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Thursday, September 22, 2011

One, Two, Skip a few....

Berry Prairie diversity.
The diversity of plants in the Berry Prairie is substantial.  Even to the untrained eye, there are quite a few species of flowers, shrubs and grasses.  We often get asked how many plant species are in the Berry Prairie – and we know there were 62 plant species installed over the summer.   However, we periodically find intruders, indicating that the true number of plant species is an unknown number greater than 62. Just yesterday, Kyle (a master’s student studying the green roof) pulled out three clumps of grasses containing pretty rubust weed grasses.  And you may recall the Globemallow Fiasco of 2011 from earlier this summer.

A more interesting question would be: How many plant species are present in a spot of the Laramie Basin, in an area the size of the Berry Prairie?  Is 62 species per 3,600 square feet average?

Sadly, the answer is almost certainly: Nobody knows. There are a lot of botanists who work in and out of the Laramie, and they know a lot about the local flora.  But determining the “true” number takes lots of time on hands and knees and in the lab, and then, the number would no doubt change next year.

Grasses and a prickly pear cactus blooming in the Laramie Basin.  Does this look diverse to you?
Photo by Dorothy Tuthill, Berry Center

Counting diversity

When field botanists go collecting, the strategy is to stop the car, get out (or get off the horse, or stop walking and take off the pack), and collect all of the plants that are blooming or have fruit. Hopefully, the botanist can stop at that site more than once during the growing season, but inevitably, some plants are missed, as are plants found only in places between stops. Therefore, the best numbers that can be provided are minimum numbers. 

Some botanists argue that just counting species numbers is not the best method to measure diversity, because some species may be closely related and fill similar niches in the ecosystem. Those ecologists are interested in functional diversity, that is, the number of kinds of processes that the plant community participates in. Since it is impossible to measure or know the function of all species, often taxonomic diversity is used to estimate functional diversity.

Laramie Basin prairies are dominated by many, many species of grasses. 
Photo by Bonnie Heidel, WYNDD

Prairies also include a lot of forbs, or wildflowers - above is a penstemon species blooming in the Laramie Basin.
Photo by Dorothy Tuthill, Berry Center

Taxonomic diversity (has nothing to do with money)
Taxonomic diversity is determined by counting at a higher taxonomic level than the species, for example, at the family or order level. Consider a one square meter plot that contains 10 species of grasses and a couple of wildflowers, and another that has three grass species and seven wildflower species. Which is more diverse—the former with 12 species, or the latter with 10? Or how about a plot with three grasses, a moss, a fern, and a couple of wildflowers? Your answer depends, of course, on what kind of diversity you are interested in, because any one of those plots could be considered “most diverse.”  The best kind of diversity is that which spans beyond just an organism group (like plants) to positively influence other organisms (like insects, microbes, mammals, birds and humans).
Here, finally, are some simple answers to the question posed in the title:

Place                     Minimum number of known species
Berry Prairie               62
Wyoming                    2,800 (vascular plants only)
North America            20,100
World                          288,000
Estimated number of plant species (known and unknown) in the world: 400,000

So, while we may think that the Berry Prairie is pretty diverse, the plant species represent only about 2% of the plant species of Wyoming, and about 0.016% of the plant species of the world. And as for functional diversity? Well, that’s for students and other researchers to discover in the coming years. We’ll keep you informed!

A common scene in southeastern Wyoming.
Photo by Bonnie Heidel, WYNDD

Written by Dorothy Tuthill, Berry Center Associate Director

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