There is a commercial apiary site in the Sugar Gum plantation. European Honeybees can forage up to 14 km from their hive (see references in Paton 1996), so all parts of the park are within reach although the bees will not travel further from the hive than they need to. The commercial hives are present for only part of the year, but Honeybees are present all year round as there are many feral hives in the park.
Honeybees, both commercial and feral, can decrease biodiversity through a number of mechanisms:
- Competing with native animals for nectar and pollen. In the park there are birds and many species of insect (including flies, wasps, beetles, moths, butterflies and native bees) which feed on nectar. Pollen feeding insects include native bees, wasps, beetles and thrips (Lomov 2010).
- Pollinating alien plant species which native pollinators do not visit, and therefore increasing weed invasion.
- Reducing reproduction of native plants by being less effective pollinators of these species than native insects or birds they displace (Gross and Mackay 1998, Celebrezze and Paton 2004).
- In the case of feral bees, competing for tree hollows with mammals and birds which need hollows for nesting or roosting. Many bat species and at least 26 species of bird found in the park use tree hollows (see the bird species list.
These mechanisms will be elaborated in the following sections, with the exception of number 3 which would need further investigation in the case of Woodlands Historic Park.
1. Competing for nectar and pollen
Research into competition for nectar and pollen between Honeybees and native animals has considered only birds and native bees. In a study by Paton (1996), the territories of New Holland Honeyeaters almost doubled (implying a halving of population) when a high level of honeybees was introduced. Paini (2004) reviewed studies into competition between European and native bees and found that no detrimental affects on native species has been proven, but that there had certainly not been enough research to alleviate the suspicion that such affects are likely. Research published by the same author one year later did find that commercial Honeybees reduced the fecundity of a species of native bee (Paini and Roberts 2005).
2. Increasing weed invasion
Simpson and others (2005) found that the Honeybee was the only pollinator of English Broom (also known as Scotch Broom) at Barrington Tops, NSW, which means that without Honeybees this plant would not be a weed. (Broom is listed as occurring at Woodlands Historic Park but I don't know of any plants at present.) Honeybees have also been found to be the only or major pollinator of at least two other weed species in Australia (Gross 2010, Goulson and Derwent 2004), and there are likely to be others.
4. Competing for tree hollows
Birds and mammals have specific requirements or preferences for tree hollows with regard to volume, depth, entrance size and height above ground, and also the size of the tree. Honeybees in Australia are less fussy, the main requirement possibly being a minimum volume. Oldroyd and others (1994) studied hollow requirements for bees and Regent Parrots in the riparian Red Gum/Black Box woodland of Wyperfeld National Park, Northwest Victoria. They found 77 feral bee hives per km2. The area of hive entrances ranged from 4 to 1000 cm2, and height above ground ranged from 0 to 13 m. The volume of hollows was not measured. My own limited observations of feral hives confirm that there is no restrictions on the entrance size or elevation of hollows used by bees. I have even seen Honeybees going in and out of a small hole in the ground, although there may have been a hollow tree root underneath it. Bees use both living and dead trees, including fallen trees.
In the Wyperfeld study, 50% of hives were in hollows with an entrance size and elevation suitable for a Regent Parrot nest. In this study bees were occupying a very small proportion of hollows and there was no evidence of nesting hollows being a limitation for the parrots. However, different animals have different requirements and many hollows used by bees are probably suitable for some species of native animal. We don't know if tree hollows are limiting for any species of animal in Woodlands Historic Park. Even if they are not, they might become so as older, hollow bearing trees die, since regrowth trees will not be old enough to contain hollows for at least another 100 years.
In the case of Brush-tailed Possums tree hollows possibly do limit the population, since possums have been observed to use very shallow hollows offering little protection, and even rabbit burrows. However the density of possums in the park is probably unnaturally high since some predators (including people) have been eliminated since European invasion.
Of more concern is the threatened Brush-tailed Phascogale, one of which was recently found in the vicinity of the park. While the population density of these animals is undoubtedly low, they require nest hollows throughout their home range - Van der Ree (2006), in a three month radio tracking study, found that females used an average of 11.4 nest hollows, with one animal using 19. The number increased throughout the study so the actual number of hollows used is likely to be higher.
National parks exist to protect biodiversity among other things. Commercial bee hives should not be permitted in national parks unless it can be proven that Honeybees do not reduce biodiversity. This has not been proven, and there is evidence to the contrary.
One argument for allowing commercial bee-keeping in parks is that feral hives exist anyway, and if commercial hives are present only at times of peak nectar production then they will have less affect than feral hives which are present all year round. Paton (1996) in one of the few studies of the densities of feral colonies found an average of 0.3 colonies per hectare in Flinders Chase National Park on Kangaroo Island, with up to 10 colonies per hectare locally. Even if average densities at WHP are much lower than this, and even if a feral hive is on average much smaller than a commercial hive (Paton 1996 p. 18), it seems likely that most honeybees in the park are feral.
State government policy is basically to allow unlimited bee-keeping anywhere except built-up areas and reference areas (wilderness), and this would be hard to change. In the case of feral bees both conservationists and bee-keepers should agree that they are undesirable, but any control is unlikely. Oldroyd (1998) reviewed possible control methods and found that the most feasible method was swarm trapping. However a trap density similar to the feral hive density is required, and it would have to be done forever to prevent re-colonisation, so it would be quite expensive.
The one ray of hope is the possibility of biological control. Of course there is absolutely no chance of a deliberate and legal release of a biological control agent for honeybees. However the parasitic mite Varroa destructor, having transferred from the Eastern Honeybee in the mid-twentieth century, has spread to every significant bee-keeping country in the world except Australia (Iwasaki 2015). It is considered unlikely that Australia will remain free of Varroa (Department of Agriculture, Fisheries, and Forestry 2011).
Varroa or viruses that it carries kill 95-100 per cent of unmanaged hives within three to four years of infestation. Commercial bee-keeping can continue, but with increased costs for controlling the mite. Offsetting this will be increased honey yields due to the lack of competition from feral hives. It will be important to ensure that commercial hive numbers in natural areas are not allowed to increase.
The main economic cost of Varroa is expected to be born by the horticulture industry, due to decreased pollination services from feral honeybees. Broad-acre oilseed (unless self-pollinating) and grain legume crops and the legume component of pastures are also likely to be affected. There are three possible solutions to this:
- Increased use of managed hives of honeybees providing paid pollination services.
- Use of domesticated native bees to provide pollination.
- Encouraging increased pollination by wild native pollinators, for example by replanting native vegetation and avoiding the use of broad-spectrum insecticides. In other words, adopting more sustainable farming practices.
Any conservationist should support the strengthening of Australia's biosecurity system, but in the case of Varroa destructor they should hope that it fails as soon as possible.