Does increasing biodiversity in an urban woodland setting promote positive emotional responses in humans? A stress recovery experiment using 360-degree videos of an urban woodland

problems [4–7]. Several theories have proposed explanatory mechanisms behind these bene- fits, which rely on the content or on the quality of green space. The Attention Restoration the- ory [8] postulates that space must provide engaging but low-effort stimuli (soft fascination) to be restorative. The Stress Reduction theory [9] suggests that spaces with unthreatening nature and moderate complexity reduce stress most effectively. The Biophilia hypothesis [10] indi- cates human well-being is enhanced by interacting with other species. More recently, research work addressed some of the physical aspects associated with green space such as phytoncides [11] and beneficial microbial communities which affect the human immune system and mood regulation [12, 13]. It has been argued that biodiversity (i.e. the diversity of species of plants and animals in a given location) is an attribute of the landscape [14] and one of the distinctive qualities of urban greenspaces [15]. Biodiversity can be quantified with objective measurements (i.e. actual biodi- versity) but also estimated subjectively (perceived biodiversity), based on the number of spe- cies an observer thinks could be in the location [16]. According to the theories referenced above, a green space that is (or is perceived to be) richer in species should provide more oppor- tunities to encounter wildlife and promote soft fascination (Attention restoration), and inter- actions with unthreatening nature (Stress reduction). Indeed, a number of papers suggest that increased bird [15, 17–19], invertebrate [15] and/

or plant diversity [15, 17, 18, 20] increases the health-promoting potential of the landscape. Biodiversity in green space has been linked to both reduced stress [21–23] and enhanced Posi- tive Affect [18, 19]. However, Lovell et al. [24] and Marselle et al. [25] state that the links between biodiversity and health are often correlational, and recommend more experiments to better explore cause and effect. Botzat et al. [26] also argued that, in urban green spaces, biodiversity was more frequently studied at the ecosystem and habitat level than at the species level. A recent review [27] noted that only six studies (out of the 52 reviewed) were set up to specifically explore the influence of species richness on human health. Two studies were natural experiments, using locations at different levels of biodiversity. Hussain et al. [28], measured self-reported well- being, blood pressure and heart rate before and after exposing participants to six mountain meadows. Participants reported higher well-being after visiting meadows with high plant biodiversity, while blood pressure and heart rate did not differ. Simkin et al. [29] tested the effect of visiting forests on Attention Restoration, Vitality and Positive/Negative Affect. The participants visited four forests which were all dominated by spruces (Picea abies), but dif- fered in terms of maturity (old vs young) and location (urban vs rural). The results showed that rural mature forests (i.e. more biodiverse) induced higher Attention Restoration, Vitality

and Positive Affect than young or urban forests. Four experiments manipulated species rich- ness directly. Wolf et al. [18] showed videos comparing tree (1 vs 4 species) and bird (1 vs 5 species) species richness and found that videos with more species reduced anxiety and increased Positive Affect and Vitality. In contrast with Hussain et al. [28], the creation of urban meadows at three levels of species richness (low, medium and high) elicited non-sig- nificant differences in self-reported physical health and mental well-being, compared with mown grass [30]. The remaining two experiments linked increased biodiversity levels to better stress recov- ery. Placing stressed individuals in front of one out of five arrangements of potted plants (with 0, 1, 16, 32 and 64 plant species respectively), showed optimal stress recovery (regulation of blood pressure) with the 32 species treatment [22]. Schebella et al. [31] also indicated that some, but not necessarily high biodiversity, reduced stress. They used 360-degree videos to both stress their participants and expose them to parks at different levels of species richness. Applying a multisensory approach, species richness was controlled via visual (2, 4, 7 vegetation PLOS ONE Does increasing biodiversity in an urban woodland setting, promote positive emotional responses in humans? PLOS ONE | https://doi.org/10.1371/journal.pone.0297179 February 7, 2024 2 / 20 https://reshare.ukdataservice.ac.uk/856311/ DOI: https://dx.doi.org/10.5255/UKDA-SN-856311. Funding: SF received a PhD Studentship funding

from the UKRI Economic and Social Research Council, via the White Rose Doctoral Training Partnership (WRDTP). Award reference: 2273610. https://www.ukri.org/councils/esrc/ The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.