Anatomical Types of Xylem Growth-Ring Boundaries in 16 Tree Species from a Rainforest in Southern Ecuador

This study analyzes wood anatomical properties and growth-ring boundaries in 16 tree species across a tropical humid forest along an altitudinal gradient in southern Ecuador. We extracted 64 wood cores, subjecting them to meticulous microscopic examination and thin section preparation with safranin and astrablue staining for growth-ring identification following IAWA standards. Correspondence analysis linking wood anatomical features and environmental variables revealed a nuanced connection between ecological factors, elevation and microscopic growth-ring distinctiveness. Species at lower altitudes (1000 m a.s.l.) exhibit indistinct growth rings, whereas those at higher altitudes (2000 m a.s.l.) often display distinct growth-ring boundaries with thick-walled latewood fibers. Apart from the deciduous Schefflera morototoni, evergreen tropical rainforest trees dominate at both elevations. This study provides new insights into growth-ring occurrence and anatomy in Ecuadorian tropical mountain rainforest trees, setting the stage for future dendrochronological research. The analysis of microscopic growth-ring features across species, elevations, and locations in the southeastern Andes offers new perspectives on wood structure. In the context of climate change, acquiring high-quality wood anatomical and dendrochronological data is crucial to advance our understanding of how forest trees respond to climate change and to develop adapted conservation and management strategies.