PS 22-38 - CANCELLED - Small-old trees are common and deserve urgent conservation attentions.

Abstract: Ancient trees are irreplaceable keystone organisms contributing to multifaceted ecosystem benefits to human cultural landscape. Current understanding on ancient trees were mostly concentrated on large old trees (LOTs), while small-old trees (SOTs), which have greater stress resistance and adaptation than LOTs, have been ignored. Using a global tree-ring dataset with accurate tree age and diameter of 119,631 trees from 5,060 sites, we addressed whether SOTs are common and have different distribution pattern with LOTs. Tree diameter could only explain 9% age variation of old trees (older than 266 yr), among which 64% are less than 50 cm in diameter. These results support that SOTs are common, challenging traditional conception that older trees are larger. Most of SOTs (diameter ≤20.94 cm) occur in colder and drier ecoregions, with -0.3 ℃ on mean temperature and 547 mm on mean precipitation, compared to LOTs (diameter ≥71.70 cm) which are mainly confined in poorly explored areas with warmer (8 ℃ on average) and wetter (808 mm on average) climate. Widely living beyond the habitats that support LOTs result in overlooking of current LOTs-dominated conservation strategies on SOTs. Our results highlight the urgency to establish identification guidelines of ancient trees that consider comprehensive morphological and biogeographical characteristics of old trees rather single tree size. Such thorough recognition system is fundamental for conserving ancient trees, thus restoring and maintaining forest integrity for a sustainable future.