Using iNaturalist to Help Solve A Desert Southwest Phenological Mystery

Last Fall, something strange happened in Joshua Tree National Park. Joshua Trees flowered in November, according to multiple reports. This flowering timing is very unusual. The normal period of flowering for Joshua Trees is March through May, and the very earliest park-documented flowering previous to this last Fall was late February. The best coverage of this very strange event is probably found in this Desert Sun article, which also discusses why unusual flowering events may actually be bad news for Joshua Tree reproductive success.

Here is a great shot of a Joshua Tree in bloom on Thanksgiving (November 22nd, 2018) taken by @nofrakes.

My lab has been interested in this topic of phenology, the timing of plant and animal life cycle stages such as flowering, fruiting or leaf emergence and senescence. Phenology is a great topic because it’s also one familiar to all of us. We all note the passing of seasons, such as leaves emerging in Spring, and indeed the word “Fall” is an apt description of what happens to plants and their leaves. But while we all notice seasonal changes, actually documenting the exact timing of events across the globe is a daunting challenge, and these seasonal cycles may themselves be changing with a changing world. Along with studying phenology, our lab has also been working to assemble phenology data in a way that we can understand the broad-scale environmental factors affecting phenology. So when we saw that there was this unusual flowering event in Joshua Tree National Park, we wondered if we could learn more about it -- did Joshua Trees bloom early across their whole range? Did other Yuccas also have abnormal flowering? So many questions, but how the heck to answer them?

Our first thought was that we should look at the National Phenology Network (NPN), since NPN monitors some key Yucca species, including Joshua Trees and a few other Yucca species. We are huge fans of the NPN but unfortunately, the reporting over space is relatively sparse, although on the plus side, the same plant is often monitored over a long period of time. And then, 💡! iNaturalist can tell us about phenology! And it can probably tell us a lot about the spatial, temporal and taxonomic extent of this unusual flowering.

So we decided to devote our lab meetings for the 2019 Spring Semester to see how to develop the best possible way to utilize iNaturalist observations to look at the phenology of Yucca broadly, and whether we could answer some simple questions about unusual flowering of desert Southwest Yucca during Fall 2018. Along the way, we learned that to get the best quality data for reporting phenology, we had to develop a relatively detailed methodology and set of best practices. And we also learned a ton about Yucca phenology, some of which is still ongoing work in the lab. If you are interested in what we did and found, we have recently submitted that work to the journal Applications in Plant Sciences, and also have made available a preprint draft on BioRXive. We welcome any and all comments and thoughts on the preprint, which you can find here.

Most importantly, we want to use this journal post to thank all the people who have taken the time to photograph and identify Yuccas. @ck2az has photographed 9,708 Yuccas, an incredible effort, and @aspidocelis has identified 2,979 Yucca photos, dwarfing the 700 or so I have identified. But every single observer out there who has uploaded a photograph, and every single identification, has been important. As we show in our paper, we can actually get a fairly good idea of just where, when and to-whom those flowering anomalies happened, and we can also ask some neat follow-up questions, too. For example, did species in areas that had unusual flowering events have reduced or no flowering during normal flowering times? And while I am excited about the work we’ve done, I think there is enormous and yet-untapped potential to look at phenology trends at scale using iNaturalist data.

Finally, we are passionate about Open Data, so we took the time to publish the annotations about flowering to plantphenology.org, a global resource for plant phenology observations, and you can check out the data we compiled there. For example, searching the genus “Yucca” and looking for “open flowers present” will show you the results from our iNaturalist scoring of images, including a link back to the iNaturalist record itself. Plantphenology.org assembles data about phenology from multiple places so you can also get all the Yucca phenology reporting from NPN or other sources.

Again, thanks to iNaturalist and the community here for making this work possible.

Posted on September 2, 2019 12:23 PM by robgur