Human occupation and ecosystem change on Upolu (Samoa) during the Holocene

Abstract

Aim To track the peopling of the South Pacific and assess their impact on terrestrial and aquatic ecosystems. Location Upolu, Samoa. Taxon Terrestrial and aquatic plants Methods A sedimentary record covering the last c. 10,500 years was recovered from the volcanic crater that contains Lake Lanoto'o near the centre of Upolu Island. Information on past ecological change was obtained from microscopic and macroscopic remains extracted from the sediments: charcoal (fire history), pollen/spores and plant remains (vegetation history), and lake status (algae/cyanobacteria). Information on the depositional environment and climate was obtained from geochemical and sedimentary analysis: loss‐on‐ignition (sediment composition), cryptotephras (volcanic eruptions) and precipitation regime (Ti/inc). The environmental history developed was compared with the archaeological record from the region. Results Charcoal material was found in the Lake Lanoto'o sediments at higher abundances and more frequently in samples from the period after the first archaeological evidence of people on Upolu (c. 2900–2700 years ago). No abrupt shift is recognized in the vegetation or aquatic ecosystem assemblages coincident with the arrival of people on the island. Main conclusions Macrocharcoal is demonstrated to be an effective proxy for detecting human occupation of Upolu around 2,800 years ago. The immediate impact of these settlers on the vegetation seems to have been minimal; however, a subsequent opening up of the landscape is suggested through the gradual increase in ferns. The absence of any significant change in the aquatic community associated with, or after, the arrival of people on the islands suggests that humans rarely visited the lake. We suggest that on Upolu a simple model of decreasing human impact away from coastal areas is applicable.

Human settlement of East Polynesia earlier, incremental, and coincident with prolonged South Pacific drought

“…Lake Lanoto'o (13°54′37.73″S, 171°49′39.72″W), 'Upolu Island, Samoa is a closed freshwater body within an extinct volcanic crater at 760 m.a.s.l. The crater dates to around 1 to 0.1 million y old and has deeply weathered, silty-loam, red lateritic soils of 2 to 6% organic carbon content (15,16). The freshwater lake is 0.11 km 2 in area with a maximum depth of 17 m and a closed catchment area of 0.23 km 2 .…”

The human dimension of biodiversity changes on islands

“…The recent nature of human settlement means that the archaeological, paleoecological, and climate records are often more precisely resolved on well-studied islands compared with continents, and potentially more relevant for understanding remnant ecosystems and informing conservation and ecosystem restoration agendas. Hence, island ecosystems provide opportunities to quantify the critical ecological transition from pre-human to human-dominated ecosystems (4,15), and allow anthropogenic impacts on ecosystems to be placed within the context of long-term pre-human ecological dynamics (16)(17)(18)(19)(20). While numerous studies have documented the timing, waves, and processes of species extinctions that accompanied human arrival on islands (18)(19)(20)(21)(22)(23)(24), paleoecological data networks now allow systematic quantification of ecosystem transformations on islands globally.…”

“…Hence, island ecosystems provide opportunities to quantify the critical ecological transition from pre-human to human-dominated ecosystems (4,15), and allow anthropogenic impacts on ecosystems to be placed within the context of long-term pre-human ecological dynamics (16)(17)(18)(19)(20). While numerous studies have documented the timing, waves, and processes of species extinctions that accompanied human arrival on islands (18)(19)(20)(21)(22)(23)(24), paleoecological data networks now allow systematic quantification of ecosystem transformations on islands globally. Here, we analyze fossil pollen time-series for multiple independent islands from all the major archipelagos and oceans and across latitudes, using a breakpoint regression approach to test for altered rates and directionality of pollen and hence vegetation compositional turnover connected with human colonization (25) within an overall timeframe of the past 5000 years.…”

Leaf Wax Hydrogen Isotopes as a Hydroclimate Proxy in the Tropical Pacific

“…sediments, and are well-established archives of ecological, anthropogenic, and broad climatic changes in the region (Southern, 1986;Hope & Pask, 1998;Stevenson et al, 2001;Prebble & Wilmshurst, 2009;Prebble et al, 2019;Gosling et al, 2020). More recently, such sediments have also been used to reconstruct past hydroclimate change in the western tropical Pacific at higher temporal resolution (Sachs et al, 2009;Smittenburg et al, 2011;Konecky et al, 2016;Richey & Sachs, 2016;Hassall, 2017;Sachs et al, 2018;Sear et al, 2020).…”

“…Age ranges presented represented the mean age for the top and bottom of each interval, and the full range of possible ages for both sites. # Lakes with greater than 50% vegetation cover $ Age ranges are provided from sites with existing age models, the details of which are provided by Maloney et al (2019), Krentscher et al (2019), Gosling et al (2020), andSear et al (2020)…”