Effect of vertical and horizontal temperature gradient on growth and development of <i>Thuja occidentalis ‘Smaragd’</i>

Abstract The adaptive potential of plants in urban environments, due to the influence of factors such as air pollution, radiation and specific microclimate features, is still poorly understood. In our study, we focused on the vertical and horizontal temperature gradients of Th. o. ‘Smaragd’ , which is common in the urban landscape of Lviv. The study was carried out in one of the most environmentally loaded cities in western Ukraine. In conditions of positive vertical and horizontal temperature gradients (yard), it shows good apical (19.5 cm) and lateral (6.0 cm) growth. This indicator is much lower in street planting conditions, 12.0 cm and 2.1 cm, respectively. According to the research results, three groups of tree vitality were identified: healthy, depressed, and severely depressed. The first group includes all individuals of the cultivar growing in optimal edaphic and climatic conditions of the courtyard, and the second and third groups include those growing along the sidewalk under the negative influence of vertical and horizontal temperature gradients. A vitality scale for Th. o. ‘Smaragd’ was developed using both biometric indicators and visual inspection. A negative gradient will appear when the temperature of the point that is compared to the starting point is higher, and vice versa, the gradient will be positive when the temperature of the second measurement point is lower than the starting point. The gradient will be zero when there is no temperature difference between the two measurement points.