Abstract: Wood density (WD) indicates important plant functions and plays a key role in carbon cycling of forest ecosystems by affecting wood decomposition. However, how WD varies globally and how it evolved through the evolutionary history of angiosperms remain unclear. Here, by integrating data of WD, phylogeny and distributions for angiosperms worldwide, we estimated global spatiotemporal patterns of WD and their relationships with modern climate and paleoclimate. We found that mean WD decreased with latitude in the northern hemisphere but increased with latitude in the southern hemisphere. The interspecific WD variation within each geographic unit did not show clear latitudinal gradients. Temperature was the best predictor of the global geographic pattern in mean WD, while the geographic variation in mean WD across high-temperature regions could be explained by geographic variation in precipitation and precipitation seasonality (PS). Since the Cenozoic (66 million years ago (Mya)), WD increased first (until 20 Mya) and then decreased. In general, the Cenozoic WD was positively correlated with paleotemperature and negatively correlated with paleoprecipitation, especially during more arid periods. Interestingly, the evolutionary trends of WD on different continents differed, which corresponded to the divergence in WD patterns and their relationships with modern climate on different continents. Our results highlight the dominant effect of environmental temperature on global variation in angiosperm WD with an additional strong effect of PS. Our study also demonstrates the critical role of aridity and biogeographic idiosyncrasies in driving angiosperm WD evolution.

Key words: angiosperms, Cenozoic, global variation,  modern climate, paleoclimate, phylogeny, trait evolution, wood density