A Paean to Warm-Season Grasses

A follow-up to my previous post, on the drought. I took a trip down to Nichols Arboretum, a beautiful property run by the University of Michigan. They have a restored tallgrass prairie fragment there, called "Dow Field". For you botany nerds, it was first described by Henry Gleason as he passed by on the train on his way out of town (Ann Arbor).

Dow Field, like most tallgrass prairie, is dominated by C4 grasses, especially Big Bluestem (Andropogon gerardii).  I wanted to see whether my idea of having C4 (warm-season) grasses as part of a pasture base could be supported by a visual inspection here (i.e. am I just full of shit?).

What I saw was encouraging, although not quite as lush as it should be this time of year. When I read the site description for Dow Field a couple years ago, I recall it mentioning the soils were droughty- so there's  reason to believe that the grass would be even healthier in a better soil. But nevertheless, check it out:

Big Bluestem (Andropogon gerardii). Fairly typical of the exposed portions of Dow field.

I found a seemingly inexplicable clearing in a side portion of the field. There was a layer of dead grass, with younger growth of Big Bluestem, and lots of thistle. I suspect that the Natural Areas Preservation Program may have treated the area with herbicides earlier in the season to fight "invasive" (C3) grass.

A pretty prairie flower. Don't know what it is yet! 

The next photo shows my dog, Chloe, standing next to some fresh Bluestem growth. It was looking reasonably healthy, and would be at a good time to graze- still lush and vegetative. This gives me confidence in the warm-season grasses as providing valuable diversity and resilience for pasturage and hay. Imagine what this field would look like in a better soil, with more shade, and possibly flood irrigation...

Not far from the cleared patch, I shot this photo to show the awesome height of mature Big Bluestem. This was the tall-grass prairie that impressed the early settlers of the Middle West. It was a beautiful, diverse ecosystem, intergrading on the eastern front with oak savanna, and oak-hickory and mixed deciduous woodlands. These ecosystems sustained many herds of Bison, and numerous tribes of native Americans, adapted to the periodic vagaries of an intense continental climate. Indians burned the prairies annually to facilitate hunting drives, particularly in the fall (October-November). The immense heat and smoke from these fires so intimidated the early white settlers that they coined a term "Indian summer" to refer to the fire season

Chloe and the Big Bluestem 

I know the agriculturally-minded will scoff at my faith in the utility of the warm-season grasses for hay and pasture. It is true that, normally, their growing season is shorter, and the growth coarser and lower in protein than most of the introduced cool-season grasses (e.g. bluegrass, orchardgrass, etc.) Switchgrass is already well-accepted for this role south of Ohio. I'm not suggesting that, this far north, they should be the main basis of a pasture program. But I think that handled correctly, they could contribute mightily to resilience in the face of increasing climate vagaries. For comparison's sake, check out some local, similarly unirrigated cool-season grass:

Where's the nutritive value here? 

Chris

Responding to the Drought

As I work on a longer post about livestock and methane, I wanted to say a few words about the unfolding drought catastrophe in this country.

2012 is officially one of the worst years on record for nation-wide drought. It is severely affecting the landscape- be it farms, ranches, or forests-- all around the country. I've been in Michigan these past couple of months, and the land here is parched. A combination of unseasonably high temperatures, very little winter snow, and spotty rainfall have combined to produce these conditions.

In SE MI (photo (c) Chris Wilson 2012) 

 Agriculture has been deeply effected. I'm told this is the worst year in memory for agriculture in the state of Michigan. The cherry harvest is hosed. The apple harvest isn't far behind. The corn and soy around here look patchy at best. Grass hasn't been growing (see post-script), so pastures are in bad condition, and hay prices have sky-rocketed. It's going to be a hard year for farmers, especially those with livestock and those in the fruit business.

 NOAA has recently released work directly connecting extreme weather events and (anthropogenic) climate change (see: http://m.npr.org/story/150072685), belying USDA secretary Vilsack's politically-motivated refusal to connect the dots between climate change and the current drought. Their models suggest a 20X risk for heat wave events in the coming decades compared to the 20th century.

Nevertheless, I want to point out that there is much that poor land-management has contributed, both in terms of drought susceptibility and in contributing to climate change locally, regionally and globally. Drought occurs as a function of effective, not total, precipitation. Effective precipitation is that which infiltrates into the topsoil, and is retained either for plant growth, or percolates to recharge groundwater flows and sources. Non-effective precipitation, by contrast, either runs off in the first place, or infiltrates the topsoil only to be lost through bare-ground evaporation.

Dry (C3) Grass

 The goal of ecological land management is to make effective precipitation approach total precipitation.

In turn, the key to this is management of the soil surface and the health of the topsoil. On both counts, conventional agriculture and ranching is a big fail. Arable monocultures are mostly bareground, subject to repeated tillage, and a barrage of chemical fertilizers, herbicides and pesticides. Heavy equipment compacts the topsoil, adding insult to injury. These factors cause depletion of organic carbon stocks and soil structure, decreasing infiltration and water retention capacity. In turn, this guarantees much higher rates of soil erosion, water runoff, and evaporative losses (a non-effective water cycle).

Without further elaboration, it should be clear that land management plays a big role in whether droughts develop, and, if they do, how severe they get. I'm not saying that rainfall isn't important- it obviously is, along with temperature- but it's a mistake to go into victim-mode and blame everything on factors outside of our control.

How to respond?

The first thing is we need to get a serious energy and climate policy. That means reducing personal consumption of fossil-fuel energy in all its guises, and investing in efficiency and renewables, both locally and federally.

Secondly, we need to get serious about land management- which means agriculture, ranching and, to some extent, forestry have to change in fundamental ways. This will mitigate GHG emissions by building soil carbon stocks, and foster resilience to drought, flood, wildfires, etc.

Finally, we should all look at ways of using water wisely, and investing in strategies to harvest and retain water (e.g. rain-barrels, ponds, keyline dams) in our landscapes.


Chris

A note on pastures: grass growth ceased this year for two main reasons, water stress and C3 physiology. C3 grasses have lower optima for temperature than do C4- plus are generally less deeply rooted hence more susceptible to drought. The combination of high temperatures and suboptimal rainfall caused extremely premature dormancy and senescence in our C3 grasses.

I suggest that farmers should look at setting aside 1/4 to 1/3 of their pasture-land into C4 grasses (Switchgrass and Eastern Gamagrass would be good choices), for hay and grazing. Although traditionally scorned by more northerly farmers, the Warm-Season grasses may play a big role in adapting to the 20-fold increased in heat wave risk forecast by NOAA.