Selection of ornamental species with different degrees of shade tolerance
Abstract: The ornamental green of urban areas is determined by the choice of the species and their combination or integration with pre-existing plants. The herbaceous and shrub species must be positioned so that the availability of light is sufficient to ensure the satisfaction of the basal metabolism throughout the vegetation period which includes the different seasons.
Ornamental species, according to shade tolerance or the need for good irradiance, are classified into shade and sun plants. To properly position the plants, especially when in the immediate vicinity of buildings, it is necessary to study the projection of shadows during the year and in particular in the most critical periods such as July and August. As with light, shadow can also be classified and for simplicity, three levels of shading can be identified:
• light or bright shade: the area of interest can be completely shaded for a few hours a day, every day. The sun’s rays are blocked for several hours a day by a building or a wall, but the rest of the day the area is sunny.
• partial or partial shade: the area is shaded for most of the day, but in the early morning or in the evening the plants are reached by the sun’s rays.
• complete or total: the area is shaded all day.
The position of species with different degrees of shade tolerance can be obtained by the determination of the light compensation point for each species, that is, the minimum amount of light that allows equating the assimilation of carbon dioxide with photosynthesis to the carbon dioxide emitted by respiration. This state of biological stalemate for the plant represents the most critical condition that the plant itself can endure during the critical summer period. The distribution of the species within an area should follow the minimum light intensity that guarantees to compensate for respiration such that net photosynthesis is greater than zero in a 24hr period. In this context, this study classifies, on an objective basis, the most common ornamental species used in the Mediterranean environment based on light requirements.