bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐consumptive effects of predatory mites on thrips and its host plant
Authors: Walzer Andreas , Schausberger Peter
Published: February 2009

Recent reviews on trait‐mediated interactions in food webs suggest that trait‐mediated effects are as important in triggering top–down trophic cascades as are density‐mediated effects. Trait‐mediated interactions between predator and prey result from non‐consumptive predator effects changing behavioural and/or life history traits of prey. However, in biological control the occurrence of trait‐mediated interactions between predators, prey and plants has been largely ignored. Here, we show that non‐consumptive predator effects on prey cascade down to the plant in an agro‐ecological food chain. The study system consisted of the predatory mites P. persimilis and N. californicus, the herbivorous non‐target prey western flower thrips F. occidentalis and the host plant bean. Irrespective of predator species and risk posed to prey, the presence of predator eggs led to increased ambulation, increased mortality and decreased oviposition of thrips. Furthermore, the presence of predator eggs reduced leaf damage caused by thrips. To our knowledge this is the first experimental evidence suggesting a positive trophic cascade triggered by non‐consumptive predator effects on non‐target prey in an augmentative biological control system.
Development of lengths of stay and DRG cost weights in dermatology from 2003 to 2006
Authors: Wenke Andreas , Müller Marcel L. , Babapirali Judith , Rompel Rainer , Hensen Peter
Published: February 2009

Background: The G‐DRG per case payments are calculated annually on the basis of present output and cost data provided from German hospitals. The economic valuation of dermatology‐related DRGs depends largely on inpatients’ length of stay. At present, longitudinal analyses of dermatologic hospital data considering the development of length of stay under DRG conditions are not available.

Methods: A multicenter, longitudinal study of clinical data from hospitals with different care levels was performed (n = 23). Frequent and relevant dermatologic diagnoses were grouped and analyzed over a time period of four years (2003–2006). The development of lengths of stay and of G‐DRG cost weights were studied in detail. Descriptive statistical methods were applied.

Results: After introduction of DRG, the data reveal a) reduction of length of stay in inpatient dermatology and b) after an initial abrupt rise, DRG valuation of dermatologic groups moderately decreased over time. Both trends changed most rapidly in the early years but reached a stable niveau in 2006. The study furthermore points out that not only length of stay, but also other type of costs influence DRG calculations.

Conclusions: German dermatology reflects the international trend showing reductions of length of stay after introduction of a DRG‐based hospital funding system. The DRG calculation and valuation of inpatient services depend on the duration of hospital stay. However, increasing per diem costs resulting from higher performances of every inpatient bed day are also taken into account. Further reduction of length of stay must not threaten the quality of inpatient care in dermatology.
Complete remission of cutaneous and subcutaneous melanoma metastases of the scalp with imiquimod therapy
Authors: Heber Giada , Helbig Doris , Pönitzsch Iris , Wetzig Tino , Harth Wolfgang , Simon Jan‐Christoph
Published: February 2009

Multiple cutaneous and subcutaneous melanoma metastases represent a therapeutic challenge. A 63‐year‐old man presented with multiple cutaneous and subcutaneous melanoma metastases on his right parieto‐occipital region that appeared ten weeks after surgical excision of the primary tumor. Staging showed no further metastases. Because of the large area of cutaneous metastatic spread, the location and the limited possibility of a complete excision, we decided to begin immunomodulatory therapy with imiquimod applied for eight hours daily five days a week. After six weeks of imiquimod monotherapy, a partial remission of the cutaneous metastases had occurred. After 17 months, the remission of these metastases was complete. Four months later the patient is still free of cutaneous, visceral, cerebral and lymph node metastases.
A nationwide study on hospital admissions due to dehydration in exclusively breastfed infants in the Netherlands: its incidence, clinical characteristics, treatment and outcome
Authors: Pelleboer Rolf AA , Bontemps Sander TH , Verkerk Paul H , Van Dommelen Paula , Pereira Rob Rodrigues , Van Wouwe Jacobus P
Published: February 2009

Aims: To estimate the incidence and clinical characteristics in hospital admissions due to dehydration or undernutrition and their laboratory evaluation and treatment outcome in exclusively breastfed infants.

Methods: All hospital admissions during the first 3 months of life assessed by the Dutch Paediatric Surveillance Unit (DPSU) between mid 2003 and mid 2005.

Results: Nationwide 158 cases reported, correspond to an incidence of 58/y/100 000 breastfed infants; it is lower for severe dehydration at risk for hypernatraemia; 20/y/100 000. Sixty‐five per cent of cases were <2 weeks old, their median weight loss was 9.3% and median age at admission 5 days; Serum sodium value was measured in only 12% of all cases. Insufficient volume intake and inadequate growth were most frequently reported (61% and 41%). Lethargy, jaundice or clinical dehydration was scored in 11–25%, seizures or shock in 3%. A breast pump at home was used in only 31%. In the hospital breast pumps were available (82%) as lactation consultants (73%). For treatment 65% was offered formula, in 30% by nasogastric drip. Most admissions lasted up to 3 days, all recovered fully and 33% were breastfed exclusively at discharge.

Conclusion: The incidence of severe dehydration in the Netherlands is relatively low. With extended use of breast pumps at home it could be lower. To prevent complications, we recommend applying a reference weight chart, a full clinical examination and more extensive screening of serum sodium and glucose.
Density‐dependence in common tree species in a tropical dry forest in Mudumalai, southern India
Authors: John Robert , Dattaraja H.S. , Suresh H.S. , Sukumar R.
Published: February 2009

Abstract. Density‐dependence in tree population dynamics has seldom been examined in dry tropical forests. Using long‐term data from a large permanent plot, this study examined 16 common species in a dry tropical forest in southern India for density‐dependence. Employing quadrat‐based analyses, correlations of mortality, recruitment and population change with tree densities were examined. Mortality in 1–10 cm diameter trees was largely negatively correlated with conspecific density, whereas mortality in > 10 cm diameter trees was positively correlated. Mortality was, however, largely unaffected by the basal area and abundance of heterospecific trees. Recruitment was poor in most species, but in Lagerstroemia microcarpa (Lythraceae), Tectona grandis (Verbenaceae) and Cassia fistula (Fabaceae), species that recruited well, strong negative correlations of recruitment with conspecific basal area and abundance were found. In a few other species that could be tested, recruitment was again negatively correlated with conspecific density. In Lagerstroemia, recruitment was positively correlated with the basal area and abundance of heterospecific trees, but these correlations were non‐significant in other species. Similarly, although the rates of population change were negatively correlated with conspecific density they were positive when dry‐season ground fires occurred in the plot. Thus, the observed positive density‐dependence in large‐tree mortality and the negative density‐dependence in recruitment in many species were such that could potentially regulate tree populations. However, repeated fires influenced density‐dependence in the rates of population change in a way that could promote a few common species in the tree community.
Natural regeneration of trees in urban woodlands
Authors: Lehvävirta Susanna , Rita Hannu
Published: February 2009

Abstract. We studied tree regeneration, a key process for the existence of urban woodlands. We hypothesized that, besides the usual biological factors, anthropogenic ones (fragmentation, wear, pollution etc.) determine the regeneration success of tree species in urban woodlands. To test this hypothesis, within an observational setting, we collected data from 30 urban woodlands in the cities of Helsinki and Vantaa, Finland. We defined the number of living saplings (30–200 cm in height) as an indicator of regeneration success and used regression analysis to test different factors as independent variables. The results showed that different tree species responded differently to urban pressure. The regeneration of Picea abies decreased with increasing fragmentation of the forest landscape, whereas for the other most common (deciduous) species, regeneration increased. Wear, measured as total path area per study site, had a negative effect on regeneration success. An a posteriori examination of the data suggested that coarse woody debris might promote regeneration. We conclude that, although tree regeneration in general is not threatened in urban woodlands in the area we studied, the species composition may gradually change. We discuss some management implications for counteracting the urban pressures on tree regeneration.
Distribution of plant life history types in California chaparral: the role of topographically‐determined drought severity
Authors: Meentemeyer Ross K. , Moody Aaron
Published: February 2009

Abstract. Spatial patterns of shrub life history and Ceanothus distribution are examined in relation to topographically‐mediated differences in drought severity within 3 watersheds on the coastal and inland flank of the Santa Ynez Mountains, California. Spatially distributed fields of drought severity are simulated for the studied watersheds using high‐resolution digital terrain data and daily climate data in combination with a process‐based hydro‐ecological model (RHESSys). Field samples of species composition are spatially integrated with the distributed drought data for analysis of ecological relationships. Patterns of seedling recruitment type correspond to topographic variability in drought severity in ways that are consistent with concepts presented in the literature. Species that depend on fire for recruitment are increasingly represented with increasing drought severity, the converse also applies. Sites that experience moderate drought severity permit co‐dominance of species from both recruitment modes. Residual analysis suggests that some of the unexplained variability is related to substrate. Analyses also indicate that the distribution of 5 Ceanothus shrubs reflect differences in drought severity in ways that are consistent with their resistance to water stress‐induced xylem dysfunction. Species from the subgenus Cerastes sort in accordance with moisture availability and have unique spatial distributions. Results are evaluated and discussed with respect to studies on plant morphology, resource use and seedling establishment patterns.
Patterns of plant species and community diversity at different organization levels in a forested riparian landscape
Authors: Decocq Guillaume
Published: February 2009

Abstract. Integrated synusial phytosociology combined with traditional measures of diversity is used to describe the structure of vascular vegetation diversity along the forested riparian landscape of the upper Oise valley (Belgium and France). The two dimensions (longitudinal and lateral) of the geomorphological complex are examined at four scales: synusia, phytocoenosis, tesela and catena. The results support the following hypotheses: (1) the environmental gradients observed, particularly the lateral ones, are very complex; (2) there is a clear lack of coupling between the tree, shrub and herb layers, which indicates a differential response to the underlying influence of environmental controls; (3) moderate flooding‐induced disturbance enhances herb species richness; (4) stressful environments support a low plant species diversity but a high synusial richness; (5) natural factors (substrate, climate, disturbance) are more important at the synusia and phytocoenose scales, but (6) anthropogenic disturbances, mainly through forest and river management, are more important at the landscape level. By considering plant communities as structural‐dynamic entities of ecosystems in a landscape context, integrated synusial phytosociology provides a basis for decomposing a complex system since the different hierarchical levels are both nested and thus strongly relational and process‐based.
‘Surprising’ ecological results and the carbon balance gradient in European forests
Authors: Roxburgh Stephen H.
Published: February 2009

Abstract. Piovesan & Adams (2000) criticized the EURO‐FLUX network of carbon flux measurements based on the assumption that the results were ‘surprising’, as they appeared to contradict the generally accepted relationship that rates of soil and plant respiration increase with increasing temperature. The EUROFLUX studies showed an overall opposite trend, with higher rates of ecosystem respiration at the cooler, northern latitudes. In this paper the concept of ‘surprising’ results in ecology is reviewed and the original claims of Piovesan & Adams reassessed. It is concluded that results from the EUROFLUX network do not contradict the established respiration/temperature relationship for at least two reasons. First, ecosystem respiration is the net outcome of a wide range of underlying processes and a simple respiration/temperature relationship may not be observed if other non‐temperature dependent processes dominate. Second, relatively higher temperatures at the northern hemisphere sites during the period over which the EUROFLUX observations were made are consistent with the hypothesis that the measured fluxes reflect a non‐equilibrium, transient loss of carbon. It is further concluded that the potential importance of inter‐year variability for determining short‐term patterns of carbon flux may provide the key to reconciling the temperature/respiration relationship highlighted by Piovesan & Adams, and the latitudinal respiration trends evident in the EUROFLUX results.
Patterns of β‐diversity in a Mexican tropical dry forest
Authors: Balvanera Patricia , Lott Emily , Segura Gerardo , Siebe Christina , Islas Angeles
Published: February 2009

Abstract. Patterns of β‐diversity in a highly diverse tropical dry forest tree community are described; the contribution of environmental heterogeneity and distance to β‐diversity was assessed. Significant differences in elevation, insolation, slope and soil water holding capacity (p < 0.01), variables related to water availability, were found among 830 m × 100 m transects laid along contrasting slopes of a system of three parallel microbasins. A gradient in elevation and insolation was found within north‐facing transects, among 10 m × 10 m sites; south‐facing transects showed an elevation gradient while crest transects showed a gradient in water holding capacity. In total 119 species were registered, with 27 to 64 species per transect, and 4 to 16 species per site. A large β‐diversity was found among and within transects; two indices of β‐diversity consistently showed a higher β‐diversity within transects than among them. Among transects, 64% of the variance in species composition could be attributed to the environmental variables; an additional 22% to the spatial distribution of sites. Within transects, 42% of the deviance in β‐diversity values was explained by insolation, and 19% by distance. β‐diversity increased with distance and with difference in insolation among sites; north‐facing transects, those with most contrasting insolation conditions, had the steepest increase in β‐diversity with distance. Such increase was clearly associated with changes in species composition, not with changes in species richness.
Seedling bank dynamics of Fagus grandifolia var. mexicana before and after a mast year in a Mexican cloud forest
Authors: Alvarez‐Aquino C. , Williams‐Linera G.
Published: February 2009

Abstract. Fagus grandifolia var. mexicana seedling dynamics were studied in a relict forest inside the crater of a volcano where it is the only canopy tree species. The objectives of the study were (1) to determine changes in seedling density before and after a mast year, as well as to monitor seedling recruitment, mortality and growth rate in relation to the micro‐environment, and (2) to discuss the impact of masting on seedling dynamics of the population. Before masting, seedling density was 8.8 seedlings m–2, afterwards seedling density peaked at 51.5 seedlings m–2, then decreased by 50% in 3 months and by 85% after 8 months, down to levels of before the mast year (9.9 seedlings m–2) after 16 months. Seedlings in the forest floor before the mast‐seeding event showed a low relative growth rate – 0.14 mm mm–1 mo–1 against 1.27 mm mm–1 mo–1 for seedlings that emerged immediately after masting. Seed germination was high (83%) and rapid (L50= 7 days) following masting. Seedling growth was positively correlated with soil water content but not with temperatures and relative humidity. Data suggested that seed production in mast years is important in maintaining the seedling bank, and thus the viability of relict Fagus populations.
Small‐scale turnover in a calcareous grassland, its pattern and components
Authors: Otsus M. , Zobel M.
Published: February 2009

Abstract. We studied small‐scale turnover in a calcareous grassland community in 2 cm × 2 cm subplots within 46 10 cm × 10 cm plots from 1996 to 1999. In different years, 73–84% of the subplots were occupied by rooted plant individuals, but the location of empty subplots varied considerably between years. Seedlings were the most mobile components in subplots – during one year (from July to July), seedlings either appeared or disappeared in on average 85% of all subplots where seedlings had occurred during that year. Within a one‐year period, vegetative ramets appeared or disappeared in an average of 30% of all subplots that had rooted plants at either the beginning or the end of that year. When only previously empty subplots were taken into account, 80% of appearances were due to clonal growth and 20% due to seedling establishment. Ca. 75% of the seedlings, however, established in subplots that already contained a rooted plant individual. There were significantly less generative appearances when a moist summer was followed by a dry one, and significantly more vegetative appearances when a dry summer was followed by a moist one. 24–33% of the established seedlings survived the first year; from the second year onwards the annual survival was greater than 50%. Seedling survival was higher among shortlived species. Generative turnover varied between species, but we found no correlation with life history characteristics or frequency. Vegetative turnover of species was dependent on the year and on species traits. Sedges had a significantly higher turnover than grasses. Species potentially able to move clonally > 10 cm per year had a higher turnover than slower species. Turnover was not dependent on species frequency in the community. Forbs with more seedlings also had a higher vegetative turnover. There were no evident links between spatial mobility and species coexistence; predominating species exhibited contrasting turnover rates, subordinate species had contrasting turnover rates as well. Turnover is important in more general terms as a process resulting in free gaps – arenas for recruitment of whatever species.
Sensitivity of the woodland herb Anemone hepatica to changing environmental conditions
Authors: Tyler Torbjörn , Brunet Jörg , Tyler Germund
Published: February 2009

Abstract. The decline of deciduous woodland populations of Anemone hepatica L. in southern Sweden is documented and possible causes are discussed. The study was based on (1) re‐investigations of 6.25 km2 grid‐squares first studied in 1938–1970, (2) distribution of A. hepatica in woodland sites with well‐known soil chemical properties and (3) a detailed study over 12 consecutive years into the relationships between biological characteristics of the species (number of individuals, vegetative development, flowering frequency) and environmental variables (temperature, precipitation), soil chemistry and time. There was a close relationship between soil acidity (pH, solubility of Al3+) and both distribution and biological characteristics. The biological variables declined significantly over time but were not related to climatic variability. Increasing soil acidity and Al3+ solubility are concluded to be the main factors responsible for the decline of A. hepatica in S. Swedish deciduous woodlands.
Clonal plants and plant species diversity in wetland ecosystems in China
Authors: Song Minghua , Dong Ming
Published: February 2009

Abstract. Clonal plants play important roles in maintaining wetland ecosystems in China. By analysing 108 wetland quadrats distributed throughout China, we evaluated (1) the importance of clonal growth forms in different Chinese wetlands, (2) how the abundance of clonal plants is related to climatic and geographical conditions, and (3) how plant species diversity is related to the abundance of clonal plants.

Significant differences in clonal plant importance values were found between different regions of China. Clonal plants were more important in wetland ecosystems located towards the West and North and at higher elevations and, accordingly, experiencing a colder and drier climate. Plant species diversity showed a significant inverse correlation with the importance value of ‘guerilla’‐type plants in most of the wetland regions. However, we found no significant correlation between plant species diversity and importance values of ‘phalanx’‐type plants. In most Chinese wetlands, plant species diversity decreased with increasing importance of guerilla plants and also with an increase of the entire guild of clonal plants. In wetlands with low species richness, however, plant species diversity increased with increasing importance of guerilla plants and of all clonal plants together, suggesting that in these disturbed habitats clonal growth may facilitate the establishment of other, non‐clonal wetland plants.
BOOK REVIEWS
Authors: Abrams Marc D.
Published: February 2009

Frelich, L.E. 2002. Forest Dynamics and Disturbance Regimes — Studies from temperate evergreen‐deciduous forests.
Spatial characteristics of AVHRR‐NDVI along latitudinal transects in northern Alaska
Authors: Jia Gensuo J. , Epstein Howard E. , Walker Donald A.
Published: February 2009

Abstract. Two‐weekly AVHRR images were used to examine spatial patterns of the normalized difference vegetation index (NDVI) and their relationships with environmental variables for moist acidic tundra (MAT) and moist non‐acidic tundra (MNT) along two latitudinal transects in northern Alaska. The NDVI database was derived from a 5‐yr time series (1995–1999) of two‐weekly AVHRR composites for Alaska. A digital climate map, digital elevation map and vegetation map were processed and overlain with the NDVI grid. Homogeneous vegetation patches for both MAT and MNT were defined as sample sites using infrared aerial photos, MSS images and the vegetation map along the transects. Linear and non‐linear regression modeling were performed between NDVI indices and environmental variables, total summer warmth (TSW) and elevation. It was demonstrated that along both western and eastern transects, there were obvious latitudinal trends of peak NDVI (AP‐NDVI), average growing season NDVI (GS‐NDVI), and early June NDVI (EJ‐NDVI). In most cases, MNT had lower NDVI values than MAT throughout the year. There were significant (p<0.01) relations between NDVI (AP‐NDVI, GS‐NDVI and EJ‐NDVI) and total summer warmth (TSW) and elevation in the region. EJ‐NDVI showed the strongest correlation with TSW or elevation, making it the most sensitive NDVI indicator along environmental gradients in northern Alaska. NDVI was likely controlled by TSW and elevation, with the former being dominant.
Implications of floristic and environmental variation for carbon cycle dynamics in boreal forest ecosystems of central Canada
Authors: Yu Zicheng , Apps Michael J. , Bhatti Jagtar S.
Published: February 2009

Abstract. Species composition, detritus, and soil data from 97 boreal forest stands along a transect in central Canada were analysed using Correspondence Analysis to determine the dominant environmental/site variables that differentiate these forest stands. Picea mariana stands were densely clustered together on the understorey DCA plot, suggesting a consistent understorey species composition (feather mosses and Ericaceae), whereas Populus tremuloides stands had the most diverse understorey species composition (ca. 30 species, mostly shrubs and herbs). Pinus banksiana stands had several characteristic species of reindeer lichens (Cladina spp.), but saplings and Pinus seedlings were rare. Although climatic variables showed large variation along the transect, the CCA results indicated that site conditions are more important in determining species composition and differentiating the stand types. Forest floor characteristics (litter and humus layer, woody debris, and drainage) appear to be among the most important site variables. Stands of Picea had significantly higher average carbon (C) densities in the combined litter and humus layer (43530 kg‐C.ha‐1) than either Populus (25 500 kg‐C.ha‐1) or Pinus (19 400 kg‐C.ha‐1). The thick surface organic layer in lowland Picea stands plays an important role in regulating soil temperature and moisture, and organic‐matter decomposition, which in turn affect the ecosystem C‐dynamics. During forest succession after a stand‐replacing disturbance (e.g. fires), tree biomass and surface organic layer thickness increase in all stand types as forests recover; however, woody biomass detritus first decreases and then increases after ca. 80 yr. Soil C densities show slight decrease with ages in Populus stands, but increase in other stand types. These results indicate the complex C‐transfer processes among different components (tree biomass, detritus, forest floor, and soil) of boreal ecosystems at various stages of succession.
Carbon and nitrogen dynamics across a natural precipitation gradient in Patagonia, Argentina
Authors: Austin Amy T. , Sala Osvaldo E.
Published: February 2009

Abstract.Both ecosystem carbon gain and nutrient availability are largely constrained by the magnitude and seasonality of precipitation in arid and semi‐arid ecosystems. We investigated the role of precipitation on ecosystem processes along an International Geosphere Biosphere Programme (IGBP) transect in temperate South America. The transect consists of a contiguous precipitation gradient in the southern region of Argentinean Patagonia (44–45° S), from 100 mm to 800 mm mean annual precipitation (MAP) and vegetation ranging from desert scrub to closed canopy forest. Gravimetric soil water content tracked changes in seasonal and annual precipitation, with a linear increase in soil water content with increasing MAP. Above‐ground net primary production (ANPP) increased linearly along the gradient of precipitation (ANPP =– 31.2 + 0.52 MAP,r2= 0.84,p= 0.028), supporting the relationship that carbon assimilation is largely controlled by available water in these sites, and was in general agreement with regional models of ANPP and rainfall. However, inorganic soil nitrogen was also highly linearly correlated with both MAP ([N] = 0.19 MAP – 32,r2= 0.96,p= 0.003) and ANPP (ANPP = 2.6 [Ninorganic]+59.4,r2= 0.79,p= 0.042), suggesting a direct control of precipitation on nitrogen turnover and an interaction with nitrogen availability in controlling carbon gain. The asynchrony of precipitation and changes in dominant vegetation may play important roles in determining the carbon‐nitrogen interactions along this rainfall gradient.
Responses of grassland ecosystems to precipitation and land use along the Northeast China Transect
Authors: Zhou G. , Wang Y. , Wang S.
Published: February 2009

Abstracts.The Northeast China Transect (NECT) has been used to study how water availability influences the composition of plant functional types, soil organic matter, net primary production, trace gas flux, and land‐use patterns. We discuss relations of plant species number, soil C and N and above‐ground biomass with a precipitation gradient and interactions with land‐use practices (grassland fencing, mowing and grazing), on the basis of data from the west part of NECT. The results indicate: 1. The above‐ground biomass of grassland communities has a linear relationship with precipitation under three land‐use practices, while plant species number, soil C, and total soil N have linear relationships with precipitation under fencing and mowing; under grazing the relationships are non‐linear. 2. Plant species number, soil C and total soil N have strong linear relationships with above‐ground biomass under both fencing and mowing, while they seem to have nonlinear relationships under grazing. 3. Land‐use practices along the precipitation gradient result not only in changes in grassland communities but also in qualitative changes of their structure and function. 4. Grasslands are more vulnerable to changes in climate under mowing than under fencing, and are more capable to store C in soil and plants. 5. At a given precipitation level, number of plant species, above‐ground biomass, and soil C are higher under low to medium intensity of human activities (mowing and grazing). A better understanding of how different intensities of human activities will affect the structure and function of grassland will require further research.
Variation in vegetative water use in the savannas of the North Australian Tropical Transect
Authors: Cook Garry D. , Williams Richard J. , Hutley Lindsay B. , O'Grady Anthony, P. , Liedloff Adam C.
Published: February 2009

Abstract. The decline in tree density on sandy soils in savannas is highly correlated with declining mean annual rainfall along the North Australian Tropical Transect (NATT). We reanalyse various data on water use by individual trees and argue that a common relationship can be used to estimate annual water use by tree stands along the NATT from ca. 600 mm mean annual rainfall to at least 1600 mm. Where rainfall is less than 600 mm, trees of a given size use less water than at sites where rainfall is higher. We use these relationships to relate water use at the stand scale with mean annual rainfall along the NATT. From this we show that the empirical data imply that the minimum depth of sandy soil that needs to be exploited by trees declines with increasing aridity along the NATT from more than 5 m to less than 1 m. This finding is consistent with other observations and the pattern that with increasing aridity, an increasing proportion of rainfall coming from isolated storms rather than from periods of extended monsoon activity.
A model of alpine species distribution in relation to snowmelt time and altitude
Authors: Heegaard Einar
Published: February 2009

Abstract. The focus of this study is the response of species to time of snowmelt and altitude in alpine areas and an examination of changes in species response to snowmelt as altitude increases and temperature decreases. Transects (n= 43) were placed evenly along an altitudinal gradient at Finse, Hardanger‐vidda, western Norway, from ridges to late snowbeds. These gradients were systematically sampled (‘Repeated Gradient Analysis, RGA’) and an adjusted F‐test was used to determine repeated trends in species distribution along the transects. Of the 41 taxa analysed 22 showed a significant change in expected occurrence in response to time of snowmelt (when a site becomes free of snow) as altitude increased. Three types of response were observed: (1) no change in response: (2) increased occurrence as altitude increases, i.e. the taxon invades snow‐free sites as altitude increases, and (3) decreased occurrence as altitude increases, i.e. the taxon retreats from snow covered areas. It is suggested that the changes in response are due to both environmental factors (temperature related) and biological interactions. Decreases in expected occurrence are probably due to increased environmental severity as altitude increases (temperature related decreases). These species are represented by taxa preferring intermediate cover of snow. The invasion of earlier snow‐free sites is probably due to reduced competition from lee‐side taxa as altitude increases. A predictive model based on the species‐environmental relationships suggests that a 1°K temperature increase changes the limits of occurrence in response to time of snowmelt from 3 to 20 days for the different taxa.
Nurse effect of Bolax gummifera cushion plants in the alpine vegetation of the Chilean Patagonian Andes
Authors: Cavieres Lohengrin , Arroyo Mary T.K. , Peñaloza Alejandro , Molina‐Montenegro Marco , Torres Cristian
Published: February 2009

Abstract. It has been proposed that in the harsh arctic and alpine climate zones, small microtopographic variations that can generate more benign conditions than in the surrounding environment could be perceived as safe sites for seedling recruitment. Cushion plants can modify wind pattern, temperature and water availability. Such modifications imply that cushion plants could act as ‘nurse plants’ facilitating the recruitment of other species in the community. This effect should be more evident under stressful conditions. We tested these hypotheses comparing the number of species that grow inside and outside Bolax gummifera cushions at two elevations (700 and 900 m a.s.l.) in the Patagonian Andes of Chile (50°S). At both elevations, and in equivalent areas, the number of species was registered within and outside cushions. A total of 36 and 27 plant species were recorded either within or outside B. gummifera cushions at 700 and 900 m a.s.l., respectively. At 700 m a.s.l., 33 species were recorded growing within cushions and 29 outside them, while at 900 m a.s.l. these numbers were 24 and 13 respectively. At both elevations there were significantly more species growing within than outside cushions, and the proportion of species growing within cushions increased with elevation. Thus there is a nurse effect of cushion plants and it is more evident at higher elevations. Shelter from wind and increased soil water availability seem to be the factors that increase plant recruitment within cushions.
Formation and maintenance of community boundaries in a sub‐alpine forest landscape in northern Japan
Authors: Nishimura Takashi B. , Kohyama Takashi
Published: February 2009

Abstract. We focused on community boundaries in a sub‐alpine forest landscape in the Shiretoko Peninsula, northern Japan. Gradient‐directed transects were conducted on the northwestern slope (ranging 500–600 m a.s.l.) of Mount On'nebetsu (1331 m), where complex topography was formed by past landslides. Pioneer Picea glehnii made up a mosaic of pure stands related to landslides. Structural and compositional changes from P. glehnii pure stands to P. glehnii and Abies sachalinensis mixed stands were characterized by ca. 20 m transitional zones over the landscape. Stand density of the species changed across boundaries. A. sachalinensis preferred less undulated slopes with deep soil and P. glehnii preferred undulated rocky sites. Positive spatial associations between overstorey‐understorey P. glehnii were found at undulated core parts of P. glehnii pure stands. Short‐lived A. sachalinensis grew faster to the smaller maximum size than long‐lived P. glehnii. Undulated topography controlled the increase of A. sachalinensis and provided regeneration sites for P. glehnii, which prevented the general trend of canopy replacement from P. glehnii to late‐successional A. sachalinensis. However, the locations of current boundaries were not accordant with the topographic changes in the meso‐scale landscape. Initial P. glehnii pure stands would extend to larger areas if current patterns reflect vegetation recovery since the last landslide. P. glehnii pure stands with accurate boundaries were not maintained by topographic complexity, but were dynamically arranged by the one‐sided canopy replacements from P. glehnii to A. sachalinensis at less undulated slopes in the sub‐alpine forest landscape.
Long‐term dynamics of winter and summer annual communities in the Chihuahuan Desert
Authors: Guo Qinfeng , Brown James H. , Valone Thomas J.
Published: February 2009

Abstract. Winter and summer annuals in the Chihuahuan Desert have been intensively studied in recent years but little is known about the similarities and differences in the dynamics between these two communities. Using 15 yr of census data from permanent quadrats, this paper compared the characteristics and temporal dynamics of these two distinct, spatially co‐existent but temporally segregated communities. Although the total number of summer annual species recorded during our 15 yr of observation was higher than winter annuals, the mean number of species observed each year was higher in the winter community. The winter community exhibited lower temporal variation in total plant abundance and populations of individual species, lower species turnover rate and higher evenness than the summer community. The rank abundances of species in winter were significantly positively correlated for a period of up to 7 yr while in summer significant positive correlations in rank abundance disappeared after 2 to 3 yr. The higher seasonal species diversity (i.e. number of species observed in each season) in winter rather than the overall special pool (over 15 yr) may be responsible for the greater community stability of winter annuals. The difference in long‐term community dynamics between the two communities of annual plants are likely due to the differences in total species pool, life history traits (e.g. seed size), and seasonal climatic regimes.
Hyperdynamism in fragmented habitats
Authors: Laurance William F.
Published: February 2009

Abstract. Are the dynamics of most ecological processes fundamentally increased in frequency or magnitude in fragmented habitats? Hyperdynamism could alter a wide range of population, community, and landscape phenomena, and appears to be evident in fragmented tropical, temperate, and boreal communities. I suggest some potential causes and consequences of hyperdynamism, and argue that the responses of many species and ecological processes to habitat fragmentation can be understood in this context.
Light partitioning among species and species replacement in early successional grasslands
Authors: Werger Marinus J.A. , Hirose Tadaki , During Heinjo J. , Heil Gerrit W. , Hikosaka Kouki , Ito Takehiko , Nachinshonhor U.G. , Nagamatsu Dai , Shibasaki Katsuhiko , Takatsuki Seiki , van Rheenen Jan W. , Anten Niels P.R.
Published: February 2009

Abstract. We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above‐ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan.Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above‐ground architecture of these two species. In all stands light capture of plants increased with their above‐ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better‐lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands ‘later successional’ species had higher light harvesting efficiencies for the same plant height than ‘early successional’ species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves.

This shows how plant stature, plasticity in above‐ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series.
Use of artificial seedlings to estimate damage of forest seedlings due to litterfall and animals
Authors: Gillman Len N. , Wright Shane D. , Ogden John
Published: February 2009

Abstract. The artificial seedling assay method has been used in several tropical and temperate forests to estimate seedling damage and subsequent mortality due to non‐trophic micro‐disturbances such as litterfall and trampling. However, there has been no evidence presented to support the assumption that artificial seedling damage correlates with natural seedling mortality. In this study we evaluated the use of artificial seedlings in five New Zealand forests by comparing damage rates of artificial seedlings with damage and mortality rates of an equal number of selected natural seedlings. A total of 1200 artificial, and 1200 natural seedlings were monitored monthly for two years.

Litterfall damage rates of natural seedlings were correlated with those of artificial seedlings. However, there was no relationship found between artificial and natural seedling damage due to animals, or between artificial seedling damage and natural seedling mortality for either cause. Artificial seedlings should not therefore be used to estimate seedling mortality due to non‐trophic microdisturbance. Monitoring natural seedlings enabled non‐trophic animal damage to be readily detected and provided additional information on animal‐plant interactions.

The value of using artificial seedlings is that they provide a measure of the litterfall disturbance potential that is independent of the patchy distribution of natural seedlings within safe sites, and independent of species specific resistance to damage. They therefore provide an indication of the selective pressure on seedlings due to litterfall and are useful for comparing the relative ‘safety’ of different forests and microsites. Monitoring natural seedlings provides a measure of the damage and mortality due to litterfall for a specific seedling size class. Concurrently monitoring artificial and natural seedlings for litterfall disturbance provides more information than the same effort expended on either method alone.
Resprouting in the Mediterranean‐type shrub Erica australis afffected by soil resource availability
Authors: Cruz Alberto , Pérez Beatriz , Quintana José R. , Moreno José M.
Published: February 2009

Abstract. Soil resource availability may affect plant regeneration by resprouting in disturbed environments directly, by affecting plant growth rates, or indirectly by determining allocation to storage in the resprouting organs. Allocation to storage may be higher in stressful, low resource‐supply soils, but under such conditions plant growth rates may be lower. These factors could act in opposite directions leading to poorly known effects on resprouting. This paper analyses the role played by soil resources in the production and growth of resprouts after removal of above‐ground plant tissues in the Mediterranean shrub Erica australis. At 13 sites, differing in substrate, we cut the base of the stems of six plants of E. australis and allowed them to resprout and grow for two years. Soils were chemically analysed and plant water potential measured during the summer at all sites to characterize soil resource availability. We used stepwise regression analysis to determine the relationships between the resprouting response [mean site values of the number of resprouts (RN), maximum length (RML) and biomass (RB)] and soil nutrient content and plant water potential at each site. During the first two years of resprouting there were statistically significant differences among sites in the variables characterizing the resprouting response. RML was always different among sites and had little relationship with lignotuber area. RN was less different among sites and was always positively correlated with lignotuber area. RB was different among sites after the two years of growth. During the first months of resprouting, RN and RML were highly and positively related to the water status of the plant during summer. At later dates soil fertility variables came into play, explaining significant amounts of variance of the resprouting variables. Soil extractable cations content was the main variable accounting for RML and RB. Our results indicate that resprout growth of E. australis is positively affected by high water availability at the beginning of the resprouting response and negatively so by high soil extractable cation content at later periods. Some of these factors had previously shown to be related, with an opposite sign, to the development of a relatively larger lignotuber. Indeed, RML and RB measured in the second year of resprouting were significantly and negatively correlated with some indices of biomass allocation to the lignotuber at each site. This indicates that sites favouring allocation to the resprouting organ may not favour resprout growth.
Community structure of endemic Mimosa species and environmental heterogeneity in a semi‐arid Mexican valley
Authors: Camargo‐Ricalde Sara Lucía , Dhillion Shivcharn S. , Grether Rosaura
Published: February 2009

Abstract. In this paper we analyse six communities with seven Mimosa species in the Tehuacán‐Cuicatlán valley, Mexico. All species are endemic to Mexico and four are endemic to the valley. Mimosa species are found in (1) the ‘matorral xerófilo’ (arid tropical scrub): Mimosa calcicola, M. lacerata, M. luisana, M. polyantha and M. purpusii, and (2) the ‘selva baja caducifolia’ (tropical deciduous forest): M. adenantheroides, Mimosa texana var. filipes. Most of them occur in similar soil environments, while M. polyantha and M. calcicola establish in particular soil conditions and only M. luisana establishes in two different sites showing a wider range of adaptation to soil characteristics. The communities studied include 24 plant families, 51 genera and ca. 70 species (5% of the total flora estimated in the valley). Heterogeneity was found among the communities. Our results point to the replacement of ‘matorral xerófilo’ and ‘selva baja caducifolia’ by ‘matorral espinoso’ (thorny scrub). Thorny species (e.g. Acacia cochliacantha, Mimosa spp.) are becoming the dominant/codominant elements in the communities. Within the communities, Mimosa species have a significant influence on soil pH, organic matter and electrical conductivity values. These species contribute to ameliorate soil nutrient conditions (OM, Ntot, P, Ca, Mg, Na and K contents) as well as other environmental factors (e.g. temperature, shade) under their canopy in degraded plant communities and may serve as ‘resource islands’.