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Nurse plants play a crucial role on plant biodiversity in drylands. While the nurse's impacts in biodiversity are documented, we know little about such impacts of different nurse's life forms; and how these impacts associate to climatic gradients. In this regard, we re-analyzed a dataset of 72 dryland sites, established across climatic gradients in 10 countries, and assessed changes of plant taxonomic, functional and phylogenetic diversity with respect to presence of nurse plants from different plant life forms (i.e., grasses, shrubs and trees) and their absences (i.e., open communities). We observed a more substantial increase in functional and phylogenetic diversity associated to nurse grasses communities than their open pairs, with greater functional and phylogenetic dissimilarity between the communities under moderate climatic gradients. Such findings were consistent with an increase in the strength of correlations between these biodiversity facets. In communities including nurse shrubs, taxonomic and functional diversity were positively changed especially at the middle of climatic conditions, with stronger dissimilarities and relationships for taxonomic than for functional diversity. In contrast, nurse trees promoted negative impacts on all biodiversity facets under moderate climatic conditions, while the contrary pattern (except in functional diversity) was observed in their paired open communities, showing an increase with strength of correlations between biodiversity facets. Therefore, our results suggested different facilitatory mechanisms of nurse plants depending on their life forms to affect plant biodiversity. Such specific mechanisms might partly be explained by controlling beneficiary relatedness that may be significantly related to climatic conditions. [ABSTRACT FROM AUTHOR]

Restoration of degraded environments is essential to mitigate adverse impacts of human activities on ecosystems. Plant–plant interactions may provide effective means for restoring degraded arid lands, but little is understood about these impacts. In this regard, we analyzed the effects of two dominant nurse plants (i.e., Artemisia sieberi and Stipa arabica) on taxonomic, functional, and phylogenetic diversity across different ages of land abandonment (i.e., control, recent, and old ages) in a limestone mine site in Iran. In addition, we considered two spatial scales: i) the plot scale (i.e., under 1m2 plots) and ii) the vegetation‐patch scale (i.e., under the canopies of nurse plants), to assess nurse plant effects, land abandonment ages, and their relative importance on biodiversity facets by performing Kruskal–Wallis H test and variation partitioning analysis. Our results indicated an increase in taxonomic, functional, and phylogenetic diversity at the plot scale, when considering the presence of nurse plants under old ages of land abandonment. Such significant differences were consistent with the positive effects of Artemisia patches on taxonomic diversity and Stipa patches on functional and phylogenetic diversity. In addition, we found a larger contribution from nurse plants than land abandonment age on biodiversity variation at both spatial scales studied. Therefore, these results indicate the importance of plant–plant interactions in restoring vegetation, with their effects on the presence of beneficiary species and their functional and phylogenetic relatedness depending on the nurse life forms under the stress‐gradient hypothesis. [ABSTRACT FROM AUTHOR]

Aim: Plant–plant interactions are an important factor in structuring plant biodiversity. However, most studies on the impacts of plant–plant interactions on biodiversity focus on species richness and to a lesser extent on other facets of diversity. When other facets of biodiversity are considered, studies often include a limited set of environmental conditions. We aimed to quantify the impacts of nurse plants on taxonomic, functional and phylogenetic facets of plant biodiversity and how these impacts change across environmental gradients. Location: We report data on 28 alpine and 50 dryland sites, established in 11 countries. Time period: 1998–2019. Major taxa studied: Vascular plants. Methods: We analysed plant–plant interactions using co‐occurrence analyses and obtained information on the functional traits and phylogenetic relationships of the beneficiary species. We calculated the change in taxonomic, functional and phylogenetic diversity caused by the presence of nurse plants and environmental conditions. Results: Nurse plants enhanced taxonomic and phylogenetic diversity in alpine communities and enhanced functional and phylogenetic diversity in dryland communities. However, they had a positive effect on functional and taxonomic diversity only in moderate environments in alpine and dryland communities, respectively. The effects of nurse plants were larger in drylands for functional and phylogenetic diversity and in alpine communities for taxonomic diversity. Interestingly, nurse plants induced nonlinear changes in all facets of biodiversity across environmental gradients, whereas biodiversity tended to increase linearly toward more benign conditions in open interspaces. Main conclusions: Facilitation is important in alpine environments to maximize taxonomic diversity and has a more consistent positive effect on the functional and phylogenetic diversity of drylands. In general, effects of facilitation on biodiversity peak in moderate environmental conditions, which suggests that nurse plants can protect biodiversity from impacts of climate change mostly in those places currently under low environmental stress and that will be likely to experience moderate stress levels in the future. [ABSTRACT FROM AUTHOR]

The interspecific plant interactions along grazing and aridity stress gradients represent a major research issue in plant ecology. However, the combined effects of these two factors on plant–plant interactions have been poorly studied in the northeast of Iran. To fill this knowledge gap, 144 plots were established in 12 study sites with different grazing intensities (high vs. low) and climatic characteristics (arid vs. semiarid) in northeastern Iran. A dominant shrub, Artemisia kopetdaghensis, was selected as the model species. Further, we studied changes in plant life strategies along the combined grazing and aridity stress gradients. In this study, we used relative interaction indices calculated for species richness, Shannon diversity, and species cover to determine plant–plant interactions using linear mixed‐effect models (LMM). The indicator species analysis was used to identify the indicator species for the undercanopy of shrub and for the adjacent open areas. The combined effects of grazing and aridity affected the plant–plant interactions and plant life strategies (CSR) of indicator species. A. kopetdaghensis showed the highest facilitation effect under high stress conditions (high grazing, high aridity), which turned into competition under the low stress conditions (low grazing, low aridity). In the arid region, the canopy of the shrub protected ruderals, annual forbs, and grasses in both high and low grazing intensities. In the semiarid region and high grazing intensity (low aridity/high grazing), the shrubs protected mostly perennial forbs with C‐strategy. Our findings highlight the importance of context‐dependent shrub management to restore the vegetation damaged by the intensive grazing. [ABSTRACT FROM AUTHOR]

Questions: (a) Do patterns of species diversity and composition differ between plots exposed to high vs. low grazing intensity? (b) Do these differences vary among three regions with different climates, representing a gradient from arid to sub‐humid conditions? Location: Northeastern Iran. Methods: We compared plots intensively grazed by sheep and goat (HG) to plots with low grazing intensity (LG), across three climatic regions: arid, semi‐arid and sub‐humid. Species diversity (expressed as Shannon H) was compared using linear mixed‐effect models. Dissimilarity analysis was used to estimate the compositional heterogeneity of different types of plots, reflecting the differences in species composition. Indicator Species Analysis was used to identify individual species associated with particular types of plots. Results: The HG plots had lower values of Shannon H than LG plots, across all climatic regions. Further, the effect of grazing on species diversity varied between the climatic regions, with the most pronounced differences between the HG and LG plots in the sub‐humid region. Although no differences in species diversity were detected between the three climatic regions, compositional heterogeneity was the highest in the sub‐humid region and the lowest in the semi‐arid region, with the most pronounced differences between the HG and LG plots in the sub‐humid region. Indicator Species Analysis showed significant main effects of both climate and grazing on species composition, revealing species that respond to grazing in each of the three climatic regions. Conclusions: Overgrazing was detected to reduce the diversity of species in all three climatic regions, even though its effect was most pronounced in the sub‐humid region. Therefore, the control of overgrazing or reduction of its intensity appears an effective management tool for protecting species diversity, applicable in areas with different climates. [ABSTRACT FROM AUTHOR]

Understanding the responses of vegetation characteristics and soil properties to grazing in different precipitation regimes is useful for the management of rangelands, especially in the arid regions. In northeastern Iran, we studied the responses of vegetation to livestock grazing in three regions with different climates: arid, semiarid, and subhumid. In each region, we selected 6–7 pairwise sampling areas of high versus low grazing intensity and six traits of the present species were recorded on 1 m2 plots—five grazed and five ungrazed in each area. The overall fertility was compared using the dissimilarity analysis, and linear mixed‐effect models were used to compare the individual fertility parameters, functional diversity indices, and species traits between the plots with high and low grazing intensity and between the climatic regions. Both climate and grazing, as well as their interaction, affected fertility parameters, functional diversity indices, and the representation of species traits. Grazing reduced functional evenness, height of the community, the representation of annuals, but increased the community leaf area. In the subhumid region, grazing also reduced functional richness. Further, grazing decreased the share of annual species in the semiarid region and seed mass in the arid region. Larger leaf area and seed mass, smaller height and lower share of annuals were associated with intensive grazing. Species with large LA and seed mass, lower height and perennials can be therefore presumed to tolerate trampling and benefit from high nutrient levels, associated with intensive grazing. By providing a detailed view on the impacts of overgrazing, this study highlights the importance of protection from grazing as an effective management tool for maintaining the pastoral ecosystems. In general, the composition of plant traits across the pastures of northeastern Iran was more affected by intensive grazing than by the differences in climate. [ABSTRACT FROM AUTHOR]

Aims Species composition and diversity of the mountainous rangelands are results of interactions between environmental severities, heterogeneous topography and facilitative effects by nurse plants. This research was aimed to compare relative effects of these three environmental variables on the natural vegetation of a mountainous rangeland. For a more detailed understanding, effects of four different nurse species were separately compared on the various plant growth forms and on two community plant responses (diversity and abundance). Methods A mountainous semiarid rangeland was selected in Baharkish, Quchan, Northeast of Iran. Density and canopy cover of all plant species were recorded under the canopy of four different shrubs and in open areas, in north and south-facing aspects, and in a normal and a drought year. Shannon diversity, total abundance (% cover) and the abundance of different growth forms were used as criteria for assessing effects of the environmental variables. Data were arranged in a factorial combination and analyzed by three-way analysis of variance using a GLM analysis. Important Findings (i) Drought, aspect and canopy created niche differentiation: annual forbs and shrubs were more affected by drought, whereas geophytes and grasses were more responsive to slope aspects. Effects of drought and slope aspect were more profound on species diversity, whereas that of canopy facilitation was stronger on plant abundance. (ii) Canopy facilitation was dependent on severity of the abiotic factors and life history of interacting species. Canopy facilitation allowed for the persistence of only annual forbs, but it was disadvantaged during the drought year. Plant community responses to abiotic factors (slope and drought) were more dependent on the plant growth form, while responses to canopy facilitation were more dependent on the morphology and/or ecology of nurse shrubs. (iii) Effect of shrubs was dependent on their morphology and ecology: shrubs with larger canopy area and nitrogen fixation capability increased, but those with allelopathic effects or a dense canopy structure decreased the diversity of the understory species. [ABSTRACT FROM AUTHOR]