Palaeoecological perspectives on Holocene environmental change in Scotland

ABSTRACTPalaeoecology has been prominent in studies of environmental change during the Holocene epoch in Scotland. These studies have been dominated by palynology (pollen, spore and related bio-and litho-stratigraphic analyses) as a key approach to multi- and inter-disciplinary investigations of topics such as vegetation, climate and landscape change. This paper highlights some key dimensions of the pollen- and vegetation-based archive, with a focus upon woodland dynamics, blanket peat, human impacts, biodiversity and conservation. Following a brief discussion of chronological, climatic, faunal and landscape contexts, the migration, survival and nature of the woodland cover through time is assessed, emphasising its time-transgressiveness and altitudinal variation. While agriculture led to the demise of woodland in lowland areas of the south and east, the spread of blanket peat was especially a phenomenon of the north and west, including the Western and Northern Isles. Almost a quarter of Scotland is covered by blanket peat and the cause(s) of its spread continue(s) to evoke recourse to climatic, topographic, pedogenic, hydrological, biotic or anthropogenic influences, while we remain insufficiently knowledgeable about the timing of the formation processes. Humans have been implicated in vegetational change throughout the Holocene, with prehistoric woodland removal, woodland management, agricultural impacts arising from arable and pastoral activities, potential heathland development and afforestation. The viability of many current vegetation communities remains a concern, in that Scottish data show reductions in plant diversity over the last 400 years, which recent conservation efforts have yet to reverse. Palaeoecological evidence can be used to test whether conservation baselines and restoration targets are appropriate to longer-term ecosystem variability and can help identify when modern conditions have no past analogues.

Woodland dynamics and use during the Bronze Age: New evidence from Irish archaeological charcoal

Swathes of roads and pipelines cut through the Irish landscape during the ‘Celtic Tiger’ years (approximately 1994–2008) leading to an unprecedented number of archaeological excavations and creating a unique opportunity for extensive research of past landscapes on a broad scale. The vast quantities of bulk soil samples suddenly available necessitated the development and adaptation of new methodologies. Despite the huge volumes of these samples, of which charcoal is the most ubiquitous ecofact, to date charcoal analysis has been considerably under-utilised in the study of past Irish woodlands. This research presents one of the largest Bronze Age archaeological charcoal datasets in Europe. It provides new palaeoecological evidence contributing to the understanding of woodland cover transformation on the island of Ireland during the late-Holocene period. The most common taxa identified in the charcoal assemblage compare well with regional pollen diagrams, particularly the use of Quercus and Corylus. With intensifying human activity during the middle Bronze Age, the proportion of Maloideae, a light demanding family rose. This is the first clear evidence of anthropogenic influence during the middle Bronze Age in Ireland derived from archaeological charcoal. The size of the charcoal dataset makes it possible to evaluate woodland cover and resourcing from two perspectives – both archaeological and palaeoecological.

Did the elephant and giraffe mediate change in the prevalence of palatable species in an East African Acacia woodland?

We report on a 2009 survey of Acacia woodlands in the Seronera area of central Serengeti, Tanzania, and compare the results to previous surveys from the 1970s–1980s. We document a substantial change in woodland structure and composition. From 1978 to 2009, woody plant density (mean ± SD) declined from 255 ± 35 trees ha−1 to 147 ± 14 trees ha−1. Canopy cover declined from 15.1 ± 1.9% to 5.7 ± 0.6%. Canopy volume declined from 1810 ± 207 m3 ha−1 to 1410 ± 121 m3 ha−1. A 19% increase in the relative canopy volume of Acacia robusta, a species avoided by the giraffe, represents a sharp decline in the quality of the giraffe's food supply, which was last comprehensively assessed in 1978. We examine these changes in the context of Pellew's 1983 woodland dynamics model describing the impacts of elephant, giraffe and fire on an Acacia tortilis tree population and determine that our data are qualitatively consistent with this model. We hypothesize that selective elephant and giraffe browsing has contributed to an increase in the relative dominance of unpalatable species, consistent with Pellew's predictions.

Dynamics and Conservation Management of a Wooded Landscape under High Herbivore Pressure

We present the use of a spatially explicit model of woodland dynamics (LANDIS-II) to examine the impacts of herbivory in the New Forest National Park, UK, in relation to its management for biodiversity conservation. The model was parameterized using spatial data and the results of two field surveys and then was tested with results from a third survey. Field survey results indicated that regeneration by tree species was found to be widespread but to occur at low density, despite heavy browsing pressure. The model was found to accurately predict the abundance and richness of tree species. Over the duration of the simulations (300 yr), woodland area increased in all scenarios, with or without herbivory. While the increase in woodland area was most pronounced under a scenario of no herbivory, values increased by more than 70% even in the presence of heavy browsing pressure. Model projections provided little evidence for the conversion of woodland areas to either grassland or heathland; changes in woodland structure and composition were consistent with traditional successional theory. These results highlight the need for multiple types of intervention when managing successional landscape mosaics and demonstrate the value of landscape-scale modelling for evaluating the role of herbivory in conservation management.