Relative Neighbor Effect Research Articles

Invasion of Trifolium repens L. aggravated by biodegradable plastics: adjustable strategy for foraging N and P

The invasion of alien plant and the pollution caused by soil microplastics have emerged as significant ecological threats. Recent studies have demonstrated aggravating effect of non-biodegradable microplastics on plant invasion. However, the impact of biodegradable microplastics (BMPs) on plant invasion remains unclear. Therefore, it is imperative to explore the impact of BMPs on plant invasion. In this study, a 30-day potting experiment with Trifolium repens L. (an invasive plant) and Oxalis corniculata L. (a native plant) was conducted to evaluate the influence of BMPs on T. repens's invasion. The findings revealed that BMPs results in a reduction in available N and P contents, thereby facilitating the colonization of arbuscular mycorrhizal fungi on T. repens 's roots. Consequently, T. repens adjusted its N and P foraging strategy by increasing P absorption ratio, and enhancing the accumulation of N and P in leaves. This ultimately led to the decrease of relative neighbor effect index of T. repens, indicating an aggravated invasion by T. repens. This study significantly enhances and expands the understanding of mechanisms by which microplastics aggravate plant invasion.

The relative importance of drought stress and neighbor richness on plant–plant interactions shifts over a short time

Exploring how plant–plant interactions between species and their neighbors vary with biotic and abiotic factors is vital to understanding community assembly mechanisms in the context of global changes. In this study, using a dominant species (Leymus chinensis (Trin.) Tzvel.) in the semiarid Inner Mongolia steppe as the target species and ten other species as neighbors, we carried out a microcosm experiment to evaluate how drought stress, neighbor richness and season affected the relative neighbor effect (Cint) (the ability to reduce growth of target species). The factor of season interactively affected the effect of drought stress or neighbor richness on Cint. In the summer, drought stress decreased Cint directly and indirectly by decreasing SLA hierarchical distance and neighbor biomass. In the subsequent spring, drought stress increased Cint, and neighbor richness increased Cint directly and indirectly by increasing neighbor community functional dispersion (FDis) and neighbor biomass. Specifically, SLA hierarchical distance was positively associated with neighbor biomass, while height hierarchical distance was negatively associated with neighbor biomass in both seasons, which increased Cint. These findings show that the relative importance of drought stress and neighbor richness on Cint shifted over seasons, which provides strong empirical evidence of how plant–plant interactions respond to changes in biotic and abiotic factors in the semiarid Inner Mongolia steppe over a short-term time. Furthermore, this study provides novel insight into community assembly mechanisms in the context of climatic aridity and biodiversity loss in semiarid regions.

ROW SEEDING CONFIGURATION REGULATES YIELD, QUALITY AND COMPETITION IN COMMON VETCH (Vicia sativa L.)-SUDANGRASS (Sorghum sudanense (Piper.) Stapf.) MIXTURE

Intercropping used in modern agricultural systems is designed for growing more plant species in the samefield for maximized growth parameters. This study was conducted to understand the effects of row seedingconfiguration (same, alternate and cross seeding row) and different Sudangrass ratios (25 and 50%) on yield,quality, and competitive ability of common vetch in second crop production. Among row seedingconfiguration, same row seeding maximized the aboveground biomass production but decreased belowgroundbiomass, crude protein content and NDF (Neutral Detergent Fiber). Plant height, ratio, ADF (Acid DetergentFiber) content, AGRNE (Aboveground Relative Neighbor Effect), and BGRNE (Belowground RelativeNeighbor Effect) were not affected by row seeding configurations. In order to maximize the utilization fromthe row seeding configuration, the same row seeding can increase the aboveground biomass but mitigatebelowground biomass and crude protein content. The row seeding configuration may represent a potential foryield, quality, and competitive ability when sown as a mixture using 25% Sudangrass ratio.

Effects of above- and below-ground herbivore interactions on interspecific relationship between the invasive plant Alternanthera philoxeroides and its native congener Alternanthera sessilis

Biological invasion is a major threat to global biodiversity. The relative interspecific competition abilities of invasive species compared to those native species determine their invasion success. In this study, we examined the effects of the specialist leaf beetle Agasicles hygrophila and the nematode Meloidogyne incognita on the growth and interspecific relationship between the invasive plant Alternanthera philoxeroides and its native congener A. sessilis. Compared without herbivory, nematode herbivory alone significantly reduced shoot height of A. sessilis by 28.1%, but conversely significantly increased the shoot height of A. philoxeroides by 52.8% and aboveground biomass of A. sessilis by 63.7%. Beetle herbivory alone significantly reduced shoot height of A. sessilis by 40.7%, but did not affect that of A. philoxeroides. The combination of beetle and nematode herbivory significantly reduced shoot height of A. sessilis by 35.3% as well as the belowground biomass of A. philoxeroides by 62.2%, but significantly increased the aboveground biomass of A. sessilis by 69.1%. Herbivore stress did not affect stem diameter, branch number, and root length of both species. The relative neighbor effect index (RNE) of the two species without herbivory were positive, and the RNE value of A. philoxeroides was 21.3% higher than that of A. sessilis. However, the RNE values of A. philoxeroides were negative under all above- and below-ground herbivory treatments. The RNE values of A. sessilis were positive under the beetle or the nematode herbivory alone and negative under the beetle + nematode herbivory combination. These results indicated that above- and below-ground herbivore interactions could change the interspecific relationship between the two species, and in turn might accelerate the invasion of A. philoxeroides.

Resource competition and allelopathy in two peat mosses: implication for niche differentiation

Separating the effect of resource competition from allelopathy in plants is challenging and it has never been attempted in closely related co-occurring bryophytes. In peatlands, peat mosses (Sphagnum spp.) show niche differentiation along water table level (WTL) gradient. Our aim was to evaluate whether the hummock species, S. magellanicum would be a winner at low WTL due to its allelopathic advantage and the hollow species, S. angustifolium would win by virtue of its superior competitive ability but not of allelopathy at high WTL due to dilution of its allelochemicals. We used a nested, field experimental design, with two WTL treatments—low WTL (hummock habitat) and high WTL (hollow habitat)—and three different inter-specific interactions: 1) monoculture; 2) mixed culture without activated charcoal; and 3) mixed culture with activated charcoal added to the neighbor. We measured growth and biochemical traits of the two species and compared the index of relative neighbor effect on each other. We discovered a trade-off between biomass production (competitive outcome) and phenolic content (allelopathy) in these species. At low WTL, allelopathy of the hummock species is the main mechanism to suppress the hollow species, whereas at high WTL, competition is the main driver to suppress the hummock species. Competitive advantage in Sphagnum is mediated by both resource competition and allelopathy of the co-occurring species through niche differentiation along a WTL gradient. Unlike vascular plants, Sphagnum mosses can serve as excellent model organisms in studying allelopathic interaction since they bypass the complexity of plant-soil interactions.

Performance of Bangladesh indigenous rice in a weed infested field and separation of allelopathy from resource competition

This study aimed to identify the potential allelopathic indigenous rice (Oryza sativa L. ssp. indica) varieties from Bangladesh using a performance study in a weed‐infested field and to assess the extent of allelopathic interference relative to resource competition in a glasshouse experiment. Six varieties – namely, “Boterswar,” “Goria,” “Biron” and “Kartiksail” as the most allelopathic, “Hashikolmi” as weakly allelopathic and “Holoi” as nonallelopathic – were raised following a nonweed control method. The infestation levels of weed species were calculated using Simpson's Diversity Index (SDI), which ranged from 0.2 to 0.56. However, a significant correlation coefficient (0.87, P < 0.001) was obtained from these field data compared with the root inhibition percentage from the laboratory bioassay, and the “Boterswar” variety was the most allelopathic. The interactions between the allelopathic variety “Boterswar,” weakly allelopathic variety “Hashikolmi” and Echinochloa oryzicola via a target (rice)‐adjacent (E. oryzicola) cogrowth culture were determined in a hydroponic arrangement. The relative competitive intensity (RCI) and the relative neighbor effect (RNE) values showed that the crop–weed interaction was facilitation for “Boterswar” and competition for “Hashikolmi” and E. oryzicola in rice/E. oryzicola cogrowth cultures. The allelopathic effects of “Boterswar” were much higher than the resource competition in rice/E. oryzicola cogrowth cultures. The converse was observed for “Hashikolmi.” Moreover, the mineral content of E. oryzicola was severely affected by “Boterswar”/E. oryzicola cogrowth cultures’ exudate solution. Therefore, the allelopathic potential of “Boterswar” variety might be useful for developing the weed‐suppressing capacity of rice, which will likely have a significant influence on paddy weed control.

Plantation age, understory vegetation, and species‐specific traits of target seedlings alter the competition and facilitation role of Eucalyptus in South China

AbstractThe Chinese government is considering ways to reconstruct Eucalyptus plantation monocultures in order to improve their ecosystem services. However, the effects of competition or facilitation of Eucalyptus on native species during the reconstruction have not been identified, especially during the formation of novel ecosystems. To better understand these relationships, in this study we tested the effects of competition and facilitation of Eucalyptus on three target species (Schima superba, Michelia macclurei, and Castanopsis fissa), in Eucalyptus plantations with different ages and understory vegetation. The results showed that the survival and growth of S. superba and M. macclurei were not sensitive to plantation age and understory removal treatment. The survival of C. fissa in understory removal was significantly higher and the growth of C. fissa increased gradually with increasing plantation age. The relative neighbor effect (RNE) index for growth indicated that the relationship between Eucalyptus and target species switched from competition to facilitation with an increase in plantation age. A redundancy analysis (RDA) showed that survival was positively correlated with soil water content and soil phosphorus. Growth was positively correlated with soil organic matter and soil nitrogen and negatively correlated with soil bulk density. Our results indicate that plantation age, understory vegetation, and species‐specific traits of target seedlings could change the competition and facilitation roles of Eucalyptus. Higher survival and growth rates indicated that C. fissa was an appropriate species for the reconstruction of mature Eucalyptus plantations and understory removal will benefit the process.

The Effect of Artificial Mowing on the Competition of Phragmites australis and Spartina alterniflora in the Yangtze Estuary.

Spartina alterniflora Loisel. is one of the most invasive species in the world. However, little is known about the role of artificial mowing in its invasiveness and competiveness. In this work, we studied the effect of mowing on its interspecific interactions with native species Phragmites australis (Cav.) Trin ex Steud of the Yangtze Estuary, China. We calculated their relative neighbor effect (RNE) index, effect of relative crowding (Dr) index, and interaction strength (I) index. The results showed that the RNE of Phragmites australis and Spartina alterniflora was 0.354 and 0.619, respectively, and they have competitive interactions. The mowing treatments can significantly influence the RNE of Phragmites australis and Spartina alterniflora on each other. Concretely, the RNE of Spartina alterniflora in the removal treatments was significantly higher than the value in the controls. But the RNE of Phragmites australis in the removal treatments was significantly lower than the value in the controls. Meanwhile, Dr of the two species on the targets was higher in the removal treatments than that in the controls, and the opposite was for I. We concluded that artificial mowing could promote the invasion of Spartina alterniflora by increasing its competitive performance compared with native species.

Shrub cover expressed as an ‘arthropod island’ in xeric environments

Based on the vague importance of shrub cover, an attempt was made to create a theoretical concept framework known as an ‘arthropod-island’ analytical model. These models were based on the multi-bond correlation between shrubs, soil properties, and above- and below-ground biotic communities. By utilizing published datasets on (i.e., above- and below-ground) arthropod communities related to shrub species and age, the proposed models for an ‘arthropod island’ were applied in order to determine their fitness for xeric ecosystems. It was found that the ‘arthropod-island’ concept could be the result of statistical differences in ecologically adaptive (i.e., preferable) redistribution of arthropods among the microhabitats beneath the shrub canopy and in the open spaces. Taxon density, relative to the richness and Shannon indices, was found to be more sensitive to the selected models. The relative interaction intensity index [RII = (A − B)/(A + B), A = shrub canopy value, B = intershrub value] was found to be more suitable for the ‘arthropod island’ at the community level. The relative neighbor effect [RNE = (B − A)/max(A, B)] and RII were found to be suitable at the population level, while the fitted model heavily depended on the variety of arthropod taxon. It was suggested that there were consistent ‘arthropod island’–shrub relationships between shrub species and between shrub ages in terms of arthropod density at the community level. The arthropod taxon was found to indicate an inconsistent ‘arthropod island’–shrub relationship between shrub species that differed from shrub ages at the population level.

Competition between two wetland macrophytes under different levels of sediment saturation

Plant-plant interactions have been widely studied under various environmental conditions. However, in wetland ecosystems how plant interactions change in response to variation in sediment saturation remains largely unclear, even though different levels of sediment saturation play important roles in determining plant growth performance in wetland ecosystems. To this end, a competition experiment with two typical wetland species, Carex brevicuspis (neighbor plant) and Polygonum hydropiper (target plant), was conducted in a target-neighbor design. Two water levels (0 cm and -40 cm water levels representing waterlogged and drained sediments, respectively) and three neighbor plant densities (0 plants m -2 , 400 plants m -2 , and 1600 plants m -2 ) were tested in a factorial design. Biomass accumulation of P. hydropiper decreased along with enhanced C. brevicuspis density in the waterlogged treatment. However, in the drained treatment, biomass accumulation did not change under two C. brevicuspis densities. Above-ground relative neighbor effect index (ARNE) and relative neighbor effect index (RNE) of C. brevicuspis on P. hydropiper increased along with enhanced C. brevicuspis density only under waterlogged conditions. The below-ground relative neighbor effect index (BRNE) was not affected at the different water level and density treatments. The below-ground mass fraction of P. hydropiper was much higher in the waterlogged treatment than it was in the drained one, especially with no C. brevicuspis treatment. However, the leaf mass fraction displayed the opposite pattern. The longest root length of P. hydropiper was much shorter under waterlogged treatment than under the drained treatment. These results suggest that the competition intensity of C. brevicuspis to P. hydropiper increased along with increasing C. brevicuspis density only under waterlogged conditions. Moreover, this study also confirms that P. hydropiper can acclimate to water stress mainly through modulating its root architecture, for example reducing the root system length or increasing the root mass fraction.

An invasive clonal plant benefits from clonal integration more than a co-occurring native plant in nutrient-patchy and competitive environments.

Many notorious invasive plants are clonal, however, little is known about the different roles of clonal integration effects between invasive and native plants. Here, we hypothesize that clonal integration affect growth, photosynthetic performance, biomass allocation and thus competitive ability of invasive and native clonal plants, and invasive clonal plants benefit from clonal integration more than co-occurring native plants in heterogeneous habitats. To test these hypotheses, two stoloniferous clonal plants, Alternanthera philoxeroides (invasive), Jussiaea repens (native) were studied in China. The apical parts of both species were grown either with or without neighboring vegetation and the basal parts without competitors were in nutrient- rich or -poor habitats, with stolon connections were either severed or kept intact. Competition significantly reduced growth and photosynthetic performance of the apical ramets in both species, but not the biomass of neighboring vegetation. Without competition, clonal integration greatly improved the growth and photosynthetic performance of both species, especially when the basal parts were in nutrient-rich habitats. When grown with neighboring vegetation, growth of J. repens and photosynthetic performance of both species were significantly enhanced by clonal integration with the basal parts in both nutrient-rich and -poor habitats, while growth and relative neighbor effect (RNE) of A. philoxeroides were greatly improved by clonal integration only when the basal parts were in nutrient-rich habitats. Moreover, clonal integration increased A. philoxeroides's biomass allocation to roots without competition, but decreased it with competition, especially when the basal ramets were in nutrient-rich sections. Effects of clonal integration on biomass allocation of J. repens was similar to that of A. philoxeroides but with less significance. These results supported our hypothesis that invasive clonal plants A. philoxeroides benefits from clonal integration more than co-occurring native J. repens, suggesting that the invasiveness of A. philoxeroides may be closely related to clonal integration in heterogeneous environments.

Interspecific interactions between Phragmites australis and Spartina alterniflora along a tidal gradient in the Dongtan wetland, Eastern China.

The invasive species Spartina alterniora Loisel was introduced to the eastern coast of China in the 1970s and 1980s for the purposes of land reclamation and the prevention of soil erosion. The resulting interspecific competition had an important influence on the distribution of native vegetation, which makes studying the patterns and mechanisms of the interactions between Spartina alterniora Loisel and the native species Phragmites australis (Cav.) Trin ex Steud in this region very important. There have been some researches on the interspecific interactions between P. australis and S. alterniora in the Dongtan wetland of Chongming, east China, most of which has focused on the comparison of their physiological characteristics. In this paper, we conducted a neighbor removal experiment along a tidal gradient to evaluate the relative competitive abilities of the two species by calculating their relative neighbor effect (RNE) index. We also looked at the influence of environmental stress and disturbance on the competitive abilities of the two species by comparing interaction strength (I) among different tidal zones both for P. australis and S. alterniora. Finally, we measured physiological characteristics of the two species to assess the physiological mechanisms behind their different competitive abilities. Both negative and positive interactions were found between P. australis and S. alterniora along the environmental gradient. When the direction of the competitive intensity index for P. australis and S. alterniora was consistent, the competitive or facilitative effect of S. alterniora on P. australis was stronger than that of P. australis on S. alterniora. The interspecific interactions of P. australis and S. alterniora varied with environmental conditions, as well as with the method used, to measure interspecific interactions.

Separation of allelopathy from resource competition using rice/barnyardgrass mixed-cultures.

Plant-plant interference is the combined effect of allelopathy, resource competition, and many other factors. Separating allelopathy from resource competition is almost impossible in natural systems but it is important to evaluate the relative contribution of each of the two mechanisms on plant interference. Research on allelopathy in natural and cultivated plant communities has been hindered in the absence of a reliable method that can separate allelopathic effect from resource competition. In this paper, the interactions between allelopathic rice accession PI312777, non-allelopathic rice accession Lemont and barnyardgrass were explored respectively by using a target (rice)-neighbor (barnyardgrass) mixed-culture in hydroponic system. The relative competitive intensity (RCI), the relative neighbor effect (RNE) and the competitive ratio (CR) were used to quantify the intensity of competition between each of the two different potentially allelopathic rice accessions and barnyardgrass. Use of hydroponic culture system enabled us to exclude any uncontrolled factors that might operate in the soil and we were able to separate allelopathy from resource competition between each rice accession and barnyardgrass. The RCI and RNE values showed that the plant-plant interaction was positive (facilitation) for PI312777 but that was negative (competition) for Lemont and barnyardgrass in rice/barnyardgrass mixed-cultures. The CR values showed that one PI312777 plant was more competitive than 2 barnyardgrass plants. The allelopathic effects of PI312777 were much more intense than the resource competition in rice/barnyardgrass mixed cultures. The reverse was true for Lemont. These results demonstrate that the allelopathic effect of PI312777 was predominant in rice/barnyardgrass mixed-cultures. The most significant result of our study is the discovery of an experimental design, target-neighbor mixed-culture in combination with competition indices, can successfully separate allelopathic effects from competition.

Competition and Facilitation in Three Marsh Plants in Response to a Water-Level Gradient

Biomass accumulation and neighbor effects (measured with a relative neighbor effect index, NEI) were investigated in three marsh plant species (Carex lasiocarpa, Glyceria spiculosa, and Deyeuxia angustifolia) grown at three water levels (0, 20, and 40 cm relative to the soil surface). The three species occur naturally along a water-level gradient in the Sanjiang Plain, the largest freshwater marsh in China. Both intraspecific and interspecific competition were measured using a target-neighbor design, which subjected the three species to different intensities of inter- and intra-specific competition. Biomass accumulation and NEI differences among water levels and competition treatments suggested that intra- and inter-specific competition was strongest at 0 cm inundation. In contrast, neighboring plants stimulated the growth of C. lasiocarpa and D. angustifolia at the 40 cm water level. These results indicate that the strength of intra- and inter-specific competition decreases and the strength of facilitation increases with increasing water levels. Our results support the prediction of the stress-gradient hypothesis (SGH) that plant-plant interactions should switch from competition to facilitation along an increasing water-level stress gradient.

Do Facilitative Interactions with Neighboring Plants Assist the Growth of Seedlings at High Altitudes in Alpine Australia?

During the early life-history stages, plants are especially susceptible to the abiotic conditions present in high mountain environments. At high altitudes, facilitative interactions between close neighboring plants may buffer seedlings from these abiotic pressures by providing shelter from frosts and winds. At lower altitudes, seedlings may not be so limited by the abiotic environment, and may therefore compete for resources with close neighboring plants. Using four alpine sites at different elevations (representing an abiotic stress gradient), we investigated how the presence of close neighboring plants influences seedling growth in their first growing season. We experimentally cleared above-ground vegetation and transplanted seedlings of three species into cleared and control plots. We quantified the stress gradient of abiotic conditions across sites by measuring ambient and soil temperatures, soil moisture, and soil frost heave. We used the “Relative Neighbor Effect” index to show the direction of the interaction between transplanted seedlings and their close neighboring plants. Aciphylla glacialis seedlings showed neutral interactions across the gradient of alpine sites, with undetectable change across the growing season, compared with Brachyscome rigidula seedlings which showed positive interactions with neighbors across the growing season at most sites. Trisetum spicatum seedlings showed mostly neutral interactions with neighbors at the higher elevations, and often negative interactions at the lower elevations, particularly midway through the growing season. Our findings highlight the importance of spatial and temporal plant-plant interactions with regard to seedling performance across altitudinal stress gradients.

Contrasting community responses to fertilization and the role of the competitive ability of dominant species

AbstractQuestion: Do contrasting biotic contexts in nutrient‐poor grasslands affect the predictability of invasion by exploitative species following fertilization?Location: French Alps.Methods: We examined community responses after 2 years of nutrient addition for two nutrient‐poor European calcareous grasslands, a mesoxeric community dominated by the short bunchgrass Bromus erectus and a mesic community dominated by the tall rhizomatous grass Brachypodium rupestre. We also performed reciprocal transplantations of these two dominant slow‐growing species and Arrhenatherum elatius, a tall fast‐growing grass that dominates nutrient‐rich communities and is likely to invade nutrient‐poor communities after fertilization. Transplants were grown with or without neighbors, in order to measure their individual responses (without neighbors) and competition intensity (by comparing performances with and without neighbors using the Relative Neighbor Effect index – RNE) during one growing season in all three communities.Results: In the Bromus community, fertilization induced a strong increase in fast‐growing grasses (including A. elatius). Competition intensity was low for the three transplanted grasses, but strongly increased with resource addition, to reach values observed in the Arrhenatherum community. In the Brachypodium community, no change in competition intensity with fertilization was detected, because of the high mortality of the two “non‐resident” species, irrespective of the presence of neighbors.Conclusions: Community responses to nutrient improvement are context‐dependent and vary as a function of the biotic environment. Soil processes are proposed as the main drivers of community resistance to the invasion of fast‐growing species in the mesic, nutrient‐poor grassland dominated by the large conservative competitor B. rupestre.

Effects of growing conditions on the growth of and interactions between salt marsh plants: implications for invasibility of habitats

A common but often less tested explanation for the successful invasion of alien species is that invasive alien species outcompete their co-occurring natives, which may not always be the case. In this study, we established artificial environmental gradients in a series of pot experiments with controlled environments to investigate the effects of salinity, sediment type and waterlogging on the performance of and interactions between Phragmites australis (native) and Spartina alterniflora (alien), which generally co-exist in the saline intertidal zones of Chinese and American coasts. Significant effects of salinity and waterlogging were detected on biomass production and morphological characteristics of S. alterniflora and P. australis, and the competitive interactions between the two species were found to vary with all three environmental factors in our experiments. Relative Neighbor Effect (RNE) analyses indicate that competitive dominance of S. alterniflora occurred under the conditions of high salinity, sandy sediment and full immersion, whereas P. australis showed competitive dominance under the conditions of low salinity and non-immersion. Our results suggest that S. alterniflora might outcompete P. australis under conditions present in early salt marsh succession, which support the viewpoint that the outcomes of competition between co-occurring native and invasive alien plants depend on the growing conditions. The implication of this study is that in response to the environmental changes expected from seawater intrusion and sea-level rise, the range of S. alterniflora is expected to expand further in the Yangtze River estuary in the future.

On the indices of plant–plant competition and their pitfalls

The index of relative competition intensity (RCI) has serious built‐in biases, due to its asymptotic behavior when competition intensity is high and its tendency to obtain very low values when plants with neighbors intact perform better than neighbor removal plants. These biases have been partially corrected in the index of relative neighbor effect (RNE), but the existence of fixed upper and lower bounds (−1≤RNE≤+1) still creates problems and biases in communities where the average intensity of competition or facilitation is high and plant performance pronouncedly varies in space. The third commonly used index, the logarithm of response ratio (lnRR), is mathematically and statistically sound, but when computed from pair‐wise comparisons between neighbor removal and control plants, this index reflects the geometric mean of the treatment effect. Moreover, linear patterns in lnRR reflect exponential patterns in the intensity of competition. As the interest of ecologists usually focuses on arithmetic means, we propose a corrected index of relative competition intensity, CRCI=arc sin (RNE). This index is fairly linear within the observed ranges of competition and facilitation, and for the range of competition intensities where RNE behaves reasonably, the two indices obtain almost identical values.We compared the performance of the four indices, using both imagined and real data, the latter from systems where the responses of plants to neighbor removal ranged from weak to moderate, so that RNE and CRCI were expected to behave similarly. The indices were computed both from pooled data for each community and as averages of pair‐wise comparisons. lnRR and CRCI were found to behave in a consistent and bias‐free manner, yielding similar results regardless of method of computation. This was, by and large, the case with RNE, too, but as the values of indices grew, the values from pair‐wise comparisons became increasingly smaller than values computed from pooled data. RCI yielded grossly aberrant results in computations based on pair‐wise comparisons. Therefore, the further use of RCI is unadvisable and studies where RCI has been derived from pair‐wise comparisons should be excluded from meta‐analyses.