Two studies demonstrate the superiority of native seed mixes
Regional seed material performs better
When foresters plant new trees, they no longer use just any seed material – copper beech is not simply copper beech. Each species has variants that have adapted to the specific challenges presented by the habitat. For example, some may be able to withstand drought better than others, while others specialize in adaptations that enable them to survive in harsh winter conditions. For this reason, forestry practice has regulations that specify the precise region from which seed material for a particular plantation must originate.
“Up to a few years ago, there was no equivalent regulation for the planting of compensation areas, for example in association with the construction of a highway,” explains Professor Johannes Kollmann from the TUM’s Chair of Restoration Ecology. “We carried out tests on plants over a period of three years and were able to establish that seed material from the native environment was generally better than mixes from neighboring regions or abroad.”
In 2007 and 2008 alone, Germany imported 13,000 tons of grass seed and 280 tons of herbaceous plant seed. As demonstrated by the two studies carried out by the research group, which have now been published in the “Journal of Applied Ecology”, this seed material is often unsuited to the location in which it is sown and cannot compete with regional seed material as a result.
Does the regional seed concept actually work?
Until recently, the data needed to provide a well-founded answer to this question were unavailable. The extent of the actual genetic discrepancies between members of the same species from different areas of origin was unknown – not to mention whether such differences influence how well the plants thrive or not.
The research team, which involved scientists from the Technical University of Munich (TUM), the UFZ Halle, and the Universities of Tübingen and Münster, studied seven common grassland plants from 22 German areas of origin. “Genetic differences between the plants from the different regions were found in the examined species,” explains Professor Kollmann. “This is a new finding, as the diversity of grassland species was not adequately studied up to now.” The extent of the differences depends on the biology of the individual plants, however.
Grasses that are pollinated by the wind and cannot fertilize themselves exchange their genetic information over relatively large distances. For this reason, the researchers found the smallest genetic differences between the regions in the very common false oatgrass species. A very different picture emerged in the case of the ragged robin, a species that uses insects to spread its pollen – sometimes even between flowers on the same plant. Moreover, the ragged robin is considerably rarer than false oatgrass. “All of these factors mean that there is little gene flow between populations and considerable genetic differences as a result,” explains Dr. Walter Durka, a biologist at the UFZ.
The researchers also identified a definite trend in some species, for example the white bedstraw: the greater the distance between two regions of origin and the more different their climates, the greater the genetic differences between the plants. This is a clear indicator that these plants have adapted to the conditions in their regions. They do better in locations close to their original habitat than in other parts of Germany.
The team investigated whether this is actually the case in a second study. For this purpose, the researchers sowed the seven species from the eight regions in Freising, Tübingen, Halle and Münster, and observed how well they grew and when they flowered. The regional plants produced seven percent more biomass and ten percent more inflorescences on average than members of the same species that came from other regions of origin. “This is a clear indicator that we must conserve regional genotypes,” notes Professor Kollmann.
Reactions to climate change
Even unusually high temperatures like those recorded in the summer of 2013, when the tests were carried out, had no impact on the results. Critics of the regional seed material concept argue that it is not future-proof in a period of climate change: they argue that plants from southern regions may perform better in the context of rising temperatures. Although temperatures in the test gardens in 2013 exceeded the long-term mean by 1.5 to 2 degrees, the plants from warmer regions were not at any advantage.
This may be due to the fact that temperature is not the only factor that influences better or poorer growth. Day length and the composition of the microbial community in the location can also play an important role here. If the regional plants are better adapted to such factors, they can obviously bring their advantages into play in hotter years.
Durka W, Michalski SG, Berendzen KW, Bossdorf O, Bucharova A, Hermann JM, Hölzel N, Kollmann J (2016): Genetic differentiation within multiple common grassland plants supports seed transfer zones for ecological restoration. Journal of Applied Ecology, DOI: 10.1111/1365-2664.12636
Bucharova A, Michalski SG, Hermann JM, Heveling K, Durka W, Hölzel N, Kollmann J, Bossdorf O (2016): Genetic differentiation and regional adaptation among seed origins used for grassland restoration: lessons from a multispecies transplant experiment. Journal of Applied Ecology, DOI: 10.1111/1365-2664.12645