Urban Tree Ordinance

Introduction

An urban tree is that specimen or collection of them growing within an urban or suburban location. In a broad sense, it includes any kind of woody plant growing in human settlements. In a narrower sense (fitting into forest park) it describes areas where ecosystems lack wild survivors or remnants. Urban trees are considered to be those that, being located outdoors and being primarily of public utility, affect the environment of a city, whether integrated into it in the street, or in urban/forest interface areas (Novelo, 2009).

The care and management of the urban tree is called urban forestry.

Trees play an important role in the ecology of human habitats in many ways: they filter air, water, sunlight, noise; they cool the environment; They provide shade for animals and other plants, and a recreational area for the inhabitants. They moderate the urban climate, reduce winds and storms, provide shade to homes and businesses, helping to conserve energy. They are critical in cooling the urban heat island, and shading by reducing the potentially dangerous ozone depletion days that plague megacities in the peak summer months.

In many countries there is a growing understanding of the importance of ecology in urban forestry. Numerous projects arise to restore and preserve ecosystems, from the simple removal of fallen leaves, to the elimination of invasive plants, and the reintroduction of original native species.

Benefits

Contenido

Los beneficios del arbolado urbano son muchos: embellecimiento, reducción de los efectos de la isla de calor, reducción de las escorrentías y escurrimientos, reducción de la contaminación atmosférica (química, física, biológica), reducción de costos de energía por perfeccionar el sombreado de edificios y de calles, mejora del valor de la propiedad, atenúa la amenaza a la fauna y flora silvestres, y en general mitiga todos los impactos urbanos ambientales.

The abundant presence of trees reduces stress, benefiting the psychophysical health of the urban inhabitant. Pleasant shading of streets and parks encourages socialization and play. Again, planning and community involvement are important for positive results.

Urban Tree Ordinance

Introduction

The care and management of the urban tree is called urban forestry.

Benefits

Contenido

Biogenic volatile organic compounds

An important aspect to consider when assessing the effects of trees on urban air quality is that they emit some biogenic volatile organic compounds (VOCs). These chemical compounds (mainly isoprene and monoterpenes) form essential oils, resins and other organic compounds that plants use to attract pollinating agents and repel predators. As mentioned above, BVOCs react with NO to form ozone. This means that VOCs emitted by trees contribute to ozone production. While that contribution should be considered small, BVOC emissions can exacerbate the smog problem.

Not all tree species, however, emit high amounts of BVOCs. The species that emit the greatest amount of isoprene and that should be planted carefully are:

Trees that are well adapted to the environment and are healthy should not be removed or replaced just because they emit VOCs. The amount of hydrocarbon emissions that can be produced by maintaining a tree that emits low amounts of BVOCs can be more harmful than the large emissions of BVOCs from some species listed above.

Trees should not be classified as pollutants since their benefits on air quality are much greater than the damage that COVB emissions may cause by increasing the concentration of ozone. Emissions of BVOCs grow exponentially with temperature. Therefore, greater emissions will occur at higher temperatures. In desert climates, native trees adapted to hostile conditions emit significantly lower amounts of BVOCs than trees from humid climates. As discussed above, ozone production is also temperature dependent. Thus, the best way to reduce the production of ozone and VOCs is to reduce urban temperatures and the heat island effect. As suggested above, the best way to reduce urban temperatures is to increase green cover and particularly the number of trees.

The effects of urban trees on ozone production were recently discovered by the scientific community, although extensive and conclusive research has not yet been carried out. Some studies were carried out quantifying the effects of BVOC emissions on ozone formation, but the contribution of urban trees to this production was not conclusively determined. Important questions remain unanswered. At this time, it is unknown whether there are enough chemical reactions between BVOC and NO emissions to produce harmful amounts of ozone in urban environments. It is necessary and important for cities to be aware that these investigations continue and the conclusions should not be exposed until the pertinent evidence has been collected. New studies and research may resolve these questions.

Biogenic volatile organic compounds

Not all tree species, however, emit high amounts of BVOCs. The species that emit the greatest amount of isoprene and that should be planted carefully are:

Navegación

Urban Tree Ordinance

Introduction

Benefits

Contenido

Urban Tree Ordinance

Introduction

Benefits

Contenido

Economic benefits

Reduction of air pollution

Biogenic volatile organic compounds

Economic benefits

Reduction of air pollution

Biogenic volatile organic compounds

Navegación

Urban Tree Ordinance

Introduction

Benefits

Contenido

Social, psychological, recreational, wildlife

Urban Tree Ordinance

Introduction

Benefits

Contenido

Economic benefits

Reduction of air pollution

Biogenic volatile organic compounds

Social, psychological, recreational, wildlife

Economic benefits

Reduction of air pollution

Biogenic volatile organic compounds