bluuebunny/crossref_metadata_2025 huggingface dataset:
Relations between acid atmospheric deposition and the surface pH of some ombrotrophic bogs in Britain
Authors: Proctor M.C.F. , Maltby E.
Published: May 2003

1  Analyses are presented of major ion concentrations in surface water samples, and exchangeable cations in peats, collected in November–December 1992 from 16 ombrotrophic bogs in England and Wales and one in Scotland, spanning most of the range from the lowest (Dartmoor, west Wales, west Highlands) to the highest (south Pennines, north Yorkshire) of the mean 1986–88 rainwater concentrations of hydrogen ions and non‐marine sulphate (NMS).

2  There was a strong positive correlation (r = +0.89) between surface water pH and mean rainwater pH, and a less close correlation (r = +0.71) between surface water pH and total hydrogen ion deposition.

3  The correlation between surface water pH and mean concentration of rainwater NMS (which may be taken as a surrogate measure of acid deposition) was r = –0.85, and that between surface water pH and total deposition of NMS was r = –0.65.

4  The intercept of the regression of surface water pH on NMS is at pH 4.40 (95% confidence limits 4.22–4.58), suggesting this as the winter pH of an ombrotrophic bog surface in the absence of acid atmospheric pollution.

5  Total sulphur content of intact surface peats from 11 sites correlated well (r = +0.90) with mean rainwater total sulphate concentration.

6  The H+ ion concentration in wet deposition, plus the net H+ input resulting from metabolism of deposited NO3– and NH4+, is insufficient to account for the difference between the inferred pH of an unpolluted bog surface and pH values (up to 0.8 pH units lower) measured in the field in polluted sites. Analogy with deposition of NMS suggests that this discrepancy is accounted for quantitatively by seeder–feeder enhancement, cloudwater deposition, and dry deposition of acidity.

7  Ombrotrophic bog surface waters are buffered by the cation‐exchange properties of the peat. They are likely to be less sensitive to moderate acid deposition than weakly bicarbonate‐buffered near‐neutral peats, soils and fresh waters.
Long‐term change in an unmanaged population of wych elm subjected to Dutch elm disease
Authors: Peterken G.F. , Mountford E.P.
Published: May 2003

1  Changes in a population of Ulmus glabra in Lady Park Wood (UK), a mixed deciduous native woodland, were studied by means of permanent transects. All individuals reaching 1.3 m height were recorded at irregular intervals from 1945 to 1993.

2  Dutch elm disease struck this population in about 1972. Most of the canopy and subcanopy stems were killed, but a few, slow‐growing, subcanopy individuals survived unscathed.

3  Subsequent seedling regeneration and growth of sprouts from rootstocks of infected trees was substantial and vigorous. Twenty‐three years after the outbreak of disease the number of elm individuals had increased by about 40%. Disease has, however, continued to afflict vigorous, exposed individuals.

4  The large‐scale distribution of elm has been unaffected, but the small‐scale pattern has changed due to the concentration of seedling regeneration in gaps.

5  The elm population appears to be differentiating into (i) a large high‐turnover subpopulation of fast‐growing, but repeatedly diseased maiden individuals and sprouts, and (ii) a small, low‐turnover subpopulation of slow‐growing individuals rooted in suboptimally dry, secluded sites.
An isotopic (15N) assessment of intraclonal regulation in C4 perennial grasses: ramet interdependence, independence or both?
Authors: Derner J.D. , Briske D.D.
Published: May 2003

1  A series of three experiments was conducted with three C4 perennial grasses, Panicum virgatum (short rhizomes forming distinct clones), Schizachyrium scoparium (caespitose) and Bouteloua gracilis (caespitose), to determine whether intraclonal regulation was characterized by interdependence, independence or a combination of both processes. Specific hypotheses tested were: (i) all ramets within individual clones are physiologically integrated; (ii) ramet hierarchies (several connected generations) within individual clones are capable of acquiring soil nitrogen equally from localized nutrient‐rich pulses; and (iii) nitrogen is retained within individual hierarchies through allocation to sequentially developed ramet generations.

2  Mean 15N atom percent excess values within labelled ramet hierarchies were 10–21‐fold greater than in immediately adjacent ramet hierarchies, and 105–137‐fold greater than in the remaining ramet hierarchies within clones for all three species. This pattern of 15N distribution demonstrates that physiological integration does not occur among all ramets within individual clones and that ramet hierarchies function as integrated physiological individuals.

3  Ramets in closer proximity to a 15N pulse in soils acquired disproportionately greater amounts of the isotope compared to more distant ramets within clones for all three species. Inequitable resource acquisition among ramet hierarchies establishes the potential for asymmetric intraclonal competition below‐ground and the development of size inequalities among hierarchies.

4  Approximately 21.7%, 3.5%, 1.7% and 2.3% of the initial 15N pool was allocated from the first ramet generation to the second and third (spring cohort), third (autumn cohort) and fourth generations, respectively. However, the magnitude of nitrogen allocation from parent to juvenile ramet generations was relatively consistent, with 17–32% of the 15N pool within parental ramets allocated to juvenile ramets. Intergenerational 15N allocation in S. scoparium clones therefore demonstrates a high degree of interdependence within individual ramet hierarchies.

5  Clones of the rhizomatous and two caespitose grasses investigated functioned as assemblages of autonomous ramet hierarchies, but ramet generations within individual hierarchies were effectively integrated. Consequently, intraclonal regulation in these temperate, perennial grasses is characterized by both ramet interdependence and independence. The occurrence of ramet independence throughout much of the life history of perennial grasses demonstrates the ecological importance of clonal fragments to genet and population maintenance and emphasizes that this may be the most relevant scale to investigate further the ecology of this important and widely distributed group of clonal plants.
Consequences of sexually dimorphic timing of emergence and flowering in Silene latifolia
Authors: Purrington Colin B. , Schmitt Johanna
Published: May 2003

1 Males and females of dioecious plant species often differ in a variety of secondary characteristics, such as size, flower number and flowering time, suggesting that dioecious species have sex‐specific selection histories. However, a potential source of these dimorphic traits is age differences between males and females. By sowing 3000 seeds of the dioecious perennial, Silene latifolia (Caryophyllaceae), on a single day, we were able to assess the contribution of sex differences in emergence time to the development of sexually dimorphic adult traits.

2 Females emerged before males in our experimental field population, but on average males flowered first. Age differences between males and females did not therefore cause the earlier flowering of males.

3 The consequence of the detected differences in emergence and phenology between males and females was explored by path analysis. Emergence time had a strong direct effect on flower production as well as an indirect effect through flowering time. The regression coefficient of flowering time on emergence time was significantly larger for male plants.

4 A phenotypic selection analysis revealed that seedlings emerging early suffered greater mortality than those emerging later. Seedlings emerging early, however, developed into plants with more flowers, indicating that there was a trade‐off between survivorship and reproductive performance. Seeds with intermediate emergence times had the highest total fitness, indicating the presence of stabilizing selection. Despite the strong mortality selection against early emergers, we detected no shift in the sex ratio compared with the sex ratio of seeds matured under low‐mortality greenhouse conditions.
Plant foraging and rhizome growth patterns of Solidago altissima in response to mowing and fertilizer application
Authors: Stoll Peter , Egli Philipp , Schmid Bernhard
Published: May 2003

1  The rhizome growth patterns of the clonal plant Solidago altissima were studied in response to mowing and fertilizer application in a field experiment. Rhizome systems of 120 clonal fragments were harvested in the spring of 1993, after 6 years of mowing (1987–92) and 2 years of fertilizer application (1991–92). The results were interpreted in the light of plant foraging theory.

2  The ages of the individual rhizomes comprising each rhizome system were determined and their length, number of offspring rhizomes, branching angles and the height of emerging shoots measured. Rhizomes were then washed, dried and weighed.

3  Persistent rhizomes, i.e. rhizomes that survived more than 1 year, were shorter and less numerous in mown plots and their dry mass was less than 50% of that in unmown plots. Thus, repeated mowing depleted the rhizomes of their stored resources and has been used as a measure to control the further spread of S. altissima.

4  In contrast, rhizomes established in 1992 produced 10% more daughter rhizomes, which were also 23% longer in mown than in unmown plots.

5  There was little evidence that the length, and no evidence that the number of rhizomes, was increased by fertilizer application. Nevertheless, fertilizer application increased the dry mass and decreased the specific length (length per unit dry mass) of rhizomes.

6  Rhizome branching angles were not consistently altered by the treatments. However, there was a significant interaction, i.e. angles increased in response to fertilizer in unmown but not in mown plots.

7  The observed rhizome growth patterns (3–5) could be explained by adaptive growth plasticity, i.e. foraging, in the first year followed by differential survival of long rhizomes in later years. However, the greater length of newly formed rhizomes in mown plots could also have been due to increased soil temperatures caused by the removal of standing biomass and litter, which increased irradiance at the soil surface. This suggests that the observed growth responses of the rhizome systems to mowing and fertilizer application were due to ‘passive growth’ rather than adaptive foraging.
Abundance–range size relationships in the herbaceous flora of central England
Authors: Thompson Ken , Hodgson John G. , Gaston Kevin J.
Published: May 2003

1 Using data from a survey of over 10 000 1‐m2 quadrats in a 3000‐km2 area, we examined the relationship between abundance and range for the vascular plant flora of central England.

2 At the level of the whole landscape, abundance was not related to local, regional or national range. Local, regional and national range were closely related to each other.

3 At the level of the whole landscape, range was significantly and positively related to both niche breadth (expressed as the range of habitats exploited) and to habitat availability, although niche breadth appeared to be more important. Abundance was not related to niche breadth or habitat availability. Since specialist species are mainly confined to uncommon habitats (especially wetlands), we conclude that the relationship between range and niche breadth is not an artefact of widespread species passively sampling more habitats.

4 At the level of individual habitat types, significant positive relationships between range and abundance were common. These relationships remained after controlling for the effects of phylogeny. For predominantly annual weed communities, the relationship was linear, but for perennial communities it was markedly ‘upper triangular’, i.e. all combinations of range and abundance were found except wide range/low abundance. The evidence suggests that this difference can be attributed to the greater mobility of annual weeds.
Contrasting ecological breadth of co‐occurring annualPolygonumspecies
Authors: Sultan S. E. , Wilczek A. M. , Hann S. D. , Brosi B. J.
Published: May 2003

1 Understanding the relative distributions of ecological generalists vs. specialists requires precise characterization of the environmental ranges of closely related taxa. The ecological breadth of four annual species in the genusPolygonumwas determined from field measurements taken from five natural populations per species in a common geographical range.

2Significant early and late‐season differences among the species were found for available light (photosynthetically active radiation) at canopy and mid‐canopy levels, and for soil temperature, moisture availability, macronutrient content, pH, cation exchange capacity (CEC) and structure, at two depths. Field sites within each species also differed significantly for these variables.

3The field distribution ofP. persicaria covers the broadest range of habitats, from moderate shade with very dark microsites to full insolation, cool to very warm soils, flooded to dry moisture conditions, and organic, high‐nutrient to nutrient‐poor soils.

4Polygonum lapathifoliumis comparatively intolerant of shade, particularly early in the growth season. Although this species occurs in flooded to moderately dry conditions and in poor as well as rich soils, its moisture and nutrient ranges do not include such low extremes as those ofP. persicaria, and its range of soil temperatures is also narrower.

5Polygonum cespitosumis restricted to low‐light habitats and to consistently moist soils that do not flood. The species is, however, found in a moderately broad range of soil types and macronutrient availabilities.Polygonum cespitosumoccurs in extremely low‐light habitats that are evidently beyond the shade tolerance of the other species.

6Polygonum hydropiperis restricted to high‐light sites with highly organic, consistently very moist or flooded soils. Unlike its congeners, this species can tolerate flooded soils during seedling establishment. The species is limited to soils with high early nitrate and calcium content, moderate CEC, and pH close to 6.0, but tolerates a broad range of soil temperatures.

7The occurrence of spatial and temporal environmental variability within as well as among field populations ofPolygonumspecies suggests that tolerance of such variability may result from individual phenotypic plasticity rather than from ecotypic adaptation of entire populations.
The occurrence of thermophilous trees in the Scandes Mountains during the early Holocene: evidence for a diverse tree flora from macroscopic remains
Authors: Kullman Leif
Published: May 2003

1 Macroscopic remains of the fairly thermophilous tree species Alnus glutinosa, Tilia cordata and Betula pendula were recovered in subalpine and adjacent boreal environments far above and beyond their present‐day distributional limits. This establishes that the early Holocene tree flora of the Scandes Mountains in northern Sweden was indeed richer than it is today.

2 Dates ranged between c. 8600 and 7000 radiocarbon years bp. These are much earlier than previous estimates by conventional pollen stratigraphical analyses of the arrival of these species at their maximum geographical limits. This highlights problems in using only pollen data for vegetation reconstruction, and suggests re‐evaluation of earlier records.

3 The results, together with similar macrofossils for Picea abies and Larix sibirica in northern Sweden, suggest that many tree species spread rapidly and became established at their most extended range limits during the early Holocene. Abundances have subsequently varied in accordance with the ecology of individual species as well as with climatic change.

4 Palaeoclimatic inferences may suggest a strongly continental climate, i.e. warmer and drier summers and possibly fairly cold winters between 8600 and 7000 bp relative to the present. Some change towards a more oceanic climate regime with less pronounced seasonal contrasts may have occurred towards the end of the period.
A spatially precise study of Holocene fire history, climate and human impact within the Maurienne valley, North French Alps
Authors: Carcaillet Christopher
Published: May 2003

1 If, within a vegetation type, fire regimes are climate dependent, then fire patterns should be synchronous at regional scales. If they are not synchronous, then fires may be dependent on local processes such as human‐induced disturbances.

2 Two fire chronologies were developed using 34‐radiocarbon dating measured by accelerator mass spectrometry (AMS) from wood charcoal buried in soil. These charcoal fragments were sampled in two study sites 10 km apart in the Maurienne valley (Southern Vanoise massif, Savoy, France).

3 Asynchronous temporal fire patterns were seen at Aussois and Saint‐Michel‐de‐Maurienne. This demonstrates the dependence of fires on local‐ or stand‐scale environmental forcing; any direct relationship with climate is therefore rejected.

4 Slash‐and‐burn practices are probably the main source of Holocene fires in the Maurienne valley. However, deforestation did not occur throughout a site in any period, nor simultaneously at the same elevation in two different sites 10 km apart. The cultural landscape was shaped as early as the Neolithic and the Bronze Age, between 6000 and 3000 bp.

5 Deforestation at both study sites probably occurred in many stages in many small areas. The fire intervals were c. 500–1000 years. Deforested areas increased in extent over 2000–4000 years, until the present‐day cultural landscape was established. This process stopped c. 2500 bp at Saint‐Michel‐de‐Maurienne but is still active at Aussois.
Can comparative approaches based on plant ecophysiological traits predict the nature of biotic interactions and individual plant species effects in ecosystems?
Authors: Wardle D. A. , Barker G. M. , Bonner K. I. , Nicholson K. S.
Published: May 2003

1 The development of general principles regarding biotic interactions involving plants, or plant species effects in ecosystems, is best achieved through simultaneous evaluation of several species. We utilized a comparative approach involving 20 dicotyledonous herbaceous species, to explore possible relationships between several plant ecophysiological traits and plant litter decomposition, interactions involving competition and herbivory, and plant species effects on soil properties.

2 Decomposition rates of plant stem and leaf litter were negatively related to plant mass, time until flowering and vegetative growth rate, and positively related to stem nitrogen content. Root decomposition was also related to several traits. Multiple regression relationships showed that 74% and 84% of the variation across species for stem and root litter decomposition, respectively, could be predicted by plant traits; this suggests that plant traits may be powerful predictors of decomposition and have potential as alternative predictors to the litter quality characteristics that previous studies have concentrated on.

3Palatability of both seedlings and leaf discs by the invertebrate herbivoresDeroceras reticulatumandListronotus bonariensiswere frequently related to plant traits. Those traits that showed the strongest relationships with the palatability data included various vegetative growth characteristics and (for the leaf disc data) nitrogen concentrations of flowering plant stems.

4Competitive effects of the dicotyledonous species against a phytometer species, the grassLolium perenne, were negatively related to leaf nitrogen concentration, and multiple regression relationships involving this trait in combination with others explained over 50% of the variation across species. The competitive response of both plant mass and total seed production toL. perennewas poorly related to plant traits.

5The effects of plant species on soil properties including microbial biomass and activity, pH, nitrate concentration and total nitrogen were often closely related to various plant traits. Multiple regression relationships revealed that combinations of several traits were often important in determining these effects; the strongest relationships found were for effects of senescent plants on soil respiration and for the effects of flowering plants on soil nitrate. Plant traits were therefore clearly important in determining plant species effects on soils.

6Our study emphasizes the importance of plant traits in understanding (and predicting) species interactions and effects in communities and ecosystems, and shows that properties considered at the whole plant level have the potential to manifest themselves over much larger scales. We therefore conclude that there are clear linkages between plant ecophysiological traits, biotic interactions involving plants, and ecosystem level properties and processes.
Migration of vascular plants to secondary woodlands in southern Sweden
Authors: Brunet Jörg , Von Oheimb Goddert
Published: May 2003

1 We studied the migration of field layer plants across ecotones between ancient woodlands and recent deciduous woods on former arable land varying in age between 30 and 75 years.

2 Number and percentage cover of woodland species in recent woods decreased with increasing distance to the ancient woods, and increased with the age of the recent woods, indicating dispersal limitation during secondary succession.

3 Colonization by typical woodland plants was observed in 183 of 200 species × site combinations. In 72 combinations, a colonization front was characterized by logarithmic or linear decrease in species cover, indicating establishment of isolated individuals and gradual infill of gaps. This pattern was most common in ant‐dispersed species and less frequent in species with adhesive or ingested seeds.

4 Migration rates were calculated for 49 woodland species. Mean migration rates based on maximum cover in recent woods varied from 0.00 to 1.00 m year−1 between species, with a median migration rate of 0.30 m year−1. Migration rates calculated on occurrence of the farthest individual ranged from 0.00 to 1.25 m year−1, with a median rate of 0.53 m year−1.

5 Ant‐dispersed species had lower migration rates based on maximum cover compared with species with adhesive or ingested seeds. No differences between dispersal modes were found when comparing migration rates based on the farthest individuals. Most of the calculated migration rates (84%) exceeded the rate of possible vegetative spread of woodland species.

6 Establishment of a field layer vegetation in secondary woods comparable to that of the adjacent ancient stands proceeded at a rate of c. 0.3–0.5 m year−1. We conclude that scale and intensity of temperate forest management should be adjusted to the relatively slow migration of the field layer flora in order to enable complete recovery during a management cycle.
Disturbance‐induced density‐dependent seed set in Shorea siamensis (Dipterocarpaceae), a tropical forest tree
Authors: Ghazoul Jaboury , Liston Katharine A. , Boyle T. J. B.
Published: May 2003

1 The reproductive output of Shorea siamensis, a widespread dipterocarp tree, was assessed in relation to disturbance and tree density at three sites in western Thailand during the 1996 and 1997 flowering seasons. The locations were similar except in disturbance history, which was reflected in decreasing tree density from undisturbed via moderately disturbed to disturbed sites.

2 Hand pollination experiments showed S. siamensis to be partially self‐incompatible due to differential pollen tube growth and abortion of inbred fruit. Although more than 90% of flowers from trees at all sites were pollinated, pollen tubes developed in only a small proportion of these flowers. Both pollen tube development and initial fruit production were highest at the undisturbed site. Many fruit, presumably selfed, were aborted during development at all sites, but significantly more fruit were aborted at the disturbed site, resulting in lowered production of mature fruit.

3
Shorea siamensis was pollinated by small Trigona bees, which exhibited significant declines in intertree movements with increasing distance between flowering trees. As resource availability did not differ between sites, differences in mature fruit set were considered to be mediated by changes in pollinator foraging behaviour at differing tree densities. Variation in seed set was found to be negatively correlated with distance to nearest conspecific both within and between sites.

4 At the two least disturbed sites observed seed set values corresponded with those expected by calculation. However, seed set at the disturbed site was significantly lower than expected.

5 Our results suggest that high reproductive success of S. siamensis is dependent upon cross‐pollination which, through pollinator behaviour, is a function of tree isolation. This species may thus be subject to the Allee effect, where population viability is reduced disproportionately with a decline in population size or, as in this study, population density. The implications of these results for population recovery and genetic structure following disturbance are discussed.
Cleistogamy as a bet‐hedging strategy in Oxalis acetosella, a perennial herb
Authors: Berg Henrik , Redbo‐torstensson Peter
Published: May 2003

1 Phenology and reproduction were studied in three populations of the cleistogamous herb Oxalis acetosella during three growing seasons, in order to see how the balance between chasmogamous (CH) and cleistogamous (CL) reproduction varies with temporal and spatial environmental variation and with plant size. The numbers of CH and CL flower buds, flowers, immature capsules and mature capsules were counted per ramet, ramet sizes were estimated, and mature capsules were collected for seed counts.

2 Both CH and CL flower numbers were positively correlated with ramet size expressed as leaf number, but the correlation was much stronger in the CL phase. CL flower production also varied significantly between years and sites. Thus, CL production in O. acetosella was not independent of resources and climatic variation.

3 When the effects of year and site were taken into account, the probability of an individual flower developing into a mature fruit was not higher in the CL phase than in the CH phase.

4 CL production was affected by fertilization success in the CH phase. Ramets with one or more CH flowers left unfertilized generally produced more CL buds than ramets with all their CH flowers fertilized. The former group also tended to have more seeds per CL capsule.

5 Since reproductive success in the two phases varies in different temporal and spatial patterns, cleistogamy in O. acetosella is considered to be a bet‐hedging strategy optimizing reproductive output in fluctuating environments.

6 The findings of this study are in conflict with the general view on cleistogamy as a fail‐safe mechanism for back‐up seed production, unaffected by variations in resource supply and environmental conditions.
Nutrient limitations and their implications on the effects of atmospheric deposition in coastal dunes; lime‐poor and lime‐rich sites in the Netherlands
Authors: Kooijman A. M. , Dopheide J. C. R. , Sevink J. , Takken I. , Verstraten J. M.
Published: May 2003

1 A survey of plant and soil parameters was carried out in dry dune grasslands along the Dutch coast in the lime‐ and iron‐poor Wadden district and initially lime‐ and iron‐rich Renodunaal district, in order to detect differences in nutrient availability related to soil characteristics and potential sensitivity to atmospheric deposition of nitrogen.

2 Plant biomass and phosphorus pools in the shoot were higher in the Wadden district. The low foliar nitrogen concentrations and nitrogen/phosphorus ratios in the Wadden district suggested nitrogen‐limitation, while in the Renodunaal district there appeared to be a balanced supply of both nitrogen and phosphorus.

3 Soil pH, soil organic matter, soil nitrogen and phosphorus concentrations and total amounts were generally higher in the Renodunaal district. In both districts mineral phosphorus decreased with acidification and phosphorus oxalate (iron and aluminium bound) increased.

4 In the Wadden district iron is present primarily in iron–organic matter complexes, which leads to reversible binding of phosphorus. In the Renodunaal district large amounts of iron (hydr)oxides occur and at high pH may contribute to reversible phosphorus‐sorption, but at low pH this probably leads to immobilization of phosphorus.

5 While pools of soil phosphorus are low in the Wadden district, the phosphorus availability may be relatively high due to the comparatively loose nature of phosphorus‐sorption. As a result the area may be nitrogen‐limited and grass‐encroachment may thus have resulted from atmospheric deposition of nitrogen.

6 In the Renodunaal district, atmospheric deposition probably only accelerates grass‐encroachment, because deposition of acid and nitrogen increases the availability of both nitrogen and phosphorus and maintains the ‘co‐limitation’.
Effects of supplementary feeding on growth and reproduction of three carnivorous plant species in a subarctic environment
Authors: Thorén L. Magnus , Karlsson P. Staffan
Published: May 2003

1 The effect of supplementary feeding on growth and reproduction of three carnivorous plants species was investigated over a 6‐year period. Pinguicula alpina, P. villosa and P. vulgaris populations growing at two altitudes in a subarctic environment were fed with fruit flies (Drosophila melanogaster).

2 Fed plants increased in size relative to control plants during the first years. Subsequently a stable size difference between feeding levels was established. The weight of the over‐wintering part was higher in fed plants than in control plants.

3 The flowering frequency (i.e. proportion of plants in a population carrying flowers) was also higher in the fed plants. The proportion of flowering plants increased in the feeding treatment compared to control plants during more‐or‐less the whole experimental feeding period (5–6 years). Seed production also increased slowly in response to feeding.

4 No feeding effect on nitrogen and phosphorus concentrations in seeds and over‐wintering parts was found.

5 In most characteristics the high‐altitude populations were less responsive than populations growing at low altitude. In the high‐altitude population reproduction failed repeatedly, suggesting that seed output may be more dependent on abiotic factors than on resource availability in cold environments.

6
Pinguicula villosa and P. vulgaris used the new resources the same summer for increased leaf rosette growth and current reproduction, showing these species to be income breeders, while the third species (P. alpina) allocated a larger proportion to storage and future reproduction, characteristic of a capital breeder.
Quantitative representation of local forest composition in forest‐floor pollen assemblages
Authors: Jackson Stephen T. , Kearsley Jennifer B.
Published: May 2003

1 We compared modern pollen assemblages from 60 moss polster sites in northern New York with forest composition data within 20–120 m of the sites using extended R‐value (ERV) models, which correct for non‐linearities arising from use of pollen percentage data. Our sites were concentrated in two regions, one dominated by Tsuga and hardwood (Acer, Betula, Fagus) forests, and the other by Tsuga, Pinus, Betula, Acer and Quercus forests.

2 Our results confirm that forest‐floor pollen assemblages are dominated by pollen originating from trees growing more than 20 m from the site of deposition. However, our results suggest that background pollen percentages were overestimated by Jackson & Wong in 1994, owing to unusually high Pinus pollen production in the year of their sampling.

3 Expansion of our vegetation sampling radius from 20 to 120 m resulted in modest but consistent improvement in model fit and a decrease in background pollen percentages.

4 ERV model parameters (slope and background) differed substantially between the two study regions, primarily owing to differences in background pollen productivity and dispersal from regional sources.

5 High background pollen percentages may lead to poor estimation of calibration parameters in regions of complex vegetation patterns. Expansion of the vegetation sampling radius to reduce the background component may lead to better parameter estimates.

6 Calibration of pollen–vegetation relationships requires definition of the vegetation term so that it approximates the vegetation sampled by the pollen assemblages. Critical challenges are to define better the appropriate vegetation sampling area and distance‐weighting functions for application to pollen–vegetation calibration.
An experimental test of limits to tree establishment in Arctic tundra
Authors: Hobbie Sarah E. , Chapin F. Stuart
Published: May 2003

1 Five treeline species had low seed germination rates and low survivorship and growth of seedlings when transplanted into Alaskan tundra. Seed germination of all species increased with experimental warming, suggesting that the present treeline may in part result from unsuccessful recruitment under cold conditions.

2 Growth, biomass and survivorship of seedlings of treeline species transplanted into tundra were largely unaffected by experimental warming. However, transplanted seedlings of three species (Betula papyrifera, Picea glauca and Populus tremuloides) grew more when below‐ground competition with the extant community was reduced. All three measures of transplant performance were greater in shrub tundra than in the less productive tussock or heath tundra. Establishment of trees in tundra may thus be prevented by low resource availability and competition.

3 Two species (Alnus crispa and Populus balsamifera) had low seed germination and survivorship of germinated seeds; transplants of these species did not respond to the manipulations and lost biomass following transplanting into tundra. Isolated populations of these two species north of the present treeline in arctic Alaska probably became established during mid‐Holocene warming rather than in recent times.

4 Of all the species studied here, Picea glauca was the most likely to invade intact upland tundra. Its seeds had the highest germination rates and it was the only species whose seedlings survived subsequently. Furthermore, transplanted seedlings of Picea glauca had relatively high survivorship and positive growth in tundra, especially in treatments that increased air temperature or nutrient availability, two factors likely to increase with climate warming.
Sources and consequences of seed mass variation in Banksia marginata (Proteaceae)
Authors: Vaughton Glenda , Ramsey Mike
Published: May 2003

1 We examined the sources and consequences of seed mass variation in Banksia marginata occurring in fire‐prone heath on nutrient‐poor soils to determine factors influencing seed size and possible fitness benefits of large seeds.

2 Individual seed mass varied fivefold. Variation occurred among populations (29% of total), among years (10%) and among plants (plants, 6%; year × plants, 13%), but was most pronounced within plants (42%). Within plants, seed mass variation was greater within infructescences (35%) than among infructescences (7%).

3 Seed mass variation within infructescences was not related to whether follicles contained one or two seeds. Seed mass was also unaffected by ovule position within follicles and follicle position within infructescences.

4 Seed mass variation among infructescences and plants was related to the limited availability of nutrient resources during seed provisioning. Mean seed mass was negatively related to seed number per infructescence and per plant. When resources decreased late in the flowering season and after defoliation, seed mass declined by 7–10% and seed number by 31–45%. When resources increased after inflorescence removal, seed mass increased by 8% but seed number was unaffected. Plants thus had only a limited capacity to maintain seed mass by adjusting seed number when resources varied.

5 The N and P contents of seeds (mg seed−1) increased linearly with seed mass, indicating costs of producing larger seeds in terms of limited environmental nutrients.

6 Seedling size increased with seed mass, implying fitness benefits of larger seeds in terms of increased seedling establishment on nutrient‐poor soils. Seed mass had little or no effect on seed germination, relative growth rates and root:shoot ratios.

7 Although stabilizing selection should eliminate seed mass variation occurring within plants, such variation persists because resource constraints limit the ability of plants to control individual seed size.
Variation in the demography of a woodland understorey herb (Primula vulgaris) along the forest regeneration cycle: projection matrix analysis
Authors: Valverde Teresa , Silvertown Jonathan
Published: May 2003

1 Gaps in the forest canopy allow establishment of many understorey species. As gaps close, their demographic behaviour is affected by changing environmental conditions. A demographic analysis of Primula vulgaris populations in forest patches with varying canopy openness was carried out to investigate the effect of forest canopy dynamics on the demography of this forest understorey herb.

2 Eight P. vulgaris populations across a range of light conditions were studied in three deciduous temperate forests in Britain. Demographic data were collected in each population during summer 1992, 1993 and 1994, and stage‐based population projection matrices were built to describe their demography for two growth periods (1992–93 and 1993–94).

3 Population growth rate (λ) varied from 0.97 to 1.98 in 1992–93, and from 0.88 to 1.23 in 1993–94. There was a significant positive correlation between λ and diffuse light for the two periods studied: generally, population growth rate was lower in darker patches, implying that populations decline as the canopy closes. Lower λ‐values in 1993–94 were the result of increased mortality and decreased fecundity compared to 1992–93. In most cases the observed population structures were significantly different from the calculated stable‐stage distributions.

4 Sensitivity analysis showed that λ was most sensitive to changes in matrix transitions that corresponded to growth from small to adult stages, especially those that implied fast growth. Elasticity analysis revealed that the contribution of fecundity elements to λ was small, but populations in brighter patches showed comparatively higher fecundity elasticities than populations under the closed canopy. High elasticities corresponded to the entries that implied growth (especially in brighter patches) or persistence in adult categories (predominantly in darker patches).

5 The observed variation in the demography of P. vulgaris in different patches along the forest regeneration cycle stresses the importance of studying the variation in plant population dynamics across the range of habitat patches in which the plant naturally occurs.
A comparative study of the seedbanks of heathland and successional habitats in Dorset, Southern England
Authors: Mitchell R. J. , Marrs R. H. , Auld M. H. D.
Published: May 2003

1 Many areas of lowland heaths are being lost due to invasion by Betula spp., Pinus sylvestris, Pteridium aquilinum, Rhododendron ponticum and Ulex europaeus. One of the factors influencing the success of restoration of heathland on such sites will be the content of their viable seedbanks.

2 Ten heathland areas in the Poole Basin area of Dorset, where succession to one or more of the above species had occurred were studied. The viable seedbanks of the successional sites were compared with those of nearby heathland using Canonical Discriminant Analysis.

3 The seedbanks of all the successional stages were significantly different from the seedbank of the heath.

4 The seedbanks from the Pinus sylvestris and Pteridium aquilinum successional stages contained significantly lower numbers of heathland species than did the heathland seedbank, although few non heathland species were present.

5 The seedbanks from the Betula spp., Rhododendron ponticum and Ulex europaeus successional sites contained both significantly lower numbers of heathland species and significantly higher numbers of non heathland species than the heathland seedbank.

6 The results are discussed in relation to the restoration of heathland on successional sites and the use of the seedbank as a source of propagales for the establishment of heathland species.
Seedling growth response to added nutrients depends on seed size in three woody genera
Authors: Milberg Per , Pérez‐Fernández María A. , Lamont Byron B.
Published: May 2003

1 We tested whether seedlings of small‐seeded species were more reliant on soil nutrients than large‐seeded ones by growing 21 species from three woody genera (Eucalyptus, Hakea and Banksia) along a gradient of nutrient availability.

2 At very low nutrient availability, larger seeds produced larger seedlings. This was seen especially among the eucalypts, but the difference was eliminated at optimal soil nutrient levels. Hakea species with large seed mass, and all Banksia species, appeared unable to exploit additional soil nutrients for growth, whatever the level supplied.

3 Larger seeds tended to have proportionately higher contents of N, P and K and, under nutrient‐poor conditions, supplied more of these to their seedlings, although at a diminishing rate.

4 We suggest that large‐seededness could be an adaptation to the high‐light, nutrient‐impoverished habitats in which these species occur by providing the seedling with the mineral nutrients, rather than carbon‐based metabolites, needed for maximizing initial root growth. Reaching reliable moisture before summer (drought avoidance) is an alternative strategy to physiological tolerance of drought.
Exercising Market Power in Proprietary Aftermarkets
Authors: Borenstein Severin , Mackie‐Mason Jeffrey K. , Netz Janet S.
Published: May 2003

Over 20 recent antitrust cases have turned on whether competition in complex durable‐equipment markets prevents manufacturers from exercising market power over proprietary aftermarket products and services. We show that the price in the aftermarket will exceed marginal cost despite competition in the equipment market. Absent perfectly contingent long‐term contracts, firms will balance the advantages of marginal‐cost pricing to future generations of consumers against the payoff from monopoly pricing for current, locked‐in equipment owners. The result holds for undifferentiated Bertrand competition, differentiated duopoly, and monopoly equipment markets. We also examine the effects of market growth and equipment durability.
Recruitment rates in forest plots: Gf estimates using growth rates and size distributions
Authors: Kohyama Takashi , Takada Takenori
Published: May 2003

1 In censuses of tree populations in permanent plots, short census intervals and small population size lead to uncertainty in the observed recruitment rate of a minimum size. Increasing the census interval, however, underestimates the rate because of unrecorded ‘recruit and die’ events.

2 We propose a new Gf procedure for estimation of recruitment rates. Recruitment rate per area is obtained by multiplication of the density in the smallest size class (f) and the average size growth rate in that class (G) divided by the width of the class. This procedure is valid when the size distribution of the population examined is continuous with size.

3 When tree size structure is negative‐exponentially distributed, as is often the case in natural rain forest populations, the Gf estimate of the recruitment rate for a given size class was least biased close to the midpoint size of this class.

4 Gf estimates agreed well with census estimates of recruitment rate from permanent plots in rain forests. A tendency for Gf estimates to be larger than census estimates disappeared when census estimates were corrected for mortality after recruitment.

5 The effects of plot size, census interval and variation in growth rate on estimates of recruitment rate were simulated using model populations. Small plot size caused substantially more among‐plot deviation for the census count of recruitment events than for the Gf estimate. The census recruitment rate also showed larger variation among plots for shorter intervals than the Gf estimate, which was independent of census interval. The Gf estimates were therefore more accurate than census counts in many situations. More than several tens of trees were needed in a size class to allow a reliable Gf estimates.
Survival and growth of woody plant seedlings in the understorey of floodplain forests in South Carolina
Authors: Jones Robert H. , Sharitz Rebecca R.
Published: May 2003

1Survival and height growth of permanently tagged understorey seedlings in four river floodplain forests in South Carolina were monitored for 8 years. Regression models were used to determine if a common survival pattern emerged and if the pattern varied according to species, spatial location, time, seedling size and seedling growth.

2For most of the populations, per capita survival was initially poor but increased steadily with age. A few populations, however, had relatively high survival rates for 1–3 years after establishment, or brief periods (1–2 years) with much lower survival. Although the underlying survival function was best described by a negative power curve, a log‐logistic model also fit the data and provided more versatility for fitting individual populations.

3Significant differences in general survival pattern were found among species, sites (forests), years of establishment (cohorts), and all two‐way interactions of species, site and cohort. Species differences were large. Spikes in mortality for individual species and cohorts were synchronized within sites and to a lesser degree among sites. In some sites, weak relationships were noted between mortality and peak river discharge during summer (negatively correlated) and winter (positively correlated).

4Species differed strongly in their initial height, but effects of cohort and site on height were also significant as were all two‐way interactions of species, site and cohort. During the 8 years of this study, very few seedlings grew taller than 30 cm. For most species, taller seedlings had greater per capita survival. Height growth, however, was not consistently related to survival. Since mean size of survivors changed little with time, age may be a better variable than size to use in models of survival.

5Simulation models could probably be developed using a log‐logistic function that includes (in order of importance): seedling age, species, intensity of winter floods (some sites) and occurrence of summer droughts (some sites).