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Abstract:

Erica is a dominant vegetation type in many sub-afroalpine ecosystems, such as the Bale Mountains in Ethiopia. However, the past extent of Erica is not well known and climate versus anthropogenic influence on altitudinal shifts are difficult to assign unambiguously, especially during the Holocene. The main objective of the present study is to chemotaxonomically characterize the dominant plant species occurring in the Bale Mountains using lignin phenols and n-alkane biomarkers and to examine the potential of those biomarkers for reconstructing vegetation history. Fresh plant material, organic layer and mineral topsoil samples were collected along a northeastern and a southwestern altitudinal transect (4134–3870 and 4377–2550ma.s.l., respectively). Lignin-derived vanillyl, syringyl and cinnamyl phenols were analyzed using the cupric oxide oxidation method. Leaf-wax-derived n- alkanes were extracted and purified using Soxhlet and aminopropyl columns. Individual lignin phenols and n-alkanes were separated by gas-chromatography and detected by mass spectrometry and flame ionization detection, respectively. We found that the relative contributions of vanillyl, syringyl and cinnamyl phenols allow us to chemotaxonomically distinguish contemporary plant species of the Bale Mountains. Erica in particular is characterized by relatively high cinnamyl contributions of > 40 %. However, litter degradation strongly decreases the lignin phenol concentrations and completely changes the lignin phenol pat- terns. Relative cinnamyl contributions in soils under Erica were < 40 %, while soils that developed under Poaceae (Festuca abyssinica) exhibited relative cinnamyl contributions of > 40 %. Similarly, long-chain n-alkanes extracted from the leaf waxes allowed for differentiation between Erica versus Festuca abyssinica and Alchemilla, based on lower C31 =C29 ratios in Erica. However, this characteristic plant pattern was also lost due to degradation in the respective O layers and Ah horizons. In conclusion, although in modern-day plant samples a chemotaxonomic differentiation is possible, soil degradation processes seem to render the proxies unusable for the reconstruction of the past extent of Erica on the Sanetti Plateau, Bale Mountains, Ethiopia. This finding is of high relevance beyond our case study.

Abstract:

Aim: One objective was to quantify the impact of the Giant Mole Rat (Tachyoryctes macrocephalus) on vegetation communities and their composition. A second objective was to assess plant biomass (plant volume) via photography at the Sanetti Plateau. Third objective was to assess spatial distribution of the Giant Mole Rat across the Bale Mountains. In order to do that a predictive model has been applied. Location: Bale Mountains in south-eastern Ethiopia. Taxon: Tachyoryctes macrocephalus (Spalacideae). The species is related to other rats in eastern Africa and endemic to the Bale Mountains. Methods: The vegetation was sampled using a paired plot design along a transect from the southern to the northern rim of Sanetti Plateau and at sites where Giant Mole Rats were most abundant. Therefore, a total of 94 plots were established, 47 on Giant Mole Rat mounds and 47 in the zonal vegetation as control plots. Species identification and vegetation cover was investigated and photographs taken for further analysis of plant biomass. GPS data of around 1200 Giant Mole Rat mounds were recorded in order to upscale points on a larger area and detect the distribution of the Giant Mole Rat across the Bale Mountains. For that purpose Sentinel-2 satellite data was used with spatial resolution of 10 m, using a Forward Feature Selection. Results: We found out that the Giant Mole Rat is distributed across the whole Afroalpine zone of the Bale Mountains. It concentrates on the northern part of the Sanetti Plateau, in Sodota and Morebawa in wet and swampy habitat structures. Giant Mole Rats cover an area of 8301,16 ha and an estimated population density of 22 individuals/ha via upscaling could be proved. The Giant Mole Rat provides advantages to plants that require mixed and heterogen soil characteristics. The genera of Alchemilla and Salvia are examples for that and could be found on a major part of the Giant Mole Rat mounds. The genus of Helichrysum is abundant in the normal vegetation pattern and is almost completely absent on the Mole mounds. The presence of Helichrysum causes higher plant volume in the normal vegetation, which is 1,7 times higher than on the Mole mounds. Main conclusions: Giant Mole Rats change habitat and plant community structures. Shrub or woody plants do not occur on Giant Mole Rat mounds. The Giant Mole Rat is distributed across the whole Sanetti but most abundant in the northern part of Sanetti, Sodota and Morebawa. It prefers wet and swampy habitat.

Abstract:

The Bale Mountains of Ethiopia are a biodiversity hot spot in the south-eastern African highlands. Human pressure on the ecosystem strongly increases steadily because of a vast growing population of that region and the people's dependence on natural resources. The main impact of human land use is initial burning which shapes a whole vegetation zone: The Ericaceous belt. A plethora of research was and is conducted to analyze where fire has been and is set, to identify fire hot spots - areas which are very likely to be burnt - and ultimately to develop a fire management plan which might be applied in the future. Yet, the effect fire has on the vegetation of the Ericaceous belt of the Bale Mountains is unknown. In my study, I investigate the present post-fire floristic composition of the Ericaceous belt and identify the drivers of its dynamics. Especially altitude, climatic conditions and regeneration time as well as browsing by livestock were examined pertaining to their effect on vegetation's recovery. Data was first generated through vegetation assessment then subsequently through plant identification and analyzed by linear ordination methods. The vegetation's age was revealed applying different age methods of remote sensing, interviews and dendrochronology. In the whole Ericaceous belt not a single unburnt area was detected. The oldest recorded vegetation was determined to be 25 years old. Within these 25 years of regeneration no significant changes in floristic composition occurred. Little variation in floristic composition within the vegetation zone could be observed and was mainly associated with the slope of the mountains while elevation was of the second largest impact. Age, inclination, distance to settlements and browsing of the youngest vegetation additionally affected the species composition. Up to 70 % of variation of the floristic composition in the recently burnt areas and 50 % in older vegetation were associated with these variables. The name-giving Erica regenerated by resprouting from fire-surviving biomass. It's growth of height showed large variability in the researched areas and was directly and indirectly related to livestock browsing. With the baseline of information on post-fire vegetation recovery which I provide, I aim to contribute to prove that the current Ericaceous belt - contrary to previous considerations - does not consist of natural vegetation but was rather shaped by humans for a long time.

Abstract:

The hydrogen isotopic composition of leaf wax–derived n-alkane (δ2Hn-alkane) and oxygen isotopic composition of hemicellulose–derived sugar (δ18Osugar) biomarkers are valuable proxies for paleoclimate reconstructions. Here, we present a calibration study along the Bale Mountains in Ethiopia to evaluate how accurately and precisely the isotopic composition of precipitation is imprinted in these biomarkers. n-Alkanes and sugars were extracted from the leaf and topsoil samples and compound–specific δ2Hn-alkane and δ18Osugar values were measured using a gas chromatograph–thermal conversion–isotope ratio mass spectrometer (GC–TC–IRMS). The weighted mean δ2Hn-alkane and δ18Osugar values range from − 186 to − 89‰ and from + 27 to + 46‰, respectively. Degradation and root inputs did not appear to alter the isotopic composition of the biomarkers in the soil samples analyzed. Yet, the δ2Hn-alkane values show a statistically significant species dependence and δ18Osugar yielded the same species–dependent trends. The reconstructed leaf water of Erica arborea and Erica trimera is 2H– and 18O–enriched by + 55 ± 5 and + 9 ± 1‰, respectively, compared to precipitation. By contrast, Festuca abyssinica reveals the most negative δ2Hn-alkane and least positive δ18Osugar values. This can be attributed to “signal–dampening” caused by basal grass leaf growth. The intermediate values for Alchemilla haumannii and Helichrysum splendidum can be likely explained with plant physiological differences or microclimatic conditions affecting relative humidity (RH) and thus RH–dependent leaf water isotope enrichment. While the actual RH values range from 69 to 82% (x̄ = 80 ± 3.4%), the reconstructed RH values based on a recently suggested coupled δ2Hn-alkane –δ18Osugar (paleo–) hygrometer approach yielded a mean of 78 ± 21%. Our findings corroborate (i) that vegetation changes, particularly in terms of grass versus non–grassy vegetation, need to be considered in paleoclimate studies based on δ2Hn-alkane and δ18Osugar records and (ii) that the coupled δ2Hn-alkane –δ18Osugar (paleo–) hygrometer approach holds great potential for deriving additional paleoclimatic information compared to single isotope approaches.