bluuebunny/crossref_metadata_2025 huggingface dataset:
Promotion of species co‐existence in old‐growth coniferous forest through interplay of life‐history strategy and tree competition
Authors: Nishimura Naoyuki , Hara Toshihiko , Kawatani Midori , Hoshino Daisuke , Yamamoto Shin‐Ichi
Published: February 2009

Question:

Does the interplay of life‐history strategy and tree competition promote tree species co‐existence? Using a growth dynamics model, we investigated mechanisms of co‐existence among major tree species in a sub‐alpine old‐growth coniferous forest.

Location:

Sub‐alpine old‐growth coniferous forest at 1850–1920 m a.s.l. in the Ontake Forest Reserve of central Japan.

Methods:

We investigated the growth and mortality rates of trees ≥ 5.0 cm stem DBH and recruitment processes in a 2‐ha study plot, and developed a model for individual growth that incorporated both intra and interspecific competition and analysed the direction and degree of competitive effect.

Results:

Four species, Picea jezoensis var. hondoensis, Tsuga diversifolia, Abies mariesii and Abies veitchii co‐occurred as dominant species in the canopy layer. P. jezoensis var. hondoensis and T. diversifolia had low stem densities and bell shaped DBH distributions. In contrast, A. mariesii and A. veitchii had high stem densities and inverse J‐shaped DBH distributions. The growth of the species with inverse J‐shaped DBH distributions (Abies spp.) was governed by the abundances of the species with bell shaped DBH distributions (Picea and Tsuga). However, Picea and Tsuga were inferior to Abies spp. in terms of recruitment rate (the number of juveniles that grow up to 5.0 cm DBH per year). Therefore, it was suggested that there was a trade‐off between recruitment pattern and interspecific competition for species co‐existence.

Conclusions:

Picea and Tsuga, with inferior recruitment, coexisted with Abies spp., with superior recruitment, by suppressing the growth of potential successors of Abies spp. The interplay of life‐history strategies (recruitment and longevity) and interspecific competition therefore plays an important role in promoting species co‐existence in this sub‐alpine old‐growth coniferous forest.
Disturbance dynamics of old‐growth Picea rubens forests of northern Maine
Authors: Fraver Shawn , White Alan S.
Published: February 2009

Question:

How have the spatial and temporal aspects of past disturbance shaped the current structure and composition of old‐growth Picea rubens forests?

Location:

Northern Maine, USA.

Methods:

We established three 50 m × 50 m plots in old‐growth Picea rubens forests and mapped the location of trees and saplings. We extracted increment cores from canopy trees, and recorded growth releases indicating past disturbance. By linking spatial data (tree positions) and temporal data (dated growth releases), we reconstructed the location and size of former canopy gaps back to 1920, and determined a more general disturbance chronology extending as far back as 1740.

Results:

We found no evidence of stand‐replacing disturbances. The disturbance dynamic includes pulses of moderate‐severity disturbances caused by wind storms and host‐specific disturbance agents (spruce budworm, spruce bark beetle) interposed upon a background of scattered smaller canopy gaps. Consequently, rates of disturbance fluctuated considerably over time. Reconstructed canopy gaps were temporally and spatially scattered; during disturbance peaks, they were both larger and more numerous.

Conclusions:

Despite peaks in disturbance, several of which created relatively large gaps, this system has experienced no significant change in species composition. Instead, the shade‐tolerant Picea rubens has maintained canopy dominance. The patch dynamics described here consist of dramatic structural, not compositional, changes to the forest. The persistence of Picea rubens is attributed to a combination of traits: (1) abundance of advance regeneration; (2) ability to endure suppression and respond favourably to release; and (3) longevity relative to ecologically similar species.
Impacts of global change on plant diversity and vice versa: Old and new challenges for vegetation scientists
Authors: Berendse Frank
Published: February 2009

Abstract. The desire to stop the current dramatic loss of biodiversity has been a major stimulus for many vegetation ecologists to unravel the mechanisms responsible for the coexistence of species. After the Rio Janeiro Convention many ecologists were convinced that nature conservation would gain strong societal support if they could prove that the loss of species would have important negative effects on the ecosystem functions that are relevant to society. I conclude that in order to understand such possible effects, it is necessary to analyse the effects of individual species on those ecosystem processes that we consider to be relevant in the context of specific questions. The great challenge for the near future is to scale the effects of plant species on their local environment up to the level of the whole planet, so that we learn about possible feedbacks that might regulate or destabilize those characteristics of the globe that are essential to our society.
Tree seedling performance in microhabitats along an elevational gradient on Mount Koma, Japan
Authors: Akasaka Munemitsu , Tsuyuzaki Shiro
Published: February 2009

Questions:

How do biological invasion patterns of Larix kaempferi seedlings change with different microhabitats along an elevational gradient on a volcano? How are seedling attributes such as establishment, competitive ability and morphological plasticity, advantageous to the invasion of stressful disturbed areas?

Location:

Mount Koma, Hokkaido, Japan.

Methods:

Seed sowing experiments and natural seedling censuses were conducted with L. kaempferi and the dominant native tree Betula ermanii. Seed germination, seedling survival and allocation were investigated on three microhabitats (bare ground, Salix reinii patch and Larix understorey) in three elevational zones for three years.

Results:

Seed germination was higher in Larix understorey than in bare ground and Salix patches, but did not differ between elevations. Survival rates were not different between elevations and microhabitats. Larix had a higher survival rate than Betula. Larix showed the highest natural seedling density in Salix patches, independent of elevational differences, while Betula density was nearly zero. Larix seedlings changed allocations between microhabitats, while the ratio of leaf to total biomass was constant. In bare ground Larix was more stunted and branched and increased its allocation to the roots. This form is adaptive to windy, nutrient‐poor environments. Larix seedlings were taller and more slender in Salix patches, indicating that the priority was light acquisition in shaded habitats. Little change in Betula allocation was detected.

Conclusion:

Invasive species establish themselves more efficiently than native species in every microhabitat investigated, especially at higher elevations, by having higher survival and growth rates derived from superior seedling performance. Plant communities on and above the tree line are modified by the biological invasion.
Fine‐scale post‐fire dynamics in southern Brazilian subtropical grassland
Authors: Overbeck Gerhard Ernst , Müller Sandra Cristina , Pillar Valério DePatta , Pfadenhauer Jörg
Published: February 2009

Question:

How does fire influence species richness and diversity in subtropical grassland in southern Brazil?

Location:

Recurrently burned grassland in Porto Alegre, Brazil (30°03′S, 51°07’W; max. altitude 311 m a.s.l.) and abandoned grassland near São Francisco de Paula, Brazil (29°47′S, 50°22’W; ca. 900 m a.s.l.).

Methods:

In the burned grassland, between‐year changes in community composition and single‐plot diversity, species number and vegetation structure were analysed in two consecutive years for plots with different time since last fire. Responses to fire of individual species were analysed. At the abandoned site, diversity, species number and vegetation structure were examined.

Results:

Species number and small‐scale species turnover were highest ca. one year after the burn, and decreased as caespitose grasses increased in cover with time since fire until reaching a stable, but less diverse state three to four years after a fire. The abandoned grassland showed higher dominance of caespitose grasses and lower richness and diversity.

Conclusions:

Fire clearly leads to a short‐term increase in species richness and diversity at the plot scale, as competitive interactions are being reduced and recruitment possibilities are high in early post‐fire vegetation development. Overall community composition does not change after a fire. While small herbs seem to be slightly favoured in the early post‐fire environment, no clear group of fire following species (absent in vegetation unburned for longer) was observed. The results indicate that the community is adapted to the current fire regime and is being maintained under the influence of fire.
Hurricane disturbance accelerates invasion by the alien tree Pittosporum undulatum in Jamaican montane rain forests
Authors: Bellingham Peter J. , Tanner Edmund V.J. , Healey John R.
Published: February 2009

Questions:

Do past disturbance, soil nutrients, or species diversity predict the invasion success of the alien tree Pittosporum undulatum in an island montane rain forest? What are the consequences of its invasion for forest composition and species diversity?

Location:

Blue Mountains, Jamaica.

Methods:

Censuses of trees ≥ 3 cm DBH in permanent plots in four sites within ca. 7 ha; 1974–2004 (intensive sites) and in 16 plots within 250 ha; 1990–2004 (extensive plots).

Results:

Pittosporum was unrecorded in the intensive sites before a severe hurricane in 1988: by 2004 all four sites were invaded. Pittosporum had invaded 25% of the extensive plots in 1990 and 69% in 2004, where its basal area increased from 0.5 ± 0.4 (SEM) m2.ha‐1 in 1990 to 2.8 ± 1.3 m2.ha‐1 in 2004. It had zero stem mortality and diameter growth rate exceeded that of native species fourfold. Pittosporum's basal area in the extensive plots in 2004 was positively related to the stand basal area damaged in the 1988 hurricane and negatively related to soil N concentrations. Pittosporum invasion was unrelated to stand‐level tree species diversity in the extensive plots but as its basal area increased over time the basal area of native species and stand‐level diversity declined.

Conclusions:

There are no obvious functional attributes of Pittosporum unrepresented in the native tree flora although it has high photosynthetic efficiency compared with native trees. More widespread invasion of these forests by Pittosporum seems inevitable since hurricanes, which accelerated the invasion, affect these forests frequently.
Competition and herbivory influence growth and survival of shrubs on old fields: Implications for restoration of renosterveld shrubland
Authors: Midoko‐Iponga Donald , Krug Cornelia B. , Milton Suzanne J.
Published: February 2009

Question:

How does competition by grasses, grazing by indigenous large herbivores, and their interaction affect the establishment, growth and survival of transplanted native woody and herbaceous seedlings on an abandoned agricultural field?

Location:

West Coast Renosterveld, Cape Floral Region, South Africa.

Methods:

Indigenous shrub seedlings were planted in different treatments, where either grass competition or herbivory or both were manipulated. Survival, growth and canopy cover of the seedlings were measured on a monthly basis over 14 months, and compared between treatments.

Results:

Experimental transplanting of indigenous shrubs into an old field showed that most of the plants investigated competed for resources with grasses on the field, and competition negatively affected the seedlings throughout the experiment. Mortality was higher, and growth was reduced for seedlings exposed to grass competition. Herbivory alone had no significant impact on the target species with the exception of Olea europaea ssp. africana. There was no significant interaction between competition and herbivory.

Conclusion:

Reduction of herbaceous competition significantly accelerates shrubland recovery on abandoned agricultural fields in renosterveld.
Spatial distribution of regeneration patches in an old‐growth Pinus Jeffrey‐mixed conifer forest in northwestern Mexico
Authors: Stephens S.L. , Fry D.L.
Published: February 2009

Question:

What are the shape, abundance, size, and structural characteristics of sapling patches in an old‐growth Pinus jeffreyi‐mixed conifer forest with a relatively intact disturbance regime?

Location:

Sierra San Pedro Martir, Baja California, Mexico.

Methods:

Regeneration was quantified by sampling sapling patches on seven 1200 m permanently marked line transects. For all patches intersected, tree size, species, age, and patch canopy cover were recorded. Patch structural characteristics were statistically compared to data from unbiased forest inventory plots. The minimum regeneration patch was defined as three saplings in a 49‐m2 area.

Results:

We sampled 54 sapling regeneration patches. Patch size varied from 6.6 to 674.8 m2. A small portion of the forest was in patches (patch fraction = 3.8%, patch abundance = 8.5 per ha). The majority of the patches were small; 64.8% were less than the mean patch area of 100.1 m2. Patches were shaped as a rhombus. For all forest characteristics, mean values inside patches were significantly different than those from the unbiased forest inventory plots.

Conclusions:

These forests have a fine‐grained pattern of regeneration patches. Our largest patch size of 674.8 m2 is the smallest reported in Pinus jeffreyi, P. ponderosa, and mixed conifer forests; other studies have probably had more difficulty delineating regeneration patches because of forest ingrowth from fire exclusion. Frequent fire, irregular seed crops, and seed dispersal by small mammals and birds could create this regeneration patch regime. High variation in nutrient availability after fire could also contribute to increased stand patchiness.
Stress tolerance abilities and competitive responses in a watering and fertilization field experiment
Authors: Liancourt P. , Corcket E. , Michalet R.
Published: February 2009

Question:

Do water gradients produce patterns of responses to stress and competition similar to those induced by nutrient gradients?

Location:

French Alps.

Methods:

We established a split‐plot design in a calcareous grassland, with watering and fertilization as main plot treatments and competition as subplot treatment. We followed individual and competitive responses of transplants of the three potential dominant grass species: Bromus erectus, Brachypodium rupestre and Arrhenatherum elatius, in all plots during two growing seasons. Changes in natural relative abundances of the three grass species were also monitored.

Results:

The growth and the relative abundance of A. elatius were primarily stimulated by nutrient addition and those of B. rupestre by water addition, whereas B. erectus decreased in abundance and had a very low flexibility with enhanced resource supply. Competition intensity increased for all species with both watering and fertilization and the ranking in competitive responses did not change with treatments: A. elatius > B. rupestre > B. erectus.

Conclusions:

Patterns of dominance were efficiently explained by stress tolerance abilities and competitive responses for dry and poor sites, and wet and rich sites for B. erectus and A. elatius respectively, whereas competitive responses were poor predictors of dominance for B. rupestre in wet and nutrient‐poor sites. Further studies are needed to assess the potential role of other processes, such as increasing competitive effect on light with increasing age as well as interference, to explain the dominance of this conservative competitor type of species in wet and nutrient‐poor sites.
The fate of seeds in Mediterranean soil seed banks in relation to their traits
Authors: Traba Juan , Azcárate Francisco M. , Peco Begoña
Published: February 2009

Question:

Is there any change in seed density and species richness in Mediterranean surface soil banks during summer? Are there any relationships between these summer variations and seed traits (weight, length and shape), without and with controlling the phylogenetic effect?

Location:

Central Spain.

Methods:

Samples of the surface soil seed bank were collected in two Mediterranean systems, grassland and scrubland, at two points in the year: immediately after the summer production peak and immediately prior to the autumn germination peak. We used Canonical Correspondence Analysis ordination to check for changes in floristic composition and ANOVAs to check for changes in seed density and species richness between summer and autumn samples. We used multiple regression analysis to analyse the relationship between summer variations in soil seed density and form traits, with and without controlling phylogenetic relations.

Results:

Soil seed density dropped significantly during the summer in the two systems (28% in grasslands, repeated measures ANOVA test;F= 58.19,P< 0.01; 72% in scrublands, repeated measures ANOVA test;F= 75.67,P< 0.001). Species richness, however, only dropped significantly in the scrubland (32%; repeated measures ANOVA test;F= 9.17,P< 0.05). Variation in the floristic composition of the shallow banks was only significant in the scrubland.

Changes in shallow bank density were related significantly to seed morphology features, with greater drops in species with heavier seeds in grasslands and species with longer seeds in scrubland.

Conclusions:

Our results show a substantial loss of seeds in the uppermost soil layer during the summer period between the point of peak production and the autumn germination peak. This drop was clearer in the scrubland than in the grassland. Longer and/or heavier seeds underwent the greatest declines in density at the end of summer, indicating a more intense effect of post‐dispersal predation on large‐seeded species.
Effects of altitude and topography on species richness of vascular plants, bryophytes and lichens in alpine communities
Authors: Bruun Hans Henrik , Moen Jon , Virtanen Risto , Grytnes John‐Arvid , Oksanen Lauri , Angerbjörn Anders
Published: February 2009

Question:

What is the relationship between species richness of vascular plants, bryophytes and macrolichens, and two important gradients in the alpine environment, altitude and local topography?

Location:

Northernmost Fennoscandia, 250–1525 m a.s.l. corresponding to the range between timberline and mountain top.

Methods:

The vegetation was sampled in six mountain areas. For each 25 vertical metres, the local topographic gradient from wind‐blown ridge to snowbed was sampled in quadrats of 0.8 m × 0.8 m. Patterns in species richness were explored using Poisson regression (Generalized Linear Models). Functional groups of species, i.e. evergreen and deciduous dwarf‐shrubs, forbs, graminoids, mosses, hepatics and lichens were investigated separately.

Results:

Functional groups showed markedly different patterns with respect to both altitude and topography. Species richness of all vascular plants showed a unimodal relationship with altitude. The same was true for graminoids, forbs and lichens analysed separately, but forb richness peaked at much higher altitudes than total richness. The richness of dwarf‐shrubs decreased monotonically with altitude, whereas richness of mosses and liverworts showed an increasing trend. Significant interactions between altitude and local topography were present for several groups. The unimodal pattern for total plant species richness was interpreted in terms of local productivity, physical disturbance, trophic interactions, and in terms of species pool effects.

Conclusions:

Patterns in local species richness result from the action of two opposing forces: declining species pool and decreasing intensity of competition with altitude.
A long‐term study of neighbour‐regulated demography during a decline in forest species diversity
Authors: Yi‐ching Lin , Augspurger Carol K.
Published: February 2009

Question:

Did disturbance, no density‐dependence of the dominant species, and negative neighbourhood interactions on rare species affect tree demography during a decline in species diversity associated with the increase ofAcer saccharumfrom 1939–2001?

Hypotheses:

1. The rise in dominance ofA. saccharumwas because of its advantage in disturbances and lack of density‐dependence of its demography. 2. Rare species were not favoured by disturbances, including those from Dutch elm disease, and demonstrated negative neighbourhood interactions withA. saccharum.

Location:

Brownfield Woods in Illinois, USA.

Methods:

Historical maps of trees (≥ 7.6 cm DBH) from 1939, 1951, 1988, and 2001 in 16 quadrats (48 m × 68 m) were used to compare demography of eight tree species. Effects of disturbances, density‐dependence, and neighbourhood interactions on mortality and recruitment of tree species within a 6‐m radius of individual target trees were studied.

Results:

A. saccharumdemonstrated a demographic advantage over rare species. It had lower mortality and higher recruitment rates. Disturbances facilitated recruitment ofA. saccharum, but did not enhance rare species. Density‐dependence of both mortality and recruitment ofA. saccharumoccurred, but population projection models indicated that ecological conditions became more favourable forA. saccharumin the past 62 years. Furthermore, negative neighbourhood interactions were detected between rare species andA. saccharum. The increase in neighbouringA. saccharumsignificantly increased mortality and reduced recruitment of the rare species.

Conclusions:

The general disturbance regime, enhanced by Dutch elm disease, in Brownfield Woods facilitated the rise of dominance ofA. saccharum. Meanwhile, rare species declined as a result of their disadvantage in disturbance and negative neighbourhood interactions withA. saccharum.
Tree rings show competition dynamics in abandoned Castanea sativa coppices after land‐use changes
Authors: Fonti Patrick , Cherubini Paolo , Rigling Andreas , Weber Pascale , Biging Gregory
Published: February 2009

Questions:

As a consequence of socio‐economic changes, many Castanea sativa coppices have been abandoned and are now developing past their usual rotation length. Do we have to expect changes in stand structure and composition of abandoned Castanea sativa coppice invaded by other species? Is a tree ring‐based approach adequate to early recognise changes in inter‐specific competitive interaction?

Location:

Lowest alpine forest belt of the southern Swiss Alps.

Methods:

We selected a 60‐year old abandoned Castanea sativa coppice stand with sporadic Fagus sylvatica and Quercus cerris mixed in. Using tree‐ring based indices we analysed differences in the species‐specific response to competition. Analyses were performed by comparing how subject dominant trees (10 Castanea, 5 Fagus, 5 Quercus) have differently faced competition from their immediate Castanea coppice neighbourhood, taking into account the changes over time and space.

Results:

Although no species appears yet to have made a difference in the surrounding coppice mortality, there are species‐specific differences in growth dominance, which indicate potential successional processes. Castanea sativa growth dominated in the early stages of stand development. However, after approximately 30–35 yr Fagus sylvatica and Quercus cerris became much more dominant, indicating a change in competitive potential that does not favour Castanea sativa.

Conclusions:

Without interventions this coppice will develop into a mixed stand. A tree‐ring based approach allows an early recognition of forthcoming changes in stand composition and structure and is likely to be an important tool for forest landscape management.
Braun‐Blanquet's legacy and data analysis in vegetation science
Authors: Podani János
Published: February 2009

Abstract.This article investigates whether the Braun‐Blanquet abundance/dominance (AD) scores that commonly appear in phytosociological tables can properly be analysed by conventional multivariate analysis methods such as Principal Components Analysis and Correspondence Analysis. The answer is a definite NO. The source of problems is that the AD values express species performance on a scale, namely theordinalscale, on which differences are not interpretable. There are several arguments suggesting that no matter which methods have been preferred in contemporary numerical syntaxonomy and why, ordinal data should be treated in an ordinal way. In addition to the inadmissibility of arithmetic operations with the AD scores, these arguments include interpretability of dissimilarities derived from ordinal data, consistency of all steps throughout the analysis and universality of the method which enables simultaneous treatment of various measurement scales. All the ordination methods that are commonly used, for example, Principal Components Analysis and all variants of Correspondence Analysis as well as standard cluster analyses such as Ward's method and group average clustering, are inappropriate when using AD data. Therefore, the application of ordinal clustering and scaling methods to traditional phytosociological data is advocated. Dissimilarities between relevés should be calculated using ordinal measures of resemblance, and ordination and clustering algorithms should also be ordinal in nature. A good ordination example is Non‐metric Multidimensional Scaling (NMDS) as long as it is calculated from an ordinal dissimilarity measure such as the Goodman & Kruskal γ coefficient, and for clustering the new OrdClAn‐H and OrdClAn‐N methods.
Restoration of lichen diversity in grass‐dominated vegetation of coastal dunes after wildfire
Authors: Ketner‐Oostra R. , van der Peijl M.J. , Sýkora K.V.
Published: February 2009

Question:

Can lichen diversity of an earlier succession stage be restored in dune grassland after fire in a region with high nitrogen deposition?

Location:

Calcium‐poor coastal dunes in the Wadden district, The Netherlands.

Methods:

We sampled dune grassland by using a large continuous transect of 4 m × 4 m blocks on both a south slope and a west slope. The sampling was conducted in the lichen‐rich Violo‐Corynephoretum in 1966, in the vegetation dominated by tall graminoids in 1990 and in the recovering vegetation for eight years after a wildfire in 1993. Vegetation succession in the blocks is visualised in stacked bar graphs and ordination diagrams (DC A). In 1966 relevés were made within the blocks, and from 1990 until 2001 permanent quadrats were studied.

Results:

Between 1966 and 1990 the lichen‐rich open grassland became dominated by tall graminoids and developed partly into a dwarf‐shrub heath, resulting in a severe loss of lichen diversity. After the fire a lush vegetation of tall graminoids with an abundant moss cover developed. In 2001 the vegetation was still very different from the lichen‐rich vegetation in 1966.

Conclusions:

Fire alone will not change dunes dominated by tall graminoids into open lichen‐rich grasslands in an area with high aerial nitrogen deposition. After fire, additional intervention is recommended, such as large‐scale clearing of the burned vegetation and actively promoting deposition of sand, either blown in from foredunes, from re‐activated blow‐outs or artificially brought to the site.
Variables influencing the distribution of epiphytic lichens in heterogeneous areas: A case study for Liguria, NW Italy
Authors: Giordani Paolo
Published: February 2009

Questions:

What are the most relevant environmental variables influencing the distribution and the species richness of epiphytic lichens in heterogeneous areas of the Mediterranean region? What is the relative importance of substrate‐ vs. environmental‐related variables? How do climatic and disturbance factors interact?

Location:

The study was carried out in the Liguria region (northwestern Italy). This is a complex region where steep environmental gradients occur over a few kilometres of longitude and latitude.

Methods:

Data on lichen species frequencies, collected on the basis of stratified random sampling, were analyzed using non‐metric multidimensional scaling (NMS) and DCA. Indicator Value Analysis (IVA) analysis was used to find indicator species for the environmental predictors.

Results:

In the survey area, epiphytic lichen distribution depends on both substrate‐ and environment‐related factors. Climatic variables (in particular average yearly temperature and rainfall), anthropogenic pressures (particularly harvesting and atmospheric pollution), bark pH and texture were associated with the main axes of variability in the dataset. Mean annual rainfall is the best predictor for epiphytic lichen richness in the survey area. The particular effects of the Mediterranean region (e.g. the influence of forest fires) and of heterogeneous areas (the variability of diversity in relation to habitat) were pointed out. Several indicator species, closely linked to particular ecological conditions, were found for both substrate‐and environment‐related variables.

Conclusions:

The main variables involved seemed to be the same reported for other areas, but their relative importance and their spatial scale of action were in some cases different, probably due to the geomorphological and climatic heterogeneity of the survey area. The significant influence of climatic predictors and disturbance factors on epiphytic lichens was confirmed, suggesting that these organisms may be used successfully to describe ecological trends in natural environments, also providing practical information at ecosystem level.
The influence of carbon—nutrient balance on herb and woody plant abundance in temperate forest understories
Authors: Graves James H. , Peet Robert K. , White Peter S.
Published: February 2009

Question:

We present a general structural carbon—nutrient balance hypothesis parallel to Bryant et al.'s defensive chemistry hypothesis. Our hypothesis suggests that because herb species require a lower investment of carbon per unit length of stem than do woody plants, herbs should be at a competitive advantage where the leaf area of plants in the ground layer is limited by light (or fixed carbon, C) rather than soil resources (R) such as nutrients or water. We test the derivative predictions that in temperate deciduous forests (1) herb cover and species richness increase as soil resources increase, and (2) woody ground‐layer cover, density, and species richness increase as soil resources decrease.

Location:

To maximize generality, the eight temperate deciduous forest sites were dispersed along an 800 km band from the Coastal Plain of eastern North Carolina to the Central Basin of middle Tennessee, USA.

Methods:

Soil nutrients and moisture, herb cover and woody stem densities were observed in six plots at each site, randomly located in high, medium, and low herb cover areas. Multiple regression, correlation, and Redundancy Analysis ordination were used to test predictions.

Results:

Plants with herbaceous (low C:R) stems are generally abundant where soil moisture and basic cations (Ca, Mg) are high (low C:R environments), and woody (high C:R) plant cover, basal area, stem density, and species richness are all greatest on dry or nutrient‐poor soils (high C:R environments). Plots with intermediate soil resource availability and herb cover have the most species, and maximum herb species richness occurs at higher soil resource levels than maximum woody species richness.

Conclusions:

Our observations are consistent with our structural carbon—nutrient balance hypothesis.
Sample size and the detection of a hump‐shaped relationship between biomass and species richness in Mediterranean wetlands
Authors: Espinar J.L.
Published: February 2009

Questions:

What is the observed relationship between biomass and species richness across both spatial and temporal scales in communities of submerged annual macrophytes? Does the number of plots sampled affect detection of hump‐shaped pattern?

Location:

Doñana National Park, southwestern Spain.

Methods:

A total of 102 plots were sampled during four hydrological cycles. In each hydrological cycle, the plots were distributed randomly along an environmental flooding gradient in three contrasted microhabitats located in the transition zone just below the upper marsh. In each plot (0.5 m × 0.5 m), plant density and above‐ and below‐ground biomass of submerged vegetation were measured. The hump‐shaped model was tested by using a generalized linear model (GLM). A bootstrap procedure was used to test the effect of the number of plots on the ability to detect hump‐shaped patterns.

Result:

The area exhibited low species density with a range of 1—9 species and low values of biomass with a range of 0.2 ‐87.6 g‐DW/0.25 m2. When data from all years and all microhabitats were combined, the relationships between biomass and species richness showed a hump‐shaped pattern. The number of plots was large enough to allow detection of the hump‐shaped pattern across microhabitats but it was too small to confirm the hump‐shaped pattern within each individual microhabitat.

Conclusion:

This study provides evidence of hump‐shaped patterns across microhabitats when GLM analysis is used. In communities of submerged annual macrophytes in Mediterranean wetlands, the highest species density occurs in intermediate values of biomass. The bootstrap procedure indicates that the number of plots affects the detection of hump‐shaped patterns.
Changes in the abundance, composition and species richness of mountain vegetation in relation to summer grazing by reindeer
Authors: Eskelinen Anu , Oksanen Jari
Published: February 2009

Question:

How do reduced levels of summer grazing by reindeer affect the abundance, composition and species richness of mountain plant communities?

Location:

Arctic‐alpine mountain vegetation 700–850 m a.s.l., Saana Conservation Area, northwestern Finnish Lapland.

Methods:

Permanent plots were established in 1990 and resampled in 1999 or 2001. The number of reindeer had considerably declined from the 1980s to the 1990s and we followed the recovery of vegetation. The comparisons between 1990 and 1999/2001 were made at seven sites differing in their original grazing pressure.

Results:

At the initially heavily grazed sites, lichen abundances increased, but at the lightly grazed sites the abundances of lichens decreased. Graminoids declined at all sites, but the change seemed to be greatest at the most heavily grazed sites. Forbs increased slightly across all sites. At the species level, lichens and graminoids responded most notably to the reduction of grazing pressure. Individual species responses in shrubs were variable and among forbs, typical species of species‐richDryasheaths increased. Total species richness increased at all sites and the change was greater at heavily grazed sites. This increase resulted mainly from increased bryophyte and lichen species richness but also from a slight increase in vascular plant species richness.

Conclusions:

These results suggest that lichens are the group most responsive to the reduction of heavy summer grazing by reindeer and that lichens and forbs typical in arctic‐alpineDryasheaths are favoured over graminoids under reduced grazing. Heavy grazing decreases overall species richness with the most pronounced effects on bryophyte and lichen species richness. The results support the hypothesis that heavy summer grazing may shift the composition of mountain plant communities towards that of grasslands and show how this shift may be reversed under reduced grazing.
Structure of biological soil crust communities inCallitris glaucophyllawoodlands of New South Wales, Australia
Authors: Thompson Wendy A. , Eldridge David J. , Bonser Stephen P.
Published: February 2009

Question:What is the nature of the relationships between cover, diversity and abundance of biological soil crusts, cover and diversity of vascular plants, and annual rainfall, soil texture and forestry practices inCallitris glaucophyllawoodlands? Location: Arid and semi‐aridCallitris glaucophylla‐domi‐nated woodlands of eastern Australia.

Methods:We documented soil crust‐forming mosses, lichens and liverworts at 83 woodland sites along a gradient of declining rainfall. Linear and non‐linear regression were used to examine relationships between soil crust species and attributes of vascular plant communities, and a similarity matrix (species abundance X sites) was subjected to Non‐metric Multi‐Dimensional Scaling (MDS), and Analysis of Similarities (ANOSIM) to show the degree of association between groups of taxa, and soil texture, rainfall classes and forestry practices.Results: We collected 86 taxa. Mosses were dominated by the familyPottiaceae, and lichens were dominated by squamulose forms. Average annual rainfall was highly correlated with soil crust community composition, and loamy soils supported a greater cover and diversity of taxa compared with sandy soils. Increases in tree cover were associated with significant, though weak, increases in abundance, but not diversity, of crusts. Crusts tended to be more diverse in areas that (1) had a sparse cover of ground‐storey plants; (2) were relatively stable ‐ as indicated by the proportion of perennial and/or native plants; (3) had more stable soil surfaces; and (4) were unlogged. Litter cover, overstorey thinning, and livestock grazing had no appreciable effect on crust diversity or cover.Conclusions:Callitris glaucophyllawoodlands provide substantial habitat for soil crust organisms, and the dense tree cover and closed canopies ofCallitrisdo not appear to have a major influence on the structure of biological crust communities. Unlike other woodland systems, relatively few patches would be required to reserve a high diversity of crust species.
Variation in tree growth, mortality and recruitment among topographic positions in a warm temperate forest
Authors: Tsujino Riyou , Takafumi Hino , Agetsuma Naoki , Yumoto Takakazu
Published: February 2009

Questions: Do the population dynamics of trees differ among topographic positions and, if so, how does topographic position affect the population dynamics of species that are distributed in a topography‐specific manner? Which is the most important life stage in determining vegetation patterns?

Location: Primary and secondary warm temperate evergreen broad‐leaved forest (40 ‐ 280 m a.s.l.) on the western part of Yakushima Island, Japan.

Methods: Mortality, recruitment, DBH growth and distribution of stems (= 5 cm DBH) in a 2.62‐ha plot were surveyed in 1992 and 2002 to determine the relationships between population parameters and (1) topography and (2) distribution patterns of 17 common tree species.

Results: Common species (n = 17) were classified into three distribution pattern groups: group A, distributed mainly on convex slopes; group B, on concave slopes, and group C, not aggregated with respect to topographic position. Stem mortality, recruitment and DBH growth were greater in group A than in group B within each topographic class. The hierarchy of stem mortality among topographic classes for groups A and B was convex > planar > concave. Stem recruitment density was relatively high on the convex and concave slopes, respectively, for groups A and B.

Conclusions The topographical positions of adult trees were not always most suited for adult survival and growth. For group A, the distribution pattern of adults was determined in the juvenile stage, while this was not the case for group B. Studies of juvenile stages are important for understanding the demographic basis of vegetation distribution patterns.
The significance of spatial and temporal patterns of algal mat deposition in structuring salt marsh vegetation
Authors: van Hulzen J.B. , van Soelen J. , Herman P.M.J. , Bouma T.J.
Published: February 2009

Question: Are there hot spots of algal mat deposition in space and time at the marsh scale and, if so, how does this affect the coexistence of a dominant (Spartina anglica) and gap dependent (Salicornia europaea) species?

Location: The Rattekaai salt marsh in the Scheldt estuary in the southwestern Netherlands (NW Europe).

Methods: Mat cover and the abundance of the gap dependent species Salicornia europaea were monitored at the scale of a marsh. The effects of mat cover on the vegetation structure were studied by applying three mat removal treatments over three growing seasons.

Results: The low marsh border was found to be a hot spot of algal mat deposition during the growing season, which had a correlated spatial pattern between two successive years at a 20 m X 20 m scale. The combination of duration, timing and repetition of mat cover determined growth inhibition of the competitive dominant Spartina anglica, and thereby the abundance of subordinates such as Salicornia europaea. Mat cover reduced the storage of carbon reserves in Spartina and our results imply that repetition of non‐lethal mat cover can lead to ‘gap creation’. Gaps gave only temporary habitat to less dominant species since Spartina quickly re‐invaded them. The gap dependent annual Salicornia was most abundant at intermediate levels of disturbance measured as a function of both space and time.

Conclusions In addition to disturbance level, the spatial and temporal distribution of disturbance are important in creating and maintaining habitat for gap dependent species. Relatively small disturbances will have a large effect on diversity if the spatial and temporal distribution of the disturbances leads to ‘disturbance hot spots’.
Effects of sampling time, species richness and observer on the exhaustiveness of plant censuses
Authors: Archaux Frédéric , Gosselin Frédéric , Bergès Laurent , Chevalier Richard
Published: February 2009

Question: How may sampling time affect exhaustiveness of vegetation censuses in interaction with observer effect and quadrat species richness?

Location: French lowland forests.

Methods: Two data sets comprised of 75 timed, one‐hour censuses of vascular plants carried out by five observers on 24 400‐m2 forest quadrats were analysed using mixed‐effect models.

Results: The level of exhaustiveness increased in a semi‐logarithmic way with sampling time and decreased with quadrat species richness. After one hour, 20 to 30% of the species remained undetected by single observers. This proportion varied among observers and the discrepancy increased with increasing sampling time. Fixing the sampling time may make richness estimates vary less between observers but the time limit should be at least 30 min to reduce the bias in exhaustiveness between rich and poor quadrats.

Conclusions We advocate the use of sampling methods based on spatially or temporally‐replicated censuses and statistical analyses that correct for the lack of census exhaustiveness in vegetation studies.
Long‐term changes of the vascular epiphyte assemblage on the palm Socratea exorrhiza in a lowland forest in Panama
Authors: Laube Stefan , Zotz Gerhard
Published: February 2009

Question: What are the qualitative and quantitative long‐term changes in the vascular epiphyte assemblage on a particular host tree species?

Location: Lowland rain forest of the San Lorenzo Crane Plot, Republic of Panama.

Methods: We followed the fate of the vascular epiphyte assemblage on 99 individuals of the palm Socratea exorrhiza by three censuses over the course of five years.

Results: The composition of the epiphyte assemblage changed little during the course of the study. While the similarity of epiphyte vegetation decreased on individual palms through time, the similarity analysed over all palms increased. Even well established epiphyte individuals experienced high mortality with only 46% of the originally mapped individuals surviving the following five years. We found a positive correlation between host tree size and epiphyte richness and detected higher colonization rates of epiphytes per surface area on larger trees.

Conclusions Epiphyte assemblages on individual S. exorrhiza trees were highly dynamic while the overall composition of the epiphyte vegetation on the host tree species in the study plot was stable. We suggest that higher recruitment rates, due to localized seed dispersal by already established epiphytes, on larger palms promote the colonization of epiphytes on larger palms. Given the known growth rates and mortality rates of the host tree species, the maximum time available for colonization and reproduction of epiphytes on a given tree is estimated to be ca. 60 years. This time frame will probably be too short to allow assemblages to be ever saturated.
Within‐year variation in the vegetative spread of five temperate grasses
Authors: Barthram G.T. , Elston D.A. , Griffiths J.H. , Bolton G.R. , Wright G.
Published: February 2009

Questions: Do species planted outdoors in native soil differ in the timing of their period of vegetative spread during the growing season?

Location: Cleish Hills, Fife, Scotland, UK.

Methods: Patches (20 cm × 20 cm) of Agrostis capillaris, Festuca rubra, Holcus lanatus, Lolium perenne and Poa trivialis were arranged in plots so that every species patch had all the remaining species as neighbours. The plots were cut every 14 days at 3 cm and photographed monthly from above. The photographs of species boundaries were traced and digitised. Measurements were made on the digitised images of the distances each species spread and of the area occupied by each species.

Results: Fitting some simple models to the data indicated firstly that species varied in their vegetative competitive ability, with A. capillaris and P. trivialis being the most and least competitive respectively, and secondly that the ability of a species to colonize can differ from its ability to resist colonization, the most discrepant species being H. lanatus. Our analysis also indicated statistically significant variation in the data over and above the simple models, providing evidence of additional, genuine, complexity in the seasonal patterns of spread.

Conclusion: This study provides evidence to support the hypothesis that clonal grass species do not spread vegetatively at the same times within a growing season. Since sward height is known to affect species spread, there is some opportunity for the manipulation of species composition simply through temporal control of sward height.
Ecosystem changes associated with grazing in subhumid South American grasslands
Authors: Altesor A. , Piñeiro G. , Lezama F. , Jackson R.B. , Sarasola M. , Paruelo J.M.
Published: February 2009

Question:What are the changes in vegetation structure, soil attributes and mesofauna associated with grazing in mesic grasslands?

Location:Southern Campos of the Río de la Plata grasslands, in south‐central Uruguay.

Methods:We surveyed seven continuously grazed and ungrazed paired plots. Plant and litter cover were recorded on three 5‐m interception lines placed parallel to the fence in each plot. We extracted soil fauna from a 10 cm deep composite sample and analysed the oribatids. Soil attributes included bulk density, water content, organic carbon (in particulate and mineral associated organic matter) and nitrogen content and root biomass at different depths. Changes in floristic, Plant Functional Types and mesofauna composition were analysed by Non‐metric Multidimensional Scaling.

Results:Species number was lower in ungrazed than in grazed plots. Of 105 species in grazed plots only three were exotics. Shrub and litter cover were significantly higher inside the exclosures, while the cover ofCyperaceae‐Juncaceaewas lower. Grazing treatments differed significantly in plant and oribatid species composition. Grazing exclusion significantly reduced soil bulk density and increased soil water content. Carbon content in particulate organic matter was lower in the upper soil of ungrazed sites, but deeper in the profile, grazing exclosures had 8% more carbon in the mineral associated organic matter.

ConclusionsOur results generally agree with previous studies but deviate from the results of previous analyses in (1) the increase of shrub cover in ungrazed sites; (2) the redistribution of the soil organic carbon in the profile and (3) the low invasibility of the prairies regardless of grazing regime.