Up to 80% of trees in the urban area of Chile They shed their leaves in autumn, losing color in the crowns and taking it to the ground during the coldest season of the year.
Trees such as sweetgum (Liquidambar styraciflua), oriental bananas (Platanus hydride), the golden ginkgos (Ginkgo biloba) and maples (Acer negundo) they go through different shades of yellow, orange and reddish, until it is only in branches. The same goes for acacias (Robinia pseudoacacia), the sophoras (Styphnolobium japonicum) and the poplars (Populus nigra and Populus deltoides), among other species.
Why do tree leaves change their colors in autumn?
“Our cities have ornamental trees that do not represent the vegetation that originally existed in the sector in which it is inserted. Most of the grove is introduced and of diverse origins, mainly from Europe and North America. This is, in general, deciduous, which means that in winter they have no leaves and that they are completely naked in a state of latency,” explains Gloria Rojas, curator and researcher at the SGO Herbarium of the National Museum of Natural History (MNHN).
“Precisely in the cities where a large population is concentrated and are more polluted, they do not have a grove of trees that mitigate pollution and increase oxygen production”, he emphasizes.
The influence of leaves in winter
Winters in the capital and several communes in the country usually come accompanied by several episodes of air pollution. The use of firewood for heating and cities in geographic basins where contaminated air is encapsulated, are among the main causes of this accumulation of pollutants. AND evergreen trees could help reduce the amount of particles throughout the year.
Years ago, studies led by researchers from the University of Santiago detected that Native species are not only more suitable in terms of water requirements, but they also combat pollution better in the city.
Trees that retain their leaves during the winter, They can capture small particles produced by pollution. Ornamental species such as privet (Ligustrum lucidum) or the laurel in bloom (Nerium oleander), are more efficient in retaining atmospheric particles and could increase the mitigating effect by 10% to 20%.
Thermal inversions and their influence on air pollution
“A evergreen grove in winter, will improve air quality, retain suspended dust, consume CO2, produce more O2, it will reduce environmental noises, attract bees, butterflies and other insects, birds, lizards, and other living beings. They will contribute to forming a biological corridor. On the other hand, this flora is pollinated by insects and birds, and its pollen production is low, making it less likely to cause allergies,” explains Gloria Rojas.
It refers to native trees such as peumo (Crytocarya alba), the quillay (Quillaja saponaria), the maiten (Maytenus boaria), the patagua (Crinodendron patagua), the northern acorn (Beilschmiedia miersii), the liter (Lithraea caustica) and the molle (Schinus molle), among others. Even introduced species such as the gomero (Ficus elastica) and the cork oak (Quercus suber).
“We must plant more evergreens, to have functional leaves in winter: That is, they carry out photosynthesis, capture carbon dioxide and produce oxygen,” adds the botanical specialist.
Diversity of leaves in their natural habitat
Despite its advantages since More than 85% of native trees in Chile are evergreenIn cities, generally, those chosen are exotic and deciduous, representing between 60% and 80% of urban trees, in some cases, indicates Sergio Donoso, academic at the Department of Forestry and Nature Conservation of the University of Chile.
By geographical area, we can find ua wide variety of species that do not lose their leaves in winter, because it is the most efficient for each area. In the north, queñoas (Polylepis tarapacana), in the central area, the liter (Lithraea caustica), the quillay (Quillaja saponaria), the peumo (Crytocarya alba) and the boldo (Peumus boldus); in the south central area the araucaria (Araucaria araucana), the larch (Pinus cupressoides), the tepa (Laureliopsis philippiana), the olivillo (Aextoxicon punctatum), the language (Persea lingue) and the laurel (Laurelia sempervirens), among others, while in the south, the Guaitecas cypress (Pilgerodendron uviferum), Magellan’s coihue (Nothofagus betuloides) and cinnamon (Drimys winteri).
Drought and heat are reducing the carbon absorption capacity of forests
The loss of leaves in nature, on the other hand, is also necessary. “In deciduous forests, where oaks dominate (Nothofagus obliqua), raulíes (Nothofagus alpina), hualos (Nothofagus glauca), lengas (Nothofagus pumilio) and ñire (Nothofagus antarctica), to the lose their leaves in winter, the rains reach the forest floor more directly, allowing more water to be available.
Also, the microclimate of the forest, more closely resembles environmental conditions outside the forest, since there is less capacity to attenuate temperature variations, as a perennial forest can do,” explains Donoso.
For the academic from the University of Chile, both types of trees have advantages in certain contexts. “In urban spaces, deciduous trees tend to be preferred, since in winter they allow more light and improve the temperature on sunny days.. An adverse effect is that falling leaves can obstruct rainwater drainage. In rural areas, it is preferable to establish trees that are adapted to the environmental conditions of the area and the needs of the people, and may be deciduous or perennial,” he maintains.
