Foliar and bark-surface arthropod communities of pinyon and juniper trees vary with host tree species and long-term site climatic context.

Abstract

Pinyon-Juniper (PJ) woodlands are critical arid habitats that host diverse biotic communities. We examined tree-arthropod relationships across elevational gradients in northern Arizona, comparing foliar and trunk communities on the 2 dominant tree species, pinyon and juniper. Understanding these dynamics is vital for climate-change adaptation and biodiversity management. Using trunk-refugia traps and sweep-netting, we sampled arthropods on trunks and foliage of both hosts and tested how host tree, elevation, and precipitation structured assemblages. We hypothesized (i) trunk and foliar communities would be compositionally distinct; (ii) communities would differ between pinyon and juniper because of host-specific taxa rather than dominance by a single tree species; and (iii) peaks in foliar diversity would occur where cooler, wetter conditions coincided (mid-elevation sites). The study confirmed distinct foliar and trunk communities and strong, taxon-specific host-tree effects. Juniper foliage supported higher foliar richness and diversity in both years, whereas pinyon trunks supported higher arthropod abundance and several trunk-associated taxa. Pinyons and junipers therefore supported unique trunk and foliar assemblages, contradicting previous studies on ground arthropods. We observed host-specific preferences, with spiders, leafhoppers, and parasitoid wasps more common on juniper foliage, while mites were more abundant in pinyon foliage. Climate associations were year- and taxon-specific: precipitation and elevation structured foliar richness in 2019 but were weaker in 2020. Our findings show that host-tree identity was the more consistent predictor in this dataset, whereas elevation and precipitation proxies captured site-level associations with long-term climatic context rather than year-specific weather, providing a spatial baseline for future monitoring under vegetation and climate change.