bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seed dispersal, seedling establishment and gap partitioning among tropical pioneer trees
Authors: Dalling J. W. , Hubbell Stephen P. , Silvera Katia 
Published: May 2003

1 We examined the abundance and distribution patterns of pioneer seeds in the soil seed bank, and of pioneer seedlings in 53 recently formed gaps, in a 50‐ha forest dynamics plot on Barro Colorado Island (BCI), Panama. The aim was to assess the importance of dispersal limitation (failure of seeds to arrive at all sites suitable for their germination) and establishment limitation (failure of seeds having reached a site to germinate successfully and establish as seedlings) in determining patterns of gap occupancy. 2 The abundance of seeds in the soil seed bank was strongly negatively correlated with seed size, but was not correlated with the abundance of reproductive‐sized adult trees in the plot. In contrast, the abundance of pioneer seedlings > 10 cm height in natural gaps was strongly correlated with adult abundance, but was not correlated with seed size. 3 Seedlings were non‐randomly distributed among gaps, but seedling abundance was not directly related to gap size, and there was no evidence of partitioning of the light environment of gaps by small seedlings. Large differences in growth and mortality rates among species were observed after 1 year, and this may result in the gap size partitioning previously found in saplings of the same species. 4 Seedlings of most species, particularly those with large seeds, were relatively more abundant than expected in gaps close to their conspecific adults. Proximity to reproductives, and by inference dispersal limitation, therefore exerts some effect on seedling distribution. None the less, large differences between seed and seedling abundances for some species, and low seedling occupancy rates in some gaps close to adult conspecifics, suggest that seedling emergence probabilities and species‐specific establishment requirements may also be important determinants of local abundance.
Comparative ecology of 11 sympatric species of Macaranga in Borneo: tree distribution in relation to horizontal and vertical resource heterogeneity
Authors: Davies Stuart James , Palmiotto Peter A. , Ashton Peter S. , Lee Hua Seng , Lafrankie James V. 
Published: May 2003

1 Horizontal and vertical heterogeneity of resource availability, coupled with the specialized use of resources by tree species, results in complex patterns of tree species distributions in tropical rain forests. We studied the horizontal and vertical distributions of 4014 individuals in 11 species of early successional Macaranga (Euphorbiaceae) in tropical rain forest in Sarawak, Malaysia. 2 The horizontal distribution of individual trees was assessed with respect to crown light levels, establishment microsites, and broader scale variation in soil textural properties. Vertical distribution was assessed using an allometric approach to estimate maximum tree height (Hmax) and the slope of the sapling height–diameter relationship. 3 Average light levels intercepted and the proportion of individuals in each of five crown illumination classes varied significantly among the 11 species. Species ranged from extremely high‐light demanding, to quite shade tolerant. Average light levels intercepted by trees generally increased through ontogeny, but the ranking of species did not change significantly. 4 Fewer individuals of the more shade‐tolerant species established on disturbed microsites, irrespective of light levels. Among the more high‐light demanding species, the proportion of trees on different types of disturbed sites varied. 5 Trees of seven species were significantly more common on clay‐rich soils, two preferred sand‐rich soils, and two were not strongly affected by soil texture. 6 Hmax ranged from 5.5 to 31.3 m and was negatively correlated with shade tolerance among species, although among the more high‐light demanding species there was a wide range of tree sizes. Among species, Hmax was negatively correlated with both the slope and y‐intercept of the sapling height–diameter relationship, indicating that small‐statured species (also more shade tolerant) had more slender saplings than larger statured species. 7 Heterogeneity of resource availability leads to differences in horizontal and vertical tree distribution, which are important for the coexistence of 11 Macaranga species.
The effects of air‐borne nitrogen pollutants on species diversity in natural and semi‐natural European vegetation
Authors: Bobbink Roland , Hornung Michael , Roelofs Jan G. M. 
Published: May 2003

Summary

The effects of increased atmospheric nitrogen inputs, from both NOy and NHx, on diversity in various semi‐natural and natural ecosystems are reviewed. The severity of these impacts depends on abiotic conditions (e.g. buffering capacity, soil nutrient status and soil factors that influence the nitrification potential and nitrogen immobilization rate) in the particular system. The sensitivity of fresh water ecosystems, wetlands and bogs, species‐rich grasslands, heathlands and field layer of forests, all of which have conservational value, are discussed in detail.
The most important effects of nitrogen deposition are: (i) accumulation of nitrogenous compounds resulting in enhanced availability of nitrate or ammonium; (ii) soil‐mediated effects of acidification; and (iii) increased susceptibility to secondary stress factors.
Long‐term nitrogen enrichment has gradually increased the availability of nitrogen in several vegetation types, leading to competitive exclusion of characteristic species by more nitrophilic plants, especially under oligo‐ to mesotrophic soil conditions.
Soil acidification (with losses of buffering capacity and increased concentrations of toxic metals) is especially important after nitrification of ammonium in weakly buffered environments: acid‐resistant plant species then become dominant at the expense of the often rare plants typical of intermediate pH. The related change in the balance between ammonium and nitrate may also affect the performance of several species.
The susceptibility of plant species to secondary stress factors (pathogens; frost and drought) may be affected by air‐borne nitrogen but data are only available for a few communities (e.g. dry heathlands).
Most global biodiversity is contained within natural and semi‐natural vegetation. It is thus crucial to control emissions of nitrogenous compounds to the atmosphere, in order to reduce or prevent effects on diversity in these systems. Most research has focused on acidification in forestry stands and lakes and on the effects on trees. We highlight serious gaps in knowledge of other ecosystems.
Modelling the impact of small‐scale heterogeneities on tree—grass coexistence in semi‐arid savannas
Authors: Jeltsch F. , Milton S.J. , Dean W.R.J. , van Rooyen N. , Moloney K.A. 
Published: May 2003

Summary

Savanna ecosystems show codominance of trees and grasses, and the mechanisms involved in their coexistence remain unresolved. We investigated the possible influence of small‐scale heterogeneities and disturbances in determining tree spacing and tree‐grass coexistence in semi‐arid savannas, using a spatially explicit, grid‐based simulation model.
We added factors such as seed clumping, locally improved moisture conditions, vegetation clearing and combinations of all three of these variables to a previously published model. We also examined the influence of changing the size and spatiotemporal correlation among individual heterogeneities.
Increased seed availability in localized clumps, especially in combination with the other heterogeneity types, had the strongest impact on the long‐term tree‐grass coexistence in the model. Localized deposition of tree seeds in herbivore dung and underground seed caches built by seed‐collecting rodents may act as a determinant of the distribution of trees in savannas.
Spatially autocorrelated small‐scale heterogeneities led to a more stable coexistence of trees and grasses than uncorrelated heterogeneities did, and at high levels of autocorrelation runs with all three variables led to long‐term coexistence in up to 60% of the rainfall scenarios tested.
The size of individual heterogeneities, also played a significant role in determining whether trees would establish as lone individuals or in clumps. In simulations that included small‐scale heterogeneities, the number of isolated trees scattered throughout the landscape increased, whereas large heterogeneity patches and high spatiotemporal autocorrelation tended to promote tree clustering.
Simulations based on rainfall data from the southern Kalahari produced a realistic density and spatial distribution for trees in this semi‐arid savanna for a realistic range of small‐scale heterogeneities.
Small‐scale disturbances and heterogeneities, at least those that furnish better establishment conditions for tree seedlings, therefore act to increase the range of environmental conditions under which trees and grasses can coexist as savanna.
Effects of nitrogen addition on successional dynamics and species diversity in Michigan old‐fields
Authors: Huberty Lisa E. , Gross Katherine L. , Miller Carolyn J. 
Published: May 2003

Summary

We examined the impact of nitrogen addition on early successional dynamics and plant species diversity in replicate plots of an old‐field succession treatment in south‐western Michigan, USA, for 7 years following abandonment from agriculture.
Nitrogen addition significantly increased above‐ground plant biomass, but had no effect on the displacement or persistence of different life‐history groups. Annual species made up a similar proportion of community biomass and decreased at equivalent rates in control and nitrogen‐addition microplots. Perennial species biomass increased at similar rates in the control and nitrogen‐addition microplots.
Annual species dominated initially, but declined in abundance over the first 4 years and were replaced by biennials and then herbaceous perennials. The resulting high numbers of species losses and gains were not affected by nitrogen addition.
Nitrogen addition did not affect mean species density or the Shannon index of diversity. There was also no temporal change in the similarity of species composition between control and nitrogen‐addition microplots, indicating that nitrogen addition did not cause divergence over time in community composition. In year 7, similar species dominated the nitrogen‐addition and control microplots, but there were differences in species composition and abundance of the subordinate species in each community.
Only in year 6 of this study was there a significant negative relationship between community biomass and the Shannon diversity index. There was no significant relationship between community biomass and species density in any of the first 7 years following abandonment. Thus, the community response to increased biomass due to nitrogen addition was expressed primarily through changes in community structure, not richness.
The effects of nitrogen addition on the early successional dynamics, species composition and consequently diversity of a plant community may depend on initial site conditions. The response to nitrogen enrichment may be slower in sites such as ours with fertile soils that become dominated by herbaceous perennial dicots.
Fire and vegetation dynamics in a jack pine and black spruce forest reconstructed using fossil pollen and charcoal
Authors: Larsen C.P.S. , Macdonald G.M. 
Published: May 2003

Summary

Fire and vegetation dynamics in a boreal Pinus banksiana and Picea mariana forest are reconstructed using a 580 year fossil pollen and charcoal record obtained from 128 contiguous samples, each representing c. 4.55 years of sediment.
The general post‐fire vegetation changes, as indicated by cross‐correlation analyses, are an increase in ground layer taxa and shrubs, followed by an increase in coniferous trees and Betula papyrifera. The size and exact timing of the peak abundance in each taxon differs after individual fires.
Sixteen fires are identified using pollen and charcoal records. The mean fire interval is 34 years, similar to fire cycle estimates of 38 and 39 years from dendrochronological studies.
On two occasions, Picea mariana appears to replace Pinus banksiana as the local dominant, each time taking less than 70 years.
An unusual decline in Pinus pollen between c. AD 1816 and 1861 corresponds with a similar decline in a pollen record from 50 km WSW of this site. This may have been caused by Little Ice Age cooling.
Demographic and growth responses of a guerrilla and a phalanx perennial grass in competitive mixtures
Authors: Humphrey L. David , Pyke David A. 
Published: May 2003

Summary

The advantages of guerrilla and phalanx growth for the guerrilla Elymus lanceolatus ssp. lanceolatus and phalanx E. l. ssp. wawawaiensis were evaluated over 2 years in two taxon mixtures with a range of densities of each subspecies and under two levels of watering.
Ramet numbers and biomass of the guerrilla subspecies were higher than those of the phalanx grass in the first year but in the second year declined greatly, while the phalanx grass showed no change in biomass and an increase in ramet numbers. High neighbour densities affected the phalanx subspecies more strongly than the guerrilla subspecies in the first year, but in the second year there were few differences between subspecies. Biomass of the guerrilla grass remained greater than that of the phalanx grass but ramet numbers were similar in the second year.
For both subspecies in both years, probability of flowering decreased at higher neighbour densities, indicating adaptation for competitive ability. In the first year, biomass was more strongly reduced by densities than flowering was, but in the second year, when crowding was apparently greater, flowering was more severely affected.
Genet survival was high and similar for both subspecies.
The presumed advantage of guerrilla subspecies in exploiting open space was supported. The guerrilla grass exploited resources more quickly in the first year by faster growth and greater ramet production, but its biomass, ramet numbers and rhizome growth, and thus its advantage, were reduced in the second year.
The phalanx subspecies had slower growth, produced more ramets in later years, and delayed flowering until later years. Although less able to exploit open resources, it appeared adapted to more stressful conditions, and may be able to exploit temporal resource pulses more effectively.
Pre‐school children with and without developmental delay: behaviour problems and parenting stress over time
Authors: Baker B. L. , McIntyre L. L. , Blacher J. , Crnic K. , Edelbrock C. , Low C. 
Published: May 2003

AbstractBackground  Children with intellectual disability are at heightened risk for behaviour problems and diagnosed mental disorder.Methods  The present authors studied the early manifestation and continuity of problem behaviours in 205 pre‐school children with and without developmental delays.Results  Behaviour problems were quite stable over the year from age 36–48 months. Children with developmental delays were rated higher on behaviour problems than their non‐delayed peers, and were three times as likely to score in the clinical range. Mothers and fathers showed high agreement in their rating of child problems, especially in the delayed group. Parenting stress was also higher in the delayed group, but was related to the extent of behaviour problems rather than to the child's developmental delay.Conclusions  Over time, a transactional model fit the relationship between parenting stress and behaviour problems: high parenting stress contributed to a worsening in child behaviour problems over time, and high child behaviour problems contributed to a worsening in parenting stress. Findings for mothers and fathers were quite similar.
Child behaviour problems and partner mental health as correlates of stress in mothers and fathers of children with autism
Authors: Hastings R. P. 
Published: May 2003

AbstractBackground  Previous research has suggested that the mothers and fathers of children with disabilities experience stress differently. Although there has been a great deal of research exploring how children affect parents, there have been many fewer studies of the interrelationships between mothers’ and fathers’ psychological well‐being.Methods  Eighteen married couples who were the parents of children with autism reported on their stress and their general mental health (i.e. anxiety and depression). Teachers rated the behaviour problems of the children with autism.Results  Mothers and fathers did not differ in their levels of stress and depression, but mothers reported more anxiety than fathers. Partial correlation analyses revealed that child behaviour problems and fathers’ mental health were associated with mothers’ stress. However, neither child behaviour problems or mothers’ mental health was associated with fathers’ stress.Conclusions  Although requiring replication, the results suggest that stress in mothers of children with disabilities may be affected by the psychological health of other family members, whereas fathers’ stress is affected more by other factors. Methodological and conceptual issues, and the practical implications of these results are discussed.
Depression: its trajectory and correlates in mothers rearing children with intellectual disability
Authors: Glidden L. M. , Schoolcraft S. A. 
Published: May 2003

AbstractBackground Rearing a child with an intellectual disability (ID) is a lifelong activity, and research needs to reflect the extended nature of the task as well as its complexity. The present longitudinal study reports on an 11‐year follow‐up of adoptive and birth families rearing children with ID. Its focus was on depressive symptoms and how these changed over time in a sample of 187 mothers. In particular, the authors were interested in whether initial differences in depression between adoptive mothers who knowingly and willingly decided to rear their children with disabilities, and birth mothers for whom the diagnosis of disability was unexpected and frequently crisis‐inducing, would persist over time.Methods A longitudinal method with three times of measurement provided data which were analysed with analysis of variance and regression techniques. Moreover, several other individual and family adjustment measures were examined with respect to their correlations with depression and an outcome variable that measured subjective well‐being with regard to the child. Furthermore, mothers were classified as typical or atypical for their adoptive/birth group based on their depression scores at the first time of measurement. The authors predicted that later depression would be different based on the earlier scores.Results Both adoptive and birth mothers reported low depression, not significantly different from each other, at the 11‐year follow‐up. The personality variable of neuroticism was the strongest predictor of depression for both adoptive and birth mothers, accounting for 24% and 23% of the variance, respectively, but it did not predict the mother's subjective well‐being with regard to the child. Mothers classified as typical or atypical for their groups at initial measurement continued to report significantly different depression scores 11 years later.Conclusions The low depression scores, not significantly different for birth and adoptive mothers, portray the long‐term prognosis for adjustment to rearing children with disabilities as primarily positive. Moreover, the predictive value of neuroticism suggests that general mental health is an important component influencing this adjustment. Nevertheless, a different pattern for a different outcome variable suggests that multiple measures are necessary to portray accurately the complexity of reaction over time.
Stress, social support and well‐being of Arab mothers of children with intellectual disability who are served by welfare services in northern Israel
Authors: Duvdevany I. , Abboud S. 
Published: May 2003

AbstractBackground  The present study examined the influence of a social support system on the level of stress and the sense of personal well‐being of 100 Israeli Arab mothers of young children with special needs.Methods  Fifty mothers were served by the welfare services in the Nazareth area while 50 did not get help on a regular basis. A comparison was done between educated, urban mothers, and less‐educated, rural mothers.Results  The research results point to a relationship between informal support resources, and the marital and economic stress of the mothers: the higher the amount of the informal support resources, the lower the level of stress that was experienced by the mothers. A relationship between the amount of informal support and level of parental stress was not confirmed. A relationship between the amount of support resources and the personal well‐being of the mothers was found: the higher the amount of informal support resources, the higher the sense of well‐being of the mothers. A relationship between formal support (the welfare services), and level of stress or personal well‐being was not found. Education and place of living were not related to level of stress or personal well‐being. Educated mothers from urban areas used the formal support (the welfare services) less than less‐educated mothers who lived in rural areas.Conclusions  The findings are interpreted with respect to practice and previous studies.
Fathers of children with Down's syndrome versus other types of intellectual disability: perceptions, stress and involvement
Authors: Ricci L. A. , Hodapp R. M. 
Published: May 2003

AbstractBackground  The present study examined fathers’ perceptions of, stress relating to and involvement with children with Down's syndrome (DS) (n = 30) versus those with other types of intellectual disability (ID) (n = 20).Methods  Fathers and mothers completed questionnaires about their children's personalities and maladaptive behaviours, their own parenting stress, and the fathers’ level of involvement.Results  Both fathers and mothers rated their children with DS as having more positive personality traits and fewer maladaptive behaviours. Possibly because of these positive perceptions, fathers of children with DS also reported less child‐related stress, particularly in the areas of acceptability, adaptability and demandingness. The two groups of fathers were very similarly involved in child rearing. The personality, age and maladaptive behaviours of the children related to stress levels in the fathers of children with DS, while maladaptive behaviours, gender and the fathers’ education levels related to stress levels in the fathers of children with other types of ID.Conclusions  These results highlight the importance of examining parental stress and involvement with children with different types of ID.
The Family Stress and Coping Interview for families of individuals with developmental disabilities: a lifespan perspective on family adjustment
Authors: Nachshen J. S. , Woodford L. , Minnes P. 
Published: May 2003

AbstractBackground  The present study investigated the psychometric properties of the Family Stress and Coping Interview (FSCI), a questionnaire designed to quantitatively and qualitatively examine the experiences of parents of children with developmental disabilities (DDs).Methods  The participants consisted of 106 primary caregivers of 106 individuals with DDs from centres in Eastern, Central and North‐western Ontario, Canada. The participants completed a demographic questionnaire, the FSCI, and the Vineland Adaptive Behaviour Scales.Results  The results of this study indicate that the FSCI has adequate reliability (i.e. internal consistency and long‐term stability) and validity (i.e. independent item ratings and discriminant validity).Conclusions  The results of this study support the use of the FSCI as a measure of family stress in research and practice.