bluuebunny/crossref_metadata_2025 huggingface dataset:
Ecological amplitude inSilene nutansin relation to allozyme variation at the western margin of its distribution
Authors: Van Rossum Fabienne , Meerts Pierre , Gratia Emmanuelle , Tanghe Martin
Published: May 2006

Abstract.At the western border of its geographical range,Silene nutans(Caryophyllaceae) has evolved two groups of parapatric populations showing distinct allozyme patterns and apparently occurring on different bedrock types. This study tests the hypothesis that these groups represent edaphic ecotypes. With this in view, the ecological amplitude of 36 populations ofSilene nutansfrom Belgium was investigated and their synecology specified using vegetation composition and soil parameters; Ellenberg indicator values were used for ecological interpretation of the vegetation analyses. The results provide evidence that allozyme and habitat variations are correlated, the two groups occurring on contrasting soil with distinct vegetation types. One group is restricted to alkaline soils and typically occurs in open calcareous grasslands, fringes and scrub. The other group is characterized by wider autecological and synecological ranges with a bimodal pH‐ distribution, occurring on two kinds of siliceous soils: (1) neutral soils, supporting vegetation with a high species richness comprising many mesophilous species, and (2) CaCO3‐free bedrocks characterized by acidophilous, species‐poor, open dry grasslands and woodlands. It also appears that factors not related to soil chemistry, such as microclimate, are involved in the ecological specialization of the two ecotypes. It is argued that these ecotypes exemplify adaptive radiation and parapatric speciation at the margin of a species distribution area.
The effect of spatial scale on evenness
Authors: Wilson J. Bastow , Steel John B. , King Warren McG. , Gitay Habiba
Published: May 2006

Abstract. The effect of spatial scale on species evenness has not previously been investigated. As the area of each sample of vegetation (i.e. the spatial grain) increases, evenness could in theory increase, decrease, or stay the same, though the simplest model predicts an increase. We use biomass data from four dune slack sites and two semi‐arid grasslands, sampled to allow calculation of evenness at a range of spatial grains. In all six sites, evenness decreases as grain size increases, almost monotonically. It is hypothesized that such a pattern is a result of a general feature of plant species abundance distributions and of vegetation response to environmental microheterogeneity.
Tree‐shrub interactions in a subtropical savanna parkland: competition or facilitation?
Authors: Barnes Paul W. , Archer Steve
Published: May 2006

Abstract. Prosopis glandulosa var. glandulosa has played a central role in the encroachment of woody plants in southern Texas, grasslands and savannas by acting as a nurse plant for various shrubs that establish in its understory. To test for continued facilitation of established understory shrubs by Prosopis and to determine if established shrubs compete with the Prosopis nucleus, selective removal experiments were conducted and monitored over a 2–5 yr period. Short‐term (1–3 days) and long‐term (2 yr) growth and physiological activities (midday net photosynthesis and leaf/shoot water potential) of two common understory shrubs, Zanthoxylum fagara and Berberis trifoliolata, growing with Prosopis, were generally comparable to those of individuals occurring in clusters where Prosopis was removed. Shrubs growing with an intact Prosopis occasionally showed significantly higher leaf‐[N] and pre‐dawn water potentials than those in clusters lacking a live Prosopis, especially under drought conditions; however, these differences did not translate into greater midday leaf gas exchange or shoot growth. By comparison, removal of understory shrubs elicited large increases in Prosopis net photosynthesis, annual trunk growth in each of the 5 yr monitored, and seed pod production in three of the four years monitored. Seven of 26 Prosopis plants in experimental clusters with an intact understory died over a 5‐yr period, compared to only two of the 26 plants in clusters with the cleared understory.

Results indicate that (1) the founding overstory Prosopis plant may continue to facilitate understory shrubs following their establishment, but these beneficial effects appear to be small and transitory, and (2) the understory shrubs have a pronounced negative effect on Prosopis, such that competition between overstory and understory woody plants is strongly asymmetrical. These findings suggest that understory shrubs will likely persist despite changes in microclimate and soils (potentially) that occur after the Prosopis plant, which facilitated their ingress or establishment, has died. Soil resource depletion by shallow‐rooted understory shrubs appears to be a primary factor contributing to the demise of the deeply rooted, overstory Prosopis plants, especially on upland sites with duplex soils where below‐ground competition is accentuated.
Predicting competitive interactions between pioneer plant species by using plant traits
Authors: Rösch H. , Van Rooyen M.W. , Theron G.K.
Published: May 2006

Abstract. A competitive effect hierarchy for 15 Namaqualand pioneer plant species was established by using the mean mass of the phytometer (Dimorphotheca sinuata) when grown in combination with itself and 14 other species. There were no clear groupings of species in the hierarchy. This competitive hierarchy (gradient) indicated which species are strong competitors (resulting in a low phytometer mass) with D. sinuata and which species are weak competitors (resulting in a high phytometer mass).

Each plant species has a certain combination of plant traits which determines its life history strategy and competitive ability. Regressions of various plant traits (measured on plants grown singly) against phytometer biomass indicated which traits were significantly correlated. The traits, most being size‐related, were: maximum shoot mass, total mass, stem mass, reproductive mass, leaf area, stem allocation, specific leaf area (SLA), vegetative height × diameter, leaf area ratio (LAR); and mean number of days to flower initiation. A forward stepwise multiple regression of the significant traits was used to determine an equation to predict competitive effect.
Effects of prescribed fire on the composition of woody plant communities in southeastern Texas
Authors: Liu Changxiang , Harcombe Paul A. , Knox Robert G.
Published: May 2006

Abstract. The response to prescribed burning of plant communities ranging from dry to wet habitats was monitored using permanent plots sampled from 1989 to 1993. Temporal controls for fire effects were provided by matched sets of plots protected from fire by newly constructed fire breaks. Changes in species composition were studied by ordination of strata of trees (> 5 cm DBH), small trees (2–5 cm DBH), large saplings (1–2 cm DBH), and small saplings and seedlings (50–140 cm tall). Results show that changes occurred largely in the small tree stratum, in which xeric species increased in importance. Although there were changes in sapling and seedling strata, no clear direction of change was recognized. Fire had little effect on the tree stratum.

Of the seven community types under study, three types, sandhill, upland pine, and upperslope pine‐oak, were most strongly affected, as indicated by post‐fire change in positions of samples representing these communities in ordination space and reduction in understory species abundance. Samples representing the other four mesic and wet communities showed little or no change in their positions.

These short‐term results indicate that changes in vegetation resulting from fire were small and were mostly restricted to the dry types in which possible compositional change is expected to occur. This differential effect of fire suggests that the influence of fire is secondary to that of topographical and soil gradients in determining vegetation pattern under current fire regimes. Fire seems to reinforce an overall vegetation gradient controlled by soil in southeastern Texas.
Spatial variation in a grassland on soil rich in heavy metals
Authors: Babalonas D. , Mamolos A.P. , Konstantinou M.
Published: May 2006

Abstract. The vegetation in a grassland area in the prefecture of Kilkis (N. Greece), known for its surface Cu‐mineralization, was studied. 43 quadrats were established along a transect through an area where the vegetation formed patches of different size. Cover‐abundance and frequency estimates for all species were made. Normal Association Analysis revealed five quadrat groups characterized by Trifolium scabrum, Linaria pelisseriana, Anthoxanthum ovatum, Gypsophila muralis and Minuartia hirsuta ssp. falcata. 43 soil samples were analysed for pH, organic C, CaCO3, total content of Fe, Zn, Pb, Cu, Mn, Ca, Mg, K, Na and soil texture. From a discriminant analysis performed on soil data five soil groups resulted, which are highly related to the five vegetation groups. Thymus sibthorpii, Minuartia hirsuta ssp. falcata and Rumex acetosella are the most important taxa with respect to physiognomy and patchi‐ness of the vegetation. The number of species in each group of quadrats is affected by the relative favourableness or severity of the soil conditions. Metal contents, mainly Zn, Cu, Mg and Na, and soil texture are considered to be among the main factors controlling the structure and physiognomy of the vegetation.
Gap regeneration of shade‐intolerant Larix gmelini in old‐growth boreal forests of northeastern China
Authors: Ban Yong , Xu Huacheng , Bergeron Yves , Kneeshaw Daniel D.
Published: May 2006

Abstract. Stand mapping and vertical and oblique tree crown projections were used to study gap characteristics and gap effects on the regeneration and stand development of Larix gmelini. The hypothesis is that waves of advance Larix regeneration are recruited into the canopy layer following the creation of canopy openings. In old‐growth Larix forests of the northern Da Xingan Ling Mts., at 52 °N, obliquely projected gaps (OPG) begin at a distance of 60 ‐ 80% of the canopy tree height from the southernmost stems bordering the gap and thus the OPGs may extend beyond the northern boundaries of the vertically projected gaps (VPG). Changes in the environment and resource availability in the OPG result in increased Larix sapling survival. Due to a greater incidence of light, 10 ‐ 30 yr old OPG saplings were more abundant than saplings in either a near‐oblique projected gap (NOPG) or in the shadow of obliquely projected crowns (SOPC). The survival of saplings more than 30‐yr old was highest when they were found in the OPG of one canopy opening and the VPG of another. This means that, following recruitment into an OPG, saplings then require the space found in a VPG to permit growth into the canopy. Thus, various‐sized gaps contribute to the survival of different aged saplings by increasing the complexity of stand structure. Although individuals may regenerate in an OPG, successful recruitment into the canopy requires the available growing space of a VPG. This research suggests that shade intolerant Larix gmelini can maintain its canopy dominance without fire via gap regeneration.
Fine‐root production in small experimental gaps in successional mixed boreal forests
Authors: Campbell Johanne J. , Finér Leena , Messier Christian
Published: May 2006

Abstract. The effects of small 10m × 10m experimental above‐ground gaps on fine‐root production for the first two years were studied in three fire‐initiated stands of the northwestern mixed broad‐leaf‐conifer boreal forest of Québec. The 48‐yr‐old forest is dominated by Populus tremuloides (Trembling aspen), the 122‐yr‐old forest by a mixture of P. tremuloides, Abies balsamea (balsam fir) and Picea glauca (white spruce), and the 232‐yr‐old forest by Thuja occidentalis (eastern white cedar) and A. balsamea, with some P. tremuloides. 40 root‐ingrowth bags were installed in different locations in and around each gap (at gap center, 1 to 2 m either side of gap edge and in adjacent control plots). Half of the ingrowth bags were harvested after one year following gap creation, the other half after two years. Roots were sorted into different species grouping. Fine‐root production was statistically (P < 0.05) larger in the youngest forest compared to the two older ones after one year, but not after two years. The individual species or groups of species increased, decreased or showed no change in fine‐root production in gaps, but overall we did not observe a major shift in species proportion between gap and control plots after two years. Some herbs and also Taxus canadensis seemed to benefit in terms of fine‐root growth from such small openings after two years. No statistical differences (P > 0.10) in total fine‐root production were found among locations within and outside gaps in either year. However, there was a clear tendency for fine‐root production to be smaller in gap center than in the other locations for the two younger successional forests the first year after gap creation. We conclude that small above‐ground gaps (i.e. < 100 m2) do not produce a significant and long‐lasting below‐ground gap in terms of total fine‐root production in the successional forests investigated.
The occurrence of herbs and woody juveniles in a hardwood floodplain forest in relation to flooding and light
Authors: Siebel Henk N. , Bouwma Irene M.
Published: May 2006

Abstract. A study of the distribution of herbs, seedlings and vegetative propagules of woody species in a hardwood flood‐plain forest along the Upper Rhine in France revealed that the occurrence of most species is significantly correlated to elevation above river level and light transmission in summer. Species confined to higher‐lying sites which are only occasionally and briefly flooded in the growing season show most damage upon flooding. Tall herb species occur on sites where more than 5% daylight reaches the herb layer and they only reach a dense cover where flooding is occasional. The occurrence of woody juveniles is negatively correlated with tall herb cover and largely confined to more shaded sites or more frequently flooded sites. The results indicate that both shading and flooding are important for regeneration of woody species and for maintaining species diversity in hardwood flood‐plain forests.
Environmental variables influencing the carbon balance at the alpine treeline: a modeling approach
Authors: Cairns David M. , Malanson George P.
Published: May 2006

Abstract. Growth of coniferous trees at alpine treeline locations has traditionally been viewed as primarily temperature dependent. In this study, we use a physiologically mechanistic process model, ATE‐BGC (Alpine Treeline Ecotone ‐ BioGeochemical Cycles), to study the effects of a suite of environmental variables on the carbon balance of krummholz growth forms of subalpine Abies lasiocarpa under environmental conditions representative of treeline locations in Glacier National Park, Montana, USA. We perform a sensitivity analysis of ATE‐BGC to determine the relative effects of temperature, insolation, snow, rain, soil depth, leaf area index, winter injury and elevation on krummholz carbon balance. Our results indicate that ATE‐BGC carbon balance estimates are most highly influenced by temperature and winter injury. Leaf area index, soil depth, rainfall, insolation and snowfall follow temperature and winter injury in their effect on carbon balance. Due to the sensitivity of the model to moisture related variables, we propose that local irregularities in the location of the alpine treeline ecotone are the result of localized xeric conditions.
Facilitation by nurse shrubs of resprouting behavior in a post‐fire shrubland in northern Patagonia, Argentina
Authors: Raffaele Estela , Veblen Thomas T.
Published: May 2006

Abstract. The nurse‐plant syndrome is a widely recognized example of positive (facilitative) influences of plant species on the establishment and growth of other species. Most studies of the nurse‐plant syndrome have been on species that reproduce mainly from seed rather than vegetatively. In this study, we experimentally compared the influences of two species of nurse shrubs, Schinus patagonicus and Berberis buxifolia, on the survival and growth of vegetatively reproducing herbaceous and woody plants in a post‐fire shrubland in northern Patagonia, Argentina. The vegetation beneath shrubs was removed by clipping and, in a paired‐sample design, one half of the canopy of each shrub was removed. We determined species richness, counted number of resprouts, and measured photon flux density and soil moisture beneath cut and uncut halves of each shrubs.

Abundances of resprouts were several times greater beneath the uncut vs. the cut shrubs, as was the mean number of species. Thus, shrubs have a strong facilitating influence as measured by resprout densities and the number of species. Numbers of resprouts and of species were twice as high beneath Schinus as beneath Berberis, implying important differences in the facilitative effects of the two shrubs species. Microsites beneath Schinus were characterized by lower and more heterogeneous light levels but by greater soil moisture. Even though the reproductive mode in this post‐fire shrubland is overwhelmingly vegetative, facilitation by nurse shrubs is important and differentially effective for different species of nurse shrubs.
Size‐structure dynamics of two conifers in relation to understorey dwarf bamboo: A simulation study
Authors: Takahashi Koichi , Kohyama Takashi
Published: May 2006

Abstract. Size‐structure dynamics and co‐existence of the conifers Abies sachalinensis and Picea glehnii in subalpine forests in Japan, in relation to the understorey dwarf bamboo Sasa, were examined using a simulation model. This model explicitly incorporated recruitment rate, size growth rate and mortality. Recruitment and growth rates were assumed to be suppressed by the cumulative basal area of taller trees and the density of Sasa. As for the one‐sided crowding effect, two types of model were examined. The total basal area of the two species suppresses the growth and recruitment rates in an additive model, while the basal area of each species has a separate effect included in a specific model. Two types of recruitment process were examined, i.e. open and closed systems; recruitment rates of open and closed systems are independent of, and proportional to, the basal area of the same species within the plot, respectively. Parameters were estimated from data of plot censuses for four years. The parameters of the specific model showed that recruitment and size growth rates were more suppressed by the same species than the other species. Recruitment of A. sachalinensis was more sensitive to suppression by Sasa compared with P. glehnii. The stationary size structure of the two species, generated from both the models with the open system, fitted well to the observed size structures across various Sasa densities. A. sachalinensis and P. glehnii dominated at lower and higher densities of Sasa, respectively. However, the closed‐system simulation showed that the stable co‐existence of the two species with a good fit to the observed size structure occurred only in the specific model.

These results suggest that within‐species interference, which is more severe than between‐species interference, is important for the co‐existence of the two species and that the relative dominance of the two species readily explained the differential responses to Sasa abundance.
Phytogeographical and community similarities of alpine tundras of Changbaishan Summit, China, and Indian Peaks, USA
Authors: Qian Hong , White Peter S. , Klinka Karel , Chourmouzis Christine
Published: May 2006

Abstract. We compared the diversity, phytogeography, and plant communities in two mid‐latitude alpine tundras with comparable aerial and elevational extents: Changbaishan Summit in eastern Asia and Indian Peaks in western North America. Despite wide separation, the two areas shared 72 species. In all, 43% of the species on Changbaishan Summit are also distributed in the alpine zones of western North America, while 22% of the species on Indian Peaks are also distributed in the alpine zones of eastern Asia. Almost all the shared species also occur in the Beringian region. Phytogeographical profiles of species and genera showed that 69% of species and over 90% of genera in both alpine tundras belong to the three phytogeographical categories: cosmopolitan, circumpolar, and Asian‐North American. We attributed the current floristic relationship between these widely separated areas to the periodic past land connection between the two continents during the Tertiary and Pleistocene. Indian Peaks has a closer floristic relationship with the Arctic tundra than does Changbaishan Summit. Indian Peaks also has 45% higher species richness and lower vegetation cover than Changbaishan Summit.

Plant communities from the two areas were completely separated in the two‐way indicator species analysis and non‐metric multidimensional scaling on floristic data at both species and generic levels, whereas ordination of communities by soil data produced a greater overlap. The plant communities on Changbaishan Summit in general have lower alpha diversity, higher beta diversity (lower between‐community floristic similarity), and more rare species than does Indian Peaks. Mosaic diversity does not differ in the two alpine tundras, although the analysis suggests that Changbaishan Summit communities are more widely spaced on gradients than the Indian Peaks communities.
Vegetation patterns in heterogeneous landscapes: The importance of history and environment
Authors: Motzkin Glenn , Wilson Paul , Foster David R. , Allen Arthur
Published: May 2006

Abstract. Throughout the eastern United States, plant species distributions and community patterns have developed in response to heterogeneous environmental conditions and a wide range of historical factors, including complex histories of natural and anthropogenic disturbance. Despite increased recognition of the importance of disturbance in determining forest composition and structure, few studies have assessed the relative influence of current environment and historical factors on modern vegetation, in part because detailed knowledge of prior disturbance is often lacking. In the present study, we investigate modern and historical factors that control vegetation patterns at Harvard Forest in central Massachusetts, USA. Similar to the forested uplands throughout the northeastern United States, the site is physiographically heterogeneous and has a long and complex history of natural and anthropogenic disturbance. However, data on forest composition and disturbance history collected over the past > 90 years allow us to evaluate the importance of historical factors rigorously, which is rarely possible on other sites.

Soil analyses and historical sources document four categories of historical land use on areas that are all forested today: cultivated fields, improved pastures/mowings, unimproved pastures, and continuously forested woodlots. Ordination and logistic regressions indicate that although species have responded individualistically to a wide range of environmental and disturbance factors, many species are influenced by three factors: soil drainage, land use history, and C:N ratios. Few species vary in accordance with ionic gradients, damage from the 1938 hurricane, or a 1957 fire. Contrary to our expectation that the effects of disturbance will diminish over time, historical land use predicts 1992 vegetation composition better than 1937 composition, perhaps because historical woodlots have become increasingly differentiated from post‐agricultural stands through the 20th century.

Interpretations of modern vegetation must consider the importance of historical factors in addition to current environmental conditions. However, because disturbances such as land use practices and wind damage are complex, it is often difficult to detect disturbance effects using multivariate approaches, even when the broad history of disturbance is known.
A fragmented landscape in northern Spain analyzed at different spatial scales: Implications for management
Authors: Rescia A.J. , Schmitz M.F. , Martin de Agar P. , de Pablo C.L. , Pineda F.D.
Published: May 2006

Abstract. Changes in landscape pattern are analyzed through sampling plots of different size taken along a time series of aerial photographs at three scales of observation. The results indicate that variation in the landscape pattern shows a less pronounced change at the local scale than at larger scales and that appreciation of the structure of this landscape and description of its temporal variation are scale‐dependent.

Analysis of the spatial complexity on different scales, measured by the C(s) index (Rescia et al. 1994), shows that the number of types of boundary between patches is the most important landscape component on all scales. Spatial complexity and the number of boundary types are related to woody plant diversity at a local scale.

In the studied landscape, human activities on a local scale strongly influence the spatial configuration on a regional scale. This concerns territorial planning, the main problem of which is not found in selecting a correct observation scale, but in recognizing that the change under study occurs at various scales at the same time. This underlines the importance of analysing the landscape pattern at different scales with the design of plans and conservation programs in mind.
Climatic discrimination of Mediterranean broad‐leaved sclerophyllous and deciduous forests in central Spain
Authors: Gavilán Rosario , Fernández‐González Federico
Published: May 2006

Abstract. Climatic differences between three types of deciduous (Quercus pyrenaica) and three types of sclerophyllous (Quercus rotundifolia) Mediterranean forests in the Spanish Sistema Central were analyzed by means of Canonical Discriminant Analysis and Jancey's Discriminant Analysis, applied in successive steps to data from 252 meteorological stations. Climatic data included temperature and precipitation records as well as bioclimatic indices. Discriminant analysis was applied to broad‐leaved sclerophyllous and deciduous forest communities sampled at each meteorological station using phytosociological methods. Annual and seasonal (summer, spring) water availability are the most important factor controlling the distribution of the two physiognomic forest types; southwestern associations of Quercus pyrenaica and Q. rotundifolia differ from their colder homologues by annual and monthly temperatures; western associations were separated from eastern ones in terms of annual and seasonal precipitation gradients. Discriminant analysis was a good technique to explore climatic gradients not shown by other general ordination or classification methods.
History of aPinus strobus‐dominated stand in northern New York
Authors: Kearsley Jennifer B. , Jackson Stephen T.
Published: May 2006

Abstract.Pollen, plant macrofossils and charcoal from a small forest hollow were analyzed to determine the formation and dynamics of aPinus strobus‐dominatedforest stand on outwash soil in northern New York.P. strobus, Betula papyriferaandAbies balsameacolonized the upland surrounding the hollow following a major disturbance that occurred ca. 360 yr ago. Pre‐disturbance vegetation consisted of shade‐tolerantTsuga canadensis, Fagus grandifoliaandPicea ruhens. The size‐class distribution of modern vegetation suggests continuing recruitment ofA. balsameaandAcer rubrumat the site. The status ofP. strobusandB. papyriferain the stand is uncertain, but there is no evidence for recolonization ofT. canadensis, F. grandifoliaorP. rubens. Frequent windthrow has probably played a role in stand dynamics since ca. 310 yr BP due to the high wind‐susceptibility of overstory and understory tree taxa in the modern forest patch.

Vegetation change that occurred following fire(s) ca. 310 yr BP was recorded by plant macrofossils but not by pollen, indicating that the pollen assemblage was insensitive to vegetation change within at least 30 m (and potentially 60 m) of the hollow. The apparent insensitivity of this small‐hollow pollen assemblage to local vegetation change may be related to the relatively large size of the hollow (75 m2) and/or to its close proximity to a 0.24 ha kettle pond.
Fine‐scale spatial population patterns and mobility of winter‐annual herbs in a dry grassland
Authors: Geißelbrecht‐Taferner Leonore , Geißelbrecht Jürgen , Mucina Ladislav
Published: May 2006

Abstract. Winter annuals were mapped in a series of permanent plots located in gaps in an Austrian dry grassland over a period of 3 yr. Great differences in abundance were found among nine winter annuals — Arabis auriculata, Arenaria leptoclados, Cerastium glutinosum, Erophila spathulata, Holosteum umbellatum, Hornungia petraea, Saxifraga tridactylites, Thlaspi perfoliatum and Veronica praecox –‐ occurring in the gaps. The absolute frequency of species varied considerably from year to year, while their relative proportions remained nearly constant in the plots over the study period.

High spatial dissociation (low level of spatial coincidence) between populations was observed; this was ascribed to boleochory, known to generate monospecific patches. No trend in self‐replacement of a species was found. This means that occupying a place in one year does not necessarily mean the same place will be occupied in following years. The probability of a species replacing another was found to be low. The space could be inhabited by any species or remain unoccupied. We suggest that the distribution patterns of species are controlled by dispersal and preference for microhabitats, at least at the scale of 20 cm × 20 cm. It was shown by a permutation method based on cumulative frequencies, that at smaller scales the habitat differentiation vanishes. We suggest that, up to a typical dispersal range of the winter annuals, the Carousel model can be applied due to the lack of coincidence (and presumably also interactions) of individuals. Nevertheless, time may eliminate the habitat differentiation at any scale. A design of an improved data‐sampling and a handling procedure was developed.
Individual‐centered analysis of mapped point patterns representing multi‐species assemblages
Authors: Podani János , Czárán Tamás
Published: May 2006

Abstract. On the basis of Ripley's combined count‐distance method, Juhász‐Nagy's information theoretical functions and the proposition of Williams et al. for the study of small‐scale community pattern, a new procedure is suggested for elucidating multi‐species point patterns based on digitized field data. The method utilizes nested circular plots with increasing radii drawn around each individual and determines changes in floristic composition along this space series. The information provided by detecting the species composition around the sample plant is calculated, and its observed mean for all individuals is compared, for each radius, to the expectation under the null model, i.e. for complete spatial randomness of all points. The departure from randomness is illustrated by conventional profile diagrams and is tested for significance based on confidence envelopes simulated by Monte Carlo methods. One advantage of the individual‐centered sampling strategy is that the role of each species in influencing its own neighbourhood can be analyzed separately, providing information for the assessment of guild structure and assembly rules in communities. The performance of the method is evaluated using artificial and simulated point patterns.
Herodotus and an Egyptian mirage: the genealogies of the Theban priests
Authors: Moyer Ian S.
Published: May 2006

This article re-evaluates the significance attributed to Hecataeus' encounter with the Theban priests described by Herodotus (2.143) by setting it against the evidence of Late Period Egyptian representations of the past. In the first part a critique is offered of various approaches Classicists have taken to this episode and its impact on Greek historiography. Classicists have generally imagined this as an encounter in which the young, dynamic and creative Greeks construct an image of the static, ossified and incredibly old culture of the Egyptians, a move which reveals deeper assumptions in the scholarly discourse on Greeks and ‘other’ cultures in the Mediterranean world. But the civilization that Herodotus confronted in his long excursus on Egypt was not an abstract, eternal Egypt. Rather, it was the Egypt of his own day, at a specific historical moment – a culture with a particular understanding of its own long history. The second part presents evidence of lengthy Late Period priestly genealogies, and more general archaizing tendencies. Remarkable examples survive of the sort of visual genealogy which would have impressed upon the travelling Greek historians the long continuum of the Egyptian past. These include statues with genealogical inscriptions and relief sculptures representing generations of priests succeeding to their fathers' office. These priestly evocations of a present firmly anchored in the Egyptian past are part of a wider pattern of cultivating links with the historical past in the Late Period of Egyptian history. Thus, it is not simply the marvel of a massive expanse of time which Herodotus encountered in Egypt, but a mediated cultural awareness of that time. The third part of the essay argues that Herodotus used this long human past presented by the Egyptian priests in order to criticize genealogical and mythical representations of the past and develop the notion of an historical past. On the basis of this example, the article concludes by urging a reconsideration of the scholarly paradigm for imagining the encounter between Greeks and ‘others’ in ethnographic discourse in order to recognize the agency of the Egyptian priests, and other non-Greek ‘informants’.
‘Eumelos’: a Corinthian epic cycle?
Authors: West M.L.
Published: May 2006

The author surveys the evidence for the three antiquarian epics commonly ascribed to Eumelos: theTitanomachy, KorinthiakaandEuropia. He elucidates and restores details, and endeavours to grasp their poets' objectives. He argues that they were products of the Corinthian-Sikyonian sphere, and to a degree mutually complementary; that they were composed between the late seventh and the late sixth century, considerably after the supposed lifetime of Eumelos; and that they were perhaps attributed to him for lack of other claimants, he being famous as the Corinthian poet of the Messenians' treasured Prosodion.
Wild and Cultivated Plants: a Note on the Peasant Economy of Roman Italy
Authors: Frayn Joan M.
Published: May 2006

It has long been surmised that the Italian peasant in the Roman period could not have subsisted entirely upon his heredium, even when it was considerably more than two iugera. Juvenal was speaking for many of those before him, as well as for his own contemporaries, when he said of the traditional allocation:

‘Nunc modus hic agri nostro non sufficit horto’.

(Satires XIV, 172)

Yet amid much speculation upon this point one aspect of the countryman's livelihood seems to have attracted little attention. In addition to any other resources he had the use of the wild plants of the extensive forests, the mountains, pastures and fallow fields. In general, food obtained from wild plants did not in Roman times, any more than it does in Italy today, take the place of grain, the staple article of diet. This may account for Pliny's statement in the Natural History XXI, 50 (86) where, after mentioning the large number of ‘herbae sponte nascentes’ used for food by other peoples, he writes: ‘In Italia paucissimas novimus, fraga, tamnum (wild vine), ruscum (butcher's broom), batim marinam (samphire), batim hortensiam, quam aliqui asparagum Gallicum vocant. …’ Such a remark seems astonishing in view of the numerous other examples Pliny himself has previously given, but its interpretation depends on the meaning to be assigned to the word cibus, as well as on the limiting effect of the phrase ‘herbae sponte nascentes’, which may not include all the plants we call ‘wild’. It is clear from the conclusion of the paragraph cited above, where ‘oblectamenta’ are compared with ‘cibos’, that cibi is being used here to mean ‘staple foods’.
Construction of Truth Predicates: Approximation Versus Revision
Authors: Barba Juan
Published: May 2006

§1. Introduction. The problem raised by the liar paradox has long been an intriguing challenge for all those interested in the concept of truth. Many “solutions” have been proposed to solve or avoid the paradox, either prescribing some linguistical restriction, or giving up the classical true-false bivalence or assuming some kind of contextual dependence of truth, among other possibilities. We shall not discuss these different approaches to the subject in this paper, but we shall concentrate on a kind of formal construction which was originated by Kripke's paper “Outline of a theory of truth” [11] and which, in different forms, reappears in later papers by various authors.

The main idea can be presented as follows: assume a first order language ℒ containing, among other unspecified symbols, a predicate symbolTintended to represent the truth predicate for ℒ. Assume, also, a fixed modelM= 〈D, I〉 (thebase model)whereDcontains all sentences of ℒ andIinterprets all non-logical symbols of ℒ exceptTin the usual way. In general,Dmight contain many objects other than sentences of ℒ but as that would raise the problem of the meaning of sentences in whichTis applied to one of these objects, we shall assume that this is not the case.
Step by Recursive Step: Church's Analysis of Effective Calculability
Authors: Sieg Wilfried
Published: May 2006

Alonzo Church's mathematical work on computability and undecidability is well-known indeed, and we seem to have an excellent understanding of the context in which it arose. The approach Church took to the underlying conceptual issues, by contrast, is less well understood. Why, for example, was “Church's Thesis” put forward publicly only in April 1935, when it had been formulated already in February/March 1934? Why did Church choose to formulate it then in terms of Gödel's general recursiveness, not his own λ-definability as he had done in 1934? A number of letters were exchanged between Church and Paul Bernays during the period from December 1934 to August 1937; they throw light on critical developments in Princeton during that period and reveal novel aspects of Church's distinctive contribution to the analysis of the informal notion ofeffective calculability. In particular, they allow me to give informed, though still tentative answers to the questions I raised; the character of my answers is reflected by an alternative title for this paper,Why Church needed Gödel's recursiveness for his Thesis. In Section 5, I contrast Church's analysis with that of Alan Turing and explore, in the very last section, an analogy with Dedekind's investigation of continuity.
The Complexity of Propositional
Proofs
Authors: Urquhart Alasdair
Published: May 2006

§1. Introduction.
The classical propositional calculus has an
undeserved reputation among logicians as being
essentially trivial. I hope to convince the reader
that it presents some of the most challenging and
intriguing problems in modern logic.

Although the problem of the complexity of
propositional proofs is very natural, it has been
investigated systematically only since the late
1960s. Interest in the problem arose from two
fields connected with computers, automated theorem
proving and computational complexity theory. The
earliest paper in the subject is a ground-breaking
article by Tseitin [62], the published version of
a talk given in 1966 at a Leningrad seminar. In
the three decades since that talk, substantial
progress has been made in determining the relative
complexity of proof systems, and in proving strong
lower bounds for some restricted proof systems.
However, major problems remain to challenge
researchers.

The present paper provides a survey of the
field, and of some of the techniques that have
proved successful in deriving lower bounds on the
complexity of proofs. A major area only touched
upon here is the proof theory of bounded
arithmetic and its relation to the complexity of
propositional proofs. The reader is referred to
the book by Buss [10] for background in bounded
arithmetic. The forthcoming book by Krajíček [40]
also gives a good introduction to bounded
arithmetic, as well as covering most of the basic
results in complexity of propositional
proofs.
Frege's Theorem and the Peano Postulates
Authors: Boolos George
Published: May 2006

Two thoughts about the concept of number are incompatible: that any zero or more things have a (cardinal) number, and that any zero or more things have a number (if and) only if they are the members of some one set. It is Russell's paradox that shows the thoughts incompatible: the sets that are not members of themselves cannot be the members of any one set. The thought that any (zero or more) things have a number is Frege's; the thought that things have a number only if they are the members of a set may be Cantor's and is in any case a commonplace of the usual contemporary presentations of the set theory that originated with Cantor and has become ZFC.

In recent years a number of authors have examined Frege's accounts of arithmetic with a view to extracting an interesting subtheory from Frege's formal system, whose inconsistency, as is well known, was demonstrated by Russell. These accounts are contained in Frege's formal treatise Grundgesetze der Arithmetik and his earlier exoteric book Die Grundlagen der Arithmetik. We may describe the two central results of the recent re-evaluation of his work in the following way: Let Frege arithmetic be the result of adjoining to full axiomatic second-order logic a suitable formalization of the statement that the Fs and the Gs have the same number if and only if the F sand the Gs are equinumerous.
Definability in the Recursively Enumerable Degrees
Authors: Nies André , Shore Richard A. , Slaman Theodore A.
Published: May 2006

§1. Introduction. Natural sets that can be enumerated by a computable function (the recursively enumerable or r.e. sets) always seem to be either actually computable (recursive) or of the same complexity (with respect to Turing computability) as the Halting Problem, the complete r.e. set K. The obvious question, first posed in Post [1944] and since then called Post's Problem is then just whether there are r.e. sets which are neither computable nor complete, i.e., neither recursive nor of the same Turing degree as K?

Let be the r.e. degrees, i.e., the r.e. sets modulo the equivalence relation of equicomputable with the partial order induced by Turing computability. This structure is a partial order (indeed, an uppersemilattice or usl)with least element 0, the degree (equivalence class) of the computable sets, and greatest element 1 or 0′, the degree of K. Post's problem then asks if there are any other elements of .

The (positive) solution of Post's problem by Friedberg [1957] and Muchnik [1956] was followed by various algebraic or order theoretic results that were interpreted as saying that the structure was in some way well behaved:

Theorem 1.1 (Embedding theorem; Muchnik [1958], Sacks [1963]). Every countable partial ordering or even uppersemilattice can be embedded into .

Theorem 1.2 (Sacks Splitting Theorem [1963b]). For every nonrecursive r.e. degreeathere are r.e. degreesb, c < asuch thatb ∨ c = a.

Theorem 1.3 (Sacks Density Theorem [1964]). For every pair of nonrecursive r.e. degreesa < bthere is an r.e. degreecsuch thata < c < b.
The Franks in the Peloponnese
Authors: Tozer H. F.
Published: May 2006

The period which succeeded the fourth crusade is perhaps the most intricate period in the history of Greece. The capture of Constantinople which then took place, and the partition of the Eastern Empire between the invading Powers, displaced for a time and permanently enfeebled the Byzantine government, and the various western principalities which arose on its ruins had no real bond of unity, nor strength to impart vitality to them severally. Hence their subsequent history is composed of a succession of struggles and changes, accompanied by shiftings of boundaries which are almost bewildering. According to the treaty of partition which was ratified beforehand by the attacking parties, the empire was to be divided into three parts, one of which should be assigned to the Latin emperor who was to rule at Constantinople, another to Venice, and a third to the remaining powers who took part in the expedition: but in practice this was never carried out, and large portions of the conquered territory fell to the share of adventurers. The position of Emperor of Romania was conferred on Baldwin, Count of Flanders; most of the islands, as might be expected, passed into the hands of Venice; Boniface, Marquis of Monferrat, who had held the office of commander-in-chief of the Crusaders, was established as King of Salonica, with the province of Macedonia; other chieftains occupied various parts of Greece Proper as feudatories of the empire; and Athens itself became the seat of an important principality under a Burgundian nobleman, Otho de la Roche, who received the title of Μέγας Κύριος, or Grand-sire, which was subsequently exchanged for that of Duke. It is in imitation of this title that Dante, who was a contemporary of this dukedom during its flourishing period, speaks of Theseus as ‘Duca d'Atene,’ while he calls Pisistratus ‘Sire’ of the same city. Hence, also Shakespeare, following the Italian writers, introduces Theseus as Duke of Athens, in Midsummer Night's Dream It is noticeable also that though the majority of these new occupants were not French either by descent or by political allegiance, yet the French language was so generally spoken by them that the name Frank, which I have introduced into the heading of this paper, came to be used at that time, as it is at the present day, in those countries as a common title for the inhabitants of Western Europe.
Monuments Relating to the Odyssey
Authors: Harrison Jane E.
Published: May 2006

The object of this paper is to bring before the notice of the Society two unpublished vases relating to the escape of Odysseus and his comrades from the cave of Polyphemus. I shall endeavour to show:

1st. The place that these two vases take in the history of vase painting, and certain special points of interest that attach to each of them.

2nd. The relation of the designs on each of these vases to what I must call the ‘typography’ of the myth they represent.

The two questions can in fact, as it is now well understood, scarcely be considered apart. To analyse a vase satisfactorily it is as necessary to consider its ‘typography,’ i.e. the exact form in which the legend is embodied, and the relation of that form to other forms preceding and following, as it is to discuss the actual technique of the design.