bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of vertebrate herbivores on soil processes, plant biomass, litter accumulation and soil elevation changes in a coastal marsh
Authors: Ford Mark A. , Grace James B. 
Published: March 2003

1 Submergence of coastal wetlands in Louisiana is currently rapid and widespread. A number of factors contribute to this loss of habitat, including the activities of herbivores. The objective of this study was to examine the effects of large mammals, predominantly nutria and wild boar, on processes controlling soil elevation in coastal marshes. 2 Effects of herbivores on soil and vegetation were assessed by the use of paired fenced and unfenced plots over two successive growing seasons. Above‐ground biomass, litter production, changes in soil elevation, vertical soil accretion, shallow subsidence, below‐ground production of roots and rhizomes, the thickness of the root zone, soil bulk density, and soil organic matter were measured. 3 Above‐ground biomass, below‐ground production, soil elevation and the expansion of the root zone decreased due to herbivore activity. Litter production, the rate of soil surface accretion and shallow soil subsidence were all higher in grazed compared to ungrazed plots, while soil organic matter and bulk density did not differ significantly between treatments. 4 The results indicate that herbivores can have a negative effect on soil building processes, primarily by reducing below‐ground production and expansion of the root zone. Where natural rates of mineral sediment deposition are high, coastal marshes are expected to persist, despite herbivore activities. However, where sediment inputs are substantially less, herbivores may lead to destruction of habitat.
Forest fragmentation effects on palm diversity in central Amazonia
Authors: Scariot Aldicir 
Published: March 2003

1The effects of fragmentation on quantitative measures of floristic diversity in a palm community were examined in the Biological Dynamics of Forest Fragments study area in central Amazonia. Three 1‐ha, three 10‐ha, two 100‐ha and three continuous forest reserves, distributed among three sites, were surveyed. In each reserve, 10 20 × 20 m plots were sampled, resulting in a total of 110 plots representing 4.4 sampled hectares.2The taxon composition of this palm community was dominated by stemmed, understorey palms. A total of 23 225 individuals from 36 taxa was recorded; five of the taxa were not sampled in continuous forest.3Taxa richness did not vary across reserve size or sites unless taxa not sampled in the continuous forest were removed from the analysis. Smaller forest fragments then harboured fewer taxa in the seedling stage than large forest fragments or continuous forest, despite the short time since isolation (10–15 years). There was a significant effect of location on the number of taxa per plot for all life stages, but only seedling and total were significantly affected by reserve size.4Reserve size did not affect the Shannon and Evenness indices. Reserves of similar sizes were floristically more similar than reserves of very different sizes.5Palms are important for the structure and composition of the forest. Their conservation may require the establishment of a number of large reserves.
Spatial and temporal dynamics of epidemics of the rust fungus Uromyces valerianae on populations of its host Valeriana salina
Authors: Ericson L. , Burdon J. J. , Müller W. J. 
Published: March 2003

Summary 1 Analysis of the dynamics of rust disease caused by Uromyces valerianae in 30 discrete populations of Valeriana salina occurring on an archipelago of small islands in the Gulf of Bothnia, central Sweden, showed strong temporal and spatial effects. 2 Over a 13‐year period, the population dynamics of the pathogen varied across the metapopulation, with disease incidence (presence/absence), prevalence and severity all showing strong population and year effects, indicative of heterogeneity among years and host populations in the suitability of conditions for the pathogen. While some individual populations were infected for the entire study period, others were infected for only 1 or 2 years. Local pathogen population extinction and recolonization events were relatively common, with annual recolonization rates of previously healthy populations ranging from 0% to 13.3%. 3 The incidence of disease within individual host populations was significantly affected by host population size, the prevalence of disease in the previous year and the proximity of neighbouring populations that were infected in the current year. The prevalence of disease in infected populations only depended on the prevalence of disease in the previous year. There was little to choose between disease prevalence and severity in predictive power. 4 Overall, the dynamical behaviour of this set of pathogen demes best fit that predicted for a metapopulation with considerable asynchrony in epidemiological patterns between different demes, despite evidence of among‐population migration.
Foliage area and crown nitrogen turnover in temperate rain forest juvenile trees of differing shade tolerance
Authors: Lusk Christopher H. , Contreras Olga 
Published: March 2003

Summary 1 Shade‐tolerant angiosperm trees are reported to require relatively fertile soils in temperate forests. We explored the possibility that high foliage allocation in shade‐tolerant species could result in higher whole‐plant nitrogen demands than in light‐demanding trees of comparable diameters. We measured foliage mass and area, leaf life span, and nitrogen (N) content of fresh foliage and leaf litter for juveniles of 11 evergreen angiosperms in a Chilean temperate rain forest. This permitted estimation of annual nitrogen losses in leaf litter fall by individuals of a given diameter. 2 Leaf life spans were longest in shade‐tolerant species. The highest leaf N levels were found in small short‐lived early successional trees, whereas among longer‐lived species there was no general relationship of leaf N with shade tolerance level. Shade‐tolerant species had lower N resorption efficiencies, and therefore higher leaf litter N concentrations on an area basis, than light‐demanding associates. 3 Foliage mass, foliage area and total crown N pool were strongly positively related to shade tolerance level. 4 Interspecific variation in annual N losses in leaf litter fall was more closely related to foliage area (R2 = 0.52) than to N concentration of leaf litter (R2 = 0.31) or leaf lifetimes (R2 = 0.01). Although the short‐lived early successional species Embothrium coccineum had the highest annual crown N losses of the 11 species, shade‐tolerant species had higher annual losses than light‐demanding overstorey dominants of comparable longevities. 5 The results are consistent with the proposal that the costs of obtaining enough N for crown maintenance and expansion may constrain the fitness of shade‐tolerant angiosperm trees in late successional stages on infertile sites, when soil nutrient availability is reduced by increased uptake and sequestration in biomass and litter. On the other hand, high N loss rates may be more sustainable for short‐lived early colonists that complete their life cycles in the initial stages of secondary succession, when nutrient availabilities are often relatively high.
Infection of Trientalis europaea by the systemic smut fungus Urocystis trientalis: disease incidence, transmission and effects on performance of host ramets
Authors: Piqueras Jesús 
Published: March 2003

Summary 1 The effects of fungus infection on a natural population of the pseudoannual plant Trientalis europaea were followed for 4 years. 2 The incidence of the disease was low, showed little temporal variation during the period of study and was not affected by ramet size. Disease reduced flowering, fruiting, stolon length and the number and size of daughter tubers, all of which were positively correlated with ramet size. The year–disease interaction was not significant, except for flowering, suggesting little variation in the aggressiveness of the pathogen. 3 Disease reduced survival of ramets to the end of the growing season, although the effect varied with ramet size, and decreased tuber survival both by reduction of tuber size and by reduction of the overwintering ability of tubers of a given size. 4 For two of the three annual transitions the size of the offspring ramets was affected negatively by infection in the previous year. 5 Disease transmission occurred along the stolons of only 31% of the diseased ramets. The probability of disease being shown in the following year decreased with stolon length. 6 Although disease had a detrimental effect on ramet fitness, the low level of incidence and the stability of the clone dynamics in simulation models suggest only a minor role of the disease in population regulation in this species.
Seed bank formation during early secondary succession in a temperate deciduous forest
Authors: Hyatt Laura A. , Casper Brenda B. 
Published: March 2003

Summary 1 Seed banks are dynamic entities, with input occurring through dispersal and loss occurring through germination and various sources of mortality. Measures of abundance of seeds in the soil at one point in time cannot distinguish those seeds destined to germinate or die in the next growing season from those entering the long‐term seed bank, and cannot therefore reveal the proportion of seeds that are carried over from year to year. 2 We studied seed bank dynamics in a 2.5‐ha deciduous forest gap by following the fate of a single year’s cohort of seeds over 2 years. Seed input for 1 year, subsequent in situ germination and survivorship were measured at 60 locations. We examined how temporal changes in seed bank composition were affected by the presence of the dominant gap colonizing species Rubus allegheniensis. 3 Over the course of 2 years, both mean seed density and its variance declined. The temporal changes in density were not, however, accompanied by detectable changes in diversity. 4 Three species (R. allegheniensis, Phytolacca americana and Paulownia tomentosa) dominated the seed bank. Seed bank accumulation patterns in Rubus and Phytolacca showed contrasting responses to the presence of Rubus, with Phytolacca excluded from seed banks in such patches through reduced input and increased mortality. 5 First year germination and post‐dispersal mortality interact with seed input to influence the spatial distribution of density and diversity in the long‐term seed bank. Substantial long‐term seed banks do form within temperate forest gaps and patterns of above‐ground vegetation can have substantial effects on their dynamics.
Root hemiparasites and plant diversity in experimental grassland communities
Authors: Joshi Jasmin , Matthies Diethart , Schmid Bernhard 
Published: March 2003

Summary 1
We studied the relationship between the diversity of grassland communities and the effects of the generalist hemiparasitic plant Rhinanthus alectorolophus. We compared resistance against biomass loss as a consequence of infection, performance of the parasite and resistance of the parasitized communities to invasion by other plant species. Seeds of the parasite were sown into experimental plots containing 1, 2, 4, 8 or 32 plant species belonging to one or more of three functional groups (grasses, legumes and non‐leguminous herbs). 2  We predicted that infection will reduce host biomass, total community biomass and resistance to invasion, particularly in host communities with low diversity, but that the performance of the parasite will be at its lower level in such communities. 3  The presence of the parasite caused an overall reduction in host biomass per plot, which was mainly due to a strong reduction in the biomass of grasses. As predicted, the effect was smaller in communities with greater functional diversity. However, total community biomass (including the parasite biomass) was increased by more than a third in infected communities of one or two host species, while the parasite had no effect on total biomass of species‐rich communities. 4
Germination of the parasite was hardly influenced by the diversity of its host community, but early survival decreased with increasing number of functional groups and was lower in plots with legumes than without. However, our hypothesis that the performance of the surviving parasites would benefit from a high functional diversity of hosts was supported. Parasite biomass per individual and per m2 increased with the number of functional groups in the host community, as did reproductive potential. 5  Death of the parasite led to a higher proportion of bare ground in communities when the previously infected communities had low functional diversity, thus enabling subsequent colonization by weeds.
Origin and temporal development of macro‐scale vegetation patterns in the cultural landscape of Denmark
Authors: Odgaard Bent Vad , Rasmussen Peter 
Published: March 2003

Summary 1 Since the introduction of agriculture, 4000 bc, the Danish region has witnessed a change from almost complete woodland cover to the landscapes present at ad 1800 that were dominated by heathland, cultivated areas, grassland or patchy woodland. We used a combination of pollen records and landscape data to identify the timing and major pathways of this land‐cover transformation. 2 Pollen assemblages dated to about ad 1800 were collected from 20 Danish lakes with a median size of 26 ha. Fossil pollen records for the interval 4500 bc − ad 1800 were compiled from 11 of these 20 sites and divided into 11 time units corresponding to major archaeological periods. 3 Land cover around the 20 sites was digitized from historical maps, dating from the same period as the pollen assemblages. Percentage cover of woodland, heathland, wetland and agricultural land within 2‐ and 5‐km radii were calculated (calculations were also made within 10‐ and 20‐km radii for woodland). Environmental data within 5 km of each site were collected from soil, geological and topographical maps. 4 The ad 1800 pollen assemblages formed three clusters characterized by either a dominance (> 20%) of Calluna (group A), a dominance (> 10%) of Fagus (group B) and a dominance of Poaceae with Fagus < 10% and Calluna < 20% (group C). Respectively, these clusters correspond well to sites where heathland is the dominant land cover, where it has a strong woodland element and where agricultural land is dominant with little, if any, woodland or heathland. 5 Direct and indirect ordinations suggest that the main variation in the pollen assemblages from the 20 sites is related to gradients in soil clay content and in the degree of landscape openness. Land‐cover data from within a 2‐km radius account for almost as much of the variation in pollen data as do land‐cover data from within a 5‐km radius. 6 Indirect ordinations of ad 1800 samples with the fossil records as passive samples reveal that long‐term records from cluster B sites (the ‘1800 woodland type’) show little landscape variation through time. Samples from cluster C sites (the ‘1800 agricultural area type’) show the same starting point as cluster B but their development diverge to more open landscapes. Cluster A sites (the ‘1800 heathland type’) either develop directly from rather wooded landscapes to heathland or by heathland expansion after initial development towards landscapes producing cluster C type pollen assemblages. 7 Chord distances between the ad 1800 sample and the (pre)historic samples at 10 long‐term sites strongly suggest that the between‐site variation in land‐cover characteristic of the early 19th century was already in existence by 1000 bc. Direct ordination of the fossil samples using woodland cover at ad 1800 as an environmental variable and soil clay content as a covariable also indicates that the macro‐scale land‐cover patterns of the historical cultural landscape in Denmark has been present for more than 3000 years.
The role of Equisetum in nutrient cycling in an Alaskan shrub wetland
Authors: Marsh Anne S. , Arnone John A. , Bormann Bernard T. , Gordon John C. 
Published: March 2003

Summary 1 Although plants of Equisetum spp. are generally thought to be of little value to ecosystems, a study of a cold‐temperate Alaskan shrub wetland showed that they acquired and cycled phosphorus and other nutrients more efficiently than other plant community members. While Equisetum plants represented only 5% of the above‐ and below‐ground biomass in the community, they contained 16% of the P and 24% of the K. 2 Equisetum plants accounted for 29% of the P and 39% of the K in annual community foliage litterfall. Over a 2‐year period, losses from Equisetum litter contributed 55, 41, and 75% of the P, K and Ca litter inputs into soil nutrient pools. 3 The ability of different species of Equisetum to acquire nutrients is linked to their deep rooting habit. While the majority of their roots and rhizomes, and particularly the fine roots, were located in the C horizon, the majority of roots and rhizomes of other species were located in the overlying O horizon. The biomass of Equisetum plants was also correlated with edaphic characteristics of the C horizon. 4 The absorption of nutrients from the C horizon by Equisetum helped bring P and other minerals to the soil surface, increasing the amount of minerals in the O horizon and thus making them potentially available to other species, including Myrica gale, Salix spp., and Carex spp. Productivity in this community is limited by P and N, and the ability of Equisetum to act as a nutrient pump may help explain why its net primary productivity is high for a cold‐temperate wetland.
Morphological plastic responses to water depth and wave exposure in an aquatic plant (Myriophyllum spicatum)
Authors: Strand John A. , Weisner Stefan E. B. 
Published: March 2003

Summary

We investigated morphological responses of the submerged macrophyte Myriophyllum spicatum L. to water depth and wave exposure when grown in the same substrate at two sites in two eutrophic lakes. Periphyton production was 4–8 times higher at sheltered than at wave‐exposed sites and its influence was further investigated in a glasshouse experiment. Morphological responses in both experiments were compared by allometric analyses, with shoot weight as covariate.
In the field study, plants shoots exhibited similar responses (increased plant height and branch length, and decreased branch number) to sheltered conditions as to deep water. The partitioning between above‐ and below‐ground biomass however, differed, with below‐ground decreasing with an increasing water depth, but increasing or remaining unaffected at sheltered compared with exposed conditions.
In the glasshouse experiment, plant responses to water depth were similar to those in the field study. Furthermore, plant height increased when plants were overgrown with periphyton.
High production of periphytic algae at sheltered sites appears to cause light limitation of macrophytes. However, other factors such as nutrient uptake also appears to determine morphological responses. At sheltered sites, where leaf nutrient uptake is reduced by abundant periphyton and thick boundary layers, plants allocate more biomass to roots. At deep and wave‐exposed sites, the absence of periphyton allows plants to take up nutrients through their leaves and allocation of biomass to shoots increases photosynthesis.
Overall, relative allocation to shoot and root biomass appears to be primarily controlled by nutrient availability, whereas allocation of available shoot biomass to particular structures is controlled by light availability.
The relationship of total and per‐gram rankings in competitive effect to the natural abundance of herbaceous perennials
Authors: Howard Timothy G. 
Published: March 2003

Summary

Using a field experiment and a garden experiment, I estimated the rankings in total and per‐gram competitive effect of non‐woody perennial old‐field species.
Total competitive effects were defined as the relative reduction in growth of a target from no‐neighbour to with‐neighbour conditions. Per‐gram competitive effects were defined as the per‐unit relative reduction in target growth among increasing neighbour densities, and were determined from the shape of a nonlinear curve fit through a distribution of normalized target performance against neighbour mass.
In both experiments, mean total competitive effect differed significantly among species, indicating a strong competitive hierarchy. In the garden experiment only species at opposite ends of the ranking differed significantly in per‐gram competitive effect, resulting in a weaker competitive hierarchy based on this measure.
Nonetheless, rankings of per‐gram competitive effect were more strongly correlated with rank in abundance than were rankings of total competitive effect.
Per‐gram competitive effect may be more predictive of natural abundance than total competitive effect for at least two reasons. The effects of neighbour abundance on targets are nonlinear, and unlike total effects, per‐gram estimates of competitive effect may therefore indicate how competition changes over time with changing neighbour densities. Also, if higher per‐gram competitive effect reflects higher per‐unit nutrient uptake rates, it would probably be advantageous to a species throughout the individual’s life span, rather than only when the individual is larger than its surrounding neighbours.
Rodent‐limited establishment of bush lupine: field experiments on the cumulative effect of granivory
Authors: Maron John L. , Simms Ellen L. 
Published: March 2003

Summary

Plants often suffer substantial loss of seeds to consumers. However, because the seed‐to‐seedling transition is frequently ignored, quantitative estimates of the effects of seed consumers on plant population dynamics are rare.
We examined how post‐dispersal seed predation by rodents affected seedling emergence and subsequent adult plant abundance of bush lupine (Lupinus arboreus), a large N‐fixing shrub common to coastal dunes in California. We monitored patterns of seedling emergence and survival over 3 years for seeds sown into exclosed and control plots.
We sowed additional cohorts of seeds in the second and third years and compared interannual variation in emergence patterns.
Rodent exclusion substantially reduced seedling emergence, with an average of 109 seedlings emerging over 3 years from 476 seeds sown in rodent exclusion plots vs. 26 from control plots. The intensity of granivory, however, varied between years, with rodent exclusion increasing emergence from seeds sown in year one, but not in year two.
Winter seedling mortality, due to cutworm herbivory, was similarly high in rodent‐free and control plots, and its net impact was to reduce the difference in seedling abundance. Thus, by mid‐summer in each of the three years, there were only marginally more seedlings in rodent‐excluded vs. control plots.
The cumulative effect of protecting seeds, was, however, large. After 3 years, an average of four adult lupines were established in rodent‐free plots, whereas only 0.5 were found in control plots and lupine biomass was more than 5‐fold higher in exclusion plots.
Taken together, the results indicate that rodents play a critical role by limiting the abundance and biomass of a large N‐fixing shrub in dunes.