Long-term fire resilience of the Ericaceous Belt, Bale Mountains, Ethiopia

Abstract

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.

Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications

“…xyl) and (fuc ? xyl)/ara indicate a lower terrestrial OM input, which is supported by the reduced vegetation cover at that time in the lake's catchment (Gil-Romera et al 2019). These findings represent a drought period, which is in agreement with an arid period found in a speleothem record in southern Oman (Fleitmann et al 2007).…”

“…A shift to arid conditions at 4.5 kyr may mark a late termination of the AHP in the Garba Guracha record and may indicate a late response of a high-altitude aquatic system. However, Erica pollen already decreased at 5.2 kyr (Gil-Romera et al 2019). A return to wetter conditions between 2.5 and 1.5 kyr concurs with rising lake levels in the Horn of Africa region (Lezine et al 2014).…”

“…In either scenario, we would expect to see not only a change in sedimentation but also a lower OM input into the lake. This is supported by low TOC values and decreased dominance of Erica heathlands, which, as revealed in the Garba Guracha pollen data, dominated the local vegetation during this phase (Umer et al 2007;Gil-Romera et al 2019). Additionally, aquatic production would likely have been reduced due to lower insolation during ice cover and lower input of nutrients.…”

“…3), we combined the 210 Pb, bulk sediment, bulk n-alkane and charcoal radiocarbon ages into a Bayesian modeling framework (Blaauw 2010;Blaauw and Christen 2011). Note that a preliminary version of this age-model underlies the paleoenvironmental dataset published by Gil-Romera et al (2019). All 14 C ages with a carbon mass smaller than 19 lg were rejected and not used for our agedepth model.…”

“…This implies a fast filling glacial cirque, potentially fed by a melting glacier forced by rising temperatures. Sparse vegetation in the catchment (Umer et al 2007;Gil-Romera et al 2019) and low algal productivity in the meltwater-fed lake could have been a small OM source represented by low TOC values of up to 1%. Low TOC/N values of 5 and relatively positive d 13 C values (-19 to 14 %) point to aquatic algae as the dominant OM source (Meyers 2003;Brenner et al 2006).…”