bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biotic resistance to invader establishment of a southern Appalachian plant community is determined by environmental conditions
Authors: VON HOLLE BETSY 
Published: January 2005

Summary

Tests of the relationship between resident plant species richness and habitat invasibility have yielded variable results. I investigated the roles of experimental manipulation of understorey species richness and overstorey characteristics in resistance to invader establishment in a floodplain forest in south‐western Virginia, USA.
I manipulated resident species richness in experimental plots along a flooding gradient, keeping plot densities at their original levels, and quantified the overstorey characteristics of each plot.
After manipulating the communities, I transplanted 10 randomly chosen invaders from widespread native and non‐native forest species into the experimental plots. Success of an invasion was measured by survival and growth of the invader.
Native and non‐native invader establishment trends were influenced by different aspects of the biotic community and these relationships depended on the site of invasion. The most significant influence on non‐native invader survival in this system of streamside and upper terrace plots was the overstorey composition. Non‐native species survival in the flooded plots after 2 years was significantly positively related to proximity to larger trees. However, light levels did not fully explain the overstorey effect and were unrelated to native survivorship. The effects of understorey richness on survivorship depended on the origin of the invaders and the sites they were transplanted into. Additionally, native species growth was significantly affected by understorey plot richness.
The direction and strength of interactions with both the overstorey (for non‐native invaders) and understorey richness (for natives and non‐natives) changed with the site of invasion and associated environmental conditions. Rather than supporting the hypothesis of biotic resistance to non‐native invasion, my results suggest that native invaders experienced increased competition with the native understorey plants in the more benign upland habitat and facilitation in the stressful riparian zone.
Multiple resources limit plant growth and function in a saline‐alkaline desert community
Authors: JAMES J. J. , TILLER R. L. , RICHARDS J. H. 
Published: January 2005

Summary

We investigated resource limitations in a saltbrush scrub community along a salinity‐alkalinity gradient in the Mojave Desert of North America. Previous studies have shown that, as productivity declines with increasing soil stress, there are parallel declines in leaf Ca and Mg, suggesting availability of these resources may limit growth in addition to water, N and P limitations expected in deserts.
To determine which soil resources limited growth of the dominant shrub, Atriplex parryi, and whether this differed along the soil stress gradient or among life stages, water and nutrients were applied in combination at different rates to plants at high‐ and low‐stress sites. We developed and applied a conceptual model to identify resource limitations from this experiment. We also investigated how those limitations interacted to influence A. parryi growth and physiological function at the high‐stress site.
Availability of soil N and P limited growth at the low‐stress site and N, P and Mg limited growth at the high‐stress site for both adult and juvenile life stages. There was no evidence that availability of water alone or K, Ca or other nutrients, or increasing soil Na and B, limited growth along the soil stress gradient.
When N, P, Mg and water were supplied in combination, plant growth increased more than 16‐fold. Supply of these resources interacted to influence both plant growth and function. Because of the high demand for N relative to other resources, N supply rate was the major driver of these interactions, influencing the magnitude by which P and Mg affected growth. The major mechanism behind these growth responses was an increase in allocation to leaves relative to fine roots, rather than nutrient or water effects on water relations, photosynthesis or water use efficiency.
Multiple, interacting resources limit the growth and distribution of A. parryi on a saline, alkaline Mojave Desert site. Similar interactions between multiple limiting resources are likely to be instrumental in shaping community and species distributions along other abiotic stress gradients.
The impact of hemiparasitic plant litter on decomposition: direct, seasonal and litter mixing effects
Authors: QUESTED HELEN M. , CALLAGHAN TERRY V. , CORNELISSEN J. HANS C. , PRESS MALCOLM C. 
Published: January 2005

Summary

Nutrient‐rich litter of hemiparasites (and N‐fixers) has the potential to influence ecosystem‐level decomposition and nutrient cycling, which may be important in ecosystems where productivity is nutrient limited. This influence may be both direct, and indirect via impacts on the decomposition of other species’ litters in mixed‐species litter layers.
We investigate the importance of these direct and indirect effects of sub‐arctic hemiparasite litter in a litterbed study and a field litterbag experiment, and compare these data with those from a microcosm study also involving litter mixtures.
Field‐placed litterbags demonstrate for the first time the direct importance of hemiparasite litter on decomposition and nutrient cycling in a field setting: litter of the hemiparasite Bartsia alpina lost 18 times more N over 2 years than Betula nana litter.
The majority of this N was released during the growing season, strongly supporting the proposal that hemiparasites can have a substantial direct impact on nutrient availability to other plants. The short spring and autumn periods were important for litter mass and N dynamics, with consequences for predicting effects of environmental change.
However, hemiparasite litter did not indirectly affect the decomposition rate or nutrient release from litter mixtures in field‐placed litterbags. Furthermore, the direction and magnitude of litter mixing effects on mass loss varied strongly between methods; interactions were absent or negative in the litterbed, non‐significant in field litterbags and positive in microcosms.
We thereby demonstrate the importance of the decomposition environment, rather than species‐specific litter quality, in determining litter‐mixing interactions, with implications for evaluating the impact of particular species on ecosystem carbon and nutrient fluxes via litter mixing
We conclude that hemiparasites have a particular functional role in sub‐arctic heath systems: in effect they ‘short circuit’ generally slow nutrient cycles, with potential impacts on resource patchiness and local scale biodiversity.
An evaluation of peripheral blood eosinophil/basophil progenitors following nasal allergen challenge in patients with allergic rhinitis
Authors: Wilson A. M. , Duong M. , Crawford L. , Denburg J. 
Published: January 2005

SummaryObjective
To evaluate the effect of a single nasal allergen challenge on peripheral blood eosinophil/basophil (Eo/B) progenitor cells and induced sputum eosinophil counts in subjects with allergic rhinitis.Methods
Sixteen adults entered a sequential nasal control and allergen challenge study, outside the pollen season. Blind assessment of peripheral blood Eo/B progenitor colony forming units (CFU), induced sputum and nasal lavage cell counts was made before and 24 h after both challenges. Subjects recorded their rhinitis symptoms and nasal peak inspiratory flow, hourly at home, following both challenges.Results
When comparing the values 24 h after the control vs. the allergen challenge, there were no significant differences in Eo/B progenitor CFU (control (mean, SD): 3.6 (1.0)/106 cells; allergen: 4.4 (1.1)/106 cells) or sputum eosinophils (control (median, inter‐quartile range): 1.0 (0.3–1.7)%; allergen: 0.7 (0.0–1.3)%) despite a significant increase in the percentage (median (inter‐quartile range) of eosinophils in nasal lavage (control: 0.6 (0.1–0.9)%; allergen; 1.9 (0.9–8.1)% and significant worsening of nasal peak inspiratory flow and rhinitis symptoms.Conclusions
Despite a significant increase in nasal symptoms and lavage eosinophil counts, a single nasal allergen challenge was not sufficient to elicit a measurable haemopoietic response in circulation, or an increase in sputum eosinophil counts.
Induction of nasal hyper‐responsiveness by allergen challenge in allergic rhinitis: the role of afferent and efferent nerves
Authors: Sheahan P. , Walsh R. M. , Walsh M. A. , Costello R. W. 
Published: January 2005

SummaryBackground
Hyper‐responsiveness of nasal secretory function and volume changes are features of allergic rhinitis (AR) that are mediated in part by neural mechanisms. The finding of nasal hyper‐responsiveness in subjects with AR who are currently symptomatic, but not in those who are currently out of season and asymptomatic, suggests that induction of neural reflexes in allergic subjects occurs as a result of allergic inflammation.Objectives
To investigate whether allergen exposure in subjects with asymptomatic seasonal allergic rhinitis (SAR) may lead to induction of neural reflexes, and to investigate the components of the reflexes involved in this induction.Methods
Asymptomatic subjects with (out‐of‐season) SAR underwent a nasal bradykinin challenge, before and 24 h after preceding ipsilateral (n=11) and contralateral (n=11) antigen challenge. Challenges were performed and nasal secretions collected using filter paper disks, and changes in nasal minimal cross‐sectional area (Amin) were measured using acoustic rhinometry.Results
Preceding ipsilateral antigen challenge led to the induction of a contralateral secretory reflex (P=0.01), which was absent in control experiments (P=0.34). Ipsilateral secretion weights were also enhanced. Preceding contralateral antigen challenge also induced a contralateral secretory reflex (P=0.03). Enhancement of the reduction in contralateral Amin was also seen (P=0.02). Ipsilateral responses were unchanged.Conclusions
Allergen exposure in asymptomatic allergic subjects leads to induction of neural reflexes, resulting in nasal hyper‐responsiveness, which persists beyond the resolution of the acute allergic response. Our data suggest that the mechanisms of allergen‐induced hyper‐responsiveness involve both afferent and efferent components.
Atopy, asthma, and experimental approaches based on the linear model of T cell maturation
Authors: Loza M. J. , Peters S. P. , Penn R. B. 
Published: January 2005

SummaryThe linear model of maturation of IFN‐γ‐producing cells from a proliferative pool of type 2 cytokine‐producing T cells represents a fundamental shift in interpreting how changes in cytokine production by T cell populations are regulated. A major tenet of this model is antigen‐independent, bystander proliferation of type 2 T cells and their maturation to IFN‐γ+ cells. Both clinical observations and prevailing theories of immune system development in asthma are consistent with this highly interpretative in vitro model, which allows unambiguous characterization of the modulation of the intrinsic features of T cell proliferation and differentiation by environmental and genetic factors. Hypotheses based on the linear model of T cell maturation are readily testable and should lead to a greater understanding of not only allergen‐specific responses, but also the non‐specific, bystander effects associated with specific responses to allergens or pathogens. Topics to be discussed in the context of the linear model of T cell maturation in this review include: (1) allergic responses to an inciting allergen that may enhance sensitivity to subsequent yet different allergens; (2) dampening the preferential accumulation of type 2 T cells during a typical immune response against viral and bacterial pathogens; (3) allergen‐independent sensitization in asthmatics: (4) the ‘hygiene hypothesis’ for the reported increased allergy development in industrialized countries; (5) elevated IFN‐γ levels in asthmatics, in addition to the expected high levels of type 2 cytokines; (6) testing the effects of inflammatory mediators, as well as various anti‐inflammation therapies on T cell maturation; and (7) testing the influence of gene variation on T cell maturation.
Forest dynamics and agents that initiate and expand canopy gaps inPicea–Abiesforests of Crawford Notch, New Hampshire, USA
Authors: WORRALL JAMES J. , LEE THOMAS D. , HARRINGTON THOMAS C. 
Published: January 2005

SummaryData from elevations ranging from mixed hardwood‐conifer forest at 600 m to subalpineAbies balsameaforest at 1120 m indicate that canopy gaps are not static but expand over time due to mortality of trees at the gap margin and coalescence of gaps. Gap expansion is more frequent than gap initiation. Ultimately such disturbance patches may become more extensive than is normally considered as typical of gap‐phase disturbance, but the processes of development are the same.Disturbance agents involved in gap initiation tend to differ from those involved in gap expansion. Spruce beetle, dwarf mistletoe and most root diseases predominate as agents of gap initiation, while windthrow/windsnap, chronic wind stress and Armillaria root disease are important agents of gap expansion.Concepts of equilibrium gap‐phase dynamics and a shifting‐mosaic steady state do not fully account for the dynamics of these spruce‐fir forests. A spruce beetle outbreak in the late 1970s/early 1980s killed most of a cohort of dominant, emergentPicea rubens. This epidemic initiated a long‐term cycle of disturbance and release that is likely to be repeated in many years when a new cohort ofP. rubensbecomes sufficiently large to sustain another major bark beetle outbreak.Episodic disturbance agents affect long‐lived, dominant species at infrequent but regular intervals (up to hundreds of years) and operate at the landscape level. Gap‐phase cycles appear to be nested within the long‐term cycle. Over the long term, episodic disturbance drives such ‘nested bicycle’ dynamics.Spatial and temporal distribution of disturbance results not only from stochastic events such as storms, but also from host specificity of agents of disturbance, their tendency to attack certain age classes of trees, local and regional contagion, and susceptibility of trees at the edge of disturbance patches.
Climate change effects on species interactions in an alpine plant community
Authors: KLANDERUD KARI 
Published: January 2005

Summary

I examined the role of species interactions on the population dynamics of the herb Thalictrum alpinum and the sedge Carex vaginata by removing the dwarf shrub Dryas octopetala over four growing seasons at Finse, in the alpine region of south Norway, Furthermore, by increasing temperature (open top chambers) and nutrient availability (nutrient addition), I assessed the effects of climate warming on biotic interactions.
Dryas removal increased the number of Thalictrum and Carex leaves, and flowering frequency of Carex. Flower stems and leaf stalks of Thalictrum, and the leaves of Carex, became significantly shorter following Dryas removal. Warming and nutrient addition increased vegetative plant growth, whereas warming alone had positive effects on sexual reproductive effort of the target species. My results suggest that there is both competition for nutrients, and a facilitative shelter effect of Dryas on its neighbours.
Species interactions affected population dynamics of Thalictrum and Carex. Interactions between the impacts of Dryas removal and abiotic factors on leaf production, suggested that interactions between Dryas and neighbouring species might be modified if temperature and, in particular, nutrient availability increase under global warming.
This study shows that both biotic interactions and abiotic environmental conditions may affect alpine plant population dynamics. Furthermore, it shows that climate change may modify species interactions.
Species interaction effects should be included in climate change experiments and in future models predicting plant community changes under global warming.
Drought, fire and tree survival in a Borneo rain forest, East Kalimantan, Indonesia
Authors: VAN NIEUWSTADT MARK G. L. , SHEIL DOUGLAS 
Published: January 2005

Summary

Droughts and fires are increasingly recognized as a significant component of tropical rain forest dynamics but detailed large‐scale assessments of such events are scarce. Here we examine tree mortality in a lowland rainforest in East Kalimantan after an extreme drought (the most severe ever reported in a tropical forest study), and a subsequent fire. Eighteen 1.8‐ha paired permanent plots that crossed a firebreak allowed us to examine the separate effects of the two events.
Eight months after the drought, stem mortality in unburned forests reached 18.5 ± 5.6% (average ± SD ≥ 10 cm diameter breast height, d.b.h.). After 21 months, this increased to 26.3 ± 5.0%. Mortality was higher in larger stems, being 46.6 ± 18.7% in stems > 80 cm d.b.h., but falling to 23.9 ± 3.7% in stems 10–20 cm d.b.h. (after 21 months). The burned forest showed an overall mortality of 64.2 ± 12.2%. This increased to 79.0 ± 10.2% after 21 months.
By subtracting mortality after drought alone from mortality with fire in each plot pair, we can estimate the distinct influence of drought and subsequent fire. Fire caused near complete mortality for individuals < 10 cm d.b.h., but did not increase tree mortality for individuals > 70 cm d.b.h.
Drought contributes approximately 30% of the stem death observed in the burned forest after 21 months but the estimated contributions to dead basal area and biomass are higher at 52% and 63%, respectively. The forest contained around 7.3 tonnes ha−1 (± 2.2, 95% confidence) of above‐ground biomass as dead trees (≥ 10 cm d.b.h) prior to the drought, rising to 133 ± 30 tonnes ha−1 21 months after drought alone, and 207 ± 50 tonnes ha−1 in burned forest.
Eusideroxylon zwageri survived the drought with only 5% mortality after 21 months. Overall per‐species mortality appears negatively correlated to wood density, though Koompassia malaccensis, with 64% mortality, is an outlier.
Though species‐specific mortality varied from 11 to 91% in burned forest, overall stem survival after fire was significantly correlated with greater bark thickness at larger sizes. Consequently, species well represented at large sizes, mainly Dipterocarpaceae, increase in relative dominance compared with smaller taxa. Palm mortality was low, reaching only 3% after drought and 10% in burned forest.
The stem mortalities recorded in this study are amongst the most severe ever observed in rainforest. Such droughts, though rare, are potent determinants of forest structure and composition. Drought and fire are an especially destructive combination as they act on larger and smaller stems, respectively.
Forest edges benefit adults, but not seedlings, of the mistletoe Alepis flavida (Loranthaceae)
Authors: BACH CATHERINE E. , KELLY DAVE , HAZLETT BRIAN A. 
Published: January 2005

Summary

We tested the hypothesis that different life‐history stages of the same plant species show different responses to forest edge and interior environments. We investigated the effects of forest edges on growth, survival and density of seedlings, juveniles and adults of an endemic New Zealand mistletoe, Alepis flavida, over a 5‐year period.
Rates of establishment and growth were significantly higher for seedlings in forest interior than on forest edges but both juveniles and adults grew significantly faster on forest edges.
Mortality rates were greater for juveniles than for adults, but there was no significant difference between forest edge and interior.
Densities of seedlings and the larger size class of juvenile plants were significantly greater in the forest interior than on forest edges, whereas densities of the larger size class of adults were significantly greater on edges.
Changes in densities over 5 years showed that larger juveniles increased in density only in the forest interior, whereas larger adults increased in density only on forest edges.
Thus, seedlings of A. flavida have strong advantages in the forest interior, whereas juveniles and adults grow faster on forest edges.
This study emphasizes the need to examine multiple life‐history stages in studies of edge effects.
Do vigour of introduced populations and escape from specialist herbivores contribute to invasiveness?
Authors: STASTNY MICHAEL , SCHAFFNER URS , ELLE ELIZABETH 
Published: January 2005

Summary

Plant species may become invasive due to a lack of natural enemies (e.g. herbivores) in their introduced range. Absence of herbivores may result in selection for the loss of costly herbivore‐resistance traits, which are expected to show a trade‐off with vigour or competitive ability (the evolution of increased competitive ability, or EICA, hypothesis).
We conducted a common garden experiment in Switzerland, in which we compared herbivore resistance and vigour of Senecio jacobaea plants exposed to the specialist flea beetle Longitarsus jacobaeae, for four populations originating within the native range (Europe), and four from regions where it had been introduced (New Zealand, USA) and was unaffected by L. jacobaeae. Our predictions were that, compared with plants from the native populations, plants from introduced populations would experience greater herbivory (due to loss of resistance traits), and exhibit more vigorous growth.
As expected, we found that introduced S. jacobaea grew larger, and had greater reproductive output, than plants from the native range. Larger plants experienced more feeding damage, and introduced plants were consumed more even when size differences were controlled. Introduced plants also exhibited a greater relative ability to reproduce after damage was sustained, i.e. higher tolerance to herbivory.
Contrary to predictions, however, plants from introduced populations had higher total pyrrolizidine alkaloid production (chemical defence against herbivores).
Although plants from introduced ranges exhibited life‐history traits consistent with EICA predictions, similar phenotypes were common in one of the populations from the native range, suggesting that EICA may not fully explain the invasion success of S. jacobaea.
Our results imply that increased competitive ability (vigour) of invasive plants may be associated with changes in resistance as well as tolerance to herbivory, and both types of anti‐herbivore defence may need to be examined simultaneously to advance our understanding of invasiveness.