Abstract

1. Factors shaping arthropod and plant community structure at fine spatial scales arepoorly understood. This includes microclimate, which likely plays a large role inshaping local community patterns, especially in heterogeneous landscapes charac-terised by high microclimatic variability in space and in time.

2. We explored differences in local microclimatic conditions and regional species poolsin two subarctic regions: Kilpisjärvi in north-west Finland and Varanger in north-eastNorway. We then investigated the relationship between fine-scale climatic variationand local community characteristics (species richness and abundance) among plantsand arthropods, differentiating the latter into two groups: flying andground-dwelling arthropods collected by Malaise and pitfall traps, respectively. Arthropod taxa were identified through DNA metabarcoding. Finally, we examined ifplant richness can be used to predict patterns in arthropod communities.

3. Variation in soil temperature, moisture and snow depth proved similar betweenregions, despite differences in absolute elevation. For each group of organisms, wefound that about half of the species were shared between Kilpisjärvi and Varanger,with a quarter unique to each region.

4. Plants and arthropods responded largely to the same drivers. The richness and abun-dance of both groups decreased as elevation increased and were positively correlatedwith higher soil moisture and temperature values. Plant species richness was a poorpredictor of local arthropod richness, in particular for ground-dwelling arthropods.

5. Our results reveal how microclimatic variation within each region carves pro-nounced, yet consistent patterns in local community richness and abundance out ofa joint species pool.