The Takoma Park Tree Selection Guide presents the following definition of native species at the outset (pages 2-3) because it helps explain why native species are critical to biodiversity.
native: a plant or animal that has evolved in a given place over a period of time sufficient to develop complex and essential relationships with the physical environment and other organisms in a given ecological community.Rick Darke & Doug Tallamy
The Living Landscape
However, this is not a practical definition that allows one to decide if, say, the Shumard oak (Quercus shumardii) is native to Takoma Park. For that purpose, the guide developed a second definition,
“native to Maryland and with a significant population, i.e., are not considered rare, in Montgomery County and at least one adjoining county.”
This practical definition is explained below and on page 11 in the guide.
The practical definition of native trees is based on data provided in The Biota of North America Program (BONAP): North American Plant Atlas.
The Bonap website has a Maryland page listing the genera native to the state. Clicking on any genus listed produces a page with a map for each species native to Maryland and in that genus. The map for the species shows all the U.S. states and Canadian provinces where the species is native, and the status of each species in each county, to the extent data is available.
Example: Below is a species map for Amelanchier canadensis, which Bonap indicates is native to Maryland.
Bonap defines “native species” only at the state level, arguing that data are not consistently reliable at the county level.
The procedure just described therefore identifies species that have likely evolved in Maryland over a period of time sufficient to develop complex and essential relationships with their ecosystem. However, Maryland does not have a single ecosystem. A plant that has evolved in a brackish coastal wetland may NOT have many interactions with species that have evolved in the Western Maryland mountains.
In other words, the practical definition of native species can better approximate the theoretical definition, in the blue box above, by eliminating native Maryland species that don’t grow anywhere near Takoma Park.
To carry out this second cut, only species identified as “not rare” (lime green color) in Montgomery County and at least one adjoining county were included in the guide.
Note that the guide only present native species that are included on the City of Takoma Park Approved Species List. In other words, there may well be other tree species native to Maryland and “not rare” in Montgomery County. This decision makes the guide easier to use by residents searching for species that qualify as replacement tree species under the City of Takoma Park Tree Ordinance.