Revealing Hidden Peatland Diversity: A Tropical Sphagnum Peatland Ecosystem in Lowland Belize

Abstract

Tropical peatlands are globally significant ecosystems for carbon cycling and storage 1–3, hydrological regulation 4,5 and unique biodiversity 6,7. There is a diversity of tropical peatland types globally 8, but tropical peat-forming ecosystems are typically forested without the Sphagnum groundcover 3,9–11 that is often typical of high latitude peatlands. Here we report on a unique tropical peatland situated among mangrove swamp in southern Belize that challenges our understanding of both tropical and extra-tropical peatlands due to the presence of Sphagnum in the undergrowth. We employed a suite of methods to investigate its composition, distribution and history. The 2175 ha peatland is comprised of a complex mosaic of open scrub and forested communities which are compositionally similar to northern temperate peatlands at higher taxonomic levels. Palaeoecological data show that peatland originated as a mangrove swamp beginning > 7,700 yrs BP and Sphagnum spores suggest it was locally established by c. 6,000 yrs BP. Lower regional precipitation from 4,500 yrs BP impacted carbon accumulation rates and may have enabled burning in the ecosystem, but the peatland remained intact despite these pressures. Floristics and structural affinities with coastal Panamanian peatlands 12,13 suggests the existence of a rare Central American peatland type that is underreported and may be already fragmented and threatened. This previously undocumented peatland highlights the extent of knowledge gaps in biodiversity and its loss in the tropics and the Global South 14 that conceal important ecological and biogeographical insights. The first insight into this unreported tropical peatland type, provided here, is vital to uncovering the origin, functional diversity and climate resilience of globally important tropical peatland ecosystems.

Keywords: Tropical peat dynamics, Tropical Biodiversity, Mangroves, Historical biogeography, Palaeoecology, Palaeohydrology