Fire is the most frequent disturbance in the Ericaceous Belt ( ca 3000–4300 m.a.s.l.), one of the most important plant communities of tropical African mountains. Through resprouting after fire, Erica establishes a positive fire feedback under certain burning regimes. However, present-day human activity in the Bale Mountains of Ethiopia includes fire and grazing systems that may have a negative impact on the resilience of the ericaceous ecosystem. Current knowledge of Erica –fire relationships is based on studies of modern vegetation, lacking a longer time perspective that can shed light on baseline conditions for the fire feedback. We hypothesize that fire has influenced Erica communities in the Bale Mountains at millennial time-scales. To test this, we (1) identify the fire history of the Bale Mountains through a pollen and charcoal record from Garba Guracha, a lake at 3950 m.a.s.l., and (2) describe the long-term bidirectional feedback between wildfire and Erica, which may control the ecosystem's resilience. Our results support fire occurrence in the area since ca 14 000 years ago, with particularly intense burning during the early Holocene, 10.8–6.0 cal ka BP. We show that a positive feedback between Erica abundance and fire occurrence was in operation throughout the Lateglacial and Holocene, and interpret the Ericaceous Belt of the Ethiopian mountains as a long-term fire resilient ecosystem. We propose that controlled burning should be an integral part of landscape management in the Bale Mountains National Park.

Previous paleolimnological studies demonstrated that the sediments of Garba Guracha, situated at 3950 m asl in the afro-alpine zone of the Bale Mountains of Ethiopia, provide a complete Late Glacial and Holocene paleoclimate and environmental archive. We revisited Garba Guracha in order to retrieve new sediment cores and to apply new environmental proxies, e.g. charcoal, diatoms, biomarkers, and stable isotopes. Our chronology is established using 210 Pb dating and radiocarbon dating of bulk sedimentary organic matter, bulk n-alkanes, and charcoal. Although bedrock was not reached during coring, basal ages confirm that sedimentation started at the earliest * 16 cal kyr BP. The absence of a systematic age offset for the n-alkanes suggests that ''pre-aging'' is not a prominent issue in this lake, which is characterised by a very small afro-alpine catchment. X-ray fluorescence scans and total organic carbon contents show a prominent transition from minerogenic to organic-rich sediments around 11 cal kyr BP coinciding with the Holocene onset. While an unambiguous terrestrial versus aquatic source identification seems challenging, the n-alkane-based P aq proxy, TOC/N ratios, d 13 C values, and the sugar Electronic supplementary material The online version of this article (

How to cite:Lemma, B., Mekonnen, B., Glaser, B., Zech, W., Nemomissa, S., Bekele, T., Bittner, L., and Zech, M.: Chemotaxonomic patterns of vegetation and soils along altitudinal transects of the Bale Mountains, Ethiopia, and implications for paleovegetation reconstructions -Part II: lignin-derived phenols and leaf-wax-derived n-alkanes, E&G Quaternary Sci. J., 68, 189-200, https://doi.org/10.5194/egqsj-68-189-2019, 2019. 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 4377-2550 m a.s.l., respectively). Lignin-derived vanillyl, syringyl and cinnamyl phenols were analyzed using the cupric oxide oxidation method. Leaf-wax-derived nalkanes 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-Published by Copernicus Publications on behalf of the Deutsche Quartärvereinigung (DEUQUA) e.V. 190 B. Lemma et al.: Lignin-derived phenols and leaf-wax-derived n-alkanes 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 C 31 / C 29 ratios in Erica. However, this characteristic plant pattern was also lost due to degradation in the respective O layers and A h 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. Kurzfassung:Erica prägt als dominante Pflanzengattung viele Subafro-alpine Ökosysteme, so auch die Bale Berge in Äthiopien. Das Ausmaß d...

Abstract. Today, on the Sanetti Plateau in the Bale Mountains of Ethiopia, only fragmented patches of Erica species can be found at high altitudes (between 3900 and 4200 m a.s.l.). However, it is hypothesized that during the later part of the last glacial period and the early Holocene the plateau was extensively covered by Erica shrubs. Furthermore, it is assumed that the vegetation was later heavily destroyed by human-induced fire and/or climate change phenomena. The objective of this study is to contribute to paleovegetation reconstructions of the Sanetti Plateau by evaluating the potential of stable isotopes (δ13C and δ15N) and sugar biomarkers for distinguishing the dominant plant species, including Erica, and the soils below the plants. In a companion paper (Lemma et al., 2019a) we address the same issue by evaluating lignin-derived phenols and leaf-wax-derived n-alkane biomarkers. The stable carbon (δ13C) and nitrogen (δ15N) isotope values of the plant samples range from −27.5  ‰ to −23.9  ‰ and −4.8  ‰ to 5.1  ‰, respectively. We found no significant δ13C and δ15N differences between the dominant plant species. Mineral topsoils (Ah horizons) yielded more positive values than plant samples and organic layers (O layers), which reflects mineralization processes. Moreover, the δ15N values became generally more negative at higher altitudes. This likely indicates that the N cycle is more closed compared to lower altitudes. δ15N maxima around 4000 m a.s.l. point to fire-induced opening of the N cycle at the chosen study sites. Erica species yielded the lowest overall total sugar concentration (ranging from 58 to 118 mg g−1), dominated by galactose (G) and mannose (M). By contrast, Festuca species revealed much higher total sugar concentrations ranging from 104 to 253 mg g−1, dominated by the pentose sugars arabinose (A) and xylose (X). Although a differentiation between Erica versus Festuca, Alchemilla and Helichrysum is possible based on (G + M) ∕ (A + X) ratios, Erica cannot be unambiguously distinguished from all other plant species occurring on the Sanetti Plateau. In addition, plant-characteristic (G + M) ∕ (A + X) sugar patterns change during soil organic matter formation in the Ah horizons. This can be likely attributed to degradation effects and soil microbial build-up of galactose and mannose. In conclusion, soil degradation processes seem to render sugar biomarker proxies unusable for the reconstruction of the past extent of Erica on the Sanetti Plateau, Bale Mountains, Ethiopia. This finding is of relevance beyond our case study.