Environment

Save trees: Urban forests are threatened by never ending construction in cities

Save trees: Urban forests are threatened by never ending construction in cities

Many big cities have set ambitious targets to increase their tree umbrella. The city of Montreal has targeted to plant 185,000 trees by 2025. Credit: Shutterstock

City trees are important: they purify the air, reduce it Heat island, Helps in regulating the water cycle and provides immense health benefits. Still unbridled development Urban forests are threatened by survival And full range of ecosystem services it provides.

The magnitude of these services is closely linked to the importance of the canopy, an area covered by treetops. It is usually characterized by an index that covers the area topped by the total size of a region.

Recent study of natural canopy in areas covering Quebec City, Bupré, L’लेle d’Orléns, Lewis and other communities along the banks of the St. Lawrence River Generates over $ 1.1 billion in annual profits.

Water supply, flood reduction, air quality improvement and carbon sequestration were among the ecosystem services — the benefits that people receive from the ecosystem — which were considered. In this context, several major cities have set ambitious canopy expansion targets.

However, these objectives present several important challenges. Residential construction and infrastructure development and renovation reduce the urban umbrella. Part of this deficiency is directly related to the occupied space of the infrastructure, while another part is the result of damage during installation.

As a forest engineer and professor of Forest science And urban forestry, my research examines the stability of trees against wind in natural, urban and rural environments. I was interested in the influence of species, And obvious defects on stem breakdown and uprooting resistance.

Direct damage

Construction in a wooded environment brings about a general change in the growing environment of trees. By opening the canopy, trees are exposed to strong winds, which increases their water needs and may compromise their stability.

During construction in a wooded environment, the surface may be impermeable. It reduces water flow in the soil and promotes water runoff. In combination, these two factors can lead to water stress and eventually to trees that die after a few years of construction.

Construction near existing trees can directly damage the aerial part of the tree, which is quite easily visible. Damage to the root system will be more subtle, but may have more significant consequences.

Save trees: Urban forests are threatened by never ending construction in cities

Construction work near trees often involves digging that damages part of the root system. Work is done here on Saint-Denis Street in Montreal. Author provided

Roots play many roles, including accumulation, anchoring for the ground and draining water and nutrients. Damage to the roots will affect their ability to perform these various functions, with consequences on the normal functioning of the tree.

Construction work near trees often involves digging that damages part of the root system. The study found that Resistance to cutting roots can be reduced.This effect may persist for several years after initial damage.

The magnitude of the effect is related to the amount of root loss, which is a function Trunk distance. Although the root extension may extend beyond the space below the crown, it is generally believed that the area is the most important part. The effect of root cutting will also depend on the stability of the tree. Root system configuration.

Lack of development

There may be difficulty in replenishing the tree’s water reserves after root damage. Foramen closure, Pores that control gas exchange during photosynthesis. Growth may decrease after this closure. After root destruction, the tree redirects the products of photosynthesis to rebuild the root system at the expense of developing the aerial part of the tree.

In some cases, the effect on growth and mortality will be limited, but severely damaged trees will take time to recover, which may make them more susceptible to other stresses. When the root loss is too high, the tree will collapse over many years and eventually die. when Able to reconstruct itself, development can resume its normal rhythm. Retrieval is more likely to occur when the trench is temporary and material conducive to root development is put back at the end of the work.

Further studies are needed

Soil compaction by machinery or adding soil above the original level may change the soil and its flow Conditions. Diffusion of air to roots and diffusion of CO2 The roots produced by respiration will then decrease, thus hindering their proper function.

However, the effect of soil growth will depend on the thickness and nature of the soil. Installation of underground aeration systems for large soil additions has often been recommended but Studies on their effectiveness are inconclusive.

Safety measures are planned in advance to minimize the effects of construction, and the construction site is closely monitored. Several standards and guides exist, but sometimes their recommendations are reversed. Those measures are often based on a limited number of well-documented studies. Additional research efforts are needed to validate them and make new proposals.


Contaminated soil determines root characteristics


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