Aim: Palms are an iconic, diverse, and often abundant component of tropical ecosystems that provide
6 many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically, and
7 physiologically distinct from other trees, and these differences have important consequences for
8 ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate
9 change. We quantified global patterns of tree palm relative abundance to help improve understanding of
10 tropical forests and reduce uncertainty about these ecosystems under climate change.
11 Location: Tropical and subtropical moist forests
12 Time period: Current
13 Major taxa studied: Palms (Arecaceae)
14 Methods: We assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified
15 tree palm (i.e., ≥ 10 cm diameter) abundance relative to co-occurring non-palm trees. We compared the
16 relative abundance of tree palms across biogeographical realms, and tested for associations with
17 paleoclimate stability, current climate, edaphic conditions, and metrics of forest structure.
18 Results: On average, relative abundance of tree palms was more than five times larger between
19 Neotropical locations and other biogeographic realms. Tree palms were absent in most locations outside
20 the Neotropics but present in >80% of Neotropical locations. Relative abundance of tree palms was more
21 strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility,
22 shallower water table, and lower plot-mean wood density) than metrics of long-term climate stability. Life
23 form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many
24 non-tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above-ground
25 biomass but the magnitude and direction of the effect requires additional work.
26 Conclusions: Tree palms are not just quintessentially tropical, they are overwhelmingly Neotropical.
27 Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be
28 particularly critical in Neotropical forests.