The positive impact of natural scenery on individuals well being has been well studied. I found a few studies looking at the physiological effects of viewing natural scenes.
Electroencephalography (EEG) has been used to access the electrical activity of the localized brain cortex associated with natural and urban environments (Ulrich, 1981; Nakamura, 1992). Ulrich reported that subjects shown urban and scenes produced more alpha (relaxation) activity when viewing nature scenes. High alpha amplitudes are associated with lower levels of physiological
arousal as well as feelings of wakeful relaxation.
More recently Kim at al (2010) conducted a functional magnetic imaging (fMRI) study exposing participants to either rural (natural) or urban scenery, they found that different areas of the brain were active when viewing the different scenes:
Activation of the anterior cingulate gyrus, globus pallidus, putamen
and head of the caudate nucleus was dominant during rural scenery
viewing, whereas activation of the hippocampus, parahippocamus and
amygdala was dominant during urban scenery viewing (p < 0.01). These
findings allow better characterization of neural activation,
suggesting an inherent preference towards nature-friendly living.
In terms of hormones, cortisol, amylase and adrenaline would be the ones changed by exposure to natural scenes as these are the hormones most associated with stress (Rashkova et al, 2012; Takahashi, 2005; Takai, 2004).
Park et al (2007) got two groups of participants to spend time in either a forest or a city for a day and then swap and spend a day in the opposite environment they found that:
The concentration of salivary cortisol in the forest area first group was significantly lower than that of the group that went to the city area first even after being in both landscapes.
It's worth noting however that a meta-analysis by Bowler et al (2010) found that research looking at hormones and natural environments was not consistent:
Meta-analysis of data on blood pressure and cortisol concentrations
found less evidence of a consistent difference between environments
Other hormones, or measures of hormone activation, apart from
cortisol, have also been investigated such as adrenaline and
noradrenalin and salivary amylase. Across these different studies and
outcomes, their results provide mixed findings, with no clear,
consistent difference emerging in the effect of different
Bowler, D. E., Buyung-Ali, L. M., Knight, T. M., & Pullin, A. S. (2010). A systematic review of evidence for the added benefits to health of exposure to natural environments. BMC public health, 10(1), 456.
Park, B. J., Tsunetsugu, Y., Kasetani, T., Hirano, H., Kagawa, T., Sato, M., & Miyazaki, Y. (2007). Physiological effects of Shinrin-yoku (taking in the atmosphere of the forest)-using salivary cortisol and cerebral activity as indicators. Journal of Physiological Anthropology, 26(2), 123-128.
Takai, N., Yamaguchi, M., Aragaki, T., Eto, K., Uchihashi, K., & Nishikawa, Y. (2004). Effect of psychological stress on the salivary cortisol and amylase levels in healthy young adults. Archives of oral biology, 49(12), 963-968.
Takahashi, T., Ikeda, K., Ishikawa, M., Kitamura, N., Tsukasaki, T., Nakama, D., & Kameda, T. (2005). Anxiety, reactivity, and social stress-induced cortisol elevation in humans. Neuroendocrinology Letters, 26(4), 351-354.
Rashkova, M. R., Ribagin, L. S., & Toneva, N. G. (2012). Correlation between salivary α-amylase and stress-related anxiety. Folia medica, 54(2), 46-51.
Ulrich, R. S. (1981). Natural versus urban scenes some psychophysiological effects. Environment and behavior, 13(5), 523-556.
Nakamura, R., & Fujii, E. (1992). A comparative study of the characteristics of the electroencephalogram when observing a hedge and a concrete block fence. Journal of the Japanese Institute of Landscape Architects, 55(5), 139-144.
Kim, G. W., Jeong, G. W., Kim, T. H., Baek, H. S., Oh, S. K., Kang, H. K., ... & Song, J. K. (2010). Functional neuroanatomy associated with natural and urban scenic views in the human brain: 3.0 T functional MR imaging. Korean Journal of Radiology, 11(5), 507-513.
Kim, T. H., Jeong, G. W., Baek, H. S., Kim, G. W., Sundaram, T., Kang, H. K., ... & Song, J. K. (2010). Human brain activation in response to visual stimulation with rural and urban scenery pictures: A functional magnetic resonance imaging study. Science of the total environment, 408(12), 2600-2607.