Small Hollows Research Articles

Reconstructing fire regimes with charcoal from small-hollow sediments: a calibration with tree-ring records of fire

Interpretations of charcoal records from small hollows lack a strong theoretical and empirical foundation, and thus their potential for providing useful fire-history records is unclear. To evaluate this potential, we examined charcoal records in 210Pb-dated cores from 12 small hollows and looked for evidence of 20 local fires reconstructed with tree-ring records from the surrounding forest. Using all charcoal > 0.15 mm wide we established an optimum threshold that identified charcoal peaks corresponding to known fires while minimizing charcoal peaks identified that were not associated with known fires (i.e., false positives). This threshold detected four of four high-severity fires, five of 10 moderate-severity fires, and three of six low-severity fires. Analysis of larger charcoal alone (> 0.50 mm wide) yielded nearly identical temporal patterns and detection rates, but four false positives were identified, twice as many as identified using all charcoal >0.15 mm wide. Charcoal peak magnitude was highly variable within severity classes: although half of the low-and moderate-severity fires left no detectable peaks, others left peaks larger than some high-severity fires. Our results suggest that fire detection depends strongly on fire severity and that fine-scale spatial patterns of lower-severity burns play an important role in determining the charcoal signature of these events. High detection rates for high-severity fires and low false-positive rates indicate that charcoal records from small hollows will be most useful in systems where fires are large, severe and infrequent.

How open were European primeval forests? Hypothesis testing using palaeoecological data

Summary The Vera hypothesis that large herbivores maintained an open landscape in the primeval landscape of lowland Europe is tested using palaeoecological data. The hypothesis suggests that the high abundance of Quercus and Corylus apparent in European pollen diagrams could not have derived from a landscape dominated by closed canopy forests. If natural forest landscapes were indeed more open, current forest conservation management policy across Europe would need to be reconsidered. Relative proportions of Quercus and Corylus pollen are compared from regions which supported large herbivores with data from Ireland, where large herbivores were excluded. Similarity between the two data sets indicates that large herbivores were not required to maintain these taxa in the primeval landscape. Fine spatial resolution pollen data from small hollows in Europe and eastern USA were also reviewed. Data from moss polsters show that percentage arboreal pollen is a reliable indicator of canopy openness in theses sites. The palaeoecological data demonstrate that open canopy forest has only ever been maintained by human exploitation. Large herbivores in Europe do not therefore appear to have maintained an open landscape in primeval times although evidence suggests that they would have influenced the species composition of the forest canopy. It is proposed that data sources other than pollen should be explored as proxies for past forest structure to test this hypothesis more thoroughly.

Pancam multispectral imaging results from the Spirit Rover at Gusev Crater.

Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high- to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface.

Direct observation of poly(3-hydroxybutyrate) depolymerase adsorbed on polyester thin film by atomic force microscopy.

Poly[(R)-3-hydroxybutyrate] (PHB) depolymerases adsorbed on poly(L-lactide) (PLLA) thin film were directly observed by atomic force microscopy (AFM). A PLLA thin film of 100 nm thickness was prepared on a silicon wafer by spin-cast method. The PLLA thin film was treated at 220 degrees C and quenched to room temperature, resulting in the formation of a completely amorphous film with a smooth surface. Then, the PHB depolymerases from Pseudomonas stutzeri YM1006 and Ralstonia pickettii T1 were dispersed on the amorphous PLLA thin film. Direct AFM observation has revealed that the PHB depolymerases bind in an elliptic shape on the surface of the PLLA thin film and that a small ridge is created around each enzyme molecule. After removal of the enzymes with 40% ethanol aqueous solution, small hollows were found on the PLLA thin film. These results suggest that a PHB depolymerase interacts with polyester molecules during their adsorption to make a hollow on the substrate surface.

A Neolithic Wetland Site at Abercynafon, Talybont, South Wales

This paper presents the results of an integrated archaeological and palaeoecological investigation following the discovery of waterlogged worked-wood in a small boggy hollow on the southern edge of the Brecon Beacons in south Wales. Analysis of the pollen, radiocarbon and dendrochronological evidence suggests the main phase of activity at the site involved local clearance of the primary oak forest in the early 3rd millennium BC. Later activity at the site is indicated by dates in the mid 1st millennium AD along with two pewter bowls of known Roman form. A tree-ring chronology spans the period 3098–2730BC. Neolithic woodworking techniques are examined from what was for the most part debris from the processing of large trees. Possible parallels for the site are discussed and suggestions made for its use.

1451 ディンプル球の抗力低減特性とその最適設計条件

Golf balls are pitted on their surface with hundreds of small hollows called dimples in order to lengthen the range. The effects of dimples are known as the results of boundary layer control; (1) drag reduction, (2) lift rise in spinning, and (3) trajectory stabilization. The present paper describes the effect of (1) drag reduction mentioned above. We measured the drag coefficient of model dimpled spheres, visualized the flow field around each dimpled sphere by means of the smoke wire method, and made clear the characteristics of drag reduction dependent on the dimensions of dimples and their optimizing design conditions. Furthermore we also propose the concrete procedure to design optimally the dimpled spheres with the effect of drag reduction for general purpose.

Regular spatial structures in arrays of Bose–Einstein condensates induced bymodulational instability

We show that the phenomenon of modulational instability in arrays ofBose–Einstein condensates confined to optical lattices gives rise to coherentspatial structures of localized excitations. These excitations represent thin discs in1D, narrow tubes in 2D, and small hollows in 3D arrays, filled in with condensedatoms of much greater density compared to surrounding array sites. Aspects ofthe developed pattern depend on the initial distribution function of thecondensate over the optical lattice, corresponding to particular points of theBrillouin zone. The long-time behaviour of the spatial structures emerging dueto modulational instability is characterized by the periodic recurrenceto the initial low-density state in a finite optical lattice. We propose asimple way to retain the localized spatial structures with high atomicconcentration, which may be of interest for applications. A theoretical model,based on the multiple-scale expansion, describes the basic features of thephenomenon. Results of numerical simulations confirm the analytical predictions.

Interaction between Ionized and Molecular Gas in the Active Star‐forming Region W31

We have carried out 21 cm radio continuum, H76_\alpha radio recombination line, and various (CO, ^13CO, CS, & C^34S) molecular line observations of the W31 complex. Our radio continuum data show that W31 is composed of two extended HII regions, G10.2-0.3 and G10.3-0.1, each of which comprises an ultracompact HII region, two or more compact components, and diffuse envelope. The W31 cloud appears as an incomplete shell on the whole and consists of southern spherical and northern flat components, which are associated with G10.2-0.3 and G10.3-0.1, respectively. We detect two large and massive CS-emitting regions in the northern and southern cloud components. The large amount of dense gas may suggest that the W31 cloud has ability to form rich stellar clusters and that star formation has only recently begun. The extended envelopes of both G10.2-0.3 and G10.3-0.1 are likely to be results of the champagne flows, based on the distributions of ionized and molecular gas and the velocity gradient of H76_\alpha line emission. We find strong evidence of bipolar molecular outflows associated with the two ultracompact HII regions. In the vicinity of the ultracompact and compact HII regions in G10.3-0.1, the CO J=2-1/J=1-0 intensity ratio is high (1.4) and a small but prominent molecular gas hollow exists. These observations strongly indicate that the HII regions and their ionizing stars are interacting with the molecular cloud. Therefore, it is most likely that recently formed massive stars are actively disrupting their parental molecular cloud in the W31 complex.

LATE HOLOCENE STAND-SCALE INVASION BY HEMLOCK (TSUGA CANADENSIS) AT ITS WESTERN RANGE LIMIT

The movement of plant range limits in the past has been clearly documented as a response to changing climate, but the pattern and timing of local invasions that result from these plant migrations are not well understood. Sedimentary evidence from small forest hollows is used here to reconstruct the pattern of stand-scale invasion by eastern hemlock (Tsuga canadensis (L.) Carr.) at its current range limit in Wisconsin. Pollen records from lakes show a slowly increasing regional hemlock population over the past 2500 yr, as its range expanded from the east in response to cooler, wetter climate. In contrast, hemlock pollen in each of the forest hollows increased abruptly within the past 500 yr, demonstrating stand-scale dynamics at a time when regional changes were small. Moreover, this abrupt rise in hemlock is part of a two-phase sequence of local invasion. First, stands were initially colonized as much as 2000 yr ago, but the size of these local populations remained low for as long as 1800 yr. This pattern suggests that scattered, small populations grew beyond the continuous range limit of hemlock, which was tens of kilometers to the east. Second, these small hemlock populations expanded in size between 100 and 500 yr ago during a time of cooler, wetter climate, which was apparently limiting population growth. These results illustrate contrasting patterns of change between local and regional populations, and the importance of outlying colonies as sources of rapid population expansion when environmental conditions become favorable.

Hollows in jarrah ( Eucalyptus marginata) and marri ( Corymbiacalophylla) trees : I. Hollow sizes, tree attributes and ages

One hundred and fifty-four jarrah ( Eucalyptus marginata) and 85 marri ( Corymbia calophylla) trees were measured and assessed, and the numbers and sizes of hollows in these trees were determined by destructive sampling; 665 hollows were located and measured. The relationship between tree diameter and tree age was determined from counts of annual growth rings on 162 of these trees. Large trees and trees with moderately senescent crowns individually bear the most hollows. Although the number of hollows found in individual trees increased with tree diameter, the distribution of tree diameters in the forest is skewed and the large number of small trees with diameters between 40 and 80 cm contribute approximately 50% of all hollows in the jarrah forest. The distributions of entry size, and of hollow depth, are highly skewed, with small hollows occurring more frequently than large hollows. Although jarrah trees bear more hollows than marri trees and the distribution of entry sizes is similar for both tree species, the hollows in jarrah are significantly smaller than the hollows in marri. Most hollows are cylindrical in shape, vertically oriented and occur in dead wood in the tree crown. Relatively few hollows (14%) occur in the tree bole or at crown break. Counts of hollows made from ground level are inaccurate as estimates of the actual number of hollows in trees.

Persistence of coastal spruce refugia during the Holocene in northern New England, USA, detected by stand‐scale pollen stratigraphies

Summary1 Pollen data from wet, forested hollows in five spruce (Picea) stands on the eastern coast of Maine, USA, reveal that spruce has been well‐established (spruce pollen > 6%) for at least 5000 years at four of the sites (Isle au Haut, Schoodic Peninsula, and Roque Island). Spruce became dominant in the fifth stand (Blackwoods, Mount Desert Island) only in the last 2000 years. This is in contrast to pollen stratigraphies from two inland forest hollows and from inland lakes that indicate a significant region‐wide increase in the abundance of spruce only 1000 years ago.2 All five coastal pollen stratigraphies suggest that conditions along the east coast of Maine became cooler and moister sometime between 6000 and 5000 years ago. Mid‐Holocene changes in vegetation and sediment accumulation correspond with the timing of rapid increases in tidal amplitude and diurnal mixing of cold water in the Gulf of Maine, suggestive that these resulted in increased marine effects on the local climate at a time that was generally warmer than present.3 Two inland forest‐hollow stratigraphies do not show evidence of mid‐Holocene cooling. Coastal effects therefore persisted for several thousand years despite regional climate changes.4 The pollen data suggest that refugia along the coast (and probably in isolated sites inland), may have played a critical role in allowing the rapid regional expansion of spruce around 1000 years ago. The steep increases in the abundance of spruce pollen in all forest‐hollow and lake pollen stratigraphies in northern New England at that time corroborate other evidence of a region‐wide shift to cooler and moister conditions.5 Pollen stratigraphies from small forested hollows provide a means to examine local vegetation dynamics and interpret those dynamics in the context of regional signals.

Hollow cathode PVD of nitride and oxide films at low substrate temperatures

Highly oriented crystalline films of aluminum nitride and titanium dioxide were grown from Al or Ti hollow cathode in the nitrogen and oxygen gas mixtures with argon. Films were grown on unheated substrates fixed at a holder with temperature sensor. Both cylindrical and linear hollow cathodes were powered by a radio frequency (r.f.) 13.56 MHz generator and arranged with the gas flow through the cathode. The properties of films deposited on glass and silicon samples at different hollow cathode regimes were tested by X-ray diffraction. The film surface topographies were studied by AFM. Highly oriented crystalline AlN films were deposited at substrate temperatures below 50°C. The best AlN films were deposited in a pure nitrogen plasma. Variations in the deposition parameters at constant r.f. power can be used for modifications of AlN microstructure. Highly textured TiO 2 films can be deposited both as anatase or rutile structure, which can be controlled by small changes of the oxygen content in argon. Films can be deposited on selected areas or inside holes by small cylindrical hollow cathodes. However, the deposition process can be scaled up to large substrates by magnetized M-M (Magnets-in-Motion) linear hollow cathodes.

A 5000-year record of disturbance and vegetation change in riparian forests of the Queets River, Washington, U.S.A.

We used fossil pollen, charcoal, and sediment stratigraphy in three small hollows to investigate disturbance events and changes in the composition of riparian forests on a small section of the Queets River floodplain, Olympic Peninsula, Washington. The records ranged in age from approximately 500 years at two sites 300 and 550 m from the river, to 5000 years at a site 800 m from the river. Approximately 400–600 years BP, the two sites nearest the river were either inundated by a very large flood or covered by the active channel, which would have occupied a substantially different position than its present course. Following inundation or channel movement, the pollen record suggests that Alnus rubra Bong., the primary mesic forest colonizer in the Pacific Northwest, increased and was then replaced by Picea sitchensis (Bong.) Carrière and Tsuga heterophylla (Raf.) Sarg. At the site farthest from the river, two fires occurred within the last ca. 4500 years. One of the fires was followed by a period of shrub dominance and succession to Tsuga heterophylla. The other fire did not cause a change in the pollen record. A recent unprecedented rise in Tsuga heterophylla pollen, which began ca. 1000 years BP, might be in response to cooling during the Little Ice Age. Overall, the small hollow records highlight the complex effect of floods, fire, and possibly climate change on riparian forests of the Queets River.

Hollow‐particle latexes: Preparation and properties

AbstractHollow‐particle latexes were prepared according to the following stages: (1) the preparation of the methyl methacrylate–methacrylic acid (MAA)–ethylene glycol dimethacrylate copolymer (I) latex, (2) the preparation of a shell (II) based on polystyrene or styrene–acrylonitrile–divinyl benzene copolymer polymerized onto copolymer (I) particles, and (3) the neutralization of the core (I) carboxyl groups with a base (NH4OH or NaOH) at temperatures close to the glass‐transition temperature of the polymer (II). The neutralization resulted in the expansion of the particles and formed water‐filled hollow particles. The microspheres had an overall diameter of 460–650 nm and a hollow diameter of 300–450 nm. Rheological studies and particle size measurements by transmission electron microscopy and dynamic light scattering of the copolymer (I) latex indicate that the maximum particle swelling occurred at an approximately equimolar MAA/base ratio. It was found that even without the neutralization of the MAA units, a small hollow formation in the latex particles occurred during stage 2 because one volume of the copolymer (I) retained about 8 volume parts of water. It was also discovered that the final hollow‐particle geometry after neutralization depends on the shell copolymer thickness and type as well as on the conditions during stage 3, that is, the time, temperature, base type, and concentration. The opacifying ability of the synthesized hollow particles was investigated in latex coatings. The opacifying ability values were generally in agreement with the hollow‐particle geometry. The only exception was related to the copolymer (I)/copolymer (II) ratio. The maximum hollow volume was obtained at this value equal to 1/8, whereas the highest opacifying ability was observed at 1/10. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1435–1449, 2001

Les érables dans l’étage subalpin : une longue histoire

Pollen analysis was carried out on lacustrine sediment of a small hollow (15 m × 25 m) at the treeless sub-Alpine belt (202 m) of the inner Maurienne valley in the northern French Alps. A 2 500-year-long maple settlement was demonstrared. Three AMS dates of terrestrial plant macroremains support the chronology. First, Betula and Salix spread prior to 9 000 C 14 BP. The first pollen grains of Acer, Abies and Pinus cembra are quoted at 8 600 C 14 BP. High frequencies of Alnus glutinosa/incana (20 %) and Acer (10 %) show that mixed communities of Acer and Alnus persisted above the mountainous Abies forest between 7 490 and 5 850 C 14 BP. After 5 850 C 14 BP, the decrease in Acer stands could be attributed to fire as suggested by the strong increase in Betula and by the delayed expansion of Pinus cembra.

Epibiont molluscs on neogastropod shells from sandy bottoms, Pacific coast of Mexico

This study quantifies the prevalence, abundance, and spatial distribution of epibiotic molluscs on six common neogastropod species in sandy bottoms, Hexaplex nigritus, Chicoreus regius, C. erythrostomus, C. brassica, Vasum caestus and Pleuropoca princeps. A total of 1478 epibiont specimens belonging to 74 mollusc species were examined. The most of epibiotic species were typical of hard-bottoms, but a few species were typical of soft-bottoms. The results indicate H. nigritus is significantly more fouled than the other five species. This can be due to a greater availability of small hollows and a strongly ornamented shell in this species. The spatial distribution of epibionts on the neogastropod shells varied significantly among the different areas into which the shell was subdivided for this study. Fifteen sedentary epibiotic species dominated on all host shells. The costs and benefits of epibiosis are reviewed and the epibiont/host relationship appears to be principally beneficial to epibionts, without a clear benefit for hosts.

Forest Vegetation and Boulder Streams in the Central Appalachian Valley and Ridge Province, Southwestern Virginia

MILLS, H. H. (Department of Earth Sciences, Tennessee Technological University, Cookeville, TN 38505) AND S. L. STEPHENSON (Department of Biology, Fairmont State College, Fairmont, WV 26554). Forest vegetation and boulder streams in the central Appalachian Valley and Ridge province, southwestern Virginia. J. Torrey Bot. Soc. 126:188-196. 1999.-The pattern and structure of forest vegetation in small boulder-floored streamless hollows vary as a function of the type of surficial deposit and topographic position on a scale of tens of meters. Data collected for a 50 m long belt transect across a 20 m wide boulder stream showed that tree species characteristic of mesic sites were most abundant near the center of the boulder stream. In addition, the lowest values of absolute tree den$ity were recorded near the center. Some tree species were found to display noticeable differences in distribution. For example, black birch was much more abundant on the boulder stream than along its margins, whereas chestnut oak, although abundant at the margins, rarely occurred on the stream. Because boulder size reached a maximum in the lowest part of the hollow cross section (i.e., the center), it was not possible to decide whether the main effect was the nature of the substrate or the topographic position (i.e., higher levels of moisture in the lower part of the cross section and lower levels of moisture in the higher parts). To distinguish these effects, a second transect was established across one side of a much wider boulder stream that showed large lateral variation in boulder size. Data collected for this transect showed that for several tree species the main factor affecting distribution was topographic position (i.e., near to or distant from the lowest part of the hollow cross section). However, black birch showed an affinity for areas underlain by large boulders, regardless of their topographic position.

Landscape openness and pollen records: a simulation approach

Quantitative reconstruction of the area cleared of forest in the past is essential to assess the possible indirect anthropogenic impacts on the past environment of Europe, including past climate. We apply a simul ation model of pollen dispersal and deposition (1) to re-examine the relationship between pollen and landscape openness, often uncritically inferred from non-arboreal pollen (NAP) percentages alone, and (2) to predict the relevant source area of pollen, the smallest spatial scale of vegetation that can be reconstructed from pollen records. The simulations use landscapes simplified from the modern open agricultural and semi-open forested regions in southern Sweden where traditional cultural landscapes still remain. The model is appropriate, because the simulated pollen assemblages resemble the pollen assemblages observed in each of the two landscape types, and because the simulated relationships between NAP percentages and percentage cover of open land within 1000 m agree with the empirical relationships. The simulated relevant source area of pollen is the area within 800–1000 m from both small hollows and 3-ha ponds. NAP percentages give only a rough first approximation of the percentage cover of open land. More comprehensive methods will be required to obtain quantitative estimates of open land from fossil pollen.

The establishment of Fagus sylvatica at the stand-scale in southern Sweden

Pollen analysis was carried out on peat profiles from small forest hollows at four sites in southern Sweden in order to investigate the establishment of Fagus sylvatica at the stand-scale. Viewed on a continental scale the migration pattern of Fagus can be correlated with climatic change, but at finer scales such a correlation is weaker. At the stand-scale there are factors other than climate that are crucial for the establishment of Fagus(e.g., disturbance, seed dispersal, human activities). The establishment of Fagus does not show any regional coherence in southern Sweden, and this may imply that climate was not the limiting factor for its establishment. Fagus seeds are highly dependent on ground disturbance for successful establishment. A semi-open cultural landscape may be optimal for Fagus establishment, as cultural activities may create conditions particularly suitable for its regeneration. At two of the studied sites cultural activities probably created conditions that favoured the establishment of Fagus at 400 and 900 BP respectively. At the other sites the local forest stands were relatively unaffected by cultural activities prior to the establishment of Fagus at 950 BP and 1450 BP respectively, where, fires (natural?) or slight human influence were effective. The present-day distribution of Fagus in southern Sweden suggests migration with a discontinuous front and outlying populations, and this model probably applies to its past distribution. This type of migration means that the landscape becomes filled in by dispersal from outlying stands. The timing of stand-scale establishment is then largely influenced by site-specific factors and chance. Fagus may still be migrating northwards in Sweden. It grows well in its outlying area, and it seems that present-day land use, not climate, is the limiting factor for the local expansion of Fagus. The northern distribution limits of Fagus probably still represent an active front, and outlying stands act as‘infection centres’.

PATCHY INVASION AND THE ORIGIN OF A HEMLOCK–HARDWOODS FOREST MOSAIC

The record of forest invasion by eastern hemlock (Tsuga canadensis) during the course of Holocene migration provides useful information about invasion processes in temperate forest, a system that has been invaded by few exotic species. We used fossil pollen preserved in small forest hollows, which record forest composition on the scale of 1-3 ha, to study hemlock invasion of forests in the Sylvania Wilderness in the upper peninsula of Michigan, where there is now a mosaic of 3-30 ha stands dominated either by hemlock or by sugar maple (Acer saccharum) and basswood (Tilia americana). Fossil pollen was interpreted by comparison with 66 surface samples from small hollows in Michigan and Wisconsin, using three different statistical methods: pollen ratios, a dissim- ilarity index, and canonical variates analysis (CVA) ordination. We found that four hemlock stands along a 10-km transect across Sylvania originated as patches of white pine (Pinus strobus) forest that were invaded by hemlock -3000 yr ago (calibrated 14C dating) when hemlock expanded its range in northern Michigan. Invasion occurred at about the same time (within 800 yr) at all sites but was not associated with disturbance at any site. Over the next several thousand years hemlock coexisted with white pine, but eventually, at a time that differs from site to site, hemlock became dominant, and white pine disappeared from all but one of the four stands. These changes were apparently driven by climate changes over the last 4000 yr that caused the water table to rise (Brugam and Johnson 1997). The history of four nearby maple stands is more variable and less well understood. Unlike the hemlock stands, three of the four maple patches were not dominated by pine at the time of hemlock invasion, but instead had abundant oak (Quercus) and/or maple. Two of these stands were not invaded by hemlock, and the third, if invaded at all, was invaded for a few centuries by low densities of hemlock trees. Thus invasion by hemlock was sensitive to the species composition of the resident forest. Sugar maple and basswood increased in these stands, and by 2000 to 800 yr ago, depending on site, they resembled modern maple stands. The fourth patch was invaded by hemlock, but it was converted to a maple stand 1000-500 yr ago. A wood layer in the sediment is evidence that a catastrophic windstorm may have been responsible.