Substantial variation in leaf senescence times

Posted by Amanda Gallinat, photos by Richard Primack

"October is the month of painted leaves.  Their rich glow now flashes round the world." 

-Henry David Thoreau, "Autumnal tints” in Excursions

In recent years, the Primack lab has worked in partnership with 5 other research groups at botanic gardens around the world to monitor the timing of leaf senescence (leaf color change and leaf drop) across a wide range of species. The results of this international collaboration have been published in Annals of Botany, in a paper led by Zoe Panchen of Carleton University.

Prunus sargentii leaves changing from green to yellow and red coloration.

The paper, entitled "Substantial variation in leaf senescence times among 1360 temperate woody plant species: implications for phenology and ecosystem processes" demonstrates that autumn leaf senescence dates vary broadly between species and botanic gardens. Within each botanic garden, the sequence of leaf senescence was fairly consistent between years, but did not have a strong phylogenetic signal. 

Leaves senescing in the Morus section of the Arnold Arboretum in Boston, MA

These results are in stark contrast with the results of a similar study on spring leaf-out times that our botanic garden collaborative published last year, which showed that the sequence of leaf-out is largely consistent between years and locations, and contains strong phylogenetic patterns. We conclude that while leaf-out is strongly driven by spring temperatures, the lack of patterns in leaf senescence timing means it is likely driven by a combination of local environmental factors, including soil moisture, frost, wind, and temperature.