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.
