Developing a Tree Planting Plan for Your Community Project

The difference between a successful tree planting with healthy trees and a line of dead and dying stems often comes down to the analysis of the sites and selection of appropriate tree species for the conditions that exist at each site. 

Spending the time examining each planting site, taking notes, and then (and only then) using that data and knowledge collected in the field to select several species that will survive and hopefully thrive on that site is critical to success.

In the context of developing community forestry planting projects, the majority of these projects involve planting trees along streets and roads, which adds some site stressors and site restrictions that need to be examined and understood. Other community forestry tree plantings might take place in parks, green spaces, stormwater bio-swales or rain gardens, and schools. Usually, those sites are less restrictive and have more room (above and below ground) to grow a large tree compared to a curbside setting in a community.

Finding Planting Sites for Trees in Your Community

It is good to start with a map of the community or utilize some satellite images on Google Earth or Google Maps before you start driving around town. Often the satellite images are up-to-date, and you can begin to see what room exists on certain streets, boulevards, and parks. If you have an inventory of your trees, or an urban tree canopy assessment, you should pull that out and begin to look for potential planting sites on public property through the community. In Pennsylvania, communities can utilize the TreeKeeper online platform provided by DCNR Bureau of Forestry. You can input any newly planted trees or inventory data for existing trees in your community into this GIS-based system.  

Another approach to finding tree planting sites in your community is to look at areas where trees have recently been removed. If your community has a shade tree commission or committee (and it should), you might have a list of tree removals from the past 2-3 years you can work with and prepare for replacement trees. If you don't have an active list, you can ask the public works director for areas that have lost trees over the years or drive around and look for stumps (although fresh stumps will add some work to site preparation). 

The last approach for finding community tree planting sites (especially street trees) is to ask residents if they would like a tree planted in front of their house (roadside, or within the right-of-way). Writing an article for the local newspaper or community newsletter, posting something on the community's social media accounts, or holding a public meeting are all good ways to involve the community and solicit requests for new tree plantings.

Getting public input and interest in newly planted trees is important for community buy-in and survival of the trees. Although state statutes allow a municipality to plant trees along their streets and roads, it is best to ask an adjacent property owner if they would like a tree. Alternatively, you could ask them if they have any objections to seeing the street planted with new trees. If you want the trees to survive and not disappear during the evening hours, it is best to communicate with the adjacent property owners. It might take some convincing and explaining that the tree you are proposing to plant will improve their property value and provide numerous benefits (including summer cooling, energy savings, stormwater and street flooding mitigation, and walkable safe streets, to name a few) and the newly planted trees should not cause future conflicts because you will be selecting an appropriate species for that location. You can even involve the residents in the species selection, but you might want to conduct the site analysis first and develop a short list of tree species that will work for that site before you open selection to a resident and soon find out you can’t find that tree species or should not plant that tree roadside.

Examining the Planting Locations

Once you have a list of addresses or park locations you think will work or could use some new trees, you should plan to take the time to drive around town and visit each location. This part can be time-consuming, but I don’t believe you can truly examine the site and understand the constraints or growing conditions by just looking at a map or aerial image. Over the years, I have seen too many landscape designers select species for a project and add them to a map or plan without physically visiting the site to see the soils are highly compacted or there are potential conflicts. A tree may grow too large for the site, growing up into overhead electrical lines or growing out and in the path of school busses or delivery trucks travel past or park in that area. 

When evaluating a planting site, it is important to ask the following questions, or utilize a site assessment checklist, like the one created by Dr. Nina Bassuk at the Cornell University Urban Horticulture Institute. Here are some of the questions you want to think about when on site:

• What are the soils like? Are they compacted? Are they clayey, silty, or sandy in texture? Do the soils drain well or is their standing water after a rain event?
• Is there heavy vehicle and truck traffic along the street? Or in a park setting, is there heavy foot traffic?
• Are there overhead primary electric lines on poles? This can be a tough one because there are lots of lines on poles along our streets, including telephone, cable TV, and secondary lines feeding electricity to homes and businesses. We are most concerned with the lines at the top of the poles that connect to insulators and transformers. They are high-voltage, uninsulated electric lines that trees cannot make contact with and are pruned for clearance every few years (see image). It is best to plant a tree species that is compatible with the limited growing space and will not mature into the primary powerlines.
• How much distance do we have between the curb and the sidewalk to grow a tree? Or what are the dimensions of the tree pit (growing space surrounded by concrete on all sides)? The more room we have between the curb and sidewalk, the less likely we will have issues with a tree lifting sidewalks or outgrowing its space, creating conflicts.
• How close to the corner is the planting site? Is there a stop sign or light at the corner? It is typically best to avoid street intersections by about 40 feet to maintain lines of sight for both drivers and pedestrians, especially if there is a stop sign or other traffic controls that must remain visible for safety.
• How close is the building or home to the planting site? If a building is close, we would want to select a more upright or columnar variety to fit that site.
• Do cars park adjacent to the planting site or tree pit? If so, we would want to locate the new tree and parking space relative to each other to avoid car doors opening into the tree.
• What species of trees are growing at the site or on the street? Examine the surrounding vegetation (trees) in the planting area and determine what tree species are doing well and which are declining or struggling to grow. You might be able to gather some information about soils, drainage, heat, or light levels just by looking at what is growing well on the site. Or you might find a species on the street that is not working well for various reasons. For example, salt damage to sugar maples (even young trees), or mite and lace bug damage to serviceberry that was misplaced in a hot, full sun location (serviceberry likes and needs some shade because they are an understory tree). 
• Look for the presence of diseases or insects impacting existing trees. If you know oak wilt is in the immediate area, you may want to avoid or limit planting red oak group species. If fire blight has impacted crabapples or callery pears nearby, you should select disease-resistant varieties of crabapple or plant another species not susceptible to fire blight.
• Are there shop signs present downtown or commercial area? If so, we would want to plant in between signage and businesses to try and avoid blocking business signage. We would also want to select an upright branching (or columnar) tree whose lower branches can be pruned for clearance (for sign visibility and pedestrian and vehicular traffic).
• Will the planting site be heavily salted during the winter months? Is it a busy road that receives lots of deicing salts? Or a commercial district, hospital, or school where sidewalks will be salted heavily? Remember, every street tree will have to have some salt tolerance, but some sites tend to receive more than others and most trees struggle to survive in these areas. Only a handful of species can tolerate lots of deicing salts.  
• Consider the use of the site. If you are planting in a park setting, think about whether the new trees will function as a shady grove for users or line a path or trail. Perhaps they will be in the way of an impromptu game of frisbee or touch football. If you are planting street trees, consider the amount of traffic, parking, commercial areas, bus or truck loading zones, etc.
• If you are planting in a park or natural setting, consider focusing on native trees that will provide more benefits to wildlife, pollinators, or aquatic insects. Avoid planting anything invasive or could become invasive. If you are planting a street tree in a tough location, sometimes native trees cannot tolerate the conditions, so planting a non-native makes sense. You should always avoid planting known invasive species like callery pear and Norway maple. Non-native, but also non-invasive species like Ginkgo, London planetree, hybrid elms, hardy rubber tree, and Japanese tree lilac are selected to grow in various sites like downtown tree pits because they will survive some of the harshest conditions.

Sometimes taking notes about each planting site works well for small plantings or similar sites, but it might be best to develop a spreadsheet or checklist where you can either place coded notes about things like the presence of primary electric lines, size of the tree lawn, < and compacted soils conditions. Having a camera on our phones these days allows you to take some pictures of the planting sites you can review later and incorporate into the planting plan. Images are especially helpful if you are preparing a planting plan for a grant as they help the grant reviewers to better understand the plan for a site they may not be familiar with. Developing a written plan with pictures of the sites can also help sell the project to municipal officials, residents, or outside funders.

An example of good visual tree planting plan (with pictures of each site) is the Milford Borough Tree Planting Plan.

Maximizing Benefits and Tree Canopy

Once you determined what size trees will grow in the planting site, it is best to try to maximize the amount of canopy you can grow. Large canopy trees such as oaks, maples, and elms provide eight times the benefits or ecosystem services of small trees like flowering cherry, crabapple, or dogwood (USDA Forest Service Research). It seems like everyone these days wants a small tree, often because they are concerned larger trees will cause them problems, such as outgrowing the site or causing damage should they fail in a storm. In most cases, with proper maintenance, the trees we are planting should not become a problem in our lifetimes and we want to make sure the new trees are providing the maximum benefits to future generations.

Selecting Several Species that Might Work at the Site

It is usually best to first determine what type or size of tree will fit the size of the site. Next, use other site conditions (soils, drainage, salt, usage, reflected heat loads) to begin selecting several species and cultivars that might work well in that site. Why select more than one species, you might ask? Nursery availability of some species might impact your selections, so it is good to be flexible and have three or four trees that work and rank them. For example, if there are overhead primary (high voltage) electric lines running through the planting site, a small stature tree should be planted and the species options could include Japanese tree lilac, hedge maple, amur maple, crabapple (if I am not concerned about fruit dropping or sidewalks are not present), flowering cherry, or a cultivar of zelkova called 'Wireless.' If we are looking at a tree pit in a downtown streetscape setting, then we know the site will be hot, have limited rooting space, and de-icing salts will be spread heavily. In that location, we would be looking for a species (and cultivars) tolerant of salt, heat, and droughts. Avoiding the planting of some species like red and sugar maples would be a smart move if we want the trees to live long and provide numerous benefits.

Learning more about species tolerances to various site conditions takes time, research, reading, and familiarizing yourself with the characteristics of different species and cultivars. I would start with some online resources such as Cornell University's Urban Horticulture Institute’s Recommended Urban Trees: Site Assessment and Tree Selection for Stress Tolerance and the Woody Plant Database. Or consider Penn State Extension's – Landscape Tree Factsheets, which contains color images of over 200 urban tree species and cultivars, and contains an excellent six-page chart of species and their tolerances to site conditions such as soil drainage, salts, urban stresses, as well as mature size, hardiness, ease of transplant, and tolerance to diseases and insects. The book might have a few species that we no longer recommend planting due to their invasiveness, but information on urban species and color images, still makes this publication a "go-to" when selecting trees for urban planting sites.

Another useful short publication is the TreeVitalize Guide for Tree Selection, Planting, and Care, which can be downloaded for free.

A short video produced by Dr. Nina Bassuk at Cornell, Tough Trees for Tough Sites, covers site analysis.

Diversity in the Planting

When developing a planting plan for a streetscape or park, there are some design considerations to weigh against the need for plant diversity. Our history of overplanting just one or two tough urban tree species along our streets and in our landscapes has created unhealthy ecosystems impacted greatly when a new disease or insect appears. The result of this limited species diversity is the loss of thousands of trees over a short period of time, leaving behind clearcut streets and shock to the system. Dutch Elm Disease and Emerald Ash Borer come to mind as examples of those situations. It is best to build diversity to your plantings so we work towards an urban tree population that fits the 10-20-30 rule. In urban forests, we should strive towards having no more than 10% of the tree population be one particular species, no more than 20% be of any one genus, and no more than 30% of any single family of trees. It is not a perfect rule, and it can be a challenge to achieve, but it is a good goal to work towards when we consider the possible devastating impacts of the arrival of an insect like Asian Long-Horned Beetle if your community, as is quite common, has a high percentage (30-50%) of maple trees (these beetles like to borer into maple trees).

When designing a streetscape, a row or line (allée) of the same species of trees often looks appealing and uniform to the human eye. This can still be achieved without compromising the need for diversity. When designing a run of the same species down the street or park walking path, it is best to switch species when there is a natural break in the system such as a cross street or even driveways and buildings. An even better option to consider is alternating two or three species of similar size and form when planting the street. Should one species become impacted by insects or disease, hopefully the other species survives to continue to provide some canopy into the future compared to losing the entire population of trees on a given street.

Developing planting plans takes some time and knowledge of both the site conditions as well as the species attributes (size, form, color, flowers, etc.) and tolerances (salt, heat, soils, drainage, droughts, insects, diseases, and storm damage). Once the plan is developed and you have some species in mind, have an experienced urban forester, landscape architect, or ISA Certified Arborist take a look at the plan and provide comments. Don't be afraid to change species as needed, whether because the trees can't be found in the nursery, or the species selected might not survive the conditions of the site. Once planting plans are developed, they can be used to acquire a grant or funding source and help illustrate to others the need for trees in the community. As long as the site is not significantly changed, planting plans don't expire and can sit until your community is ready to plant or funding becomes available. Remember, a good plan developed by detailed site analysis and species selection can be the difference between healthy and beneficial future canopy cover in the community or rows of unhealthy, dying stems detracting from the community and not providing benefits.