What “Bee Services” Can Different Temperate Lowland Ecosystems Really Provide?
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The natural environment delivers many goods and services that human beings cannot manage without. Health, energy, and safety are just a few of the basic benefits that spring to mind, but most “ecosystem services” are found to depend on complex interactions among living and non-living components of the environment. And only if necessary conditions are fulfilled does delivery of a given, much-needed service actually take place.
Like their more-familiar commercial counterparts, ecosystem services may be analyzed and quantified from the supply-and-demand point of view, as well as in terms of the flows that characterize service delivery. In my work, the focus has been on the supply side of those services whose final providers are bees. While crop pollination is the most-highlighted “bee service,” these insects, in fact, offer other benefits which are only rarely taken account of, like honey production and the pollination of non-crop plants. These services also help sustain human well-being.
Previous assessments of the supply of pollination have mostly been indirect, tending to involve regional or even continental scales, and, therefore, referencing land-cover mapping that mostly assigns equal value to patches of semi-natural or natural cover (ecosystems) when it comes to their serving as a habitat for bees.
My goal was, therefore, to try and develop a more insightful picture, one specifically bridging the gap between labor-intensive work on the detailed ecology of bees and melliferous plants and large-scale mapping and modeling inevitably based on far-reaching generalization. To do this, I looked for differences among (semi-) natural patches of different temperate ecosystems in terms of their capacity to supply bee-mediated pollination and honey-production services.
A given ecosystem’s capacity to provide “bee services” was related to a maximum theoretical supply of service, possible in an ecosystem of a given type, in its regional context. That assessment was based on a calculated version of the environmental setting offering the best supply of the service (for example, on account of the plants present, soil quality, or water balance).
The work demanded an original categorization of rural landscapes present under temperate climatic conditions. This extended to 43 different types, of which 29 were considered relevant to bees. Actually involved here was an extended version of the “Mapping and Assessment of Ecosystems and their Services” (MAES) project applied across the EU. The basic variety of land cover was obviously important, but greater subtlety could be achieved by identifying forest types and successional stages, and more specific habitat properties, all in line with the capacity to foster the diversity regarded as crucial to the supply of ecosystem services.
I then developed key indicators further focusing this approach on an ecosystem’s potential to supply “bee services,” i.e. on theoretical determinations of how much honey a hectare of ecosystem patch can give rise to and how many flowers the wild bees inhabiting that patch are able to pollinate.
I considered an ecosystem’s potential to generate honey to depend on the quality of bee pasture, with this relating to some maximum possible per-hectare yield of honey that a given ecosystem could supply each year, assuming beekeepers maintained an optimum abundance of honeybees. The availability of raw material (flower nectar, honeydew, and indirectly also pollen) was, in turn, assumed to point to an ecosystem’s potential to contribute to honey production. Calculations were then based on literature data on different plant species’ supplying of raw material, as combined with phytosociological data on plant composition in each ecosystem type. I, in particular, drew on research unique in the world and carried out in Poland since the 1950s, as now incorporated into the “Great Atlas of Melliferous Plants” (Kołtowski, 2006; in Polish). The Atlas tells of the nectar and pollen production sustained by more than 250 “honey plants” growing under temperate-zone conditions.
The raw materials bees collect to make honey also include the sticky substance excreted by aphids known as “honeydew”, in particular, deposited on such trees of temperate-zone forests as firs, spruces, limes, and oaks.
It is because of the objective difficulties of directly identifying and mapping pollination services that proxy indicators have usually been applied. In my work, I propose the potential abundance of nesting wild bees (Apoidea) as I seek to depict different ecosystems’ capacities to provide pollination services. This estimate excludes managed honeybees since their abundance reflects beekeepers’ decisionmaking, rather than natural conditions.
The potential maximum abundance of wild bees during a growing season could be estimated by integrating data from the entomological literature concerning food resources, nesting sites, the actual abundance of bees and species richness. Food resources were calculated in the same way as for honey production, while ideas on the availability of nest sites emerged by setting ecosystem characterizations against the knowledge of bees’ habitat requirements.
Temperate ecosystems’ potential to provide “bee services”
As anticipated, a more-detailed categorization of ecosystems brought to light huge differences in potentials to supply “bee services,” including among areas that general land-cover classifications like CORINE and MAES would categorize as the same. Interestingly, the highest potential to produce honey (at ca. 300 kg/ha) related to arable fields on fertile soil, assuming that the crop grown is one that sustains good honey production, like phacelia (Phacelia tanacetifolia) or buckwheat (Fagopyrum esculentum). Dry grassland or young pine forests in swamps also stand out in their very high (up to 250 kg/ha) capacities to provide honey. In contrast, the lowest (0-20 kg/ha) capacity characterizes different alder forests, middle-aged riparian forests, and most wetlands. The only ecosystems still-less favorable are open bodies of water and non-vegetated areas.
The potential of forest ecosystems to produce honey – or supply pollination – differs with age, as the youngest and oldest stands gain higher assigned values than middle-aged or mature forests. Forest communities with trees over 120 years old experience more natural disturbance, and that improves lighting conditions. Indeed, forest clearings and young forests are viewed as a better habitat for wild bees than mature stands with dense canopies.
In turn, the title of best European ecosystems delivering pollination goes to dry grasslands, and to clearings in coniferous forests with an abundance of insect-pollinated plants and potential nesting sites. A single hectare of either of these can sustain 1000-2000, or even 8000, naturally-nesting individual bees. Equally, while a cropland full of honey-generating crops does indeed have the highest recorded densities of pollinators, the overall status is only as averagely good habitat for wild bees (with 100-200 nesting individuals/ha). This reflects both the brief flowering period within the monoculture, as well as soil-nesting opportunities regularly disturbed by tillage, as well as by doses of agricultural chemicals.
Areas of rural settlement can be considered moderately good bee habitats (with 300 or 400 nesting individuals per ha). This reflects the presence of garden or orchard areas rich in melliferous species, as well as abundant buildings featuring the wood or clay in which bees can nest.
More conventionally built-up areas offer much less, especially where land is paved over. Nevertheless, the overall trend is clearly for far more bees to occur in anthropogenic habitats. That leaves “bee services” differing from many other crucial ecosystem services (like carbon sequestration, timber production, flood and erosion control, and water retention), which all develop beneficially as succession proceeds and biomass in the environment increases.
There is thus a service provision “tradeoff” needing to be addressed by overall decisionmakers, as well as in practice by both foresters and proponents of active or passive conservation measures.
Study outcomes and possible applications
Unsurprising as it may be, the reality that (semi-) natural ecosystems differ greatly in their support of bees leaves models rating all such patches equally looking biased. The inclusion of ecosystem attributes beyond basic land cover — like a successional stage and soil quality — can offer a fuller and better assessment of “bee services.” Beekeepers are obviously keen to gain more reliable information on potential honey production, while farmers’ livelihoods in fact depend on pollination potential and the environmental conditions promoting pollinators. The value of this kind of approach to nature conservation authorities is also beyond doubt, though the revealed “tradeoff” between supplying “bee services” and other ecosystem services presents a dilemma for those working on conservation approaches.
While my evaluation is confined to temperate lowland ecosystems, there is no bar to the same kind of approach and indicators being used elsewhere, provided only that data are available, as local or regional assessments of bee-related services are made.
These findings are described in the article entitled Indicators of ecosystem potential for pollination and honey production, recently published in the journal Ecological Indicators. This work was conducted by Andrzej Affek from the Institute of Geography and Spatial Organisation of the Polish Academy of Sciences, as supported by a grant from Poland’s National Science Centre [No. 2012/07/B/ST10/04344].