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09/2021: September’s fieldwork: mental and thermal wellbeing

Post by Loïc Gillerot and Kevin Rozario

In a rental car loaded with quadrilingual questionnaires, portable electrocardiography (ECG) devices, and a mountain of Covid-tests, we set out for what is likely to be our last fieldwork campaign in the context of Dr. Forest. We traveled to Leipzig (Germany), Vienna (Austria), and Louvain-La-Neuve (Belgium) to roll out an ambitious study combining surveys on mental health and wellbeing, as well as thermal comfort. The itinerant core team was composed of Max, a psychology intern but by now a fully fletched surveyor, Rachel, who guided the team based on the vast experience with socio-ecological surveys she got from her PhD, Kevin, the main investigator for the mental health and wellbeing part (PhD student on T1.1), and Loïc, focusing on the thermal comfort part (PhD student on T2.1). Even though we could not have dreamt of a better team, we would absolutely not have been able to conduct this experiment without the crucial help of our local Dr. Forest and non-Dr. Forest partners!

The survey’s main idea is simple: comparing participants’ well-being before and after exposing them to one of three different forest settings which have contrasting species diversity levels (i.e. 1, 2 or > 4 tree species) or an urban control setting. The logistics, in contrast, were less simple. First of all, it was truly challenging to find enough participants in the 1-2 months before the study’s onset. Still, we managed to gather a total of 224 participants over the three sites! Second, having four participant cohorts with overlaps per day and five different sites to transport them in a synchronized fashion, demanded fast and lucid thinking. At last, the logistics required a lot of local help with, for example, the transportation of participants. We were very lucky to count on great help, as even small mistakes could have led to important delays and incomparable data.

Let us give you a first-person view of the study’s design (Figure 1). If you had agreed to participate, you would have started at the ‘central meeting point’. This location was chosen to be a ‘neutral’ condition, meaning not too green, nor too urban. Once you would have taken a seat, you would have received the first questionnaire so we could measure your baseline measures. This is also the moment where you would be asked to take a first salivary cortisol sample and to attach your ECG device so we could continuously monitor your heart rate and heart rate variability throughout the study. About 40 minutes after you arrived, a blinded van would bring you to one of the forest plots – or the urban setting if you are out of luck… The forest plots were selected based on their contrasting tree diversity levels, going from monospecific stands to stands with at least five tree species. Once there, you would get 20 minutes to take in the atmosphere of your surroundings, with a focus on whatever you hear or see. At last, you would get a second questionnaire to fill in, another saliva sample to take and we would free you from the ECG. Hopefully, you had a relaxing experience!

Figure 1 | Overview of the survey procedure. After letting participants acclimatize for about 40 minutes on the central meeting point (CMP), they were transported in a blinded van to one of the three forest conditions or the urban control. The vans were blinded to avoid pre-exposure to nature before the intervention’s start. Once seated in the respective plots, participants focused on their environment for 20 minutes using their hearing and seeing. At both the CMP and the different plots, various measures were taken. Each plot was ecologically characterized (biodiversity, stand density, and structure) and provided with heat stress sensors and audio loggers (T1.2). Participants filled in questionnaires on mental health and well-being and thermal comfort. These data were further complemented with physiological data from portable electrocardiography (ECG) and saliva samples for assessing cortisol levels – proxies for stress and relaxation.

To thank the 224 volunteers that participated, we contacted forest bathing guides in each city to take the participants on a 45-min forest bath ‘teaser’, accompanied by some herbal or fruity forest tea and snacks. Judging from the participants’ feedback, most people really enjoyed themselves – even those who were sent to the urban condition! Most motivating were the dozens of participants that came to ask how they could follow up on the results and when these would be made available. Quite a tricky question and we are also very curious ourselves! Judging from the first microclimate data illustrated in Figure 2, the forest’s sheltering effect is crystal-clear. Whether forest biodiversity is also of significant influence, will have to be assessed using statistics. Our expectations are that mental health and wellbeing parameters will approximately analogously be affected by the forest, i.e. a strong forest effect and a more modest forest biodiversity effect. As to when we would be able to demonstrate this with preliminary results, we tried to stay cautious when replying to interested participants: “Hopefully in four to six months… So make sure to keep an eye on the Dr. Forest website!”.

Figure 2 | An overview of the heat stress participants experienced throughout the two days of the survey in Wienerwald, Vienna, as an example. Heat stress is here characterised as the Wet-Bulb Globe Temperature (WBGT), a common heat stress index. Remark how the control condition (CMP) experienced very fast fluctuations and hot conditions (a WBGT of > 25° is already quite hot for Europeans), while the forests plots never experienced any heat stress and much fewer fluctuations. Even though it looks like the most diverse forest did have the strongest buffering effect (red curve), further statistics are needed to confirm that this is a general and significant trend.

Pictures from Louvain -La-Neuve by Aurore Delsoir, except for the picture of the heat loggers and the girl hugging a tree, which are taken by Adriaan Devillé.