Gina E. Hannon

A long-term perspective on ungulate–vegetation interactions

The fossil record of vegetation and ungulates places present conditions and trends in a temporal perspective. Ungulate–vegetation interactions during the last 500 000 years were primarily driven by the climatic variation of the glacial–interglacial cycle. There were distinctive faunas associated with each temperate period and a loss of species diversity only in the present interglacial. Climate change and human activities have interacted during the most recent glacial cycle, accelerating extinction rates. This unique course of events has the consequence that no stable, ‘base-line’ conditions can be recognised. A review of the full-glacial ‘mammoth-steppe’ debate suggests that ungulate populations were limited by available forage, but a mosaic of habitat supported a diverse fauna in Beringia. In the debate over early–mid Holocene ‘wood pasture’, past ungulate populations are one of a range of disturbance factors, including burning, that influenced regional vegetation composition and structure in northern Europe. These debates concerning the scale and impacts of past ungulate–vegetation interactions will not be fully resolved until more is known about past ungulate population sizes. Modelling past scenarios would enhance the value of retrospective studies and help provide goals for management of near-natural ecosystems.

Climatic change, human influence and disturbance regime in the control of vegetation dynamics within Fiby Forest, Sweden

1. The immigration and rise to dominance of Picea abies within Fiby Forest, Sweden, was investigated by pollen and charcoal analysis of tiny (c. 1-m 2 ) bogs which contained a 4000-year record. 2. A mixed deciduous forest that existed 4000 years ago was replaced in a stepwise manner by a boreal community. The detailed dynamics of the changeover were controlled by catastrophic disturbances 2500 and 2200 years ago. 3. Two long periods of disturbance by burning and grazing kept the woodland open in structure. Eventual abandonment of this management practice initiated a succession that resulted in the present dominance of Picea, over 2000 years after its immigration into Fiby

High-altitude vegetational pattern on the Iberian Mountain Chain (north-central Spain) during the Holocene

Pollen, plant macrofossil. charcoal, sedimentary analyses and magnetic susceptibility measurements have been carried out on a C-14 dated sediment sequence from Las Pardillas Lake (1850 m a.s.l., Iberian Mountain Chain). The interpretation of the pollen diagram has been assisted by the analysis of an altitudinal transect of moss-polsters collected in the same area. After 9310 BP, a Pinus-Betula-Quercus open woodland developed. Between c. 9000 BP and 7100 BP, the woodland became a mixed forest with Pinus vylvestris. The beginning of the continuous curve of Corylus c. 9000 BP dated the local population expansion of this tree and is 1000 years earlier than the age previously attributed to its expansion in north-central Spain. At c. 7400 BP a local fire is associated with a possible first establishment of Fagu.s in the area. From c. 7100 BP to c. 3700 BP, Taxus, Rex and Hedera were present in the forest vegetation. During this interval, the pollen and sedmentological record indicated a stable period of rich, mixed Quercus forest. At the same time, the community of floating-leaved aquatics was replaced by submerged plants, suggesting that a rise in lake water level may have occurred between 7200 and 6400 BP. Fagus became continuously present in the Las Pardillas Lake area c. 3200 BP. As Fagus is fire-sensitive, the expansion and stand scale establishment may be linked to an increase in fire regime, a type of disturbance which has facilitated the spread of this taxon elsewhere in Europe. A significant forest reduction, involving all the trees, took place c. 1500 BP. Between 1000 and 400 BP, Pinus and Fugus re-expanded associated with the first clear evidence of agricultural activity. The well-represented, mixed Quercus forest around Las Pardillas Lake, and the early development of Coryluw compared to other Mediterranean zones, suggests that oceanic conditions prevailed on the northern slopes of these mountains in north-central Spain.

The Mjáuvøtn tephra and other Holocene tephra horizons from the Faroe Islands: a link between the Icelandic source region, the Nordic Seas, and the European continent

Six different tephra horizons were found in peat and lacustrine sediments on the Faroe Islands in the North Atlantic. Their geochemistry showed that they were of Icelandic origin. Three of these can be correlated with previously described tephra horizons from the Faroe Islands: the Saksunarvatn tephra (c. 9000 BP), the Hekla-4 (c. 3800 BP) and Hekla-Selsund (c. 3600 BP). A previously unrecorded basaltic tephra dated to c. 5700-5300 BP was found in two lacustrine successions. This horizon is named the Mjáuvøtn tephra after Mjáuvøtn Lake on the island of Streymoy. Two further tephras were recorded: the basaltic phase of the ‘Landnám’ tephra (VIIa, c. AD 870s), and the rhyolitic Tjørnuvik tephra. These were found in sediments deposited shortly after the first phase of human settlement at Tjørnuvik, which is AMS dated to AD 675-861 (calibrated age). The Faroe Islands are an important link between the volcanic sources on Iceland, and the established tephrochronological frameworks on the British Isles, Scandinavia and Germany. Their position within a sensitive region of the northeastern branch of the North Atlantic Drift make the Faroe Islands ideal for registering climate changes during the Holocene. The establishment of a modern tephrochronology may provide a tool for more precisely dating and correlating regional climate events in and around the Nordic Seas.

Reconstruction of climatic and environmental changes in NW Romania during the early part of the last deglaciation (∼15,000–13,600 cal yr BP)

High resolution pollen, plant macrofossil, charcoal, mineral magnetic and sedimentary analyses, combined with AMS 14 C measurements, were performed on multiple sediment sequences alonga transect through the former crater lake Preluca Tiganului in

The role of fire in southern Scandinavian forests during the late Holocene

Charcoal fragments preserved in small, wet basins are used to characterise the fire regime of temperate and mixed boreal forest (hemiboreal) zones of southern Scandinavia during the last 3500 years. There was far less charcoal recorded from the temperate zone than the hemiboreal zone during the last 3500 years, yet the low temperate zone values showed a clear trend of continuous increase until 1500 AD, after which the values decreased sharply. The record from the hemiboreal region showed a greater temporal variability with far higher charcoal influx values than in the temperate zone. There were significant positive correlations between charcoal influx and Betula, Calluna and Pinus pollen abundance and negative correlations with pollen indicators of anthropogenic impact such as Rumex and Cerealia. Charcoal influx in the temperate zone showed a strong association with the period of major anthropogenic impact, whereas the hemiboreal data reacted more to climatic change. The temporal and spatial pattern of charcoal influx was only a minor explanatory factor for vegetation composition at a regional scale in southern Scandinavia. The fire return interval was often long and irregular in most of the region and anthropogenic factors such as grazing, mowing and establishment of arable fields were probably more important than fire as drivers of vegetation change.

Climate change and human settlement as drivers of late-Holocene vegetational change in the Faroe Islands

Changes in Faroese land surfaces during the late Holocene reflect intimate interactions between cultural and environmental development. Analyses of fossil wood, pollen and plant macrofossils indicate that the present open landscape replaced shrubby vegetation that was present from c. 6000 BC Up to C. AD 660. Conditions altered during the late Holocene, with loss of woody vegetation and increasing erosion: trends that were initiated prior to human settlement. AMS dating of sub-fossil Betula, Salix and Juniperus found buried in peat profiles from the islands of Su8uroy, Sandoy, Eysturoy, Vagar and Streymoy, revealed that the islands had at least partial woody vegetation cover up to the time of continuous settlement. The settlement horizon, identified in a lacustrine sequence on the island of Eysturoy, dated to c. AD 570. It comprised pollen evidence for the cultivation of Hordeum, cultural macrofossil assemblages, charcoal fragments, diatom assemblage changes indicating lake nutrient enrichment and physical measurements showing increased sedimentation rates. The pollen record showed that heathland development was initiated prior to anthropogenic impact. The ecosystem impacts of settlement were therefore superimposed on landscape changes that began around AD 250. The earlier changes were most likely forced by increased storminess and declining atmospheric temperatures.

Recent vegetation dynamics on two Connemara lake islands, western Ireland

Primary woodlands are of scientific interest for the study of natural population dynamics and of conserva- tion interest because of their formerly widespread distribu- tion in Europe. Field recognition of primary woodland based on the present vegetation alone can be difficult, and no system for recognition of such sites has been established in Ireland. Many Connemara lake islands support dense, low woodlands that have been proposed to be representa- tive of Irish ancient woodland. Thick mor humus layers occur on these islands which form a contrast with the tree- less mainland covered by blanket peat. Pollen analysis of the humus layers from two islands of different size revealed that the present woodland was about 300 years old, and both islands were cleared of trees before that time. An earlier phase of more diverse woodland on

Forest continuity and conservation value in Western Europe

Long forest continuity has often been linked with high conservation value in western European Quercus and Fagus woodlands, but this assumption of long continuity has rarely been tested. Birks discussed the antiquity of bryophyte-rich Quercus woodland in western United Kingdom, presenting evidence that the modern plant communities developed during the late Holocene influenced by human activities. We use pollen data from forest hollows to show that the modern communities within ancient woodlands are all significantly influenced by recent human disturbance. A short period of deforestation in Johnny’s Wood, Cumbria, UK dates from the late 19th century and is not of Viking age as previously thought. The brief opening of the forest is associated with the local loss of Tilia cordata and Taxus baccata, but a rich bryophyte community exists today. Rich lichen floras of high conservation interest growing on Fagus sylvatica in south-western Sweden occur despite a recent history of human disturbance and local immigration of Fagus as recently as the 9th century ad. Wistman’s Wood, Cornwall, UK had a diverse tree flora until the 11th century ad and then experienced heavy browsing and grazing until ad 1850, after which time the present Quercus woodland developed with its associated flora of high conservation value. Most western European forests today have long and diverse histories of anthropogenic disturbance and current conservation values incorporate both natural and cultural features. Pollen studies with high spatial resolution demonstrate that simple temporal concepts like ‘natural baselines’ and the continuity of forest cover underestimate the complexity of the past. Long forest continuity may be of importance for the local survival of higher plants, but for the insects, fungi, lichens and bryophytes that are so valued in contemporary European temperate and boreal forests, habitat diversity maintained by dynamic processes would appear to be of greater significance.

Holocene History of Alpine Vegetation and Forestline on Pyhakero Mountain, Northern Finland

Abstract Paleoecological analyses were carried out from two sediment cores from lake sites at the alpine treeline on Pyhäkero mountain, the northernmost peak of an isolated mountain range, Pallastunturi-Ounastunturi, south of the polar forestline in western Finnish Lapland. Plant macrofossils, supported by pollen data, show presence of pine (Pinus sylvestris) and birch (Betula pubescens) on the top of the mountain from 9500 cal yr BP (birch) and 8300 cal yr BP (pine) up to 2000 cal yr BP (pine) and 1500 cal yr BP (birch). However, the major floristic elements of the modern alpine vegetation, as evidenced by plant macrofossils of a number of typical alpine taxa, including Salix cf. polaris, show persistence through the warmer periods of the Holocene, and indicate that the scattered pine-birch forest never completely replaced the low-alpine plant communities. The current low-alpine vegetation on the mountain top has therefore long continuity from the time of regional deglaciation. Dispersal of these alpine species took place primarily during the deglaciation phase and it is unnecessary to invoke dispersal of the arctic-alpine plants from the arctic regions of Fennoscandia during the mid- or late-Holocene to explain the origin of the alpine flora of the mountain range.