Putting the Tree Back into the Landscape

This book began with the archaeology of the Ullujaya and Samaca basins of the lower Ica Valley on the south coast of Peru. The archaeological investigations described here were undertaken to answer the following questions. Were these basins ever significantly more productive and vegetated landscapes? If so, when and how did change take place, and why? And how did these ecological and landscape changes correlate with cultural ones? The second part of the book conducted a thorough review of the botanical and agroforestry literature, together with the researchers' own observations, on the ecological keystone species of the region, the huarango — a tree of the genus Prosopis — to show how important a role this genus plays in the desert ecosystem of the south coast of Peru. This concluding chapter seeks to achieve a synthesis between these two parts to offer answers to those aforementioned questions posed by today's austere landscape of the lower Ica Valley. In so doing, it proposes a model for geomorphological, ecological, and land-use changes through time for the basins of the lower Ica Valley. It also aims to relate this model to cultural trajectories.

Tracing Human Ecology: The Archaeobotanical and Malacological Record

This chapter examines the ancient plant and other remains recovered from excavations. The purpose of archaeobotanical work was to reconstruct the human utilisation of plants in the past. The excavations focused on archaeological middens — the rubbish of ancient settlement. This is because they offer a record of human ecology, not least of changing human diet as evidenced in food refuse.

Tracing Landscape Change: The Geomorphological Record

This chapter sets out the geomorphological history of the basins of the lower Ica Valley — those processes of erosion and deposition which have formed and destroyed their archaeological record, and indeed given rise to today's landscape there. It reviews the results and interpretations of the geomorphological survey, which included: the definition of the basic geomorphic units across the lower Ica Valley; investigating the character of the relict river terraces of H-13 and G-8/9, which underlie most of their archaeology; understanding the extent of landscape and ecological change across the Samaca and Ullujaya basins, as revealed by buried ancient land surfaces; and evaluating those contexts from which archaeological and archaeobotanical data were extracted and subsequently analysed.

Introduction

This introductory chapter first sets out the book's purpose, which is to present a new archaeological case for prehistoric human impact on the environment: a study of ecological and cultural change from the arid south coast of Peru, beginning around 700 bc and culminating in a collapse by about ad 1000. Its focus is the lower Ica Valley, today largely depopulated and bereft of cultivation, but whose abundant archaeological remains attest to substantial prehistoric occupations and thereby present a prima facie case for changed environmental conditions. This is a place of extreme environmental juxtaposition: one of the world's oldest and driest deserts, crossed by lush riverine oases, and sporadically impacted by El Niño floods or long droughts. An overview of the subsequent chapters is also presented.

Deforestation

The loss of riparian woodland recorded in the archaeological and geomorphological records of the basins of the lower Ica Valley is but one early part of a larger and still ongoing history of the deforestation of the coast of Peru. This is an old and gradual story that can be read through the Spanish chronicles, administrative records, and recent memory. This chapter follows the traces of this tale, beginning in the deep past with the archaeology of the south coast, beyond the lower Ica Valley. It then turns to historical documentation, firstly to review the uses of Prosopis by humans on the coast of Peru and in arid lands elsewhere in South America, before finally returning to focus on the south coast to examine the historical record of deforestation there.

A Lost Landscape: Ancient Settlement of Samaca and Ullujaya

This chapter explores the archaeology of the lower Ica Valley. This is based upon many seasons of archaeological fieldwork with the purpose of gathering different datasets with which to reconstruct geomorphological, ecological, and land-use changes in the Samaca and Ullujaya basins. The chapter looks at the rich archaeological record in these basins from the Early Horizon (c.750 bc) through to the Inca Late Horizon that ended abruptly with Spanish conquest in ad 1532, as revealed through detailed archaeological survey and excavation.

The Huarango in the Desert Riparian and Agricultural Ecosystem

This chapter considers the subtler role of Prosopis in underpinning a fragile desert ecology. It is perhaps difficult to exaggerate the dominance of this genus within its desert environments, especially on the coast of Peru, where rather few tree species occur naturally. It is shown that no other desert tree has as pervasive an influence upon the soil's physical, chemical, biological, and moisture properties; the sub-canopy microclimate; the neighbouring vegetation; and the wildlife and insect populations. The huarango integrates diverse parts of the desert ecosystem. In modifying the environmental extremes characteristic of deserts, especially one as arid as the Peruvian south coast, Prosopis makes what would otherwise be inhospitable lands habitable for other species, including humankind. In other words, if we are to lay bare the ecological consequences of deforestation on the south coast, we need to understand why, here, the huarango is what ecologists term a ‘keystone species’.

The Huarango: The Genus Prosopis on the South Coast

The huarango are a species of the genus Prosopis, one of the most common plants found along the watercourses of New World deserts and members of a family of nitrogen-fixing, bean-producing plants — the legumes — whose importance to humankind is second only to that of the cereal grasses and with which our relationship is even older. Today, perceptions of the genus are deeply divided between appreciation of its value on the one hand, and intense dislike of it as a thorny, invasive weed on the other. This chapter sifts through the reasons for this and a history of misidentification, in order to identify the particular characteristics of the huarango and, thereby, its true value as a human resource in the past. It suggests that thousands of years of co-evolution with humans have left their mark on the tree's form on the south coast of Peru.

The Sonoran Desert: An Ethnoecological Analogue?

The relationship between humans and the genus Prosopis in the arid lands of the New World is almost as ancient as human occupation itself. This chapter explores this in one particular part of these American drylands: the Sonoran Desert of the south-western United States or, to be more specific, within the riparian basins of the Salt and Gila rivers of that desert. For here, a more recent human ecology offers an analogue for the far deeper time-depths of the Peruvian south coast. In the Sonoran, and elsewhere in the United States, several species of section Algarobia of the Prosopis genus are known collectively as ‘mesquite’. Mesquite is the one of the most common plants along the washes of North American arid lands and was a vital resource for its peoples.

The South Coast Desert

This chapter describes the area of interest — the basins of the lower Ica Valley on the Peruvian south coast — which lies within one of the world's oldest and driest deserts. It starts by examining the causes of that desert's age and extreme aridity. It distinguishes the climate, geology, geomorphology, and hydrology of the south coast from the rest of the Peruvian coast. It goes on to explore those peculiarities of the south coast since they underlie the particular sensitivity of its human ecology. It also shows how our archaeological impressions of the south coast's ‘limitations’ are coloured by the effects of long human impact. In fact — thanks to those factors of climate and geomorphology explored here — its riparian valleys are among the most potentially productive in the world.