Plant Community Evenness Research Articles

Non‐natives are linked to higher plant diversity across spatial scales

AbstractAimAlthough non‐native and invasive plants often pose a significant threat to biodiversity, global‐scale studies have yet to conclusively demonstrate a systematic pattern of reduced native plant diversity in areas affected by these invasions. Here, we aim to explore the association of non‐native and invasive plants with the species richness and evenness of plant communities from the local to global scale.LocationGlobal.MethodsWe use the world's largest vegetation plot repository—sPlot—to compare species richness and community evenness between invaded (by invasive or non‐natives) and native plots of equal size, paired within 32 km2 grid cells distributed across all continents. Aggregating plots at the cell, biome and global level, we also quantified differences in gamma diversity at different spatial scales.ResultsWe found that invaded plots had higher species richness and similar community evenness, a trend largely consistent across biomes. The higher total species richness was not the result of additional invasive or non‐native species, as the number of native species was also higher in invaded plots. These patterns persisted at larger spatial scales. Cell, biome and global gamma species richness of invaded plots were consistently higher than of native plots. All these patterns held regardless of whether the non‐native species in a plot were invasive or non‐invasive.Main ConclusionsOur study reveals a globally consistent pattern: plant diversity, both total and native, is higher when invasive or non‐native plants are present, spanning spatial scales from local to global. Although we cannot infer causal effects, our results challenge the prevailing hypothesis that non‐native and invasive species universally depress plant diversity.

Plant diversity enhanced nematode-based soil quality indices and changed soil nematode community structure in intensively-managed agricultural grasslands

Plant productivity, decomposition and nutrient cycling are controlled by plant-soil-biota interactions. However, it remains poorly understood how plant species diversity impacts belowground communities that modulate these processes in intensively-managed grassland systems. In managed grassland communities comprising species selected for agronomic performance, we investigated how plant species diversity affected the soil nematode community and associated ecological indices with a focus on assessing aboveground-belowground interactions. A total of 27 nematode taxa were identified from 61 experimental field plots in which plant species diversity was systematically manipulated from a pool of six plant species within three functional groups (FGs; grasses, legumes, herbs). In general, there were strong effects of plant species identity on the nematode community; interspecific interaction effects did not consistently occur, but where they did were best related to plant community evenness. The equi-proportional six-species plant community had a significantly higher nematode diversity, maturity index (MI), structure index (SI) and proportion of sensitive taxa (omnivore and predators) but a lower enrichment index (EI) than the individual monocultures. The two legumes (Trifolium pratense and Trifolium repens) had the highest EI but lowest abundance of fungivores and channel index, indicating a bacterial-dominated decomposition pathway. Moreover, the community structure of nematodes in the equi-proportional six-species community was significantly different from that in the monocultures. This change in community structure was associated with factors highly correlated with plant diversity, including higher aboveground biomass yield and total nitrogen in harvested biomass as well as lower biomass of weed species. Overall, our results show that multi-species forage sward mixtures that include grasses, legumes, and herbs can have a positive effect on the soil nematode community and nematode-based soil quality indices. This is of practical relevance for farmers and for EU agricultural policy targeted at sustainability, soil health and farming for biodiversity benefits.

Increases in functional diversity of mountain plant communities is mainly driven by species turnover under climate change

Warming in mountain regions is projected to be three times faster than the global average. Pronounced climate change will likely lead to species reshuffling in mountain plant communities and consequently change ecosystem resilience and functioning. Yet, little is known about the role of inter‐ versus intraspecific changes of plant traits and their consequences for functional richness and evenness of mountain plant communities under climate change. We performed a downslope translocation experiment of intact plant‐soil mesocosms from an alpine pasture and a subalpine grassland in the Swiss and Austrian Alps to simulate an abrupt shift in climate and removal of dispersal barriers. Translocated plant communities experienced warmer and dryer climatic conditions. We found a considerable shift from resource conservative to resource acquisitive leaf‐economy in the two climate change scenarios. However, shifts in leaf‐economy were mainly attributable to species turnover, namely colonization by novel lowland species with trait expressions for a wider range of resource use. We also found an increase in vegetative height of the warmed and drought‐affected alpine plant community, while trait plasticity to warming and drought was limited to few graminoid species of the subalpine plant community. Our results highlight the contrast between the strong competitive potential of novel lowland species in quickly occupying available niche space and native species' lack of both the intraspecific trait variability and the plant functional trait expressions needed to increase functional richness under warming and drought. This is particularly important for the trailing range of many mountain species (i.e. subalpine zone) where upward moving lowland species are becoming more abundant and abiotic climate stressors are likely to become more frequent in the near future. Our study emphasizes mountain plant communities' vulnerability to novel climates and biotic interactions under climate change and highlights graminoid species as potential winners of a warmer and dryer future.Keywords: alpine grassland, functional diversity, invasion, species turnover, traitspace, translocation

Intraspecific trait variability is relevant in assessing differences in functional composition between native and alien aquatic plant communities

AbstractThe loss of plant functional diversity associated with biological invasion is a main subject of invasion biology, but still understudied in case of aquatic plants. We calculated functional richness, evenness, divergence and community-weighted mean trait values of aquatic plant communities for 20 plots, half invaded and half non-invaded by alien species, in a thermal effluent of West Hungary. Three traits [specific leaf area (SLA), leaf dry matter content (LDMC), leaf area (LA)] were considered to explain how alien species alter ecosystem function. We differentiated interspecific and intraspecific trait variation and investigate its effect on the community-level functional diversity. We found that alien species invasion causes significant changes in the functional composition of aquatic plants whereby alien species become able to absorb light more efficiently, which will directly enhance their increased biomass production. Our study highlights the importance of local adaptation, showing that calculating functional diversity with global pooling of trait measurements causes significant over- or underestimation of functional diversity indices. Consequently, this can potentially result in erroneous conclusions regarding the impact of invasion.

AMONG-SPECIES VARIATION IN FLOWER SIZE DETERMINES FLORIVORY IN THE LARGEST SEASONALLY FLOODED TROPICAL WETLAND.

Floral damage caused by florivores often has negative consequences for plant reproduction. However, the factors affecting plant-florivore interactions are still poorly understood, especially the role of abiotic factors and interspecific variation in florivory within ecosystems. Thus, it is largely required to investigate the patterns of florivory levels and its consequences for plant communities. We assessed the influence of abiotic factors related to climatic seasonality, of phylogenetic relationships among plants, and of functional attributes associated with attractiveness to pollinators on florivory levels (incidence and intensity) in the Pantanal, the world's largest tropical wetland. Between December 2020 and November 2021, the percentage of both flowers attacked (incidence) and area removed from petals (intensity) by florivores were examined in 51 species from 25 families, considering flowering season, the substrate where the plants occur, and floral attributes as potentially determining factors on florivory levels. Phylogeny and environmental factors did not have a significant influence on florivory. The only determinant of interspecific variation in florivory incidence and intensity was flower size, where larger flowers experienced higher florivory levels regardless of season and substrate, while flower arrangement and color were not significant factors. Our study is one of the first to estimate the community-wide effects of biotic and abiotic factors on both the incidence and the intensity of florivory. The magnitude of this plant-florivore interaction may reduce reproductive success and entail selective pressures on plant attractiveness to pollinators. This article is protected by copyright. All rights reserved.

Plant community-mediated effects of grazing on plant diseases.

Grazing is one of the most important management practices for grasslands. To date, most studies on how grazing affects plant diseases have focused on a single plant species, ignoring plant community characteristics and phylogeny. We used data from a 6-year yak grazing experiment (0, 1, 2, and 3 yak(s) ha - 1 treatment) in an alpine meadow ecosystem of Qinghai-Tibetan Plateau, from which we tested grazing effects on foliar fungal diseases at both population and community levels. By measuring plant community variables (including richness, evenness, phylogenetic diversity, and composition) and disease severity, we evaluated the relative importance of plant community-mediated effects of yak grazing on community pathogen load with a multi-model inference approach. We found significant differences in pathogen load among different grazing treatments; we recorded the highest and lowest pathogen loads in the 1 yak ha - 1 treatment and in the 3 yaks ha - 1 treatment, respectively. Pielou's evenness index and community proneness (i.e., an estimate of the capacity of plant communities to support diseases) best explained variation in pathogen load, indicating that plant community-mediated effects (through evenness and proneness) of yak grazing determined pathogen load. Our study provides empirical evidence that grazing influences foliar fungal disease prevalence through plant community evenness and composition, which demonstrates the necessity of incorporating host plant community characteristics into disease load prediction frameworks.

Standardized indices to estimate sensitivity to drought across ecosystems

AbstractQuestionClimate change scenarios predict alterations in interannual variability of precipitation and increases of extreme droughts. Drought effects will reflect ecosystems' sensitivity (i.e. the magnitude of the response relative to the change in amount of precipitation), with different consequences for plant communities and ecosystem functioning. However, sensitivity estimations across ecosystems and among years are contingent upon the metric applied. Here, we asked how different sensitivity indices reflect the responses to drought in contrasting ecosystems.MethodsWe proposed a novel index to estimate sensitivity in drought experiments, which consider the change in the response variable in relation to the reduction in precipitation, standardized by the mean precipitation use efficiency of the site, making it suitable to compare among contrasting ecosystems. We compared the information gained from the new index with two indices commonly used in experimentally induced droughts, through simulated scenarios. Besides, we applied the indices to data from previous field drought experiments to evaluate relative and absolute sensitivity to drought in worldwide grassland ecosystems along a wide precipitation gradient.ResultsWe found that both relative and absolute approaches yielded important information to determine drought sensitivity in different simulated scenarios and under interannual precipitation variability. When the indices were applied to real situations, relative sensitivity to drought showed a significant increase as mean annual precipitation decreases whereas absolute sensitivity did not change significantly with precipitation.ConclusionsOur findings highlighted that absolute and relative indices to estimate drought sensitivity, rather than being redundant, may complement each other to inform how ecosystems respond to drought and to provide a more holistic assessment of vulnerable systems toward increasing interannual precipitation variability. This complementary approach enhances our understanding of ecosystem response under different conditions of precipitation variability and of the mechanisms that determine ecosystem changes during extreme droughts.

Metagenetics of fairy rings reveals complex and variable soil fungal communities

Although fairy rings are widely observed, little is known of community processes associated with them. We studied fairy rings in natural grassland in Northern Mongolia, sampling soils outside (‘future’), directly under (‘present’), and within (‘past’) the rings, to represent different time stages during expansion of fairy rings. Soil DNA was extracted for amplicon sequencing of fungal ITS region. The present stage had reduced diversity, and the fungal community showed various differences, most strikingly an increase in the pathogenic fungus Fusarium/Gibberella in the present stage of many rings, and the saprotrophic fairy ring fungus Lepista luscina in several. However, no mushrooms of Lepista had been recorded from any of these rings in several years of observations. Known fairy ring fungi were not found in the present stage of every ring, even in some known to have previously displayed mushrooms of fairy ring species. It is possible, however, these fungi occurred or were more abundant at the unsampled leading edge of the ring. The increase in Fusarium/Gibberella is intriguing, but its importance – if any – is unclear. It is also unclear whether consortia of fungi or other microbes might be at work in these rings. The absence or low abundance of the previously reported fairy ring mushroom species suggests their presence is transient, with rapid replacement by other fungi. No differences in soil parameters were found between stages, except aluminium. There is a need for broader sampling, including analysis of non-fungal biota, towards understanding functional diversity of fairy ring fungi and consequences for plant communities.

Role of soil biotic and abiotic properties in plant community composition in response to nitrogen addition

AbstractNutrient addition can alter plant–soil‐microbe interactions. However, knowledge remains limited about how the soil biotic and abiotic properties drive changes in plant community composition and diversity after nitrogen (N) addition. In this study, four N addition rates (N0, N3, N6, and N9: 0, 3, 6, and 9 g N m −2 yr−1) were applied to a grassland community on the Loess Plateau (China) to evaluate the response of plant community biomass, evenness, and composition to N addition. Overall, N addition significantly increased plant shoot and root biomass by 27.75%–31.37% and 39.60%–65.42% compared with N0, but no significant difference was observed among N3, N6, and N9. N addition significantly decreased shoot/root biomass ratio by 7.17%–21.84%, and plant community evenness by 3.80%–8.80% compared with N0, particularly under N3 and N6 treatments. Furthermore, N addition enhanced the abundance of bacteria and fungi, but their composition was not altered. Responses of plant biomass and evenness to N addition were correlated to changes in NO3−‐N, soil total phosphorus, and the abundance of bacteria and fungi; additionally, the composition was primarily affected by the microbial abundance. Our research indicates that N addition can significantly alter plant community composition, particularly at low addition rates, and such alteration may be more affected by the soil microbial abundance. The findings of this study have important implications for the sustainable management of grassland ecosystems.

Pulse grazing by reindeer (Rangifer tarandus) can increase the phylogenetic diversity of vascular plant communities in the Fennoscandian tundra.

Herbivore grazing is an important determinant of plant community assemblages. Thus, it is essential to understand its impact to direct conservation efforts in regions where herbivores are managed. While the impacts of reindeer (Rangifer tarandus) grazing on plant biodiversity and community composition in the Fennoscandian tundra are well studied, the impact of reindeer grazing on phylogenetic community structure is not. We used data from a multiyear quasi‐experimental study in northern Fennoscandia to analyze the effect of reindeer grazing on plant community diversity including its phylogenetic structure. Our study design used a permanent fence constructed in the 1960s and temporary fences constructed along the permanent fence to expose plant communities to three different grazing regimes: light (almost never grazed), pulse (grazed every other year), and press (chronic grazing for over 40 years). Similar to previous studies on low productivity ecosystems in this region, the species richness and evenness of plant communities with pulse and press grazing did not differ from communities with light grazing. Also consistent with previous studies in this region, we observed a transition from shrub‐dominated communities with light grazing to graminoid‐dominated communities with pulse and press grazing. Interestingly, communities with pulse, but not press, grazing were more phylogenetically dispersed than communities with light grazing. If grazing pulses can increase the phylogenetic diversity of plant communities, our result suggests changes in reindeer management allowing for pulses of grazing to increase phylogenetic diversity of plant communities.

Linear infrastructure habitats increase landscape-scale diversity of plants but not of flower-visiting insects

Habitats along linear infrastructure, such as roads and electrical transmission lines, can have high local biodiversity. To determine whether these habitats also contribute to landscape-scale biodiversity, we estimated species richness, evenness and phylogenetic diversity of plant, butterfly and bumblebee communities in 32 4 km2 landscapes with or without power line corridors, and with contrasting areas of road verges. Landscapes with power line corridors had on average six more plant species than landscapes without power lines, but there was no such effect for butterflies and bumblebees. Plant communities displayed considerable evenness in species abundances both in landscapes with and without power lines and high and low road verge densities. We hypothesize that the higher number of plant species in landscapes with power line corridors is due to these landscapes having a higher extinction debt than the landscapes without power line corridors, such that plant diversity is declining slower in landscapes with power lines. This calls for targeted conservation actions in semi-natural grasslands within landscapes with power line corridors to maintain biodiversity and prevent imminent population extinctions.

Plant community and soil nutrient of alpine meadow in different degradation stages on the Tibetan Plateau, China.

We examined soil physical and chemical properties and plant community characteristics of four Kobresia alpine meadows at different degradation stages in Damxung County, Lhasa City, Tibet Autonomous Region, China, with the method of spatial sequence instead of time succession. The results showed that soil organic carbon, total nitrogen, available phosphorus, available potassium, ammonium, nitrate, and water content showed a decreasing trend as the degree of soil degradation increased, while pH showed an increasing trend. Plant community height, richness, diversity index and evenness index of the moderately degraded meadow were the highest. Community coverage and total biomass were the largest in undegraded meadow and the smallest in the severely degraded meadow. As the degree of meadow degradation intensifies, the biomass and proportion of Cyperaceae decreased, the biomass and proportion of legumes and weeds increased, and the biomass and proportion of Gramineae first increased and then decreased. The aboveground biomass of meadow was significantly positively correlated with soil organic carbon content, total nitrogen content, total phosphorus content, and soil water content, and significantly negatively correlated with soil pH. With the vegetation degradation in meadow, soil degradation had worsened, which ultimately manifested as a significant decline in grassland productivity.

Temporal variability in production is not consistently affected by global change drivers across herbaceous-dominated ecosystems.

Understanding how global change drivers (GCDs) affect aboveground net primary production (ANPP) through time is essential to predicting the reliability and maintenance of ecosystem function and services in the future. While GCDs, such as drought, warming and elevated nutrients, are known to affect mean ANPP, less is known about how they affect inter-annual variability in ANPP. We examined 27 global change experiments located in 11 different herbaceous ecosystems that varied in both abiotic and biotic conditions, to investigate changes in the mean and temporal variability of ANPP (measured as the coefficient of variation) in response to different GCD manipulations, including resource additions, warming, and irrigation. From this comprehensive data synthesis, we found that GCD treatments increased mean ANPP. However, GCD manipulations both increased and decreased temporal variability of ANPP (24% of comparisons), with no net effect overall. These inconsistent effects on temporal variation in ANPP can, in part, be attributed to site characteristics, such as mean annual precipitation and temperature as well as plant community evenness. For example, decreases in temporal variability in ANPP with the GCD treatments occurred in wetter and warmer sites with lower plant community evenness. Further, the addition of several nutrients simultaneously increased the sensitivity of ANPP to interannual variation in precipitation. Based on this analysis, we expect that GCDs will likely affect the magnitude more than the reliability over time of ecosystem production in the future.

Increasing soil configurational heterogeneity promotes plant community evenness through equalizing differences in competitive ability

Compared to homogeneous soils, soil heterogeneity is thought to promote plant species diversity through niche differentiation. The number of patch types within the heterogeneous soil (i.e. the difference in soil configurational heterogeneity) may also play a key role in regulating plant diversity. However, most empirical studies examining heterogeneity-diversity relationships involved only two contrasting types of patches. Moreover, the shape of heterogeneity-diversity relationships may also be changed by background soil fertility. To test how soil heterogeneity and number of patch types within the heterogeneous soil influence plant community evenness and their potential dependence on background soil fertility, we constructed plant communities consisting of four plant species in low- and high-nutrient soils, and manipulated the soils in heterogeneous configurations consisting of two or four types of soil patches and in a homogeneous condition where these soil patches were homogenized. Neither evenness of the plant community nor the difference in competitive ability between plants within the community was significantly different between the homogeneous soil and the heterogeneous soils, suggesting that soil heterogeneity overall had no effect on community evenness. However, evenness was higher and the difference in competitive ability between plants was lower in the heterogeneous soils with four types of soil patches than in the heterogeneous soils with two types of soil patches and also in the low-nutrient soils than in the high-nutrient soils. These results suggest that lowering soil fertility and increasing soil configurational heterogeneity can promote plant community evenness through reducing the difference in competitive ability between plant species within the community.

Floral visitors and pollinator dependence are related to floral display size and plant height in native weeds of central Mexico

Pollinator dependency is a life history trait that affects the evolutionary trajectory of individual plant species and their pollinators. It has consequences for plant communities, particularly in the context of human-modified landscapes. We used Mesoamerican weed vegetation as a model to explore the influence of structural plant features on the relationship of plants with pollinators. This vegetation type has some characteristics that are different from the well-known communities of Mediterranean/European origin; the differences are mostly related to the stature of the most important crop, maize. We evaluated the effect of an inflorescence bagging experiment on seed set to assess pollinator dependence of the ten most important species, all native annual herbs, in two maize fields of the central Mexican highlands and observed floral visitors. The tallest herbs had the largest floral display and the most visitors. They were dependent on animal pollination for seed set, which is unusual for annual plants and more so for weeds. Medium-sized species in the interior of the field were facultatively pollinator-dependent, and small species fully dependent on autonomous self-pollination. Pollinator dependency was correlated with plant stature and floral display area, probably related to conspicuousness or ease of detection by animals. We conclude that plant species composition of this vegetation type is related to pollinator access.

Growth traits of the exotic plant Hydrocotyle vulgaris and the evenness of resident plant communities are mediated by community age, not species diversity

SummaryBiological invasions are determined by interactions between resident plant communities and exotic plants. Time of invasion and species diversity of resident plant communities may greatly affect exotic plant invasions. We assembled low‐ and high‐diversity resident plant communities by sowing seeds of four and eight grassland species, respectively, and at each of three time periods (1, 4 and 7 weeks after sowing), the resident communities were invaded by Hydrocotyle vulgaris or not. We also constructed a plant community with H. vulgaris alone. Presence of H. vulgaris had no effect on biomass of the resident communities or biomass of each component species. Community age significantly affected biomass and evenness of the resident communities, and their competition with H. vulgaris, but the priority effect of the resident communities was slight. Increasing species richness did not change the interaction between H. vulgaris and the resident plant communities. These findings suggest a weaker competitive exclusionary effect of H. vulgaris on the resident communities with early germination, and H. vulgaris tended to have no significant impact on intact resident terrestrial plant communities. Thus, the potential risk of H. vulgaris invasion is low, especially in the communities with young age.

Separating effects of soil microorganisms and nematodes on plant community dynamics

AimsSoil food webs include multiple groups of organisms that each can favor or repress particular plant species in a plant community. This study explores how microbes and nematodes alter the temporal dynamics of specific plant species and functional groups (i.e. grasses and forbs) in mixed grassland communities.MethodsWe extracted communities of nematodes and microorganisms from natural grassland soil and inoculated them, separately and in combination, into containers filled with sterilized grassland soil to examine how these groups of soil organisms influence the compositional dynamics of a diverse grassland plant community consisting of 12 species.ResultsAddition of soil microorganisms altered the composition of the plant community by enhancing forb species and promoting evenness, but these effects took time to develop and became significant only 6 months after inoculation. Addition of soil nematodes showed faster effects and reduced plant community evenness via suppressing several subordinate plant species. The nematode community was dominated by root-feeding nematodes that were less abundant when microorganisms were present, indicating a potential inhibitory effect of microorganisms on plant-feeding nematodes.ConclusionsOur results show that soil microorganisms and nematodes may differ in the magnitude and direction of their effects on the compositional dynamics of plant communities in natural grasslands, and that these effects may operate at different timespans. This study highlights the complexity of plant-soil biotic interactions and the importance to explore these interactions at multiple temporal scales.

Alpine grassland degradation reduced plant species diversity and stability of plant communities in the Northern Tibet Plateau

The alpine grassland in the Northern Tibet Plateau has been degraded in recent decades. This study aimed at addressing the effects of the degree of degradation on species diversity and stability of plant communities and the relationships between diversity stability. Stability of plant communities decreased with the increasing degree of degradation probably due to the significantly decreased diversity and evenness of plant communities with degradation. Diversity (including Shannon and Simpson diversity, Pielou evenness, and species richness) was positively correlated with the corresponding stability of plant communities. This suggets that high levels of plant diversity lead to higher levels of complementary resource use via niche complementation. The relative abundance of the most dominant species was negatively correlated with the stability of the corresponding plant communities. This suggests that the stability of plant communities decreases with increasing degradation but the relative abundance of the most dominant species increases with degradation. In conclusion, diversity and the corresponding stability of plant communities decrease with increasing degradation in the alpine grassland in the Northern Tibet Plateau.

Within-species phylogenetic relatedness of a common mycorrhizal fungus affects evenness in plant communities through effects on dominant species.

Arbuscular mycorrhizal fungi (AMF) have been shown to influence plant community structure and diversity. Studies based on single plant–single AMF isolate experiments show that within AMF species variation leads to large differential growth responses of different plant species. Because of these differential effects, genetic differences among isolates of an AMF species could potentially have strong effects on the structure of plant communities. We tested the hypothesis that within species variation in the AMF Rhizophagus irregularis significantly affects plant community structure and plant co-existence. We took advantage of a recent genetic characterization of several isolates using double-digest restriction-site associated DNA sequencing (ddRADseq). This allowed us to test not only for the impact of within AMF species variation on plant community structure but also for the role of the R. irregularis phylogeny on plant community metrics. Nine isolates of R. irregularis, belonging to three different genetic groups (Gp1, Gp3 and Gp4), were used as either single inoculum or as mixed diversity inoculum. Plants in a mesocosm representing common species that naturally co-exist in European grasslands were inoculated with the different AMF treatments. We found that within-species differences in R. irregularis did not strongly influence the performance of individual plants or the structure of the overall plant community. However, the evenness of the plant community was affected by the phylogeny of the fungal isolates, where more closely-related AMF isolates were more likely to affect plant community evenness in a similar way compared to more genetically distant isolates. This study underlines the effect of within AMF species variability on plant community structure. While differential effects of the AMF isolates were not strong, a single AMF species had enough functional variability to change the equilibrium of a plant community in a way that is associated with the evolutionary history of the fungus.

Effects of disturbance type and microhabitat on species and functional diversity relationship in stream-bank plant communities

Spatial heterogeneity in site conditions and differing disturbance types are common features of natural landscapes. We asked: does the relationship between species diversity and functional trait diversity (SD-FD relationship) of plant communities vary among habitats experiencing different types of disturbance and among microhabitats (i.e., landscape position) within a landscape? We quantified the relationship between species richness and functional richness (FRic) and between species evenness and functional evenness (FEve) of riparian plant communities along small headwater streams at five spatially adjacent microhabitats in two types of disturbed (wildfire and clearcut logging with buffer) and reference habitats (unlogged mature forest) in northwestern Ontario, Canada. We found significant dependence of species richness vs. FRic relationship on microhabitat, but not on disturbance type. Species evenness vs. FEve relationship varied slightly among reference and wildfire sites, but not among microhabitats. A significant variation in functional trait dispersion (FDis) among microhabitats offered a mechanistic explanation to the observed variation in the SD-FD relationship. A very weak effect of disturbance type on the SD-FD relationship indicates that clearcut with buffer retention may emulate riparian plant composition created by wildfire. However, the microhabitat dependent variation in the SD-FD relationship indicates that the same range of species diversity may refer to different ranges of functional trait diversity depending on microhabitat. We suggest that microhabitat plays a stronger role than disturbance type in trait dispersion and ultimately modifies the SD-FD relationship in our studied communities. This result highlights the role of spatial environmental heterogeneity of a landscape and different dimensions of species diversity and functional trait diversity, e.g. richness and evenness, in understanding the functioning of a natural landscape.