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Focus: honey flows, botanic source and honey quality (copy)
Like in many cities, a growing interest in beekeeping has been observed in the Brussels Region. In order to increase the knowledge of the general beekeeping situation within the urban environment, a monitoring system for bee colonies has been established in the Brussels Region. The regular monitoring of the weight gain of production beehives situated in Uccle, as well as the analysis of honey obtained from various beehives in the Region have provided interesting results: • honey flows from the Uccle beehive are still higher than the average measured in other beehives situated in rural areas (Walloon Region); • the spring honey flows from the Uccle beehive come earlier than in rural areas; • in the Brussels Region, bees are mainly interested in a relatively limited number of plants: brambles, clovers, fruit trees, chestnut trees, willows, oleaceae (Ligustrum), lime trees and horse chestnut trees, as well as black locust; • as in the Walloon Region, the majority of the Brussels honeys analysed are "polyflora" types, and their quality is the same as that of the honeys harvested in rural areas.
Monitoring of bee colonies
Bees play a vital role in the pollination of plants, and therefore also in their reproduction. It is important to develop a strategy to manage and integrate beekeeping practice as effectively as possible in the urban environment, with the aim of encouraging regional biodiversity. Specifically, this means ensuring a good balance between all pollinators and, in the context of limited food resources, avoiding competition between domestic and wild bees.
In order to increase the knowledge of the general beekeeping situation within the urban environment, a monitoring system for bee colonies has been established in the Brussels Region. Four electronic weighing scales are placed under good production beehives spread throughout the regional territory. Regular measurements are sent via cellphones and include a dataset: the weight of the beehive, air humidity and outside temperature. This information supplements the information already collected by the beekeepers of the SRABE (Royal Beekeeping Society of Brussels and Surrounding Areas). Each year, various samples of honey produced in the Brussels Region have been sent to the CARI laboratory (Centre for Beekeeping Research and Information) in order to analyse their quality and the botanic source of the pollen grains they contain. All of the available information is analysed and compared with data from the network of Walloon beehives, which have been monitored by CARI since 1998. It should be noted that in the context of the present analysis, only data provided by the weighing scale at Uccle could be used.
The chart below makes it possible to analyse the profile of daily nectar inflows (weight range on the right) in the production beehive at Uccle, during the 2014 beekeeping season, in relation with temperature data (range on the left). In order to retain just the data pertaining to honey flows, the significant weight variations associated with interventions by the beekeeper have been eliminated (the placing of supers, collecting, feeding, etc.). The recording of negative weights can be explained by swarming, the partial consumption of reserves stored in the beehive, a visit by the beekeeper resulting in slight weight variations (marking the queen, checking the health status of colonies, etc.).
Variations in weight and temperature recorded in the beehive at Uccle - 2014 beekeeping season
Source: CARI 2015 (Uccle weighing scale managed by SRABE)
The lower figure compares, for the same year, the weight gain of the Brussels beehive with the average, minimum and maximum weight gain in 15 beehives of the Walloon network. Since beehives do not all have the same weight, an initial common weight - set arbitrarily at 40 kg - has been defined so as to be able to compare results. The addition or removal of material has also been eliminated during the data processing, in order to make comparisons possible.
Comparison between the weight gain of the beehive at Uccle compared with that in 15 Walloon beehives - 2014 beekeeping season
Source: CARI 2015 (weighing scale at Uccle managed by SRABE)
For the 3 years during which this comparison was made (2012-2014), it was observed that the weight gain of the beehive at Uccle systematically started earlier than that of the Walloon beehives. The higher temperatures in the urban environment (see Focus: urban heat islands) are reflected in earlier blossoming, and consequently earlier bee foraging. Moreover, the overall weight gain on the scale at Uccle was higher than the Walloon average. This difference is specifically linked to larger inflows of nectar in the spring. As for summer honey flows, these are much more normal (except in 2012). However, it would be useful to analyse the data from more weighing scales to be able to confirm this trend.
When bees forage a flower, they also bring the pollen which is present in the nectar. The pollen analysis of honeys using a microscope makes it possible to identify which flowers have been foraged and which are therefore interesting for bees.
When pollen from a given species is present in a sample, it is considered as "primary pollen", "accompanying pollen", or "isolated pollen" depending on whether its grains represent respectively more than 45% of the total pollen grains present, between 10 and 45%, or less than 10%. Furthermore, pollen will be identified as "significantly isolated" if its frequency is less than 10%, but it comes from a species where the pollen is under-represented due to the morphology of the flower or because it comes from a species with low pollen production.
Botanic origin of pollens from nectar-producing species or plant families (192 samples of Brussels honeys analysed over the period 2007- 2014)
Source: CARI 2015
The chart above, which was drawn up from the pollen analysis of 192 Brussels honeys produced over the period 2007-2014, shows that most of the nectar inflows came from brambles and clovers, as well as from tree species. Compared with rural areas, we can observe a greater proportion of pollens from trees which are usually present in parks (Horse chestnut trees, Evodia trees, Black locust trees, etc.).
In some honeys, we can also find pollen from anemophilous plants, in other words when the pollen is transported by the wind (grass pollen, birches, pines, etc.). These pollens stick to droplets of honeydew, which are very sweet secretions produced by phloem-feeding insects from plant sap, and which are regularly found in tree species. By foraging these honeydews, the bees bring the stuck pollen grains with them, which are subsequently found in the honey.
The quality of Brussels honeys
The physicalphysico-chemical analysis of 192 honeys produced in the Brussels Region between 2007 and 2014 shows in particular that:
- the water content of all the honeys analysed is lower than the regulatory standard of maximum 20% and, for the vast majority of the honeys analysed, lower than 18% (the threshold which ensures good product stability and the absence of fermentation);
- all the honeys analysed comply with the CARI quality criteria (which are more restrictive than the legal standards) with regards to the deterioration indicator parameters related to excessive heating or ageing (hydroxymethylfurfural content and sucrase index);
- the honeys analysed present an average pH of 4.5 and an acidity of 9.0 to 17.7 meq/kg, values which suggest good honey stability;
- the Fructose/Glucose ratio of almost all the honeys analysed is situated in the range of honeys with rather slow crystallisation and with an unctuous to spreadable consistency, although 8 honeys (primarily honeys from black locust) have a F/G ratio higher than 1.45, ensuring fluid consistency.
The physico-chemical analyses combined with the pollen and organoleptic analyses make it possible to determine the botanic source of honeys. In the Brussels Region, as in the Walloon Region, most of the honey produced is "polyflora". During years in which the meteorological conditions allow the intense foraging of certain varieties, monofloral or predominantly monofloral honeys are also developed; these are mainly honeys from black locust trees, lime trees, horse chestnut trees and rutaceae (Evodia trees). Honeys containing honeydew regularly supplement the supply, due to the numerous wooded sites in the Brussels Region.
Overall, the Brussels beehives benefit from a very favourable environment linked in the first instance to milder temperatures at the start of the season, which enables an earlier starting of colonies. The fact of benefiting from floral nectar-producing species (trees) ensures significant yields. Moreover, the significant technical know-how of the beekeepers ensures that the honey sold is of good quality. As such, Brussels consumers can enjoy honeys which comply with the highest quality criteria.
Despite this positive situation, it is advisable to guard against any simplistic approach, and instead conduct a thoughtful and balanced policy with regards to the establishing of beehives within the urban environment, and in green spaces more generally. In fact, the introduction of too many domestic bee colonies in certain sensitive areas could potentially lead to impacts on biodiversity. However, studies still need to be carried out to objectivise this risk at the Brussels level.
State of the Environment's sheet(s)
Focus : Heat islands (edition 2011-2014 )
Other publications from Brussels Environment
Study(ies) and report(s)
CARVALHEIRO L.G., KUNIN W. E., KEIL P., AGUIRRE-GUTIERREZ J., ELLIS W.N., FOX R., GROOM Q., HENNEKENS S., VAN LANDUYT W., MAES D., VAN DE MEUTTER F., MICHEZ D., RASMONT P., ODE B., POTTS S.G., REEMER M., ROBERTS S.P.-M., SCHAMINEE J., WALLISDEVRIES M.F. and BIESMEIJER J.C., 2013. « Species richness declines and biotic homogenisation have slowed down for NW-European pollinators and plants », in Ecology Letters 16, p 870-878. (.html)
LEFEVBRE M., BRUNEAU E., 2005. « Etat des lieux du phénomène de dépérissement des ruches en Région wallonne », Convention entre la Région wallonne (DGRNE) et le CARI, 50 pp. (in French only )
Potts S.G., Biesmeijer J.C., Kremen C., Neumann P., Schweiger O. et al., 2010. “Global pollinator declines: trends, impacts and drivers”, in Trends in Ecology & Evolution 25 (6): 345–353. doi:10.1016/j.tree.2010.01.007. (.pdf)
TOMMASI D., MIRO A., HIGO H.A., WINSTON M.L., 2004. « Bee diversity and abundance in an urban setting », in Canadian Entomologist 136 (6): 851–869. doi:10.4039/n04-010. (.pdf)
Vaissière B., Morison N., Carré G., 2005. « Abeilles, pollinisation et biodiversité », in Abeilles & Cie n°106, p 10-14. Editeur responsable Etienne Bruneau, Louvain-la-Neuve. (.pdf, in French only)
Plan(s) and programme(s)