Bees and moths are globally important pollinators. Xeric barrens in the largely mesic northeastern USA support high levels of pollinator diversity, including rare bees and moths. We investigated the response of bee vs moth communities to abiotic and vegetation drivers in barrens across the region. We sampled environment, vegetation, bees, and moths for 2-4 years in 20 preserves. Employing random forest analysis, we tested the role of 26 abiotic and vegetation predictors of bee vs moth abundance, species richness, Shannon-Wiener Diversity Index, evenness, and species composition. Variables related to climate, canopy cover, and soils were the most important predictors of abundance, diversity, and species composition for both bees and moths. Vegetation variables, such as species richness of shrubs and hostplants, were also important for bees. The direction of these relationships contrasted sharply between bees and moths: bees were more abundant and species rich in more open, sandy sites and moths the opposite. Surprisingly, bee-moth contrasts in diversity did not hold for Shannon-Wiener Diversity. Habitat preferences for a subset of moth xeric specialists were much more similar to bees than to other moths, with a preference for open, sandy conditions. Contrasts between bees and moths in habitat preferences likely stemmed from differences in life history: bees rely on flowers for feeding and porous substrates for nesting, whereas most moth adults rely on flowers but many moth caterpillars use woody plants as hosts. The contrast between bees and moths for species richness vs. Shannon-Wiener Diversity raises important general questions about the conservation value of these two metrics. Our results suggest that, because of differences in habitat preferences among pollinators, barrens management for spatial and temporal heterogeneity is likely to promote the highest abundance and diversity of resident pollinator communities.

Aim: Drastic changes in fire regimes are altering plant communities, inspiring ecologists to better understand the relationship between fire and plant species diversity. We examined the impact of a 2011 megafire on woody plant species diversity in an arid mountain range in southern Arizona, USA. We tested recent fire-diversity hypotheses by addressing the impact of the fire severity, fire variability, historic fire regimes, and topography on diversity. Location: Chiricahua National Monument, Chiricahua Mountains, Arizona. USA., part of the Sky Islands of the US-Mexico borderlands. Taxon: Woody plant species. Methods: We sampled woody plant diversity in 138 plots before (2002-2003) and after (2017-2018) the 2011 Horseshoe Two Megafire in three vegetation types and across fire severity and topographic gradients. We calculated gamma, beta, and alpha diversity and examined changes over time in burned vs. unburned plots and the shapes of the relationships of diversity with fire severity and topography. Results: Alpha species richness declined and beta and gamma diversity increased in burned but not unburned plots. Fire-induced enhancement of gamma diversity was confined to low fire severity plots. Alpha diversity did not exhibit a clear continuous relationship with fire severity. Beta diversity was enhanced by fire severity variation among plots and increased with fire severity up to very high diversity, where it declined slightly. Main Conclusions: The results reject the intermediate disturbance hypothesis for alpha diversity but weakly support it for gamma diversity. Spatial variation in fire severity promoted variation among plant assemblages, supporting the pyrodiversity hypothesis. Long-term drought probably amplified fire-driven diversity changes. Despite the apparent benign impact of the fire on diversity, the replacement of two large conifer species with shrubs signals the potential loss of functional diversity, emphasizing the importance of intervention to direct the transition to a novel vegetation mosaic.