Assessment of Charlotte's trees.
The first step in assessing an urban forest centers on the trees themselves. Using data from both the tree canopy assessment and the city public tree inventory, Charlotte's trees can be evaluated in eight criteria: amount of tree canopy cover, distribute of size/age of trees, condition (public and natural areas), trees on private property, tree species diversity, suitability, and equitable distribution. Performance levels of these indicators are summarized in the table to the right and shown in more detail below.
|
Charlotte Trees Rating: MODERATE
|
Urban Tree Canopy
Tree canopy cover is the one metric that spans both public and private trees. Charlotte has had multiple tree canopy assessments performed over the last 15 years. In 2002, 48% of the city was reported to be covered by tree canopy when viewed from aerial imagery. In 2008, that amount decreased to 46.5%, then slightly increased to 47% in 2012. Charlotte has set a canopy goal of 50% tree canopy cover by 2050.
|
Charlotte UTC Results |
The general concensus is that large losses in tree canopy since 2012 are due to high levels of development, though this must be confirmed with another tree canopy assessment in the coming years (called for in the recommendation for an updated canopy assessment).
Is Charlotte on track to reach the 50% goal by 2050? As of 2012, there were 86,000 acres of tree canopy in Charlotte. 91,500 acres of canopy are required to to reach the 50% goal, meaning 5,500 additional acres of trees are needed. However, this number will be higher to compensate for tree canopy lost to age and development during this time period (especially given the volume of development happening now). Only after a new canopy assessment occurs will progress or loss be discernible.
How does Charlotte's canopy compare to other cities? Comparing Charlotte's canopy cover to other cities can be a helpful exercise, with the caveat that every city is unique. Some cities assess their canopy cover county-wide; some assess on the urban core. Other cities have geography or climates that affect canopy levels. For example, Cincinnati and Pittsburgh have high canopies, but both have many undevelopable hillsides that require trees for stabilization. Other western cities like Phoenix or Las Vegas have very little natural vegetation, so high rates of canopy cover are unrealistic.
What is the industry standard? American Forests, a recognized leader in conservation and community forestry, has established standards and goals for canopy cover in metropolitan areas. They recommend that cities east of the Mississippi have an overall canopy of 40%, with 15% in the central business district, 25% in urban neighborhoods, and 50% in suburban neighborhoods. |
Location of Tree Canopy. Whether looking at overall tree canopy cover or individual public trees, the location of the trees across all city neighborhoods is critical. This is primarily because the location of the trees dictates which residents benefit from the services those trees provide. This concept is covered further in the section that discusses tree benefits in more detail. Tree canopy in Charlotte is not equal across the city. Despite high overall canopy (47%), disparities in caopy cover are evident when canopy data is divided into twelve geographic areas (as shown in the map and table below). The Airport (12%) and Uptown (20%) areas have the lowest canopies, while the Outer North East and Urban Core East have both achieved the city goal of 50% canopy.
Public Trees
Data on individual trees managed by the city can also provide a snapshot of existing conditions. From this data, the range of size/age, condition (public and natural areas), diversity of species, and site suitability can be measured. However, it should be noted that the city inventory is only 80% complete (an update is called for in Recommendation #4). Charlotte has an estimated 180,000 public trees managed by the city arborist and team. Approximately 150,000 of these trees have been inventoried.
Condition is important to assess the overall health of the urban forest, but as it also includes risk, condition is the primary driver in day-to-day public tree management. Current data shows that 80% of Charlotte's publicly-owned trees are in Fair or better condition, and only 4% are in Poor or worse condition. Condition data is missing on approximately 28,000 trees.
|
Condition of Charlotte's Public Trees (2016) |
Along with condition, the diversity of species, the range of size/age and proper placement of Charlotte's public trees can also be considered predictors of the city's future tree canopy. Poor species selection, planting practices, and inadequate growing space translate to short-lived, high-maintenance trees. Likewise, poor age distribution translates to an unsustainable population of trees in the long term. Contrary to anticipated results, citywide analysis shows that public trees fall into most of the accepted thresholds.
Range of Tree Size/Age Across the City |
Species Diversity Across the City |
Size/Age Distribution. Maintaining a wide range of ages of trees (assessed by size) is based on the need to maintain the flow of urban forest benefits overtime. The number of newly planted trees must exceed losses from death and removal.
The recommended distribution is shown in the chart below (in red). Charlotte's public tree size is shown in blue. Charlotte is not far off the overall recommended rates, though these numbers are much different when looking at trees per neighborhood. For example, the neighborhoods of Dilworth and Myers Park have large numbers of older trees and minimal quantities of small, younger trees. This is a real indicator of risk to future canopy in those areas (learn more about the aging canopy issue). |
Species Diversity. Tree diversity is crucial to urban forest management. Diverse urban forests provide habitat for a wider range of animals, but more importantly, they increase the community's resilience to pests and disease (thus increasing longevity).
History has taught this lesson over and over, yet we continue to plant on the whole without diversity in mind. Lack of diversity in a neighborhood can result in drastic changes from what was a beautiful cathedral of street trees to a treeless community - in the course of just a couple years. Chestnut blight at the turn of the century led to the loss of millions of trees within only a few years. In urban areas, these were often replaced with elms, only to lose them later to Dutch elm disease between 1930-1970s (see photos at right), also by the millions. Sadly, many elms were replaced with ash, which we are now losing by the millions as well. The breakdown of diversity of Charlotte's publically owned trees is shown in the three charts below. Industry standards state that no one species should comprise more than 10% of the population, no one genus should comprise more than 20% of the population, and no one family should comprise more than 30% of the population. As with size/age, Charlotte is not far off the recommended rates overall, though these numbers are much different when looking at trees per neighborhood. |
Tree Site Suitability. A number of factors can be used to assess whether a site is suitable for tree species, or for a future planting.
- Power Lines/“Right Tree, Right Place.” Just over 21,000 public trees (14% of all trees) are sited under primary power lines, only 8,000 (less than 40%) of which are considered unsuitable species for such a location (will eventually grow into the lines).
- Growspace/Sidewalks. Data is not yet available to adequately assess the grow space on public trees.
- Threatened Species or Invasives. Threats from pests, climate changes, and storms can transform a once-suitable species into an unsuitable one. Invasives can also be considered unsuitable. Charlotte's threatended trees (thus unsuitable) could include 1,200 trees made up of:
- Ash. The ash genus Fraxinus, susceptible to the emerald ash borer, comprises less than 1% of the public tree population.
- Pear. Pears are now considered invasive and make up over 6% of Charlotte's tree population.
The full matrix used to assess the trees in Charlotte using 8 indicators of a sustainable urban forest follows: