From the Holocene to the Anthropocene: A historical framework for land cover change in southwestern South America in the past 15,000 years
Introduction
Today, anthropogenic land cover change (Houghton, 1994, Vitousek, 1994) is arguably the main driver of future biodiversity loss (Sala et al., 2000), disruption of ecosystem services, spread of exotic species, and pollution of land and water (Tilman, 1999, Millennium Ecosystem Assessment, 2003). Since the onset of the human enterprise, growing demands for food, timber and water drove changes in the extent, structure, and diversity of wild habitats. Yet for the most part of human history such impacts were unplanned, local and transient, and therefore rapidly reversed by ecological succession. It is only during the past few centuries that industrialized agriculture, forestry, and rapid urban and rural population growth has led to global homogenization of landscapes (Turner, 1990, Houghton, 1994, Mather et al., 1998). Because continental-scale land cover transitions occurred largely in the past two centuries, climatic, social and ecological modulators of such changes are only beginning to be understood (e.g., Mather et al., 1998, McKinney and Lockwood, 1999, Millennium Ecosystem Assessment, 2003). It seems relevant therefore to evaluate, as a case study, the relative importance of physical versus anthropogenic drivers of land transitions during the Holocene in southern South America, and discuss how can we anticipate or modify the impending outcomes of land cover trends. Such analysis is a complex challenge because of the trans-disciplinary nature of factors involved. Only through integrated social and ecological understanding, we shall develop better explanatory models to guide sensible land use policies. This integration is even more urgent in Latin America, where the fast pace of land cover change threatens one of the richest biocultural landscapes in the world (Primack et al., 2001, Rozzi et al., 2000). This biocultural diversity underlies large differences in land use patterns and modes of living.
In the developed world, forest loss has been moderated by the concentration and intensification of agricultural production and by a broader social recognition of the environmental values of forest ecosystems beyond timber production. This has led to postindustrial recovery of forest cover, reversing the trend towards deforestation that dominated through the industrial age (Mather et al., 1998, Mather et al., 2006). However, this northern hemisphere transition is coupled to increasing deforestation in many developing nations, which are now the suppliers of timber and other natural capital needed to sustain the economic growth of developed countries (Siebert, 2003). In this context, land use trends in most developing countries in the beginning of the 21st century are ultimately driven by the demands of global economy (Siebert, 2003, Liverman and Vilas, 2006). Current ecological and social effects of land cover change in the developing world can be best viewed as externalities of the prevailing global free-market economy.
Analyses of forest transitions in Chile have generally spanned only a few decades (Fuentes and Hajek, 1979, Achard et al., 2002, Echeverria et al., 2006). Here, we review the history of land cover change in south-central Chile, from the first records of human habitation, at the end of the Last Glacial Age about 15,000 calendar years before the present (cal. yr. BP) (Dillehay et al., 2008) to the present (Lara and Veblen, 1993, Donoso and Lara, 1996, Claude, 1997, Armesto et al., 1994, Armesto et al., 2001a), with the aim of identifying major transitions and their underlying climatic and socio-economic drivers. We start this review by analyzing the transition from the last glacial to the present interglacial in the mid-latitudes of western South America, which was primarily associated with global warming, forest expansion, and sparse indigenous populations of hunting-gatherers living in river basins (Dillehay et al., 2008). We show that postglacial events bear important consequences for the present latitudinal distribution of biodiversity in Chile and are relevant to assess the impacts of preindustrial and industrial land use change. Secondly, we examine pre-Hispanic forest cover transitions in south-central Chile, as human populations grew in number and diversified their agricultural and land use practices. Thirdly, we analyze the massive land transformations and deforestation beginning with the arrival of Europeans and culminating with the transition from industrial to postindustrial society. From this analysis, we propose a general framework for forest transitions in mid-latitude ecosystems of southern South America that encompasses the interval that begins in the Holocene and ends in the Anthropocene, defined by escalating human domination of global ecosystems starting in the late 19th century (Vitousek et al., 1997, Crutzen, 2002, Sanderson et al., 2002).
For the longest temporal scale, we focus on the western margin of South America, from Mediterranean to sub-Antarctic latitudes (Fig. 1A). When looking at the more recent transformations that took place from the arrival of Europeans through the mid-20th century, we focus on a more restricted area in south-central Chile, from the Mediterranean region to Chiloé Island (Fig. 1A). Our analysis of contemporary changes focuses mainly on two areas where agriculture and forestry impacts can be more precisely assessed. We rely on paleoecological data for the prehistorical events (Latorre et al., 2007) and on historical accounts for the period starting with the European settlement (Otero, 2006, Camus, 2006, Castro-Lobos, 2002, Molina et al., 2006). Recent trends over the last decades are documented by available land cover statistics (INFOR, 2005, CONAF-CONAMA-BIRF, 1999, Instituto de Estudios Públicos, 2002) and by the examination of aerial photos and satellite images. Finally, we discuss the regional and global policy implications of our analysis in the face of rapidly changing climate and socio-economic drivers.
Section snippets
Postglacial forest recovery and the pattern of tree species richness
Chilean forests presently occupy about 13.5 million hectares (CONAF-CONAMA-BIRF, 1999), along the western margin of southern South America (Fig. 1A), representing the most extensive, continuous climatic gradient from mid to high latitudes in the southern hemisphere. Vegetation records based on fossil pollen in sediments (e.g., Heusser, 1983, Villagrán, 1988, Villagrán, 1991, Villagrán et al., 1996, Moreno and Leon, 2003, Heusser et al., 2000) show that the latitudinal range of forests was
Holocene fire history
Global paleoecological studies show that in the past 20,000 years fire activity has been controlled primarily by climate and fuel load (Power et al., 2008). Records for southern South America suggest a low incidence of fire prior to the end of the last glacial period, which increased significantly during the interval between 12,000–6000 cal. yr. BP (Huber et al., 2004, Whitlock et al., 2007, Power et al., 2008, Abarzúa and Moreno, 2008, Abarzúa, 2009). Humans inhabited this region concurrently
The fuel wood catastrophe
With the arrival of Europeans, begins a period characterized by increasing rates of wood extraction from native ecosystems, mainly for the construction of villages, boats, fence posts, etc. In the following centuries, large volumes of timber were exported to the nearest and richer colonies in Peru (Camus, 2006). In addition, woodlands were cleared to open land for agriculture and livestock grazing, and intensely logged to supply fuel for domestic use and mining operations. It is estimated that
A historical framework for forest transitions
We summarized the history of land cover transitions in southwestern South America in the past 18,000 years since the LGM and examined the main climatic and human-population drivers that led to either loss or gain of vegetation cover. We used the chronosequence of events effecting Chilean forests to illustrate these transitions. The main drivers of these land cover changes and their consequences, as discussed in this paper, are summarized in Table 2. This analysis offers a broad framework for
Land use policies for the 21st century
Table 2 suggests that environmental policies born from imminent threats to public good may promote human behavior and regulations that reduce the externalities of land use. Future land policy decisions should incorporate social values and ecological factors that are presently absent from predominantly economic reasoning. New land development policies should define socially acceptable targets considering non-instrumental values, different cultural relationships between people and the land, the
Acknowledgements
Work funded by FONDAP-Fondecyt grant 1501-0001 to CASEB, Pontificia Universidad Católica de Chile, by Millennium Scientific Initiative (Chile) grant P05-002 and Fondecyt PFB-23 to the Institute of Ecology and Biodiversity-Chile, and by Reforlan Project of INCO-DC, European Union, Framework 6. We thank María Uriarte and Tom Rudel for encouragement and two anonymous referees for valuable comments on the manuscript. This is a contribution to the research programs of Senda Darwin Biological
References (119)
- et al.
Deglacial and postglacial climate history in east-central Isla Grande de Chiloé, southern Chile (43°S)
Quat. Res.
(2004) - et al.
Changing fire regimes in the temperate rainforest region of southern Chile over the last 16.000 yr
Quat. Res.
(2008) - et al.
Rapid deforestation and fragmentation of Chilean temperate forests
Biol. Conserv.
(2006) - et al.
Spatially explicit models to analyze forest loss and fragmentation between 1976 and 2020 in southern Chile
Ecol. Model.
(2008) - et al.
Assessing the transition from deforestation to forest regrowth with an agent-based model of land cover change for south-central Indiana (USA)
Geoforum
(2008) - et al.
Submillennial palynology and palaeoecology of the last glaciation at Taiquemo (∼50,000 cal yr. MIS 2-4) in southern Chile
Quat. Sci. Rev.
(2006) - et al.
Geographical and temporal trends in Late Quaternary fire histories of Fuego-Patagonia, South America
Quat. Sci. Rev.
(2004) - et al.
Post-productivism and rural land use: cul de sac or challenge for theorization?
J. Rural Stud.
(2006) - et al.
Biotic homogenization: a few winners replacing many losers in the next mass extinction
Trends Ecol. Evol.
(1999) Climate, fire, and vegetation between about 13.000 and 9200 14C yr B.P. in the Chilean Lake District
Quat. Res.
(2000)