Thursday, September 22, 2011

Fire in grasslands and savannas: a trip to Afri-homa

William Bond with a Gulliver post oak at Tallgrass Prairie Preserve.  

I spent four days last week driving around Oklahoma with William Bond from South Africa. I'm not sure why we chose the state, except in many ways it is the area most analogous (ecologically) to southern Africa that we have in North America. Old soils, intermediate precipitation, native prairies and savannas, and fire.

I've spent a fair amount of time over the past decade with William learning about things I never thought cared about. This trip quickly became a study on the roles of fire, drought, and herbivory in vegetation. It's hard to summarize William's view of the world, but he spends a lot of time thinking about how ecosystems and floras have developed over the past hundred million years. It's not a narrow topic.

I'll do my best to summarize, but essentially we visited different ecosystems such as the Cross Timbers to look for evidence of the antiquity of fire in grasslands, if not the antiquity of grasslands themselves. We'd go to a place like Tallgrass Prairie Preserve and look at oaks to see whether they promote fire. We traveled to Wichita Mountains, another old landscape, to look at how trees were coping with drought. We traveled to Black Kettle grasslands to look for plants with spines as evidence of histories with browsing mammals.

You can't necessarily look at a place and see back 10 million years, but you can try. For example, you can look under a Cross Timbers canopy and try to understand whether fire would rely on grass or oak leaf litter to work through the savanna. Or look at the canopy to see whether the oaks try to shade out the understory or not. Things like this provides evidence of the evolutionary history between these plants and fire.

A place like Black Kettle isn't too far from the Cross Timbers, but it's a radically different ecosystem. Grass there is grazed short. All the woody plants are structurally defended. I'm still picking out prickers from that place. It was never likely a fire world. It was likely always an herbivore world.

Long story short, there are still some great syntheses to be made. We haven't mixed everything up enough such that an old-fashioned field trip can't provide insight into the forces that have structured our world.

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