bluuebunny/crossref_metadata_2025_split huggingface dataset:
Competition between Asian pink salmon (Oncorhynchus gorbuscha) and Alaskan sockeye salmon (O. nerka) in the North Pacific Ocean
Authors: Ruggerone G. T. , Zimmermann M. , Myers K. W. , Nielsen J. L. , Rogers D. E. 
Published: May 2003

AbstractThe importance of interspecific competition as a mechanism regulating population abundance in offshore marine communities is largely unknown. We evaluated offshore competition between Asian pink salmon and Bristol Bay (Alaska) sockeye salmon, which intermingle in the North Pacific Ocean and Bering Sea, using the unique biennial abundance cycle of Asian pink salmon from 1955 to 2000. Sockeye salmon growth during the second and third growing seasons at sea, as determined by scale measurements, declined significantly in odd‐numbered years, corresponding to years when Asian pink salmon are most abundant. Bristol Bay sockeye salmon do not interact with Asian pink salmon during their first summer and fall seasons and no difference in first year scale growth was detected. The interaction with odd‐year pink salmon led to significantly smaller size at age of adult sockeye salmon, especially among younger female salmon. Examination of sockeye salmon smolt to adult survival rates during 1977–97 indicated that smolts entering the ocean during even‐numbered years and interacting with abundant odd‐year pink salmon during the following year experienced 26% (age‐2 smolt) to 45% (age‐1 smolt) lower survival compared with smolts migrating during odd‐numbered years. Adult sockeye salmon returning to Bristol Bay from even‐year smolt migrations were 22% less abundant (reduced by 5.9 million fish per year) compared with returns from odd‐year migrations. The greatest reduction in adult returns occurred among adults spending 2 compared with 3 years at sea. Our new evidence for interspecific competition highlights the need for multispecies, international management of salmon production, including salmon released from hatcheries into the ocean.
Competition between tree seedlings and herbaceous vegetation: support for a theory of resource supply and demand
Authors: Davis Mark A. , Wrage Keith J. , Reich Peter B. 
Published: May 2003

1 We measured competition intensity (CI) between herbaceous vegetation and tree seedlings (Quercus macrocarpa and Q. ellipsoidalis) along an experimental moisture–light gradient. Contrasting theories were tested by comparing variation in competition intensity to changes in neighbour biomass and resource supply and demand. 2 CI based on survival was inversely correlated with net soil water supply (gross supply minus demand by herbaceous vegetation). CI was not positively correlated with either gross resource supply or neighbour biomass, contrary to predictions of Grime's triangular model for plant strategies. 3 Many of the inconsistencies and conflicting results that have characterized the recent literature on plant competition could be eliminated if changes in competition intensity along a resource gradient are compared with changes in net resource supply rather than changes in productivity or neighbour biomass. 4 Tree seedling success in savannas and grasslands may be strongly influenced by the intensity of competition from herbaceous vegetation. Factors that reduce soil water content are likely to increase competition intensity (and reduce seedling success) in these environments, while factors that increase soil water content will favour seedling success through decreased competition for water with herbaceous vegetation.
Advantages of early germination for growth and survival of seedlings of Acer mono under different overstorey phenologies in deciduous broad‐leaved forests
Authors: Seiwa Kenji 
Published: May 2003

1  Acer mono is one of the earliest germinating species in hardwood forests of northern Japan. To evaluate the advantage of early germination for the seedling establishment, differences in the temporal pattern of leaf development between the seedlings and overstorey trees were investigated, together with the timing of dry mass gain and allocation, survival and mortality agents of seedlings. These traits were contrasted at four sites with different types of foliage phenology in the overstorey trees (FU‐1 and FU‐2, forest understorey in which overstorey trees unfolded and shed the leaves as a flush and succeedingly, respectively; SG, small gaps; and FE, forest edge). 2  Seasonal growth patterns of the seedlings were greatly affected by the differences in the coupling of leaf development between the seedlings and the overstorey trees. For early germinating cohorts of Acer mono, 79, 61, 50 and 53% of annual dry mass gain occurred within 2 months of germination, in FU‐1, FU‐2, SG and FE, respectively. After this point (canopy closure) mass increment decreased abruptly in both FU sites, but continued to increase in both SG and FE. Seedling mass, however, increased after September again in FU‐2 but not in FU‐1, mainly due to earlier leaf shedding of the canopy trees in FU‐2. 3  After canopy closure, leaf mass ratio was greatest in FU‐1 where light was most limited, but lowest in FE. In contrast, root mass ratio was greatest in FE but lowest in FU‐1 where soil moisture was most abundant. These traits might lead to the optimization of growth by making all resources equally limiting even after canopy closure in forest understorey. 4  Higher seedling survival resulting from early germination was observed in all four sites, since predators and pathogens selectively attacked late germinating individuals. The advantage of early germination was greater in both FU‐1 and FU‐2 than in FE, mainly due to large differences in available light for early vs. late germinating individuals in both FU sites compared with the FE site. 5  These observations suggest that phenological traits of A. mono such as rapid germination in early spring and earlier deployment of leaves compared with overstorey trees has been selected to maximize annual mass gain and survival in understorey habitats of deciduous broad‐leaved forests.
Effects of population size on performance in the rare plant Gentianella germanica
Authors: Fischer Markus , Matthies Diethart 
Published: May 2003

1  We studied the relationships between population size, reproduction and population growth rate in 23 populations of the rare, short‐lived plant Gentianella germanica. We also investigated a possible correlation of population size effects with environmental variation in climate, topography, soil, vegetation, and management. To ascertain whether the differences between populations have a genetic basis, we grew 20 seed families from each of the populations in a common garden experiment. 2  In 1993, population sizes ranged from 40 to 5000 flowering plants in the field populations (geometric mean 386). Plants in small populations had fewer seeds per fruit and fewer seeds per plant than plants in larger populations, whereas seed mass was independent of population size. From 1993 to 1995 population size decreased in most populations (mean annual population growth rate 0.876), and this decrease was larger in small populations than in large populations. 3  In the common garden the positive correlation between the number of surviving plants per planted seed and original population size increased steadily over time. After 17 months there were significantly more flowering plants and more flowers per planted seed for seeds from large populations than for those from small populations. 4  Although environmental variables accounted for significant variation in population growth rate and plant performance both in the field and in the common garden, effects of population size detected in stepwise multiple regressions were not confounded with environmental effects. 5  We conclude that the reduced performance observed in plants from smaller populations was explained by genetic effects rather than by habitat quality, although pollinator limitation may have contributed to fitness reductions in the field. The observed patterns suggest further reductions of population sizes in Gentianella germanica in the future, especially in already small populations. Our study lends support to the view that genetic problems are a major concern in plant conservation.
Effects of raised CO2 on potential CH4 production and oxidation in, and CH4 emission from, a boreal mire
Authors: Saarnio Sanna , Alm Jukka , Martikainen Pertti J. , Silvola Jouko 
Published: May 2003

1  In a glasshouse experiment we studied the effect of raised CO2 concentration (720 p.p.m.) on CH4 emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH4 production and oxidation was measured at the end of the emission experiment. 2  The vascular cores (‘Sedge’) consisted of a moss layer with sedges, and the moss cores (‘Sphagnum’) of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures. 3  In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the potential CH4 oxidation. A raised concentration of CO2 increased CH4 efflux weakly and only at the highest peat temperatures (17–20 °C). 4  The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO2 concentrations, and would thus retard any consequent increase in CH4 emission.
Forage variation in brood‐rearing areas used by pacific black brant geese on the Yukon‐Kuskokwim delta, Alaska
Authors: Person Brian T. , Babcock Christopher A. , Ruess Roger W. 
Published: May 2003

1  We investigated the effects of grazing by black brant geese on Carex subspathacea lawns on the Yukon‐Kuskokwim delta, Alaska. 2  We compared variation in growth and forage quality in both grazed and temporarily exclosed sites to determine responses of C. subspathacea to grazing at landscape scales within two nesting colonies that had experienced different population dynamics over recent decades. 3  Landscapes differed in forage quality, grazing patterns, and in the effect grazing had on C. subspathacea forage characteristics. We found no effect of grazing on net above‐ground primary productivity (NAPP) over a wide range of natural grazing intensities at the landscape scale. 4  No differences in forage quality, NAPP, or response of C. subspathacea growth rates to grazing pressures could be detected between colonies. This suggests that goose grazing does not have deleterious effects on C. subspathacea in this ecosystem. 5  It has been suggested that gosling growth rates are sensitive to seasonal declines in forage availability and quality. Spatial variation in forage quality and availability per sampled area exceeded seasonal variation in these characteristics and is likely to have dramatic effects on gosling growth and recruitment rates.
A new species index for forest vascular plants: development of functional indices based on mineralization rates of various forms of soil nitrogen
Authors: Diekmann Martin , Falkengren‐Grerup Ursula 
Published: May 2003

1  Soil nitrogen mineralization rates for ammonium, nitrate and total‐N were determined by incubation experiments for 661 sample plots of deciduous forest from different regions in southern Sweden. 2  Species N indices for nitrate and ammonium were calculated as the weighted averages of mineralized N in those plots where the species were present. 3  Optimized linear models were used to combine mineralization rates for NH+4 + NOminus;3 to produce a functional N index for plots (FNIP) and to combine the species indices for NH+4 + NOminus;3 to produce a functional N index for species (FNIS). 4  The sample scores along the first axis of a detrended correspondence analysis (DCA) were highly correlated with soil acidity and mineralized ammonium, whereas total‐mineralized N accounted for most of the variation along the second DCA axis. The species scores along the first axis were highly correlated with the ammonium index. 5  FNIP was somewhat better correlated with the sample scores along axis 1 than mineralized ammonium, but only slightly better correlated than total‐mineralized N relative to axis 2. Similar results were obtained for FNIS. 6  Ammonium index and FNIS explained more of the floristic variation along the ordination axes than Ellenberg's N indicator values. Weighted averages of these indices also showed higher correlations with the sample scores along the axes than corresponding averages of Ellenberg's N values. However, when ammonium index and FNIS for the most frequent species were transformed into classes, they were generally similar to the Ellenberg scale. 7  The ammonium indices differed considerably between regions, caused by differences in N deposition, total‐N mineralization and nitrification rate. In one of the regions with comparatively low nitrification, the ammonium index was found to be uncorrelated with the species scores along the first DCA axis. FNIS differed much less between regions and thus was more robust; it appears to be a good and generally applicable expression of the species’ responses to N availability in deciduous forest soils.
The carbon balance of grazed and non‐grazed Spartina anglica saltmarshes at Skallingen, Denmark
Authors: Morris James T. , Jensen Arne 
Published: May 2003

1  Canopy‐level CO2 exchange and biomass were measured monthly for 9 consecutive months during 1990 on grazed and non‐grazed portions of a Danish salt marsh dominated by Spartina anglica. The empirical measurements were used to calibrate a model of canopy photosynthesis and soil respiration that was subsequently integrated to provide estimates of annual net ecosystem production (NEP). 2  Standing total and green biomass on the non‐grazed site reached maxima during September of 1.9 ± 0.2 and 1.1 ± 0.2 kg m–2 ( ± 1 SD, n = 3), respectively. Corresponding maxima (0.8 ± 0.1 and 0.5 ± 0.05 kg m–2), were achieved during July at the grazed site. 3  Sediment organic matter as a percentage of dry weight was 31.6% and 5% at the non‐grazed and grazed sites, respectively. Accounting for the higher sediment bulk density at the grazed site meant that concentrations of organic carbon were 0.027 and 0.021 g cm–3 at non‐grazed and grazed sites, respectively. Thus, the fraction of NEP removed by grazing animals significantly reduced the accumulation of sediment organic matter. 4  Estimate of NEP varied between 17 and 38 mol m–2 year–1 of carbon at the grazed site and between 5 and 38 mol m–2 year–1 at the non‐grazed site, depending on assumptions about canopy geometry. Soil respiration, 36 mol m–2 year–1, did not differ between sites. Canopy respiration was less (21 mol m–2 year–1) at the grazed site than at the non‐grazed site (28 mol m–2 year–1), and accounted for 22–29% and 28–41% of gross photosynthesis at grazed and non‐grazed sites, respectively. The decrease in canopy respiration compensated the grazed canopy for losses to herbivores. 5  A canopy photosynthesis model was used to calculate a theoretical envelope of canopy biomass, termed the production window, inside of which NEP is positive and outside of which NEP is negative. The production window is bisected by the optimum canopy biomass, which is the theoretical biomass at which NEP is maximized. The seasonality of NEP is determined by the trajectory of actual canopy biomass through the production window. It was shown that canopy biomass on the grazed site was close to the theoretical optimum biomass late in the season, while the non‐grazed canopy biomass was supraoptimal.
Attributes of the seed bank after a century of primary succession on islands in Lake Hjälmaren, Sweden
Authors: Grandin Ulf , Rydin Håkan 
Published: May 2003

1  A large number of islands was created when the water table of Lake Hjälmaren, south central Sweden, was lowered between 1882 and 1886. We have complete lists of vascular plant species for 40 of these islands from 1886, 1892, 1903–04, 1927–28 and 1984–85. 2  We have investigated the seed bank on nine of these islands and compared species composition at different soil depths with the species lists from the islands in 1886–1985, and with the present vegetation in the area of seed bank sampling. We have also investigated the distribution in the soil of seeds from species with different ecological attributes, including seed longevity, successional status, seed weight, seed form and species longevity. 3  Seeds in soil samples were allowed to germinate over the course of two summers with an intermediate cold storage. We found 1944 seeds representing 65 taxa. The mean seed density was 84 seeds dm–2. 4  The similarity between the surface soil (0–3 cm) seed bank and the vegetation at the different vegetation analyses increased from 1886 to 1993. The similarity between the present vegetation and the seed bank decreased with increasing soil depth, and the soil at 12–15 cm had no species in common with the present vegetation. Several species now absent from the vegetation were found in the seed bank. 5  Deeply buried seeds came from early successional, annual species with long‐term persistent and low‐weight seeds, as expected from seed bank theories, but were slightly elongated, which was in contrast to theories. Spherical seeds were associated with the surface soil, as were short‐lived and high‐weight seeds from late successional, perennial species.
Nutrients, competition and plant zonation in a New England salt marsh
Authors: Levine Jonathan M. , Brewer J. Stephen , Bertness Mark D. 
Published: May 2003

1  We examined the effects of nutrient availability on the competitive interactions of the New England salt marsh perennials that occupy discrete vegetational zones parallel to the shoreline. 2  Fertilized and unfertilized plots of pair‐wise mixtures and monocultures of Spartina alterniflora, S. patens and Juncus gerardi were compared in order to assess the effects of nutrient addition on the competitive dynamics of these species in the field. In addition, we examined competition between some of these species and Distichlis spicata, a species common to disturbed marsh habitats. 3  After two growing seasons, changes in above‐ground biomass of the species indicated that in fertilized plots, S. alterniflora outcompeted S. patens, S. patens outcompeted J. gerardi, and D. spicata outcompeted both J. gerardi and S. patens. This was the reverse of the interactions seen under ambient marsh conditions, and suggested that, under conditions of nutrient limitation, competitive dominance may result from efficient competition for nutrients. 4  Using a conceptual model of salt marsh zonation as a function of competition, physical stress and nutrient limitation, we hypothesize that a nutrient‐induced reversal in the competitive dynamics among salt marsh perennials may result in modification of the pattern of plant zonation in this and similar marshes.
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.