Who is the report targeted at?
This report will be relevant to the forest and apiary industry as well as organisations charged with the responsibility of conserving and managing Australia’s nectarivorous fauna.

Background
State forests provide the major honey resource for the apiary industry in NSW. Recent surveys of beekeepers using state forests have highlighted the beekeepers’ concern about the effects of logging on nectar production, especially the perception that young trees do not produce as much nectar as mature trees. Forest NSW research has partly investigated this concern with a ten year study on flowering patterns of forest trees and the effects of climate and logging (Law et al. 2000). However, this research did not measure nectar production.

Aims/Objectives
The project aimed to investigate the impact of logging on nectar production in the canopy of spotted gum and grey ironbark. In addition we quantified the magnitude of canopy nectar production and how this varied over the different years we sampled in relation to prevailing and preceding climate. Given the variability in flowering and nectar production between years we also benchmarked our nectar measurements with the amount of honey produced by local beekeepers as determined by questionnaires distributed to them.

Methods used
The study was undertaken on the south coast of New South Wales, where nectar was measured on large and small trees between 2003 and 2006. Cherry-pickers and cranes were used to access the canopy in replicate sites in different logging histories – recently logged, regrowth and mature/old regrowth forest. Nectar was measured in flowers bagged over-night (to prevent access by pollinators) and in unbagged flowers. Nectar production was then scaled up from the flower level to the forest stand by incorporating transect counts of the number of flowers per tree and trees per hectare. Spotted gum nectar was primarily measured in 2005, although some measurements of unbagged flowers were also undertaken in 2003. Nectar was measured in Eucalyptus paniculata over three consecutive years (2004-2006) in each of the logging histories. We benchmarked our nectar measurements against honey yields by distributing questionnaires to local beekeepers.

Results/Key findings
For spotted gum in 2005, we found that neither logging history nor tree size significantly affected over-night nectar production in bagged flowers; a significant interaction indicated that nectar production per flower was low in small trees in recently logged sites and high in small trees in regrowth sites. When nectar production was scaled up to the forest stand, mature forest produced almost ten times as much sugar per hectare as recently logged forest, with regrowth being intermediate. Less nectar after logging is explained by the fact that regrowing canopy is mainly formed by small and medium sized trees. We found that these trees flower less often than large trees.

At the compartment scale, the difference between mature forest and recently logged forest was reduced to a factor of two times when the extent of areas left unlogged under current practices was considered. Areas reserved from logging in NSW include riparian buffers, high conservation old growth forest, over-ridge connection corridors, threatened species habitat as well as habitat trees and recruits within logging zones.

One distinctive characteristic of Corymbia maculata nectar in 2005 was its high sugar content (40-60 %), much higher than the concentrations measured in 2003 (mean = 18 %). Nectar was not a limiting resource in 2005 as extensive flowering was recorded across the south coast and it was found that nectar was only slightly depleted in unbagged flowers measured in the morning and the afternoon.

Logging history had no effect on the degree of nectar depletion. We estimated that, on average, mature spotted gum forest produced a vast resource over-night. This is by far the greatest nectar energy density yet published: 35,000 kJ ha-1.

Flowers measured in 2003 provided a strong contrast with occasional flowering stands with much less sugar per flower early in the morning and virtually unmeasurable quantities after 0930 hours. At such times, nectar is limiting with morning nectar presumably consumed most quickly in areas recently logged. Models of nectar production collated over both years, using climate and site variables, indicated nectar volumes and sugar concentration respond differently to environmental conditions.

Predicting the nectar resource, which is made up of both components, was most consistently related to recent conditions that were unfavourable to foliage production. In general, more nectar was produced after a week of colder than average mornings, regardless of rainfall or after warmer mornings (if rainfall in the previous month was below average and there were only a few flowers on the tree).

Our results for Eucalyptus paniculata showed similarities to Corymbia maculata with regard to the impact of logging, but the species differed markedly in other aspects of nectar production. Nectar was produced during the day and night, unlike spotted gum which has been observed previously to produce nectar over-night. We found great similarity in nectar production between autumn flowering in 2004 and late-winter flowering in 2005, but these differed considerably from early summer flowering in 2006. Low average floral sugar levels in the early morning bagged flowers in 2004 and 2005 (1 mg sugar per flower) corresponded to the low levels for spotted gum in 2003 (1 mg sugar), while the sugar-rich nectar in grey ironbark in 2006 (5.3 mg sugar) was similar to spotted gum for 2005 (4.8 mg sugar). This means that nectar in Eucalyptus paniculata flowers was a limited resource in 2004, to a lesser extent in 2005 and not in 2006. Nectar standing crops were determined by an interaction between environmental conditions that influenced nectar production and the feeding activity of flower visitors at the time, which itself is affected by prevailing temperatures and nectar attributes, such as sugar concentration.

Logging history and tree size, when taken individually, had no significant effect on nectar production per flower in Eucalyptus paniculata, although they did differ when compared between logging histories. However, these differences were relatively minor in comparison to the negative effect of drought. Little nectar was produced under any logging history in droughts, while during good conditions nectar production varied depending on logging history. When scaled up to the forest stand, logging history had a marked effect on nectar production with old regrowth forest producing seven times as much sugar per ha as recently logged forest, with regrowth forest 15-20 years old being intermediate. However, at the compartment scale, the difference between old regrowth forest and recently logged forest was reduced to a factor of two times when the extent of areas left unlogged under current practices was considered.

Environmental correlates of nectar production per flower in Eucalyptus paniculata were primarily related to drought. Sugar-rich flowers were only found when our drought index indicated better than average conditions for up to 12 months prior to flowering. The negative effect of drought is surprising as Eucalyptus paniculata is more drought-tolerant than co-occurring species and it clearly differed from the factors that influenced nectar production in Corymbia maculata. We can summarise the differences between the two species as follows: the winter-flowering spotted gum appears to maximise nectar production when conditions are unsuitable for growth, such as when it is dry or cold, while the slower-growing grey ironbark, which can flower in a variety of seasons, yielded its richest nectar in summer that was warm and moist.

Benchmarking our nectar measurements with records of honey production from local beekeepers revealed that Corymbia maculata flowering in 2005 had honey yields (54 – 83 kg/hive from April- October) above the typical maximum values reported for the species. This confirms the prolific and extensive nature of the flowering in that year. In contrast, during the poor flowering year of 2003 few hives were deployed in the forest and no honey production was reported at this time. For Eucalyptus paniculata, the yearly differences in the quantity of sugar produced per flower were related to considerable variations in honey production. In particular, summer 2006 saw prolific honey production close to the maximum previously reported for this species, reflecting the copious, sugarrich nectar that we measured. Differences in honey production in 2004 and 2005 were apparently related to nectar standing crops rather than actual nectar production.

Honey productivity was comparable across the three treatments of logging history. Also, comparisons of the estimated requirements of hives with the amount of sugar produced by the forest indicate that the spotted gum forest in 2005 was producing excess nectar for commercial honeybees. This demonstrates that, when flowering is prolific, good honey yields can be obtained from recently logged and regrowth sites. Yet in years when flowering is less prolific (e.g. 2003), nectar may be limiting and retained areas of unlogged and regrowth forest are very important in ameliorating the effects of logging in such years.

We estimate that a hive of commercial honey bees produced about 1 kg honey/ha/month during 2005 and that a 1000 ha spotted gum forest flowering from April-August could yield 5 tonnes of honey.

Given a wholesale price of spotted gum honey in 2007 of $2.20 per kg, this values the spotted gum honey resource per 1000 ha of spotted gum forest in 2005 as $11,000. It should be noted that was a prolific flowering year for spotted gum and there was little blossom in the immediately preceding years.

Implications for relevant stakeholders
This project has shown that current logging practices in NSW halve the nectar resource, but that in years of good flowering there is a surplus of nectar and honey production. However, there is justification for the existing additional prescriptions that retain mature trees of locally important flowering species, because in years of poor flowering nectar is rapidly consumed in the mornings and is thus a limiting resource at those times.

Recommendations
The main recommendation of this report is to further disseminate the results of the project to promote sustainability in forest management, to raise the awareness of forestry organisations that the nectar resource requires careful management and to raise the beekeeper’s awareness about current forest management. Improving communication between apiarists and foresters would be valuable to establish formal guidelines on the management of apiary sites and the nectar resource in forests. Further research on how climate change will affect flowering levels and subsequent nectar production could be critical to the apiary industry and the conservation of nectarivorous fauna.