Low Impact Development: Best Management Practices

Storm water runoff is a significant environmental problem for the Los Angeles area, as it contributes to ocean pollution and exacerbates drought conditions. Low impact development (LID) is a development strategy that seeks to manage storm water runoff more effectively by dealing with runoff water on site, rather than trying to channel the water away as quickly as possible.

Low impact development principles embrace and utilize a variety of specific techniques and structures to accomplish this task. The United States Environmental Protection Agency uses the term “Best Management Practices,” or BMPs, to refer to some of the best-suited techniques and structures, for reducing the amount of surface pollutants carried by storm water runoff.

Vegetated Swales and Rain Gardens

One of the simplest ways engineers and city planners can help reduce runoff water is to break up extensive paved areas with small “islands” of vegetation. This allows the plants to absorb and store the water, before ultimately releasing it back into the atmosphere. Most often, these areas are installed in low-lying areas, to take advantage of the natural lay of the land.

Rain Cisterns

Rain cisterns are valuable tools for managing rainfall and reducing an area’s runoff water. By storing rainwater, rain cisterns transform the surplus water from a liability to an asset. Cisterns collect the water pouring out of downspouts, thereby reducing the amount of storm water filling sewers and collecting pollutants. Additionally, they serve as a source of clean water, suitable for watering lawns, irrigating crops and other outdoor uses.

Green Roofs

At first glance, the notion of sod-covered roofs (pictured above) seems like a joke. However, upon closer examination, it becomes obvious that the concept has many merits. The grass absorbs most of the rainfall landing on the roof, which helps to address runoff water problems, and it helps to keep homes cooler in the winter, courtesy of the insulating value of the plants and soil. Additionally, as the grass transpires – drawing water from its roots and releasing it into the atmosphere – it lowers the local temperature further.

Permeable Pavers and Pavement

Some places simply require extensive paved areas; shopping malls, municipal centers and grocery stores are rarely feasible without large parking lots and pavement. Fortunately, engineers have devised a solution for these areas, called permeable surfaces. Unlike traditional surfaces composed of solid concrete or asphalt, permeable pavements allow water to trickle through them, rather than run across the surface.

Curb Cuts and Bump-Outs

Curb cuts are a brilliantly simple solution to storm water. Whereas conventional curbs contain water, preventing it from reaching the vegetation and soil a few short inches away, curbs designed with low impact principles have periodic gaps cut into them. These cuts allow water to pass through to the planted areas, reducing the overall volume of water flowing along the curb, and use it in the immediate vicinity to water plants and trees.

Tree Installations

Simply planting medium or large canopy trees along sidewalks and roads drastically reduces the amount of runoff water in the area. Trees absorb water from the soil, use what they need and allow the excess to evaporate into the air via small holes in the leaves. This process not only manages runoff water, but it provides all of the other benefits trees do, such as shading the area, cooling the environment through the process of transpiration, improving the aesthetics of the area and raising property values.

curitiba street

Trees: A Neglected, but Essential Component of Municipal Infrastructure

Nearly 6,000 years ago, in what is now Iraq, the Mesopotamians took an important step that would forever change the world: They turned the region’s well-worn footpaths, born of countless generations’ foot traffic, into the first stone-paved roads. In doing so, they enabled goods and services to flow easily through the region, and the civilization prospered. Many years later, humans civilization is utterly dependent on these and similar resources.

Today, we call these types of common goods “infrastructure.” Other examples include canals, reservoirs, dams, bridges, and tunnels. They are those things that make life easier for all citizens, and are often provided and maintained by local municipalities.

Gray vs. Green

Infrastructural assets are often divided into two different classes. “Gray” infrastructure includes those things made from concrete, plastic or steel, such as buildings and transportation routes. On the other hand, “green” infrastructure refers to living entities, such as rain gardens and street trees.

While the two classes have obvious dissimilarities, they provide similar infrastructural value, often at a lower cost to the taxpayer. For example, most major municipalities must implement and maintain a system for dealing with storm water runoff – a task that can be accomplished with gray assets (for example, a sewer system), green assets (such as rain gardens, street trees or wetlands) or – as common sense dictates – a combination of both gray and green solutions.

The Advantages of Incorporating Green Infrastructure

While civilization is unlikely to ever jettison sewers, bridges and dams completely, street trees, wetlands and other green infrastructure projects offer numerous benefits that traditional strategies do not. For example, trees and plants improve the quality of the air and reduce local temperatures through the process of transpiration. Virtually any tree installation will help reduce the area’s runoff water, but projects specifically designed to divert, absorb or store water – such as rain gardens – are especially helpful in this regard.

Additionally, while roads, dams and bridges usually fail to improve the aesthetics of an area, living plants and trees almost invariably make an area more beautiful. This increased aesthetic appeal translates to greater demand for local properties, which increases home values.

Empirical Evidence

It is important that green infrastructure projects are elegantly planned and suitably maintained. One challenge to implementing natural solutions is the perception that trees are an expensive and damaging resource, which will cause municipalities to pay more than they will save.

According to a recent study, nothing could be further from the truth.

Conducted by the American Society of Landscape Architects, American Rivers, the Water Environment Federation and ECONorthwest, the study examined almost 500 different green infrastructure projects in the United States. The researchers concluded that the majority of the projects (75 percent) cost the same or less to implement and maintain as similar, gray infrastructure projects did.

The study’s authors also determined that green infrastructure projects help cities use less energy and promote greater health among their citizens. This occurs as trees and their roots help filter bacteria and other pollutants from local waterways.

Additionally, many city managers and strategic planners worry that trees and plants will damage hardscapes, through the destructive action of their roots. However, as explained in a 1998 paper by Professor Kim D. Coder of the Warnell School of Forestry Resources, many problems blamed on trees are more appropriately placed at the feet of flawed hardscape designs.

From the study:

“Many infrastructures that concentrate and transport required resources for people are poorly designed and built to withstand natural processes over time. These engineering flaws are exacerbated by opportunistic tree roots colonizing new resource spaces.”

Simply put, better designed sidewalks and subterranean features will result in less damage from tree roots.

The Takeaway

The bottom line is that distinguishing between gray and green infrastructure is not always helpful – they both provide value for citizens and require resources to maintain. Moving forward, stakeholders must consider the empirical evidence and proceed deliberately, carefully considering all available strategies for coping with municipal challenges. Some solutions are better met with the help of trees, while others are more appropriately addressed through the construction of traditional infrastructural components.

elm avenue

Street Trees: Separating the Superlative from the Second-Rate

While few disagree with the need to increase the number of trees lining the nation’s cities and streets, it is important that such advances proceed deliberately, in accordance with well-conceived plans. While it is true that most trees provide tangible, quantifiable benefits, they also require resources to maintain.

Selecting the wrong trees for a given location not only fails to maximize the potential benefits — which a better species could provide — but it increases the likelihood of negative consequences. If a city plants labor-intensive trees, maintenance costs chip away at the realized savings; likewise, a city that plants trees with invasive root systems must allocate sufficient funds to repair damaged sidewalks and other components of the infrastructure.

The ideal trees for a given location vary greatly, so policy makers are wise to consult with an industry expert before designing a tree plan and selecting the species, which will make up the planting. Different species thrive in different hardiness zones and under different hydrological conditions.

Nevertheless, most street trees have a few common characteristics. None of these traits is singly essential, but the more of the characteristics present in a tree, the more effective it will perform as a street tree.

Reasonable Roots

Tree roots are opportunistic, and they can exacerbate any faults or flaws present in the surrounding hardscape. Given enough time, even relatively modest-sized trees can raise sidewalks or compromise foundations. Accordingly, it is important to plant trees that have manageable root systems. Avoid installing species that produce large surface roots, such as Blackwood acacia (Acacia melanoxylon), Norway maples (Acer platanoides) and camphor trees (Cinnamomumcamphora) in areas adjacent to concrete features. Instead, opt for species that are unlikely to cause such problems, such as Pacific wax myrtles (Myrica californica), Pacific dogwoods (Cornus nuttallii) and madrones (Arbutus menziesii).

Suitable Stature

One of the most important considerations regarding street tree selection is the mature height and spread of the crown. Trees that outgrow their allotted space may end up rubbing against buildings, blocking the right-of-way and growing dangerously close to utility lines. The pruning necessary to mitigate these problems increases maintenance costs, thus reducing the economic impact of the tree. Several small species, including western redbuds (Cercis occidentalis) and Macnab cypresses (Hesperocyparis macnabiana), have many of the attributes one would want in a street tree, while usually remaining under about 25 feet or so in height. Of course, there is nothing wrong with planting tall species in areas without overhead obstructions; however, the crown’s spread – horizontal growth – is still an important consideration for street plantings. Trees with a columnar growth habit are often helpful in this regard, such as Columnar Sargent Cherries (Prunus sargentii ‘Columnaris’), which grow up to 35 feet high, but usually have a crown spread of less than 15 feet.

Limited Labor Liabilities

While the cost benefit ratio of many street trees is a net positive, selecting species that require frequent maintenance increases the odds of ending up in the black. For example, wild-type mulberries (Morus spp.) and sweetgums (Liquidambar styraciflua) produce copious fruit, which often necessitates frequent attention. Either select cultivars that produce no fruit – such as “Rotundiloba” sweetgums (Liquidambar styraciflua ‘Rotundiloba’) – or select lower-maintenance species entirely. Additionally, drought tolerance is an important consideration for all southern California tree installations. Some species with exceptional drought tolerance include scrub oaks (Quercus dumosa) and “Shademaster” honeylocusts (Gleditsia triacanthos var. inermis ‘Shademaster’), which although unsuitable for use near sidewalks, require little maintenance and allow enough light penetration that grass grows well underneath them.

Superb Solar Solutions

Some deciduous trees provide two different solar-related benefits at opposite ends of the calendar. During the summer, they provide dense shade, but in the winter, when their leaves carpet the ground below, these trees allow the warm rays of the sun to penetrate to ground level. The maidenhair tree (Gingko biloba) – especially the Autumn Gold cultivar (Gingko biloba ‘Autumn Gold’) – provides a great example of this. In fact, gingko trees are not only “solar friendly” and capable of surviving the indignities of urban living, their leaves turn marvelously yellow in the fall. Unlike normal (female) maidenhair trees, the Autumn Gold cultivar does not produce the smelly fruit, characteristic of the species.


Whether by runoff water, soil contamination or through the air, street trees exist under the constant assault of pollutants. These substances stress many trees, causing a reduction in vigor, often preventing them from thriving. Ideally, trees planted along streets should be very tolerant of pollution – especially air pollution, which constantly bathes the trees in harmful chemicals. Hedge maples (Acer campestre) are particularly well suited for urban environments, although they thrive best in moist, cool locations. Hedge maples not only tolerate pollution well, but they rarely produce roots that cause problems, nor do they struggle with compacted soils. Additionally, hedge maple leaves are often brilliant gold in the fall, making them a gorgeous addition to any street.

mushrooms on tree

Know When to Get Help: 6 Concerning Signs of Tree Problems

Tree professionals commonly encourage property owners to consult a certified arborist whenever confronted with a tree-related problem; but, while sound, this advice is incomplete. Lacking the training of an arborist, property owners often fail to notice problems that are glaringly obvious to experienced eyes.

It is impossible to list all of the possible symptoms that indicate a tree is in trouble, but the following are several of the most common warning signs. Seek professional advice anytime you observe any of the following signs.

Root Movement

Trees whose roots begin pulling lose from the soil or lift the surrounding substrate are in imminent danger of toppling. This is especially true of trees that suddenly shift position. This can occur because of excessive rainfall or disease in the tree’s roots. In fact, it is a good practice to have all leaning trees inspected, even if the ground at their base looks solid.

Sudden Limb Drop

Trees that jettison limbs seemingly “out of the blue” are often at risk of dropping further limbs or failing outright. Sometimes these failures occur when trees draw too much water from the ground, but they can also occur because of cracks, decay or improper pruning practices.  Traumatic events that cause trees to fail – such as high winds or ice storms — are not necessarily indicative of disease or decay, but it is wise to have such trees inspected to ensure they are not at risk of further failure.

Canopy Die Back

Trees that begin shedding leaves prematurely are said to be experiencing “dieback.” Dieback can occur in discrete locations within the tree or it can be spread throughout the canopy. The causes of dieback are not always serious, as relatively minor maladies such as drought stress can cause trees to drop their leaves. However, it is always best to determine the cause of the dieback, and begin taking steps to support the tree, as diseases and pests can also cause the symptoms.

Fungal Bodies

Mushrooms growing from the trunk, roots or major branches of a tree can indicate extensive fungal growth within the tree. While some fungi can eat away at the wood of a tree, compromising its structural integrity, not all fungi are pathogenic — some live harmlessly on and within the tree’s wood. Nevertheless, laypersons are likely to struggle trying to arrive at a positive identification, so professional guidance is crucial.

Cavities or Hollows

Many hardwood species become hollow as they age. While trees can often lose a significant portion of their interior wood and remain structurally sound, thorough examination of the tree is required to determine the tree’s likelihood of failure.  To err on the side of caution, always have large hollows checked by a competent tree professional. If the sides of a cavity appear to curl inward, it is likely that significant decay lurks within.

Cracks and Fractures

Unless they are incredibly minor, cracks located in branches or trunks indicate an immediate danger. Vertical cracks are slightly less troubling than horizontal cracks, but all such flaws are sure to fail – the only question is when. You will need professional help removing the branch or tree, but it is also important to determine why the crack occurred in the first place.

bitch bark

The Bark Barrier

While a few traits characterize the bark of all trees, these protective coverings are remarkably diverse. As with other tree components, such as leaves, branches and roots, every bark is adapted to suit its environment and the life history of the species.

Although bark hardly seems as exciting or fascinating as so many other aspects of trees, this complex tissue, comprised of many layers of both living and dead cells, tells an intriguing tale, to any curious enough to listen.

Catch-All Definition

Bark is actually an informal term that refers to several of the outer layers of trees and other woody plants. Specifically, it includes all layers occurring outside of the cambium – namely, the phloem, phelloderm, cork cambium and cork. This outer layer of dead cork cells comprises most of what people think of as “bark.”

Whereas the cambium is a lateral meristem (area of cell division and growth) that produces the xylem (wood) and phloem, and it is largely responsible for the tree’s increase in girth, the cork cambium is a secondary lateral meristem, which produces the cork and phelloderm.

The inner layers of bark – specifically the phloem – are responsible for transporting chemicals and calories through the tree. Accordingly, damage to this layer can cause great stress for a tree. This is one of the reasons trees are easily killed by “girdling” – a technique used for deliberately killing trees in which a wide swath of bark is removed around the trunk’s circumference.

Slipping into a Stronger Skin

Bark production is resource intensive, meaning that there is a very good reason trees produce it. After all, plenty of green plants thrive in the modern landscape, bereft of bark.

One key distinction is that trees are perennial plants whose lifecycle depends on lasting for many years – sometimes many hundreds of years. By contrast, many herbaceous plants, grasses and shrubs are annuals that die off each year – producing such a robust outer covering is a frivolous use of precious resources for these ephemeral species.

Bark protects the interior and vulnerable portions of the tree, just as skin or scales protect animals. It reduces water loss from the wood and deters some predators and pests. Some species have even developed spines and thorns that confer additional protection.

Bark Reflects Habitat History and Evolutionary Patterns

Many trees have bark that clearly reflects the specie’s survival strategy. For example, the deeply fissured bark of black oaks (Quercus velutina), tuliptrees (Liriodendron tulipifera) and other species that inhabit areas with cold winters is an adaptation that provides protection from freezing temperatures.

However, the bark of some trees reflects the evolutionary history of the species more than it serves a current need. For example, beech trees (Fagus grandifolia) arose from within a largely tropical lineage, native to habitats with saturated atmospheres. Epiphytic plants abound in such locations, where they have grown on the trunks of trees for millennia. To prevent the plants from colonizing the trunk, the ancestors of beech trees developed smooth, thin bark, making it hard for the plants to obtain a secure “grip.”

Animal Assaults

Bark provides a number of important resources for various animals. Porcupines, beavers and many other mammals munch on the delicate inner bark and cambium of aspens (Populus tremuloides), beech and basswood (Tilia sp.) trees. Countless insects and other arthropods take shelter under the bark of trees, using it to not only shield themselves from predators, but to provide them with a thermally appropriate microclimate.

Humans also derive resources from tree bark. Aspirin is derived from chemicals present in willow (Salix sp.) bark, while quina trees (Cinchona sp.) gave humanity quinine – an important malarial medication.

Incredible Examples

A number of species produce truly unique bark. Check out the following links to learn about some rather spectacular species and the bark that helps them survive.

California’s Fall Color

Contrary to popular perception, California does change colors during autumn. While evergreen conifers may dominate portions of the state, the green leaves of many broadleaf species slowly transition from green to yellow, orange or red from September through December. In fact, because of the state’s unique combination of climate and geography, California offers some of the finest foliage-watching opportunities in the country.

Why Leaves Change Colors

Green plants derive their color from a pigment called chlorophyll. By combining chlorophyll with carbon dioxide, water and sunlight, the plants produce sugars, which form their primary food source. However, as the days become shorter and the nights become longer, trees produce less and less chlorophyll. Without chlorophyll to turn the leaves their characteristic green color, brown, yellow, orange or red colors become visible, courtesy of the other pigments and structures of the leaves. Around the same time, the leaves begin building up a layer of cells – called the abscission layer — which halts the flow of resources to and from the leaf. The abscission layer also weakens the attachment point of the leaves, allowing them to eventually fall off.

Because the leaves of different tree species have different chemical compositions and structures, they exhibit different colors during the fall. For example, most dogwood leaves turn magenta or burgundy, while hickory leaves turn a brilliant gold. Other species, such as the beautifully gaudy maples, may turn a variety of colors; a single tree may even bear leaves of many different colors. Some of the most remarkable specimens are cultivars that have been artificially selected for brilliant fall color.

Factors Influencing Color

Not all autumns are created equally. Some autumns seem to be painted with eye-popping colors, while others tend toward more muted tones. Differing environmental variables, such as temperature, windfall and precipitation, cause this year-to-year variation.

In general, cool, yet sunny, days and cold nights often elicit the finest colors that local trees have to offer. By contrast, warm autumn temperatures typically reduce the intensity of fall colors. Droughts are similarly detrimental to fall color (a particularly important variable in California), while moist soils in the fall enhance fall colors. Poor weather, such as torrential rain or high winds, often causes the trees to lose many of their leaves, which effectively shortens the duration of the fall colors.

Searching for Fall Color

Adventurous souls often enjoy taking road trips to enjoy the fall color. In most locations, timing is critical for catching the colors at their peak. Arrive a week too soon, and the colors will still be developing; arrive one week too late, and many of the trees will have jettisoned their leaves for the year. Fortunately, this is not the case for much of the Sunshine State.

California’s geography provides a unique advantage for viewing fall color. In fact, California tree lovers often have a better chance to catch peak fall colors than New Englanders do. The timing of the New England fall color change varies largely with latitude; the farther south a given location is, the later the leaves begin to change. Accordingly, each given latitude has a narrow window of peak color.

By contrast, at a given latitude, Californians can view trees at a wide range of altitudes. This variation in altitude affects the timing of the color change just as variation in latitude alters the timing of New England’s color change. This means that while standing at the bottom of the Sierra Nevada Mountains, you can see the color change progressing from the top of the tree line towards the bottom. While the entire slope is unlikely to change at the same time, some part of the slope is likely to be clad in glorious colors during a large portion of autumn.

If you want to see the best fall colors that the state has to offer, check out this list from the California Department of Parks and Recreation. You can also check out to see photos of the current colors of various locations around the state.

Planting for Fall Color

You do not have to chase fall colors to enjoy crimson, gold and blaze colors; you can grow your own colors in your yard. Many common species and cultivars produce stunning fall foliage. By planting several different varieties, you can create gorgeous fall landscapes. It is generally wise to rely heavily on native species, but you can use also use suitable exotics to incorporate colors and textures unseen in the natural landscape.

Some California natives that display good fall color include:

  • Vine MapleAcer circinatum

  • Mountain MapleAcer glabrum

  • Big Leaf Maple Acer macrophyllum

  • Quaking AspenPopulus tremuloides

  • Black CottonwoodPopulus trichocarpa

  • Oregon White Oak Quercus garryana

Several non-native, yet hardy species (which are unlikely to become invasive) include:

  • Gingko TreeGinkgo biloba

  • Pin OakQuercus palustris

  • Black GumNyssa sylvatica

  • Red MapleAcer rubrum

  • Japanese Maple Acer palmatum

Be sure to check out this list of trees by the Arbor Day Foundation. It details nine different species that usually produce excellent fall color, are unlikely to spread and are suitable for planting in a wide variety of locations.

How Much Is My Tree Worth?

While it is obvious that trees have considerable ecological, societal, psychological and aesthetic value, it is often difficult to quantify this value. While property owners can estimate the general value of a given tree by using various calculators or formulae, determining a precise figure requires the services of a qualified tree professional.

Different Types of Value

Property owners may be interested in the value of their trees for many different reasons. They may have experienced storm damage and require guidance for making claims – this is known as the replacement value of a tree. Determining the replacement value of a tree requires comparing the tree in need of replacement with the market value of a comparable specimen. This is most commonly applied to small- and medium-sized trees, as it is rarely realistic for property owners to replace large specimens.

Alternatively, property owners may be planning to install new trees and want to know how they will affect the resell value of the property. Determining the real estate value of a tree (or group of trees) requires understanding the local ordinances, growing conditions and market conditions, as well as the characteristics and relative value of the trees in question.

In other circumstances, it is desirable to know the value of a tree in terms of utility savings. Trees can drastically alter the heating and cooling costs of a home, and several different protocols have been developed for determining the dollar value of these savings.

Arborists and tree appraisers consider a variety of criteria when determining the value of a tree. They consider the size, species, location and condition of the tree to determine the value to replace a given tree or group of trees.

Nature of the Value

Trees provide a variety of benefits for properties. Some of the most important ways trees do so include:

  • Reducing storm water runoff. Runoff water causes erosion problems and ferries pollutants from roads and parking lots to rivers, lakes and streams, where it harms many different aquatic organisms.

  • Absorbing and storing carbon dioxide. This helps to reduce the amount of greenhouse gases in the atmosphere, which cause the Earth’s climate to change.

  • Reducing air pollution. The extensive surface area of trees helps give airborne particulate matter a surface to which it can adhere.

  • Cooling the surrounding area. Trees cool yards, neighborhoods and commercial areas by providing shade and through the process of transpiration. Trees needn’t mature before producing benefits: Even small trees can be placed so that they shade air conditioning units, which may significantly lower cooling costs (depending on the location of the unit and other factors).

  • Increasing property values. Home buyers often prefer those properties that feature numerous mature trees. This increases the curb appeal of a property and, ultimately, the sale price.

  • Providing food for wildlife. Trees are important components of local ecosystems. Properties that feature numerous trees with high wildlife value support the local wildlife community — a highly desirable benefit for most properties.

  • Improving the aesthetics of a property. Simply put, trees are pretty. They help make a property look mature, complete and visually balanced; all of which increase your enjoyment of the property as well as its value.

Determining the Yearly Savings

The best way to determine the value of your trees is to have a qualified arborist appraise them for you. By having an arborist carefully examine your property and analyze the location, size and species of trees present, you can learn not only the value of your trees, but also what steps you can take to raise their value further.

You can arrive at a ballpark figure for the replacement cost of a tree by researching the cost of similar trees. However, a homeowner’s assessment is usually insufficient for claim purposes; a professional opinion is necessary in almost all cases. Real estate value is slightly more subjective, and it is very difficult to make apples-to-apples comparisons by perusing the classified ads, making this another situation in which a professional opinion is necessary.

Determining the amount of energy savings a given tree produces usually requires the help of a professional. However, the USDA Forest Service has produced a tool, called i-Tree, which allows you to learn a great deal about the value of the trees in your yard. You needn’t be an expert to use the software either; you simply answer a few straight-forward questions, including the species in question, the tree’s size and condition and your location, and the software estimates the tree’s value.

The package only presents broad estimates – you still need a good arborist for detailed information – but it is a very helpful to for homeowners, landscapers and commercial property owners to understand how their trees are affecting their wallet.

Vertical Value: Trees Raise Property Values

Few property amenities are as beneficial when selling a property as trees are. Their beauty increases a property’s curb appeal, while the shade they provide lowers cooling costs. They provide privacy and reduce street noise, and many will continue to appreciate for longer than you will live.

Average Estimates

The precise dollar amount by which trees increase a particular property’s value varies greatly. The location, extent of canopy cover, species present and health of the trees all factor into the valuation. Accordingly, authorities offer a wide range of estimates:

  • The International City/County Management Association contends that well-tended, tree-laden landscapes may increase property values by up to 20 percent.

  • The USDA Forest Service is more conservative, contending that trees increase property values by about 10 percent.

  • The Council of Tree and Landscape Appraisers estimates that a single, mature, healthy tree increases a property’s value by up to 10,000 dollars.

As evident by this wide range of estimates, determining a precise value for a given property’s trees requires considerable knowledge, experience and expertise. Most property owners must solicit the services of a qualified tree professional to arrive at such a number, otherwise they may leave money on the table at closing.

Assets and Liabilities

Tree maintenance does represent a financial liability; but tree advocates have long contended that on balance, trees remain a net positive. The available empirical data supports this assertion.

In a 2003 cost-benefit analysis of ten street tree species in Modesto, California, author E. Gregory McPherson cited a 1999 study, which found that for every one dollar invested in the area’s street tree maintenance, local residents received $1.89 in benefits. (McPherson, 2003)

The study found that the most significant cost associated with the trees was pruning, which represented about 73 percent of the annual maintenance costs for the tree. In dollars, this value ranged from $6.14 for London plane trees (Platanus acerifolia), to $49.70 for sweetgums (Liquidambar stryaciflua). Plane trees created $7.66 in total annual maintenance costs, while it took $54.31 to maintain each sweetgum.  These maintenance costs are easily offset by the $186.24 in value that plane trees contributed annually, or the $132.95 contributed by sweetgums.

You can mitigate some of the costs associated with trees through careful planning, species selection and design. For example, planting fruitless sweetgum cultivars rather than those that litter sidewalks and driveways with their infamous “spike balls”, will save in maintenance costs. Similarly, by planting trees it the correct place for their water needs, you can alleviate a great deal of the supplemental watering required to keep them healthy.

Increasing Interest

Aside from increasing the asking price of a property, trees increase the property’s overall appeal. This is especially true of properties with elegantly designed tree concepts that feature a variety of species, sizes and groupings. While an increasing number of buyers are considering the environmental benefits of trees (including the decrease in utility costs they provide), the aesthetic appeal that trees provide is attractive to the vast majority of buyers.

Those in the business of selling properties certainly find that trees are attractive to buyers. According to, 83 percent of realtors surveyed in one study held that trees increase the appeal of moderately priced homes. Ninety-eight percent of those surveyed found that trees increased the appeal of high priced homes (those listed at more than $250,000). (Arbor Day Foundation, n.d.)

Trees Living on the Street

Street trees – those planted between the sidewalk and the road – also raise property values. According to a 2008 study by Geoffrey H. Donovana, David T. Butry, which examined the effects that street trees had on property values in Portland, Oregon, the increase in value is quite significant. Researchers found that a single tree with a 300-square-foot canopy, placed within 100 feet of a home, raised the property’s value by about 7,000 dollars – akin to increasing the home’s footprint by 100 square feet. (Geoffrey H. Donovana, 2010) These benefits do not exist in a vacuum; the researchers found that street trees also increase the values of properties within 100 feet by about 1,200 dollars each.


Even if you intend to rent your property, rather than sell it, trees will increase the relative appeal of the property and – in most cases – increase the amount of rent you can charge for the property. In 2011, Donovana and Butry tackled another aspect of Portland’s trees; this time, they investigated the effect trees had on rental rates. Perhaps unsurprisingly, they found that rental rates for properties with trees were greater than for those properties without trees.

According to the study, each additional tree on a given property increased the monthly rent by about $5.62 ($67.44 annually). Rental rates soar when the tree is located in the public right of way. According to the study, trees in the right of way increase the rent by $21 each month. Savvy renters may also appreciate the utility savings that trees provide, thus increasing the appeal of the property.


Arbor Day Foundation. (n.d.). Benefits of Trees. Retrieved from

Geoffrey H. Donovana, D. T. (2010). Trees in the city: Valuing street trees in Portland, Oregon. Landscape and Urban Planning.


Critical Condition: Protect the Roots to Protect Your Trees

tree rootsA tree’s fate is largely tied to the health of its roots and the state of the surrounding soil. Unfortunately for many homeowners and arborists, the bulk of the tree’s roots are out of view. Without taking drastic or invasive investigative steps, the health of the tree’s roots must be inferred, rather than directly observed.

Accordingly, the best way to protect your tree is to protect enough of the tree’s roots to sustain it through any damage. With luck, the tree will survive the trauma, generate new roots and thrive for years to come.

The Basics

Roots perform four key functions for trees. Drawing water from the ground is among their most important duties, but roots also absorb essential minerals from the soil. Roots support the weighty trunk, branches and canopy; serve as a conduit for the transport of different substances; and store energy for future use.

When roots sustain damage, the leaves often wilt or drop prematurely. This reduces the amount of water and minerals that can travel up the tree, and it reduces the amount of food that the tree can produce. If enough of a tree’s roots suffer damage or disease, death is all but certain.

Just as a tree’s branches do not all perform the same functions; a tree’s roots delegate different tasks to different portions of the root system. While the large, woody roots at the base of the trunk help stabilize the tree and serve as a shared conduit for the transfer of water and minerals, the fine, white roots absorb most of the tree’s water and minerals.

The Damage Done

A variety of traumatic events can compromise a tree’s roots, but construction damage is one of the most common culprits. Heavy vehicles and foundation work cause soil compaction, which damages roots and alters the soil structure. Grade changes are also damaging — raising the grade buries the tree’s roots too deeply, while lowering the grade exposes the roots, which can lead to further damage and decay.

Trenches dug for utility lines may cut large swaths of a tree’s root system, and landscaping equipment may slice through surface roots. Even if the tree is capable of coping with the reduced water and mineral uptake caused by such events, it is more likely to fail in high winds.

Because few treatments can help repair damaged roots, preemptive strategies are of paramount importance.

Critical Root Zone

Not all root damage is deadly. Trees can survive with some portion of their existing roots – they do not need the entire network. Over time, trees recover from root damage by generating more roots. However, some portion – a critical portion – of these roots is necessary for the tree’s survival.

Tree care professionals call this portion of roots the tree’s critical root zone. Although the tree’s entire root system may extend two to three times farther from the tree than the critical root zone does, this area must be protected at all costs.

Measurable Maps

Different authorities calculate the critical root zone of a tree in different ways. A 1991 study by Patricia Lindsey and Nina Bassuk, published in the Journal of Arboriculture, recommends allowing 2 cubic feet of root zone space for each 1 square foot of canopy spread. (Bassuk, 1991) This usually translates to a circle with a radius of about 1.5 times the radius of the drip line.

Another formula in common use requires 1-foot of critical root radius for every 1-inch of diameter at breast height (4.5 feet above the ground). In other words, a 6-inch thick tree requires a critical root radius of 6 feet. Other tree professionals recommend allowing 1.25 feet for each inch of trunk diameter.

The critical root zone varies with species, site and soil conditions, so determining the critical root radius of a tree accurately requires extensive knowledge and experience. However, by using the formulae above, you can determine the general size of a given tree’s critical root zone.


Bassuk, P. L. (1991). Specifying Soil Volumes to Meet the Water Needs of Mature Urban Street Trees and Trees in Containers. Journal of Arboriculture.

Trees, Jobs and the Economy


It is abundantly clear that trees help people to feel good, heal fast, keep cool and stay safe; but can they help the bottom line? According to the available evidence, trees are unquestionably good for reducing costs and increasing profits. In fact, because of the perpetually warm temperatures of Southern California, Los Angeles area merchants are among those who stand to benefit the most from capitalizing on the economic benefits of trees in their operations.

Preempting the Pushback

Retail merchants often worry that trees will reduce their store’s visibility or require additional labor to maintain. While it is understandable that they do not want to impair marketing efforts or waste employee time sweeping up leaves, such problems are often overstated. In practice, careful species selection and proper pruning can eliminate many visibility problems. Many cultivars are available that do not exhibit the litter problems associated with the wild species. For example, non-fruiting sweetgum (Liquidambar styraciflua) cultivars do not produce the woody “spike balls” for which the species famous.

Utility Usage

If planted in a well-conceived manner, trees reduce heating and cooling costs. Consider, for example, a large retail shop with a large, south-west-facing wall. This wall absorbs the sun’s most intense rays, and causes a sharp rise in summer cooling costs. Now, imagine the same building, but with a row of trees along the exposed wall. The trees not only provide shade, but they create a cooling effect on the environment through the process of transpiration. A 2002 study by H. Akbari provides some of the most compelling evidence that trees help reduce utility costs. According to the study, the annual electricity savings of an office building surrounded by three trees amounts to between 10 and 35 dollars for every 100 square meters of roof area. (Akbari, 2002)

Air-Conditioned Asphalt

Trees in parking lots are beneficial as well. According to a 1999 study of trees in Davis, California, trees significantly improved the parking lot environment. The study, which was published in the “Journal of Arboriculture,” found that trees reduced the ground-level temperatures by as much as 36 degrees Fahrenheit. (Klaus I. Scott, 1999) This undoubtedly leads to a better customer experience, which encourages return visits.

Money Does Grow on Trees

Trees do not just reduce costs; they actually attract and help retain customers. According to study, after study, after study, customers prefer well-planted shopping areas to those without trees. The Ontario Heritage Tree Alliance has published a partial list of the economic benefits that accompany trees, including those that relate to retail sales. The Alliance cites a 1999 study that found that consumers were willing to pay more for parking, goods and services in well-planted business districts. (Heidenreich)

Trees Don’t Trim Themselves

On the other side of the equation, trees create an abundance of jobs as well. In 2009 alone, California ReLeaf put $3.3 billion in employee pockets. Because the jobs associated with trees are so diverse, it is difficult to estimate how many people nationwide are employed by trees in some fashion (check out this list of 50 tree-related professions by the Tree Foundation of Kern, a non-profit group that works with urban forests).   According to the U.S. Bureau of Labor Statistics, 40,000-odd people were employed as tree trimmers or pruners in 2013. However, this number represents only a percentage of those who work in tree care, as the Bureau does not include self-employed tree trimmers in its statistics. (U.S. Bureau of Labor Statistics, 2013)


Akbari, H. (2002). Shade trees reduce building energy use and CO2 emissions from. Environmental Pollution.

Heidenreich, B. (n.d.). The VALUE OF TREES: Making the Case for Tree Protection. Retrieved from


U.S. Bureau of Labor Statistics. (2013). Tree Trimmers and Pruners.