bluuebunny/crossref_metadata_2025 huggingface dataset:
Plant functional types as predictors of transient responses of arctic vegetation to global change
Authors: Chapin F. Stuart , Bret‐Harte M. Syndonia , Hobbie Sarah E. , Zhong Hailin
Published: May 2006

Abstract. The plant functional types (growth forms) traditionally recognized by arctic ecologists provide a useful framework for predicting vegetation responses to, and effects on, ecosystem processes. These functional types are similar to those objectively defined by cluster analysis based on traits expected to influence ecosystem processes. Principal components analysis showed that two major suites of traits (related to growth rate and woodiness) explain the grouping of species into functional types. These plant functional types are useful because they (1) influence many ecological processes (e.g. productivity, transpiration, and nutrient cycling) in similar ways, (2) predict both responses to and effects on environment, including disturbance regime, and (3) show no strong relationship with traits determining migratory ability (so that no functional type will be eliminated by climatic change simply because it cannot migrate). Circumstantial evidence for the ecological importance of these functional types comes from the distribution of types along environmental gradients and the known ecological effects of traits (e.g., effects of litter quality on decomposition and of plant height on winter albedo) that characterize each functional type. The paleorecord provides independent evidence that some of these functional types have responded predictably to past climatic changes. Field experiments also show that plant functional types respond predictably to changes in soil resources (water and nutrients) but less predictably to temperature. We suggest that evidence for the validity of arctic plant functional types is strong enough to warrant their use in regional models seeking to predict the transient response of arctic ecosystems to global change.
Functional types of trees in temperate and boreal forests: classification and testing
Authors: Bugmann Harald
Published: May 2006

Abstract. Impacts of climatic change on ecosystems over large areas cannot usually be assessed on a species basis. The definition of plant functional types (PFTs) may make this task feasible, but its potential and limitations need to be evaluated carefully by quantitative tests. This paper presents such a method for testing a hypothesis about PFTs.

A deductive approach is used to elaborate a functional classification of temperate and boreal trees based on their response to climatic change and their feedbacks to the climate system using four attributes: (1) evergreen/deciduous; (2) cold tolerance; (3) drought tolerance; (4) shade tolerance. These attributes are combined to yield six PFTs.

The classification is tested by implementing the six PFTs in the forest gap model ForClim, and the behaviour of the PFT‐based model is compared to species‐based simulation results in Europe and in eastern North America.

The six PFTs provide an accurate description of both the physiognomy and the composition of European forests in both transient and equilibrium phases. Under the IPCC ‘Business‐ As‐Usual’ scenario of climatic change for southern and central Europe, some differences in the forest composition are simulated, pointing at the need of testing PFT schemes not only under current, but also under hypothesized future climates.

For eastern North America it was necessary to estimate the parameters characterizing the six PFTs anew. When this was done, the PFT‐based simulation yielded results paralleling those of the species‐based model closely.

The potential and limitations of the present classification are discussed. It is concluded that deficiencies in current gap models, but probably also different evolutionary pathways in North America as compared to Europe, are responsible for the different parameterizations on the two continents.
Assessing the response of plant functional types to climatic change in tropical forests
Authors: Condit Richard , Hubbell Stephen P. , Foster Robin B.
Published: May 2006

Abstract. We propose and test a classification of plant functional types for tropical trees based on demography, growth form, phenology, and moisture requirements, using data from a 50‐ha forest dynamics plot in Panama. Correlations among demographic variables for individual species ‐ mortality, growth, and the tendency to colonize light gaps ‐ were strong, and a single principal component (PC) accounted for a large fraction of the demographic variability. Most species ‐ shade‐tolerants ‐ were clustered at the low end of the PC axis (low growth, low mortality), while the rest were continuously distributed over a wide range. Three demographic guilds could be defined from scores on this axis: we call these pioneer, building phase, and shade‐tolerant trees, following earlier terminology.

Leaf lifetime correlated negatively with the demographic axis, and there was a weak relationship between demography and moisture‐preference: no species with high demographic scores also had high moisture requirements. There was no significant relationship between deciduousness and the demographic axis, but deciduousness was negatively correlated with leaf lifetime and moisture index. Altogether, 11 different combinations of demographic variables, deciduousness, moisture needs, and growth form (canopy vs. understory species) were identified.

We evaluated how these functional types changed in abundance between 1982 and 1995. Because of a recent run of dry years and long dry seasons, we predicted that deciduous species, canopy species, pioneers, and drought‐tolerant species would be increasing at the expense of their counterparts. Only one aspect of this prediction was borne out: moisture‐ demanding species declined sharply in abundance relative to drought‐tolerant species. Neither deciduousness nor growth form was associated with population change, and pioneer species declined in abundance more often than shade‐tolerants. The overall structure of the forest ‐ the density of deciduous, pioneer, and understory species ‐ did not change much, but the decline of the moisture‐demanding guild indicates that a change in composition is preceding a structural change.
Effects of forest soil desiccation on the growth of Eucalyptus regnans F. Muell. seedlings
Authors: Ashton D.H. , Kelliher K.J.
Published: May 2006

Abstract. The growth rate of Eucalyptus regnans seedlings in their first year can be much increased if the soil is first dried and then rewetted. The ratio of growth on predried soil to growth on undried soil (the Growth Ratio or GR) reaches a maximum at air‐dryness (pF 6.0–6.4). In E. regnans forest soil, GR is greatest in humus‐rich topsoil and declines with depth. The effect of air‐drying persists for several months after rewetting when soil is stored under glasshouse conditions. It is largely unaffected by repeated drying and wetting, by the rate of drying or by the season of collection. The mixing of dried and undried soil or the placement of a layer of dried soil above undried soil produces an enhancement of growth proportional to the amount of dried soil added. Firing of a litter layer above soil at wilting point increases subsequent seedling growth to that in air‐dried soil. The addition of ash from a litter fire to undried soil produces an increase in growth approximately equal to that caused by air‐drying

The drying effect is most pronounced in soils from mature E. regnans forest and nearby brackenland and is less in dense younger forest, frost‐hollow grasslands and old grassy gaps in the mature forest. The effect is restored by the inoculation of E. regnans mycorrhizal roots from both dried and undried soil. The effect varies along an gradient from 500 to 1500 m a.s.l. and is a maximum in the wet E. regnans climatic zone and a minimum in zones or local aspects where forests are normally subject to frequent drying. The stimulatory effect on seedling growth in soils of the E. regnans zone may have an effect on the outcome of competition during regeneration in large gaps. Part of the growth responses previously ascribed to the ‘ash‐bed’ effect may be due to the desiccation effect in these soils.
Permanent plots as tools for plant community ecology
Authors: Herben Tomáš
Published: May 2006

Abstract. Permanent plots provide information on spatio‐temporal patterns in plant communities, which could be analyzed to yield correlated changes in pairs of species and information on species replacements in space. The potential use of permanent plots to study underlying processes of interspecific interactions (namely competition) is discussed. Two examples (one simulated, using a cellular automaton model, and one from a removal experiment in grasslands) are used to demonstrate that this use is not straightforward, since (1) radically different underlying mechanisms (symmetric founder control with little competitive replacement vs. asymmetric dominance control strongly structured by competition) may produce very similar spatio‐temporal patterns; and (2) topology of species replacements in space may be very different from the competitive hierarchy as determined by the removal experiment.

Permanent plot data can be used to study interspecific interactions in the following ways: (1) if there is additional information to decide which of the potential underlying models is acceptable, permanent plot data may enable further articulation of the model, such as estimation of the model parameters; this approach is similar to that used in many other plant ecology fields (fine scale patterns, chronosequences, plant size distribution and dynamics); (2) data from permanent plots constrain the number of feasible underlying models; (3) permanent plot data provide verification of predictions of experimental studies; in this respect, they are much superior to non‐repeated studies of pattern.
Species coexistence in grasslands: questionnaire on techniques and spatio‐temporal scales
Authors: Herben Tomáä , Krahulec Frantiäek
Published: May 2006

Abstract. All participants at the conference ‘Species coexistence and diversity maintenance in temperate grassland ecosystems’, in Bedřichov, Czech Republic, were asked to fill in a questionnaire about the spatio‐temporal parameters, study type, and species performance measures used in studies presented at the conference. 57 out of 90 participants responded. Most of the reported studies were field experiments. The major differences in approach and spatial parameters divided the studies into singular or repeated recordings. Repeated recording studies tend to use more precise measures of species quantity for species (biomass, number of individuals) than one‐time recording studies. Repeated recording studies cover whole range of plot sizes, whereas singular observation studies are confined to ranges from ca. 10−2 to 102 m. The plot size is not related to the extent in time duration, with several fine‐ scale studies of rather long duration. Most common experimental manipulations (biomass removal, nutrient addition) indicate that the species coexistence is addressed in a rather indirect way at the community level.
Regeneration of a Gentiana pneumonanthe population in an oligotrophic wet meadow
Authors: Křenová Zdeňka , Lepš Jan
Published: May 2006

Abstract. The aim of this study was to evaluate the critical phases of the life cycle of Gentiana pneumonanthe, the marsh gentian, a threatened species of the Bohemian flora. The effect of various conditions on germination and seedling establishment and the possible effect of competition on the performance of the species were tested. Seeds were sown in plots which were subjected to four treatments in a randomized complete blocks experiment: unmanaged meadow, mown meadow, burned meadow, and meadow with cut sod. The significantly highest recruitment was found in plots with cut sod, the lowest in the unmanaged control plots. Seedling survival also differed among the treatments. In the following year surviving individuals were only found in plots with cut sod. The influence of neighbouring vegetation on target gentian individuals was evaluated by removing the surrounding vegetation and comparing the performance of these individuals with controls. The initial height of each individual was measured and used as a covariable. No significant effect of neighbouring vegetation on performance was detected. Thus, the establishment phase appears to be critical for population persistence and is also more influenced by the management regime than other stages of the life cycle.
Influence of overstory composition on understory colonization by native species in plantations on a degraded tropical site
Authors: Parrotta John A.
Published: May 2006

Abstract. Patterns of understory colonization by native and naturalized trees and shrubs were evaluated in 4.5‐year‐old plantations of three exotic tree species, Casuarina equisetifolia, Eucalyptus robusta, and Leucaena leucocephala, on a degraded coastal grassland site with reference to overstory composition and understory environmental conditions. 19 secondary forest species were established in the plantation understories (with a total area of 0.52 ha), while no natural regeneration occurred in unplanted, though protected, control areas. The majority of these species (90 %) and the total seedling population (97 %) were zoochorous, indicating the importance of frugivorous bats and particularly birds as facilitators of secondary forest species colonization. Understory species richness and seedling densities were affected significantly by overstory composition, the most abundant regeneration occurring beneath Leucaena and least under Casuarina. Understory colonization rates within mixed‐species stands were intermediate between those of single‐species stands of the trees comprising their overstories. Significant negative correlations were found between understory species richness and seedling density, and forest floor depth and dry mass, especially for small‐seeded ornithochorous species. Higher colonization rates near the peripheries of plantation plots relative to plot interiors were due in part to roosting site preferences by frugivores, particularly bats.

The study results indicate that overstory species selection can exert a significant influence on subsequent patterns of colonization by secondary forest species and is an important consideration in the design of plantations for ‘catalyzing’ succession on deforested, degraded sites.
Soil nutrient fluxes and vegetation changes on molehills
Authors: Canals Rosa‐Maria , Sebastià Maria‐Teresa
Published: May 2006

Abstract. The hypothesis that mole burrowing activity alters soil nutrient fluxes and that, as a response to the new conditions, a specialized guild of species develops on the molehills, was tested in an area located in the southwestern Spanish Pyrenees, on a spectrum of montane grassland communities that varies from xeric to temporally waterlogged.

Evidence for an association between disturbance and nutrient availability was reported for nitrogen. Mole‐disturbed soils had elevated amounts of inorganic nitrogen compared to soils in surrounding pastures. At the first stages of mound revegetation, changes in nitrate flushes and in species competitive relationships following disturbance appeared to facilitate the establishment of ruderal and non‐mycorrhizal species. The diversity of the whole grassland was enhanced by the existence of these sets of species, abundant on mounds and rarer in the pasture. However, the difference was mainly quantitative, as exclusive colonizers of molehills were not found.
Invasion of temperate grassland by a subtropical annual grass across an experimental matrix of water stress and disturbance
Authors: White Todd A. , Campbell Bruce D. , Kemp Peter D.
Published: May 2006

Abstract. An experimental matrix of water stress and disturbance was superimposed on a Lolium perenne‐Trifolium repens grassland using a crossed‐gradient design, and the annual subtropical grass Digitaria sanguinalis was introduced into the pasture as seeds and transplanted seedlings. Digitaria plants achieved maximum biomass at high water availability and high disturbance. Digitaria plants grown from transplanted seedlings attained greater biomass further from the conditions of high water availability and high disturbance, compared with those that had grown from seed. The biomass of the temperate species was maximized with high water availability and low to intermediate disturbance conditions. The reproductive effort of Digitaria was maximized under intermediate to high water availability and intermediate to low disturbance. Combinations of water stress and disturbance that gave rise to maximum growth of the temperate and subtropical species were consistent with those predicted by C‐S‐R theory. Results suggest that processes in the regenerative phase of the plant life cycle were constraining the success of Digitaria in New Zealand grassland. Addition of seed to the soil seed bank would probably be maximized in patches of grassland with high disturbance and water availability; these patches will subsequently act as foci for future invasions by Digitaria.
Effects of trampling and vegetation removal on species diversity and micro‐environment under different shade conditions
Authors: Kobayashi T. , Hori Y. , Nomoto N.
Published: May 2006

Abstract. The effects of disturbance by trampling and vegetation removal on herbaceous communities and their micro‐environments were examined at two sites with different levels of shade. The dominant species of the original vegetation were the perennial herb Artemisia princeps at the sunny site and the dwarf‐bamboo Pleioblastus chino at the shady site. With no disturbance and marked dominance of these species, diversity was low. After vegetation removal there was a rapid recovery, leading to a more diverse vegetation with many more species, each with a lower dominance. Continuous trampling induced a short vegetation while the light intensity under the foliage was increased. At the sunny site, species richness was depressed by trampling because the soil water potential decreased markedly during summer and only the stress‐tolerant annual Digitaria adscendens grew vigorously. Thus, the lowest species diversity was observed in the heavily trampled vegetation in late summer. At the shady site, soil water availability was not affected by trampling. This allowed the survival of many species and prevented a strong decline in diversity.

The results suggest that the pattern of change in diversity in communities subjected to various disturbances, was always determined by the original environments.
Small‐scale plant dynamics in temperate Themeda triandra grasslands of southeastern Australia
Authors: Morgan John W.
Published: May 2006

Abstract. Vegetation subjected to two long‐term burning regimes (annual or biennial burning) was studied in permanent plots, at two spatial scales: 0.01 m2 and 1 m2, to determine the small‐scale dynamics of plants in temperate Themeda triandra grasslands of southeastern Australia. Species turnover rates were estimated by presence/absence data while species mobility was assessed using cumulative frequency data.

While mean species richness did not fluctuate greatly between years, the vegetation was internally dynamic rather than static. Cumulative species richness increased by 50% at both spatial scales and sites over the 4‐yr study period. However, few species became cumulatively frequent (i.e. occurred in 80% of plots in the first and/or subsequent years), suggesting that cumulative species richness increases were due to small‐ or local‐scale movements of plants, rather than ‘shifting clouds’ of species moving across the entire site. The vegetation's dynamics did not differ greatly at sites subject to different (frequent) fire intervals.

Species turnover and mobility were individualistic, but the dynamics of many species was greater at the smaller spatial scale: 31–48% of the species present at both spatial scales at the two sites had higher turnover rates at the 0.01 m2 scale. Similarly, some ‘non‐mobile’ species at the 1‐m2 scale (i.e. ‘constant’ or ‘local’ mobility types), were more mobile at the smaller‐scale. Turnover rate and mobility type were strongly associated with life form in some cases, particularly at the annually‐burnt site. In general, therophytes (and to a lesser degree, geophytes) were positively associated with high turnover and mobility in most years, while hemicryptophytes were negatively associated with high turnover in many instances. Hemicryptophytes included many species with a range of mobility types and hence, few significant associations between mobility and this life form were found.

The previously unrecognized internal dynamics of this community under ‘stable’ management regimes contributes to species coexistence by allowing plants with different dynamics properties to persist in a spatially and temporally unpredictable manner. Frequent burning is presumably the important component driving much of the non‐directional, small‐scale dynamics because it regularly destroys individual plants and aerial plant parts and creates opportunities for seedling regeneration, whilst permitting the vegetative persistence and spread of established plants in non‐light‐limited microsites.
The role of water level and salinity in the regulation of Juncus gerardi populations in former ricefields in southern France
Authors: Charpentier A. , Mesléard F. , Grillas P.
Published: May 2006

Abstract. In the Rhône delta (southern France) Juncus gerardi is a dominant, strongly aggregating species in artificially flooded former rice fields. In order to explain this pattern, the effects of water depth, salinity and their interaction were measured on (1) seed germination and seedling development and (2) vegetative growth of J. gerardi in a controlled‐environment experiment.

The germination pattern of J. gerardi was affected by salinity. Low salinity (2 g/l NaCl) delayed germination while moderate salinity (12 g/l NaCl) reduced germination rate. In contrast, the germination of J. gerardi was not affected in the range of water depths tested (i.e. 0–10cm). Salinity negatively affected the development of below‐ground parts, shoots and inflorescences. This negative effect of salinity on the vegetative growth of J. gerardi was amplified when combined with flooding. Flooding with fresh water (0–20 cm depth) did not limit biomass production during the experiment. However, a decrease in the ratio of below‐ground/above‐ground dry weight at deeper water depths suggests a limitation of the vegetative propagation of J. gerardi under prolonged flooding conditions. This hypothesis is supported by the negative correlation between the cover of J. gerardi and water depth found in an abandoned rice field. The limitation on seedling recruitment imposed by salinity and the depression of vegetative growth of J. gerardi due to a combination of salinity and water depth could explain the aggregate distribution of J. gerardi in former rice fields.
Comparative ecology of seedling recruitment in an oligotrophic wet meadow
Authors: Kotorová I. , Lepš J.
Published: May 2006

Abstract. For the regeneration niche to contribute to the maintenance of species diversity interspecific differences in sensitivity of seedling recruitment to environmental conditions is assumed. We experimentally tested differences between meadow species for the response of seed germination to chilling, and sensitivity of seedling recruitment to microscale heterogeneity. We also compared the dynamics of seedling recruitment in gaps. Seed germination was tested in standard laboratory germination tests, comparing control seeds with seeds chilled at +4 °C, and at –14°C for one month. Species responses varied from significant increases in germinability after chilling (e.g. Cirsium palustre, Betonica officinalis, Angelica sylvestris) to significant decreases (e.g. Hieracium umbellatum, Succisa pratensis, Selinum carvifolia). In some species, chilling at + 4 °C has a similar effect to chilling at –14 °C, in others the effect of chilling at + 4°C was intermediate, and in some, there was no effect of chilling at + 4°C, but an effect of chilling at –14°C. Different chilling temperatures also affect timing and speed of seed germination under greenhouse conditions.

The dynamics of seed germination under field conditions was studied by sowing seeds into artificially created gaps and following their germination, both where the seedlings were removed after emergence and where they were not removed. Species differ in their germination dynamics: they all start late April, but then differentiate from an abrupt maximum and early finish of germination (in the second half of May), to prolonged germination without a marked maximum. Seedling removal increased the total number of germinated seeds, with a marked density dependence at this stage. Seeds were also sown into plots with treatments (1) gaps, sod stripped, above‐ground vegetation removed; (2) mown, moss layer removed; (3) mown; (4) untouched control. Seedling emergence was monitored for 3 yr. Seedling recruitment decreased from treatments (1) to (4), but sensitivity differed between species. With increasing seed weight, the difference between gaps and other treatments decreased. The results show that there are considerable differences in seedling recruitment sensitivity between species.
Plant competition in mediterranean‐type vegetation
Authors: Vilà M. , Sardans J.
Published: May 2006

Abstract. Plant competition in communities subjected to stress and disturbance is an important ecological issue. We review studies on plant competition in mediterranean‐type plant communities in order to discuss its effect on plant‐ and plant community structure, to determine the type of competition that takes place and the interaction between competition and effects of fire. Competition can intermittently effect all stages of the plant life cycle. Water and light seem to be the most frequent resources for which plants compete. Competition for nutrients also occurs and seems to be more intense when nutrient availability is high. Plant interference through allelopathy is also important. Competition may also occur after fire but it is not clear if it is less intense than in mature stands. As most of the studies have been carried out in California. More field experiments that combine the effect of competition and fire along with environmental gradients differing in water and nutrient levels should be conducted in other mediterranean regions in order to draw generalizations on the mechanisms of competition in plant communities.
The ‘innovation period’ of vegetation classification in the former USSR; a complement to the paper by L. Mucina
Authors: Solomeshch A.I. , Mirkin B.M.
Published: May 2006

Abstract. Some remarks are made on the innovation of ideas concerning vegetation classification in the former USSR as a complement to the paper by Mucina (1997).
Rain forest composition and patterns of secondary succession in the Vava'u Island Group, Tonga
Authors: Franklin Janet , Drake Donald R. , Bolick Leslie A. , Smith Darren S. , Motley Timothy J.
Published: May 2006

Abstract. The Vava'u island group, Tonga, comprises ca. 60 limestone islands on a single submarine platform overlain with rich soils derived from tephra deposits from nearby volcanic islands. The island group has moderate topographic relief (215 m) and is characterized by plateaus and steep cliffs. Humans settled in Tonga ca. 3000 yr ago and have exploited the flatter terrain for agriculture since that time. We conducted the first survey of forest composition in Vava'u, sampling remnant patches of late‐successional forest as well as stands in various stages of secondary succession following agricultural abandonment. Plant species composition did not vary greatly with elevation over this short gradient, in contrast with patterns found on‘Eua, a higher island in Tonga. The most significant environmental gradient affecting species composition was coastal or maritime influence. However, the greatest variation in species composition and structure appeared to be related to species turnover during secondary succession, and we hypothesize a sequence of species replacements. Secondary forest begins to resemble late‐successional forest in 30–50 yr in terms of structure and native species richness and therefore is of significant conservation value.
Explaining the distribution of Pinus spp. in a Canadian boreal insular landscape
Authors: Bergeron Yves , Leduc Alain , Li Ting‐Xian
Published: May 2006

Abstract. To evaluate the respective contributions of habitat, fire regime and colonization‐extinction processes to the distribution of northern Pinus species, we investigated the distribution of P. banksiana (jack pine), P. resinosa (red pine) and P. strobus (white pine) on 117 islands of Lake Duparquet in northwestern Québec. Stepwise logistic regressions indicated that the extent of xeric areas on the islands was the sole factor predicting jack pine distribution. The distribution of white pine was predicted primarily by the combined effects of distance to the shoreline and elevation, with a smaller effect of area of xeric habitat. The distribution of red pine was predicted by other populations of red pine nearby, with a slightly smaller effect of the combined effects of distance to shoreline and elevation. None of the species completely saturates all available islands nor is any restricted to specific, very exposed aspects. The results suggest that pine is more frequent on islands with characteristics that promote lightning strikes and thus higher fire occurrence. However, absence of pine in several islands may not be explained by abiotic characteristics or recent fire history. The presence of very small populations, together with low invasion potential, suggests that the observed distribution is mainly driven by the process of random extinction. A disequilibrium between present and past fire regimes may explain why northern pines have discontinuous distributions inside their range limits.
Cryptogam communities on fallen logs in the Duke Forest, North Carolina
Authors: McAlister Suzanne
Published: May 2006

Abstract. I studied cryptogam (i.e. bryophyte and lichen) communities on fallen logs in the Duke Forest, Durham and Orange Counties, North Carolina, USA, to determine the relationship of log characteristics and microsite to community composition. Species composition and abundance were estimated for 111 randomly selected fallen logs. Interior wood samples were used to identify the tree species. I determined physical and chemical characteristics for each log, and described the log microsite.

Canonical Correspondence Analysis (CCA) detected a clear gradient in cryptogam species composition which is correlated with the species of log and the presence of bark. Communities on hardwood bark, hardwood wood, and pine substrates were the most distinct. CCA also revealed that the microsite is not as closely related to species composition as are substrate pH and density. The majority of the cryptogam species encountered on the fallen logs are commonly reported from other substrates in the forest. However, within the habitat type of fallen logs, several species were apparently restricted to certain substrate types.
Neighbour influence on the tiller demography of two perennial pampa grasses
Authors: Laterra Pedro , Maceira Néstor O. , Deregibus V. Alejandro
Published: May 2006

Abstract. The aim of this study was to evaluate the possibility to use neighbour species composition to explain demographic variations in seasonal tillers in perennial grasses. Two warm‐season species of the Argentina flooded pampa, Paspalum dilatatum and Sporobolus indicus, were used as models. Tiller structure and dynamics of target plants and the identity of their nearest neighbours were analyzed within a natural grassland community for an entire annual growth cycle. Canonical Correlation Analysis of tillering behaviour of target plants and neighbour species composition showed significant relationships for summer neighbourhood data. Community components affecting tiller demography were identified, and their spatial variation was described as different gradients of neighbourhood composition (NCG). NCG varied between target species, determining different spatial variation in neighbouring canopy dynamics and tiller dynamics. The tiller structure and dynamics of P. dilatatum plants were significantly correlated with the seasonal pattern of their neighbouring canopy density (NCD). Plants placed on the NCD‐fluctuating extremes along NCG showed an unstable modular structure and short‐lived tillers, as compared to those placed in the centre of the gradient. Relative density of the neighbouring canopy showed little variation along the NCG of S. indicus plants, which presented a tiller structure more stable and uniform than P. dilatatum plants did. Identification of NCG may be a promising approach to understanding changes in tiller dynamics of target species in relation to spatial and temporal changes in community structure.
Mapping species diversity patterns in the Kansas shortgrass region by integrating remote sensing and vegetation analysis
Authors: Lauver Chris L.
Published: May 2006

Abstract. Field reconnaissance data are used in a supervised classification of a 1989 Landsat Thematic Mapper (TM) scene to create a digital database of high and low quality grasslands for northwestern Kansas. To test the classification of grassland quality, plot‐based vegetation data collected from 32 sites are analyzed for differences in species composition, and evaluated for relationships between TM data and plant diversity. Significant differences between predicted high and low quality grassland sites are identified for the following variables: cover of the dominant and common species, overall species richness, number of forbs, number of grasses, and plant diversity using Shannon's index. Linear regression analysis reveals a significant relationship (r2= 0.61) between species diversity and the prediction of grassland quality from the supervised classification. The addition of spectral data to this model did not improve the prediction of species diversity, but spectral brightness is identified as a key feature in mapping shortgrass vegetation diversity patterns with TM data.
Do spatial effects play a role in the spatial distribution of desert‐dwellingAcacia raddiana?
Authors: Wiegand Kerstin , Jeltsch Florian , Ward David
Published: May 2006

Abstract.We investigated the spatial pattern ofA. raddianain the Negev desert of Israel in order to gain insights into the factors and processes driving the dynamics of this species. Using a scale‐dependent measure, the ring statistic, we analysed both patterns observed in the field and time series of spatial tree distributions produced by a simulation model. In the field, random spacing was the predominant pattern observed. However seedlings were clumped on small scales. We ran the model under two contrasting scenarios representing hypotheses that explain the clumping of seedlings and the random distribution of trees. One hypothesis is that there is spatial heterogeneity in seed distribution, germination and seedling mortality, but that these heterogeneities are not correlated with each other in space. The second hypothesis assumes a correlation between these heterogeneities leading to areas suitable for establishment. However, the suitability of the sites is temporally variable. Furthermore, the second hypothesis assumes density‐dependent tree mortality due to competition. Both hypotheses lead to spatial distributions that are in qualitative agreement with the patterns observed in the field. Therefore, the classical view that a clumped seedling distribution and a random pattern of older trees is due to clumped regeneration and density‐dependent mortality may not hold forAcaciatrees in the Negev.
Woody species tolerance to expansion of the perennial tussock grass Ampelodesmos mauritanica after fire
Authors: Vilà M. , Lloret F.
Published: May 2006

Abstract. In Mediterranean shrublands, post‐fire accumulation of above‐ground biomass of resprouters is faster than that of seeders. This suggests that resprouters may have a competitive advantage. To test this hypothesis, we used a removal experiment to study the effect of the presence of the dominant tussock‐grass Ampelodesmos mauritanica on the resprouting shrubs Erica multiflora and Globularia alypum and on the seeders Rosmarinus officinalis and Pinus halepensis three and four years after a wildfire. Water potential of target plants was also measured to see if Ampelodesmos removal increased water availability. Ampelodesmos marginally reduced growth of all target species but did not influence survival or water potential of any target species. Our results suggest that the effect of climatically influenced water stress was stronger than the effect of Ampelodesmos neighbours. Plant‐plant interactions in this Mediterranean community are weak after fire and the magnitude of the Ampelodesmos effect does not differ between seeders and resprouters.
An Interpolation Theorem
Authors: Otto Martin
Published: May 2006

Lyndon's Interpolation Theorem asserts that for any valid implication between two purely relational sentences of first-order logic, there is an interpolant in which each relation symbol appears positively (negatively) only if it appears positively (negatively) in both the antecedent and the succedent of the given implication. We prove a similar, more general interpolation result with the additional requirement that, for some fixed tuple of unary predicates U, all formulae under consideration have all quantifiers explicitly relativised to one of the U. Under this stipulation, existential (universal) quantification over U contributes a positive (negative) occurrence of U.

It is shown how this single new interpolation theorem, obtained by a canonical and rather elementary model theoretic proof, unifies a number of related results: the classical characterisation theorems concerning extensions (substructures) with those concerning monotonicity, as well as a many-sorted interpolation theorem focusing on positive vs. negative occurrences of predicates and on existentially vs. universally quantified sorts.
Measures: Back and Forth Between Point sets and Large sets
Authors: Goldring Noa
Published: May 2006

It was questions about points on the real line that initiated the study of set theory. Points paved the way to point sets and these to ever more abstract sets. And there was more: Reflection on structural properties of point sets not only initiated the study of ordinary sets; it also supplied blueprints for defining extra-ordinary, “large” sets, transcending those provided by standard set theory. In return, the existence of such large sets turned out critical to settling open conjectures about point sets.

How to explain such action at a distance between the very large and the rather small? Rather than having an air of magic, could these results rest on deep structural similarities between the two superficially distant species of sets?

In this essay I dissect one group of such two-way results. Their linchpin is the notion of measure.

§1. Vitali's impossibility result. Our starting point is a problem in measure theory regarding the notion of “Lebesgue measure.” Before presenting the problem, I would like to review the notion of Lebesgue measure. Rather than listing its main properties, I would like to show how Lebesgue measure is born out of an attempt to generalize the notion of the length of an interval to arbitrary sets of reals. One tries to approximate arbitrary sets of reals by intervals, in the hope that the lengths of the intervals will induce a measure on these sets.
Games and Definability For FPC
Authors: McCusker Guy
Published: May 2006

A new games model of the languageFPC, a type theory with products, sums, function spaces and recursive types, is described. A definability result is proved, showing that every finite element of the model is the interpretation of some term of the language.
Completeness Before Post: Bernays, Hilbert, and the Development of Propositional Logic
Authors: Zach Richard
Published: May 2006

Some of the most important developments of symbolic logic took place in the 1920s. Foremost among them are the distinction between syntax and semantics and the formulation of questions of completeness and decidability of logical systems. David Hilbert and his students played a very important part in these developments. Their contributions can be traced to unpublished lecture notes and other manuscripts by Hilbert and Bernays dating to the period 1917–1923. The aim of this paper is to describe these results, focussing primarily on propositional logic, and to put them in their historical context. It is argued that truth-value semantics, syntactic (“Post-”) and semantic completeness, decidability, and other results were first obtained by Hilbert and Bernays in 1918, and that Bernays's role in their discovery and the subsequent development of mathematical logic is much greater than has so far been acknowledged.
Antefixes from Tarentum
Authors: Anderson J. R.
Published: May 2006

The four antefixes from Tarentum, shown in Plate XXXII., where they are reduced in size to about half the actual diameter, are only specimens selected from the not inconsiderable number of types found in recent excavations. All that I have seen are marked by great breadth and freedom of execution. Even those which seem to have been originally cast, in the rough, in the same mould have undergone such subsequent touching up and remodelling as makes them distinct works of art. Identical types sometimes occur in slightly varying sizes which implies successive moulds imitative of some established original. The faces when found are covered with a hard and rough lime-deposit, but the removal of this often reveals traces of colour laid as usual on a white priming. The Medusa, head in the plate appears to have been coloured to the life—cheeks pink, lips red, and not only the pupil, but even the iris of the eye painted. The colour of eyebrows and lashes is dark, that of the hair now a dirty brownish-yellow—like the tint of the common yellow lichen—probably modified by time or by the action of the acid used to remove the lime accretion. The modelling of the lips shows that fleshy and life-like firmness which is peculiar to the best time of Greek art. Under the chin of this, or a similar head I notice the marks of the moulder's finger, but instruments seem to have been used also. The lines of the hair, though fine in the plate, lose considerably by the absence of the part by the cheeks, where over each ear there rises a snake curved like a flattened S. The specimens which show these do not come up in features to the one figured. The colour on the snakes is blue-green. The small button above the centre of the brow is a curious feature.
Early Paintings of Asia Minor
Authors: Smith Cecil
Published: May 2006

In the history of Greek vase-painting the comparative rarity of early examples of undoubtedly Asiatic provenance is a problem that has always remained a vexed question. It is difficult to account for the fact that, whereas from the islands studding the coast of Asia Minor a rich harvest has been gathered, yet the examples hitherto recovered from the mainland itself may be counted on the fingers—at least, with the exception of a few found in the Troad. Since, therefore, anything should be valuable which adds to our information, or throws light upon the existence of an Asiatic school of black-figured vase-painting, I propose to introduce in as few words as possible the vase before us (Figs. 1, 2) as a possible product of Asiatic soil, and as a commentary upon the examples we already possess.

It is an amphora of an unusual form, rather more rounded in proportion than the customary shape, reminding us perhaps in this of the rounded outline of the so-called Oriental oinochoe; unfortunately, only about half of the many fragments into which it was broken were found in Mr. Biliotti's excavations in Rhodes, so that the painted panels on each side are sadly dilapidated; still, enough remains to show us the intention of the painter, and, what is more important, perhaps, the technical conditions under which he worked.
Two Fourth Century Children's Heads
Authors: Gardner E. A.
Published: May 2006

It is commonly supposed that the treatment of children in the finest period of Greek sculpture is a subject that can be very lightly dismissed. Children, it is said, are not represented in Greek art before Hellenistic times—not represented, that is to say, with any truth to nature or reproduction of the characteristics of childhood. Of course it is never denied that young children appear in statues or reliefs of the fifth or fourth centuries; but when they so appear, they are said to be treated carelessly, conventionally, with no regard to their proper forms or proportions, but just as men on a smaller scale. This assertion is on the whole a correct one. Of careless treatment the infant Dionysus carried by the Hermes of Praxiteles is an example; the child is regarded merely as an accessory, and the execution is in marked contrast to the extreme finish and delicacy of work which we see in the Hermes himself. Even where there is no such contrast in the execution, a conventional treatment may often be seen, as in the case of children on grave-monuments and elsewhere. Nor are one or two children in sculptural groups belonging in origin to the fourth century to be regarded as exceptions (for instance, the infant Plutus carried by the Eirene of Cephisodotus); for these only survive in later copies, and in them the child is modified to suit the requirements of a later period, when children had been studied with as much care as had been spent upon the mature figure by the sculptor of the original group.
A New Portion of the Edict of Diocletian from Megalopolis
Authors: Loring William
Published: May 2006

The inscription which follows came to light during the excavation undertaken this year, at Megalopolis, by the British School at Athens. It stood outside the house of a peasant, Βασίλєιος Πєτράκης, whose father had found it, many years previously, in a field upon the ancient site. The existence of the stone was reported first to the Ephor, Mr. Castroménos, who represented the Greek Government at our excavation. Mr. Castroménos courteously announced it to me, and both of us copied it. At that time we had no idea that it formed part of the ‘Edict of Diocletian’; this was first suggested to me by Mr. Gardner, Director of the School, on my return to Cambridge. Mr. Castroménos' copy is to appear, as I understand, in the ‘Δєλτίον.’ The text and edition which follow are from my own copy and squeeze.

The Edict of Diocletian and his colleagues, commonly spoken of either by Mommsen's title ‘De Pretiis Rerum Venalium’ or more briefly as the ‘Edict of Diocletian,’ is known to us already from a large number of fragments, Greek and Latin, found all (with one exception) in different parts of Greece or Asia Minor, and amounting together to many hundred lines. It is still however far from being complete.
The Lombards and Venetians in Euboia, 1303–1340
Authors: Bury John B.
Published: May 2006

§ 33. Disputes between Venetians and Lombards.—In 1303 a subject of dissension arose between the Republic and the Lombard barons. It was probably about this time that Beatrice da Verona, who shared the Third of her father Giberto with her mother Maria, contracted a second marriage with John de Noyers, Lord of Maisy. Thus John became on his marriage lord of one Sixth, and as the Sixth of his mother-in-law Maria would revert on her death to Beatrice, he was prospectively lord of one Third. Moreover he was practically master for the present of the Sixth in the north of the island which had belonged to Beatrice's first husband Grapozzo, and was administered by her as guardian of her son Pietro. Hence John de Noyers was in a position to make his influence felt in Euboia; and being a man of energy he asserted himself. He assumed an independent attitude towards Venice.

A demand was made by the Lombard podestà in 1303 on a Venetian citizen named Meo, who resided in Lombard territory, to pay taxes. For twenty years he had been a resident in the island and never been called on to pay them before. The requisition is very plausibly ascribed by Hopf to the suggestion of John de Noyers.