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.

Compound-specific hydrogen and oxygen isotope analyzes on leaf wax-derived n-alkanes (δ 2 H n-alkane) and the hemicellulose-derived sugar arabinose (δ 18 O ara) are valuable, innovative tools for paleohydrological reconstructions. Previous calibration studies have revealed that δ 2 H n-alkane and δ 18 O ara reflect the isotopic composition of precipitation, but-depending on the region-may be strongly modulated by evapotranspirative enrichment. Since no calibration studies exist for semi-arid and arid Mongolia so far, we have analyzed δ 2 H n-alkane and δ 18 O ara in topsoils collected along a transect through Mongolia, and we compared these values with the isotopic composition of precipitation (δ 2 H p-WM and δ 18 O p-WM , modeled data) and various climate parameters. δ 2 H n-alkane and δ 18 O ara are more positive in the arid southeastern part of our transect, which reflects the fact that also the precipitation is more enriched in 2 H and 18 O along this part of the transect. The apparent fractionation ε app , i.e., the isotopic difference between precipitation and the investigated compounds, shows no strong correlation with climate along the transect (ε 2H n-C29/p = −129 ± 14 , ε 2H n-C31/p = −146 ± 14 , and ε 18O ara/p = +41 ± 2). Our results suggest that δ 2 H n-alkane and δ 18 O ara in topsoils from Mongolia reflect the isotopic composition of precipitation and are not strongly modulated by climate. Correlation with the isotopic composition of precipitation has root-mean-square errors of 13.4 for δ 2 H n-C29 , 12.6 for δ 2 H n-C31 , and 1.2 for δ 18 O ara , so our findings corroborate the great potential of compound-specific δ 2 H n-alkane and δ 18 O ara analyzes for paleohydrological research in Mongolia.

In eastern Africa, there are few long, high-quality records of environmental change at high altitudes, inhibiting a broader understanding of regional climate change. We investigated a Holocene lacustrine sediment archive from Lake Garba Guracha, Bale Mountains, Ethiopia, (3,950 m asl), and reconstructed high-altitude lake evaporation history using δ18O records derived from the analysis of compound-specific sugar biomarkers and diatoms. The δ18Odiatom and δ18Ofuc records are clearly correlated and reveal similar ranges (7.9‰ and 7.1‰, respectively). The lowest δ18O values occurred between 10–7 cal ka BP and were followed by a continuous shift towards more positive δ18O values. Due to the aquatic origin of the sugar biomarker and similar trends of δ18Odiatom, we suggest that our lacustrine δ18Ofuc record reflects δ18Olake water. Therefore, without completely excluding the influence of the ‘amount-effect’ and the ‘source-effect’, we interpret our record to reflect primarily the precipitation-to-evaporation ratio (P/E). We conclude that precipitation increased at the beginning of the Holocene, leading to an overflowing lake between ca. 10 and ca. 8 cal ka BP, indicated by low δ18Olake water values, which are interpreted as reduced evaporative enrichment. This is followed by a continuous trend towards drier conditions, indicating at least a seasonally closed lake system.