Tom's Blog

Friday, July 13, 2012

Savanna/prairie drought effects

This may be a year for the ages as far as drought effects are concerned. However, I keep thinking back to the "dust bowl" period of the 1930s, and John Weaver's important work (summarized in North American Prairie, 1954, Johnsen Publishing Co., Lincoln, Nebraska) on how prairies responded to what was really the worst drought of the ages. "Little bluestem suffered the greatest losses....In numerous prairies not a trace remained, at least above ground....Big bluestem, although suffering great losses, withstood the ravages of drought in a most remarkable manner. It frequently persisted, even if in small amounts..." (For a detailed analysis, see Weaver and Albertson, 1936, "Effects of the great drought on the prairies of Iowa, Nebraska, and Kansas." Ecology 17: 567-639)

Not surprisingly, our little bluestem is in awful shape. The whole south-facing slope is suffering the worst from dryness and the blazing sun. Many stands of little blue have died, although there are still areas where it is hanging in there. I am assuming ground water is better in areas where it is still green. What the conditions of the roots of these plants is uncertain. We'll just have to wait until it rains, to see whether the roots are still alive. However, the response, if it comes, may not be seen until next year.

 The response of forbs is highly variable, presumably determined by the specific location, the species, and the depth of their root systems.

I was especially interested in purple milkweed. Unfortunately, it is showing signs of severe wilting. Although I haven't checked all of our stands, those I have checked are in extremely bad shape. The photo here is typical.

However, other species seem to be thriving. For instance, right next to this purple milkweed stand is a large population of a Special Concern species, upland boneset (Eupatorium sessilifolium), which is in great shape. These two are growing in the same soil under the same canopy and are getting the same moisture. The root system must be making all the difference.


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