Get yer biodiversity 'ere! Tuppence a bag!

You would think that something as innocent as creating a bit of habitat for wildlife would be a straightforward matter; after all, nature has been getting on with it unassisted for millions of years. But like anything that humans get themselves involved with, beneath the surface lies the potential for confusion.

For example, I recently came across this bald statement:

‘Designer combinations of non-native and native wildflowers can provide longer nectar and pollen flow for pollinators, but a traditional wildflower meadow will give you more biodiversity generally.'

Now clearly, as a supplier of what I guess could be termed 'designer combinations'  of pollinator-friendly plant species, I have a vested interest here, which I freely admit. And I've ranted before about the pervasive 'native is best' knee-jerk response in habitat creation circles. But leaving all that aside, I am genuinely interested in resolving this question. The ecologist in me is still very much on the fence, even if the businessman isn't (bear in mind I have 25 years of working with UK natives under my rapidly expanding belt).

A designer mix, modeled here by the lovely College Road

So I got to thinking, what exactly are the characteristics of a traditional wildflower meadow that would make it better for biodiversity?

Firstly, we need to compare like with like; an ancient hay meadow in rural Dorset doesn't compare with a recently-created patch of non-native pretties in the centre of London. The former is going to win every time, if only because of length of establishment and proximity to other bits of 'good' habitat.

So let us consider two plots, cheek by jowl, both sown at the same time, one with a 'designer' mix of non-natives, one with a traditional native meadow mix. What are the biotic features of our new native meadow that make it superior? What, indeed, are the characteristics of any patch of vegetation that allow it to support biodiversity?

Let's tackle this by looking at the groups of organisms that might make use of our two sites, and what their requirements are.


Detritivores


At the bottom of the heap, so to speak, are all those little gribblies that feed on dead plant material. Invertebrates for the most part, from the microscopic up to the worms that manufacture our soils and an inordinate number of beetles. Well, as far as I am aware, dead plant material is dead plant material, whatever part of the world it originally evolved in. So I'm not convinced there's going to be much difference there.

Local flowers for local insects

Herbivores

Again, I'm pretty confident that green stuff is green stuff, the world over. The only possible advantage I can see here for the natives is if the exotics were unpalatable due to chemical or physical defenses or somehow difficult to detect due to not smelling right. This would particularly be an issue in the case of specialist species - butterflies with a specific larval food plant, for instance. So there's potentially a point there in the favour of natives.

Predators

Again, for generalist species I would imagine that anything below you in the food chain is fair game. Unless you're a real specialist adapted to feed on only a limited range of prey species.  Glow worms with snails, for instance.

Nectar and pollen feeders

Nectar is sugar solution, basically, and pollen is little packets of protein. I have it on good authority that pollinators are not fussy about where either come from, though different flower structures have different fans. Honey bees and bumblebees, for instance, prefer different species. But overall, unless someone is growing bat-pollinated species, I think this one is a draw.

A hoverfly, showing a disappointing lack of discernment

Seed eaters

Again, seeds are little containers of fat, starch and protein and - unless they are somehow inaccessible for physical reasons - I can see no reason why a granivore would differentiate between natives and non-natives. (A granivore, incidentally, eats seeds. Not grandmothers.)


Have I missed anything? Well, probably - this is just me thinking out loud really, and not a scientific dissertation. But overall it seems to me that the only advantage a native meadow would have over a patch of non-natives would be in the case of real habitat specialists, the proper fussy species with very specific requirements. And my gut feeling is that they are in the minority, and less likely to be found in an urban setting anyway. Which is, after all, the only place you should be creating non-native vegetation.

There is, of course, a more fundamental question here: what do we mean by 'biodiversity'? The quotation at the start of this post talks about 'more biodiversity generally', as if biodiversity is a commodity like sugar. But how are we measuring 'more' here? Species diversity? Biomass? And is there a quality issue? Are a few rare species better than a wide range of common ones? Inquiring minds want to know!

So, that's my take on things. I'd welcome any thoughts or comments, but I'd particularly welcome a nudge in the direction of any proper scientific studies that have addressed this issue.

Surely somebody out there must have tackled this? If not, there's a PhD project right there...