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Planting trees for bees

Linda Newstrom-Lloyd, Tony Roper and Marco Gonzalez, New Zealand Tree Grower February 2013.

Planting trees for bees has become a topical issue in New Zealand. Security of pollination services has become a major concern for domestic and export markets and work is needed to protect pollination. This is especially important as our most important agricultural pollinator is the honey bee. The Trees for Bees programme was set up to look at bee pollinator security because a lack of pollen is an increasingly urgent problem on farms, and it has a simple solution.

Trees for Bees research

TheTrees for Bees is a research programme started in 2009 based on the work instigated by John Hartnell, of the Federated Farmers Bee Industry Group. In this project, 10 regional bee plant guides were produced and have been continually distributed throughout New Zealand. They can be downloaded from

The Bee Friendly Farming Group was formed and obtained a three-year Sustainable Farming Fund Grant. This project runs from November 2010 to October 2013. It aims to determine which bee forage plants have the highest protein pollen which will also have beneficial uses for farmers. The research targets two critical pollen dearth times, spring and autumn, for restoring pollen sources. The project aims to determine which bee plants have the highest protein pollen and to create demonstration plots on farms to test useful bee forage designs for farmers.

Eastwoodhill Arboretum

The planting list for the demonstration plots are customised for the farmer to generate economic gain or for erosion control, animal fodder, shelter, windbreaks, timber and firewood. The research was conducted in Canterbury in the first year and in Gisborne, mainly at Eastwoodhill Arboretum, in the second.

The Arboretum collection of over 3,500 species and cultivars of mature trees and shrubs has given the research a boost because of the diversity of plant species all in one place. An important part of this project is to spread the new information widely and encourage farmers, councils and the public to plant the best bee-friendly plant species wherever possible. A vital part of the project is to work alongside farmers to plant up demonstration plots on their farms.

Many farmer-beekeeper partnerships are being formed to explore the potential to amplifying bee forage on farms in plantations that are farm operations. These bee-friendly farms have young plantations which will produce results for the long term. Mixing shrubs and trees ensures that flowers are in supply while the slower growing trees are reaching maturity.

The Trees for Bees database stores the results on protein content and farm uses for trees and shrubs that have been investigated. As these new results are confirmed they are being made freely available at conferences, in publications, and on our website. The Trees for Bees regional bee plant guides are a good place to start and this information can be downloaded directly from their website.

Pollen and honey bees

Pollen shortage

Pollen dearth is a shortage of pollen which causes protein malnutrition and starvation in honey bee colonies. It is a serious concern on many farms in spring and autumn. This shortage of pollen has not always been a problem in New Zealand as in the past there was more biodiversity on farms with a mixture of crops, plentiful hedgerows, shelterbelts and specimen trees. However, many farms have now modernised, intensified and scaled up, which has included the removal of flower resources.

The plentiful supply of bees and bee forage in the past meant that pollination services were taken for granted. The results of recent large-scale removal of flowers by weed elimination and land use changes were not considered to be important. For example, gorse and willow, two plants which are the backbone of beekeeping in many regions, have had to be removed because they are noxious weeds, harming the environment in certain habitats such as native bush and riparian edges.

The varroa context

The removal of traditional bee forage is rarely replaced. The problem is that this removal is now in a new context – the long-term debilitating effects of varroa. Poor nutrition combines with other stresses, such as increased viral loadings on honey bees. Weak bees are more susceptible to the increasing number of new parasites and diseases. In addition, they cannot withstand the exposure to greatly increased toxicity in new systemic pesticides which are being added to the continual misuse of pesticides in general.

The combination and interactions of all these problems in the varroa context is now threatening bee health. Feral honey bee populations, which previously provided background pollination, have virtually disappeared since varroa arrived in the North Island 12 years ago and eventually spread to the South Island. Feral bee colonies cannot sustain themselves without treatment against the disease. Threats to bees in the long-term means that pollination can no longer be taken for granted.

Rising costs

With free pollination no longer available, having beehives close by is essential if a farmer needs good pollination services. The treatment to combat varroa has increased the labour involved to produce sufficient strong bee colonies and therefore beekeeping and pollination costs are rising. In addition has been the inevitable resistance of the varroa mite to treatment and this has already started to occur in some parts of the North Island.

Overseas, where varroa infestations date back to the 1980s, we see that the long-term effects of the disease, in combination with the other threats to bees, leads to serious colony losses at an unprecedented large scale. Internationally, poor nutrition is considered to be one of the important contributing factors in colony collapse disorder. The lack of nutritious bee forage is a main factor in population sizes and colony survival, as well as the health and longevity of individual bees.

Without adequate nutrition, the bee’s immune response is compromised and its life shortened. In Europe and North America, planting bee forage has been under way for some time. Good nutrition is one of the most important ways to mitigate the long-term effects of varroa. It improves bee health, resistance to diseases and pesticide exposure, and ensures large strong colonies with healthy long-lived bees for pollination services.

Good nutrition with high-protein pollen

Bees get their protein from pollen. Bees which do not get enough protein are weak and susceptible to diseases and pests. Lack of protein has devastating effects because the bee population diminishes as it fails to reproduce in the spring, and the entire colony can fail to survive the winter as the bees die off too easily. This can leave too few colonies available for spring build-up to prepare for pollination services.

Anecdotal evidence is indicating that large colony losses are starting to occur in some regions. Spring build- up depends on multiplying bee colonies from the 10,000 to 20,000 bees per hive which survive the winter, to a peak of the 40,000 to 60,000 needed for good pollination services. If pollination is compromised, then so are farm yields from pollinated crops and pastures.

Good nutrition, especially in the form of high- protein pollen, is very important for bee health and population numbers. Bees can be fed sugar to supplement for lack of nectar or honey, but it is difficult to supplement for the lack of high-protein pollen. Honey bees should be fed on pollen with a protein value of at least 20 per cent. Pine pollen has only nine per cent protein, so bees will not do very well if they are only foraging on this pollen source.

Species such as silver or blue wattle Acacia dealbata, has pollen with 21 per cent protein which is good for bees. Pollen from Sydney blue gum Eucalyptus saligna has 28 per cent protein and pussy willow 27 per cent, both excellent. Crack willow is poor with only 15 per cent protein in the pollen, although willow species tend to be variable in protein content.

Simple solutions with more trees

Pollen dearth and bee malnutrition are problems with simple solutions − management of a seasonal progression of good pollen-bearing bee forage plants which contain sufficient protein. Farmers have plenty of options to increase the size and number of honey bee colonies available to their crops, either as permanent residential hives or migratory hives imported for specific pollination tasks. Choosing the right plant species and providing bee forage with high-protein pollen can be achieved at the same time as planting trees for erosion control, timber, firewood, animal fodder and shelter.

In many cases planting trees for other reasons, such as riparian strips or erosion control, can include the installation of sufficient plants to fill the pollen gaps. Plants beneficial to bees do not have to be limited only to trees.

On most farms there are small pockets of land, such as along shelter belts or corners of waste ground, where bee-friendly shrubs or even perennial herbs could be planted. The expansion of the Trees for Bees plant list is based on determining the pollen protein content of more tree and shrub species and creating more diverse bee forage plantation designs for farms. The research aims to provide a list of suitable pollen-bearing plants which meet the many different purposes for trees on farms. The Trees for Bees plantation designs follow certain guidelines to ensure the periods with reduced pollen are covered in autumn and the spring. These plantation designs are made up of high quality bee forage within five kilometres of the apiary. They are optimised for high-protein pollen for significantly larger populations in the hives and a greater carrying capacity for more colonies in the apiary.

Without springtime support from sufficient bee forage, the bee population growth during spring build-up is slowed or stalled. In addition, without winter preparation support from adequate bee forage, the bee population crashes and winter colony losses are more frequent and severe. The winter survival rate influences the rate of spring build-up.

Bee-friendly trees and shrubs to consider

The new lists from our research will enable farmers to identify suitable plants which will provide high-protein pollen for bees at the times when there is practically nothing useful in flower for bees to forage on. These species can be tried on farms to increase the bee plant diversity and cover the pollen supply gaps. This autumn and winter, we will be exploring for suitable flowering plants in the Arboretum to fill in pollen supply gaps for winter preparation.

One of the current trends is for some farmers to plant up large areas of manuka to cash in on the high prices of manuka honey. Generally these farmers have entered into a partnership arrangement with a local beekeeper to put hives on their farm and have a share in the honey crop produced from their manuka. In some cases the farmers have even purchased hives themselves. However, many farmers are finding out about bee forage and starting to plant a range of bee-friendly plants to enhance the sustainability of their farm and encourage better pollination.

Timber from eucalypts is suitable for milling, but most of these trees will also provide nectar and pollen to encourage bees and even native birds. Eucalyptus viminalis looks promising as it flowers in the autumn pollen dearth period and grows well in Canterbury, surviving quite hard frosts.

The pollen from tree lucerne or tagasaste, a small spreading tree which is used for animal fodder, has a protein value of 35 per cent which is excellent, but there are questions about the amino acid profile. This tree flowers in late winter to early spring in some regions so could be important, in combination with other species.

Pollen values

Native plant species have not previously had their pollen tested for protein content. Our preliminary data shows that many native species have excellent protein levels, for example flax has 32 per cent and cabbage trees 28 per cent. A particularly important native plant is the winter flowering five finger with 20 per cent protein.

Exotic trees and shrubs have good protein content in their pollen such as California lilac with 29 per cent, Mexican orange blossom 23 per cent and rosemary 21 per cent. Large exotic trees look promising such as oaks, maples, ash and other northern hemisphere species, but we do not have the protein values of these as yet. This work is still in progress and more results will be published elsewhere.

Be cautious about weeds

Whatever bee plant has high-protein pollen, it cannot be used if it will become an environmental or agricultural weed. This is the essence of the bee nutrition problem in New Zealand – many of the most important traditional bee plants that beekeepers have relied on in the past are being removed to save the environment. In addition, many of these such as gorse, have high-protein pollen and flower abundantly at important times in autumn, winter and early to late spring. They were ideal plants in the past but are now causing problems for the environment in certain areas. The challenge is to find plant species with high-protein content which will not become a weed when planted in abundance.

Our research is cautious about weeds and potential future weeds. This means that we look to native plants and safe non-weedy species which will fill the pollen gaps by feeding bees the best bee forage possible. However, we have not yet found a good replacement for gorse in the autumn and winter. If it is not possible to find a viable replacement then more work on the gorse problem will be needed.

The research is very much a work in progress. We are expecting many trees to prove valuable once we obtain the protein content results. Making demonstration plots to try out combinations of bee forage plants will show how well the trees and shrubs serve the farmer and the bees. Some trees such as oaks, or fruit trees like pears and apples, can be planted as specimen trees that will last for nearly 100 years. A plantation of the right mixture of mature large canopy trees would provide a long-term effortless solution to the pollen dearth problem.

Linda Newstrom-Lloyd is a Research Associate at Landcare Ltd in Lincoln, and Tony Roper and Marco Gonzalez are Apicultural Officers at AsureQuality Ltd in Tauranga and Lincoln, respectively


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