Trajectory Analysis of Forest Cover Change in the Tropical Dry Forest of Burkina Faso,West Africa

Forest cover decline is one of the most important environmental issues in the tropics. The present study was carried out in Burkina Faso, West Africa, and aimed at assessing the trajectories of forest cover change and measuring landscape metrics of the trajectory classes in order to better understand the processes of change. Landsat and ASTER images acquired over a period of 30 years were used for cover change detection and the Fragstats package was used to compute landscape metrics with five unifying change classes. Results showed a substantial increase in cropland with concurrent decline in forest cover. Deforestation represented 63% of the Percentage of Landscape (PLAND) in 2006, while reforestation accounted for only 28%. Both of these classes had high Normalized Landscape Shape Index (NLSI) values, indicating that they were present as scattered small patches. The old cultivation (30-year permanent cropland) was aggregated (IJI ≈ 0) while deforestation exhibited highly interspersed patches. The old forest and old cultivation presented lower Area Weighted Fractal Dimension Index (FRAC_AM), but deforestation and reforestation had the higher FRAC_AM. These results confirmed that there was a high level of deforestation and fragmentation in southern Burkina Faso and justify the need for a proper management plan to ensure the sustainable use of forest resources.     

Low temperature sintering of (Ba0.85Ca0.15) (Ti0.90Zr0.10)O3 lead-free piezoceramic with the additive of MnO2

Lead-free (Ba_0.85Ca_0.15) (Ti_0.90Zr_0.10)O₃ (15/10 BCZT) piezoelectric ceramics were prepared by a standard solid solution and sintered at different temperature of 1300 °C and 1500 °C at a time. The 15/10BCZT piezoceramics were prepared at 1300 °C sintering temperature by doping different amount of MnO₂.The ceramics show a phase transition from a freoelectric tetragonal phase to a rhombohedral and tetragonal ferroelctric phase and to a single rhombohedral phase with increasing MnO₂ content. The addition of MnO₂ significantly improves the sinterbility of the 15/10BCZT piezoceramics, and reducing the sintering temperature from 1500 °C to 1300 °C by 200 °C but showing comparable piezoelectric properties. With 0.4 mol% of the dopant, ～96.5% of the theoretical density of the ceramics was achieved with excellent piezoelectric coefficient d₃₃ ~ 534pC/N, which is nearly equal to the value obtained from the ceramics sintered at 1500 °C which has a piezoelectric coefficient d₃₃ ~ 570pC/N, high density (~ 5.59 g/cm³), maximum remnant polarization (P_r = 24 μC/cm²), relatively large grain size (10.4 μm) and the least coercieve field (E_c = 0.42 kV/mm). However, a high concentration of MnO₂ deterioated the properties of the ceramics because of increasing of oxygen vacancies and associated defects. The results indicate that the BCTZ-y mol% MnO₂ ceramics are one of the promising lead-free piezoelectric candidates for high temperature applications.

     

Systematic and random transitions of land-cover types in Burkina Faso,West Africa

In-depth statistical analysis of forest transition between land-cover types over time can reveal the dominant signals of landscape transformation, which are needed in order to develop appropriate land management strategies. We applied a recently developed methodology to analyse the transition matrix of six land-cover classes, derived from 1986 and 2002 Landsat images of an area of 15?675 km² in southern Burkina Faso. Results show that most landscape transformations followed a systematic process. In addition, some transitions occurred as an apparently random process, probably caused by uncommon or sporadic events. Degradation of woodland to shrub-/grassland over 15.7% of the landscape, increases in biomass from woodland to dense forest on 10% of the landscape and conversion of 6% of the landscape from shrub-/grassland to cropland were the dominant signals of forest-cover transitions. From a planning perspective, the dominance of systematic processes should facilitate regional land-use planning and sustainable forest management in a context of immigration and agricultural intensification.