PALAEOECOLOGY OF ALNUS (ALDER): EARLY POST‐GLACIAL RISE IN A VALLEY MIRE, NORTH‐WEST WALES

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SUMMARYThree radiocarbon-dafed pollen diagrams are presenfed from Holocene peat and lake deposits in Snowdonia, elose to the Late Iron Age/Romano-Britisb ironworking hill-fort of Bryn y Casfell, Gwynedd, in upland north Wales. This paper discusses pollen, charcoal and peat-stratigrapbic evidence for major local vegetation changes and for tbe development of the surrounding cultural landscape during the last 10000 radioearbon yr. Pollen data from one of the sites (BYC 2) provided a vegetational record for most of the Holocene. The early part of the sequence suggests an oligotrophie lake in a landscape that is being colonized by birch-pine woodland; later, mixed deciduous woodland surrounds an infilling lake basin. Dating of peat deposits at two of tbe sites (BYC, BY'C H) indicated that their pollen records commenced between 5500 and 5000 yr BP. By this time, the lake basin was fringed by alder carr. There followed a gradual and then, c. 2700 yr BP, a more abrupt decline in woodland, such that, by tbe end of the Bronze Age and with the basin largely terrestrialized, the local landscape became dominated by mire vegetation communities, which have persisted to the present. Human activity seems to have been a major factor in the loss of woodland eover. Although there is some circumstantial evidence for earlier phases of human disturbance at BYC 2, human activity becomes increasingly apparent from c. 5000 yr BP. During the mid Holoeene, the impaet of Neolithic and early-to mid-Bronze Age cultures appears to be characterized by temporary woodland clearances, for arable and pastoral agriculture. By c. 2700 yr BP the majority of woodland cover seems to have been permanently removed from the landscape, but as there is scant archaeological evidence for late Bronze Age cultures in this part of Snowdonia, other factors, especially climate change, could be implicated. During the late Holocene, especially during part of the late Iron Age and Romano-British period, remaining local stands of woodland seem to have been exploited for iron smelting, although the overall impact of ironworking was limited.

Section: Mid Holocene (C 7000-3000 Bp)mentioning

confidence: 99%

Section: Mid Holocene (C 7000-3000 Bp)mentioning

confidence: 99%

Section: The Pollen Diagramsmentioning

confidence: 99%

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Holocene vegetation history and human impact at Bryn y Castell, Snowdonia, north Wales

Mighall

Chambers²

1995

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“…This suggests that A. glutinosa was expanding into a previously unfilled niche, or replacing a palynologically silent taxon. Before it began expanding at these sites, A. glutinosa was already present in eastern England in the Thames valley to the south (Devoy, 1979;Otlet & Walker, 1979) and the Fens to the west (Clark & Godwin, 1962), as well as at sites much further away, such as North Wales (Hibbert & Switsur, 1976;Chambers & Price, 1985), Caithness (Peglar, 1979), and south-west Scotland (H. H. Birks, 1975;H. J.…”

Section: Alnus Glutinosamentioning

confidence: 99%

Competitive Interactions Among Forest Tree Populations in Norfolk, England, During the Last 10000 Years

Bennett

1986

SUMMARYThe post-glacial pollen stratigraphies of two sequences of lake sediments (Hockham Mere and The Mere, Stow Bedon) are compared. Both suggest displacement of existing taxa when new taxa arrive from their cold-stage refugia and expand their populations. Hockham Mere is within an area of sandy soils, while The Mere at Stow Bedon is within an area of calcareous till soils. There have been differences in the forest vegetation around the two sites for most of the last 10000 years, and the competitive interactions between the forest trees differ also.

“…If this event equates with the ubiquitous Alnus rise at other sites, then its date of 6430 + 90 BP is consistent with the anticipated date as extrapolated from isopoUen curves (Huntiey & Birks, 1983;Birks, 1989). Elsewhere, associations between the arrival of Alnus and charcoal have been taken as evidence for vegetational disturbance which may have been caused by Mesolithic people (Smith, 1970(Smith, , 1984Chambers & Price, 1986). Mesolithic hunter-gatherers were active locally at Kinloch well before the time of the alder rise and the effect of their disturbance and burning activities could well have contributed to the spread of Alnus.…”

Section: « / «: Y Llll I ) I I I Rn I R I I Rn I "T Tt~i I I I I I I mentioning

confidence: 99%

Pollen and related studies at Kinloch, Isle of Rhum, Scotland, with particular reference to possible early human impacts on vegetation

Hirons

Edwards

1990

SUMMARYThe Inner Hebridean island of Rhum lies between the once wooded mainland of north-west Scotland and the now largely treeless islands of the Outer Hebrides. Rhum is more exposed than the nearby larger islands and is of particular interest since it has been occupied by humans for at least 8500 years. Pollen, charcoal and radiocarbon studies were carried out on a peat profile from Kinloch in the most sheltered eastern part of the island, some 300 m from the site of the earliest known Mesolithic occupation site in Scotland.From an estimated 7800 BP, the local mire surface was open with some hazel and willow scrub. Alder replaced willow at c. 6500 BP and with hazel, remained the dominant woody vegetation until c. 4000 BP when both were reduced and by which time evidence for agriculture is discernible. A period of reduced Alnus and Corylus between 5950 and 5700 BP, with high concentrations of charcoal, may result from human infiuence. An Alnus reduction dated to between 5250 and 4950 BP may have been caused by changes in mire hydrology. The woodland was more open than that at nearby mainland sites but it was comparable to well-wooded sites on Skye and Mull. Birch was notably less significant at the Rhum site and the preponderance of Alnus along with persistently high Osmunda values may indicate that adaptation to exposure and salt tolerance were important factors in determining the character of the early postglacial vegetation.