24 | New Scientist | 30 January 2021
James Wong is a botanist and
science writer, with a particular
interest in food crops,
conservation and the
environment. Trained at the
Royal Botanic Gardens, Kew, he
shares his tiny London flat with
more than 500 houseplants.
You can follow him on Twitter
and Instagram @botanygeekViews Columnist
I
T ISN’T an exaggeration
to say that in the world
of horticulture “native”
is frequently used as a byword
for “better”. Native plants are
often considered easier to grow
and better for wildlife, while
also being less invasive and
more resistant to pests.
This belief is so institutionalised
that many local planning rules
in the UK specify that a certain
percentage of landscaping
schemes must include native
species. Indeed, this conviction
runs so deep that some see
sharing evidence to the contrary
as being hugely controversial,
even deeply irresponsible. But
accuracy is what matters, so let’s
explore how well this entrenched
dogma stands up to analysis.
First, it is important to clarify
that, in many cases, native plants
are great choices for a garden.
What I am examining here is
whether they are automatically
a superior option for both garden
performance and ecological value,
in the context of Britain.
The problem with considering
a group of plants to be inherently
superior is that many measures
of “better” are contradictory. For
example, one of the key features
that makes a plant invasive is
it being so easy to grow that it
overwhelms efforts to manage
its spread, resulting in its escape
into natural ecosystems where
it can cause havoc. So the idea
that native plants are both less
invasive and easier to grow can
only be maintained if you are
very selective with your evidence.
You also have to ignore, for
instance, that many native plants,
such as bracken, are so invasive
that they can swamp huge areas
of land, with catastrophic effects
on local biodiversity. So if we are
concerned about biodiversity, we
should also be concerned aboutThis column appears
monthly. Up next week:
Chanda Prescod-Weinstein“ This definition
makes anything
introduced by
the Romans,
such as olives,
native to Britain”What’s so great about native anyway? There’s a tendency
among horticulturists to prefer native plant species, but we
shouldn’t assume they are better, writes James Wong#FactsMatter
What I’m reading
These days? Mainly
angry tweets.What I’m watching
The Small Axe films.What I’m working on
With a new BBC farming
documentary going out
and a houseplant course
going online, I am hoping
to take some time out...
while stuck indoors!James’s week
invasive native species. Unless, in
reality, we are worried only about
the “alien” part of “alien invasives”,
not the invasive potential or
impact on ecosystems of all plants.
Likewise, the popular claim that
non-native plants are far worse at
supporting local wildlife, while also
being less pest-resistant, requires
doublethink. This is largely
because the difference between
pests and wildlife is cultural.
Undoubtedly, the most important
way that plants support wildlife
is as a food source, but if an
animal munches on them in an
unaesthetic way, we label it a pest.This touches on a tricky reality.
What does native even mean in
the context of Britain? The island
has been subject to waves of
ecological annexation by giant ice
sheets in a series of glacial periods,
interspersed with successive
waves of colonisation by species
from further afield. As such,
they cannot be realistically
compared with highly specialised
ecosystems like, say, those of
Madagascar or the Galapagos.
To address this issue, many
botanists and ecologists consider
only species that we know were in
Britain at the end of the last glacial
period as worthy of the title native.
But this in itself is pretty arbitrary.
What is the exact date we are
choosing for the glacial period
to have finished, considering
this process took millennia?
As one solution, others have
picked an equally arbitrary cutoff
for native plants: they must havebeen in Britain 500 years ago,
based on the idea that most trade
in plants occurred after then. This
makes anything introduced by
the Romans, such as olives and
pomegranates, native to Britain.
It is understandable if you think
these examples are silly because
such species require human-
managed cultivation to survive
in Britain, but then you must
also accept that many of Britain’s
most-loved native meadowland
and cornfield plants, such as
poppies and cornflowers, are
technically also exotic species,
introduced by ancient humans
and the agricultural methods they
brought with them post-glaciation.
The arbitrary nature of the
definition of native plants isn’t
just temporal, but also geographic.
I could take delicate mosses and
ferns from the remnant patches
of temperate rainforest in the far
south-west of England and plant
them in south-east England, in
areas with a similar rainfall to
Rome or Jerusalem, and still
claim them to be native and thus
inherently better suited to the
environment than Mediterranean
plants. This once again shows that
definitions of nativeness are really
just arbitrary lines drawn on maps
and dates picked on calendars.
Using this framework, it is
frequently claimed that exotic
plants from areas like southern
Europe are automatically worse at
supporting native British wildlife,
despite many animals that are
native to Britain also being native
to vast swathes of the planet, as
far east as Siberia and as far south
as northern Africa. Just because
they aren’t native to British
people, doesn’t mean they aren’t
native to Britain’s animal species.
So while these definitions
of native can be useful pointers,
we should really consider them
in a more nuanced context. ❚