I had an interesting conversation with a landscape architect on Wednesday who was asking for some advice about creating urban habitat for pollinators. The plan was to strip turf from under the trees in a city greenspace in order to put in some flowering plants as nectar and pollen sources. I often get asked about this, not only by landscape architects, but by professional gardeners, park committees, local residents groups, and so forth. My initial advice, following the Greek physician Hippocrates, is always the same:
“First, do no harm.”
Hippocrates was of course speaking to doctors and saying: before you intervene in a patient’s health, make sure you are not making things worse for them.
So what do I mean by this? Why is it relevant to pollinators?
Well, in the case of the discussion from earlier this week, the team had no idea if there were ground nesting bees such as Andrena spp. in the area where they planned to strip the turf. Stripping the turf would likely have destroyed any nests, or at least prevented the bees from emerging, particularly if a thick mulch was applied to the area. There were also suggestions of using glyphosate to kill off the grass, though I certainly advised against it: by coincidence a meta-analysis by Lucas Battisti and colleagues was published this week showing categorically that glyphosate is toxic to bees. Imagine spraying it over an area that has a colony of one of the ground-nesting solitary species? Or where queen bumblebees might be hibernating? Queen Bombus spp. often hibernate close to the base of trees – see D.V. Alford’s classic 1969 study of bumblebee hibernation.
It’s not only pollinators that could be harmed by starting work without appropriate surveys: even unpromising-looking municipal grassland, for example in parks, can harbour a significant diversity of plants that are being suppressed by too-frequent mowing. Mow less often and they will flower, producing nectar and pollen for pollinators, then later seeds for birds.
Sometimes you can do more by doing less.
One of the things that I stress in my book Pollinators & Pollination: Nature and Society, is that habitat creation for pollinators is about much more than just planting wild flower meadows and putting up some bee hotels. It needs forethought about what is on a site already, and what may be destroyed by the proposed actions. There also needs to be a consideration of the wider landscape context in which the proposed site is situated, and whether it is providing some of the other things that pollinators need to complete their life cycles each year. The diagram above is from my book and I refer to it as the “Requirements of Pollinators Triangle”. Because pollinators are so diverse in their natural histories, no one site can hope to provide everything that they all need. However there are some general principles that I present in the book.
If you’d like to know more about any of this, or need advice, or to enquire about the training that I offer, please do get in touch via my Contact page.