Tag Archives: environmental stressors

Growing Trees in the Urban Jungle: To Sum it all Up

By Alistair Johnston

Establishing trees in the urban jungle is a difficult proposition given the many varied stressors that can impact health. To greatly improve upon the life expectancy for metropolitan trees, there has been a concerted effort amongst municipalities, arborists, and landscape architects to rethink the requirements for urban tree planting. New technologies to maximize soil volume along with research and education in planting and maintenance techniques are linking together to facilitate the successful establishment of trees. The future is positive for urban forests.

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Growing Trees in the Urban Jungle: Tree Planting

By Alistair Johnston

The final key to growing trees in the urban jungle is to employ best practices for planting. The fact is, all of the recommendations noted in this article will not matter if the tree is planted improperly.

It starts with the selection of the appropriate tree with sufficient root development and ends with proper planting in sufficient soil with enough water. Along the way, the tree must be handled with utmost care because every bump and bruise could result in a future problem.

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Growing Trees in the Urban Jungle: Ideas for Establishing a Sustainable Urban Forest

By Alistair Johnston

Reduced emissions to decrease acid rain and a reduction in the use of de-icing salts are obvious choices, but public safety tends to supersede tree preservation on these issues. The introduction of municipal tree bylaws, increased vigilance, and an understanding of construction near trees has, and will continue to decrease the extent of human impact.

Mitigating the urban heat island effect through the use of green roof technologies, and reflective (high-albedo) paving are two methods that are now commonly implemented. Further, in an effort to recharge groundwater, permeable paved hard surfaces are often utilized. This allows for the percolation of water into the subsoil, thus making it available for uptake by adjacent root systems. Where feasible, the practise of an early spring wash for roadside trees will aid in reduced salt uptake.

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Growing Trees in the Urban Jungle: Human Impact

By Alistair Johnston

Urban trees are often negatively impacted by those who benefit greatly from them, that is, humans. Poor planting practices, heavily compacted soils, utility pruning, improper maintenance, vandalism, mechanical injury from lawn equipment, or vehicle impact, are all sources of stress on tree health. Probably the most common and underappreciated human impact on trees is that of construction. Excavation associated with new buildings, pavements, and utility trenches often requires tree removal and/or results in severely damaged root systems.

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Growing Trees in the Urban Jungle: Environmental Stressors

By Alistair Johnston

There are many environmental forces, both biotic (i.e. living), such as fungus, bacteria, and insects and abiotic (i.e. non-living), such as drought, salt, and mechanical injury), that have an impact on the successful establishment of trees in the urban setting.

Air, water, and soil pollution are prime stressors that constantly affect urban trees and impact the balance, which is important for overall health. Air pollutants, including sulphur dioxide (SO2), absorbed by the foliage, interfere with photosynthesis and respiration.

Salts, which mainly enter the urban environment because of winter de-icing, are extremely harmful to trees, and may be the most common and impactful abiotic disorder. Salt, such as sodium chloride (NaCl), impacts a tree through contact from salt spray and salt-contaminated soil. Salt spray damage is particularly noticeable adjacent to streets and highways where prevailing winds consistently batter exposed trees. The resulting appearance on conifers is a browning of the needles and on deciduous trees is sparse foliage cover, severely stunted growth or mass response growth commonly known as ‘witch’s broom.’ In many cases, extended or severe exposure results in mortality.

The negative forces of Mother Nature are enhanced by the urban environment because urban trees are not equipped to withstand severe weather conditions due to their diminished overall condition. For example, during the summer, the urban heat island effect, caused by the heating of hard surfaces, increases drought stress on trees. The effects of storm impact are often more severe because swirling winds accelerate as they pass by tall buildings. Also, flash flooding along tributaries receiving mass quantities of water from adjacent hard surfaces often uproots trees.

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