Late Quaternary Montane Forest Dynamics From Equatorial East Africa: A Biome Perspective

Abstract

Aim

Understanding environmental change over large spatial and temporal scales requires working at a broad ecological scale to enable cross-site comparisons. This allows data-based comparisons to dynamic vegetation model outputs, with utility for climate and land cover modelling. We synthesise multisite pollen data at the biome level to understand Equatorial Afromontane ecosystem response to climate change over the last 50,000 years and quantitatively document the timing, character and spatial patterns of ecosystem transitions.

Location

Mountains of Equatorial East Africa.

Time Period

Late Quaternary (50,000 cal year BP–present).

Taxon

Angiosperms (trees, shrubs and grasses), gymnosperms (conifers), pteridophytes (ferns) and bryophytes (clubmosses).

Methods

A literature review revealed 58 available published pollen sites from Equatorial East African Mountains. Original geochronological and palynological data were collated from 34 sites from the African Pollen Database (APD) and directly from authors. Pollen taxonomies were updated and harmonised using the African Plant Database. The geochronologies were reanalysed and radiocarbon data (n = 219) were IntCal20 calibrated to develop linearly interpolated age-depth models. The 636 pollen taxa were grouped into 21 plant functional types and combined into seven biomes that represent the range of montane ecosystems. A rate of change analysis at each site provided a scale of the change through time at each site.

Results

Mesic montane forest biomes were present throughout the 50,000 cal year BP. Cold and dry montane biomes expanded during and after the Last Glacial Maximum (LGM). Warm and wet forest biomes expanded from the early Holocene and more open biomes expanded in the Late Holocene. Regional differences were observed, such as the Eastern Arc Mountain sites recording relatively little change in comparison with isolated volcanic mountains. The rate of change analysis highlights periods with a high rate of change (45,000–35,000, 11,000–5000 and 5000–present) while 35,000–20,000 is relatively stable.

Main Conclusions

Equatorial East African Montane forests are driven by local to regional vegetation responses to past climate changes. The research highlights that both the pace and nature of interactions in ecological systems vary widely across these montane forests.