Subfossil Wood Research Articles

Orbital Forcing and Tree-Limit History: Hypothesis and Preliminary Interpretation of Evidence from Swedish Lappland

The Holocene tree-limit history for an area in Swedish Lappland is analysed from a new set of 67 14C-dated subfossil wood remains. The species involved are Scots pine ( Pinus sylvestris), mountain birch ( Betula pubescens ssp. tortuosa) and grey alder ( Alnus incana). The highest tree-limit was established about 8000 BP by pine. Up to the present it has retreated c. 200 m in altitude at a constant rate of c. 25 m per millennium. A subalpine belt of birch above the pine forest, initially with admixture of alder, developed rapidly after 6000 BP, when birch started to invade the former pine areas and even extended higher. Birch grew at these high elevations until c. 4000 BP, although not necessarily without interruption. After 4000 BP birch also seems to have declined in elevation, although the magnitude is unknown. The steady pine tree-limit recession and the replacement of pine by birch may reflect continuous cooling and change of thermal seasonality. The present results corroborate the general hypothesis that predictable changes in the earth-sun geometry basically force climatic development, and indirectly vegetation history, during an interglacial.

Ring-width Variation in Sub-fossil Wood Samples as an Indicator of Short-term Solar Variability 2000 yr B.P.

AbstractResults from carbon 14 analysis of Bristle cone pine wood, using samples bounded by decade groups of annual rings, has established a significant long term solar periodicity of just over 200 years. Sites with large quantities of buried sub-fossil Kauri, Huon pine and Celery pine logs, which can provide data for a record possibly exceeding 20 000 years, have been identified in New Zealand and Tasmania. An initial study into periodicities, of possible solar origin, embedded in these ring-index time series can be justified on the basis that there are few other sources of annual proxy data, extending beyond the last 2000 years, that may reflect solar variability. Results from spectral analysis of a sub-fossil floating Celery pine chronology, which extends over 426 years, are considered. Carbon dating indicates that the Taupo volcanic eruption, which buried this forest, occurred about AD 177.

Tree-limit history during the Holocene in the Scandes mountains, Sweden, inferred from subfossil wood

Certain aspects of the Holocene tree-limit history of the Swedish Scandes are inferred from 14C-dating of subfossil wood. The main objective was to test an earlier hypothesis that paucity of subfossil wood from between c. 7700 and 6200 yr B.P., above the current tree-limit of Pinus sylvestris, was due to a short erosional episode c. 6300 yr B.P., rather than a long-term general climatic cooling. Sampling was carried out in a restricted area where the absence of long, steep slopes diminished the potential for extensive and rapid mass movements. Some of the new datings fall within the above-mentioned gap and thus provide support for the earlier erosion hypothesis, although the exact nature and cause of the geomorphic processes is still hypothetical. Temporal clustering of dates around 6000 yr B.P. indicates a Holocene thermal optimum for pine at that time. It is deduced that the total range of summer temperatures between the above optimum and the long-term mean of the Little Ice Age was 2.3°C or slightly more. Starting around 6300 yr B.P. climatic seasonality appears to have decreased and snow depth and longevity increased, which preconditioned the emergence of a subalpine birch forest belt. It is inferred that the cooling (summers) of the Little Ice Age (c. 1300–1850 A.D.) amounted to approx. 1°C in relation to the 1931–1960 average. This triggered vegetational retrogression and destructive geomorphic processes. A synthesis of all available dates of subfossil pine from the region suggests that no neoglacial period occurred between c. 8600 and 3300 yr B.P.

Holocene history of the forest–alpine tundra ecotone in the Scandes Mountains (central Sweden)

The Holocene history of the forest-alpine tundra ecotone in Central Sweden (Scandes Mountains) is inferred from radiocarbon analyses of subfossil wood remains. Pinus sylvestris was the dominant subalpine tree species during the early Holocene, when it ascended almost 200 m higher than currently. A short climatic episode (less than 100 years) is postulated to have triggered erosional processes around 6300 n.p., and extinguished the upper part of the subalpine pine woodland. Subsequently, a subalpine belt of Betula pubescens ssp. tortuosa and Alnus incana developed. A Holocene thermal optimum occurred around 6100 b.p., when the birch/alder belt nourished and the tree-limits probably reached their highest levels during the Holocene. Shortly after 6000 b.p., a long-term pine forest retrogression started and the birch/alder belt was disrupted by expanding snow-beds. Pine receded slightly at its tree-limit, but the uppermost belt of closed pine forest (presently dominated by birch) remained intact until c. 3300 b.p., when a severe climatic deterioration occurred. The present-day subalpine belt of pure birch forest developed successively and increased in vertical extent after c. 5300 b.p., when summer temperature declined. The evolution of the birch belt is postulated to have been ultimately a response to decreased seasonally, which favoured birch at the expense of pine. Because of the 'inertia' characterizing the highest pine forest, the birch belt was relatively narrow until a major thermal decline e. 3300 b.p., when it made a massive downslope expansion. The latest phase of pine recession was during the Little Ice Age, 800-300 b.p.

Pliocene Nothofagus Wood from the Transantarctic Mountains

Subfossil wood fragments up to 10 cm long and 2 cm in diameter recovered from a locality thought on the basis of diatom deposits to be upper Pliocene-lower Pleistocene (Oliver Bluffs, Sirius Formation, 85°10'S., between 1800 and 1900 m in the Transantarctic Mountains) were sectioned for identification. Degradation prevented observation of some wood features, but others were well preserved. All of the fragments appear to represent one species. Features of growth rings (ring porous, vessels mostly solitary in earlywood), rays (predominantly uniseriate, both erect and procumbent cells common), vessel perforation plates (simple, at least in earlywood), lateral wall pitting of vessels (predominantly transitional in earlywood, scalariform in latewood) and tyloses (present) permit one to identify the Oliver Bluffs woods as a Nothofagus. Wood sections of Nothofagus from New Guinea, New Caledonia, Tasmania, and southern South America were prepared in order to secure a more precise identification. The Oliver Bluffs woods very closely matches N. betuloides from Tierra del Fuego and southern Chile as well as N. gunnii from Tasmania in qualitative and quantitative features. Original data on wood of these Nothofagus species are presented. The nature of the Oliver Bluffs woods is discussed with relation to reports of Nothofagus wood from the Falkland Islands and Nothofagus pollen from Antarctica, and the implications of this polar flora are considered.

Evidence of flandrian valley alluviation in staindale, North York Moors

AbstractThe Dovedale Griff has incised into valley fill deposits in Staindale to expose sub‐fossil wood at the base of a meander cut bank. The wood includes oak (Quercus sp.) driftwood, and apparently in situ stumps of willow (Salix sp.) and alder (Alnus sp.). An alder stump is dated at 6270 radiocarbon years BP. Fluvial gravels approximately 1±5 m thick have accumulated above the wood, which has been exposed by renewed incision.