Tree Stands, Hemeroby, and Naturalness Jointly Shape the Functional Diversity of the Herb Layer in Urban Parks

Urban parks serve a vital function in delivering essential ecosystem services, including biodiversity maintenance and the improvement of urban well-being. This study explores how tree stand characteristics impact the hemeroby, naturalness, and functional diversity of herbaceous cover in two parks in Dnipro, Ukraine. Utilizing structural equation modelling we identified four key gradients influencing herbaceous diversity: stand density/thinning, diversity/uniformity, cooling potential, and heating potential. Higher tree density and diversity lead to cooler temperatures and increased soil and air humidity, which in turn lessens hemeroby and promotes naturalness. Reduced light intensity under denser canopies bolsters the establishment of natural herbaceous communities. Hemeroby and naturalness also impact functional diversity, which can be divided into richness, evenness, and divergence. Environmental disturbances often reduce functional richness while increasing evenness and divergence; in contrast, greater naturalness is related to increased evenness but decreased richness. Our results highlight the importance of tree stand structure in shaping microclimate and functional diversity within urban parks. A thorough understanding of these interactions is crucial for developing park management strategies that enhance biodiversity and ecosystem stability. By merging ecological theory with urban planning, this study provides a framework for sustainable management of green spaces, ensuring lasting ecological and social benefits.