Item	Question	Preparatory Sources Informing Delphi Items
	Domain 1. Target group	Systematic review	Stakeholder dialogues
1	To what extent do you agree that the target group benefits most from participating in a diagnosis-specific group intervention (e.g., only individuals with stress or anxiety)?	Systematic literature review	Theme: Needs of the Target Group
2	To what extent do you agree that the target group benefits most from participating in a mixed group intervention involving anxiety, depression and/or stress?	Systematic literature review	Theme: Needs of the Target Group
	Open-ended question: Please elaborate your considerations here:
	Domain 2. Professionals
3	To what extent do you agree that NBHIs should be delivered by an interdisciplinary team? (e.g., a physiotherapist and a nurse, or a psychologist and a nature guide)		Theme: Competency Development
	To what extent do you agree that the following professional groups should deliver the nature-based health interventions to the target group?		Theme: Competency Development
4	- Nurse
5	- Medical doctor
6	- Physiotherapist
7	- Occupational therapist
8	- Psychologist
9	- Nature educator
10	To what extent do you agree that the professional’s knowledge and experience with NBHIs is essential?		Theme: Competency Development
11	To what extent do you agree that the professional’s knowledge and experience with the target group—people with mild to moderate anxiety, depression and/or stress—is essential?		Theme: Competency Development
	Open-ended question: Are there any other important professional groups not mentioned here?
	Domain 3. Mechanisms of change
	Based on your knowledge of the target group, to what extent do you agree that the following mechanisms of change should be integrated into a NBHI for people with mild to moderate anxiety, depression and/or stress?		Themes: Added Value of Nature AND Needs of the Target Group
12	- Nature experiences and nature interaction
13	- Exchange of experiences
14	- Sensory experiences
15	- Social communities
16	- Physical activity
17	- Empowerment
18	- Body awareness
19	- Self-reflection
20	- Coping ability/self-efficacy
21	- Participation in everyday life
	Open-ended question: Are there any other important mechanisms of change you think should be included?
	Domain 4. Outcome selection
	We are interested in your assessment of which outcomes are most important to measure. How would you rank the following four outcomes? (1 being the one you consider most important to measure)	Systematic literature review	Theme: Measuring the Intervention
	- Symptoms (fx. DASS-21)
	- Quality of life (fx. EQ-5D)
	- Well being (fx. WHO-5)
	- Functioning (fx PSFS)
	Open-ended question: Are there any other more important outcomes not mentioned here?