Conversions of woodland to smallholder agriculture decreases soil organic carbon and nutrient stocks in semi-arid southern Africa

Southern African drylands are characterized by rapid deforestation, among others, related to the ongoing conversion of woodland to smallholder agriculture through slash-and-burn practices. However, empirical data on the impacts of this land-use conversion on soil fertility is rare. Our study in NE Namibia and SW Zambia aimed at quantifying the changes in soil organic carbon (SOC) and nutrient stocks upon the conversion from woodland to smallholder agriculture. We selected a total of 11 sampling clusters with a 1-km radius from two landscapes that differed in soil characteristics. Each cluster contained one or two 30 m x 30 m plots in agricultural fields and one plot in woodland, which was the reference land use. Plots within a cluster were carefully selected to have similar topographic- and soil characteristics. The selected agricultural fields ranged in age from 2 to 26 years, here age was based on the first year of agricultural usage. Moreover, we only selected agricultural fields that were established immediately after clearing of the woodland. In each plot, we measured SOC and N, and other nutrient (P, K, Ca, Mg and Na) contents and stocks down to 1-m and 0.4-m depth, respectively. In both landscapes, we found that conversions from woodland to smallholder agriculture in NE Namibia and SW Zambia decreased the topsoil (0-10-cm depth) contents and stocks of SOC and the soil nutrients N, Ca and Mg. The SOC and soil nutrient losses increased with increasing age of the agricultural fields. Soil K and Na contents did not significantly differ between woodland and agriculture. The effect of this land-use conversion on P content was not consistent between the studied landscapes

Data from: Spatial variability in soil organic carbon in a tropical montane landscape: associations between soil organic carbon and land use, soil properties, vegetation, and topography vary across plot to landscape scales

Presently, the lack of data on soil organic carbon (SOC) stocks in relation to land-use types and biophysical characteristics prevents reliable estimates of ecosystem carbon stocks in montane landscapes of mainland SE Asia. Our study, conducted in a 10 000 ha landscape in Xishuangbanna, SW China, aimed at assessing the spatial variability in SOC concentrations and stocks, as well as the relationships of SOC with land-use types, soil properties, vegetation characteristics and topographical attributes at three spatial scales: (1) land-use types within a landscape (10 000 ha), (2) sampling plots (1 ha) nested within land-use types (plot distances ranging between 0.5 and 12 km), and (3) subplots (10 m radius) nested within sampling plots. We sampled 27 one-hectare plots – 10 plots in mature forests, 11 plots in regenerating or highly disturbed forests, and 6 plots in open land including tea plantations and grasslands. We used a sampling design with a hierarchical structure. The landscape was first classified according to land-use types. Within each land-use type, sampling plots were randomly selected, and within each plot we sampled within nine subplots. SOC concentrations and stocks did not differ significantly across the four land-use types. However, within the open-land category, SOC concentrations and stocks in grasslands were higher than in tea plantations (P < 0.01 for 0–0.15 m, P = 0.05 for 0.15–0.30 m, P = 0.06 for 0–0.9 m depth). The SOC stocks to a depth of 0.9 m were 177.6 ± 19.6 (SE) Mg C ha−1 in tea plantations, 199.5 ± 14.8 Mg C ha−1 in regenerating or highly disturbed forests, 228.6 ± 19.7 Mg C ha−1 in mature forests, and 236.2 ± 13.7 Mg C ha−1 in grasslands. In this montane landscape, variability within plots accounted for more than 50 % of the overall variance in SOC stocks to a depth of 0.9 m and the topsoil SOC concentrations. The relationships of SOC concentrations and stocks with land-use types, soil properties, vegetation characteristics, and topographical attributes varied across spatial scales. Variability in SOC within plots was determined by litter layer carbon stocks (P < 0.01 for 0–0.15 m and P = 0.03 for 0.15–0.30 and 0–0.9 m depth) and slope (P ≤ 0.01 for 0–0.15, 0.15–0.30, and 0–0.9 m depth) in open land, and by litter layer carbon stocks (P < 0.001 for 0–0.15, 0.15–0.30 and 0–0.9 m depth) and tree basal area (P < 0.001 for 0–0.15 m and P = 0.01 for 0–0.9 m depth) in forests. Variability in SOC among plots in open land was related to the differences in SOC concentrations and stocks between grasslands and tea plantations. In forests, the variability in SOC among plots was associated with elevation (P < 0.01 for 0–0.15 m and P = 0.09 for 0–0.9 m depth). The scale-dependent relationships between SOC and its controlling factors demonstrate that studies that aim to investigate the land-use effects on SOC need an appropriate sampling design reflecting the controlling factors of SOC so that land-use effects will not be masked by the variability between and within sampling plots

Acacia trees modify soil water dynamics and the potential groundwater recharge in savanna ecosystems

Global change puts increasing pressure on social-ecological systems. This book features outcomes of research of SASSCAL and aims to draw the attention of a broad readership. The presented studies provide assessments of the values of resources, analyse long term environmental changes, identify risks and challenges involved and offer solutions and pathways towards climate change adaptation and sustainable land management for southern Africa

General movements in early infancy predict neuromotor development at 9 to 12 years of age

Assessment of the quality of general movements (GMs) in early infancy is a powerful instrument to predict cerebral palsy (CP). The aim of the present study is to explore the value of GM assessment in predicting minor neurological dysfunction (MND) at 9 to 12 years of age. Two groups of infants were studied prospectively: 28 low-risk full-term infants (11 females, 17 males) and 24 high-risk infants, mostly born preterm (<37 weeks; 11 females, 13 males). In each group the quality of GMs (normal or abnormal) was assessed during two developmental periods: the age at which 'writhing' GMs occur (36 weeks' postmenstrual age to 7 weeks' postterm) and the age at which 'fidgety' GMs occur (8 to 17 weeks' postterm). Eight of 24 high-risk infants were diagnosed as having CP at 4 to 9 years of age. The remaining 44 children were followed-up at 9 to 12 years. In children without CP, quality of GMs at 'fidgety age' was related to neurological condition (normal, simple MND, complex MND) at follow-up (rho=0.46, p<0.01). Abnormal GMs at 'fidgety-GM age' showed a specific relationship to the development of coordination problems (chi2=6.1, p=0.01) and fine manipulative disability (Fisher, p<0.05) at 9 to 12 years. This finding supports the notion that the quality of GMs may provide information on the integrity of complex supraspinal circuitries

Deforestation for agricultural expansion in SW Zambia and NE Namibia and the impacts on soil fertility, soil organic carbon- and nutrient levels

Global change puts increasing pressure on social-ecological systems. This book features outcomes of research of SASSCAL and aims to draw the attention of a broad readership. The presented studies provide assessments of the values of resources, analyse long term environmental changes, identify risks and challenges involved and offer solutions and pathways towards climate change adaptation and sustainable land management for southern Africa