006).
In conclusion, there are many factors that differ between natural
and urban environments. It is unclear at present which of these
differences accounts for the observed changes in affect and cognition.
It is also unclear how to best take into account the influence
that a variety of environmental covariates may have on individuals.
Noise and air pollution, population density, and other elements of
urban or natural environments may act as mediating factors for the
impacts we observe on affect and cognitive function. There is great
value in disentangling the specific components of the environment
that may be related to particular impacts. As the trend of urbanization
continues, it is important to understand the exact impacts of
nature experience, and to build a theory upon which we may begin
to understand the causal mechanisms responsible for these bene-
fits. In much the same way as the biophysical processes of natural
landscapes benefit humanity through the provision of “ecosystem
services” (Daily, 1997), which purify our water, regulate our climate,
and provide us with food, these landscapes may also provide
us with important benefits for our mental health. We call these
benefits from nature “psychological ecosystem services” (Bratman
et al., 2012) and believe that clarifying these benefits – as well as
the mechanisms underlying their provision – represents a crucial
direction for future research