Phenological analysis of Eucalyptus wandoo for honey bee foraging

As part of the project I’m involved with in the Honey Bee Products Cooperative Research Centre (CRC) I recently delivered a short presentation on current research work at the Western Australian Herbarium.

The project aims to provide a detailed phenological (flowering) analysis of the native flora species used for the foraging of pollen and nectar by honey bees (Apis mellifera). However, the issues are these:

  1. Authors (eg. Smith 1969,  Manning 2006) discuss the winter, spring and summer-flowering varieties of Eucalyptus wandoo sens lat. with no further taxonomic resolution (i.e. subspecies).
  2. While the Descriptive Catalogue publication in 2000 delivered a summary range of flowering months for every taxon in WA, based on WA Herbarium vouchered specimens, this is too coarse in terms of spatial resolution to deliver a spatial information system for WA apiarists and researchers.
  3. Likewise, although all label data for specimens in the WA Herbarium are databased, this information is too incomplete for ascribing the presence of reproductive material as it not reliably mentioned by collectors in their notes.
  4. There has been much taxonomic ‘churn’ in the ‘wandoo group’ of Eucalyptus since the major revision by Brooker and Hopper in 1991, when E. wandoo was split into c. 6 different taxonomic entities, of which 4 remain in current scientific use (see Table 1).
Herbarium specimen of Eucalyptus capillosa Figure 1. Herbarium specimen of Eucalyptus capillosa

Table 1. Classification of ‘wandoo’, according to Nicolle (2019). Taxa in grey are no longer considered ‘current’.
Classification of the 'wandoo'
The research question, therefore, was —
if apiarists continue to identify their bees foraging species by the broad concept of ‘wandoo’, yet they perceive differences in the tree (or the honey), then do these differences correlate to the modern taxonomic concepts?

To investigate, the best recourse was to rigorously score the flowering condition of all the well-identified voucher material in the WA Herbarium, of which there are thousands of specimens. The herbarium specimen label data has all been databased and geocoded where possible and one of the current generation of scientific curators – Malcolm French – had recently been through the collection and applied the most recent species concepts in the form of determinavit and confirmavit slips (Figure 1).

Each specimen was scored as to whether it was sterile, in bud, flowering or carrying either immature (current season) or mature (previous seasons) fruit; specimens without a date or geocode were not scored. The data was scored in line with current herbarium data standards so that once complete the data can be associated back with each specimen record in the WAHERB database.

In Figure 2 you can see the effect of Brooker and Hopper’s work. Before 1991 all these points were considered a part of a large and variable Eucalyptus wandoo species. Subsequently, six distinct entities were recognised.

Note also, you can see the number of records for each taxon on the right panel, and on the bottom widget you can see a breakup of the number of records by month.

In Figure 3 you can see just the set of records for which flowers were present, and you’ll notice that the pattern of collecting per month – with a peak in spring, differs from the pattern of flowering where the peak is in summer. This is a type of collector bias commonly seen, and one can’t assume that all collections possess flowers.

Distribution of Eucalyptus wandoo and related taxa, based on WA Herbarium specimensFigure 2. Distribution of collections of Eucalyptus wandoo and related taxa

Flowering records of Eucalyptus wandoo and related taxa, based on WA Herbarium specimensFigure 3. Flowering records of Eucalyptus wandoo and related taxa

Figure 4 shows just the flowering records of the most common Eucalyptus wandoo subsp. wandoo. You can discern the three peaks of flowering in the data – summer, autumn and spring.

By contrast, Figure 5 shows specimens of Eucalyptus wandoo subsp. pulverea occurring in the northern-most parts of the species range and show a distinct trend towards flowering in autumn.

Differences in flowering time may be discerned across all the ‘wandoo’ group of taxa. The next steps are to visualise the flowering times across latitude.

Preliminary data for variation in flowering time as a response to latitude is exemplified in Figure 6 by previous recent work on Marri (Corymbia calophylla), where the data shows that the peak for flowering in latitudes north of Perth is in February, while the clear peak in flowering south of Perth is a month later, in March.

The figure also contains a simple graph showing that across the species range for Marri the peak in the occurrence of buds is in February, whilst flowering peaks in March. And while eucalypt nuts persist on a tree for a number of years after flowering, it is apparent from the data that the development of capsules appears to peak around six months after flowers are fertilised.

Flowering records of <i>Eucalyptus wandoo</i> subsp. <i>wandoo</i>Figure 4. Flowering records of Eucalyptus wandoo subsp. wandoo

Flowering records of <i>Eucalyptus wandoo</i> subsp. <i>pulverea</i>Figure 5. Flowering records of Eucalyptus wandoo subsp. pulverea

Corymbia calophylla flowering data by degrees of latitude Figure 6. Corymbia calophylla (Marri) flowering data by degrees of latitude

Further vouchered specimen data is being captured for additional native species on which honey bees forage. This will provide further verifiable evidence for flowering and fruiting times across these species ranges. With enough data it may be feasible to model the effects of future climate scenarios on the distribution of foraging species, as well.  Through this work I’ve been doing with the Honey Bee Products CRC team, and with the specimens in the Western Australian Herbarium, we’ve already started to add the data we need to answer the questions that the apiarists are posing.

Why not try out this prototype phenology tool that I’ve also prepared using the ‘wandoo’ data yourself? Then leave a comment below, start a chat with me via Facebook, Twitter or LinkedIn, or email me directly via alex.chapman@gaiaresources.com.au.

Alex

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