Measuring forest comfort: Density, openness, and perceptual response patterns across landscape types

Understanding how forest structure influences human comfort is critical for designing recreational and health-oriented landscapes. However, previous studies have reported inconsistent findings, partly due to the lack of interpretable and comparable measures of perceived comfort. This study aims to operationalize forest comfort using a set of interpretable indices and to examine how perceived comfort varies with forest openness and tree density. We employed controlled computer-generated visual stimuli representing different forest structures and conducted a large-scale survey (N = 800). Our results show that perceived comfort varies consistently with forest structure. In trail landscapes, comfort increased as tree density decreased across the examined range, whereas in scenery landscapes, comfort increased with openness but plateaued beyond moderate levels (approximately 70–80%). Importantly, the proposed indices—particularly acceptance and sensitivity—capture distinct aspects of comfort responses, enabling a more structured and interpretable quantification of human–environment interactions. These findings help explain inconsistencies in previous research by distinguishing between different dimensions of comfort and by providing a quantifiable framework. From a practical perspective, the results suggest that reducing excessive enclosure in trail environments may improve perceived comfort for a broad range of users, while in scenery landscapes, achieving moderate openness appears more effective than maximizing openness. Because comfort in scenery landscapes plateaued beyond approximately 70–80% openness, additional clearing is unlikely to yield substantial perceptual benefits relative to selective or incremental interventions. The proposed indices may also support the comparison of alternative design scenarios by distinguishing between broadly acceptable conditions and conditions in which perceptual responses are especially sensitive to structural change. While the use of computer-generated stimuli introduces limitations, this study provides a methodological foundation for systematically integrating perceptual responses into forest design and management.