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.
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.
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.
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.
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.
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.
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.
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.
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.
Excellent job of helping us frame our perspective. I often turn to Weaver’s work for help with perspective (regarding root systems, differences between plant species, hydrology, and response to local climate). Your work here to bring Weaver’s work to light and compare with current conditions is very good. Thanks for all you’re doing to enlighten so many people. Keep it up.
Awesome post. People forget Weaver’s work which is unfortunate, because it could really inform what a lot of people are doing right now,.
Many of the odd early bloomers of 2012 here in NE Kansas (the C4 grasses and asters that flowered in May) are flowering again fairly close to their normal times, although I am not sure that it is generally the same individual plants…but I have seen some heath asters that have dispersed seeds and are now blooming again. Many things have flowered within days of small rains we had over the summer or the huge rain we had last weekend. I had rigid goldenrod on my plots that was poised to bloom in early July or that had opened up only a few flowers, but many of them halted development for weeks and then bloomed immediately after rains as small as fifteen hundredths of an inch. I have been meaning to post again on my blog, but field work, job search, readying a house for market have killed my time to gather my thoughts on this.
I actually did see a couple Maximillian sunflowers blooming in June when I was up on the Platte River prairies…the plant right in front of the Derr House patio was flowering then and is in seed now, but that was a rare exception. One thing that is encouraging to me is that flowering time in response to the crazy weather this year varies among individuals within a lot of species, so nature has something to work with, assuming populations contain that variability (and I think moving forward with restoration, this is one of the assurances we need to work towards making).
One thing that was very different from any year in the past, at least in NE Kansas (but I would assume also much of Nebraska) was just how anomalously warm spring was. The average March through May temperature for us was 1.5 degrees C above the year with the second warmest spring (1977…and I think at least 2C above any of the dust bowl years) and 7 C above average (Celsius! and three month averages! The chance of selecting this year’s spring temperature from a normal distribution based on the climate record was 1 in > 4,000!). I wonder if plants that were able to take advantage of that and flower before soils dried out in summer would have a long-term edge (drought avoiders), if such warm springs followed by droughty summers were more the norm.
Chris, My dad was a young farmer in Richardson County in 1934. His corn crop was “a half-wagon load of nubbins.” The grasshoppers were awful. In the face of this, however, he and my mother were married in the fall of that year. He kept farm records all his life and was convinced of a 20-year drought cycle in the area, citing the mid-50’s and mid-70’s as examples. Thanks for this post on 1934.
I appreciate the Weaver references too–good to keep the long term perspective with published papers.
Here in southwestern Minnesota the cash crops as well as pasture grass show the same soil patterns that you describe for alluvial soils. That also includes upland soils with varying parent materials such as windblown loess and glacial till. Deep subsoil moisture becomes much more important in the drought conditions.
Thanks for another helpful post~
Outstanding observations and comparisions…I am finding a lot of the same going on in the area here…I did notice butterflies of differing kinds in very early spring and a much smaller population during their normal migrations …I have seen many more honey bees then normal in my garden …
A very thorough account of these droughts. The native vegetation is so well adapted to handling this kind of stress. I only wish that we gave them the space to do what comes naturally to them.
Reblogged this on The Great Plains Trail and commented:
Dry and hot indeed – all over the Great Plains region.
Excellent post, Chris. Enjoyed it and will pass it on to others.
Wow. Have you visited my garden? It’s uncanny how the plants and conditions you described happened in my much smaller backyard. I agree, fall bloomers seem to be nearer their schedules than summer and spring bloomers, though things are still weeks ahead (I’d venture to say some of my prairie perennials were 4 weeks or more ahead this year). As for pollinators, definitely a lack of butterflies and moths in west Lincoln, but bees, flies, and wasps seem to be doing ok. Thank goodness my neighbors water their lawns which they never use–I think some of that runoff is helping the edges of my garden.
How appropriate to note John E. Weaver. Thanks for the post. Tobey, however, in “Saving the Prairies” p. 196ff, says that Weaver came to change his mind in later publications, notably in a 1938 book with his mentor Frederic Clements and in another paper with Albertson in 1940, in which he expressed doubt that original prairies could regenerate. Unfortunately, in a dispute with his employer, Weaver at his death instructed his son, the viticulturist Robert Weaver, to burn his papers, or we might know more of his views on drought and climate change.
Jon, you’re right – his later papers on the drought are a little depressing. On the other hand, the observations he makes about the way prairies looked following the dry 1930’s are really interesting – he just just went a little overboard on his interpretation of the long-term impacts. I’m glad he was wrong! Most of the plant populations he figured were doomed did indeed make a comeback. I’m hoping to go back and look at those papers again next year and do some comparisons with what we see happening in the 2013 prairies (hoping, of course, that we’ll have gotten some rain by then!).
Is Isaac going to make a difference as it moves north from the Gulf?
Bradley – not sure whether Isaac will affect us or not. Nothing in the forecast makes me think so at this point… It’d be nice for Isaac to head this way and dump on us, but I’m not holding my breath!
In WI our established plants are looking good after a few good rains in late July while the ones that were seeded last year appear to be dead or (hopefully) dormant. Poa seems to have taken over in the recently seeded areas, too.
Thanks for the heads up on Weaver, and others’ comments on his work as well.
Love the historical comparisons. It’s easy to get caught up in the here-and-now. I met with a rancher last week that seriously suggested we are entering the Apocalypse. The only trouble is that last year was exceedingly cool and wet by Wyoming standards. Perhaps an exceedingly dry year in Wyoming and the Apocalypse are not that dissimilar, but it is surprising what a difference one year can make.
Let’s hope we can avoid the Apocalypse for a bit longer. Though I bet prairies could survive that too…
There is something going on in our world that has worried me for many years.
In this part of the great plains sometimes the only place for pollinaters and wild life to find sustinance is in the road sides. Every thing else is plowed or grazed away!
During drought situations even the road sides are all mowed and bailed to feed cows in unpresidented ways.
This is a problem that needs to be addressed!!
I know this isnt in the scope of your blog…but if we dont address this then we are going to loose the battle of preserving the prairie and all the inhabitants!
Where do we start??
Great comments Chris. I saw the same things.
I was really licking my chops with the warm spring this year, since I seeded a new area the winter of 2011. lot of stuff germinated and dissappeared. I have probably taken a year or two off my life worrying about this planting….95 species. We’ll see what things look like next summer.
One good thing about the drought is I have discovered some hardy native remnant vegetation poking up through the hurting, dormant cool season grass stands (fescue). So I will have some more area to burn this next spring and see what else has been supressed. Some plants that poked through my back yard and flowered include false boneset, wild bergamot, with a few different asters on the verge of flowering. Wondering what else is back there?
It’s been a fun year to go out and poke around normally lush field corners or in your own backyard to see what’s trying to come through.
Thanks Chris for another great post. Its great to have Weaver’s early records to compare things against. Can I ask a difficult question about this sentence, “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.”
In small remnants, in particular, severe stresses like droughts may deplete populations to a degree from which it is very difficult to recover, especially if the populations were originally small.
The remnants that we see now contain only the survivors from past droughts, and its possible that populations of some species may have declined (or even gone extinct) at small sites in each successive severe drought. Unless we can compare the numbers of individuals or species that existed both before and after each drought, then we can’t really tell how well (or badly) things are trending, can we?
You are very fortunate in having such great historical information to compare things against. But without such information there is a danger of the ‘shifting baselines’ effect, where sites could be declining over time – perhaps exacerbated by severe droughts – but each generation of new observers takes the current condition as being ‘normal’, without knowing of past changes.
Thanks again for another great informative and thought provoking blog. Best wishes Ian
Ian, you make an excellent point. There’s no question that small isolated prairies have fewer species than a large contiguous prairie landscape. I’m making a fairly bold prediction (and generalization) that most of those small prairies have already reached a new equilibrium of species richness etc., and that having been through droughts before, that equilibrium has already been tested before. You’re right, of course, that a stress like a drought could spell the end of populations that are already on the edge. That may be happening, but I’m guessing that at least most populations of plants and insects in small prairies are the ones that can withstand that kind of stress. The shifting baselines effect, though, is certainly something to be wary of.
My reason for the comment was to take an optimistic view of the drought and its effects on prairies. Sitting around and worrying about how the drought might be decimating species we like doesn’t do any good, and there’s really not much we can do about it anyway. In small prairies, I think we have to trust in the resilience of species, and hope that the management we’ve done to build that resilience is paying off. And, in between droughts, we can take advantage of opportunities to enlarge and reconnect those small prairies through prairie restoration (reconstruction), where possible.
Thanks for the comment.
I am personally always amazed how much can survive in a small remnant. Many insects never travel very far. I often see more species in a tenth of an acre remnant than I do in a thousand acre restoration.
Thanks again Chris for such a detailed reply. You are right to focus on optimism. Here in SE Australia we suffered our worse drought for a century in the decade to 2010. While we undoubtedly suffered losses, the drought eventually broke with flooding rains, and ecosystems bounced back with extraordinary vitality and abundance. It is truly astonishing how much of a ‘pummeling’ many species can tolerate, but as you said, they’ve done it many, many, many times before. Keeping one’s head down and biding one’s time until conditions improve is a tried and true strategy for long-term success! Best wishes Ian
In the case of my back yard…which is adjacent to a tiny 1/2 acre remnant, i am seeing big bluestem, indian grass, and handfull of forbes expanding with this drought. The adjacent cool season vegetation is cooked and these natives are showing themselves. Most plants are within 15 feet of the remnant vegetation and most likely coming from seed rain, but others are a good 100 feet or so and maturing to flower this year. So even though it’s a been a tough year for the prairie, more species in my area have been released compared to a normal lush year where these species would have been suppressed and inconspicuous. Wild petunia, partridge pea, bergamot, false boneset, big bluestem, indiangrass, tic trefoil, rough dropseed, silky aster, smooth aster, new england aster are all very evident in a space that used to be lush fescue that was mowed to 4 inches on a bi-weekly basis for the past 10 years or so….pretty amazing.
Most noteably though, some of the forbes listed above are not in the remnant…..so in this one scenario where there’s cool season exotic species that have all but turned to dirt and are located near a known remnant, we have a remnant that is increasing in size and species diversity. Even though it will need some help to continue on the same trajectory when normal weather patterns return by eliminating the exotic grass.
The discussion of remnants (relicts) recalls the 1934 work of Frederic Clements, “The Relict Method in Dynamic Ecology.” Clements, incidentally, a prolific author, coined the term “forb” and put it into use. Of interest to Nebraskans: I have nominated Frederic and Edith Clements for inclusion into the Nebraska Hall of Fame. Public hearings are scheduled this month in Norfolk (Sept 12), Omaha (Sept 13), and Holdrege (Sept 19).
Since you asked about ants (you did ask, didn’t you?), I’ll talk about what happens to them during droughts.
– First, ants are among the more successful groups of insects in deserts, so as a group they can certainly adapt to droughty conditions. This may be in part be due to their ability to burrow deeper as the ground dries out near the surface, and to shift back and forth between diurnal and nocturnal activity when it’s cool or hot, respectively.
– In more humid climates, reduced plant productivity during droughts affects ants both directly and indirectly. Directly because, appearances notwithstanding, most ants are effectively herbivores (as nitrogen isotope ratios in their tissues attest), their main food sources being extrafloral and to a lesser extent floral nectar, juice of damaged and fallen fruits, and honeydew. Honeydew is essentially a sugary concentrate of plant sap, excreted by aphids and their relatives. No aphids are harmed in the extraction process, but plants may experience some damage.
– Indirectly, because during droughts, reduced plant productivity means reduced herbivore abundance, thus less supplemental protein, from predation on other insects, for brood growth, so colony growth is slowed.
– Since worker ants only live 1-3 years, lower productivity during a drought year can result in shrinking of the colony population. This may be mitigated by workers ceasing to forage (most mortality occurs during foraging), and by consumption of brood to sustain the adult population in hard times.
– Another mitigating factor may, however, be increased scavenging of invertebrate victims of the drought.
– Only larger colonies of ant species are able to rear the expensive winged sexuals (especially the females, which build up large fat stores before leaving the nest on a mating/dispersal flight), so reduced worker numbers results in reduced colony fitness.
And yet, ants seem surprisingly resistant and resilient to drought. For example, after one of the driest and hottest June-July periods on record this year, the common grassland species Lasius neoniger (a.k.a., cornfield ant) had large flights after the Isaac-inspired rains during the last week here in Missouri.
Thanks James! You are always welcome to inject ant information into any topic on this blog… I find it fascinating. You wrote it so nicely that some people might skip over the most important (or most morbid) part of your comment. As I understand it, a major drought survival strategy of ants is to just stay home and eat the kids?
Yep. Nature can seem cruel to us, even the nature of such admirable creatures as ants.
Chris and others – I’m sort of new to this blog and hope to be a more regular reader. I have recently retired from 35 years with NRCS as a wildlife biologist and range conservationist in Texas. I realize that central and west Texas is of out of context for being considered traditional prairie; but many of the same species grow here and many of the principles apply. Here in my location (San Angelo, Texas) we are in an 20 inch average rainfall zone and warm season grasses dominate most sites, including a mix of tall, mid and short grasses. 2011 was the driest year on record for most of Texas, going back more than 100 years. We saw lots of perennial grass die (roots and all) during 2011 and have been anxiously waiting to see how nature recovers after such a drought. Thankfully much of Texas had a very wet winter and early spring in 2012. We grew tons of weeds and wildflowers. The rains were obviously welcomed by all but were short lived. The weeds, forbs and wildflowers sapped the moisture and there was little left over for warm season growth. After the profusion of annual forbs died back, we have observed an amazing new wave of Texas wintergrass seedlings (Stipa leucotricha). This is our most common cool season native perennial grass. Now it seems that millions of acres that have always been considered to be mostly warm season ranges, may now be growing mostly cool season grass. It appears to be a major shift and will be interesting to see how long it perists. I guess anything is better than bare ground so we are happy to regain perennial grass cover but few would have predicted such a large scale increase in TWG on ranges and pasture that had formerly been dominated by warm season grasses for the previous 100 years. All of the ecological site descriptions for these sites will show TWG as having made up perhaps 5 – 15% of total annual production in historic conditions.
Have others of you noted any kind of major switch from warm to cool season dominance as a result of the drought?
Steve, this is a fascinating story – thank you for sharing it. I’ll be curious to hear from others in the south who are also further into this drought than we are here. I obviously don’t have the experience to prognosticate about the future of Texas grasslands. That said, J.E. Weaver did write some very interesting papers in the late 1930’s and early 1940’s describing major changes in prairie vegetation following the big droughts of the 1930’s in Nebraska. One of the ones I remember is a big flip from big bluestem dominance to dominance of western wheatgrass – at least somewhat analagous to your situation. I don’t know how long it took for that to flip back, but it apparently did, because we’re certainly back to big bluestem again now… Weaver also said a lot of farmers actually farmed up their prairies because they were so sure the prairie vegetation was completely dead. Weaver was also convinced that the prairies had suffered irreversible losses. Nice to read all that now, knowing that the prairies did indeed recover with time. I hope you’ll see the same thing in Texas.
Hi Chris– Received your email, but thought I could reply here. The summer of 2011 was brutal, though much of North central Texas was slightly less affected by the drought. The winter and early spring of 2012 provided abundant rain, and we saw prolific expression of native annuals such as Bifora americana and Centaurea americana this year. We can generally read this as reduction of perennial competition and bare soil. The Texas Blackland Prairie Remnants– generally small patch– have had few warm season perennial grass flowering events in the past few years. Exceptions have been Sporobolus silveanus and Tripsacum dactyloides. These are both dominants on alfisol -former vs vertisol–latter. The latter has seed set in June and responds to early rains, though it is a C4 species. Nassella leucotricha was abundant on vertisols following winter rains. I would read this as a response to reduced warm season grass competition, coupled with early growing season rain.
Opposed to the above deep soil sites, the thin-soiled Grand Prairie (about 2 million acres running from the Red River south to Johnson Co and west of the Blackland.) which is underlain by lower Cretaceous limestone (similar to the situation reported by Steve above) witnessed a huge expansion of cool season annual exotics. Areas which had supported abundant Andropogon gerardii; Panicum virgatum, and Schizachyrium scoparium were aspect dominated by Bromus. Nassella was also abundant, but less so. It was difficult to find warm season native grasses on some of the sites I examined.
Under episodic drought, I would anticipate recovery of the C4 communities. However, the question is begged as to whether we are entering a new climate regime. Over the past 20 or so years, seasonality of rainfall has definitely changed. We have experienced a change from the spring-fall bimodal distribution to primarily winter events. This would be expected to benefit cool season species. Given that our eastern prairies are relicts of a former regime, it is hard to predict composition and dominance for the future. We are seeing increased Nassella, as well as Bouteloua curtipendula and Sporobolus compositus var drummondii. These scrappy little guys might end up being dominants in the long run.
Thanks for bringing this to the discussion.
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I have another comment / question from any of you regarding recovery after drought. In the wet winter and early spring of 2012, we had he expected flush of forbs. Across much of central Texas this included at least three species of cool season annual legumes – Vicia ludoviciana, Astragalus nuttallianus and Medicago polymorpha. In many places these were very dominant with good plant density across large areas. We would hope that these added a good deal of N to the soils. Wondering if anyone can verify if these species do in fact significantly enrich soils with N via natural Rhizobium. If so, I also wonder about the fate of soil N if it stays hot and dry for months afterward. Thanks.
Steve, it’s a great question, but not one I feel qualified to answer. I don’t know the species very well, and don’t pretend to understand N cycling well enough to even guess… Hopefully, others will chime in.
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