What’s new in natural yards? May 2017

Two weeks ago, the City of Madison made a change to how it will handle emerald ash borer (EAB).

Previously, the City had decided that it would not give any ash trees that were already unhealthy a treatment to protect them from EAB. What the City did not make clear to residents was that any tree located under a power line would be considered unhealthy, regardless of what condition it was actually in.

In thinking about the impact that this decision would have, the City realized that older neighborhoods in Madison, which have overhead power lines, stood to lose a lot of trees, while newer neighborhoods, in which the lines are underground, would be able to keep their trees. Recognizing the immense value of trees to nearby residents – due to trees’ ability to clean the air, reduce flooding, moderate temperatures, increase property values, and so on – the City concluded that it would not be fair for some neighborhoods to lose a lot of trees while others are able to keep their trees.

Based on this conclusion, Madison’s Common Council voted that ash trees under power lines should be treated to protect them from EAB, provided that they meet the City’s other requirements for treatment.

The full text of the resolution can be read here.

What’s new in natural yards? May 2017

What is this week?

Recognizing the importance of trees in our neighborhoods, the city of Madison has declared the coming week to be Arbor Week. The following resolution was adopted last month:


WHEREAS, the City of Madison has been a Tree City USA for 28 years; and

WHEREAS, children and youth living in greener neighborhoods are healthier; and

WHEREAS, trees give us oxygen, clean the air, and filter air pollutants; and

WHEREAS, trees in our neighborhoods increase property values; and

WHEREAS, the continued planting and care of trees in our city shall provide the same benefits for the present and future residents of Madison.

NOW, THEREFORE, BE IT RESOLVED that the Mayor of the City of Madison, Wisconsin, does hereby proclaim the week of April 30 through May 6, 2017 as ARBOR WEEK in the City of Madison, and urges everyone able to observe this week to plant trees and to participate in programs that the sponsors of Arbor Week may provide.

What is this week?

What is a tree worth?

There are several ways of answering this question.

First, as described in an earlier post, a mature tree can add thousands of dollars to the value of a property, in addition to saving the occupants money on utility bills.

Second, trees provide measurable value to a city through their role in absorbing and filtering stormwater, cleaning the air, and improving human health. New York City has calculated that its street trees are worth $122 million a year, and that every dollar spent on improving this urban forest generates a return of $5.60.

Third, a recent study found that adding ten trees to a city block produces benefits to the health of nearby residents that are equivalent to giving those residents an extra $10,000 a year of household income.

Urban trees have also been found to decrease childhood obesity, improve ADHD symptoms, deter crime, reduce traffic accidents, improve memory, speed recovery from illness, and even lower the rates of suicides and premature births.

Trees are usually the last thing to be considered in development projects, getting treated as nice-to-have amenities that are added at the end if there’s any money and space left. Experts on urban trees, however, say that the presence of trees in our neighborhoods is crucial to our wellbeing. Their true value, these experts say, is effectively incalculable.

What is a tree worth?

Why do leaves change color in the fall?

Fall has arrived in the northern hemisphere, and leaves will soon be changing colors. We’ve all heard why they do this: the green color is created by chlorophyll, a substance key to photosynthesis, and when the chlorophyll is lost at the end of the summer, leaves reveal their true colors.

Now, some scientists think this story is wrong. They believe that, instead, trees actively work to create their brilliant fall colors.

Why would trees do this? One challenge plants face in life is being attacked by insects. To combat this, plants produce a variety of chemicals that deter insects from eating their leaves or burrowing in their bark.

Just as chlorophyll creates a green color in leaves, some of these insect-deterring chemicals create bright yellows, oranges, and reds. The more chemical a tree stores up, the more vibrant the colors.

In the same way that a male bird puts on showy colors in spring to prove that he is a healthy mate, trees display dramatic autumn hues to tell insects, “I’ve invested in defenses against you; don’t bother trying to attack me.”

Colorful fall leaves may therefore be not only a defensive strategy, but a method of communication – providing further evidence that plants are intelligent.

Why do leaves change color in the fall?

Where does rain come from?

Rain occurs when water vapor in the air condenses and falls back to earth.

But how does that water vapor get in the air in the first place? Half of it gets there by evaporating directly from bodies of water, like lakes and rivers.

The other half is put there by trees. This is because trees act like giant upside-down funnels. First, they absorb water from the soil with their roots. This water is then transported up through the tree to its leaves. From there, the water evaporates out of the leaves and into the air, as part of the process of photosynthesis.

This means that areas with lots of trees have more water vapor in the air than areas with few trees. When there’s more water vapor, rain is more likely to occur. Thus, trees affect precipitation patterns as well as temperatures.

Amazingly, this explains why rainforests are so rainy!

Where does rain come from?

What does pruning do to a tree?

Trees need their leaves in order to produce energy through photosynthesis. In order to produce energy most efficiently, they make intelligent decisions about where to place their leaves.

Sometimes, a person believes that a tree’s branch is in an unintelligent place, and responds by cutting the branch off, a practice generally known as pruning. This leads to three negative effects.

First, the tree loses some of its energy-producing capacity, which negatively affects its ability to support itself and remain healthy.

Second, a tree normally responds to the sudden loss of a branch that was productively photosynthesizing by growing a new branch in the same place. This allows the tree to continue taking advantage of the patch of sunlight it had found. However, the regrowth typically leads to a recurrence of whatever perceived problem led the person to cut off the branch in the first place. In addition, these secondary branches are always weaker than the original branch they are replacing. Thus, pruning tends to lead to a reappearance of the original problem, plus additional problems.

Finally, pruning – especially of large branches – leaves trees with open wounds that take a long time to heal. This makes the tree vulnerable to infection, creating even more opportunity for new problems that harm and weaken the tree.

Pruning rarely solves any problems with trees, and often causes additional problems. Training is a more effective way of dealing with branches in undesirable places – as is understanding that trees have spent millions of years learning how to grow, and our perception of what is an undesirable location for a branch may simply be misguided.

What does pruning do to a tree?

What happens when a tree is cut down?

As mentioned in the previous post, trees are like icebergs: a significant amount of them is underground. And from a tree’s perspective, this hidden root system is more important than the leaves and branches.

The first thing to understand, then, is that when a tree is cut down, it is not dead. The roots are still alive, and they can and will regrow. For thousands of years, it has been a common forestry practice to cut down trees, let them regrow, and then harvest them again. This technique is called coppicing.

However, a tree faces two challenges in regrowing. First, it starts out with no leaves, and thus no capacity to produce food for itself through photosynthesis. It must regrow using the energy already stored up in its roots. Second, the tree must grow new leaves and branches from its remaining aboveground surface area. This means that the closer to the ground the stump is cut back, the harder it is for the tree to regrow.

This means that if a tree is seriously damaged in a storm, the best thing to do is leave it alone. As long as the roots are in the ground, the tree is still alive and well, and will grow back. Causing more damage to the tree by cutting back the remaining trunk makes it more difficult for the tree to regrow, and increases the chances that it will not survive.

The second thing that happens when a tree is cut down – assuming that it is immediately fed into a woodchipper, rather than being left to decompose into the soil – is that all the carbon that was stored in the tree is rapidly released into the atmosphere. A middle-aged tree might be holding one ton of carbon. Releasing this carbon contributes to climate change.

Finally, cutting down a healthy, mature tree can knock thousands of dollars off the value of a residential property, in addition to driving up utility bills. It’s wise to factor in these hidden costs when considering the expense associated with cutting down a tree.


What happens when a tree is cut down?

How do trees protect themselves from falling over?

All living things behave as though they want to continue living. Plants use a variety of strategies to acquire resources and avoid hazards.

One hazard faced by plants – especially large, long-lived plants like trees – is falling over. Trees have three main strategies for avoiding this life-ending event.

The first, and most well-known, is that trees are able to move with the wind. By bending, instead of standing stiffly, trees are able to absorb the force of the wind without being harmed.

Being flexible, however, comes at a cost of structural strength. A large tree cannot have a flexible trunk, because it would not be able to hold itself up. Thus, trees employ a second strategy in parts of their structure that need to be strong. Over its lifetime, a tree learns which way the wind usually comes from, and strengthens itself in strategic locations. It does this by producing extra cellulose – the tough material that distinguishes plant cells from animal cells.

Finally, trees protect themselves from falling by tightly gripping the soil with their roots. Anyone who has ever tried to pull up a dandelion, or even a handful of turf grass, knows how tenaciously roots hold a plant in place.

A plant’s root system can be the same size as, or even larger than, the aboveground part of the plant. This provides a powerful counterbalance to any forces that may be trying to tip the plant over. Thus, when arborists say that a tree is unbalanced, they are just trying to scare homeowners into paying them money.

Even the healthiest, most structurally sound tree could fall over in a severe storm. Conversely, it is very rare for a tree to suddenly topple on a clear day. Overall, about 30 Americans a year are killed by falling trees or branches – a vanishingly small risk in exchange for all the benefits trees provide, even after they’re dead.

How do trees protect themselves from falling over?

How does natural gardening affect my utility bills?

In the Eastern states, including Wisconsin, approximately 30% of household water usage goes to keeping lawns alive. Using water systems, or landscaping with plants that require less supplemental water, can greatly reduce the monthly utility bill.

In Western states, where up to 60% of household water usage is spent on lawns, water systems are often not legal. However, the desert states are home to a wonderful variety of drought-tolerant native plants. Landscaping with these species conserves water, reduces monthly expenses, and restores a unique sense of place.

Landscaping choices can affect heating and cooling bills too. A mature shade tree can significantly reduce summertime temperatures in a neighboring building, while letting sunshine in to warm the building in colder months. A row of trees or bushes can block winds that pull heat out of a home in winter.

In summer, even smaller plants that don’t provide shade can cool a home through their processes of exchanging water with the air. A yard full of healthy plants is like a green air conditioner!

Finally, a natural yard can often be cared for with minimal use of motorized equipment, which saves gas and electricity. Letting nature work for us can improve our comfort and quality of life, while keeping money in our pockets.

How does natural gardening affect my utility bills?

Do natural yards encourage crime?


A study conducted in Chicago found that apartment buildings with more trees had lower crime. The buildings all belonged to the same housing project, all had the same architecture, and all had residents with similar characteristics. The researchers proposed two possible reasons for the reduction in crime.

Trees deter crime. That is, trees encourage potential criminals to commit a crime somewhere else. In buildings with trees, residents spent more time looking out their windows and sitting outdoors. People are less likely to commit a crime where there are observers.

Trees reduce crime. That is, trees lead potential criminals to not commit a crime at all. Studies show that nature helps us feel better, reducing our aggression and making us less likely to engage in antisocial behavior. People are less likely to commit a crime when they are in a positive mood.

Natural yards, with or without trees, draw our gaze and make us feel good. If the researchers’ theories for why trees reduce crime are correct, then natural yards also reduce crime.

Do natural yards encourage crime?