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SummaryEnvironmental extremes resulting from a changing climate can have profound implications for plant interactions in desert communities. Positive interactions can buffer plant communities from abiotic stress and consumer pressure caused by climatic extremes, but limited research has explored this empirically.We tested the hypothesis that the mechanism of shrub facilitation on an annual plant community can change with precipitation extremes in deserts. During years of extreme drought and above-average rainfall in a desert, we measured plant interactions and biomass while manipulating a soil moisture gradient and reducing consumer pressure.Shrubs facilitated the annual plant community at all levels of soil moisture through reductions in microclimatic stress in both years and herbivore protection in the wet year only. Shrub facilitation and the high rainfall year contributed to the dominance of a competitive annual species in the plant community.Precipitation patterns in deserts determine the magnitude and type of facilitation mechanisms. Moreover, shrub facilitation mediates the interspecific competition within the associated annual community between years with different rainfall amounts. Examining multiple drivers during extreme climate events is a challenging area of research, but it is a necessary consideration given forecasts predicting that these events will increase in frequency and magnitude.

1. Declining bumble bees are threatened by habitat loss, pathogens and climate change. Despite policy and management recommendations to create pollinator habitat, the habitat requirements for at-risk bumble bees remains unclear. Most studies on bumble bee habitat are descriptive, focus on floral resources, occur at one spatial scale, or do not examine at-risk species. 2. We provide the first thorough habitat description for two North American bumblebee species (Bombus terricola and Bombus pensylvanicus) at-risk of extinction. We asked the following questions: (i) What characterises B. terricola and B. pensylvanicus habitat? (ii) Are landscape variables, local variables, or flowering plant species more important determinants of habitat? (iii) do important variables change throughout the season? 3. Surveys were conducted at 25 sites with a recent occurrence of either B. terricola, B. pensylvanicus, or both species across southern Ontario, Canada. Landscape variables were extracted from a 1-km buffer around each site. Local variables related to bumble bee resource requirements (floral, nesting and overwintering) and flowering species cover were measured in spring, midsummer , and late-summer. 4. We found that the proportion of different land cover classes at 1 km was a more important predictor of B. terricola and B. pennsylvanicus presence than local transect based variables such as floral richness or the patchiness of floral cover. We did not find any evidence of important variables changing temporally, but floral resources were consistently important throughout the season. Our results highlight that management of atrisk pollinator species requires consideration of species-specific habitat requirements.

Nurse plant facilitation is a commonly reported plant–plant interaction and is an important factor influencing community structure in stressful environments. Cushion plants are an example of alpine nurse plants that modify microclimatic conditions within their canopies to create favourable environments for other plants. In this meta-analysis, the facilitative effects of cushion plants was expanded from previous syntheses of the topic and the relative strength of facilitation for other plants and for arthropods were compared globally.The abundance, diversity, and species presence/absence effect size estimates were tested as plant responses to nurse plants and a composite measure was tested for arthropods. The strength of facilitation was on average three times greater for arthropods relative to all plant responses to cushions. Plant species presence, i.e., frequency of occurrence, was not enhanced by nurse-plants. Cushion plants nonetheless acted as nurse plants for both plants and arthropods in most alpine contexts globally, and although responses by other plant species currently dominate the facilitation literature, preliminary synthesis of the evidence suggests that the potential impacts of nurses may be even greater for other trophic levels.