In the early modern period, Taoist monks cultivated Bonsai trees seeking to bring their beauty from the outside to the inside, considering them a link between the human and the divine. Likewise, in the 18th century, different tree-lined walks and avenues arose on the outskirts of some European cities, generating spaces for rest and socialization that were previously non-existent in cities at that time.
In cities today, trees are essential elements in the urbanization process and act as irreplaceable counterpoints to manmade constructions for spatial harmony. Choosing appropriate tree species and maintaining them correctly generates countless benefits, such as acoustic and visual insulation, temperature regulation, the generation of biological corridors, and control of wind speeds. The main mistake planners can make when choosing tree species is forgetting that they are living beings and have specific needs.
What should we consider to pick them correctly?
Calculation of Space
Different trees have different structures. Wider, taller, and leafier canopies are better suited for parks and open spaces, while in highly dense areas, underestimating their growth may cause long-term problems. Planners should also consider space for root development; an adult tree requires root space very similar to the reach of its crown. Limited space for root development can prevent the tree from developing properly.
Correct Doses of Light and Water
Trees will receive limited light exposure in urban areas with tall and densely packed buildings, cause excessive growth in height with low foliar development. Meanwhile, water supply is most relevant during the early stages of growth since adult trees will grow roots deep enough to supply themselves with excess irrigation from underground water sources.
Phenological and Photoperiod Characteristics
Deciduous species, which lose their leaves at certain times of the year, are the best options for areas with marked seasons—cold winters and hot summers—since during the winter they permit light entry and during the summer they effectively control temperature and humidity. On the contrary, coniferous species are advantageous in that they do not require the excessive maintenance of cleaning up leaves and plant residue. Coniferous species (Genus Cupressus and Pinus, among others) also limit the development of plant covers underneath them, such as grass or low shrubs.
Different trees may produce different externalities, such as fruits and berries, which may dirty the sidewalks. Species such as Platanus accumulate dust and particles in the villi of their leaves, generating allergies and dirt. These species also have a strong root system, and may lift the pavement or even break pipes in their development. Species such as the different types of Maple and Palm are highly recommended for areas with high vehicular traffic since their canopies develop in such a way as to clear views of the lower area.
Certain species require excessive maintenance. The Holm Oak (Genus Quercus) may develop mold and attract unfriendly insects. Species such as Willows (Genus Salix), Ficus, or Melias can also suffer dangerous snags if they are not handled with proper pruning.
Some recommended species for temperate climates according to location and other characteristics include:
For parks and squares, planners should rely on long-living species with large final sizes and a wide variety of shapes and colors.
Abies alba, Betula pendula, Cedrus deodara, Araucaria bidwilii, Catalpa bigninioides, Brachichiton discolor, Ginkgo biloba, Magnolia grandiflora, Phytolaca dioica, Quillaja saponaria, Quercus robur, Liquidambar styraciflua, Salix babilonica, Jacaranda mimosifolia, Fagus sylvatica.
Small and medium streets
Planners should use medium and small sized trees in streets, with tall and manageable "V" shaped canopies to make space for wiring while shading the sidewalk and street simultaneously. Clean species that do not generate dust or grow fruit are preferred. Final root development should also be considered.
Acer negundo, Acer palmatum, Casuarinas equisetifolia, Aesculus hippocastanum, Aesculus x carnea, Tilea americana, Robinia pseudoacacia, Fraxinus excelsior, Liriodendron tulipifera, Lagerstroemia indica.
Trees in avenues should have clear bases, grow to be medium to large, and develop cylindrical canopies. These trees should also be prevented from conflicting with traffic.
Fraxinus excelsior, Platanus acerifolia, Liriodendron tulipifera, Quercus suber, Erythrina crysta-galli, Quercus falcata, Magnolia grandiflora.
Large road intersections
In these cases, planners should use robust, long-lived trees, which can tolerate high soil compaction. Preference should be given to tall-growing species with a clear base.
Araucaria araucana, Araucaria heterophylla, Phoenix canariensis, washingtonia robusta, Cedrus libani, Gleditsia triacantos.
Choosing and maintaining trees correctly, under the right conditions, will ensure that they develop at full capacity, enriching the landscape and complementing the standard geometry of urban architecture with more organic lines. However, poor planning and care will culminate in poor development, delivering less-than-ideal results in planning.