The presence and distribution of mycorrhizal symbionts can influence plant distribution through specific host-mycorrhiza symbiosis interactions. However, generalist hosts also exist, such as dual-mycorrhizal plants that form symbiotic associations to both ectomycorrhizal-fungi (EM) and arbuscular mycorrhizal-fungi (AM). Little is known about the effect of dual mycorrhization status on the hosts’ global distribution and acclimation to specific environments. This study investigates the potential advantage of dual associations of more than 400 tree genera spread at a global scale. We found that dual host tree species occupy a broader geographical and climatic range compared to those associating exclusively with either AM or EM mycorrhiza groups. We show that an increased niche space is independent of phylogenetic architecture and evolutionary history of the tree species. Our results highlight the advantage of generalist host-microbe symbioses between trees and fungi to expand niche space, and their potential role in colonizing dry climates.