Previous work appears to be biased twice over in its focus: first
with a bias toward regulating services (Haase et al., 2014), and
second toward trees. As an important result, our review indicates
that the potential of ground vegetation to complement the services
of trees is likely underestimated. Herbaceous plants bind
particulates close to both major emission sources and humans
(Weber et al., 2014a) and help counteract temperature stress
(Shashua-Bar et al., 2011; Fig. 2). Such effects can be increased by
synergies between water- and temperature-related ES, e.g. in
bioretention swales, which enhance cooling through greater evaporation while potentially fostering biodiversity (Kazemi et al., 2011; Fig. 1). It is thus an important direction for future research to assess the relative contribution of ground versus tree
vegetation to ES/ED in streetscapes across scenarios that differ, for
example, in width and depth of street canyons and in features of
vegetation structure and composition.