The Prairie Ecologist

Here’s an aerial view of the Platte River and some of our prairies adjacent to it. Rainfall has been scarce upstream from us and river water levels have been dropping.

It’s been a while since our Platte River Prairies have seen drought. We had about six years of drought from late 1999 through 2006 and a one year extreme drought in 2012 that tapered off over the next year or so. We’ve had some dry periods since, but nothing severe or extended. The recent wet years have been productive, both from an agricultural and ecological standpoint, but here in the Great Plains, we know that drought can reappear at any time.

We started the 2020 growing season with flooding, but since mid-June, the Platte River Prairies have been drying out. The most recent drought maps show our sites right on the border between moderate and severe drought. To the east of us, much of the central tallgrass prairie region is in the same boat (which is maybe not the best metaphor when talking about drought).

Current drought map from the University of Nebraska-Lincoln Drought Mitigation Center.

Photographed a couple weeks ago, this purple prairie clover was maintaining its vibrant green color, but most of its neighbors had given up on the year and gone dormant because of the dry conditions.

This aerial photo shows how alluvial soil patterns really pop during drought. The soil beneath most of our prairies was laid down by ancient river flows. The browner strips in the above photo are where soil is characterized by especially shallow organic matter layers over sand. The greener areas have somewhat more organic matter, which helps hold and make moisture available to plants when rain becomes scarce. The patterns are particularly strong in formerly cropped areas (such as in the bottom right of the photo) where topsoil was depleted by farming before the site was restored to prairie vegetation.

In this photo, you can see vegetation response to alluvial soil patterns on the ground. Plants have gone dormant in less productive soils but are still green where there is a thicker layer of topsoil above the sand.

Drought makes life hard for people who rely on the vegetative production of prairies for their livelihood. Savvy ranchers have to incorporate drought into their ranch management plans, often including ‘trigger points’ that help them decide when to start cutting herd numbers in response to rainfall amounts by certain dates on the calendar. Economic survival relies on the ability to bank both money and prairie plant vigor during years of abundant rainfall in order to stay afloat (see, there I go again) during dry years. Inexperienced ranchers can get into trouble by ‘utilizing’ all the available grass in a wet year and then having no root reserves beneath the prairie when drought hits.

The economic impacts of drought are real and important, and they affect prairies as well as people. Across most of the Great Plains, most of the grasslands that still exist have survived (haven’t been turned to row crops or other human uses) because they can produce enough forage to support a ranching operation. More than 97 percent of Nebraska is privately owned, and most of those owners need income from the land so they can pay taxes and put food on the table. In landscapes like the Nebraska Sandhills, the survival of prairies and the survival of ranchers are inextricably linked.

As the soil dries, it becomes quickly apparent which plant species are well adapted to those conditions. Here, entire-leaf rosinweed (*Silphium integrifolium*) blooms while surrounded by dormant grasses and other brown vegetation.

From a purely ecological perspective, however, drought is not a serious threat to prairies. In fact, drought is one of the three main factors (the others are fire and grazing) that created and maintain prairie. Any prairie plant or animal species that has persisted for thousands of years has done so because of adaptations to drought. Those species can respond by changing their behavior, growth and reproductive rates, and other strategies. Populations of some species will decrease during droughts, but others thrive – often because of the lower competition from waning species.

This restored cropfield (former cropland) has green/brown patterns formed by alluvial soil patterns. However, the greenest strips are where we restored wetland/wet meadow habitat by re-excavating old swales before planting prairie vegetation. By digging those areas down closer to groundwater, we helped ensure that even during drought, there will be green vegetation and moist soil available for the species that rely on them. (The yellow in the photo is from Maximilian and sawtooth sunflowers.)

As a result, prairie communities look very different under drought conditions than when rainfall is plentiful. Plant species that were uncommon become abundant and others fade from dominance. Invertebrates and other animals respond accordingly. The populations of some animals decrease as their food source diminishes or habitat conditions become less favorable. Others simply change their diets to match the altered abundance of the prey or forage species available to them.

While prairies can look very different during drought, the resilience of prairies means the basic ecological functions and services are sustained. Plant production still feeds herbivores and those herbivores are available for the predators that consume them. Pollination still occurs, seeds are produced and dispersed, and carbon is pulled from the atmosphere. Life goes on.

This and the other aerial photos in this post were taken last week. The big green band through the middle of this photo is a riparian area where we converted a sandpit lake (from a sand and gravel mining operation) to a stream with adjacent wetlands. Through all the droughts over the last 20 years, this stream has continued to flow, providing important refuge for aquatic species and terrestrial animals that need access to water.

As this drought ramps up, there’s no way to know how long it will hang around. I feel for the ranchers and farmers who are going to have to dip into their reserves (financial and ecological) for a while. I hope they can make it through this drought, not only for their own sake, but also for the sake of the prairies they protect and care for. I don’t worry too much about the wildflowers, insects, birds, or other species living in the prairies, however, especially those living in relatively large and/or interconnected grasslands with diverse plant and animal communities. They’ve been through this before. You might say they’ve had thousands of years to either sink or swim (ok, that time I did it on purpose) during periods of drought.

If you’re interested in learning more about the resilience of prairies and the way they can respond to drought, here are links to a couple posts I’ve written previously.

The ‘Bench Strength’ of prairies in relation to climate change.

How to build and maintain the ecological resilience of prairies.

Prairie plants have deep roots, but not for the reasons we’ve always thought.

The Fellows and I made a quick trip to the Niobrara Valley Preserve last week to collect data. A recent scarcity of rain has turned the Sandhills brown and blooming wildflowers were hard to find. When Ashley and I came across a patch of plains sunflowers (Helianthus petiolaris) it was pretty clear it was acting as a magnet to a tremendous number of insects looking for pollen, nectar, and anything besides wilting plant material. Grasshoppers, in particular, were swarming all over the flowers. Here are some photos from that little patch of sunflowers.