No abstract

Fine roots are a major pathway of C input into soils. The aim of this study was to quantify fine root stocks, production and turnover in natural forest and land use systems converted from forests in Ethiopia. The study was conducted in a remnant Afromontane forest, eucalyptus plantation and grass and cropland in NW Ethiopia. Fine root dynamics were investigated using three different methods: sequential coring, in-growth cores and in-growth nets. Soil cores for sequential analyses were taken in quarterly intervals, while in-growth cores and nets were harvested corresponding to 1-, 2-, 3-, 4-, 5-, 8-and 12-month interval. Fine root stocks averaged 564, 425, 56 and 46 g•m −2 in the forest, eucalyptus, grazing land and cropland ecosystems, respectively. The values decreased exponentially with increasing soil depth. In forest and eucalyptus, fine root biomass and necromass were highest in the dry season. Estimates of fine root production differed according to the method used. Fine root production based on in-growth coring averaged 468, 293, 70 and 52 g m −2 •year −1. In general, land use conversion from forest to open lands reduced fine root production by 85-91%. The turnover rate of fine roots was 1.5 for forest and 2.1 for eucalyptus plantation.

Forest degradation due to land use change is a severe problem in Ethiopian Afromontane Forests. We investigated such degradation effects by comparing degraded agricultural land (previously covered with forest) with neighboring natural forests, 40 to 50 years after conversion. We selected four different study areas to cover the eco-climatic conditions of the Amhara region in Northwestern Ethiopia. For a paired-stand comparison we collected soil data on both land use types. We calculated forest biomass to evaluate the biogeochemical-mechanistic ecosystem model Biome-BGC, which is used as a diagnostic tool to assess the site and management impacts on productivity as well as ecosystem carbon and nitrogen accumulation. We applied Biome-BGC to assess rehabilitation options on such degraded land. Afromontane forests in the highlands of Ethiopia showed high soil C stocks, resulting from long lasting biomass accumulation. Removing the tree cover and converting forest areas to crop-or grassland, has led to a loss of 40-85% of the soil C stocks and thus a loss in soil fertility within only 40 to 50 years. Rehabilitation efforts by replanting trees will improve soil fertility, but may require over a thousand years to achieve a similar level in biomass and soil fertility versus the situation prior to the land use change.

The depletion of soil organic matter (SOM) reserve after deforestation and subsequent management practices are well documented, but the impacts of land-use change on the persistence and vulnerability of storage C and N remain uncertain. We investigated soil organic C (SOC) and N stocks in a landscape of chrono-sequence natural forest, grazing/crop lands and plantation forest in the highlands of North-West Ethiopia. We hypothesized that in addition to depleting total C and N pools, multiple conversions of natural forest significantly change the relative proportion of labile and recalcitrant C and N fractions in soils, and thus affect SOM quality. To examine this hypothesis, we estimated depletion of SOC and N stocks and labile (1 & 2) and recalcitrant (fraction 3) C and N pools in soil organic matter following the acid hydrolysis technique. Our studies showed the highest loss of C stock was in grazing land (58%) followed by cropland (50%) and eucalyptus plantation (47%), while on average ca. 57% N stock was depleted. Eucalyptus plantation exhibited potential for soil C recovery, although not for N, after 30 years. The fractionation of SOM revealed that depletions of labile 1 C stocks were similar in grazing and crop lands (36%), and loss of recalcitrant C was highest in grazing soil (56%). However, increases in relative concentrations of labile fraction 1 in grazing land and recalcitrant C and N in cropland suggest the quality of these pools might be influenced by management activities. Also, the C:N ratio of C fractions and recalcitrant indices (RIC and RIN) clearly demonstrated that land conversion from natural forest to managed systems changes the inherent quality of the fractions, which was obscured in whole soil analysis. These findings underscore the importance of considering the quality of SOM when evaluating disturbance impacts on SOC and N stocks.

Fine root turnover of trees is a major C input to soil. However, the quality of litter input is influenced by root morphological traits and tissue chemical composition. In this study, fine roots of ten tropical woody species were collected from an Afromontane forest in the northern highlands of Ethiopia. The fine roots were analysed for root morphological traits and tissue chemistry measured as proxy carbon fractionations. Based on stem increment, the 10 species were divided into faster-and slowergrowing species. Faster-growing species exhibited higher specific root length (1362 cm g -1 ) than slower-growing species (923 cm g -1 ). Similarly specific root area was higher in faster-growing species (223 cm 2 g -1) than in slower-growing species (167 cm 2 g -1). Among the carbon fractions, the acid-insoluble fraction (AIF) was the highest (44-51%). The carbon content, AIF, and the lignocellulose index were higher for slower-growing species. Root tissue density was lower in fastergrowing species (0.33 g cm -3 ) than slower-growing species (0.40 g cm -3 ) and showed a strong positive correlation with carbon content (r 2 = 0.84) and the AIF (r pearson = 0.93). The morphological traits of fine roots between faster-and slowergrowing species reflect the ecological strategy they employ. Slower-growing species have a higher tissue density which may reflect a greater longevity.

Ethiopian highland bamboo is a multipurpose and a fast growing plant that supports local livelihoods in many ways. It is a source of food, fodder, furniture, textile raw material, building material, industrial inputs, fuel and other purposes in Ethiopia. Physical properties are considered to be important factors in determining the suitability of bamboo for various applications. A sufficient knowledge of the physical properties of bamboo ensures safe design for materials used in service.  In this study, Effects of age and height on the basic density, moisture content, wall thickness and culm diameter of Ethiopian highland bamboo (Yushinia alpina) were studied on 2, 3 and 4 years-old bamboo. The result of the study show that four years old bamboo had the highest moisture content and wall thickness and the lowest density and culm diameter. Density and culm diameter did not show significant difference between 2, 3, and 4 years of old bamboo. However, variation in moisture content and wall thickness were observed between the three age groups. Density had greatest in bottom and lowest, in the top. There is no variation of moisture content, wall thickness and culm diameter at different height positions (Bottom, Middle and Top).

In the Ethiopian highlands, clearance of Afromontane dry forest and conversion to crop and grazing land lead to land degradation and loss of soil organic matter (SOM). Eucalyptus is often grown on degraded soils, and this results in the partial recovery of soil carbon stocks. The aim of this work was to assess the biological sources of SOM in this land-use sequence. In top-soils (0–10 cm) of four land-use systems, namely remnant natural forest, eucalyptus plantation, cropland, and grazing land, in the Ethiopian highlands, the origin of SOM was investigated. For this, a sequential extraction method was used, involving a solvent extraction, base hydrolysis, and a subsequent CuO oxidation. In these extracts, biomarkers (molecular proxies) were identified to characterize the SOM of the soil of the four land-uses. Putative lipid monomers of leaf, root, and microbial degradation products suggest that root inputs and microbial inputs dominate in SOM of all the land-uses, except grazing land. The ratios of syringyls, vanillyls, and cinnamyls showed that non-woody angiosperm plants were the predominant source for lignin in eucalyptus, cropland, and grazing land soil. In the soils of the natural forest, lignin originates from both woody angiosperms and woody gymnosperms. Our study shows the importance of root and microbial inputs in the formation of SOM, but also that, in the natural forest, legacies of previous forest cover are present.

This study was carried out in Tarmaber district north shewa zone Ethiopia to determine the effect of plantation forest with management intervention on woody plant species diversity, regeneration and soil seed bank species composition in five different forest types, which are adjacent natural forest, managed Cupressus lusitanica, unmanaged C. lusitanica, managed Eucalyptus globules and not managed E. globules plantation forests. A total of 75 circular sample plots of 314 m2 were established along a transect lines. Soil seed bank analysis was done from soil samples collected in each of the plots (225 samples) to examine the similarity between the soil seed bank and aboveground flora. Different diversity index and ANOVA was used in SPSS software for analysis. The result showed that a total of 51 woody plant species was recorded in adjacent natural forest (41), managed C. lusitanica (27), not managed C. lusitanica (9), managed E. globules (22) and not managed E. globules (13) species. Regeneration of seedlings were 3538, 5567, 707, 1462 and 2524 mean stems ha− 1 for natural forest, managed C. lusitanica, not managed C. lusitanica, managed E. globules and not managed E. globules respectively. Unmanaged C. lusitanica plantations had significantly lower densities of mature tree stems ha− 1 as compared to managed C. lusitanica, managed E. globules and adjacent natural forest (F = 14.03, p < 0.05).Similarly in terms of sapling density ha− 1 unmanaged C. lusitanica was significantly lower from other forest types (F = 7.37, p < 0.05). However managed C. lusitanica had significantly higher seedling regeneration (stem density ha− 1) than other plantation and adjacent natural forests (F = 16.11, p < 0.05). Generally mean stem densities including tree, sapling and seedling of woody species among different forest types managed C. lusitanica was significantly higher among different forest types (F = 13.01, p < 0.05). From the soil seed bank a total of 22 plant species (20 native and 2 exotic) species were recovered. In different forest types the number of species recorded was in adjacent natural forest (19), managed C. lusitanica (11), unmanaged C. lusitanica (4), managed E. globules (7) and unmanaged E. globules (5). The similarity of the oil seed bank was more or less similar to the above ground flora with maximum Sorenson’s similarity values of 0.633. Generally with appropriate management intervention undergrowth vegetation and soil seed bank status in plantation forest had good species composition and diversity.