PS 36-189 - Inter and intra-specific variation in the trade-off efficiency versus hydraulic safety in a Terra firme forest of the Colombian Amazon

Background/Question/Methods

The droughts that the Amazonian forests are facing are becoming increasingly prolonged and impact the recovery of forest’s dynamics. Water availability varies both spatially and temporally and is a key feature that can explain plant distribution patterns. Studies have shown that in Amazon forests species distributed in valleys have different trait combinations than species located in the hills. The latter generally have xylem vessel traits more related to hydraulic safety instead of hydraulic efficiency. In this study we quantify the inter- and intra-specific variability of a set of hydraulic traits such as vessel density, vessel area, and diameter, in relation to small-scale changes in water availability of 295 trees of 20 species in an ever-wet Amazon terra firme forest: the Amacayacu Forest Dynamic Plot in Colombia. Additionally, we aim to assess whether trait variability is related to interspecific variation in topographic habitat associations, drought responses, or the large-scale geographic distributions in relation to water availability. The questions we worked on were: what proportion of variation is attributable to topography-based specialization classes and topographic habitats? Is interspecific trait variation related to topography-based habitat associations? How do traits vary within species between individuals of different sizes and growing in different topographic positions?

Results/Conclusions

The main objective of this study was to assess the relationships between hydraulic traits and changes in water availability, to determine if species develop hydraulic strategies focused on safety or efficiency, depending on the habitat in which the species establishes. The results indicated that there was greater intraspecific than interspecific variation in all traits except vessel density (VD). The species that occupied more humid sites presented a larger vessel area and lower vessel density (hydraulic efficiency), in contrast to species in drier places which presented a lower vessel area and higher vessel density (hydraulic safety). Overall, generalist species presented greater variation and wider ranges, since they adapt to different environmental conditions such as flooded valleys and drier ridges. Vessel density and mean diameter decreased with tree size, while sapwood area increased, revealing a strategy that increases tree hydraulic efficiency without decreasing its hydraulic safety. In some species two strategies were identified However, these were not strictly defined in the specialization classes or in the topographic habitats. In conclusion, plants can develop alternative functional strategies with different combination of hydraulic traits, and topography was not an important determinant in the hydraulic traits’ variation.