The development of City limits to provide space for more homes is a contentious subject addressed by advocates of both development and local environmental preservation groups during city council meetings. I have attended some sessions to understand issues from both sides better.
With the world population expected to increase 50% by 2100, development in every part of the world is necessary, and our area is no different. Advocates from both the development and environmental sides reside in homes that sit on previously cleared lands, but the issue is how proponents and advocates can work together.
We all live in the same environment. What do we put into it during development, and how does that react with naturally occurring compounds we also help to introduce while trying to mitigate the environmental impact?
The ozone layer in the upper atmosphere protects from ultraviolet light, but ozone gas at ground level is formed when Volatile Organic Compounds (VOCs) react with nitrous oxide - the byproduct of an engine - in the presence of sunlight. The ozone gas at ground level can lead to respiratory issues.
Plants and trees emit biogenetic VOCs in different quantities and types, depending on species and size. The VOCs are cast as a by-product of the photosynthetic process that absorbs carbon from the atmosphere while delivering oxygen. There are two primary compounds: isoprene and monoterpenes. Broadleaved trees, such as oaks, primarily emit the former, and pines and conifers emit the latter. Isoprene is far more reactive with nitrous oxide than monoterpenes to produce harmful ozone gas at ground level.
My question is this: Why is there an obsession to plant open field trees that require 1000 sq ft of root space in the front yard of every home in city developments, so that city planting points are met?
The highest vehicular traffic areas should have smaller specimens that emit smaller quantities of VOCs that are less reactive with car exhaust byproducts. Mitigation areas that provide new green space away from high-traffic routes for larger specimens should be identified, so nature can balance the environment without producing a negative impact.
Strategies like this may help balance development needs with environmental responsibility requirements. The survivability of larger tree specimens depends on their access to the correct soil and neighboring tree symbiosis, along with minimum human interaction.
Trees naturally provide an ability to balance.
When meeting clients to discuss problems or requirements for their trees, I first ask, 'what do you want to achieve?'. I ask this to ensure pruning isn't required to reduce the number of leaves on their driveway or gutters and remove the critical structure from the tree that is essential to maintaining its physiological and structural health. The former is an impossibility while a tree is in the vicinity, and the latter can lead to long-term problems retaining a healthy and safe tree.
Firstly, before touching a tree, it should be remembered that no tree grows anything it doesn't need, secondly the best pruning management for a tree is no pruning and lastly, the primary objective of any plant is to capture light; everything else it uses resource for is in minimal quantities. When removing branches and limbs, the tree must divert critical resources to start compartmentalizing that wound by creating biomass, a 1Llb weight of which can take up to 4000Llb weight of soil solution to make or ten days of entire nutrient flow usually needed by the tree for its whole canopy. So, removing areas that leave large wounds should always be avoided unless necessary, not just for this reason. Most of the larger weighted areas of a tree exist at its lowest point to the ground, and as the tree increases in height, the lower limbs range further out to create stabilization. When these are removed, as is so often seen, weight is automatically transferred to the highest point, creating leverage and a higher possibility of catastrophic failure.
We often face trees that have had large areas removed by a neighbor who doesn't want limbs on their property, resulting in a 'flat' side to the tree. This allows wind into the canopy to exert pressure on joints and structures not designed to withstand these loads. This can cause the loss of a major structure that provides integral parts of a canopy, leaving the remaining areas 'open'. We often meet situations such as this, as seen in the comparison photos shown above, that require a structural reduction to part or all the remaining canopy so that it can be blended back together to form a better wind diffusion unit. Remember, the primary objective of a plant is to capture light, and when the tree loses a portion of its canopy, other areas will take advantage of this new source of direct sunlight and grow into and toward that source. This can lead to over-extended limbs that put massive pressure on their attachments to the main tree column. These areas must be carefully reduced to limit their flexion while other canopy areas catch up to form a better shape and share wind loading more evenly.
If you have any doubts about the correct pruning needs for your tree to make it 'fit' into its urban environment, please consult at least a Certified Arborist, not just someone who calls themselves an arborist who is essentially anyone who chooses to work with trees. Each Certified Arborist will carry an up-to-date certification card with their identification number shown on it that can be referenced against a form of photo ID. No card, no use!
Is My Tree Healthy and Safe?
This is one of the commonly asked questions when we attend a client’s address to assess a tree that is experiencing problems. There are two elements to a tree’s health that we look at, physiological health and structural stability. Physiological health incorporates the vascular system’s flow from root to shoot providing the canopy and its leafage with the nutrient when harnessed with sunlight to photosynthesize, produces carbohydrates and starches for energy needed to sustain its structure. Structural stability is the ability of the tree to maintain its position in achieving its primary goal of light capture. That stability is created through the integrity of woody fibers laid down in previous years that provided vascular conduits no longer used but now performing both rigidity and flexibility.
We have two methods by which each of these vital components of the tree’s health can be measured. Physiological health is measured by assessing the tree’s effectiveness in using red light during the photosynthetic process and is called chlorophyll fluorescence testing. The structural stability of the tree is measured by performing a scan through the relevant cross-section using soundwave technology known as sonic tomography.
To perform a chlorophyll fluorescence test on a tree, a sample of twenty leaves anywhere within the canopy will give us the physiological efficiency of the tree’s photosynthetic process. The measurement involves light darkening a small area of the leaf’s surface for approximately 45 minutes after which the aperture is opened, and a one-second burst of red light is passed into the photosynthetic cell. This measures the efficiency by which red light is used within the photosynthetic process before any signs are outwardly shown by the tree. This process will alert us to the direct physiological condition of the tree and how efficiently it is able to photosynthesize and create energy for its system. This is an extremely efficient way in which we can tell whether the tree is suffering from stress prior to pruning or any major work that may need to be carried out.
To perform a tree scan, soundwaves are sent from sensors positioned around the tree’s circumference with an electronic hammer tapping each sensor point in succession. Any pathogen that has entered the woody structure and started to cause fiber separation during the process of rot will produce air pockets between these fibers through which the soundwave has to travel. The soundwave speed will alter depending on the extent of fiber separation and the gap through which the soundwave now must travel, relevant speed is color-coded and sent back to the computer. The tree can be mapped to show the different degrees of fiber separation and where the potential areas of pathogenic rot are located. The scan enables us to carry out either structural reductions or general pruning to make sure that high-loading areas, where there is evidence of fiber degradation, are lessened and the chances of failure are mitigated substantially.