This summer eastern Kansas has been in an extreme drought. But what exactly does it mean to be in a drought, and did you know that there are several types of drought often not discussed? Generally, a drought is a period when an area receives below-average amounts of rain/snow. Droughts can last months, years and even decades (decadal droughts are called “megadroughts”). However, not all droughts are equal and differ in their impacts on society, plants, animals, and the landscape. The National Drought Mitigation Center (https://drought.unl.edu/) has identified five different types of droughts and their impacts, as shown in the table below.
Kansas is no stranger to droughts and since the beginning of the year, the eastern half of Kansas has been in – and continues to be in – a drought. In fact, we’ve experienced all of the droughts defined by the National Drought Mitigation Center except socioeconomic drought. Normally, Kansas receives 75% (24.6 inches) of our yearly precipitation from April to September, but this year we received only 30% (9.6 inches) during this time. With such a small amount of precipitation how does that affect the animals and plants in the prairie?
For bison, this drought has had little effect because they get most of their water (around 80%) from the grasses they eat, and the grasses they prefer are drought tolerant. Bison still need to drink water, and the drought has caused them to search more for what little water is left. Another group of animals that did not seem to be too impacted by the drought was birds. KSU Biology graduate student Sarah Winnicki reported that birds living in prairies still had nests with chicks, and the number of chicks did not change compared to a non-drought year. Grasshoppers also did well and increased in number despite the drought. But not all prairie animals fare well during droughts; most obviously, aquatic animals. It is no surprise that fish do not do well in droughts, but prairie stream fish are used to streams drying up during the summer, leaving refuge pools to live in until enough rain comes and flushes these pools, causing the stream to flow. However, this year that rain did not come, and the refuge pools continued to decrease in size over the summer.
Graduate student Garrett Hopper measured that these decreases in pool size led to less oxygen in the water, increases in water temperature and nitrogen pollution from fish excretions (poop and pee). These water conditions led to intense competition for survival between different fish species. The native redbelly dace did not fare so well, but the non-native western mosquito fish were able to survive, causing a complete reordering of dominance on this prairie stream. Despite native redbelly dace and other native fish dying in these small pools, these species are not extinct from the prairie streams because the large rivers did not dry up. These rivers will allow native fish to move back into the once dry streams when the streams begin to flow again.
This year’s drought also caused a change in plant species dominance. Generally big bluestem, Indian grass, and switchgrass are the dominant grasses in the tall grass prairie but this year we saw a switch to grasses that would normally be more at home in central and western Kansas. Our usual dominant grasses were still present but buffalo grass, side-oats grama, and blue grama became more dominant.
Besides plant species switching dominance, we also saw a decrease in growth and a delay or lack of flowering from plants. The delay or lack of flowering in prairie plants is an evolved strategy to conserve resources for growth the following year when conditions are (hopefully) better.
Prairies are dynamic ecosystems made up of many species that have evolved to withstand drought. There may be species that do not thrive under drought, but the majority of prairie species, animal or plant, will continue to persist because of evolved survival strategies. These organisms have lived through extreme droughts before, including the 1930’s Dust Bowl, and we still have many of the same species today as we did then.
Rory O’Connor is a PhD student at Kansas State University interested in how woody plants encroach into grasslands and the best ways to remove them.