*Actually, this post just looks a a couple of interesting new drought papers that caught this week. There’s a hell of a lot more data out there on this issue that would not fit in one blog post.
2012 was seriously hot and dry- the warmest year on record in the United States and the country had the worse drought in over half a century, with 80 percent of our agricultural land experiencing drought. Climate scientists predict that climate change could be creating more droughts– through warmer temperatures and changing precipitation patterns.
The USDA reports that we’ll see the impacts of the 2012 drought at the grocery store this year- with expected increases of 4% in prices for meat and milk. They estimate that the nation’s corn crop was down more than 10% from the previous year, raising prices. Because corn provides the the foundation of the feed for livestock, the price increase plays out for consumers at the butcher counter or dairy case.
Whenever people start discussing the potential impacts of climate change on agricultural production, it’s common to hear that the plants will be able to adjust. After all, isn’t that the basic story of natural selection? The genetic diversity of a species allows it to adapt to changing environmental conditions- the fittest in the new regime survive and prosper, producing more well-adapted offspring. Last week, a paper published in Nature titled “Ecosystem resilience despite large-scale altered hydroclimatic conditions,” sounded pretty optimistic, from the title at least, on the ability of plants to adapt to drier climes. They used data from a network of long-term ecological research sites in the U.S. and in Australia to compare vegetation productivity from the past decade of hotter, drier conditions to earlier, wetter decades.
They used the vegetation productivity, precipitation data and evapotranspiration estimates to determine the water use efficiency of the vegetation. Across ecosystems, they found that plants used more water when it was available, but shifted to higher water efficiency during drought conditions. That sounds like good news for plants in an era of climate chaos, but the authors also found that the water-use flexibility, also referred to as resilience, can be pushed past a breaking point. They write:
With continuing warm drought, the single linear above ground net primary production/evapotranspiration relation that forms the common cross-biome water use efficiency would collapse as biomes endure the significant drought-induced mortality that has been extensively documented over the past decade. This loss of resilience associated with dieback would probably occur first for ecosystems that respond most rapidly to precipitation variability (that is, grasslands). During this study period, grassland water use efficiency decreased with increasing aridity, indicating a decreasing resilience with prolonged warm drought in these biomes, as predicted. This suggests that these systems are closer to a threshold which, when crossed, will result in biome reorganization.
So ecosystems are only flexible to a point, and but prolonged drought can and probably will lead to “biome reorganization”- the old vegetation dying out and other species, better suited for the new climate regime moving in. Most of the data for this breaking-point theory comes from Australian grasslands, but one of the authors said in a press release that they found ecosystem resilience approaching the threshold in the southwestern U.S. as well.
Our current agricultural system is based on previous precipitation patterns, and this work suggests that while plants can adapt to a degree, eventually they’ll lose too much productivity and we’ll need to irrigate or relocated our crops, or both. Irrigation often depends on groundwater. Another paper out this week points out that increased drought and precipitation variability will only increase the stress on our groundwater supply.
For further proof that changing climate conditions will affect what plants we can grow successfully where, the USDA released it’s updated Plant Hardiness Zone Map this month. The traditional 10 degree zones have been broken down into 5 degree bands, and the USDA estimates that the zones have shifted about a half zone, or 5 degrees, from the previous map made in 1990. I have a friend here in Wisconsin who jokes that he’s starting citrus trees in the greenhouse for an orchard in the climate of the future. Right now, no one’s predicting anything quite that extreme, but it might not take extreme shifts to shake up plant production, particularly for our carefully calibrated crops.