Larger-scale restoration issues
A major challenge to larger-scale prairie restoration is obtaining enough seed of certain species, especially when local origin seed is desired for conservation purposes. There's some evidence to suggest the challenges may be compounding.A major challenge to larger-scale prairie restoration is obtaining enough seed of certain species, especially when local origin seed is desired for conservation purposes. There's some evidence to suggest the challenges may be compounding. This is especially true for the more conservative climax species that were abundant in the original prairies but are now very restricted on the landscape. In addition to their rarity, many of these species don't flower every year, and when they do, they don't produce vast amounts of seed per plant. Obtaining enough seed to plant tens of acres at a time is daunting, if not impossible.
Mass production of seed from these restricted and conservative species in tended gardens or seed orchard nurseries can certainly help overcome this hurdle. As restoration plantings mature, they may become sources of seed as well. These approaches can vastly increase the amount of seed available for large-scale projects far beyond what prairie remnants alone are capable of providing. However, there are some growing challenges to even these approaches.
The primary goal of most large conservation-oriented restoration projects is to bring back the original ecosystem on a scale that will increase its chances of long-term stability and survival for thousands of years to come. This is the goal at Mounds View Grassland, other TPE projects and elsewhere. Hence, these projects are often anchored on clusters of remnant prairie sod that have not only the original plants and their local gene pools, but also soil organisms and uncommon prairie-specialist insects and other invertebrates that give the system stability and cohesiveness.
For example, for each plant genus in a prairie, there are, on average, a dozen or more species of insects that depend exclusively upon that genus of plant. In some cases, the insect depends on a single species of plant. These specialist insects, in turn, often reach numbers large enough to suppress the vigor, growth and seed production of their host plants. Contrary to what you may be thinking, more often than not this is a positive outcome for the ecosystem. The specialist insects tend to keep their hosts from becoming overbearing and aggressive within the plant community.
To complicate matters, there are also predators and parasitic insects that help keep the specialist plant and seed eaters in check. As if that were not enough, there are also parasites that parasitize the parasites. It's all good. This complexity is what we are trying to redevelop in conservation restorations - a complete ecosystem with all of its checks and balances in place.
Now, here's the growing challenge. As we restore more and more sites back to good health, we start to become victims of our own success. The specialized insects, many of them rare and in need of conservation attention, are starting to make comebacks on managed remnants and are expanding into adjacent or nearby restorations. Although a real success story in many cases, this recovery can also impede our ability to obtain large quantities of seed needed for the big restorations, especially conservative species seed that we need to plant in high enough densities to achieve the composition of original prairie.
Following are examples of this issue and some possible solutions to consider.
Leadplant (Amorpha canescens), a conservative climax species that dominates high quality original prairie with approximately 2-3 plants per square meter, is host to the leadplant flower moth (Schinia lucens). This is a colorful specialist moth that nectars on leadplant flowers during the day and lays its eggs on the inflorescences clusters of flowers. Its larvae eat the flowers, and then the seeds, as they develop. The moth is now very uncommon and is on Wisconsin's lists of Special Concern Species and Species of Greatest Conservation Need.
At Mounds View Grassland, where TPE is attempting to restore 570 acres back to original prairie and savanna, we have been successful for the past 10 years in obtaining significant amounts of leadplant seed from the site's remnants, which have a number of dense colonies. We have been stimulating these patches to maximum seed production with rotational fire, as fire has been documented to increase flowering of leadplant by 200 to 900 percent ( based on research published in 1973 by Mary S. Richards & R.Q. Landers, and Henderson 1981). The process worked well for us until 2016.
Four years prior, the leadplant flower moth was found for the first time on the preserve. It may have been a new arrival or it may have always been present but in low numbers that went undetected. In 2015, we found a few flower moth caterpillars on leadplant inflorescences while collecting seed – a first, but we were still able to collect ample seed. Then a year later on Aug. 14, 2016, at the same location, I found many caterpillars - much more than the year before. The area had been burned in the spring and, consequently, there was abundant seed production. When I came back eight days later, more than 90 percent of the seed was gone – and so were the caterpillars.
The seed hadn't dropped; it was too early in the season for that, and no one had been there collecting seed. It appears that the caterpillars ate them. Another possibility is that leadplant seed weevils (Trichapion minor and T. modicum) may have eaten the seeds, resulting in empty pods that drop from the stems weeks before ripe seed drops. Either way, specialist insects were the likely cause of the seed loss on a massive scale.
Over the past 15 years, we have been greatly increasing the amount and flowering of leadplant at Mounds View by clearing remnants of brush and weeds, planting new areas and burning. It appears that the flower moths, and maybe the weevils, are starting to increase as well in response to this effort and, consequently, seed production is declining as our need to plant more acres at high density keeps growing. There are still occasional scattered leadplants with seed, but the numbers are not adequate for our planting needs, and collecting efficiency becomes very low as plants with abundant seed become few and far between.
Cream and white wild indigos (Baptisia spp.) are another example of the restoration success dilemma. These are also conservative climax species, and they too were abundant, even dominant, in the original prairies with several hundred plants per acre on average. Like leadplant, they too have specialist insects that eat their seeds. The primary ones are the seed weevil (Trichapion rostrum) and the 3-lined grapholite moth (Grapholitha tristrigana). The larvae of both eat the seeds within the pods and do an exceptionally thorough job of eliminating seeds. Neither species is as rare as the leadplant flower moth, but they are still indicators of a complete healthy ecosystem and thus desirable.
At Mounds View Grassland, these insects have become so abundant over the past seven years that we are unable to collect enough wild indigo seed to plant more than an acre per year at the target densities. This is a major predicament when one is striving to plant 40- to 50-acres each year.
There are likely other conservative climax species for which loss of seed to specialist insects is becoming an issue as well. For example, we are having difficulty getting good seed from prairie gentian (Gentiana puberulenta), and there are questions about just how much viable seed we are getting from purple prairie clover (Dalea purpurea) and rattlesnake master (Eryngium yuccifolium).
In fully intact prairies, a high rate of seed loss to specialist insects is not a problem for long-lived climax plant species. They don't need heavy seed production every year; once in a great while is sufficient to maintain their populations. It's in recovery and restoration of sites that this life history strategy has a downside.
So what to do about this dilemma? One possible remedy may be to establish seed production areas well away from remnants and restoration plantings in hopes that specialist insects will take many years to find the production sites. We experienced this isolation effect last year when a small production bed of cream wild indigo, located well away from remnants and plantings with wild indigo, produced pods full of seed while the remnants and plantings produced little to no seed.
The use of insecticides on production beds is tempting, until one considers the need for pollination. Possibly applications could be timed to avoid the pollinators and suppress the seed eaters, but still risky. Maybe barriers, traps and physical removal of insects could be effective on some species. Who knows? Maybe as sites mature, outbreaks of diseases, predators and parasites will suppress the seed-eating insects enough to allow for good seed production more often than not. But even then, we would have to lower our expectations on the time it takes to bring back large areas to the original diversity.
It appears that restoring prairie back to its original plant (and invertebrate) community composition on a large scale isn't going to be an easy task and will likely take a long time to accomplish. However, if we don't get the ball rolling, it will never happen. We may not live to see what a thousand acres of leadplant at 5,000 plants per acre, or cream wild indigo at 700 plants per acre, or wood lily at 7,000 plants per acre looks like, but with any luck, future generations will.