Thursday, February 22, 2018

Herbarium specimens show patterns in wild fruiting phenology

Posted by Amanda Gallinat

The timing of fruiting in New England is important for wildlife that eat wild fruits and disperse seeds. However, surprisingly little is known about when different plant species fruit and what environmental variables determine fruiting times.

An American Robin consuming whole fruits in late-autumn (photo by Sam Roberts)

In a paper published last week in the American Journal of Botany, my co-authors and I describe patterns and predictors of fruiting times for 55 woody plant species across New England. Our team recorded fruiting dates and locations for over 3,000 herbarium specimens with ripe fruit, collected in the wild from 1849-2013, and housed at 6 major herbaria. We analyzed variation in fruiting times among 37 native and 18 invasive species, as well as within-species variation.

A Buckthorn (Rhamnus cathartica) specimen with ripe fruits, available through the George Safford Torrey Herbarium digital collections

We found a moderate phylogenetic signal to fruiting dates; in other words, related species tended to fruit at similar times. With phylogeny considered we found that, on average, invasive species fruited 26 days later than native species, and had more variation in their fruiting times. Since some birds are migrating through New England later with warming temperatures, this may increase the likelihood that migratory birds will encounter and consume invasive fruits, and disperse invasive seeds.

Spring temperature and year were significant predictors of fruiting times within species, but explained a very small amount of the variation. We conclude that herbarium specimens are an excellent resource for investigating differences in fruiting times among species, but present unique challenges for analyzing variation within species. Read more about those challenges, potential solutions, and more in the full text.

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