It is an age-old question; how many trees are there? In recent years some have asked, Are there more trees on earth than stars in the Milky Way? NASA estimates that the Milky Way has approximately 100 billion stars. So let’s see how trees stack up.
In the United States, the U.S.D.A., U.S. Forest Service (USFS) supervises and assists with the collection of data. The Forest Inventory and Analysis (FIA) program has been in continuous operation since 1930 with a mission to: “make and keep current a comprehensive inventory and analysis of the present and prospective conditions of and requirements for the renewable resources of the forest and rangelands of the U.S.” The Northern Research Station FIA unit is responsible for creating and maintaining a comprehensive forest inventory for 24 States including Wisconsin. The FIA program partners with states in various ways to meet the needs of the program and the needs of each state.
Ryan Heiderman, WI DNR, oversees the data needs and collection for the State. Wisconsin partners with the USFS to get the plots collected with a mix of USFS employees and local contractors. Currently, Wisconsin is on a 7-year remeasurement interval and does a double intensity relative to the national standard. Wisconsin puts in twice as many plots, about 1 plot per 3,000 forested acres. This is about 11,600 plots total, of which about 6,400 are ‘accessible forested conditions’. Nonstocked or unaccessible plots can be those located in agricultural fields, parking lots, airports, or other nonforested lands which are not measured.
The FIA Data Collection and Analysis explains data collection consists of a three-stage systematic sample of sites. Plots are selected using remote sensing to determine forested conditions and accessibility. Some plots are remeasured from a prior survey and while other plots are new to the survey. Data collected includes type of ownership of the land where the plot is located and type of current land use. Some WWOA members have FIA plots on their woodlands.
Field crews follow specific measurement standards to collect data on forest type, tree species, tree size, and overall tree condition. A subset of sample plots are measured for a broader suite of forest health attributes including tree crown conditions, lichen community composition, understory vegetation, down woody debris, and soil attributes. Data loggers are used to collect the information measured on site. These are handheld microprocessors with forms that are completed as the data is collected in the field. The data can then be downloaded to computers for analysis. Research and pilot programs are looking into other ways to collect inventory data via remote sensing, such as using LiDAR and photogrammetry, but they are not in use yet.
In Wisconsin, there is an estimated 11.75 billion live trees >1 inch in diameter at breast height (dbh), or 2.2 billion growing stock trees. Recent, FIA data showed that the USA had 300 billion trees. In 2015, a Yale-led study reported that researchers using 400,000 forested plots to collect tree density information from around the world created a model to predict the estimated number of trees at each location around the globe. This analysis resulted in 3.04 trillion trees on Earth.
The trees win – so take a walk in your woods today to celebrate! If you are a night owl waiting for dark to enjoying the Milky Way, make sure you take in the Geminids meteor shower on December 13 and 14!