There have been a number of times when I have wondered which states are the most biodiverse in the nation. I was surprised to discover that this information is not easily found, so I set out to make my own map and resource that would help people to easily obtain this information. And, yes, I am a proud nerd.

Before I provide more commentary about my map and a precise list of the most biodiverse states, I first should explain that "biodiversity" is a term that has no 100% agreed upon scientific definition.

In this map, I have shown the most biodiverse states using "species richness" as my criteria. Richness is the total number of plant and animal species that have been documented in each state. Scientists are also usually interested in "endemism:" the number of unique species to a specific area. A "biodiversity hotspot" often refers to areas that have numerous endemic species which are found nowhere else, such as the Amazon Rainforest.  Endemism and richness also do not necessarily mean that species are "abundant." In other words, there might be many unique species in a given area, but they also might be rarely found (small in their population sizes or ranges). For a broader discussion of how biodiversity can be defined, click here.

Some Thoughts about the Map

I wanted to create a map that used shades of one color to illustrate a generalization of where biodiversity is highest in the U.S. Ultimately, I decided to use 4 shades of green. This meant that I needed to divide the states into 4 groups. The first 3 groups include 12 states, and the 4th (the group with the least species) includes 14.

A quick aside of interest: I would like to mention that making the map was more challenging than it would have seemed. First, I tried to find mapping software that would make this project a breeze. It does exist, but for a hefty price that seemed foolish to pay for such a simple project. In the end, I downloaded a public domain map from nationalatlas.gov. Then I set to work with colored pencils to try to make my color scheme.

The first attempts made for a confusing map (honestly, quite ugly as well), so I next tried 3 green magic marker sharpies that worked well. I scanned my hand-colored map and then used Photoshop for the final color. So in summary, making the map was a labor of love and sometimes frustrating. It was also quite fun. I surely am not Eratosthenes, but I'm proud of what I came up with. Alright, let's get back to some interpretation of the data.

When you look at the list of the most species rich states (see list below), it stands out that California and Texas have far more species than any other states (6,717 and 6,273 respectfully). They could very well be in their own category. I can only guess why they rank highest, but the most logical explanation would simply be that they are both  some of the larger states and have expansive coastlines, which create species-rich "ecotones." Ecotones are areas where two or more habitat types come together.

It's interesting how the center of the North American continent has the smallest number of species (the Dakotas, Nebraska, Kansas, and Iowa) and also the Northeast region. Perhaps this relates most to their respective climates. It also surprised me that Alaska fell into the least species rich category. We generally think of Alaska as an animal abundant state, but this abundance does not to translate to species richness. It probably also suffers in these rankings from a lack of plant biodiversity.

As one final thought about how the states rank, it's interesting that New York state is something of an outlier in its region. I wonder why. Perhaps as I map out some of the additional data (endemism and extinct species), we will have a better idea of why New York is different from the rest of its region.

List of Most Biodiverse States (Species Richness)

I found my data in a publication from the nonprofit NatureServe. The data may not be entirely accurate today because the report was published 8 years ago. But my guess is that there have been minimal changes to the tallies. NatureServe's detailed explanation of their data will be provided below the list. One big factor I will note here is that marine / ocean species are not included in the tallies.

Total Number of Species

1 California.................6,717
2 Texas.......................6,273
3 Arizona....................4,759
4 New Mexico............4,583
5 Alabama..................4,533
6 Georgia ..................4,436
7 Florida ...................4,368
8 Oregon....................4,136
9 North Carolina........4,131
10 Utah.......................3,892
11 Nevada...................3,872
12 Virginia..................3,803
13 Tennessee..............3,772
14 South Carolina.......3,701
15 Oklahoma..............3,616
16 Colorado................3,597
17 Mississippi.............3,580
18 Louisiana...............3,495
19 Arkansas................3,415
20 Washington...........3,375
21 Missouri.................3,340
22 New York...............3,333
23 Kentucky................3,258
23 Illinois....................3,258
25 Idaho......................3,205
26 Wyoming................3,184
27 Ohio........................3,152
28 Maryland................3,148
29 Michigan................3,135
29 Pennsylvania..........3,135
31 Indiana...................3,098
32 New Jersey.............3,022
33 Montana ................2,921
34 West Virginia.........2,873
35 Wisconsin...............2,869
36 Minnesota...............2,817
37 Kansas.....................2,778
38 Massachusetts........2,765
39 Nebraska.................2,587
40 Iowa........................2,533
41 Connecticut.............2,497
42 South Dakota..........2,406
43 Maine......................2,352
44 New Hampshire......2,327
45 Vermont..................2,274
46 Delaware.................2,244
47 Rhode Island...........2,078
48 North Dakota..........1,889
49 Alaska......................1,835
50 Hawaii.....................1,418

Source: States of the Union; Ranking America's Biodiversity. April 2002. Natureserve.

Specific information about what is included in the data set:

The state-ranking tables on the following pages are based on analyses of the status and distribution of 21,395 plant and animal species drawn from the NatureServe Central Databases. A publicly accessible version of these databases is available through the NatureServe Explorer web site (www.natureserve.org/explorer). These analyses include all species groups for which NatureServe currently has complete data for state-level distributions and global conservation status. The tables include all native U.S. species of vascular plants, all native vertebrate animal species (excluding marine fishes), and native species in the following invertebrate groups: freshwater mussels; freshwater snails; crayfishes; large branchiopods; butterflies and skippers; underwing moths; tiger beetles; and dragonflies and damselflies. The figures reflect full taxonomic species only and do not include infraspecific taxa, such as subspecies or varieties. To provide a more complete picture of extinctions across America, Table D, Extinctions, draws from the entire NatureServe central database, and includes presumed or possibly extinct species from some invertebrate groups not listed above.

Stay tuned for more maps relating to biodiversity in the near future. I'm really curious to see endemic species and extinct species mapped out in the U.S. Hopefully you are too.

If you have any other interesting observations about the data please let us know in the comments.

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