A warm and dry winter, followed by a hot dry spring and summer… Temperatures over 100 degrees Fahrenheit for weeks at a time… Wildflowers blooming two to three weeks earlier than normal, and often for much shorter periods than typical… Other plants withering and/or going dormant before they get a chance to bloom.
Sound familiar? It’s a good description of the conditions across much of the central United States in 2012. However, it’s also a description of eastern Nebraska back in 1934. The famous prairie biologist, J.E. Weaver and two colleagues published a 1935 paper detailing the response of prairie plants to the “great drought of 1934”, in which they describe the weather conditions and plant community responses in prairies near Lincoln. The similarities between the drought of 1934 and 2012 are pretty strong. The main difference is that much of Nebraska actually had fairly wet conditions during the spring and summer of 2011, whereas in 1934 the extreme drought came on the heels of dry seasons in both 1931 and 1933. Apart from that, a warm dry winter, very low rainfall, and extraordinarily long stretches of very hot temperatures characterized both 1934 and 2012.
Most prairies look pretty dry this year. In this burned and grazed prairie, only the most drought tolerant plants, including plains sunflower, western ragweed, and prairie sandreed, are still green.
The paper by Weaver, Stoddart, and Noll is interesting for a couple reasons. First, it’s nice to see evidence that prairies have been through the kind of conditions we’re experiencing this year, and to know that those prairies rebounded. We all know prairie communities are resilient, but with a high likelihood of more frequent and intense droughts in our future, it’s comforting to see some historical evidence that prairies have the capability to handle extreme weather (in fact, the drought of 1934 was followed by drought conditions for most of the rest of that decade). Second, the authors describe the way individual plant species responded to the drought conditions of 1934, and it’s both fascinating and reassuring to see the same plant species responding in similar ways now. Weaver and his colleagues describe the overall appearance of the prairie, season by season, and discuss the relationship between the ability of species to withstand drought conditions and their rooting depths and architecture. Also of interest, Weaver published a follow-up paper in 1936, describing the way prairie plant communities looked in 1935 – one year after the big drought.
When I first started working in the Platte Prairies as a graduate student in the early 1990’s, the area was experiencing some wet years. Groundwater levels were high, particularly in the spring and early summer, and I remember sloshing through meadows in hip waders trying to count birds and characterize vegetation structure. Don’t even get me started on the mosquitoes! My third season as a TNC employee was 1999, which started out wet, but then turned very dry in the mid-summer – and the ensuing drought lasted for about 5 years.
During that drought, I was more than a little worried about the prairies and wetlands I was in charge of restoring and managing. Watching the Platte River go dry and stay dry for months, taking the groundwater levels down with it, was hard to take. We were at the height of our prairie planting years at that point too, seeding 100 or more acres in each of many of those dry years, using high-diversity seed mixes we’d hand-harvested. There wasn’t much local experience with how plantings might (or might not!) establish in that kind of dry weather, so we and our partners overanalyzed and fretted quite a bit – needlessly, as it turned out.
All of our seedings from that drought period turned out just fine, though they established more slowly than we were used to. Our remnant prairies came through the drought years too. The grasses and wildflowers that wilted and died each hot dry summer kept re-emerging and growing again the next year. The Kentucky bluegrass that invaded the dried out swales in our meadows during the drought disappeared under a carpet of resurgent wetland sedges once the rains and groundwater returned.
The Platte River was bone dry along much of its length by mid-summer this year – much like it was during our last drought. Groundwater dropped with the river levels, falling below the root zones of most plants.
Looking back on that multi-year drought makes this year much easier to take. Having seen firsthand evidence that my prairies can rebound from tough conditions means that I’m not wringing my hands as I walk through the dry crunchy grass this summer. I can pay attention to how plant species are reacting to the drought, and celebrate their individual coping strategies, instead of worrying about whether or not they’ll survive. Comparing what I’m seeing this year to what Weaver saw in 1934 makes it all the more fascinating.
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Individual Plant Species Responses to Drought
By and large, Weaver’s observations of plant species responses to the 1934 drought seem to match mine from 2012. We had a little more moisture in our prairies during the spring and early summer than Weaver saw in 1934, so some of our spring wildflowers had better growing seasons. For example, we harvested strong quantities of seed from species such as pussy toes (Antennaria neglecta) and prairie ragwort (Senecio plattensis) this spring, while those were among the species that had tough years in 1934. On the other hand, the two species of blue eyed grass (Sisyrhinchium campestre and S. montanum) had banner seed production years in both 1934 and 2012.
By the time July came around in 2012, our prairies were starting to brown up considerably. Areas hit hardest were those in soils of low organic matter, and those that had been burned in the spring and subsequently grazed. The spring fires had both attracted intensive grazing and removed the insulating plant litter (from previous years’ growth) that would otherwise have helped preserve soil moisture. Then, grazing in those burned areas reduced the root masses of the grasses – and the select wildflowers that were grazed – reducing their ability to reach what little soil moisture was left. However, even in those dry crunchy areas, a few plant species looked unfazed. Prairie clovers and leadplant, for example, grew tall and bloomed vibrantly. Some of the prairie clovers were grazed, but many of them (and all of the leadplant) produced what appears to be viable seed. Other plants that appeared to thrive even in the burned/grazed dry sites included serrate-leaf primrose, wild licorice, white sage, pitcher sage, Missouri goldenrod, and stiff goldenrod – among others. All of those species were among the deeply-rooted plants that Weaver observed to be thriving in the 1934 drought.
Pitcher sage (Salvia azurea) is still green and flowering, even when surrounded by plants that have already given up for the year.
Below is a table that lists most of the plant species (and their response to drought) noted by Weaver and his colleagues in their 1935 paper. Most of the plant names he used are now outdated, but I did my best to update and correct them. I had trouble getting the resolution of the text to come through well, so I’m also providing a link to a PDF of the same table if you want to see it more clearly.
The link to the above table in PDF form: weaver drought flower list
One interesting aspect of Weaver’s observations – and mine from this summer – is that there are examples of closely related species with very different responses to drought. For example, scaly blazing star (Liatris squarrosa) has a relatively shallow root system attached to a thick fleshy corm (like a bulb). Weaver noted that the tops of this species dried up by late June in 1934, but that it’s relative, dotted gayfeather (Liatris punctata) had a very deep root system that allowed it to stay green and actively growing throughout the season. Scaly blazing star bloomed in our prairies this year, but not with the abundance we’ve seen in previous years. Dotted gayfeather plants are just now starting to bloom, and they look like little pink lighthouses in oceans of brown grass. Similarly, Weaver noted that while both Missouri and Stiff goldenrods were able to grow and bloom in 1934, Missouri goldenrod seemed much more strongly affected by the drought than its cousin.
This scaly blazing star (Liatris squarrosa) plant is a rare example of its species that was able to flower this year. This one has been grazed off (by cow, deer, or other herbivore) and is making a second attempt to bloom. Many other blazing star plants didn’t even bloom once this summer.
While I didn’t include them in the above table, Weaver wrote extensively about the condition of various grass species through the 1934 season. Cool-season (C3) grasses such as Junegrass, porcupine grass, and Kentucky bluegrass bloomed, but only at about 1/3 of their typical height, and they didn’t produce seed. Panic grasses (low-growing Panicum species) barely flowered at all. Big bluestem was the last warm-season (C4) grass species to dry up in most sites (excluding wet swales), and Weaver ascribed that to its particularly extensive root system. He noted specifically that indiangrass seemed less able to withstand the dry conditions than big bluestem, though it fared better than little bluestem, sideoats grama, and prairie dropseed.
Other Aspects of the Drought
In both 1934 and 2012, flowers were opening two to three weeks earlier than normal, and tended to stay open for shorter periods than in wetter years. One phenomenon not noted by Weaver that we – and others around the country – saw in 2012 was the extraordinarily early blooming of some of the late summer/fall species, particularly asters, which in some cases were blooming in May. I’ve heard others theorize that the flowering of those asters might have been triggered by day length, and that they had grown sufficiently by May to bloom then (before the solstice) instead of later in the fall when the same day length occurred again. I’m not sure if that’s right, but it’s a great theory.
I don’t have strong enough records to be confident, but it seems to me that the flowering time of at least some prairie wildflowers is getting closer to their regular schedule now that we’re nearing fall. Species such as showy tick trefoil, Maximilian sunflower and stiff sunflower, for example, have just started blooming recently (excepting a few outliers which bloomed a month ago), which seems to be right on schedule. On the other hand, everything is so mixed up right now – and some flowers aren’t blooming at all this year – it’s hard for me to tell.
Where it has sufficient moisture, Maximilian sunflower seems to be blooming on its regular schedule this year, as opposed to many earlier-flowering species, most of which were two to three weeks early.
One of the striking aspects of droughts in our Platte River Prairies is that the alluvial (river-deposited) soils beneath our prairies become very evident when the weather gets dry. Once groundwater drops below the easy reach of many plants, big wide stripes start appearing all over the prairies. Bands of soil consisting largely of coarse sands, with little organic matter, dry out very quickly and the plants growing there can wilt and go dormant after only a few weeks of low moisture. At the other end of the spectrum, there are bands with much more organic matter that stay green and vibrant even during the kind of heat and drought we’ve experienced this summer. We’re hoping to harvest grass seed from one particular burned prairie this fall. Much of that prairie is dry and brown, but there are quite a few stripes of 6-foot tall big bluestem and other grasses winding through the burned area, and the one inch of rain we got late last week just might give those currently-flowering grasses the boost they need to produce some seed for us.
Alluvial soils are on display in this dry summer, especially in burned Platte River Prairies. The strip of big bluestem on the right may produce a heavy crop of viable seed, while the grass in a band of sandier soil to the left of it has been brown and dormant for weeks.
There’s not enough time (nor do I have enough expertise) to discuss how the drought is affecting all the other parts of the prairie community along the Platte River. That said, much of the grassland bird nesting was completed before the drought conditions become very severe this year, so I wouldn’t think most birds noticed much of a difference from other years. However, I wonder whether the scarcity of seed-producing plants now might have impacts on seed-feeding migrant and wintering birds later this year. On the other hand, many of the big seed producers for birds and other wildlife include plants “weedy” plants like ragweeds and annual sunflowers, and they seem to be weathering the drought pretty well. Maybe birds will be ok.
Pollinators, on the other hand, are certainly being affected by the scarcity of flowers in our prairies right now. As I’ve said before, learning more about pollinators during the last several years has been very thought-provoking, and makes me see my prairies through different eyes than before. When Mike Arduser was here in July, there were still quite a few flowers blooming in some areas (though not in others), and he found an impressive number and richness of bees. The early blooming of the wildflowers seemed to be matched by the early emergence of bee species – so the drought doesn’t seem to have knocked the flowers and their pollinators out of synch. As the season continues, however, there are fewer and fewer areas where flowers are blooming abundantly, and bees, butterflies, and other pollinators must be working pretty hard to support their nests right now. I don’t know if we’ll see differences in pollinator abundance next year because of this year’s drought, but I would guess we’re making fewer new bees than we did last year… On the other hand, the bees have been through this before too, so I’m not too worried about them in the bigger picture.
One last notable observation about bees is that the drought is highlighting one of the values of the prairie restoration (reconstruction) work we’ve been doing. We’ve been stitching together degraded remnant prairies (containing relatively low wildflower diversity) with high-diversity seedings that produce abundant flowers. Now that pollinators are really scrapping for food, the flowers in our restored areas may be supporting entire populations of bees and butterflies that might not have otherwise found sufficient food in the degraded remnants in the surrounding landscape. It’s hard to measure, but I feel good about what I see happening.
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We’ll Get Through It
There’s plenty to be stressed out about in dry years like this – especially for farmers and ranchers, and others, who rely on vegetative production for their livelihoods (my own farm is looking pretty tough this year). Ecologically, however, this is just one of many bumps in the road for prairies. Even though the fragmentation of many of today’s prairie landscapes is significant, even most small and isolated prairies have survived multi-year droughts in their current state. They’ll be fine.
So – as you walk around the brown crispy grass of your favorite neighborhood prairie, think of this year as an opportunity to revel in the resilience of grassland communities. Take note of and celebrate the plants and animals that are taking advantage of the dry weather to gain an advantage over their competition, and don’t worry about the species that are hunkering down until moisture returns. They’ve done it before, and they’ll do it again.
Thanks to Mike Arduser for bringing Weaver’s paper to my attention earlier this summer.
