A Holocene record of savanna vegetation dynamics in southern lowland Papua New Guinea

Abstract

The southern lowlands of Papua New Guinea (PNG) are biogeographically distinct. Vast tracts of savanna vegetation occur there and yet most palaeoecological studies have focused on highlands and/or forest environments. Greater focus on long-term lowland environments provides a rare opportunity to understand and promote the significance of local and regional savannas, ultimately allowing non-forested and forested ecosystem dynamics to be compared. This paper examines palaeoecological and archaeological data from a lowland open savanna site situated on the south-central PNG coastline. The methods used incorporate pollen and micro-charcoal analyses, artefact recovery and sediment descriptions. We conclude with an environmental model of sedimentation and vegetation change for the past c. 5,800 years, revealing a mid to late Holocene savanna interchange between herbaceous and woody plant growth, with fluctuating fire occurrence increasing toward the present day. Increased silt deposition and modified regional hydrology are also recorded. Environmental changes correspond in timing with the start of permanent settlements and human use of fire. In particular, landscape burning for hunting and gardens for agriculture have helped create the open ecosystem still evident today.

Middle to Late Holocene near-shore foraging strategies at Caution Bay, Papua New Guinea

“…As climate changed to recurring drier and/or variable conditions, inland woodlands became more open and less diverse after 3000-2500 cal BP, with increased cross-catchment burning recorded after 3000-2000 cal BP (Rowe et al, 2013(Rowe et al, , 2020. Rowe et al (2020) highlight how drier and firemaintained ecosystems after c. 3000 cal BP appear to coincide with the start of permanent human settlements in Caution Bay, especially along the coast. A shift occurred away from thicket growth to grassland-woodland c. 1750-1300 cal BP towards the coast (Rowe et al, 2013(Rowe et al, , 2020, with modern landscapes and vegetation dating to the past c. 200 years.…”

“…Two palaeoenvironmental studies within the Caution Bay catchment document Holocene mangrove succession and coastal plain vegetation transitions (Rowe et al, 2013), as well as inland lowland savanna dynamics (Rowe et al, 2020). These local records have been linked to palaeoenvironmental trends from Waigani Lake, in the nearby coastal foothills of Port Moresby (Osborne et al, 1993), with the PNG highlands (Haberle, 2013) and Torres Strait (Rowe, 2007(Rowe, , 2015 providing broader geographical frames of reference.…”

“…Inland at Caution Bay from 5800 cal BP, dune herbaceous and mixed thicket communities became established in closest proximity to the mangrove-mudflat zones. These merged with sclerophyll woodland with distance from the coast (Rowe et al, 2013(Rowe et al, , 2020. High consistent precipitation maintained greater undergrowth and/or green broadleaf floristics through to c. 3000-2500 cal BP, with burning exerting little influence on inland vegetation (Osborne et al, 1993;Rowe et al, 2020).…”

“…These merged with sclerophyll woodland with distance from the coast (Rowe et al, 2013(Rowe et al, , 2020. High consistent precipitation maintained greater undergrowth and/or green broadleaf floristics through to c. 3000-2500 cal BP, with burning exerting little influence on inland vegetation (Osborne et al, 1993;Rowe et al, 2020). As climate changed to recurring drier and/or variable conditions, inland woodlands became more open and less diverse after 3000-2500 cal BP, with increased cross-catchment burning recorded after 3000-2000 cal BP (Rowe et al, 2013(Rowe et al, , 2020.…”

“…High consistent precipitation maintained greater undergrowth and/or green broadleaf floristics through to c. 3000-2500 cal BP, with burning exerting little influence on inland vegetation (Osborne et al, 1993;Rowe et al, 2020). As climate changed to recurring drier and/or variable conditions, inland woodlands became more open and less diverse after 3000-2500 cal BP, with increased cross-catchment burning recorded after 3000-2000 cal BP (Rowe et al, 2013(Rowe et al, , 2020. Rowe et al (2020) highlight how drier and firemaintained ecosystems after c. 3000 cal BP appear to coincide with the start of permanent human settlements in Caution Bay, especially along the coast.…”