By Tim Clancy, for Let’s Talk Plants! May 2024.
How Many of Which Kind and Where Are They?
If you happen to be in a grocery store at the right time you will see a group of people staring at the shelves counting items and then entering numbers into a handheld device about the size of a large calculator. These folks are conducting an inventory of the stock on the shelves. This is useful information for many purposes. Tree Inventories are also useful in many ways.
Tree inventories are performed for many types of clients. These days we use iPad types of devices that allow us to document not only tree attributes but also accurate locations. This results in highly accurate databases of tree information, including maps and the information is used to guide tree care decisions among other things. The data is used to create work schedules such as pruning and removals.
One of the most common clients are Homeowners Associations (HOAs). Information such as tree species and tree trunk diameter (measured at 54” above grade and referred to as “Diameter at Breast Height”) is collected. Recommendations for removal are based on criteria agreed upon before the inventory.
Other clients include property management companies, cities and towns both large and small, school districts and many casinos in Las Vegas. Just about anyone with a tree collection can make use of a tree inventory.
Most tree and plant people know a few species that are local to their area. Some maybe know species from one or two areas of the country where they have lived. In contrast, tree inventory personnel need to know hundreds of species. They may be in Chicago area one month then San Diego the next. In Chicago, most of the tree species are going to be native because of the harsh weather. In warm cities like San Diego or Houston and Miami there are plenty of species from all around the world.
There are tree identification apps available now and for the most part they are accurate. Not always. And those of us doing tree inventory work encourage newbies to use them as a learning tool for as short a time as possible lest they mis-identify a species several hundred times. Then we rely on each other and online tree identification communities.
Besides species and trunk diameter, tree height and spread are often collected (depending on the needs of the client) and most importantly a tree condition is also collected. The condition rating is used to create pruning and removal schedules. For pruning, a recommendation is made by the data collector at the time of data collection. Typically, this is a general pruning recommendation with more complicated situations flagged so the client can also look and determine what is needed.
Besides populated tree sites, “vacant” tree sites are often collected. This may be an area where a tree was previously living or it may be an area where a tree was never sited but would be a great location for a tree. Information about planting site size is included so it can be determined which mature tree size is appropriate for the site. That way recommendations can be made in the office after the population has been analyzed. For instance, one main concept is species diversity. Current thinking uses 10% as the maximum desired percentage. This is based on the percentage of trees you are willing to lose to one catastrophic event like Invasive Shot Hole Borer or Red Gum Lerp Psyllid for instance. If 50% of your tree population is an ISHB host then that’s the percentage you stand to lose if ISHB numbers swell. Torrey Pines State Park comes to mind. It has lost many trees due to beetle activity.
Invasive Shot Hole Borer on left and Red Gum Lerp Psyllid on right.
Fallen dead Torrey Pine https://images.fineartamerica.com/images-medium-large-5/fallen-dead-torrey-pine-trunk-at-torrey-pines-state-natural-reserve-randall-nyhof.jpg
Tree Inventory data can be useful for many different purposes such as tracking pest populations, tracking which trees are responding well to climate change, and of course tracking the expenses involved in maintaining trees in a safe and high vitality condition.
Tim Clancy & Associates LLC
P.O. Box 1180 – Cardiff-by-the-Sea, CA 92007
International Society of Arboriculture Certified Arborist No. WE-0806A
International Society of Arboriculture - Tree Risk Assessment Qualified
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