Fraxinus Fruit Finder Preliminary Results

Back in October we launched an expedition on the Zooniverse mobile app called Fraxinus Fruit Finder. Fraxinus is the genus of ash trees in the Olive family (Oleaceae). The basic idea was to score the specimen as having fruit or not. It seems that most people found it straightforward to tell if fruits were present and enjoyed helping out. The expedition completed in just 4 days and 48 different volunteers contributed!

A Fraxinus specimen with fruit present. The straw-colored fruits are clustered on the lower part of the stem in the picture.

This effort is part of a much larger project related to ash trees and a beetle that feeds on it called emerald ash borer. The beetle is native to north-eastern Asia, but is now spreading around North America. It is currently mostly found in the eastern part of North America, but is likely to spread much further. There is tremendous concern about environmental and economic impacts that this beetle could have on native and introduced ash trees. Ash trees are abundant in many ecosystems and are also commonly planted in parks, along streets and are used in landscaping. A group of researchers from the Huntington Botanical Gardens in California is collecting ash seeds and leaf tissue from all over the United States with the hope of finding strains that are be resistant to emerald ash borer infestations.

One of the species of interest is called Fraxinus anomala, single-leaf ash. This species is unusual for ashes in that it is a shrub (most are big trees) and it has simple leaves (most have compound leaves). The single-leaf ash grows in very arid areas and tends to flower and fruit very irregularly which can make collecting seeds more challenging.

Line drawing showing the simple leaves of Fraxinus anomala compared with the compound leaves of other species. Image from Jepson eFlora.

That brings us to Notes from Nature! We had the idea to score as many specimens of single-leaf ash as we could to get a better sense of when to go seed collecting for the single-leaf ash.

The first question we asked was whether they could be scored using this Notes from Nature method and this preliminary expeditions indicates that is was a resounding success. There wasn’t a single discrepancy in the data as all volunteers agreed whether a specimen was in fruit or not.

There were 794 records in this expedition and we set the retirement to 5 meaning we collected a total of 4,109 entries. 370 (46%) specimens were found to be in fruit at the time of collection. We also wanted to know if there was a pattern to the fruiting date. The mean date of fruiting for our specimens was June 12^th . The earliest date was March 24^th and the latest date was Dec. 30^th, which confirmed that it can fruit throughout the year. However, the majority of the fruiting specimens are from May and June. The plot below also shows that fruiting is very variable and can happen throughout the year.

Barplot showing the distribution of flowering dates among specimens used in the Fraxinus Fruit Finder expedition.

These results are very helpful and will greatly assist in seed collection this coming season. The next steps are to look at possible bias in the data as well as other factors that could affect fruiting time. For example, in the next phase we could look at elevation and latitude which could influence fruiting time.

Thanks again to all that contributed,

— Michael from the Notes from Nature Team