Plant succession in areas of scorched and blown-down forest after the 1980 eruption of Mount St. Helens,Washington

Abstract. Patterns of plant succession were studied in areas of scorched and blown-down forest resulting from the 1980 eruption of Mount St. Helens, Washington. Changes in species abundance were observed for 7 years in permanent sample plots representing four post-disturbance habitats, or site types. Total plant cover and species richness increased with time on all site types. In blown-down forests supporting snowpack at the time of eruption, understory recovery was dominated by the vegetative regeneration of species persisting through disturbance. In forests without snowpacks, plant survival was poorer. Increases in cover and diversity were dominated first by introduced grasses, then by colonizing forbs characteristic of early successional sites. Epilo-bium angustifolium and Anaphalis margaritacea showed widespread recruitment and clonal expansion throughout the devastated area. As a result, species composition on previously forested sites converged toward that on formerly clearcut sites, where early serai forbs resprouted vigorously from beneath the tephra. Total plant cover and species diversity were poorly correlated with post-disturbance habitat and general site characteristics (e.g. distance from the crater, elevation, slope, and aspect). However, distributions of several life-forms (e.g. low sub-shrubs and tall shrubs) were strongly correlated with depth of burial by tephra and with cover of tree rootwads. Thus, early community recovery may reflect microsite variation or chance survival and recruitment rather than broad-scale gradients in environment or disturbance. Recovery of pre-disturbance composition and structure will undoubtedly be much slower than after other types of catastrophic disturbance. The rate and direction of community recovery will largely depend on the degree to which original understory species survived the eruption.     

Correlation of the KHS Tuff of the Kibish Formation to volcanic ash layers at other sites, and the age of early Homo sapiens (Omo I and Omo II)

Hominin specimens Omo I and Omo II from Member I of the Kibish Formation, Ethiopia are attributed to early Homo sapiens, and an age near 196 ka has been suggested for them. The KHS Tuff, within Member II of the Kibish Formation has not been directly dated at the site, but it is believed to have been deposited at or near the time of formation of sapropel S6 in the Mediterranean Sea. Electron microprobe analyses suggest that the KHS Tuff correlates with the WAVT (Waidedo Vitric Tuff) at Herto, Gona, and Konso (sample TA-55), and with Unit D at Kulkuletti in the Ethiopian Rift Valley. Konso sample TA-55 is older than 154 ka, and Unit D at Kulkuletti is dated at 183 ka. These correlations and ages provide strong support for the age originally suggested for the hominin remains Omo I and Omo II, and for correlation of times of deposition in the Kibish region with formation of sapropels in the Mediterranean Sea. The Aliyo Tuff in Member III of the Kibish Formation is dated at 104 ka, and correlates with Gademotta Unit 15 in the Ethiopian Rift Valley.     

Land-use patterns and cultural change in the Middle to Late Bronze Age in Ireland: inferences from pollen records

In Ireland, the Middle to Late Bronze Age (1500–600 cal b.c.) is characterised by alternating phases of prolific metalwork production (the Bishopsland and Dowris Phases) and apparent recessions (the Roscommon Phase and the Late Bronze Age-Iron Age transition). In this paper, these changes in material culture are placed in a socio-economic context by examining contemporary settlement and land-use patterns reconstructed from the pollen record. The vegetation histories of six tephrochronologically linked sites are presented, which provide high-resolution and chronologically well-resolved insights into changes in landscape use over the Middle to Late Bronze Age. The records are compared with published pollen records in an attempt to discern if there are trends in woodland clearance and abandonment from which changes in settlement patterns can be inferred. The results suggest that prolific metalworking industries correlate chronologically with expansion of farming activity, which indicates that they were supported by a productive subsistence economy. Conversely, declines in metalwork production occur during periods when farming activity was generally less extensive and perhaps more centralised, and it is proposed that disparate socio-economic or political factors, rather than a collapse of the subsistence economy, lie behind the demise of metalworking industries.     

Recovery of forest understories buried by tephra from Mount St. Helens

To determine the effects of tephra (volcanic aerial ejecta) on forest understory plants, six sites were chosen along a tephra depth gradient (23 to 150 mm) northeast of Mount St. Helens, USA. All sites were in old forests beyond the limits of direct blast damage from the volcanic eruption. At each site, 150 one m² plots were permanently marked; all tephra was removed from 50 of these in 1980. Cover and density of plant species were recorded during 1980, 1981, and 1982.Tephra 23 mm deep had almost no effect on cover and density of vascular plants, and reduced bryophyte cover for only two years. Tephra 45 mm deep destroyed almost all bryophytes. Although damaged by 45 mm tephra, deciduous herbs recovered by 1982, but some evergreen species did not. Tephra 75 mm deep reduced herb cover in 1982 to 32% and density to 26% of that in cleared plots. At two sites with an average tephra depth of 150 mm, almost all herbs were eliminated except in microsites where tephra was thin, but shrub abundance was greatly reduced only where snow had been present during tephra deposition. Almost all cover was contributed by plants established previous to the eruption; seedling cover never exceeded 0.2%. Refugia with thin tephra, resulting from erosion, were vital to the survival of many species, especially bryophytes.Nomenclature of vascular plants follows Hitchcock & Cronquist (1973); moss nomenclature follows Lawton (1971).We thank T. Hill, C. Halpern and B. Smith for field assistance. The USDA Forest Service, and especially J. F. Franklin, facilitated entry into the restricted area around Mount St. Helens. This word was supported by the National Science Foundation, USDA Science and Education Administration, and the U.S. Forest Service Pacific Northwest Forest and Range Experiment Station.     

The Ngorongoro Volcanic Highland and its relationships to volcanic deposits at Olduvai Gorge and East African Rift volcanism

The Ngorongoro Volcanic Highland (NVH), situated adjacent and to the east of Olduvai Gorge in northern Tanzania, is the source of the immense quantities of lava, ignimbrite, air fall ash, and volcaniclastic debris that occur interbedded in the Plio-Pleistocene sedimentary deposits in the Laetoli and Olduvai areas. These volcanics have proven crucial to unraveling stratigraphic correlations, the age of these successions, the archaeological and paleontological remains, as well as the source materials from which the bulk of the stone tools were manufactured. The NVH towers some 2,000 m above the Olduvai and Laetoli landscapes, affecting local climate, run-off, and providing varying elevation - climate controlled ecosystem, habitats, and riparian corridors extending into the Olduvai and Laetoli lowlands. The NVH also plays a crucial role in addressing the genesis and history of East African Rift (EAR) magmatism in northern Tanzania.In this contribution, we provide age and petrochemical compositions of the major NVH centers: Lemagurut, basalt to benmorite, 2.4-2.2 Ma; Satiman, tephrite to phonolite, 4.6-3.5 Ma; Oldeani, basalt to trachyandesite, 1.6-1.5 Ma; Ngorongoro, basalt to rhyolite, 2.3-2.0 Ma; Olmoti, basalt to trachyte, 2.0-1.8 Ma; Embagai, nephelinite to phonolite, 1.2-0.6 Ma; and Engelosin, phonolite, 3-2.7 Ma. We then discuss how these correlate in time and composition with volcanics preserved at Olduvai Gorge. Finally, we place this into context with our current understanding as to the eruptive history of the NVH and relationship to East African Rift volcanism.     

A revised stratigraphic framework for Olduvai Gorge Bed I based on tuff geochemistry

Olduvai Gorge, Tanzania has rich records of Plio-Pleistocene fauna and flora, hominin fossils, and stone artifacts preserved between well-dated tephra layers (tuffs). Accurate correlation between sites in the two million year section is complicated by faulting, erosion, change in physical appearance of the tuffs, and quality of preservation. Traditional tuff geochemical techniques using glass cannot be applied because of poor glass preservation, and previous physical mapping has led to miscorrelations in Bed I. A new approach, using a combination of glass and mineral compositions (feldspar, augite, hornblende, and oxides) produced successful geochemical fingerprints for all ten major Bed I (∼2.03-1.79 Ma) tuffs. These fingerprints make available a reliable means for correlating specific tuffs between the well-dated "Junction" sites, such as FLK and HWK, and less well-dated sites at the basin margins. The new correlations provide a high-resolution stratigraphic framework for Bed I and correct previous miscorrelations in the west of the basin. Olduvai Hominin 65, from western Olduvai, was recovered from a level between Tuff IC and the Ng’eju Tuff, and therefore dates to 1.79-1.84 Ma.     

The effects of the Taupo Tephra eruption of c. 1718 bp on the vegetation of Mt Hauhungatahi, central North Island, New Zealand

Abstract. An altitudinal series of eleven fine resolution pollen diagrams were used to examine the role of volcanism in forest dynamics on Mt Hauhungatahi. Partial pollen diagrams from four of these sites, chosen to illustrate the major effects of the 1718 bp Taupo eruption, are presented. Following the eruption Libocedrus bidwillii expanded in all sites. Open sites created by the eruption may have facilitated an expansion already underway as a result of more variable climatic conditions since c. 3000 bp . Weinmannia racemosa invaded upper montane forest c. 650 bp . The current altitudinal sequence of forest types, with Libocedrus dominating the subalpine and Weinmannia the upper montane forests, has thus been synthesized only within the last 1800 years. This is interpreted as a consequence of individualistic species' responses to major disturbance by the eruption. The results support nonequilibrium theories of community composition.     

Seedling establishment patterns on the Pumice Plain,Mount St. Helens,Washington

Abstract. We examined the factors that control seedling establishment on barren substrates on the pyroclastic flows from Mount St. Helens. From June to September in 1993, we monitored seedling and microhabitat changes in 240 20 cm × 20 cm quadrats on the Pumice Plain. Seedlings emerged in 104 quadrats (43.3 %). The most abundant species were Anaphalis margaritacea, Hypochaeris radicata, Lupinus lepidus and Epilobium angustifolium. Measured site characteristics included topography, particle size distribution, ground surface movements, soil water content, organic matter, pH, and presence or absence of dead lupines. Quadrats with seedlings had higher cover of dead lupines, higher amount of rock and gravel substrate, and a greater cover of rills. More seedlings emerged where eroded material accumulated. Compared to coarse-textured surfaces, silt surfaces had higher organic matter, held more water, and showed higher pH. However, seedlings became established more frequently on coarse-textured surfaces. In greenhouse experiments, a higher percentage of Hypochaeris seeds germinated on silt than on sand or gravel. The germination of Anaphalis and Epilobium did not differ with soil texture, but was higher at higher moisture levels. Seedling colonization is more dependent on ground surface microtopography, particle size, and ground movement than on the chemical status of these volcanic deposits.     

日本的前期旧石器──高森遗址

日本的前期旧石器──高森遗址安志敏（中国社会科学院考古研究所,北京１００７１０）高森遗址是目前在日本列岛发现最早的旧石器文化,其年代可早到５０万年以前（石器文化谈话会,１９９１;东北历史资料馆,１９９３）,不仅填补了地区上的空白,在探讨亚洲旧石器文化...     

A reconstruction of the history of a Holocene sand dune on Great Barrier Island, northern New Zealand, using pollen and phytolith analyses

Aim   To reconstruct the history of a Holocene sand dune using pollen and phytolith analyses, and to identify the strengths, weaknesses and compatibility of these two methods in the interpretation of Quaternary coastal environments.
Location  Great Barrier Island, northern New Zealand.
Methods  Pollen and phytolith analyses were carried out on a sequence through a Holocene sand dune containing a palaeosol.
Results  Phytoliths were present throughout the sequence. Grass phytoliths increased at the expense of tree phytoliths following fire disturbance. Pollen (and spores) was preserved only in the palaeosol part of the profile. Pteridium fern spores increased at the expense of tall tree pollen following the fire disturbance.
Main conclusions  Lack of phytolith production by many species and problems of taxonomic specificity in many others restricts the usefulness of phytolith analysis to defining only broad vegetation types. In New Zealand, gymnosperms are invisible in the phytolith record and ferns are extremely under-represented. In contrast, pollen analysis usually provides a great deal of information regarding the composition of a particular vegetation type. The loss of microscopic charcoal fragments during the phytolith extraction process is a disadvantage in the reconstruction of environments where fires have occurred. The greater durability of phytoliths compared with pollen means that phytoliths may be found in sediments where pollen has not been preserved. The phytolith record may also provide evidence of wetter environments that are not apparent in the pollen record. Unlike grass pollen, which is widely dispersed and therefore blurs the spatial record, the presence of grass phytoliths in sediments indicates a local source. The simultaneous application of both methods potentially provides a powerful tool in ecological interpretation and the reconstruction of Quaternary coastal environments.