Without question, everyone loves and appreciates a tree! I would also suspect that everyone has a memory that is associated with a tree. Whether that memory is climbing a tree, a rope swing hung from a branch, enjoying a picnic in the shade, or – dare I say – perhaps your first kiss or a wedding proposal! We all have an emotional attachment to trees! There are also numerous reasons to appreciate trees for their varying contributions to the garden and for making your home more enjoyable! Interestingly, trees are typically not the initial focus of most homeowners when mapping out their garden design. Rather, the focus is upon adding a collection of shrubs to soften or hide the home foundation. Given that trees need 30 years to mature before they can provide many of their true benefits, they should be one of the first plants included in your garden design, not the last! Fortunately, there remain a number of gardeners willing to plant a tree today such that they or perhaps the next owner can enjoy the benefits of a mature tree.
Without argument, trees are best known for creating ‘shade’ – a cool spot for a person or animal to rest. That shade can certainly benefit more than just a person, as it can also benefit a home! If a shade tree is placed on the SW side of the home, such as the Red Maple (Acer rubrum), it will shield the house from the hot afternoon sunlight during the summer months, yet allow sunshine through during the winter months, warming the house. In effect, it is creating a microclimate around the home and according to the USDA Forest Service, can reduce annual air conditioning expenses by 30%. If some evergreens are placed along the NW side, blocking the winter’s winds, heating expenses can be lowered by 20-50% as well! The key is not to ring the house with trees, since that sets the tone for a very dark and dreary home interior! In addition, the element of shade does so much more than cool a person or building by blocking the sun; it also cools the air through evapotranspiration. Through the act of the tree losing water through the stomata in the leaves, the surrounding air is cooled much like our body is cooled through the process of perspiring. Granted, evapotranspiration is reduced during hot sunny afternoons, especially during a drought in an effort to reduce water loss. Yet, water loss still occurs and the tree imparts a cooling effect upon the air beneath and around the plant.
Shade also contributes to the process of creating depth in garden design. Most folks do not consider this attribute of shade but study a garden on a cloudy day versus a sunny day. The concept of looking past the shadows cast by the tree allows the viewer to judge depth – an attribute gardens without a tree simply cannot provide!
The shadows are not the only aspect of a tree that enhances the illusion of depth. The mere fact that you have to look past the trunk, beneath and beyond the lower branches, and body of the tree usually partially impedes viewing all of the garden at once. This act of impeding the view also enhances the illusion of depth and size of a garden. It is impossible to state exactly where a tree should be placed in order to increase the perception of depth since it is dependent upon the individual garden design. However, a tree placed near the foreground of a view, such that the viewer looks beyond into the balance of the garden, provides a ‘measuring stick’ by which a person can judge distance. Many people think their garden is too small for a tree, but this justifies why even the smallest of gardens can benefit from a tree!
Trees not only help to generate depth in garden design but also help to create and form spaces. Many homes are built in old fields, bare of most woody vegetation. Most people consider using conifers for creating the ‘walls’ of a garden since they have a presence throughout the year. Oddly, even though trees lose their leaves, they actually do a much better job of shaping space than evergreens. The pyramidal shapes of most evergreens creates an outdoor space that is not as relaxing to view or walk through than as the space created by an oval, globe or vase shape of a tree. Thus, encircling a space with shade trees creates a more comfortable and enjoyable space than evergreens. Not to say that evergreens are bad. They are important for providing winter interest and blocking winter winds. However, the emotional impact of a space surrounded by deciduous trees versus evergreens is dramatically better.
Trees are also great for subduing noise. Once again, most people think of evergreens as the ideal choice since the ever-present foliage and the denser visual appearance logically suggests they would be superior at subduing audible distractions. However, the varied angles of the tree leaves are much better at baffling noise during the spring, summer, and autumn months. Using trees in combination with conifers is often the best solution for providing a baffle for seasonal noise while creating a very aesthetic, year-round buffer. Maybe it is the reduced noise, but studies are beginning to show that shoppers linger longer and spend more when the shops are surrounded by trees!
Yet another fascination that I have with trees is texture. Not a benefit considered by most, since most trees have a medium texture in summer and a relatively fine texture in winter. Yet, there remain a number of trees with wonderfully bold or lacey foliage for textural interest. For fine texture in summer and bold in winter, consider the Kentucky Coffee Tree (Gymnocladus dioicus), or Black Walnut (Juglans nigra). Most gardeners resent Black Walnut due to the allopathic and deleterious effect of juglone on some select neighboring plants. However, both trees create a fine-textured, almost tropical appearance in the summer and a very coarse winter outline. Another great plant for texture is Magnolia macrophylla, the Bigleaf Magnolia. As the common name and species epithet impart, the leaves are enormous and can reach up to 18” in length and 6” in width. All of the plants create shade, but the visual impacts can also be truly stunning.
Interestingly, trees also allow us to live longer! Odd you might think, but a study released by Texas A&M University found that visual exposure to settings with trees produced a significant recovery from stress within a 5 minute period, as denoted by changes in blood pressure and muscle tension. The USDA has also calculated that 1 acre of forest absorbs upwards of 6 tons of CO2 and emits 4 tons of O2. That is enough to meet the needs of 18 people! In addition, Geoffrey Donovan, a research forester with the Pacific Northwest Research Station, conducted a test comparing the impact of the loss of Ash Trees from Emerald Ash Borer and human health. He looked at census data from 1990-2010 across 15 states. The loss of 1 Million Ash trees correlated with the deaths of an additional 15,000 individuals from cardiovascular disease and an additional 6,000 individuals from lower respiratory disease. The color green has long been proven to be calming and when people are immersed in the tranquility of a green setting, the reduction in stress allows us to live longer, and I am certain happier lives! Trees also remove particulate matter from the air, which explains the correlation with respiratory disease.
Obviously, I have a passion for trees, and with all of these facts, why wouldn’t I? Given their impressive size, one would think they would be hard to overlook and everyone would share in this love affair. Yet, they are often a neglected tool in the designer’s toolbox. More gardeners need to give consideration to the many benefits this group of plants can provide garden design. My hope is that my arboreal love affair proves to be highly infectious and more gardeners will consider adding one or more trees to their Garden!
Bruce Crawford, is a longtime proponent of unusual and fun plants. Bruce is the State Program Leader for Home and Public Horticulture, Director for NJAES and a member of the NJNLA board. He is also an instructor in Landscape Architecture at Rutgers University. A graduate of Bucknell University, Bruce also lectures frequently and has yet to find a plant that he does not like!