In my last post I discussed my very un-prescribed, un-controlled burn. Now it’s time to discuss the results of the burn on the prairie. As stupid as my accidental arson was, it was also something I had desired to happen. It occurred a month earlier than the idealized version my brain had imagined, but I now had an opportunity to see the results of a large experiment. A gust of wind had given me a gift and I needed to show appreciation for that gift by learning a few things.

First, I can elaborate the results on introduced cool season grasses: no effect. If a prairie manager wants to discomfit cool season grasses and benefit warm season grasses a burn should occur in May. The burn occurred in early April when there was still frost in the ground. Neither the Kentucky bluegrass (Poa pratensis) nor the smooth brome (Bromus inermis) had any appreciable growth. The world was still brown when the fire occurred. I doubt the fire gave significant advantage to native grasses. Even as I write this I can think of one possible exception. Porcupine grass (Heterostipa spartea), which is common on the better soils on this prairie, seemed to produce much more seed than usual. Whether it gained any competitive advantage versus the introduced cool season grasses is uncertain, though I am continuing to evaluate the effect.

The effects on forbs, however, were eye opening. The first example I observed was buffalo bean milkvetch (Astragalus crassicarpus), aka ground plum. Buffalo beans are not uncommon, but many crowns, heretofore hidden in and dominated by grass cover. rocketed out of the ground after the fire. Each plant produced many long stems covered in blooms. Unfortunately, I was not yet fully committed to seed gathering at that time, but thankfully my friend Ben Lardy came out one day to gather several gallons of pods. Had I invested more time and energy there might have been ten gallons more. Cool season forbs, ready to rock and roll in April and May would logically benefit from an early fire. The removal of the thatch (mimicking heavy grazing) also benefited the pasqueflowers (Anemone patens) which were blooming all over the hills by the end of the month.

Another plant which seemed to benefit from the fire was leadplant (Amorpha canescens). The hayland hadn’t been hayed for several years and the 3-4 year old growth was getting woody. My assumption was that a fire hot enough to kill the buds on woody growth (which happened) would mean a year of purely vegetative growth from crown buds. To my amazement, new stems practically leapt out of the ground and produced large spikes of flowers, and then seed. I compared those plants to the plants on the one steep hillside which had missed the burn (saved in the nick of time, so to speak, by the Waubay Fire Department). On the undamaged old growth the three foot tall leadplant shrubs had just a few flower spikes each and at best produced 25% of the seed of the first year growth in the burned area. Similar, but less dramatic results occurred with several other forbs.

While I didn’t notice any difference in prairie turnip (Pediomelum esculentum) growth that summer, I saw something that was even more interesting the next year, 2018. While walking around the prairie last summer, a year after the burn, I noticed a great number of young prairie turnips over the hills. The most parsimonius explanation is that the heat of the fire broke the dormancy on seeds produced the past couple years, and that the lack of competition and access to mineral soil on the gravel hills (where even Kentucky bluegrass struggles to live) allowed a high recruitment percentage. Regardless, it was a treat to see so many plants establish.

I saw the same thing occur with the ball cactus (Coryphantha vivipara I think). There have always been a few cactus on the ridges, particularly in the roadcuts for the section line trail, but I had never seen many in the hayland or the pasture on the other side of the trail. I was afraid that the fire might damage those few existing plants. First, the removal of the scanty mulch on the ridges revealed many more cactus than I knew existed, though the fire had obviously killed some. Soon, though, the cactus that survived showed new growth, with each clump calving many new balls. Then, last summer revealed many new plants, single balls developing after probable seedling establishment in 2017.

In summary, to my very uneducated eye there was no change in the amount or density of the introduced cool season grasses from my early April burn. Burning while frost is still in the ground removes mulch and lets the ground warm up more quickly in the spring, but doesn’t have the added benefit of causing the cool season grasses to “waste” root reserves and deplete their bud bank on early growth that burns off. It did, however, obviously give an advantage to a group of forbs, especially those growing on the more xeric sites, which produced more seed. As I did more research into price and availability of seed I realized that seed gathering needed to be integral to my restoration plan, not just a supplement. I gathered several pounds of leadplant seed and several pounds of black samson (Echinacea angustifolia) heads, along with a smattering of other species that came along for the ride. This also led directly to the decision to burn another prairie in 2018, the subject of the next post.

There is a postscript to the story concerning what I learned after gathering seed in 2018. Nothing is free. Several of the species which had prolific seed production in 2017, the year of the fire, produced much less in 2018. Buffalo bean milkvetch plants which might have produced 40 or 50 pods in 2017 only produced 10 in 2018. Perhaps too much of the stored crown/root reserves were mobilized to make the spectacular growth of 2017. The plants needed a year to build carbohydrate reserves and had nothing left in the bank after spending their reserves like drunken sailors in 2017. Alternating years of high and low fruit production has been noted in many tree fruits, from apples to olives, ever since cultivation began. The concept of carbohydrate partitioning, that a plant must “decide” where and to what use the food it makes should go because that food is a limited resource, means that you can’t have everything; there is always an opportunity cost.

In short, seed production in species which were prolific in 2017 were diminished in 2018, very noticeably in the buffalo bean milkvetch. Will seed production ramp back up this year? We will see. Conversely, some species which avoided the drunken sailor syndrome produced more seed last year, probably after enhanced vegetative growth built up food reserves, notably slender milkvetch (Astragalus flexuosus) and prairie onion (Allium stellatum). These are anecdotal observations, not controlled measurements, obviously, but that is how it appeared to me. And this now sets the stage for my next post describing my 2018 burn.