Climates of change: human dimensions of Holocene environmental change in low latitudes of the PEPII transect

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Quaternary International 118–119 (2004) 165–179

Climates of change: human dimensions of Holocene environmental change in low latitudes of the PEPII transect Simon G. Haberlea,*, Bruno Davidb b

a School of Geography and Environmental Science, Monash University, Victoria 3800, Australia Programme for Australian indigenous Archaeology, School of Geography and Environmental Science, Monash University, Victoria 3800, Australia

Abstract Rapid climate change events can have devastating impacts upon agricultural production and human society. Advances in spatial and temporal resolution of palaeoenvironmental and archaeological data enable detailed examination of the nature of human– environment interactions. Recent studies have shown that throughout the Holocene human populations responded to rapid climate change events by existing subsistence strategies adopting to novel environmental conditions. In the case of agriculturalists in New Guinea and hunter-gatherers in northern Australia, climate change set in motion a range of biological and demographic possibilities and restrictions that had long-term consequences for each region. The early Holocene climatic and ensuing environmental transformations heightened natural biomass production and population increases. Consequently, later rapid changes in climate centred around 6000 and 3500 cal yr BP, resulted in the adoption of innovative technologies and diverse subsistence strategies throughout the region that reduced the vulnerability of people in an environment of increasing unpredictable climate variability. r 2003 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction One of the outstanding features of the PEPII transect is the presence of shallow warm seas known as the IndoPacific Warm Pool that is adjacent to some of the most biologically and culturally diverse landscapes of the world (Myers et al., 2000; Cashdan, 2001). Climatically, inter-tropical parts of the transect are distinguished by enhanced tropical convection that has been shown to be fundamentally important to the general circulation of the global atmosphere and the operation of the Asian monsoon (Tapper, 2002). While the annual passage of the monsoon southward across the equatorial islands and into northern Australia is a relatively predictable phenomenon on short timescales, recent extreme climatic events associated with strong El Nin˜o conditions in 1982–1983 and again in 1997–1998 caused failure of the monsoon leading to severe drought and extensive fires across a large part of inter-tropical Austral-Asia. The impacts of these events on human populations were *Corresponding author. Resource Management in Asia Pacific Program, Research school of Pacific and Asian Studies, Australian National University, Canberra, ACT 0200, Australia. Tel.: +61-2-6125-3373, fax: +61-3-61-254896. E-mail address: [email protected] (S.G. Haberle).

significant due to increased levels of atmospheric pollutants and the loss of crop production leading to famine and human displacement (Bourke, 2000). How climate change and variability might affect people over longer timescales, both in the past and in the present, is less well understood. Recent reviews of cultural responses to climate change during the Holocene in the Old World (Dalfes et al., 1997; Weiss and Bradley, 2001) and New World (de Menocal, 2001) have emphasised the vulnerability of structurally complex societies to abrupt and widespread climate events. In a study of Mayan settlement in lowland Guatemala during the late Holocene, Hoddel et al. (1995) suggest that cultural development and population expansion occurred under climatic conditions favourable to agriculture and that the subsequent decline of the Maya cultures were associated with protracted and severe droughts. Similar sequences of cultural change are linked to the failure of wetland agricultural systems in the Bolivian altiplano (Binford et al., 1997) and in the Amazonian lowlands (Meggers, 1994), while wholesale shifts in settlement-subsistence systems following prolonged droughts have been documented for 14th century AD Anasazi-Pueblo communities of the American Southwest (e.g. Plog, 1997; Adler, 2002). These studies suggest that there are climatic

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thresholds to cultural tolerances and trends, and that abrupt, unpredictable climate changes can have devastating consequences on human populations by disrupting agricultural production forcing repeated human dispersal, conflict and realignment of social and trade networks. However, Williams (2002) also points out that the timing of climatic disasters and the demise of state structures are not necessarily synchronous and that alternative models that incorporate complex social, ecological and climatic dynamics are required to adequately account for cultural transformation. Instructive in this context are the findings of Dwyer and Minnegal (1992) amongst the Kubo of southern Papua New Guinea, documenting sustained shifts in subsistence practices following major social transformations during historical times. The occurrence of major drought episodes in the lowlands of the Central Americas and Andean highlands at around 1000 cal yr BP1 have been linked to extreme ENSO conditions (Thompson et al., 1994; Binford et al., 1997), and as such, are likely to be associated with periods of extreme drought in the western Pacific, and more specifically Southeast Asia, New Guinea and northern Australia. Historical records show that prolonged droughts of more than 5 yr have occurred on both sides of the Pacific and have impacts beyond these limits. The mega-Nin˜o of 1788–1793 represents one of the most devastating and prolonged droughts that impacted upon India, the islands of equatorial Pacific and Peru (Ortlieb, 2000). In India the ensuing famine resulted in over 11 million deaths and massive depopulation in agricultural regions (Groves, 1997). The occurrence and impact of widespread and protracted drought at earlier times than this are less well documented. How significant are rapid climate change events in human history? Bellwood (1997, p. 310) and Haberle and Chepstow-Lusty (2000) take the view that cultural shifts from hunting and gathering to agriculture, that take place during the early Holocene across the IndoMalaysian Archipelago and the island of New Guinea, signal wholesale adaptive transformations following rapid climatic and environmental changes at the end of the last glacial period. Rowland (1983, 1999) takes a similar view for late Holocene intensification of resource production within hunter-gatherer Australia. However, the evidence for catastrophic collapse of complex societies that have been linked to rapid climate change, analogous to those recorded in Mesopotamia and the New World tropics, is rare in the western equatorial Pacific. In a study of mid Holocene occupation sites in northern China, Liu (2000) considers the transformation of Neolithic culture to a state-level social complex at 1

Ages based on the radiocarbon method are given as calibrated radiocarbon years before AD 1950 (cal yr BP) based on CALIB v3.1 (Stuiver and Reimer, 1993), unless otherwise stated.

around 4600–4000 cal yr BP to be at least partially the result of large-scale climate changes. The demise or collapse of the pre-urban Longshan culture at around 4000 cal yr BP coincides with a period of climate change characterised by lower temperatures, higher precipitation and increased flooding and course alteration of the Yellow River. Liu (2000) considers that these changes triggered major population movements and possibly decline, realignment of social groups, and inter-polity conflict. In this paper, we explore the evidence for the influence of Holocene climate change on two culturally diverse human populations—hunter-gatherers of northern Australia and horticulturalists of highland New Guinea— within the low latitudes of the PEP II transect (Fig. 1). In investigating causality, the emphasis is on the degree of chronological fit between major climatic and cultural changes, and on the adaptability as well as vulnerability of people to rapid climate change events. In doing so, we address processes of adaptation, change and intensification not only in terms of shifts from one general food exploitation strategy to another—i.e. hunting and gathering to horticulture—but also in terms of their internal workings.

2. Abrupt climate change events transect during the Holocene: inter-tropical Austral-Asia There is increasing evidence for abrupt climate fluctuations at decadal to century timescales and possibly global (or at least hemispheric) spatial scales during the Holocene (Overpeck, 1996). The most significant periods of change for human populations in the Northern Hemisphere centre around prolonged episodes of aridity at 12,800, 8200, 5200 and 4200 cal yr BP that have been identified in ice cores, marine and lake sediments, and speleothem records (Weiss, 2000). The Younger Dryas event lasting from 12,800– 11,500 cal yr BP is the most severe of these fluctuations and yet evidence for terrestrial biotic or glacial response in the low latitudes of the PEPII transect remains problematic (Maloney, 1995). This is best illustrated in the contrasting marine records from just north of the equator, where the late glacial transition sea surface temperature reconstruction from the South China Sea (5–10 N) shows a well-defined B^lling-Aller^d and Younger Dryas events (Kienast et al., 2001), whereas the records from the centre of the Indo Pacific Warm Pool show no such temperature reversal over the same time period (Lea et al. 2000; Stott et al., 2002). This suggests that local climate dynamics associated with the Indo-Pacific Warm Pool may have overshadowed any influence from deglaciation in the Northern Hemisphere. Similar conclusions can be drawn for the 8200, 5200 and 4200 cal yr BP events, where there are potential

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Fig. 1. Location of the highlands of New Guinea and SE Cape York Peninsula in northern Australia. Inset: Austral-Asian Inter-tropics.

candidates in the palaeo-records (e.g. a brief cold spike centred on 8100 cal yr BP from coral records, Gagan et al., 2003) that could be matched with these episodes in time. However, these records are neither spatially coherent, nor is their dating demonstrably synchronous to justify considering them as directly associated with these identified Northern Hemisphere events. Whether or not these events are truly global, or rather as their spatial distribution suggests restricted to the Northern Hemisphere, is yet to be determined. Fig. 2 compares proxies of environmental change for inter-tropical PEP II and globally. Episodes of abrupt climate change have been recorded in the low latitudes of Australia and Southeast Asia during the Holocene. High levels of precipitation and cloudiness in the region today are strongly influenced by the Intertropical

Convergence Zone (ITCZ), where converging and seasonally fluctuating moisture-carrying winds from the north and south ascend and create high moisture and cloudy conditions. The combination of palaeoclimate evidence derived from vegetation histories and ocean sediment records suggest that the ITCZ has fluctuated significantly since the last glacial maximum around 22,000 yr ago due to changing influence from the Southern Hemisphere summer monsoon and the southeast trade winds (Huang et al., 1997; Wyrwoll and Miller, 2001). Long-term climatic and environmental trends based on equatorial glaciers (Hope and Peterson, 1976), ancient pollen, charcoal and lake levels (Barmawidjaja et al., 1993; Flenley, 1998; Haberle, 1998; Haberle et al. 2001; Jarvis, 1993) indicate that conditions were dry and possibly as much as 5–7 C cooler

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Fig. 2. Comparison between equatorial PEP-II and global climate proxies. (a) abrupt climate change events identified in the Northern Hemisphere (Weiss, 2000), (b) number of El Nin˜o events per 500 yr in an orbitally forced model of the tropical Pacific (Clement et al., 2000), (c) regional biomass burning derived from a cumulative charcoal record from Papua New Guinea and Indonesia (Haberle et al., 2001), (d) reconstructed sea surface temperatures using foraminiferal Mg/Ca in ODP Hole 806B on the Ontong Java Plateau (after Lea et al., 2000) and alkenones from Core 17940 in the South China Sea (after Pelejero et al., 1999), (e) summer insolation at low latitudes (10 S and 10 N; Berger and Loutre, 1991), (f) ice-core data from northern hemisphere (d18O, GISP2; Grootes et al., 1993) and southern hemisphere (d18O, Byrd, Broecker, 1998).

during the last glacial maximum. Some parts of northeast Queensland received only about one third of today’s rainfall levels (currently 800–1100 mm per annum in most parts). Despite the very high rainfall received today in the highlands of New Guinea (around 2000 mm per annum up to as high as 8000 mm per annum) some highland valleys did not then support forest cover due to high levels of disturbance from biomass burning (Haberle et al., 2001). This has been interpreted as a combination of lower precipitation and greater variability in rainfall patterns, enhancing the potential for frequent fires between 20,000 and 10,000 cal yr BP. Climatic ‘amelioration’ began around 17,000–15,500 cal yr BP in the highlands of New Guinea, when rainfall associated with the greater influence of the Southern Hemisphere summer monsoon began to increase. However, the impact of this change may not have been as severe until much later in areas influenced

by rapidly changing coastlines such as the Atherton Tableland (southeastern corner of Cape York), where increases in precipitation were probably most severe just prior to 11,500 cal yr BP (Hiscock and Kershaw, 1992). The highest levels of precipitation and temperature occurred across the region during the early Holocene after 10,000 cal yr BP. An early Holocene phase of mild climate is indicated by the absence of ice on the summit of Mount Wilhelm from around 9500–6000 cal yr BP (Hope, 1976), and the forest limit was 100–200 m higher than its present position. This is sometimes referred to in the literature as the ‘hypsithermal interval’ (Webster and Streten, 1978). The forest limit settled to its present level around 6000 cal yr BP on Mount Wilhelm, when slightly cooler conditions prevailed. Pollen records from the New Guinea highland valleys indicate human impact as early as 7800 cal yr BP and intensifying through to the present (Haberle et al., 1991; Haberle, 2000). Here

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human impacts may have overshadowed climate changes during this time. Proxy records of temperature change in northern Australia indicate that there may have been abrupt climate cooling centred around 8100 cal yr BP from coral records (Gagan et al., 2003) and between 6890 and 6090 cal yr BP from temperature reconstructions using Chironmidae from Lake Barrine in northern Australia (Dimitriadis and Cranston, 2001). While these records may represent real changes locally there is no indication that these are the result of widespread climate processes. Within the alpine regions where human impact is less intense there is evidence that at least four neoglacial advances of highland glaciers have occurred during the last 3500 yr (Hope and Peterson, 1976), suggesting minor temperature fluctuations were probably experienced lower down in the occupied valleys. However, the dating of these events remains problematic. Recent climate models for the early mid-Holocene under altered insolation forcing indicate links between the strengthened Asian monsoon, seasonally enhanced tradewinds in the tropical Pacific, and the frequency and magnitude of strong El Nin˜o temperature perturbations (Clement et al., 2000; Liu et al., 2000). A steady increase in large El Nin˜o events is observed during the Holocene, with a peak ca.3000–1000 yr ago (Fig. 2). The regional burning curve for the highlands of New Guinea shows a dramatic increase in response to increased climate variability after 6000 cal yr BP and peaking between 4500 and 1000 cal yr BP (Haberle et al., 2001). Rainfall levels in northern Australia decreased after 3500 cal yr BP, with more open vegetation associated with episodes of dune mobilisation during the late Holocene (Shulmeister and Lees, 1995). General agreement exists between the palaeo-ENSO results and the model scenario shown. Other smaller scale climatic factors such as drought and frost frequency may also have varied throughout the Holocene. These factors have been of particular concern to climatologists and geographers alike because of their interest in the possible links between El Nin˜o/ Southern Oscillation (ENSO) events and the occurrence of frost and drought. Allen et al. (1989) investigated the behaviour of these phenomena in New Guinea and found no systematic relationship between frost and drought events and ENSO. The persistence of severe drought and frost events back into the Holocene, similar to those apparent in recent climate records and oral histories, is as yet not visible in the palaeoenvironmental record (Brookfield, 1989). It will require not only fine resolution pollen analysis of vegetation histories but also a much better understanding of the modern climatic processes associated with drought and frost for a useful investigation of late Holocene climatic change to be carried out. While there is no convincing evidence that major climate events of 12,800, 8200, 5200 and 4200 cal yr BP,

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identified in records from the Northern Hemisphere, have a significant impact on the fossil biota of the Australasian tropics, there are periods of major climate change at around 6000–5000 and 3500–1000 cal yr BP that have been identified in the regional palaeoclimate records (Fig. 2). In such context of climate change, we can now ask whether or not it can be assumed that the large-scale and relatively rapid climatic transformations impacted existing human adaptive strategies—in both huntergatherer and horticultural systems—and, if so, how did people in the low latitude environments of New Guinea and in northern Australia respond and adapt during the Holocene? To address these questions requires exploring the climatic and archaeological records of both these regions.

3. Case studies on human–environment interactions 3.1. Australian aboriginal responses to environmental change: southeast Cape York Peninsula Cape York Peninsula is Australia’s largest peninsula. This was the last part of Australia to be attached to New Guinea during the early Holocene as rising seas finally sundered the last of the land bridge to form what has come to be known as Torres Strait. Some 800 km long, Cape York today contains a broad range of landforms, from low-lying sandy plains to plateaux, rugged hills and dissected gorges. The peninsula can be divided into three general longitudinal topographic, geological and biogeographic zones. Along the eastern seaboard is a narrow coastal plain that rarely exceeds 5 km in width, rapidly giving way to the mountains of the Great Dividing Range in the west. Along its lower western slopes, the Great Divide merges with the broad, expansive plains that stretch all the way to Cape York’s west coast, up to 300 km away. Archaeological research in the southeastern corner of Cape York began in the early 1960s. Since then, 42 caves and rockshelters have been excavated, more than in any similar-sized region of Australia. In addition, 10 shell mounds have also been radiocarbon dated. These sites occur in six main regions representing a range of environmental conditions: Princess Charlotte Bay and the Flinders Islands (small continental islands and sandstone-rich coastlines); the Koolburra Plateau and Laura (rugged, dissected sandstone ranges); the Mitchell-Palmer and Chillagoe (limestone karst outcrops on alluvial plains); and Ngarrabullgan (large conglomerate mesa surrounded by volcanic and metamorphic sediments). With the exception of three rockshelters and the shell mounds from Princess Charlotte Bay and the Flinders Islands towards the extreme north of the study region, all of these sites are situated well inland (and

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mostly west of the Great Dividing Range), in environmental settings never directly affected by rising or falling sea levels. The oldest known human occupation in southeast Cape York dates to 35,460+750/ 690 14C yr BP at Ngarrabullgan Cave. Numerous other caves and rockshelters (e.g. Sandy Creek 1, Nonda Rock) contain Pleistocene occupation (some dating to 30,000 14C yr BP or more), but the majority of sites date to the Holocene only (Table 1). Of the 38 caves and rockshelters from which radiocarbon dates have been obtained, 33 have basal or nearbasal dates. From these, we can calculate changing occupational trends for the region as a whole by plotting the number of sites known to have been occupied through time. Over the long-term, the temporal trends for southeast Cape York are clear. Most sites were inhabited after 5500 cal yr BP, with an increase in the

Table 1 The timing of earliest occupation, by site in north Queensland (for source of radiocarbon data see Appendix 16.1 in Lourandos and David, 2002) Site

First evidence of human occupation, in uncalibrated radiocarbon years BP

Hand Shelter Fig Tree Shelter Mordor Cave Grass Tree Shelter (inner) Lookout Shelter 1 Endaen Rockshelter Courtyard Rock Kookaburra Rock Alkaline Hill Rockshelter Painted Ell Gorge Creek Shelter Giant Horse Gallery Pete’s Chase Bush Peg Shelter Dragonfly Hollow Walaemini Rockshelter Initiation Cave Platform Gallery Echidna Shelter Red Bluff Rockshelter Grass Tree Shelter (outer) Sandy Creek 2 Red Horse Rockshelter Quinine Bush Shelter Green Ant Rockshelter Tunnel Shelter Magnificent Gallery Early Man Rockshelter Yam Camp Nonda Rock Hay Cave Fern Cave Sandy Creek 1 Ngarrabullgan Cave

667733 1440760 1580770 1610740 18807100 23707100 2790780 2950780 3440780 3620770 3700760 3750780 4040780 4160760 4430780 4760790 5290760 61207150 72807130 75307110 7600760 7830780 83107120 8390760 86607340 10,120760 10,250790 15,45071500 B25,000 B26,2007450 29,70071050 30,3007800 31,900+700/-600 35,460+750/-690

number of occupied sites occurring through time. If the number of sites occupied during a given period of time is a reflection of the frequency of visits and/or the length of stay at each site, then it appears that, during the Holocene, the onset of wet conditions was accompanied by: (1) more people moving across the landscape, creating and using more sites in the process; or (2) changed settlement systems as more or less stable populations moved residence more frequently. These increases in intensities of regional occupation or settlement shifts indicate that socio-demographic conditions and people-land relations—population numbers and/or residential structures—were changing. Looking at these same data in terms of the establishment of new occupational sites—a measure that relates to such things as changing settlement strategies, changing familiarity with local environments, and the establishment of new settlement locations in the face of changing demographic pressures—signals that many new sites were first occupied during the mid to late Holocene, indicating regional demographic transformations. This pattern is likely to have been caused by general rises in population numbers and densities across the regional landscape. These changes were most pronounced from the mid to the late Holocene, with a major increase in overall settlement numbers, shifts in the spatial distribution of occupation sites, or population displacement reaching a peak after ca.5500 cal yr BP (see David, 2002 for data). Irrespective of ultimate causes, expansions into new residential locations and increasing intensities of regional land use are implicated. These changes are likely to indicate increased density of human population in southeast Cape York, particularly during the late Holocene. As people occupy places, they leave behind material traces of their actions in the form of hearths, stone artefacts, food remains and the like. The deposition rates of such cultural materials within sites have been studied and used by many Australian archaeologists as gross indicators of relative intensities of site use, although it is also recognised that structural (qualitative) rather than quantitative socio-cultural changes may at times best explain such archaeological changes. Results for southeast Cape York demonstrate that, in the majority of cases, deposition rates of cultural materials, and especially stone artefacts and ochre, increase significantly during the mid to late Holocene. Some sites have more than one major peak in deposition rates. Others show erratic fluctuations. With four exceptions, the major peaks in deposition rates of stone artefacts always occur during the mid to late Holocene. These increases begin at various times between 6200 cal yr BP (Ngarrabullgan Cave) and 1700–900 cal yr BP (Early Man Rockshelter), with most taking place during the last 4500 yr and involving a doubling or tripling of rates during the mid–late

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Holocene (David, 2002). These trends cannot be explained as a function of taphonomic bias, as in many cases cultural sequences can be traced back into the Pleistocene, often with well preserved organic deposits in limestone caves. Overall, increasing intensities of site and regional land use are implied, indicating changing relations between people and their environments. Here again, then, demographic conditions are indicated to have changed after 4500–3500 cal yr BP, typically indicating a doubling to tripling of intensities of site use if artefact deposition rates can be taken to reflect general occupational intensities. Sediments are deposited under historically specific environmental conditions; changes in sedimentation rates within sites imply changes in depositional and/or erosional regimes. In general, other factors being equal, sedimentation rates in caves and rockshelters tend to increase with increasing intensities of human occupation. This correlation is largely the product of three factors: (1) the introduction of new raw materials (e.g. wood for fires) into a site; (2) the initiation or acceleration of cave wall disintegration as a result of human-induced microclimatic changes (e.g. fire-induced) and mechanical erosion (e.g. touching, trampling); and/or (3) the initiation or acceleration of slope instability and colluvial slope wash as a result of increased firing or clearing of the landscape. Sedimentation rates are therefore a potential tool for exploring changing relations between people and place. There is strong and repeated evidence for changing sedimentation rates within excavated sites across southeast Cape York. Major, 2.5- to 5.5-fold increases in sedimentation rates occurred in almost all the excavated sites during the mid to late Holocene, most sites hovering around a 3-fold increase (David, 2002). That is, sediments accumulated consistently faster during the mid and late Holocene than earlier, suggesting increasing intensities of site and regional land use. However, we must be cautious in interpretation as few detailed geomorphological studies have yet been undertaken. The results are nevertheless consistent with the findings of other proxy tests, changing sedimentation regimes apparently attesting to rising levels of regional land use during the mid and late Holocene, particularly after 4000 yr BP. Very few recognised stone artefact types have ever been excavated in southeast Cape York. The exceptions are edge-ground axes (present since the late Pleistocene), seed grinding stones and Burren adzes. Rare backed flakes are also found, but in very low numbers and in very few sites. When found, they are in mid to late Holocene contexts, the only exception being Walkunder Arch Cave where three flakes with backing were found in terminal Pleistocene deposits (Campbell, 1982, 1984). Given this limited range of recognised formal types, few typological changes can be expected through time.

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Burren adzes—stone tools that were once hafted onto wooden handles and used to shape wooden artefacts of various kinds (e.g. shields, wooden containers)—are repeatedly found across the peninsula after 4500 cal yr BP (and especially after 2400 cal yr BP), but clearly absent during earlier times. They are, therefore, an exclusively late Holocene phenomenon that continued into ethnographic times. In Australia generally, few stone artefacts can unambiguously be said to be directly related to food processing. Of these, an important and well-defined temporal trend has emerged. Food processing stone artefacts are almost always limited to seed-grinding stones, which in Cape York have never been found in contexts older than 1800 cal yr BP (at Sandy Creek 1; they also occur in the very upper, undated units of Giant Horse Gallery, the base of which site is dated to ca.4200 cal yr BP). These dates correspond favourably with similar ages for the commencement of systematic seed grinding and for the processing of toxic plants elsewhere in central and eastern Australia (see David, 2002, chapter 8). The implication is that major changes in diet occurred in Cape York during the late Holocene, changes that saw the exploitation of new staple plant foods in some regions available in vast quantities. The ramifications of such a change are not exclusively economic or demographic, but also imply changes in the way people interacted with and symbolised their immediate surroundings, transforming grasslands to harvestable fields, previously unused stone outcrops into sources of stone that could be worked into economically valuable (including tradeable) grinding stones. The commencement of seed grinding implies transformations as to how people visualised and signified their surroundings. These changes have bearing on the scheduling of everyday life and seasonal cycles. There is an implication here for both a conceptualisation of the landscape and for the use and management (and therefore labour) of the land—both instances of shifting relations between people and between people and their environments. David (2002, chapter 8) has explored these issues in considerable detail. Systematic recordings have been made in southeast Cape York of 10,746 rock pictures from 398 sites, representing 19 geographically distinct regions. Of these a clear temporal trend emerges, from early artistic conventions spread across the peninsula, to increasing regionalism beginning around 3700 and culminating after 2000 cal yr BP. The late Holocene rock-art of Cape York can thus be read as a statement of the structured division of socially engaged, marked and signified space. In the increasing regionalism of post-3700 cal yr BP times, the landscape became newly differentiated. The rock-art can be seen as a mark of regional difference and symbolic structure. What we find in Cape York is not a widespread and static socio-spatial system, but instead a

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dynamic and emerging set of geographically distinctive networks of place marking. During the late Pleistocene and early Holocene, the landscape was inscribed with geographically relatively homogeneous artistic symbols, becoming increasingly regionalised after 3700 cal yr BP. This process of regionalisation continued with increasing momentum through the course of the late Holocene, the intensity and nature of painting activity beginning to approximate the ethnographic situation around 2000 cal yr BP. At nearly 50 km across, Princess Charlotte Bay is large. Ten shell mounds represent the only open sites to have been radiocarbon dated in southeast Cape York. Measuring up to 30 m in diameter and 5 m in height, the mounded middens consist almost entirely of a single species of shell, Anadara granosa, a species of cockle that can be found in mangrove beds nearby. Such shell mounds are common on the mid-Holocene chenier plains of the bay, and date from 2000–1600 to 500– 400 cal yr BP only (Beaton, 1985 8–9). Being more recent than the chenier plains themselves (formed 7000– 4500 cal yr BP), formation of the middens can be attributed to the onset of new, centralised consumption bases, novel foraging practices, disposal patterns and site selection across the bay. The systematic exploitation of mangrove beds, especially A. granosa, implies the beginnings of a new, specialised and focused subsistence strategy from 2000 to 1600 cal yr BP. In southeast Cape York the mid to late Holocene was a period of demographic and cultural dynamism. Lourandos and David (2002) show that elsewhere in Australia similar changes have been documented, including: (1) major increases in deposition rates of stone artefacts and food refuse; (2) the advent of new tool types (including fish hooks and grinding stones) and site types (e.g. shell and earth mounds); (3) the use of new plant foods (including systematic seed grinding in the arid zone and techniques for detoxifying poisonous plants in central and north Queensland); (4) demographic expansions onto previously unused offshore islands; (5) increases in the frequency or intensity of firing of the landscape (e.g. the Sydney Basin); and (6) probably also the beginnings of complex installations to increase productive yields in some parts of Australia (e.g. inland river eel-traps in western Victoria; coastal fish traps in southeast Queensland). Together, these innovations and amplifications of existing cultural practices imply an expansion of settlement into previously unused or little-used habitats, including: (1) a more intensive use of marginal environments; (2) an ‘intensification’ of landscape management practices (e.g. burning); and (3) a broadening of resource bases during the mid to late Holocene. These changes imply marked population growth and geographical expansions, increases in intensities of site and regional land use, and increased levels of regional demographic

packing across much of Australia during the mid to late Holocene. Dynamism does not appear to have been uniform across the landscape, or contemporaneous in all cultural dimensions. This begs the question of whether a single, systemic re-modelling of socio-economic networks is indicated, or whether the various related, but to some degree regionally distinctive, changes can be attributed to a variety of proximal causes. Further, an important aspect of change appears to have been a continuing increase in the use of some regional landscapes (e.g. western Victoria), and a possible decrease or stabilisation in others (e.g. Central Queensland Highlands) during the last 2000 yr or so. These geographically distinct socio-demographic trends imply a combination of shifting and increasing demographic structures and settlement systems through time. The mid to late Holocene thus witnessed widespread cultural transformations across southeast Cape York, akin to similar transformations elsewhere on the continent. This was a period of largely unprecedented rates of change, involving the appearance of shorterspaced regions of artistic influence, new artefact forms, new manufacturing technologies, changing resource management strategies, food processing procedures and settlement-subsistence systems. These alterations were not haphazard, but involved increases in the numbers of sites occupied and in deposition rates of cultural materials and sediments within sites, as well as a broadening of site types and increasing social regionalism. Together, these innovations suggest a general, approximately 3-fold increase in intensities of site and regional land use during the mid to late Holocene; a growth in the use of regional landscapes through time. These changes were most pronounced between 3700 and 2000 yr BP. 3.2. Melanesian responses to environmental change: highlands of New Guinea The highlands of New Guinea refers to the inland regions of the island between an altitude of about 1200 and 2500 m above sea level (asl), where broad valleys support high population densities. The earliest archaeological evidence for human settlement in the highlands of New Guinea comes from two sites in the eastern part of the island: Kosipe, an open site at 2000 m asl (White et al., 1970) and Nombe, a rockshelter at 1660 m asl (Gillieson and Mountain, 1983). Both sites have initial occupation evidence dated to around 29,000 cal yr BP and contain evidence of exploitation of local resources, possibly in a seasonal manner, during a period which was cooler than present. A gradual increase in the number of occupied rockshelters occurs between 18,000 and 10,000 cal yr BP (Fig. 3) (Table 2) as temperatures along with

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Fig. 3. Time series of archaeological sites and items recovered from these sites over the last 21,000 14C yr BP (500 yr time slices) in north Queensland (see Table 2). The data has been clustered into zones based on CONISS, and statistical package associated with TILIA (Grimm, 1991).

biomass increase. This may represent an increase in population numbers within the valley systems or a greater mobility of populations at lower altitude exploiting highland valleys as species previously excluded from the highlands dispersed up slope following climatic change. Although a number of food species are excluded from the highlands during colder periods, including tubers and fruits like yams and bananas important in traditional New Guinea agriculture, a range of vegetable foods, which are recorded as cultivated in modern gardens, may have been viable in highlands valleys (Haberle and Chepstow-Lusty, 2000). These included traditionally important cultigens like taro (Colocasia esculenta), sugarcane (Saccharum officinale) and gourd (Cucurbitaceae), though there is some question as to whether these were in fact present in the

island before the Holocene (Bellwood, 1996). The occurrence of infrequent but severe droughts and associated frost particularly between 20,000 and 11,500 cal yr BP in highland New Guinea (Fig. 4), would have put sustained production of most food plants out of question, but short-term and sporadic production would have been possible in this environment. Limited and localised as forest clearances for such purposes may have been, they would have added to other benefits of extending open vegetation for hunting and ease of communication. At Sirunki (2500 m asl, Walker and Flenley, 1979) and Haeapugua (1650 m asl, Haberle, 1998) the pollen evidence points to retardation in the establishment of forest until 10,000 cal yr BP. The sporadic development of montane forest in highland valleys at the end of the

Number of occupied caves and rockshelters

Timing when stone artefact deposition rates begin to increase

Timing when sedimentation rates begin to increase

Earliest Burren adzes

Earliest blades and microblades

Earliest seed grinding stones

Timing when ochre deposition rates begin to increase

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 10,000 10,500 11,000 11,500 12,000 12,500 13,000 13,500 14,000 14,500 15,000 15,500 16,000 16,500 17,000 17,500 18,000 18,500 19,000 19,500 20,000 20,500 21,000

62 61 64 57 46 41 32 35 28 23 12 15 8 9 10 11 10 4 1 4 5 4 4 6 7 8 5 2 2 4 3 3 2 2 1 0 1 1 2 2 3 3

20 22 22 23 21 21 19 18 15 14 13 12 12 11 11 10 7 5 4 4 3 3 3 3 3 3 3 3 3 3 2 2 2 2 3 3 3 3 3 3 3 3

0 0 4 2 4 0 3 4 2 2 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0

0 1 2 0 1 0 3 2 0 1 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 2 4 2 2 0 0 1 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 1 2 2 0 2 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 1 3 4 2 0 5 5 2 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 1 1 3 1 2 1 3 3 1 1 0 1 0 1 3 2 1 0 2 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0

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Number of sites Number of when occupation carbon dates (Rick’s method) begins

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Years BP (beginning)

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Table 2 List of items recovered from excavations over the last 21,000 yr (500 yr time slices) in north Queensland (for source data see Appendix 16.1 in Lourandos and David, 2002). (for an explanation of Rick’s method see Lourandos and David (2002, p. 310) and Rick, (1987)

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Age (10 3 cal yr B.P.) 2

0

4

6

8

10

12

14

16

18

20

22

24

(a)

Severe ENSO droughts

Climate change in PEP-II tropics

Warm Wet Stable

Cool Dry Unstable

Cold -5oC

0.4 (b)

Regional Biomass Burning (Cumulative Charcoal) Scheme for development of agriculture in the highlands of New Guinea

0 megafauna

(c)

small game

Hunting Foraging Forest Swidden Swamp gardens Grassland gardens/ monocultures Agroforestry Raised garden beds

40

(d)

Number of occupied archaeological sites in the highlands of New Guinea

0 0

2

4

6

8

10

12

14

16

18

20

22

24

3

Age (10 cal yr B.P.)

Fig. 4. Comparison between climate and cultural change during the last 24,000 cal yr BP. (a) general trends in climate change in New Guinea (Haberle et al., 2001), (b) regional biomass burning derived from a cumulative charcoal record from Papua New Guinea and Indonesia (Haberle et al., 2001), (c) a possible scheme for the development of agriculture in the highlands of New Guinea (Haberle and Chepstow-Lusty, 2000), (d) number of archaeological sites occupied in the highlands of New Guinea (500 yr time slices) adapted from data in Table 2 of Haberle (1993, p. 111).

last glacial indicates that conditions were not uniformly suitable for forest development until after this time. These inconsistencies reinforce the suggestion that fire, of either natural or anthropogenic origin, may have played a significant role in reducing the suitability of new forest habitats that were liberated from cold temperatures and low atmospheric CO2, but not free from frequent fires (Haberle et al., 2001). The timing and nature of the beginnings of agriculture in the highlands of New Guinea remains a contentious issue (Spriggs, 1996; see Bird et al., 2003). If agriculture was being practiced around 10,000 cal yr BP in the Wahgi Valley, Papua New Guinea, as suggested from the archaeological evidence at Kuk Swamp (Golson, 1991), then current pollen evidence does not register clearance until 2200 yr later, in the Baliem Valley, West Papua, where forest clearance, characterised by loss of forest cover, increased secondary forest taxa and increased burning, is found (Haberle et al., 1991). This suggests that either the agricultural activity remained very localised for a long period of time or that the nature of the antiquity of early agriculture in New Guinea requires re-assessment. However, by

6000 cal yr BP and after, many swamp forest environments experienced rapid loss of old growth forest species and replacement with fast growing secondary woody species or open grass/sedge swampland (Haberle, 1998, 2000). This can be ascribed to an increase in the intensity of wetland use at Kuk Swamp by Phase 2 (Bayliss-Smith, 1996), and at different times across the highlands, coupled with an increase in climate variability due to the onset of more frequent and more intense El Nin˜o-Southern Oscillation (ENSO) events. The increase in occupation sites across the highlands at 6000 cal yr BP may reflect a dramatic increase in population numbers as technological transformations and clearance of swamp forest environments for food production took place. The implication is that: (1) more people were able to subsist in the highlands, creating and using more sites in the process; or (2) settlement systems changed as more or less stable populations utilised a greater range of environments within a more unpredictable climate regime. This is akin to the transformations in socio-demographic conditions and people-land relations that were taking place in northern Australia at the same time.

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Within the last 3500 yr of agricultural activity at Kuk the appearance of three important techniques found in contemporary gardening are recorded; soil tillage by 2500 cal yr BP, tree-fallowing by around 1200 cal yr BP and raised-bed cultivation by 400 cal yr BP (Golson, 1977; Golson and Gardner, 1990). There are no other sites in New Guinea that show an equivalent sequence of development, though fossil agricultural structures are known from the Arona Valley in the Eastern Highlands and elsewhere. The only other major events during the last 3500 yr in the highlands that have been established from the archaeological record is the occupation of open sites in the Eastern Highlands (Watson and Cole, 1977) and the development of complex systems of exchange involving stone axes from the Tuman quarries south of the Wahgi Valley (Burton, 1984). Burton’s (1984) analysis of stone axes from these quarries and fragments found in excavations of rockshelters suggested to him that the process of stone axe exchange began sometime between 2500 and 1400 cal yr BP. These changes are particularly significant as they demonstrate a possible interconnected development in land use, settlement patterns and sociopolitical structure that undoubtedly had major impact on the environment (Golson and Gardner, 1990). Comparison of the available palaeoenvironmental data from New Guinea with the record from intertropical America shows a striking synchrony between

apparent low climatic variability during the Medieval Warm Period and the absence of swamp agriculture at Kuk (Fig. 5, adapted from Haberle and ChepstowLusty, 2000). Swamp cultivation appears to occur during periods of greatest climatic variability. Periods of chronic drought stress may have initiated the need for greater groundwater control leading to the development of grid patterns of field ditches, seen in Phase 4 and onwards at Kuk swamp (Bayliss-Smith and Golson, 1992). Long-term anthropogenic landscape change, notably forest clearance and land degradation before 1190–970 cal yr BP, has been implicated in the adoption of widespread Casuarina planting as an agroforestry tree. Casuarina is a nitrogen-fixing tree used in traditional agroforestry systems that have played a significant role in sustaining human populations in a variety of tropical soil and climate conditions, and may have been adopted as a response to low crop productivity and the need to rehabilitate abandoned dryland crop lands after prolonged climatic stress. A similar process has been invoked to explain the adoption of Alnus as an important agroforestry tree by Inca peoples in the Peruvian Andes around 850 cal yr BP (Haberle and Chepstow-Lusty, 2000). These cultural transformations of the last 3500 yr are, curiously, akin to the multifarious cultural changes that took place in north Queensland during the late Holocene, including increased intensities of site and regional land

Fig. 5. Causes of social change in equatorial Americas and New Guinea. A series of climate proxy records (temperature from Huascaran ice core d18O record; drought periods from Quelcaya ice core dust particles >1.59 mm; a composite time series for the recurrence of El Nin˜o events since 1000 cal yr BP and the occurrence of the Little Ice Age and Medieval Warm Epoch from equatorial South America and archaeological phases from the Yucatan lowlands (Maya) and the Bolivian altiplano (Tiwanaku; Alnus agroforestry) are compared with inferred climate and cultural changes in highland New Guinea over the last 2000 cal yr BP. Kuk swamp agricultural phases and the development of Casuarina agroforestry show the switching from wetland to dryland agriculture under the influence of tephra impact and climate change (from Haberle and Chepstow-Lusty, 2000).

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use, socio-political regionalisation, and qualitative changes in artefact types.

4. Discussion The above investigation of past Australian and New Guinean landscape dynamics has revealed a fundamental flaw in the traditional dichotomy between the socalled natural and human-influenced landscapes. Ecosystems have been greatly modified by people for thousands of years, while natural processes have themselves played a part in influencing the transformation of human societies through time. This implies that changes in climate, resources and habitats are not simply background information of little relevance to cultural change, but that they must be considered a continually changing set of problems and opportunities altering the context for human subsistence and diversity (Cashdan, 2001). This approach challenges historical convention by the attention it gives to non-human agencies on cultural transformation. Yet in addressing causality there nevertheless remains the critical problem of linking scales of environmental change with those of human experience. We suggest that there are climatic thresholds of cultural tolerance under any pre-existing social or adaptive strategies, and that abrupt, unpredictable climate changes on decadal to century time scales can and in practice do have devastating consequences on human populations by disrupting both resource production and the social structures through which people relate to their social and physical environments. These destabilising climatic forces necessitate ongoing social and cultural responses involving demographic expansion or contraction at various social scales, or realignments of social alliance strategies and networks. Such linked processes of change are well exemplified, we argue, by the increased social regionalism of the late Holocene in north Queensland, socio-structural transformations that took place following major and sustained population increases during the early to mid Holocene climatic optimum, when natural levels of biomass productivity were at their peak. In this case, we suggest that climatic and environmental transformations during the early to mid Holocene led to noticeable increases in human populations across north Queensland by 6000 cal yr BP. When natural levels of bioproduction began to decrease and climate variability began to increase during the late Holocene, heightened regional populations began to fission into new and distinctively smaller land-owning and landusing groups, as evidenced by a regionalisation of rockart styles after 3700 cal yr BP. However, even then the process of change cannot be said to have stabilised, for through social fissioning and territorial regionalisation a new ecological dynamic was triggered. Thus, given ‘a

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reduction in the size of a group’s effective subsistence range, the number of plant species available for exploitation decreases as a power function of the scale of the reduction in area’ and as ‘subsistence area and species richness are reduced as a power function of area, hunter-gatherers normally rely more heavily on fewer animal species of smaller and smaller body size, other things being equal’ (Binford, 2001, p. 367). Predictably, in north Queensland following a regionalisation of territorial networks around 3700 cal yr BP there is evidence for a broadening of the range of foodstuffs consumed and the commencement of toxic plant exploitation, and elsewhere with the commencement of systematic seed grinding by 3000–1400 cal yr BP (David, 2002, chapter 8, and for similar modelling for southeast Queensland see McNiven, 1999, pp. 158–159). At Princess Charlotte Bay, there is the onset of large-scale exploitation of the small marine bivalve A. granosa in central residential places only after 2000–1600 cal yr BP. With such socio-structural and dietary innovations came a heightened ability to sustain increasing human populations over both the short and long terms, allowing people to transcend demographic thresholds previously shackled at this scale of analysis by climatic and environmental circumstances. Here then we suggest is evidence for a late broad-spectrum revolution in mainland Australia during the late Holocene, a transformation in ecological relations set in motion by a chain of events each of which was predicated on the operation of scalar thresholds, and in the end only indirectly resulting from climatic transformations, and therefore subject to considerable practical variability. Therefore, while these Holocene changes in strategic people–land relations can be thought of as climatically conditioned, it would be inappropriate to dismiss social agency for specific observed or hypothesised demographic and cultural circumstances, for there are usually many adaptive choices that people can make, and such choices are always contingent. This is precisely what confronts us with the parallel yet contrasting situation of the New Guinea highlands, for here people responded to heightened levels of bioproduction, low climate variability and to human population increases during the Holocene climatic optimum by either initiating, or by transforming, existing horticultural practices and in so-doing radically enhancing the land’s productivity. After 6000 cal yr BP, under the influence of increasingly intense and frequent ENSO activity, further innovation and adaptation was necessary to sustain crop production in a region susceptible to severe drought. These innovations set in motion a different set of demographic possibilities and restrictions to those conditioned by the adaptive choices made in Australia, here allowing for population densities many orders greater than the highest of the Australian mainland. With this came the diverse and

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characteristically New Guinea societies we have come to know from ethnography. As was the case in Australia, in New Guinea it was the early to mid-Holocene climatic and ensuing environmental transformations that heightened natural biomass production and population increases, and that in doing so set in course particular and ongoing dynamic relations between people, and between people and their surrounding landscapes.

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