Water management is crucial. Without smart planning and greenery architecture, there
soon won’t be any trees that provide ecosystem services for people living in the city. And,
as everything is interconnected, trying to fulfill the 3-30-300 rule goal, it brings all other
benefits altogether as well.
What is the 3-30-300 goal?
There has been a lot of talk about the 3-30-300 rule for urban greening, and it’s fascinatingly simple:
3 trees
Everyone should see at least 3 big trees from their home, workplace, or school.
Seeing greenery leads to short-term recovery from stress or mental fatigue, faster
physical recovery from illness, and long-term overall improvement on health and
well-being. The trees should be of a significant size.
30% canopy cover
Every neighborhood should be covered by at least 30 % of trees. There have been
found positive associations of green spaces on early childhood development scores
for both total vegetation and for tree cover. Tree canopy has been correlated with a
range of public health effects, with living in greener environments associated with
better mental health and lower all-cause mortality. Also, higher canopy cover
improves sleep patterns.
300m to a quality green space
Everyone should live up to 300 m far from the high-quality greenery (park).
Proximity to green spaces is important for preventing cardiovascular morbidity and
diabetes. Easy access to high-quality green spaces promotes more regular use of
these areas. A safe 5-min walk, or 10-min stroll is often mentioned as a threshold
for frequent recreational use. The Office of the World Health Organization
recommends a maximum distance of 300 m to the nearest green space of at least
one hectare in size, as it encourages the recreational use of green space with
positive impacts for both physical and mental health
Urban greenery provides a wide range of ecosystem (or ecological) services. Among the
most commonly mentioned are cooling functions, atmospheric carbon capture, and
biodiversity. However, these also include aesthetic and recreational functions, the capture
of dust and other air pollutants, and flood protection. For greenery to perform all these functions, it must be healthy and have sufficient nutrients
and, above all, water. Why?
Trees, like animals or humans, are living organisms. Unlike them, however, they cannot
escape unfavorable conditions. Instead, they have developed various adaptation
strategies that allow them to overcome environmental challenges. Different species have
different strategies, but they all share one thing in common: they cannot tolerate
everything. Every tree has its tolerance limits, and urban environments are so extreme in
many respects that a large portion of trees—sometimes even the majority in certain areas
—experience significant stress. This stress leads to depletion and loss of vitality, ultimately
resulting in death. Consequently, trees in urban settings have significantly shorter lifespans
than those in their natural habitats.
Lack of water
One of the most significant stress factors for urban trees is lack of water. There are many
reasons for this: compacted soil that cannot effectively absorb and retain rainwater,
impermeable surfaces that prevent water from reaching the soil, or soil salinization, which
prevents trees from absorbing water even when it is present in the soil.
Tips:
- Don’t let dogs mark trees.
- Sprinkle icy sidewalks with sand instead of salt
- Build hard surfaces from permeable materials, let rainwater enter the greenery (not drainage).
How does it all work, and what happens when they don’t have water?
Trees, as mentioned, need nutrients found in the soil. To transport these nutrients to the
trunk, branches, and leaves (or needles), they need water in which the nutrients are
dissolved. Water flows upward through transport pathways, and the tree determines where
to send the nutrients based on where they are most needed. The flow of water through the
tree trunk is a physical process. Trees do not have muscles or pumps to facilitate this.
Instead, transport relies on the difference in moisture between the soil (where there is
more water) and the air (where there is less water). The less water is in the air (the
hotter air is), the stronger is a force causing water loss.
After the tree absorbs water through its roots and distributes the necessary nutrients to its
organs, the water leaves the tree through microscopic openings in the leaves called
stomata. The water exits the tree as water vapor. For liquid water to become vapor, it must
be heated. The energy required for this is taken from the leaf surface, which cools as a
result, and the energy is carried away into the atmosphere with the water. In this way, the
tree cools its surroundings by losing water. These stomata also serve another crucial
function—they allow the tree to absorb carbon, enabling it to grow.
What happens if there isn’t enough water in the soil? The tree recognizes it and closes its
stomata to prevent water from escaping. It needs to conserve the water within its tissues to
avoid wilting. However, by doing so, it also stops absorbing carbon from the atmosphere
and distributing nutrients. The tree ceases performing its ecosystem functions. It stops
cooling its surroundings, capturing carbon, purifying the air, and, if its leaves scorch (since
it can no longer cool them), it also loses its aesthetic function. So: during hot summer
days, irrigate your trees.
Are you looking for ways to introduce new greenery?
