Winter 2022

GREEN ROOFS PLANT SELECTION
GROWING RESILIENCE:
PLANT PLASTICITY AND VARIATION FOR
CLIMATE-SMART GREEN ROOFS
By Dr. Elisa Olivares Esquivel, Lecturer in Planting Design, Department of
Landscape Architecture, at the University of Sheffield.
In the autumn issue of Greenscape,
Dr. Tom Young wrote the first part of
a very insightful article about green
roof challenges in the face of climate
change and the different elements
that can be tuned to achieve resilient
systems.
Plant selection is one of these elements
that goes a long way to future-proofing
the roof and a critical process that is
worthy of far more research. There
are plenty of green roof mixes on the
market, with plants suitable for many
different types of roof. However, with
the impact of climate change, some of
the species that work today may not be
optimal in the future.
Broader plant palettes
These days we often hear that we
need to work not only with broader
plant palettes of species, but also more
diverse plant material with greater
plasticity. These sources of natural
variation (and artificial selection) could
be obtained either by responsibly
and sustainably collecting plant
material from the wild, especially from
distinct populations, or by breeding
drought resistant plants, for example.
Nevertheless, before starting with these
endeavours we need to understand
what these terms mean and their
implications for climate resilience and
adaptation. Plasticity can have different
meanings depending on the discipline
or the context in which we are studying
the plants, for example ecology or
molecular biology.
The concept of plasticity
To clarify the concept of plasticity, Rob
Brooker and his team (2022) explained
how the concept can be applied in crop
breeding. This can be applied to plant
breeding as a whole or plant hunting
and screening for green roofs and / or
green infrastructure.
Brooker explains that one of the most
often applied forms of the term is
phenotypic plasticity, which often refers
to “changes to phenotype in response
to changes in environmental conditions”
(2022). Phenotype, according to
Scitable by Nature Education (2022),
“refers to the observable physical
properties of an organism; these
include the organism’s appearance,
development, and behaviour.”
This means that a plant with a high
phenotypic plasticity could respond
to drought by changing the size of
its leaves, reducing the number of
stomata, and generating a greater
number of offshoots for vegetative
propagation, for example. The plant
can adapt appropriately for its survival.
Phenotypic plasticity can be expressed
in a lower or higher degree in traits,
i.e. “a morphological, physiological, or
phenological feature of an individual
plant that is measurable” (Brooker
et al. 2022) in plants from particular
locations.
In research exploring the plasticity of
Fragaria vesca to drought, clones of
material from different locations of
the French Pyrenees and Alps were
tested in different moisture regimes. It
was found that flowering and runner
production from plants from south
facing slopes were maintained in low
moisture conditions in comparison
with material from north facing slopes,
which had reduced or no capacity for
producing them (De Kort, 2020). This
is found in a higher degree according
to gradient and aspect, more than
to elevation. There is tremendous
variation within species dependent on
a plant’s origins and this can be utilised
for resilient plant selection.
Building-in resilience
The take-home message here is that for
our urban green spaces to survive the
onslaughts of extreme weather events
brought about by the climate crisis, we
need to build-in resilience to our plant
selection now. That resilience comes
from diversity: in the number of plant
species and within-species varieties,
such as ecotype. As with our food
systems, reliance on the same small
number of species and cultivars makes
us increasingly vulnerable to the effects
of climate change and the pests and
diseases that come with it.
Contact Dr Elisa Olivares
Esquivel
Email:
elisa.olivares@sheffield.ac.uk
18 GREENSCAPE WINTER 2022 • www.greenscapemag.co.uk