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We describe the career of John Birks as a pioneering scientist who has, over a career spanning five decades, transformed palaeoecology from a largely descriptive to a rigorous quantitative science relevant to contemporary questions in ecology and environmental change. We review his influence on students and colleagues not only at Cambridge and Bergen Universities, his places of primary employment, but also on individuals and research groups in Europe and North America. We also introduce the collection of papers that we have assembled in his honour. The papers are written by his former students and close colleagues and span many of the areas of palaeoecology to which John himself has made major contributions. These include the relationship between ecology and palaeoecology, late-glacial and Holocene palaeoecology, ecological succession, climate change and vegetation history, the role of palaeoecological techniques in reconstructing and understanding the impact of human activity on terrestrial and freshwater ecosystems and numerical analysis of multivariate palaeoecological data. [ABSTRACT FROM AUTHOR]

The vast diversity of present vegetation and environments that occur throughout South America (12°N to 56°S) is the result of diverse processes that have been operating and interacting at different spatial and temporal scales. Global factors, such as the concentration of CO2 in the atmosphere, may have been significant for high altitude vegetation during times of lower abundance, while lower sea levels of glacial stages potentially opened areas of continental shelf for colonisation during a substantial portion of the Quaternary. Latitudinal variation in orbital forcing has operated on a regional scale. The pace of climate change in the tropics is dominated by precessional oscillations of c. 20 kyr, while the high latitudes of the south are dominated by obliquity oscillations of c. 40 kyr. In particular, seasonal insolation changes forced by precessional oscillations must have had important consequences for the distribution limits of species, with potentially different effects depending on the latitude. The availability of taxa, altitude and human impact, among other events, have locally influenced the environments. Disentangling the different forcing factors of environmental change that operate on different timescales, and understanding the underlying mechanisms leads to considerable challenges for palaeoecologists. The papers in this Special Issue present a selection of palaeoecological studies throughout South America on vegetation changes and other aspects of the environment, providing a window on the possible complexity of the nature of transitions and timings that are potentially available. [ABSTRACT FROM AUTHOR]

Pollen analysis of a 48 m AMS radiocarbon-dated sediment sequence from the Guadiana estuary provides the first record of Lateglacial and Holocene vegetation history in the Algarve province of Portugal. This paper focuses on the record of terrestrial pollen taxa, which document a series of forest expansions and declines during the period 13 000 cal. BP to 1600 cal. BP and provide insights into climate evolution in southwestern Iberia. The main vegetation phases identified in the Guadiana valley are (1) Lateglacial interstadial (Allerød) forest with Quercus and Pinus under a temperate, moist, continental climate; (2) a Younger Dryas forest decline (Quercus) and expansion of pinewoods, xeric scrub and open ground habitats (with Juniperus, Artemisia, Ephedra distachya type, Centaurea scabiosa type) under arid and cold conditions; (3) an early Holocene forest/scrub/open-ground vegetation mosaic developing under a warm, dry and continental climate; (4) a maximum of Quercus forest and thermomediterranean evergreen taxa (Olea, Phillyrea, Pistacia) reflecting a warm, moist oceanic climate between c. 9000 cal. BP and c. 5000 cal. BP; and (5) the expansion of shrublands with Cistaceae and Ericaceae under a drier climatic regime and increasing anthropogenic activity since c. 5000 cal. BP. Holocene episodes of maximum climatic aridity are identified in the record of xerophytic taxa (Juniperus, Artemisia, Ephedra distachya type) centred around 10 200 cal. BP, 7800 cal. BP, 4800 cal. BP, 3100 cal. BP and 1700 cal. BP. Regional comparisons suggest a correlation of arid phases across southern Iberia and northwest Africa, which can be related to abrupt North Atlantic coolings (Bond events). [ABSTRACT FROM AUTHOR]

This paper describes our recent extraction of ancient DNA (aDNA) from Holocene pollen and discusses the potential of the technique for elucidating timescales of evolutionary change. We show that plastid DNA is recoverable and usable from pollen grains of Scots pine Pinus sylvestris from 10 ka and 100 years ago. Comparison of the ancient sequences with modern sequences, obtained from an extant population, establish a first genetic link between modern and fossil samples of Scots pine, providing a genetic continuity through time. One common haplotype is present in each of the three periods investigated, suggesting that it persisted near the lake throughout the postglacial. The retrieval of aDNA from pollen has major implications for palaeoecology by allowing (i) investigation of population-level dynamics in time and space, and (ii) tracing ancestry of populations and developing phylogenetic trees that include extinct as well as extant taxa. The method should work over the last glacial oscillation, thus giving access to ancestry of populations over a crucial period of time for the understanding of the relationship between speciation and climate change. [ABSTRACT FROM AUTHOR]

Scientific research now shows that humans are pervasive in earth ecosystems, and have been so for many thousands of years. So it may seem strange to argue against a concept that has been so hard won and is now empirically incontrovertible. What is starting to seem stranger is that, to paraphrase anthropologist Tim Ingold, the best way we have to describe our role in the world is to take ourselves out of it. As human influence on the Earth and its processes increases, we face the profound paradox that most of our intellectual weapons in the environmental area—from prehistoric fire debates to projections of climate change—have maintained a separation of humans and nature. This is an argument based not on semantics but on false separations that are adversely affecting the quality of our research and practice, including the ways we attempt to integrate archaeology and palaeoecology. While 'human impacts' may be applicable to a subset of human activities, it is neither conceptually nor empirically strong enough for the detailed networks of human and non-human others now evident. We need to articulate a broader concept of agency, both human and otherwise, and to develop explanations that focus on associations and relationships rather than separations and essentialisms. [ABSTRACT FROM AUTHOR]

A paleoecological analysis of a 6-m-long sedimentary sequence from the La Encrucijada Biosphere Reserve (RBLE) from southern Pacific Mexico provides detailed information about past vegetation changes between ~6200 and 700 cal. yr BP. Highest percentages of mangrove pollen in pollen zone I (from ~6200 to 5400 cal. yr BP) suggest moister and warmer conditions than at present related with global rates of sea-level rise and northward position of the Intertropical Convergence Zone (ITCZ), suppressing El Niño-Southern Oscillation (ENSO) events. Drier conditions and decreasing rates of sea-level rise at ~5400–4500 cal. yr BP are evidenced in pollen zone II by the lowest percentages of mangrove pollen and highest presence of disturbance pollen. Recovery of mangroves and tropical forests occurred from ~4500 cal. yr BP, suggesting moister conditions. Agricultural activities are recorded around ~4900, 4700 and 2400 cal. yr BP, although human occupation was scarce in the mangrove area. ENSO variability correlates to mangrove pollen variation between 3600 and 2400 cal. yr BP. A protracted drought is observed at ~1300–700 cal. yr BP characterized by proportions in montane forest pollen and may be related with southern oscillation of the ITCZ and the Classical Mayan Demise. [ABSTRACT FROM PUBLISHER]

Biotic causes of changes in palaeorecords are discussed as a counterbalance to the (over) emphasis on climatic drivers in the interpretation of palaeoecological change. Biotic and climatic drivers are considered as competing hypotheses with particular reference to the importance of early-Holocene drought in the northern central grassland region of North America. It is concluded that the observed patterns are explained better by grazers than by the direct effects of climatic variation. The elevation of biotic factors as competing hypotheses with climate will require new conceptual and methodological approaches to palaeoecology in North America. [ABSTRACT FROM AUTHOR]

Palaeohydrological and palaeoecological investigations from five locations in northern Scotland reveal a distinct and large-scale shift to wetter climatic conditions which may reflect a major transition in climate from the mid- to late Holocene. Radiocarbon age estimates place this transition between about 3900 and 3500 cal. BP, although the transition appears to have occurred abruptly, possibly over a decadal to century timescale. This event appears to be synchronous with changes inferred for other regions, suggesting that it reflects a continental-scale, or possibly even global-scale, change in climate. Broad correlation with deep-sea sediment records suggests that the transition may reflect colder sea-surface temperatures in the North Atlantic Ocean. [ABSTRACT FROM AUTHOR]