabaiensis. We used 107 square (10 m x 10 m) sample plots distributed systematically throughout the forest to assess the extent and effects of C. odorata on P. rabaiensis forest patches. We compared the abundance of L. williamsi on 125 P. rabaiensis trees growing in a mixture with C. odorata, native trees, and in pure stands and at three canopy cover categories (0–30%, >30–50%, and > 50%). We found an inverse relationship between the abundance of C. odorata trees (diameter at breast height (DBH)> 10 cm) and the abundance of P. rabaiensis. Spatially, the two trees dominated different parts of the forest. In contrast, the abundance of L. williamsi was not significantly affected by the presence of C. odorata. However, change in the canopy cover of the trees growing above the P. rabaiensis significantly affected the abundance of L. williamsi. The abundance of L. williamsi in a 0–30% cover was significantly higher than 30–50% and > 50% canopy covers. The findings of this study suggest that if left unmanaged, C. odorata could continue to take up the space that could be occupied by P. rabaiensis and other native plants, and thus limit the population size of an endangered species.
Linking ground forest inventory and NDVI in mapping above ground carbon stock in kasane forest reserve, Botswana
(Scientific Research Publishing, 2018) Basalumi, Lesika; Kilawe, Charles Joseph; Mauya, Ernest William
Quantification of the above ground carbon stock (AGC) is important in sus- tainable forest management and policy advice on climate change mitigation. Traditional ground vegetation survey methods have been used to provide data for estimation of AGC stock but constrained by inadequate time and often too costly. Remote sensing when combined with few ground collected data has the potential of improving forest resource assessment even though this opportu- nity has not well been utilised. In this study, we mapped AGC through com- bination of ground survey data collected from 51 permanent sapling plots with Normalized Difference Vegetation Index (NDVI) derived from Landsat 5 Thematic Mapper image. Linkage of the two data sources was made during a training stage of supervised classification. The overall classification accuracy was 98%, suggesting that reliable estimate of AGC for a large area can be made through combination of medium resolution satellite imagery and few samples from the ground.
Prosopis juliflora management and grassland restoration In baringo county, Kenya: opportunities for soil carbon sequestration and local livelihoods
(John Wiley & Sons Ltd, 2021) Eschen, René; Bekele, Ketema; Mbaabu, Purity Rima; Kilawe, Charles Joseph
Climate change, land degradation and invasive alien species (IAS) threaten grassland ecosystems worldwide. IAS clearing and grassland restoration would help to reduce the negative effects of IAS, restore the original vegetation cover and sustain liveli- hoods while contributing to climate change mitigation, but uncertain financial ben- efits to local stakeholders hamper such efforts. This study assessed where and when net financial benefit could be realized from Prosopis juliflora management and subse- quent grassland restoration by combining ecological, social and financial information. 2. Impacts of Prosopis invasion and grassland degradation on soil organic carbon (SOC) Handling Editor: Rafael Zenni in nine sublocations in Baringo County, Kenya, were evaluated. Then the financial impacts of Prosopis removal and grassland restoration in the area were calculated and spatially explicit management scenarios for each sublocation modelled, combin- ing geographical information derived from satellite images taken in different years of the invasion with SOC data and socio-economic data collected in the sublocations. 3. The expanding Prosopis distribution and density since 1995 have increased cumu- lated SOC storage on former bare land or degraded grasslands. On former pristine or restored grasslands, however, Prosopis invasion has reduced total SOC storage. 4. Prosopis removal and grassland restoration are predicted to yield financial benefits through charcoal made from removed trees, increased cattle numbers and carbon credits. However, a trade-off between increased SOC and net financial benefit was found. The predicted net SOC increase would contribute around one-tenth, at most, to the net financial benefit. 5. The available budget, based on Baringo households’ average willingness to pay, would enable removal, on average, of one-fifth of Prosopis per sublocation in a single year. A larger area can be cleared if Prosopis is sparse than if it is dense. The analyses show that in some sublocations, households’ annual investments could result in restoration of all former grassland areas. 6. Synthesis and applications. This study shows how integrating and linking detailed ecological, social and financial geodata to develop accurate and realistic invasive alien species management scenarios can illustrate costs and benefits of manage- ment interventions in a spatial context. Such scenarios should be used more exten- sively to support land management decisions.
Rooting pattern of acacia mangium in pure and mixed stands of eucalyptus camaldulensis, Tectona grandis and casuarina montana in the coastal Tanzania
(Boku University, 2011) Kilawe, Charles Joseph
This study investigates if Tectona grandis, Casuarina montana and Eucalyptus camaldulensis planted in mixture with Acacia mangium would send their roots toward Acacia in attempt to benefit from its symbiotic nitrogen fixation ability and also to investigate if the roots of mixed tree species would occupy different vertical soil layers for better utilization of site resources. A soil core method was used for root and soil sampling in a 22 months old mixed stand of E. camaldulensis (E), C. montana (C), T. grandis (T) and A. mangium (A) in a 1A:8A; 1A:8E; 1A:8T; 1A:8C; 1E: 8A; 1T:8A and 1C: 8A species combination replicated at three sites. Lateral distribution showed a decreasing root biomass with increasing distance from the tree stem. The highest total root biomass was obtained at 20 cm distance reaching 306.05 g m -2 for Acacia, 229.19 g m -2 for Eucalyptus 156.5 g m -2 for Tectona and 127.0 g m -2 for Casuarina. The lowest total root biomass was observed at 180 cm distance reaching 5.44 g m -2 for Acacia and 0.01 g m -2 for Eucalyptus, Casuarina and Tectona. Lateral spread of other species was higher in the upper layer (0-10 cm) with high density of A. mangium and high in the lower layer (10-20 cm) with low density of A. mangium in the species combination. Vertical distribution revealed a decrease in root biomass with increasing soil depth for all species except T. grandis. Mean root biomass decreased from 162.41 (acacia) to 4.58 g m -2 (teak) in the 0-10 cm layer to 90.26 (acacia) to 5.40 (casuarina) g m -2 in the 10-20 cm layer. Also fine root biomass was high in the upper layer and coarse root biomass was high in the lower layer. It is concluded that, there was not sufficient evidence of other species sending their roots toward A. mangium but there was clear vertical niche separation between A. mangium and other species, particularly with T. grandis