Plant competition

Differences in yield-density models derived from an additive experimental design were used to compare the relative competitiveness of nine early-successional boreal forest plants (aster, grass, fireweed, fern, raspberry, willow, alder, birch, and aspen) on jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP). A randomized complete block split-split-plot design with three replications blocked on soil type was used. Initial density gradients were 0-4 plants/m 2 for woody and 0-8 plants/m 2 for herbaceous species. An a priori analytical approach that compared a full model (using linear regression analysis of 4th-year stem diameter of conifers under increasing cover and height of competitors) to various reduced models was used to assess competition. Increasing cover and (or) height of all competitors (except fern) significantly (P < 0.05) decreased conifer stem diameter. The final regression model (based on visual estimates of cover and differences in initial conifer size) accounted for 89% of the variation in stem diameter. During the years studied, both conifers responded similarly to competition, and herbaceous species were on average 28.9% more competitive than woody species. Under different growing conditions (e.g., a natural forest) the relative competitiveness of herbaceous and woody species may vary from these results.

English broom (Cytisus scoparius) is an aggressive invasive shrub in native sclerophyll forests of South Australia. We studied its relative growth rate (RGR) and competitive ability in soils from invaded and uninvaded woodlands, in comparison to three native species it commonly displaces:Hakea rostrata, Acacia verniciflua, and A. myrtifolia. Hakea was the slowest growing species throughout the year. Both native species had their highest RGR during spring. The RGR of broom was higher than that of both hakea and acacia in the winter and spring. Despite losing its leaves in the summer, the RGR of broom through the year was higher than that of either of the native species. Soil from the invaded stands had higher organic C, N and soluble P than that from uninvaded sites. Broom and acacia grew better in the higher nutrient soil than in the lower nutrient soil. Competition did not decrease the final biomass of any of the species in low nutrient soil. In the higher nutrient soil the biomass of broom was reduced by competition with acacia, but not by competition with hakea. Competition by broom reduced the biomass of hakea but not that of acacia. Broom's earlier and higher RGR, high competitiveness in nutrient rich soils, and probably its ability to change nutrient availability could be important contributors to the mechanisms by which it invades native woodlands.

Plant competition is thought to be driven by limiting resources. We propose that plant competition is triggered initially by the red to far-red light ratio (R:FR) originating from neighbouring plants, followed by a series of complex physiological processes, which exclude direct resource competition. Field experiments were conducted in 2005 and 2006 in which maize (Zea mays) was grown hydroponically. The effect of R:FR signal being reflected from the leaf surface of Amaranthus retroflexus was isolated by avoiding direct competition for light, water and nutrients. Results showed that the low R:FR reflected from the leaf surface of A. retroflexus did alter the carbon allocation pattern of maize when compared with maize growing free of weeds. Prior to silking, maize grown under low R:FR experienced temporal changes in plant height, persistent changes throughout the sampling period in root and shoot dry weights and rate of leaf appearance, but no changes in leaf area. At silking, low R:FR reduced ear and total plant dry weight. These results support the hypothesis that changes in R:FR acts as an early signal of pending competition by initiating a shade avoidance response. Data from this experiment suggest that once a plant is physiologically triggered into a shade avoidance response, these plants do so at a physiological cost, which may constrain plant development and possibly reduce reproductive fitness.

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In this review, we provide an overview of the role of glucosinolates and other phytochemical compounds present in the Brassicaceae in relation to plant protection and human health. Current knowledge of the factors that influence phytochemical content and profile in the Brassicaceae is also summarized and multi-factorial approaches are briefly discussed. Variation in agronomic conditions (plant species, cultivar, developmental stage, plant organ, plant competition, fertilization, pH), season, climatic factors, water availability, light (intensity, quality, duration) and CO(2) are known to significantly affect content and profile of phytochemicals. Phytochemicals such as the glucosinolates and leaf surface waxes play an important role in interactions with pests and pathogens. Factors that affect production of phytochemicals are important when designing plant protection strategies that exploit these compounds to minimize crop damage caused by plant pests and pathogens. Brassicaceous pl...

When the welfare state is under attack from neoliberal reformers, how can trade unionists and other campaigners build solidarity to defend it? Based on 45 qualitative interviews, this article compares campaigns to defend British health services and social security benefits between 2007 and 2016. Building on the macro-insights of comparative welfare-state literature and the more micro-level insights of studies on mobilisation, community unionism and union strategy, it examines the factors that help or hinder the construction of solidarity. This research finds that building solidarity is more difficult when defending targeted benefits than universal ones, not only because of differences in public opinion and political support for services, but also because the labour process associated with targeting benefits, namely the assessing and sanctioning of clients, can generate conflicts among campaigners.

Arbuscular mycorrhizal (AM) symbioses are formed by approximately 80% of vascular plant species in all major terrestrial biomes. In consequence an understanding of their functions is critical in any study of sustainable agricultural or natural ecosystems. Here we discuss the implications of recent results and ideas on AM symbioses that are likely to be of particular significance for plants dealing with abiotic stresses such as nutrient deficiency and especially water stress. In order to ensure balanced coverage, we also include brief consideration of the ways in which AM fungi may influence soil structure, carbon deposition in soil and interactions with the soil microbial and animal populations, as well as plant-plant competition. These interlinked outcomes of AM symbioses go well beyond effects in increasing nutrient uptake that are commonly discussed and all require to be taken into consideration in future work designed to understand the complex and multifaceted responses of plants to abiotic and biotic stresses in agricultural and natural environments.

We present a model-based approach for competitive analysis of manufacturing plants. As part of this approach, we propose the application of Operational Competitiveness Ratings Analysis (OCRA) to measure the competitiveness of plants in terms of their relative ineciency. We then present a conceptual framework to classify and identify the drivers of plant competitiveness in terms of decisions related to plant structure and infrastructure. Finally, we demonstrate the application of this model-based approach to conduct competitive analysis of plants in the US processed food industry. Ó

Few invaded ecosystems are free from habitat loss and disturbance, leading to uncertainty whether dominant invasive species are driving community change or are passengers along for the environmental ride. The ''driver'' model predicts that invaded communities are highly interactive, with subordinate native species being limited or excluded by competition from the exotic dominants. The ''passenger'' model predicts that invaded communities are primarily structured by noninteractive factors (environmental change, dispersal limitation) that are less constraining on the exotics, which thus dominate. We tested these alternative hypotheses in an invaded, fragmented, and fire-suppressed oak savanna. We examined the impact of two invasive dominant perennial grasses on community structure using a reduction (mowing of aboveground biomass) and removal (weeding of above-and belowground biomass) experiment conducted at different seasons and soil depths. We examined the relative importance of competition vs. dispersal limitation with experimental seed additions. Competition by the dominants limits the abundance and reproduction of many native and exotic species based on their increased performance with removals and mowing. The treatments resulted in increased light availability and bare soil; soil moisture and N were unaffected. Although competition was limiting for some, 36 of 79 species did not respond to the treatments or declined in the absence of grass cover. Seed additions revealed that some subordinates are dispersal limited; competition alone was insufficient to explain their rarity even though it does exacerbate dispersal inefficiencies by lowering reproduction. While the net effects of the dominants were negative, their presence restricted woody plants, facilitated seedling survival with moderate disturbance (i.e., treatments applied in the fall), or was not the primary limiting factor for the occurrence of some species. Finally, the species most functionally distinct from the dominants (forbs, woody plants) responded most significantly to the treatments. This suggests that relative abundance is determined more by trade-offs relating to environmental conditions (longterm fire suppression) than to traits relating to resource capture (which should most impact functionally similar species). This points toward the passenger model as the underlying cause of exotic dominance, although their combined effects (suppressive and facilitative) on community structure are substantial.

In this review, we provide an overview of the role of glucosinolates and other phytochemical compounds present in the Brassicaceae in relation to plant protection and human health. Current knowledge of the factors that influence phytochemical content and profile in the Brassicaceae is also summarized and multi-factorial approaches are briefly discussed. Variation in agronomic conditions (plant species, cultivar, developmental stage, plant organ, plant competition, fertilization, pH), season, climatic factors, water availability, light (intensity, quality, duration) and CO(2) are known to significantly affect content and profile of phytochemicals. Phytochemicals such as the glucosinolates and leaf surface waxes play an important role in interactions with pests and pathogens. Factors that affect production of phytochemicals are important when designing plant protection strategies that exploit these compounds to minimize crop damage caused by plant pests and pathogens. Brassicaceous pl...

Iron and phosphorus availability is low in many soils; hence, microorganisms and plants have evolved mechanisms to acquire these nutrients by altering the chemical conditions that affect their solubility. In plants, this includes exudation of organic acid anions and acidification of the rhizosphere by release of protons in response to iron and phosphorus deficiency. Grasses (family Poaceae) and microorganisms further respond to Fe deficiency by production and release of specific chelators (phytosiderophores and siderophores, respectively) that complex Fe to enhance its diffusion to the cell surface. In the rhizosphere, the mutual demand for Fe and P results in competition between plants and microorganisms with the latter being more competitive due to their ability to decompose plant-derived chelators and their proximity to the root surface; however microbial competitiveness is strongly affected by carbon availability. On the other hand, plants are able to avoid direct competition with microorganisms due to the spatial and temporal variability in the amount and composition of exudates they release into the rhizosphere. In this review, we present a model of the interactions that occur between microorganisms and roots along the root axis, and discuss advantages and limitations of methods that can be used to study these interactions at nanometre to centimetre scales. Our analysis suggests mechanisms such as increasing turnover of microbial biomass or enhanced nutrient uptake capacity of mature root zones that may enhance plant competitiveness could be used to develop plant genotypes with enhanced efficiency in nutrient acquisition. Our model of interactions between plants and microorganisms in the rhizosphere will be useful for understanding the biogeochemistry of P and Fe and for enhancing the effectiveness of fertilization.

Peatlands are important ecosystems in the context of biospheric feedback to climate change, due to the large storage of organic C in peatland soils. Nitrogen deposition and increased nutrient availability in soils following climate warming may cause changes in these ecosystems affecting greenhouse gas exchange. We have conducted an N and 5 P fertilization experiment in two Swedish bogs subjected to high and low background N deposition, and measured the exchange of CO 2 , CH 4 and N 2 O using the closed chamber technique. During the second year of fertilization, both gross primary production and ecosystem respiration were significantly increased by N addition in the northernmost site where background N deposition is low, while gross primary production was 10 stimulated by P addition in the southern high N deposition site. In addition, a shortterm response in respiration was seen following fertilization, probably associated with rapid growth of nutrient-limited soil microorganisms. No treatment effect was seen on the CH 4 exchange, while N 2 O emissions peaks were detected in N fertilized plots indicating the importance of taking N 2 O into consideration under increased N availability.

The distribution and abundance of the aquatic flora of Lake Naivasha has been constrained by two ecosystem-level processes . One is the natural and unpredictable fluctuation of water levels which the lake experiences, resulting in a drawdown zone of several vertical meters . The other is the consequence of herbivory by several alien species, linked with competition between rooted aquatic plants and phytoplankton .

Alterations in the structure of the vegetation and of the soil seed bank associated with primary invasions by alien species could create novel conditions that facilitate secondary invasions by other alien or weedy species. Here, we present a unique dataset collected from a site experiencing a process of secondary invasion by Fallopia japonica after having long been invaded by Gunnera tinctoria. These are among the largest herbaceous plant species in the world and among the worst invaders in Ireland. The main objectives of this study were 1) to test for differences in the soil seed bank associated with these invaders; 2) to discuss the potential role of changes in the soil seed bank associated with G. tinctoria invasions in promoting secondary invasions by F. japonica; and 3) to discuss the potential role of niche and fitness differences in determining the outcomes of competition between these species. The differences in the characteristics of the seed bank invaded by these species were evaluated by collecting samples in comparable, adjacent areas invaded by G. tinctoria and by F. japonica. Soil samples were collected at to two points in time (May and October), from three depth categories (0Á5cm; 5Á10cm; 10Á15cm). The seedling emergence approach was used to assess the structure of the soil seed bank. Fallopia japonica showed a capacity to alter substantially the structure of invaded soil seed bank within a short period of time. Significant changes in the composition, richness and abundance of the seed bank were observed, in both the transient and the more persistent component of the seed bank. A capacity for a rapid displacement (few years only) of long-term stands of G. tinctoria suggest a higher competitive ability for F. japonica and/or an availability of empty niches not occupied by G. tinctoria. Our findings show that the formation of a persistent soil seed bank by an invasive species is not a sufficient condition for preventing its displacement by another invader. This study represents an important starting point for evaluating the long-term implications of plant invasions on invaded ecosystems and on the potential causes of secondary invasions.

A longleaf pine wiregrass ecosystem in the sandhills of north central Florida, upon which turkey oak gained dominance following a wild®re, was treated with applications of hexazinone (1.1 or 2.2 kg/ha) in May 1991. All applications successfully reduced competition from oaks in the overstory and understory (mortality >80%), resulting in progressive increases in the foliar cover of wiregrass, all graminoids and forbs through time. Broadcast application caused a decline in forb cover and species richness during the initial growing season, which recovered by the following year. The 2.2 kg/ha spot application resulted in an increase in species richness, while evenness declined with the continuing expansion of wiregrass. The entire site was then burned in June 1995 by prescribed ®re, which caused a widespread decrease in the cover of oaks, shrubs, wiregrass, all graminoids and forbs and plant species richness. In the following year, forb cover increased and oak cover remained signi®cantly lower on plots treated with the combination of hexazinone plus ®re than on ®re-only plots. The overall cover of forbs, graminoids, shrubs and longleaf pines continued to increase through time. Broadcast application initially exposed a greater number of understory plants to direct contact with herbicide, posing a higher mortality risk than may be acceptable in restoration efforts. Although recovery occurred in subsequent years, the lower selectivity of broadcast application makes it a less suitable restoration technique. Spot application of hexazinone was more selective in its effects upon the plant community. The 2.2 kg/ha spot application produced increases in the cover of wiregrass, all graminoids and forbs and the highest levels of species richness and diversity. The 2.2 kg/ha application rate was also most effective in controlling woody plant competition and is therefore recommended for restoring longleaf pine wiregrass ecosystems in sandhills and similar environments. Hexazinone application followed by prescribed ®re accelerates the rate of ecosystem restoration over that achievable by using ®re alone. The ecological bene®ts of controlling competition and rebalancing¯oristic composition rapidly achieved through this combination of treatments would likely require many cycles of prescribed ®re, if used as an individual treatment, over a period of several decades. #

It is well documented that pathogens can affect the survival, reproduction, and growth of individual plants. Drawing together insights from diverse studies in ecology and agriculture, we evaluate the evidence for pathogens affecting competitive interactions between plants of both the same and different species. Our objective is to explore the potential ecological and evolutionary consequences of such interactions. First, we address how disease interacts with intraspecific competition and present a simple graphical model suggesting that diverse outcomes should be expected. We conclude that the presence of pathogens may have either large or minimal effects on population dynamics depending on many factors including the density-dependent compensatory ability of healthy plants and spatial patterns of infection. Second, we consider how disease can alter competitive abilities of genotypes, and thus may affect the genetic composition of populations. These genetic processes feed back on population dynamics given trade-offs between disease resistance and other fitness components. Third, we examine how the effect of disease on interspecific plant interactions may have potentially far-reaching effects on community composition. A host-specific pathogen, for example, may alter a competitive hierarchy that exists between host and non-host species. Generalist pathogens can also induce indirect competitive interactions between host species. We conclude by highlighting lacunae in our current understanding and suggest that future studies should (1) examine a broader taxonomic range of pathogens since work to date has largely focused on fungal pathogens; (2) increase the use of field competition studies; (3) follow interactions for multiple generations; (4) characterize density-dependent processes; and (5) quantify pathogen, as well as plant, population and community dynamics.

The relative roles of abiotic conditions and competition by grassland plants in restricting the distribution of certain alpine plant species to snowbed habitats (i.e. sites with particular long-lasting snow cover) is still a matter of debate. Here, we set up a five-year field experiment to compare three vital rates (germination from sown seeds, growth and survival of transplanted juveniles) of four calcareous alpine snowbed plants within sparsely and densely vegetated plots along a natural snowmelt gradient from the centre of a snowbed to the margins of the surrounding grasslands. Without a dense canopy, we found germination and juvenile growth to respond homogeneously across species with optimal performance under intermediate snowmelt. Dense vegetation cover reduced these two vital rates for all species, with the strongest effects of competition detectable at intermediate snowmelt times again. Survival patterns were less consistent among species. In particular, two of the four species showed lowest mortality at the grassland margins when the surrounding vegetation cover was sparse, and the effect of a dense canopy on their survival turned from competitive to facilitative towards the snowbed centre. Overall, these results indicate that the distribution limits of the studied snowbed plants are determined by a combination of abiotic and biotic effects with competition further reducing their performance in grassland sites below the already low levels caused by the abiotic conditions. With respect to climate warming, a combined negative effect of reduced snow cover protection and increased competition by encroaching grassland plants seems a worrying, but possible scenario. We concede, however, that care has to be taken when drawing conclusions on cause-effect relationships from experiments along natural gradients and discuss the uncertainties associated with our results as well as with inferences on the possible future of snowbed plants under a warmer climate.

This chapter reviews the climate factors that influence crop production and agricultural water use. It discusses (a) modeling studies that use climate-change model projections to examine effects on agricultural water allocation and (b) scenario studies that investigate economic impacts and the potential for using adaptation strategies to accommodate changing water supplies, crop yields, and pricing. The chapter concludes with sections on ranching and drought and on disaster-relief programs. • Under warmer winter temperatures, some existing agricultural pests can persist year-round, while new pests and diseases may become established. While crops grown in some areas might not be viable economically under future climate conditions, other crops could replace them. (high confidence).

Climate change can be expected to increase the frequency of summer droughts and associated low water tables in ombrotrophic peatlands. We studied the effects of periodic water table drawdown in a mesocosm experiment. Mesocosms were collected in Southern Sweden, and subsequently brought to an experimental field in the Netherlands. Two water table treatments were applied: one with constant water tables at 5 cm below the moss surface, and one in which the water table was allowed to drop, resulting in water tables fluctuating between 5 and 21 cm below the moss surface. Sphagnum growth, as well as Sphagnum and vascular plant abundance, were assessed for 2 1 2 years. Our results show that the abundance of graminoid species increased most in the constant water table treatment. In contrast, ericoid species cover increased when water tables were allowed to fluctuate. Furthermore, Sphagnum cuspidatum production decreased with fluctuating summer water tables, while Sphagnum magellanicum responded oppositely. From these results we conclude that increased occurrence of periods with low water tables may bring about a shift in dominant Sphagnum species as well as a shift from graminoid to ericoid vascular plant cover, resembling the shift from hollow to lawn or hummock vegetation. The difference in response within functional groups (vascular plants, Sphagnum) may add to the resilience of the ecosystem.

For sustainable forest management, it is important to know the response of timber species to the change in environment caused by logging. We performed a 2-year study on germination, survival and growth of four timber species, Cedrela odorata, Swietenia macrophylla, Hymenaea courbaril, and Cariniana micrantha, and one non-commercial species Tachigali vasquezii. We sowed seeds of these species in five microenvironments:

The aim of this work was to introduce competition effects in the model underlying the analysis of forest tree experiments. Results were compared with analysis in which effects were neglected. Trials with different levels of precision and mortality were used, including the following species: Gallesia gorarema Vell. Moq., Eucalyptus grandis Hill ex Maiden, Eucalyptus citriodora Hook, Pinus elliottii Engl. var.

Question: 1. How do the competitive response and the importance of competition vary between species and along a flooding gradient? 2. How does the role of competition in constraining species distribution limits along the gradient vary between lower and upper limits? Location: A 1-ha meadow within the Alzette floodplain in Luxembourg. Methods: Competitive response and importance of competition were assessed on seven meadow species differing in their tolerance to flooding. Species were cultured in monocultures and in mixtures, in three water treatments reflecting the wet, the middle and the dry end of a natural flooding gradient. We developed two models based on a multiple regression in order to express each component of competition as a function of the neighbour biomass. Results: Five species showed variations in their competitive response across water treatments; however, these species achieved either their highest or their worst competitive response in their optimal water treatment (i.e. the treatment in which the species had the highest biomass in monoculture). Competition was more important for the flood-tolerant species in the dry treatment than for the flood-intolerant species in the wet treatment. Conclusions: 1. Variations in species competitive responses along flooding gradients may be the result of either an amplified effect between competition and hydrological stresses, or a hierarchical effect of stress over competition. 2. The role of competition is more important in constraining the upper distribution limits of the flood-tolerant species than the lower limits of the flood-intolerant species along flooding gradients.

A new method to evaluate the interaction between individuals competing for light in a monospecific stand is presented. 2. Light intercepted by a leaf of a target individual is influenced by its own leaves and those of neighbours higher in the canopy. We assume that light intercepted by the leaf is the sum of the light that penetrates the foliage of the target and the foliage of neighbours. We define the degree of the interaction as the fraction of the intercepted light that penetrated the foliage of neighbours.

Increased plant population density in irrigated and fertilized maize crops enhances plant-to-plant variability since early vegetative stages, because the most suppressed individuals of the stand intercept less radiation per unit leaf area than the dominant ones (i.e. a size-asymmetric competition for light). Contrarily, a size-symmetric competition has been proposed for the acquisition of soil resources in a plant community (e.g. N capture per unit root length is similar among plants of different size). Hence, N fertilization effect on the variability of maize plants would depend on the initial plant-to-plant variability or on that promoted by a high plant population density. Two maize hybrids with contrasting tolerance to crowding (tolerant AX820 and intolerant AX877) were cultivated under different combinations of stand densities (6, 9 and 12 plants m −2 ) and N supplies (0 and 200 kg N ha −1 ) without water restrictions. Variability in plant growth rate among plants was computed along the cycle, especially after fertilizer was applied (i.e. the early reproductive period; PGR ER ) and during the critical period around silking (PGR CP ). Plant-to-plant variability in biomass partitioning to the ear (partition index; PI), ear growth rate during the critical period (EGR CP ) and kernel number per plant (KNP) was also established. Reduced N supply increased the coefficient of variation (CV) of PGR ER , PGR CP , EGR CP and KNP (0.05 < P < 0.10). The CVs of PGR CP , PI, EGR CP and KNP augmented (0.001 < P < 0.10) at the highest stand density. The CVs of PGR ER , PGR CP , PI and KNP were larger for hybrid AX877 than for hybrid AX820 (0.001 < P < 0.10). N fertilization smoothed the initial plant-to-plant variability, but the extent of this benefit in a maize crop is genotype dependent; it was much larger in the hybrid tolerant to crowding stress than in the intolerant one. For the latter, the variability held during the critical period around silking and produced a high CV of KNP.

Natural regeneration may be disrupted by the rise of the water table in surface layers after clearcutting forested wetlands. A study was initiated on eight forested wetlands that were successively clearcut and drained 3 years later. The objectives were (1) to assess conifer and deciduous regeneration on waterlogged clearcut sites, (2) to determine the effect of water table level changes after clearcutting and drainage on the growth rate of advance regeneration, and (3) to determine if sphagnum moss growth rate was in¯uenced by clearcutting, drainage and microrelief. 3 years after strip clearcutting, the area based inventory showed that softwood regeneration was abundant in the clearcut, but 84% of the seedlings were smaller than 30 cm and vulnerable to suppression from the competition. Indeed, the opening of the forest cover promoted massive invasion of pioneer species such as trembling aspen (Populus tremuloides Michx.) and white birch (Betula papyrifera Marsh.). Black spruce (Picea mariana (Mill.) B.S.P.) and red spruce (Picea rubens Sarg.) had dif®culties maintaining their presence after clearcutting. The ratio hardwood stems : softwood stems changed from 1.1 in the forest to 3.8 in the clearcut. Balsam ®r (Abies balsamea (L.) Mill.), larch (Larix laricina (Du Roi) K. Koch) and cedar (Thuja occidentalis L.) represented 93% of the softwood regeneration. 3 years after clearcutting, balsam ®r advance regeneration had a signi®cantly lower growth rate in the middle of the clearcut than near the edges of the clearcut. 2 years after drainage, seedling growth at 10 m from the drainage ditch was signi®cantly greater than at 70 m from ditch. No signi®cant differences were found between mineral and organic soil types, but height growth was positively correlated to C : N ratios of the individual site types. Abundant competition on richer sites limits the development of softwood regeneration. On a short term basis, competition more than watering-up seems a threat to softwood regeneration. Sphagnum growth rates measured with the crank-wire method showed no effect of clearcutting or drainage, but a higher growth rate in hollows (3.2 cm per year) compared to hummocks (2.0 cm per year). These growth rates indicate that sphagnum should not affect regeneration but could overgrow yearlings of slow growing species.

A number of signalling mechanisms are responsible for triggering plastic morphological and physiological responses of plants to the proximity of neighbours. Among these mechanisms, the phytochrome-mediated control of branching and elongation in response to alterations in red:far-red ratio (R:FR) has been investigated in considerable detail. 2. While the role of phytochrome B in R:FR perception has been well established, and the consequences of neighbour photo-detection on competitive ability are receiving attention, several important issues remain to be addressed regarding the ecology of plant-plant signalling in canopies. In particular, the role of other photoreceptors in neighbour detection and the impact of neighbour detection on population-level attributes, such as size structure and productivity:density relationships are poorly characterized.

Шумските екосистеми се еден од најзначајните столбови на растителниот и животинскиот биодиверзитет, но нивната стабилност и одржливост често пати е загрозувана од различни биотски, антропогени или абиотски фактори. Во одредени случаи настанува и до целосно уништување на одреден шумски екосистем. Во таквите случаи многу чест и многу сериозен причинител се шумските пожари, кои за кусо време опожаруваат големи шумски површини и значително го нарушуваат или целосно уништуваат шумскиот екосистем. Сепак, способноста за природно обновување како карактеристика на шумската дендрофлора е значаен фактор за повторно воспоставување на шумска вегетација на опожарените шумски површини и целосна ревитализација на шумскиот екосистем. Целта на овој труд е да се утврдат основите природни сукцесивни процеси на шумската дрвенеста вегетација кои се појавуваат некоку години по силен шумски пожар од кој целосно е уништен шумскиот екосистем. Со проучувањето на појавата, развитокот, квалитативните и квантитативни карактеристики на единките од природната обнова се добиени податоци за можноста и успешноста на ревитализацијата на опожарениот шумски екосситем. За таа цел извршени се теренски истражувања преку директни мерења и проучувања на природната обнова со методот на пробни површини. Добиените резултати укажуваат на тоа дека опожарената шумска површина постепено се ревитализира, првенствено со пионерски видови од шумската дендрофлора, но за целосна ревитализација на шумскиот екосистем е потребен долг временски период.
The forest ecosystems are one of the most important foundations of the biological diversity concerning flora and fauna, but forest’s natural balance and sustainability are often on impact and influence by wide spectra of biotic, anthropogenic or abiotic factors. In specific circumstances, some of the forest ecosystems can be totally destroyed. Namely, the wildfires, in particular forest fires can cause enormous consequences and devastating impact on forest ecosystems; for short period of time forest fires can burn large forest mass and make the forest ecosystem an erasure. Even so, the forest vegetation has a very important and essential ability- the dendrofloral capacity for natural regeneration, both vegetative and by seed, and for a period of time to re-establish and implicitly rehabilitate, i.e. to grew up and become a forest as it once was. The main purpose of this scientific paper is to determine and note the basic natural succession processes of the forest dynamics after forest fire, particularly the natural regeneration of the forest woody species. Thus, determination of the appearance, development, qualitative and quantitative characteristics of the individuals in a natural regeneration process were made and the data base was analyzed to see the possibility and efficiency of the rehabilitation of the burned forest ecosystem. Therefore, field examinations were made using direct measurements and research of the presence of the natural regeneration; the method of the sample plats was used. The results indicate that burned forest area gradually and progressively regenerates, primarily with pioneer species of the forest dendroflora. After all, for complete rehabilitation of the forest ecosystem there is a need of a long period of time; eventually, the forest regenerates slowly, but assuredly.

Background: Allelopathy (negative, plant-plant chemical interactions) has been largely studied as an autecological process, often assuming simplistic associations between pairs of isolated species. The growth inhibition of a species in filter paper bioassay enriched with a single chemical is commonly interpreted as evidence of an allelopathic interaction, but for some of these putative examples of allelopathy, the results have not been verifiable in more natural settings with plants growing in soil.

Herbivory Lolium arundinaceum MAXQ endophyte Neotyphodium coenophialum Predators Soil Trophc interactions a b s t r a c t We have investigated community and ecosystem consequences of endophyte symbiosis with tall fescue over the past 13 y. Lolium arundinaceum is the most abundant plant in the eastern USA, and most is infected by the wild-type KY-31 endophyte Neotyphodium coenophialum. We established two large experimental grasslands (in 1994 and in 2000) with endophyte-infected or endophyte-free seed sown on recently plowed herbaceous vegetation. Other plant species established by seed or vegetative fragments. No other treatments were applied and plots were subject to natural biotic and abiotic variation. A third experiment examined ecological influences on endophyte infection dynamics starting from an intermediate infection frequency. Finally, we synthesized recent literature investigating the impacts of the tall fescue endophyte on the abundance of associated arthropod species. We found wide-ranging consequences of the endophyte from significant effects on soil feedback and decomposition rates, to plant-plant competition, diversity, productivity, invasibility and succession, to plant-herbivore interactions and energy flow through the food web. Further, we found that herbivore pressure caused rapid increases in infection frequency. Our results suggest that endophyte symbiosis in tall fescue can have a transforming effect on ecological systems. (J. A. Rudgers).

This report documents impacts from manipulations of native forest soils and competing vegetation on development and ectomycorrhizal formation of outplanted western white pine and Douglas-fir in the Inland Northwest. Treatments were: 1) mounding surface horizons with competition left in place, 2) mounding surface horizons with subsequent physical or chemical control of competing vegetation, 3) scalping for control of competing vegetation,

1 We used a series of removal experiments to examine how species response to competition and climatic differences varied in three different years. We tested the interaction between removal of the dominant grass species, Festuca rubra , and year-to-year environmental variation in a mown mountain grassland. 2 In each year, we quantified shoot frequency and above-ground biomass of all remaining plant species. Above-ground responses were tested both by analysis of covariance and by redundancy analysis with randomization tests of changes in total species composition. 3 Analysis of above-ground biomass data showed that other species compensated for the removal of F. rubra biomass within 2 years and that the response in total biomass of the community did not differ among years in which the experiment was started. 4 Multivariate tests showed that species composition changed as a result of the removal; grass biomass and frequency increased more than that of dicotyledons. However, response of species composition to removal of F. rubra was significantly different between onset years. Specific conditions in individual years thus affect the competitive ability of individual species in a non-additive way. 5 Our results indicate that the year-to-year variation at the site has the potential to affect species coexistence and richness. As a consequence, year-to-year variation of climatic parameters may be an important driving factor in community dynamics and should be taken into account in studies of ecosystem response to climate.

Forest regeneration is a spatial multifaceted process with numerous unknown variables. The individual area or the area potentially available (APA) to an individual plant embodies an idea widely used in population ecology but it has fewer applications in forest research. It was used a Voronoi/ Thiessen tessellation in order to determine the individual area of each sapling. The study was conducted in a naturally regenerated area; using data collected from over seven thousands saplings positioned in a network of permanent rectangular sampling plots. The Voronoi/ Thiessen polygons were used to characterize spatial pattern of sapling distribution as well as the competition relations between the individuals. It is obvious that, at least from the mathematically point of view, the Voronoi tessellation represents one of the best solutions to determine neighbouring competitors of a tree. There were studied the correlations between APA values and the main biometrical attributes, height growth and competition indices. Furthermore, it is shown that APA coefficient of variation is a straight-forward indicator with positive results as an indicator of spatial pattern. The statistical significance of this indicator was evaluated by comparing the results with the values of a 95% confidence envelope generated by Monte-Carlo simulations. Two practical software tools were produced using Visual Basic (VORONOI and ARIA VORONOI) in order to simplify the analyses.

Goosegrass (Eleusine indica L.) is a serious weed in traffi cked areas of bermudagrass (Cynodon spp.) golf and sports turf. Th e objective of this study was to evaluate soil compaction and canopy cover as determinants of goosegrass competition in bermudagrass turf in sand soil. Goosegrass cover, plant density, and soil penetration resistance (SPR) were measured in traffi c and notraffi c plots in bermudagrass golf course tees and sports fi eld foul areas. Goosegrass plant density and cover were larger in traffi c plots compared with no-traffi c plots. Soil penetration resistance increased only at 5.0 cm depth due to traffi c, while other soil properties including bulk density measured in golf course tees showed no eff ect from traffi c. Two experiments measured the eff ect of controlled soil compaction on root and shoot dry weight of goosegrass and bermudagrass in containers. Th e fi rst experiment evaluated eff ects of three soil compaction levels (1.14, 1.24, 1.33 g cm-3 bulk density) on goosegrass and bermudagrass grown separately. Th e second experiment evaluated eff ects on the two species grown together in competition, from two soil compaction levels (1.07 and 1.26 g cm-3 bulk density), two N application rates (48 and 96 kg ha-1 mo-1), and two mowing heights (1.3 and 2.5 cm). Th e second experiment also evaluated goosegrass seedling emergence and tiller numbers. When species were grown separately, bermudagrass root and shoot dry weight showed no eff ect from soil compaction, but goosegrass root weight was reduced. When species were grown together, bermudagrass root weight was reduced by compaction, but goosegrass was not aff ected. Goosegrass seedling emergence was reduced 58% by high mowing height, which paralleled an increase in bermudagrass canopy cover based on shoot dry weight. Canopy cover, not compaction, more readily explained the competition and infestation of goosegrass in traffi cked areas in sand soil.

Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant-plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant-plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists.

Wheat genotypes susceptible to different races of a pathogen, Puccinia striiformis, were planted in pure stands and in three different 1:1 mixtures, in both the presence and absence of disease, in two sites, and over 3 years. Using analyses of variance, we tested whether disease and intergenotypic competition influenced a genotype's fitness and whether significant interactions existed between the effects of disease and competition on genotype fitness. Seed weight, number of inflorescences per seed planted, seeds per inflorescence, and absolute fitness were estimated for each genotype in each treatment. Absolute fitness was determined as the number of seeds collected per seed planted. Disease reduced seed weight. The other fitness measures were influenced by either disease or competition, and the impact of each factor often varied among site-year combinations. In general, interactions between the effects of disease and competition on genotype fitness were not significant. The few significant interactions indicated a less than additive effect of competition and disease on genotype fitness. The overall lack of interaction may be, in part, due to lesser disease levels in mixed as compared with pure stands, or reduced level of competition under diseased conditions. Résumé : Les auteurs ont semé des génotypes de blé susceptibles à différentes races du pathogène Puccinia striiformis en peuplement pur, et selon trois mélanges différents 1 : 1, à la fois en présence et en absence de maladie, sur deux sites, et au cours de 3 années. A l'aide de l'analyse de variance, les auteurs ont vérifié si la maladie et la compétition entre génotypes influencent l'adaptation des génotypes, et s'il existe des interactions significatives entre les effets de la maladie et de la compétition sur l'adaptation des génotypes. Le poids des graines, le nombre d'inflorescences par graine semée, le nombre de graines par inflorescence, et l'adaptation absolue ont été évalués pour chaque génotype dans chaque traitement. On détermine l'adaptation absolue comme le nombre de graines récoltées par graine semée. La maladie réduit le poids des graines. Les autres mesures d'adaptation sont influencées soit par la maladie ou soit par la compétition, et l'impact de chaque facteur varie souvent selon les combinaisons site-année. En général, les interactions entre les effets de la maladie et de la compétition sur l'adaptation du génotype ne sont pas significatives. Les rares interactions significatives indiquent un effet moins qu'additif de la maladie et de la compétition sur l'adaptation du génotype. L'absence générale d'interaction pourrait être due en partie à un taux de maladie moindre dans les peuplements mélangés, comparativement aux peuplements purs, ou à un taux inférieur de compétition en présence de maladies.

Key to climate change abatement strategies is the understanding of the comparative carbon mitigation implications of management of native forests oriented to different end-uses such as conservation, conventional management, or integrated management that includes bioenergy. In Mexico 95% of total logging is conducted in native forests, and 80% of it in pine-oak forests. In this paper we compare the carbon mitigation dynamics of mixed native pine-oak forests in Central Mexico under current management -used as a reference scenario -with two alternative scenarios: (a) oak conservation and (b) oak conservation + bioenergy. To estimate the carbon fluxes for each scenario and each forest type we used the CO2FIX V3.1 model, a user-friendly tool designed to calculate all carbon fluxes in forest stands, forest-derived products and bioenergy technologies based on forest slash and industrial residues. The CO2FIX model applies a cohort-type approach to estimate carbon fluxes in mixed or uneven-aged forests where species groups or age cohorts typically show differences in growth, biomass allocation, intra and inter-cohort competition, and mortality. The product module tracks the carbon in products derived from the forests until the decomposition is complete, whereas the bioenergy module compares total greenhouse gas dynamics of reference and alternative bioenergy technologies, applying IPCC guidelines to estimate the carbon equivalence of the various greenhouse gases. We compare the outcome of the three scenarios in a managed community forest of about 11,000 ha in Michoacan, Central Mexico. The carbon mitigation potential after 20 years varied between 8.2 and 19.3 t C/ha for the oak conservation scenario and between 21.6 and 42.9 t C/ha for the oak conservation-bioenergy scenario. The bioenergy scenario results in a continuous stream of about 1.36 t C/ha of carbon benefits per year, whereas the oak conservation scenario will stop accumulating carbon after 40 years, compared to current forest management and energy generation. #

We model effects of interspecific plant competition, herbivory, and a plant's toxic defenses against herbivores on vegetation dynamics. The model predicts that, when a generalist herbivore feeds in the absence of plant toxins, adaptive foraging generally increases the probability of coexistence of plant species populations, because the herbivore switches more of its effort to whichever plant species is more common and accessible. In contrast, toxin-determined selective herbivory can drive plant succession toward dominance by the more toxic species, as previously documented in boreal forests and prairies. When the toxin concentrations in different plant species are similar, but species have different toxins with nonadditive effects, herbivores tend to diversify foraging efforts to avoid high intakes of any one toxin. This diversification leads the herbivore to focus more feeding on the less common plant species. Thus, uncommon plants may experience depensatory mortality from herbivory, reducing local species diversity. The depensatory effect of herbivory may inhibit the invasion of other plant species that are more palatable or have different toxins. These predictions were tested and confirmed in the Alaskan boreal forest.

Global diversity loss has renewed the interest in the underlying mechanisms that explain species diversity and its maintenance in natural systems. This gave the impetus to significant new development in competition research. The aim of this chapter is to review important research results on competition among microalgae and on the effects of environmental fluctuation or disturbance on community structure. It covers mechanistic competition theory as well as new approaches questioning the central theorem of the classical theory. Recent results of competition experiments and bio essays are included, that have shown how factors other than macro-nutrients may affect the structure of microalgal communities. To explain the influence of disturbance on community structure, we report different approaches to define disturbance and explain the meaning of disturbance within the framework of this review. Intermediate disturbance hypothesis and dynamic equilibrium theory build the theoretical background for discussing competition in variable environments. Experimental results, models and simulations show how environmental fluctuation influences community structure and how different mechanisms may interact.

Designs for greenhouse studies of interactions between plants are reviewed and recommendations for their use are provided[ 1 Papers published over a 09!year period showed the replacement series design to be the most popular\ especially in studying cropÐweed interactions[ Fifty per cent of the studies involved only two species\ although studies testing the interaction between di}erent genotypes of only a few species were also popular[ 2 Limitations imposed by the choice of design\ the variables measured\ and the analysis used on the range of inferences that may be validly drawn from the experiment are frequently not well understood or appropriate for the questions that appear to be addressed[ One example is the failure to distinguish the outcome of competition "the long!term outcome of interaction# and the e}ects of species on each other[ 3 Studies in which only _nal yield is measured are severely limited as to the inferences which may be drawn[ E}ects due to interspeci_c interaction during the course of the experiment cannot then be separated from pre!existing di}erences\ and interpretation may be biased towards species whose individuals were initially larger[ In addition\ measurements at several times are necessary to understand the changing dynamics of species interaction[ 4 Simple pair!wise mixtures can assess the e}ect of treatment factors on the outcome of competition[ Replacement series and related diallel designs generally produce results that may be size!biased even when initial interspeci_c di}erences are known[ Additive designs "including targetÐneighbour designs#\ despite confounding density with species proportions\ o}er considerable scope for addressing mechanistic ques! tions about interspeci_c interactions[ Designs that allow response surface analysis can avoid many of the problems inherent in the other methods\ but all need to be adjusted for initial interspeci_c di}erences[ Designs for multiple species experiments are still largely untested\ although several designs have been used[ At the level of the individual plant\ hexagonal fan designs permit study of the e}ects of varying the spatial pattern\ and the densities and the relative proportions of interacting species\ but su}er from lack of independence and lack of randomization[ Keywords] additive\ competition\ competitive hierarchy\ diallel\ experimental design\ hexagonal fans\ interspeci_c interaction\ replacement series\ response surface\ size! bias\ targetÐneighbour design