Tuesday, January 29, 2008

Giving nature structure

Back in the day, long before GPS units and soils mapping, terrestrial natural communities were named after the three dominant plants which presented themselves in a given area. What we now call a dry chert woodland, for example, would likely be called "post oak-big bluestem-summer grape." This old nomenclature might suggest, statistically, what the three dominant plants are, but it doesn't tell you aspect, substrate, or even suggest the complex matrix that the succint "dry chert woodland" does. Dry chert woodlands are oak or oak/short leaf pine communities, often occupying ridges and backslopes. They are found on south and west facing slopes, but can also show up on protected north and east slopes. They have a developed ground layer vegetation, not necessarily dominated by big bluestem.

Many years ago, The Nature Conservancy applied this antiquated classification system to the rare terrestrial communities of the Midwest. If, for example, you wanted to learn about Ozark fens, you’d have to know that they are dominated by three sedges, namely Carex interior, C. lurida and C. leptalea. If you wanted to learn specifically about a deep muck fen, you’re out of luck with this system. All Ozark fens are clumped into one category.

The plant-based classification system is likely a useful tool to a botanist already familiar with the communities, but for someone trying to cut her teeth on, say, fens, the system was difficult to navigate. Granted, a lot of work went into this document, thousands of hours in the field, I'm sure. Lots of statistical analysis. The authors might have even employed sweet differential equations to figure out dominance. To really learn and understand Missouri’s natural communities, though, other factors besides vegetative structure need to be considered. Natural communities also include animals, rocks, soils; they're based in landscapes, not just a collection of plants. That being said, when I really want to learn a natural community, I turn to Paul Nelson, the Yoda of natural history in Missouri.

Terrestrial natural communities are defined as “interrelated assemblages of plants and animals which are found in a given area.” To determine communities, several other factors are taken into account: soil types, topography, rock substrate, hydrology, percentage of canopy closure, types and percentage of ground cover, shrubs and vines. When all of these characteristics are taken together, they will create a certain environment where specific species will survive. These specific species define the community.

According to Nelson's Terrestrial Natural Communities of Missouri (available at parks for $30, at university bookstores for $100), our state harbors 49 different community types and 64 subtypes. The systematic classification of types and subtypes requires careful deliberation (and lots of fieldwork). To borrow a community type you may remember from my time down south, the community Bottomland Forest can be broken into 5 subtypes: dry-mesic, mesic, wet-mesic, wet, and riverfront, all with their own plant and animal associations. (I use that word a lot, mesic, and I don’t think I’ve ever defined it for you: mesic describes moisture availability. Mesic sites are well drained, but the water is removed from the soil slowly, making the ground wet for a short period. Plant diversity, I find, is higher in mesic sites. More sedges than in the dry sites). It is actually the presence of certain keystone species, soil types, and hydrology that largely dictate the differences between these subtypes. Cane grows in mesic, Carex lupulina grows in wet. In prairie, for a better example, the height of the grass, the aspect of the topography and soil types will distinguish a dry loess-glacial till prairie from a dry-mesic loess-glacial till prairie. In the previous community, soils are excessively drained and dominated by little bluestem and hairy grama. These communities appear on steep slopes in the prairie. In the latter, soils are well-drained, the dominant grasses are big bluestem and Indian grass, and are generally found on gentle slopes.

Almost every acre of Missouri has been classified into a community type. Using soils and geological maps, we can determine what should be growing where St. Louis is, for example. But classification isn’t just available for plant communities. Wetlands and even caves have been broken down into subtypes. Within wetlands are 13 subsections, from pond marsh to dolomite spring. Clearly, vegetation will vary between a southeast Missouri swamp and a Barton County prairie fen. More fasciniating is that within the two types of caves (terrestrial and aquatic), even smaller communities are designated. Among them, the parietal subtype, found on the walls and ceilings in the entrance (harboring camel crickets, long tailed salamanders, and several families of flies) and the organic detritus subtype, consisting of leaf litter and detritus washed into a cave. Organic detritus supports life forms as varied as springtails, millipedes, and isopods which, in turn, support salamander and frog populations.

The delineation between subtypes is based largely in Missouri's rich biodiversity. Pristine upland flatwoods, for example, will have sedges, post oaks, little bluestem. They have been managed with fire, just as they were historically, and they now serve as the benchmark. All other woodlands with a perched water table, with clay loam, silt loam or loess-based soils, located on broad upper ridges south of the Missouri River in the Ozarks, with a 30-90% canopy cover, with an undeveloped understory...should look like that pristine upland flatwood. Having that knowledge of which plants should be there helps mandate management regimes. The irony, or the metadiscourse aspect of this, is that Nelson was able to define these subtypes so carefully because he was the one who protected and managed them for biodiversity in the first place. He was the one who could look at a south facing slope choked in cedars and see a glade. Or a woodland filled with scrubby oaks and no understory and see a savanna. With the proper management, biodiversity has returned to thousands of acres throughout Missouri, and it was largely driven by one man. He's very much alive and well, thriving within the USFS, but Missourians should erect a statue to this man nonetheless.

Since the second edition of Nelson’s book, his nomenclature has been adopted by everyone involved in natural resource management in the state. His system is easy to understand by anyone with a basic understanding of ecology. His nice, filled-with-color-plates book helps me return to the shelf the book representing classification by plants only. Nelson reminds me, daily, that earlier systems were, as botanists pre-Linnaeus were, arcane and lugubrious.

2 comments:

Anonymous said...

Allison Vaughn,

You may be interested in learning that we are working on Missouri's Light Pollution. See
http://www.house.mo.gov/billtracking/bills081/bills/HB1727.htm

I hope you will keep an eye on this and attend the hearings.

Robert Wagner
Missouri Night Sky Protection Act
http://missourinspa.googlepages.com/

Ted M. said...

Yes, the man deserves a statue. Even the entomologists are catching on - I have begun, as a matter of routine, to use his nomenclature on insect habitat labels.