Branch Area Index of Solitary Trees: Understanding Its Significance in Regulating Ecosystem Services

The chief aim of this study was to investigate how different species of solitary trees in temperate urban areas vary in their branch structure during winter by assessing branch area indices (BAIs). The BAI data showed significant differences ( < 0.0001) between species and genotypes. The lowest mean BAI in the dataset was for L., which had a BAI of 0.27. L. 'Fastigiata' represented the largest mean BAI of 2.09. The results from the BAI analysis further indicate that within the same species group differences occur between genotypes. For example, the five genotypes of L. range from a mean BAI of 1.77 for 'Globosum' to a mean BAI of 0.50 for 'Fassen Black'. A further aim was to apply the compiled BAI data in the computational modeling program of ENVI-met 3.1, which simulates the surface-air interaction and microclimates in complex urban settings. The simulations focused on mean radiant temperature and wind speed. Results illustrate how wind speed on the leeward side of the trees gradually decrease with an increasing BAI. With an increasing BAI, the Tmrt decreases to the leeward of the row of trees. The results are further discussed in the perspective of sustainable urban development (i.e., where, why, and how the species studied could be integrated in the urban fabric). This is of particular interest for the design of urban green space in densely built-up urban environments where space may be restricted.