Interactions between human activity, volcanic eruptions and vegetation during the Holocene at Garua and Numundo, West New Britain, PNG

Quaternary Research 64 (2005) 384 – 398 www.elsevier.com/locate/yqres

Interactions between human activity, volcanic eruptions and vegetation during the Holocene at Garua and Numundo, West New Britain, PNG W.E. Boyd *, C.J. Lentfer, J. Parr School of Environmental Science and Management, Southern Cross University, Lismore, New South Wales 2480, Australia Received 16 January 2005

Abstract This paper reviews recent fossil phytolith analysis from wet tropical West New Britain (Papua New Guinea). The Holocene vegetation has been influenced by spatially and temporally diverse patterns of both prehistoric human settlement and catastrophic volcanic events. We have hypothesized different landscape responses and recovery pathways to events during the last six millennia. Phytolith sequences on the coastal lowlands, the Willaumez Peninsula, and nearby island of Garua provide details of vegetational change and human interactions at different landscape scales since c. 5900 cal yr B.P. During this period four major volcanic eruptions (c. 5900, 3600, 1700 and 1400 cal yr B.P.) have disrupted the landscape. The evidence provides detailed descriptions of temporal and spatial patterning in the impacts and changes in the vegetation. In particular, vegetation responded differently from one event to another, reflecting both forest recovery from seed bank and shooting, and the influence of prehistoric people on recovering vegetation. Furthermore, after some events landscape recovery was moderately uniform, while after others there was considerable landscape partitioning. Although these differences largely relate to airfall tephra type, distribution and magnitude, the partitioning is more strongly influenced by human activity. D 2005 University of Washington. All rights reserved. Keywords: Holocene vegetation; West New Britain; PNG; Wet tropical forest; Volcanism; Prehistoric settlement

Introduction The wet tropical region of West New Britain (Papua New Guinea) has been populated since the Pleistocene. During this time, the region has experienced a series of catastrophic volcanic events related to plate margin volcanism. In addition to human activity and volcanism, the coastal zone of West New Britain has also been affected by tectonic activity, climatic change and sea-level fluctuations (Boyd et al., 1998, 1999b; White et al., 2002). Here, we examine the responses of vegetation to these important landscape influences by analysing phytolith at localities on the coastal lowlands of the Willaumez Peninsula and nearby island of Garua. Importantly, the current and emerging results provide details of vegetational change at different scales, thus allowing us to create a synthetic overview of vegetation and human interactions across the landscape. The local scale is investigated at one archaeological site on Garua Island and a sub-regional scale is investigated at * Corresponding author. E-mail address: [email protected] (W.E. Boyd).

Numundo (Fig. 1). Using phytolith analysis from discrete horizons at many exposures close to a prehistoric settlement on Garua, we were previously able to map the details of the former village and its immediate impact on the surrounding forest for one discrete period in the past (Parr et al., 2001b). We now follow this initial work with a detailed phytolith study of changes throughout the Holocene at the same site. This local history is supplemented by a parallel study on the neighboring mainland at Numundo, where we conducted phytolith analyses at seven sites along one part of the coastal plain, where the sediment sequence comprises stacks of Holocene tephras and palaeosols. These analyses allow us to identify the patterns of volcanic and human disruption to the vegetation both through time and across the landscape. In particular, we have been able to examine the balance between natural and anthropogenic disturbance, especially as it affects the recovery of forest systems in this region. By differentiating the effects of natural and human impacts, we are able to chart the different ways in which both the natural environment responded to catastrophic volcanism and people partitioned the landscape. This work, in particular, is related to archaeological studies of the area, and

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Figure 1. Location of sample sites discussed in this paper. The sites at Garua Island and Numundo are discussed in this paper, while the pollen analysis at Garu are discussed in Jago and Boyd, in this volume. (Figure by Leigh Jago).

we have a strong control over the correlation of environmental history and archaeology (Torrence and Stevenson, 2000; Torrence et al., 2000; Torrence, 2002a,b). The aim of our research is to define and explain the responses of environmental processes to catastrophic volcanism in West New Britain during the Holocene, and the interaction between these and human landscape behavior. We report here our first synthesis towards predictive models for environmental recovery under various past environmental conditions: the case studies on which this paper is based will be published elsewhere. It is important to note that this study is not just a palaeovegetation study, but that it also contributes crucial data to the regional archaeology and palaeoenvironment. Background New Britain’s Quaternary history is dominated by periodic catastrophic volcanism, dynamic human occupation and a vibrant tropical ecology. These combine to provide a valuable case study of the interactions between landscape, ecology and human behavior. The region is also a source area for the human expansion into the Pacific, and thus is of major archaeological interest. Several decades of archaeological research, while providing a sound regional history of human occupation, is producing ideas that deviate from widely accepted theories of social evolution, which focus on internal and gradual social change (e.g., Torrence et al., 2000). In particular, the role of external influences is recognized as important, and the

relationship between human activity and landscape is central to the current archaeological research. The current archaeological research in West New Britain emphasizes the importance in both archaeological and environmental studies in examining the human – landscape relationship. It is significant that West New Britain archaeology shows evidence for changing patterns of human occupation influenced by the region’s dynamic volcanic and ecological history. However, despite the focus on on-site environmental archaeology, there is little regional synthetic detail of palaeoenvironmental responses to the major volcanic events that periodically impacted huge areas within the region. Such detail is only now being sought. It builds on a broad multi-disciplined base of research over the last two decades. The regional geology provides a history of at least 1 myr of volcanic activity, with some 19 major eruptions during the last 5500 yr (Johnson, 1976). Landscape impacts are described by Machida et al. (1996), who provide geochemical characterization and geomorphological contexts. This physical framework allows identification of spatial tephra- and chrono-stratigraphic relations between sample sites. Studies of local soil erosion history and the effects of sea-level change and tectonic movement on the archaeological and sedimentary record (e.g., Boyd and Torrence, 1996) inform us about surface stability, sediment mobility, other effects of disturbance, and spatial patterning of geomorphic parameters within these landscapes. Fossil phytolith analysis provides data on key disturbance indicators, their spatial patterning, temporal vari-

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ability related to major ashfalls, and the nature and spatial patterning of regional forest regeneration. Complementing this range of studies is the ground-breaking regional archaeological study, which has recently resulted in the Torrence et al.’s (2000) publication of a critical model of patterns of past human occupation in the region, and an explanation of critical social and other processes influencing social development set in its cultural landscape (Torrence, 2002a). Drawing on a body of landscape archaeology theory and practice, the model suggests that occupation patterns and social development have been discontinuous, influenced by periodic catastrophic volcanic eruption and reflecting various adaptive coping strategies. The present archaeological focus separates social from non-social process influences to identify social responses to these natural events. Finally, crucial to our study is an ability to model the regional landscape and its biophysical elements. Combining fieldwork data from landscapes affected by the 1994 Rabaul eruptions (Lentfer and Boyd, 2001) with Thornton’s observations at Krakatau (e.g., Thornton, 1996) and models of Machida et al. (1996) and Torrence et al. (2000), we published an initial regional GIS model of the environmental and social impacts of several Holocene volcanic events (Boyd et al., 1999a). That model provides testable hypotheses regarding type, distribution and degree of initial biophysical impacts of

ashfalls and probable paths of environmental regeneration, hypotheses that are tested here. Methods The studies reported here are based on sampling during many years of archaeological fieldwork in West New Britain. The fieldwork was organized and coordinated by Robin Torrence (Australian Museum), and the phytolith sample collection was from excavated archaeological exposures. An extensive global literature provides well-established analytical methods (e.g., Berglund, 1986), and allows confidence in issues of sample representivity and analytical certainty. Laboratory analysis uses a combination of standard and newly developed Quaternary and palynological methods (Lentfer and Boyd, 1998, 1999, 2000; Lentfer et al., 2003; Bowdery et al., 2001; Parr, 2002, 2004; Parr and Farrugia, 2003; Parr et al., 2004), especially drawing on an extensive phytolith reference collection held at Southern Cross University (Lentfer, 2003). Details of specific methods used in each of the studies summarized here will be published in the full individual reports; it should be noted that slightly different techniques for presenting and interpreting the palynological data are used for the phytolith sites at Garua Island and Numundo. This reflects the differences in site-specific questions being posed at these sites.

Figure 2. Overviews of the sample sites discussed in this paper: top, Garu; bottom, Numundo (Photograph: W.E. Boyd).

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Chronological control is provided in each of the studies using a well-established tephrachronology for the study region (Machida et al., 1996; Torrence et al., 2000), which in itself is based on a substantial body of radiocarbon dating of, predominantly, fossil charcoal. Individual site chronologies are corroborated by reference to tephra stratigraphic correlation, notably by chemical identification of individual tephras (cf. Machida et al., 1996) or regional dating of recognizable horizons (cf. Torrence et al., 2000), and thus the radiocarbon ages listed in Tables 2, 3, 4, 6 and 7, and mentioned throughout the text regarding the major volcanic and stratigraphic events require no further discussion. Garua Island The sampled sites lie in the hot wet tropical zone, and are at Garua Island (5-25VS, 150-02VE), just off the east coast of the Willaumez Peninsula, and Numundo (5-30VS, 150-08VE), a coastal plain on the east coast of the peninsula isthmus. Further relevant information comes from pollen analyses at the nearby location of Garu (5-30VS, 149-58VE), a coastal swamp on the west coast of the isthmus (Jago and Boyd, in press). Garua is formed from two former volcanic cores, and the Willaumez Peninsula is formed from a series of volcanic cones (Figs. 1 and 2). All areas are naturally mantled with wet tropical rainforest, with literal tall mangrove woodlands, although substantial parts of the study areas have been converted to extensive coconut and, more recently, palm oil plantations. The forest areas form parts of customary land and have been gardened for many generations; in places not turned to plantation, the forest shows signs of recovering from former gardening. Prehistoric settlement patterns, technological trends and cultural change on Garua are well documented (Araho et al., 2002; Torrence, 2002a,b; Torrence and Summerhayes, 1997; Torrence and Stevenson, 2000; Torrence et al., 2000; Barton et al., 1998; Kealhofer et al., 1999; Parr et al., 2001b; Therin et al., 1999). Torrence (1992, 2002a) argues for patterns of continuity and a slow, steady decline in mobility over the last six millennia as land management systems gradually intensify. Table 1 Summary of the major Holocene eruptions of Witori and Dakataua volcanoes known to be represented by airfall tephra deposits on Garua Island and the adjacent mainland on the Willaumez Peninsula (based on Torrence et al., 2000) Eruption

Approximate age, cal yr B.P.

Volume, km3

Type

Dakataua Dk

1000

10

Witori W-K4

1400

6

Witori W-K3 Witori W-K2

1700 3600

6 30

Witori W-K1

5900

10

Phreatomagmatic, plinian, ignimbrite forming Phreatomagmatic, plinian, ignimbrite forming Plinian Phreatomagmatic, plinian, ignimbrite forming Plinian, ignimbrite forming

The approximate ages are currently being revised and refined with further fieldwork; in particular, the Dakataua eruption may be older than indicated here, and indeed may slightly pre-date the W-K4 eruption (Robin Torrence, personal communication, 2005).

Figure 3. The sediment sequence at site FAO1000/1000 on Garua Island, illustrating the sequence of airfall tephras (lighter horizons) with developed palaeosoils (darker horizons), containing the fossil phytolith evidence. This sequence is 2.4 m deep. The sequences sampled at Numundo are similar (Photograph: C.J. Lentfer).

However, the interactions between society, environment and vegetation under conditions of frequent, catastrophic volcanic disturbances are poorly understood (Boyd et al., 1999a; Lentfer and Boyd, 2001; Torrence, 2002b). Furthermore, it is unresolved whether emerging subsistence patterns were derived internally or externally. Fossil phytolith and starch analysis have been used to address such particular issues. Here, we combine new evidence from fossil phytolith and sediment analyses of the FAO 1000/1000 test pit on Garua Island (Lentfer, 2003) with a previous fossil starch grain analysis (Therin, 1994; Therin et al., 1999) to provide an overall picture of palaeoenvironmental change at that location from the late Pleistocene to the present. Garua Island is a small volcanic island fringed in parts by a small coastal plain, just to the east of the Willaumez Peninsula. It was cleared for coconuts in the 1920s (Hore-Lacey, 1992), and there are no pre-clearance vegetation records; the island, however, lies in a biogeographic zone of lowland rainforest consisting mainly of a closed forest with numerous species of tall trees, palms and lianes, and with typical tropical responses to disturbance (Henty, 1969; Paijmans, 1973; Saulei and Swaine, 1988; Saulei, 1989; Saulei et al., 1992; Thornton, 1996; Whittaker et al., 1997; Thornton and Mawdesley, 2000; Lentfer and Boyd, 2001). The sample site, archaeological

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excavation FAO 1000/1000, lies at the coastal end of a ridge on the north coast of the island. Garua Island has in the past been affected by eruptions from two nearby volcanoes, Dakataua and Witori, with a Holocene history of major eruptions resulting in widespread airfall tephra deposition, forming distinctive sedimentary units on the island (Machida et al., 1996; Boyd et al., 1999a) (Table 1; Fig. 3). In particular, radiocarbon dating and obsidian hydration dating provides good chronological control for the last 6000 yr. Archaeological studies at the site reveal four cultural phases on Garua Island (Torrence 1992, 2002a,b; Torrence et al., 2000; Araho et al., 2002; Kealhofer et al., 1999) (Table 3). Fossil phytolith analysis at Garua Island Details of the analyses at Garua Island (Lentfer, 2003) are being prepared for full publication. The following summarizes the main findings of analysis of 43 samples from FAO 1000/ 1000, processed using now-standard techniques (Lentfer and Boyd, 1998, 1999). Counting and identification (Lentfer, 2003; Kealhofer and Piperno, 1998; Madella et al., 2003) of at least 150 phytoliths at 400 yielded data presented as percentages and concentrations (Fig. 4). Other details will be published elsewhere. Phytolith and starch concentrations vary throughout the profile, with distinctive differences between tephra (low values) and soil horizons (high values), typical of Type-2 phytolith depth function (PDF) (Stace et al., 1968; Hart and Humphreys, 1996), with minor evidence for vertical displacement into unconsolidated tephra; values, however, indicate good phytolith/sediment integrity (also noted at other Garua sites: Parr, 1999; Parr et al., 2001b), and thus for each palaeosoil the phytolith distribution typically is Type 1 PDF.

Further detailed sedimentary interpretation based on phytolith concentrations augments this depositional story (Lentfer, 2003). The combination of phytolith and starch evidence allows the possibility of differentiating normal stable environment deposition from the damaging effects of airfall tephra. Importantly, grass phytoliths peak after the starch and dicotyledon/non-grass phytolith peaks in every instance. This indicates moderate to severe vegetation damage following the four Holocene tephra events, resulting in burial of ground plants, massive limb breakage and much tree loss (Lentfer and Boyd, 2001). A layer-by-layer interpretation of the sedimentary sequence and patterns of vegetation change is provided in Lentfer (2003) (Table 2). This provides a pattern of changing land use persisting despite the periodic major volcanic ashfalls. These are summarized relative to the archaeological periods (Table 3; Torrence et al., 2000; Torrence, 2002a,b) as follows. & Pre-Period I (layers 1– 5; Late Pleistocene to c. 5900 cal yr B.P.). Short-term/occasional human occupation of the site, possibly for hunting and foraging for Canarium nuts and other plant foods. & End of Pre-Period I and Period I (layers 6 and 7; c. 5900– 3600 cal yr B.P.). Significant change in land use following a major catastrophic volcanic event, with a shift towards long-term site occupation; evidence for Canarium nut harvesting; use of bamboo signaling a possible shift in technology and raw material use and/or a change in subsistence linked to early cultivation of useful plants close to occupation sites. & Period II (layers 8 to 10; 3600 cal yr B.P. to 1400 14C yr B.P.). Intensification of environmental use associated with the introduction of Lapita pottery; increased land clearing

Table 2 Layer-by-layer interpretation of the sedimentary sequence and patterns of vegetation change derived from phytoliths analysis at Garua Island site FAO 1000/1000 (Lentfer, 2003) Layer

Stratigraphic context

Characteristics

Layer 11

Dk soil

Layer 10 Layer 9

Dk tephra (c. 1000 cal yr B.P.) W-K3? tephra and soil (c. 1700 cal yr B.P.)

Layer 8

W-K2 soil

Layer 7 Layer 6

W-K2 ash (c. 3600 cal yr B.P.) W-K1 ash and soil, mid Holocene (c. 5900 cal yr B.P.)

Open regrowth forest with figs, euphorbs, urticaceous species, palms, gingers, and Musa and/or Heliconia species; understorey dominated by grasses, with sharp increase in bamboos. Defoliation resulting in severe damage from ashfall. Strong soil development after the ashfall; shift towards a forested landscape, with regenerating palm forest with ginger, Musa and Heliconia understorey; little evidence of vegetation damage from ashfall; burning declines early, then increases to promote increased panicoid grasses and palm decline. Early dominance by panicoid grasses and pioneer regrowth forest, followed by continued forest recovery, then accelerated burning causing severe forest degradation (also noted by Parr et al., 2001a,b,c); later forest recovery; Canarium and bamboos persist throughout the sequence, bananas become more common, and Caryota palm appears. Severe defoliation and damage at deposition of this ash. Vegetation dominated by grasses and regrowth forest, with increased indicators of burning and human occupation; bamboo appears in the middle of the sequence, associated with burning. Severe defoliation during ashfall, causing severe disturbance to the closed forest. Continued forest recovery to closed forest. Further severe forest disturbance rapid burial by (probably) wet ash, followed by recovery of regrowth forest. Forest severely disturbed, especially by defoliation, by ashfall, followed by recovery of an open regrowth forest with a ground cover dominated by Imperata cylindrica. Forest with understorey dominated by palms and gingers; grasses are also present, possibly encouraged by burning.

Layer 5 Layer 4 Layer 3 Layer 2 Layer 1

Late Pleistocene

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Figure 4. Summary phytolith diagram from Garua Island, presenting the phytolith data as percentages of sample totals. Values of <1% are shown as dots.

for gardens and/or villages; introduction (as a cultivar?) of the fishtail palm, Caryota rumphiana, a significant starch producing palm; bamboo also present (also on artifacts) in the sequence, and again, it is present as residues on stone tools in FAO 970/1000 (Kealhofer et al., 1999); possible introduction of Musa and Heliconia species; later shift towards a more forested landscape may be related to shift of settlement, population decline, or adoption of palms and Canarium arboriculture.

& Period III (layer 11; post c. 1400 14C yr B.P.). Significant intensification of land use, and forest decline; increasing reliance on bamboos as a raw material; dominance of figs (now with cultural significance in villages). The evidence from Garua allows us to differentiate the effects of major volcanic eruptions, common throughout the Holocene at least, from the effects of human activity on the island. There have been lengthy periods of environmental

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Table 3 Four cultural phases at Garua Island (based on Torrence, 2002a,b; Torrence et al., 2000) Period

Date

Characteristics

Pre-period I

Before to the W-K1 eruption (c. 5900 cal yr B.P.)

Period I

W-K1 to W-K2 (c. 5900 – 3600 cal yr B.P.)

Period II

W-K2 (3600 cal yr B.P.) to the Dakataua eruption (1400 14C yr B.P.)

Period III

Post-Dakataua (post c. 1400

Highly curated stemmed tools, carefully flaked at special-purpose quarry sites, carried around, and used and maintained for long periods Human resettlement after the eruption following a long (300 yr) abandonment; more expedient tool manufacturing with a high proportion of unretouched flakes from mostly local material and rare stemmed tools; widely distributed on the island Post-eruption abandonment of c. 250 yr; Lapita pottery and unretouched flakes; trend to expedient use of raw materials; clustered distribution of sites, mainly on coastal hilltops and ridges. Long abandonment (300 yr); clustered sites, both coastal and inland; unretouched flakes and no pottery.

14

C yr B.P.)

stability, with the vegetation fluctuating between early pioneer and regrowth forest, as expected from modern studies (Lentfer and Boyd, 2001; Paijmans, 1973; Thornton, 1996; Thornton and Mawdesley, 2000; Whittaker et al., 1997). In contrast to the recovery from major events—typically with early Imperata cylindrica domination followed by increases in gingers, palm and dicotyledonous trees and shrubs— smaller events are represented by continuity of vegetation types. There has, however, been a human presence for much of the Holocene. Conditions following major ashfalls would have been unpleasant, and abandonment of the island was likely (Torrence, 2002b). Our evidence of periodic environmental devastation implies that it is unlikely that people would have been able to survive on the dusty, sterile ash beds until a reasonable vegetation cover was re-established. Furthermore, even after minor events, human activity and levels of population declined dramatically despite good vegetation cover being sustained. The periodic volcanic ashfall since late Pleistocene, typically of the four major Holocene events, resulted in very different environmental impacts on Garua Island. These were impacts to which people adjusted either by abandoning the site or changing land management. Typically, ashfall events either had major impact (typically W-K2 and Dakataua), with significant defoliation and limb damage resulting in significant forest decline and consequential regrowth first dominated by grasses, or low impact (typically W-K3) which allowed continuity of the forest following relatively minor damage to the vegetation. Notably, and importantly in terms of the effects on the vegetation, people abandoned the site for significant periods after the major impact events. Numundo The area of Numundo is a coastal plain, mainly comprising layers of Holocene tephras, infilling former marine embayments and an undulating deeply weathered Pleistocene land surface. Torrence (2002b) describes physical changes to the Numundo landscape from the W-K1 (c. 5900 cal yr B.P.) eruption up to the W-K4 (c. 1400 cal yr B.P.) eruption in terms of the infilling of coastal shallow water, reef areas, mangroves, swamp and lake systems by successive deposits of airfall tephra and hill erosion. We

have recently confirmed that the current strand plain was not formed until after the W-K2 eruption. Numundo lies some 10 km southwest of Garua (Figs. 1 and 2). Unlike the Garua study, however, rather than sampling intensely through an individual sequence, sampling was across the landscape, with equivalent horizons from seven sites being examined. While this does not provide the site-specific details illustrated above for the Garua Island sequence, it does provide greater insight into landscape patterning. The following is a synthesis of this work, with the details of methods, data and interpretation given in Parr (2003), currently in preparation for full publication. The geological history of the area strongly parallels that described above at Garua. The prehistoric settlement of Numundo commenced in the late Pleistocene (Torrence et al., 2004), and, as for Garua, archaeological patterns of former land use and obsidian trade have been well studied (e.g., Summerhayes et al., 1998; Torrence et al., 1999; Torrence and Stevenson, 2000). Fossil phytolith analysis at Numundo Samples were collected at seven sites in the Numundo Palm Oil Plantation. These represent a range of coastal environments both now and in the past, and overlook the present strand plain and shoreline. They contain stratified sediments dating from the periods between the W-K1 (c. 5900 cal yr B.P.), W-K2 (c. 3600 cal yr B.P.), W-K3 (c. 1700 cal yr B.P.), W-K4 (c. 1400 cal yr B.P.) eruptions and the present (Machida et al., 1996; Torrence et al., 2000; Parr and Farrugia, 2003). The W-K2 tephra is c. 0.30 m thick throughout the study area, the W-K3 tephra, c. 0.5 m, and the W-K4 tephra, c. 0.35 m. As at Garua Island, the sediment sequences comprise stacks of airfall tephra, each with a palaeosoil developed on its upper surface. We have focused on the palaeosoils in this study, and therefore two or three samples were examined for each palaeosoil (two—top, bottom—for shallow soils; three—top, middle and bottom— for thicker soils); at one site, soil thickness precluded more than one sample. As reported previously (Parr, 1999), there are clear transitional zones where phytolith counts diminish rapidly downwards from the A/B palaeosol horizon into the lower volcanic glass-rich parent (C) horizon. Samples were therefore taken at the uppermost and lowermost points in the

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A/B horizons. The A/B horizons of these palaeosols range in depth from 10 to 40 cm. This allowed us to examine the immediately post- and pre-eruption environments at Numundo. Sample ages are estimated by reference to the known ages of the W-K 1, W-K2, W-K3, W-K4 and W-H eruptions (Torrence, 2002a,b) and our understanding of phytolith distribution processes within soils (Parr, 1999) (Table 4). The sites examined are as follow. & FAAH The most easterly site of the study area; c. 10.9 m above sea level (a.s.l.) and around 350 m west of the current shoreline; located beside a spring with a canopy of established palm oil trees. & FABK VII NW of FAAH, on the foot-slopes of an escarpment at c. 18.6 m a.s.l. & FAAY V SW of FAAH, on a knoll overlooking the coastal plain at c. 16.2 m a.s.l.; currently improved pasture with remnant coconut palms.

391

& FABD I On a hill in the southern end of the study site, at c. 36 m a.s.l.. & FABD t2 and FABD t3 Close to (SW) of FABD I, at c. 26 and c. 28 m a.s.l. respectively. & FABK XI E of FABK VII, on the coastal plain at c. 7.6 m a.s.l.; only the later palaeosoils were sampled at this locality. Methods (Parr, 2002, 2004; Parr et al., 2001a) differed slightly from those used at Garua, reflecting the ongoing development of methods by our group. Sediment characterization included charcoal measures. Counting and identification of phytoliths at 400 yielded data presented in terms of indicative environments (Fig. 5). These inferred environments have been derived from an interpretative likelihood analysis (Horrocks and Walsh, 1998; discussed in full in Parr, 2004) based on a digital-image database, ecological and volcanic disturbance studies (Peekel, 1984; Duar, 1999; Floyd, 1954; Cronin and Neall, 2000; Lees and Neall, 1993; Paijmans, 1973; Thornton, 1996; Turner and Hurst, 2001; Whittaker et al., 1989), and

Table 4 Summary of sites sampled at Numundo, depths of phytolith-rich horizon within the palaeosoils, inferred age rates of phytolith deposition per cm depth within the phytolith-rich horizon, and inferred calibrated 14C ages of samples for each site Site

Depth to phytolith base, cm

Inferred phytolith age rate, yr/cm

Inferred age of samples, cal yr B.P. Upper

Lower

Centre

W-K1 to W-K2 (c. 5900 – 3600 cal yr B.P.) FABK VII 15 FAAH 35 FAAY V 20 FABD I 15 FABD t2 15 FABD t3 15

153 66 115 153 153 153

3600 – 3753 3600 – 3666 3600 – 3715 3600 – 3753 3600 – 3753 3600 – 3753

5747 – 5900 5834 – 5900 5785 – 5900 5747 – 5900 5747 – 5900 5747 – 5900

W-K2 to W-K3 (c. 3600 – 1700 cal yr B.P. FABK VII 20 FABK XI 5 FAAH 35 FAAY V 20 FABD I 15 FABD t2 25 FABD t3 15

95 380 54 95 240 144 240

1700 – 1795 1700 – 2080 1700 – 1754 1700 – 1795 1700 – 1940 1700 – 1844 1700 – 1940

3505 – 3600

2555 – 2650

3546 – 3600 3505 – 3600 3360 – 3600 3456 – 3600 3360 – 3600

2596 – 2650 2555 – 2650 2410 – 2650 2506 – 2650 2410 – 2650

W-K3 to W-K4 (c. 1700 – 1400 cal yr B.P. FABK VII 20 FABK XI 10 FAAH 25 FAAY V 20 FABD I 10 FABD t2 10 FABD t3 10

15 30 12 15 30 30 30

1400 – 1415 1400 – 1430 1400 – 1412 1400 – 1415 1400 – 1430 1400 – 1430 1400 – 1430

1685 – 1700 1670 – 1700 1688 – 1700 1685 – 1700 1670 – 1700 1670 – 1700 1670 – 1700

Post-W-K4 (c. 1400 – 500 cal yr B.P.) FABK VII 10 FABK XI 40 FAAH 10 FAAY V 30 FABD I 10 FABD t2 30 FABD t3 10

90 23 90 30 90 30 90

500 – 590 500 – 523 500 – 590 500 – 530 500 – 590 500 – 530 500 – 590

1310 – 1400 1377 – 1400 1310 – 1400 1177 – 1400 1310 – 1400 1170 – 1400 1310 – 1400

The inferences are based on the regionally accepted ages of the tephra deposition events (Table 1), and the assumption that phytolith deposition and stratification within the soils developing within the upper parts of the tephras has been chronologically uniform between volcanic events. The post-W-K4 estimations are based on current best measures of the age of subsequent Witori eruptions during the last millennium; research continues into these latter events.

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Figure 5. Summary phytolith diagrams from sites at Numundo, presenting the phytolith data as interpreted environmental indicators.

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Table 5 Summary of model details for the volcanic impact zones of West New Britain during the Holocene (source: Boyd et al., 1999a) Impact zone

Ash thickness, cm

Immediate impact

Follow-on impacts

Recovery

Disruption or change

No impact Minimum impact Moderate impact Major impact Extreme impact

0 0 – 20 20 – 50 50 – 200 >200

Nil Minor, selective Extensive, major Extensive, severe Total

Possible Probable, reasonable Major Major Major, continuing

Rapid (months) Relatively rapid (years) Slow (decades) Slow (decades) Very slow (centuries)

Possible, local, minimal Probable, moderate, extensive Severe Severe, long-term Severe, long-term, absolute

principal components analysis. By assigning likelihood values to all phytoliths, it is possible to identify a weighting of likely represented environments for each sample, using the following broad categories. & Coastal habitat: the littoral beach, tidal estuaries and flats, or littoral foreshore areas. & Closed forest: predominantly rainforest or wet primaryforeshore forested areas. & Herbaceous woodland: open savannah woodland areas with varying amounts of herbaceous undergrowth.

& Disturbed areas: areas of predominantly pioneer re-growth plants and weeds, garden plots or abandoned garden plots. & Wetlands: damp areas, herbaceous wetlands and swamps. & Open grassland: open savannah areas. & Non-specific: This assumed all phytolith types that can be identified but are non-diagnostic regarding habitats. The evidence for landscape change throughout the periods represented indicates that this landscape was typically diverse, and that it responded differently in different habitats to the disruptions caused by tephra falls at each major eruption

Table 6 Summary of the effects of successive volcanic eruptions on the Willaumez Peninsula during the Holocene Garua

Numundo

Summary of volcanic effects

Summary of human effects

Post-W-K4 (post-1400 cal yr B.P.)

DK volcanic impact significant; open and managed landscape

Volcanic impact low; landscape dominated by human impact

Humans throughout the region, although effects are spatially organized

W-K3 to W-K4 (1700 – 1400 cal yr B.P.)

Low impact from volcanic event; human presence continues in forested landscape

Volcanic impact dominant; little human impact

W-K2 to W-K3 (3600 – 1700 cal yr B.P.)

Major volcanic impact, defoliation and forest decline; initial human abandonment, then shift towards intensification, increased land clearing, possible introduction of the fishtail palm, Caryota rumphiana, as a cultivar, and increase in Musa and Heliconia species; later re-establishment of forest, possible changing settlement location, and possible adoption of arboriculture Major catastrophic volcanic event; long-term site occupation, harvesting Canarium nuts, and first appearance of bamboo possibly associated with human activity Periodic but small-scale ashfall events; short-term human occupation; possible hunting and foraging plant foods, including Canarium nuts

High volcanic impact: no natural forest recovery; human impact dominant, with mosaic of regenerating, disturbed and managed vegetation

Periodic low-impact volcanism across landscape, effects spatially diverse, with DK significantly affecting Garua only Notable spatial variability in impact of W-K3, with strong spatial differentiation between areas of high and low impacts Significant volcanic impact, with major effects

W-K1 to W-K2 (5900 – 3600 cal yr B.P.)

Pre-W-K1 (pre 5900 cal yr B.P.)

Major volcanic impact; later human impact on landscape

Human impact is variable across landscape and in places not significant

Human impact is significant, with initial depopulation; on return, clearance, cultivation and arboriculture, resulting in a mosaic landscape

Significant volcanic impact

Humans present, with some spatially variable landscape effects

Periodic. Small scale impacts

Human presence slight

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Figure 6. Summary of the landscape changes at Numundo, as indicated from the analysis of fossil phytoliths at sites across the study area. The area depicted is c. 10 km (north – south) by 4 km (east – west).

(Table 5, Table 6; Fig. 6). Despite the W-K1 tephra probably causing widespread damage in the Numundo area (Boyd et al., 1999a), the vegetation was not completely devastated. The 30cm thickness of ash at Numundo would be expected to have resulted in some tree limb breakage and defoliation of plants such as palms (Lentfer and Boyd, 2001). Torrence (2002b) suggests that W-K1 occurred during the wet season, and ash was probably washed away shortly after deposition. All samples examined in this study show some evidence of disturbance and pioneer re-growth, although the form of disturbance is unevenly distributed across the landscape. Furthermore, while the immediately post-eruption samples indicate that this disturbance is predominantly due to the effects of ashfall associated with the W-K1 volcanic eruption at c. 5900 cal yr B.P., the later samples are associated with archaeological artefact evidence and, importantly, evidence for increased burning more consistent with human activity. In contrast, following the W-K2 eruption, true forest phytolith types representing re-growth from natural disturbance, and typically found in the early post-W-K1 soils, are completely absent; instead, phytoliths indicative of anthropogenic disturbances and open environments are more commonly present after the W-K2 eruption. Furthermore, inter-site variability was high throughout this period and the post-W-K2 landscape characteristically comprised a mosaic of localized regenerating, disturbed and managed vegetation. For the later events, it is notable that Torrence (2002b) suggests, from the paucity of cultural evidence, that the W-K3 eruption may have been as severe as the W-K2 eruption. The phytolith evidence suggests that the immediately post-W-K3 landscape comprised predominantly moderate to highly disturbed habitats. The W-K3 tephra is on average c. 0.50 m thick, thus being categorized as having moderate impact on the

landscape (Boyd et al., 1999a). Such impact included common to extreme tree limb breakage and defoliation, and crop burial, with good vegetation recovery from new shoots, suckers and seedlings, possibly within decades (Lentfer and Boyd, 2001; Boyd et al., 1999a). Interestingly, the tephra distributions suggest that at sites that should have been most affected, the vegetation is more similar before and after the eruption than for sites further north at Numundo. These latter sites are in an area that has been less affected by the tephra airfall, and the vegetation there displays a stronger human signal or are open wetland sites. Nevertheless, there have been some changes, with apparent replacement of palms and ginger phytoliths by Cyathula prostrata Bl. (Amaranthaceae) type, and of helophytic wetland types by geophytic grassy wetland types; there appears to be a trend towards a dryer or more seasonal landscape rather than permanent wetlands. By the time of the W-K4 eruption, the landscape had diversified again. The northern area had remained as predominantly disturbed wetland, with some areas drying slightly. Further south, there is open grassy wetland with little evidence of fire or vegetation disturbance, although some evidence of human activity. Yet farther south, areas of highly disturbed fired areas were probably strongly influenced by human activity, while elsewhere there is evidence for forest regrowth. The W-K4 tephra is thinner (c. 0.35 m), and thus probably had less impact than the prior eruptions—destruction of crops and some defoliation and limb breakage, with only months for recovery (Lentfer and Boyd, 2001). The post-W-K4 soil is notably well developed, suggesting, along with the archaeological evidence, increased human activity. The immediately post-W-K4 phytolith evidence throughout the study area provides evidence for both human and natural disturbance, and a continuing trend towards increasingly dry terrestrial conditions. These conditions

Table 7 Summary of the major trends in vegetation at Numundo, as determined by phytolith analysis at seven sequences FABK VII

FAAY V

FABD I

FABD t2

FABD t3

FABK XI

Predominantly disturbed with garden types; changes from wetland to disturbed open grassy wetland to a highly disturbed, with decreased burning.

Predominantly disturbed wetland garden types and charcoal; small decrease over time in disturbed indicators, and slight increase in grassy wetland types and charred silica.

Predominantly disturbed open herbaceous and grassland vegetation, with garden types; changes from disturbed grassy wetland to disturbed herbaceous grassland with continued burning.

Highly disturbed with some small wetlands and garden types; remains highly disturbed, with a small increase in burning.

Predominantly herbaceous woodland with garden types; remain largely undisturbed herbaceous woodland through time, with notably little evidence for burning.

Predominantly disturbed open grassland; change from disturbed grassy wetland to disturbed open grassland with decreased burning.

Post-W-K3 (post-1700 cal yr B.P.)

Predominantly disturbed, with garden types, and open grassy wetland and burning. Predominantly open grassy wetland; changes over time from wetland open herbaceous grassy wetland, with decreased burning.

Disturbed wetland with garden types and charcoal.

Predominantly disturbed and grassy wetland with garden types and burning.

Highly disturbed, with burning.

Predominantly disturbed wetland; small increase in disturbance and decline in wetland through time.

Highly disturbed, with burning of pioneer species; highly disturbed throughout period, with small ncrease in burning.

Open wetland.

Predominantly disturbed wetland.

Disturbed herbaceous wetland significant number of disturbed area types now found in garden plots; changes from predominantly wet forested area to disturbed herbaceouswetland, with continued evidence of burning. Predominantly disturbed wet forest.

Predominantly undisturbed herbaceous woodland with some garden types. Highly disturbed garden types; remain a highly disturbed area, with notable increase in burning.

Predominantly herbaceous woodland, with non-specific types and many garden types; changes from disturbed woodland to slightly more open herbaceous woodland; burning remains the same. Mainly disturbed woodland, with nonspecific types common; throughout this time. Predominantly disturbed forest garden types; changes from herbaceous woodland to disturbed regrowth forest.

Continued disturbance, a significant increase in pioneer and garden components, decrease in forest, and slight increase in estuarine vegetation. Disturbed closed woodland.

Continued disturbance, decrease in the arboreal component, and increase in disturbed area and grasses.

Grassy herbaceous woodland, with some wetland and foreshore.

Continued disturbance with increased grassland and wetlands.

Pioneer re-growth and open woodland.

Predominantly disturbed grassy herbaceous woodland, with abundant ginger.

Disturbed primary foreshore-forest with pioneer re-growth woodland and wetlands.

Pre-W-K3 (pre-1700 cal yr B.P.)

Post-W-K2 (post-3600 cal yr B.P.) Pre-W-K2 (pre-3600 cal yr B.P.)

Post-W-K1 (post-5900 cal yr B.P.)

Highly disturbed.

Predominantly highly disturbed with garden types. Continued disturbance, decreased woodland and pioneer re-growth types, some wetlands and open foreshore, and increased open grassland.

Predominantly herbaceous woodland, but with many non-specific types. Disturbance, increased grasses and wetlands, and decrease in the forest and woodland.

Predominantly pioneer re-growth and open coastal woodland.

Some pioneer re-growth, mainly closed forest and woodland.

Disturbed open grassy wetland with burning.

Disturbed wetland.

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FAAH Pre-W-K4 (pre-1400 cal yr B.P.)

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continue during the period following the eruption, with all sites yielding, for example, significant amounts of disturbed area phytolith types typical of modern gardens. Conclusion The study areas of Numundo and Garua, although geographically close and representing the same broad biogeographical conditions, provide good evidence for volcanic impacts on this landscape, impacts that differ from eruption to eruption, as well as evidence for the effects and responses of people within this landscape. Boyd et al. (1999a) argued that the effects of tephra deposition on the vegetation would vary across the landscape (Table 6). Boyd et al.’s initial model was dependent on tephra depth, although this is clearly a simplification (Lentfer and Boyd, 2001), and other environmental factors (topography, weather, chemical composition of the tephra, etc.) are also important (Cronin and Neall, 2000; Lees and Neall, 1993). Here, we take two localities, a nearmainland island and a coastal plain, each with its own relationship to the distribution of tephras deposited by successive eruptions from Witori over the last six millennia, and demonstrate the variable effects incurred over a relatively small sample of landscape (Table 7). Our results reinforce the fact that each eruption has its own characteristics, both in terms of the geological character of the eruption and the vegetational impact and recovery processes. The important implication here is that depth of tephra, while being a reasonable first-order proxy for volcanic eruption impact, cannot alone define the overall effect across the landscape. At Garua Island, we have evidence for major impact, defoliation, forest decline and regrowth dominated by lighttolerant grasses for at least two of the volcanic events (W-K2 and DK, and probably W-K1). This appears to be partly a function of continuing tephra accretion following initial eruption, and so is not solely a function of initial tephra depth. In contrast, W-K3 is notable for its low impact, resulting in continuity of vegetation, especially forest. This is an event with little subsequent tephra accretion. Typically, these different pathways are reflected in the human response: the landscape was abandoned after W-K1, W-K2 and DK, possibly for hundreds of years, but not after W-K3. In contrast, in the neighboring coastal strip at Numundo, the impacts of tephra fall were severe following W-K1 (probably), W-K2 and W-K3, and less so for W-K4. This landscape lies closer to the main distribution of Witori tephras, and so it may be expected that the effects are greater. However, there is also good evidence for the spatial distribution of impacts, with the landscape continuously responding as a mosaic; the nature of the land surface is as important as the depth of tephra deposition. Furthermore, this area appears to have experienced significant human impact, and some of the recovery pathways may have been influenced by prior human impacts on the landscape. In particular, there appears to be little natural forest recovery following W-K2, perhaps reflecting human effects on the landscape before that event, and reflecting the dominance of human disturbance after the eruption, which would have

inhibited natural regrowth and resulted in a mosaic of disturbed and managed vegetation. Unlike Garua, humans are less evident following W-K3 but are dominant in the latest stages of this landscape history. The key to this analysis is the ability to separate the vegetational effects of various influential processes on the landscape, notably volcanism, human activity and, to a lesser extent, sea level change and attendant coastal evolution. Furthermore, it is now clear that the pre-eruption conditions need to be fully determined before it is possible to understand the impact and recovery processes on the landscape at any particular place. Likewise, it is important to examine the whole landscape, as is evident in the implications of landscape partitioning in our study areas following different eruptions. Furthermore, all of the sites we examine provide evidence for the presence of people in the landscape. Much of the impact we record from human activity (e.g., dominance of grasses and other pioneer vegetation in the phytolith assemblages, presence of gardens, forest clearing, and restrictions on natural forest recovery following volcanic eruption) parallels the evidence emerging from the archaeological study of this region. Further study is still required, both to tease out the site-by-site differences, especially in terms of the human versus volcanic impacts and, notably, post-volcanic human response. Although our work in the region is beginning to provide evidence that may differentiate the patterning of human impact in the landscape (e.g., the presence of Imperata phytoliths; Boyd et al., 1999a), there is still further detail that can be extracted from our data. While at present we consider the record of volcanichuman interaction to be sound, we will be looking in further detail at the palynological evidence for patterns of vegetational disturbance that may better signal either volcanic or human influences. Once, for example, the pollen analysis at Garu (Jago and Boyd, in press) has been completed, we will be able to further examine the landscape, adding other environments to the assemblage we have already studied. At present, we note that this study emerged from a model of environmental response largely to the magnitude of volcanic impact, as measured by tephra thickness. While this still holds as a basic model, it is now clear that the characteristics and context of tephra deposition is also important. However, our study now suggests that the human response to these volcanic events, as registered in the effects that human activities have upon the vegetation, do not simply reflect an automatic response to the immediately physical conditions of the posteruption landscape. Prior vegetational patterns, determined in part by previous human activity, may be significant influences on the ability of people and environment to recover after an event. Furthermore, the archaeological study of this landscape indicates that human occupation and settlement has not been constant throughout the period of interest; our evidence indicates that the human response is in part a function of the style of the social occupation of the landscape. Human responses, and especially the ability to re-occupy the landscape after a catastrophic event, will therefore be a complex function of the physical parameters of volcanic eruption and deposition, and social processes and functionality within the landscape.

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Once the remaining studies in this larger project are completed, we will be able to define that complex function in greater detail. Acknowledgments We are especially grateful for the support and assistance provided from Dr Robin Torrence, Australian Museum, her continuing support, enthusiasm and organization, for her unfailing ability to keep the Prehistoric Archaeology of West New Britain Research Project running over the last decade and a half, and for accommodating all of us in the field over the years. We also thank the New Britain Palm Oil Ltd. for its support and access to sites. We have been funded by grants from the Australian Research Council, the Australian Institute for Nuclear Science and Engineering, the Australian Museum, and Southern Cross University. Lentfer was supported by an SCU Postgraduate Award and Parr by an Australian Postgraduate Award and an AINSE Postgraduate Award Scholarship; Lentfer, Parr and Jago have been awarded small postgraduate grants from the School of Environmental Science and Management, Southern Cross University. We thank Jim Specht, Peter White, Vince Neal, Lisa Kealhofer and Michael Therin and the many volunteers from Australia and PNG, and local people, New Britain Oil Palm Co., Walindi, Garua and Mahonia Na Dari staff, and technical support and other academic staff at Southern Cross University for their support. References Araho, N., Torrence, R., White, P., 2002. Valuable and useful: mid-holocene stemmed obsidian artefacts from West New Britain, Papua New Guinea. Proceedings of the Prehistoric Society 68, 61 – 81. Barton, H., Fullager, R., Torrence, R., 1998. Clues to stone tool function reexamined: comparing starch grain frequencies on used and unused obsidian artefacts. Journal of Archaeological Science 25, 1231 – 1238. Berglund, B.E., 1986. Handbook of Palaeoecology and Palaeohydrology. Wiley, Chichester. Bowdery, D., Hart, D., Lentfer, C.F., Wallis, L., 2001. The universal phytolith key. In: Meunier, J.D., Colin, F. (Eds.), The Phytoliths. Applications in Earth Science and Human History. Cerege, France, pp. 267 – 278. Boyd, W.E., Torrence, R., 1996. Periodic erosion and human land use on Garua Island. PNG: a progress report. Tempus 6, 265 – 274. Boyd, W.E., Lentfer, C.J., Torrence, R., 1998. Phytolith analysis for a wet tropics environment: methodological issues and implications for the archaeology of Garua Island, West New Britain, Papua New Guinea. Palynology 22, 213 – 228. Boyd, W.E., Lentfer, C.J., Luker, G.O., 1999a. Environmental impacts of major catastrophic Holocene volcanic eruption in New Britain, P.N.G.: a preliminary model for palaeoenvironmental change. In: Kesby, J.A., Stanley, J.M., McLean, R.F., Olive, L.J. (Eds.), Geodiversity: Readings in Australian Geography at the Close of the 20th Century. School of Geography and Oceanography. Australian Defence Force Academy, Canberra, pp. 361 – 372. Boyd, W.E., Webb, J., Specht, J., 1999b. Holocene shoreline change and the archaeology of the Kandrian coast of West New Britain, Papua New Guinea. In: Hall, J., McNiven, I.J. (Eds.), Australian Coastal Archaeology: Current Research and Future Directions. ANH Publications, Canberra, pp. 283 – 289. Cronin, S.J., Neall, V.E., 2000. Impacts of volcanism on pre-European inhabitants of Taveuni, Fiji. Bulletin of Volcanology 62, 199 – 213.

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