Conservation benefits of mowing vs. grazing in semi-natural grasslands
Submitted by nordicjbotany on 6 November 2015.Some projects have a long gestation period. Or rather, it can take considerable time until the right combination of ideas, people and data come together. Our recent contribution in Nordic Journal of Botany is an example of such a project.
THE DATA
The story started back in the early 1970s (when some of the current authors were not yet born). The rapid transformation of agriculture and land use in our part of the world had caused concern about the open to semi-open areas on marginal land (e.g. meadows and pastures) becoming overgrown and turned into forest. This scenario about the “darkening of the landscape” was the background for Eliel Steen (1925–2005), then at the Agricultural College of Sweden south of Uppsala, securing funding from the recently erected Environmental Protection Agency in Sweden for a series of field trials scattered across southern Sweden. The scenario of overgrowth was not uniquely Swedish – similar things was happening all over Europe – and field trials were also set up in, e.g. southern Germany and Switzerland in the early 1970s. Mowing of different intensity, grazing, mulching, spring-burning, chemical or mechanical removal of woody plants – those were the types of treatments considered.
Within the agricultural realm, replicated experiments repeated over several sites is standard procedure. But if, as in this case, one wants more elaborate data on vegetation composition, surveying 154 treatment plots of growing vegetation requires some effort. For this reason, field trials within ecology and environmental management are often not well replicated. Anyway, the Swedish trials were surveyed at the onset and after about 7 and 14 years, and then the results were presented in an extensive report in Swedish will full species-lists etc. (Hansson 1991), and funding ceased. In one instance, local conservation authorities decided to continue to run a trial and in another the farmer managing the trial had not been informed so – amazingly enough – he continued for decades (although the more elaborate treatments were given up). But in essence, the multi-site experiment had ceased after 15 years. Needless to say, with so many sites (11) and treatments (7), analysis of data is something of a challenge, and the data only found its way into the primary research literature in the form of evaluation of single trials (Milberg & Hansson 1994, Milberg 1995, Hansson & Fogelfors, Wahlman & Milberg).
THE QUESTION
Then, 15 years ago, when one of the current authors surveyed one of the still running trials mentioned above (Wahlman & Milberg 2002), the research issue at stake in our recent paper came into focus: is grazing or mowing the best treatment for preservation of biodiversity in species-rich grasslands? He was left with the impression of a surprising lack of published studies on the matter. It is not a purely an academic issue, but very much a hands-on question: what is the best management to preserve grassland biodiversity values in a nature reserve? Should economic compensation to landowners managing sites with high biodiversity values be different when grazing is used compared with mowing?
So, we now had data in a relatively accessible form (in three different Swedish reports) and the question suitable to address with the data at hand. Still, two things were missing: an analytical approach and funding.
Figure 2. One of the experimental sites in southern Sweden. The photo was taken in the summer of 2013, before grazing and mowing. Photograph by Malin Tälle.
THE ANALYTICAL APPROACH
Inspired by evidence-based medicine and meta-analyses, our group has started to use odd ratios (Andersson et al. 2014, Milberg et al. 2014a, Milberg et al. 2015). Although not much used in ecology, it is a preferred outcome from clinical trials and can very easily be used in meta-analyses. The idea then grew that one should be able to convert a species list from sample or treatment plots into “the odds of a species recoded being an indicator species” of something or the other, and then compare the odds between treatments. When it comes to grassland management, we thought it appropriate to use existing classifications of species as indicating (i) good management, (ii) poor management or abandonment, and (iii) levels of high soil nitrogen (Milberg et al. 2014b, Tälle et al. 2014). Apart from turning long species lists into a simple metric (odds) – allowing different vegetation types in the same analyses – an additional advantage is that one can handle data collected with somewhat different methods (which was another challenge in the current data set).
In addition to the analytical approach, there is also a conceptual one that was a prerequisite for our current project: evidence-based decision support. Put briefly, within applied sciences, researchers need to put the results in a context and shape so that it can be used for decision-making in society (Milberg 2014). Some researchers might find the odds for a species being an indicator as un-informative for scientific progress. But we believe that the two research and publication policy paradigms – i.e. writing exclusively for other researchers vs writing also for decision makers – could complement each other.
THE FUNDING
With the analytical solution proposed, we succeeded in procuring funding from the Swedish Board of Agriculture for a project called “Evidence-based management of grassland: making better use of existing data”. We compiled the present contribution within this ongoing project, in which we also review the literature on matters related to mowing and grazing. So there will be more coming out in the not too distant future.
So, 45 years in the making, we are now very pleased to present our findings in the pages of Nordic Journal of Botany. But was our finding: was grazing or mowing best? Well, check our article (Tälle et al. in press)!
Andersson K, Bergman K-O, Andersson F, Hedenström E, Jansson N, Burman J, Winde I, Larsson MC, Milberg P (2014) High-accuracy sampling of saproxylic diversity indicators at regional scales with pheromones: the case of Elater ferrugineus (Coleoptera, Elateridae). Biological Conservation, 171, 156-166. http://dx.doi.org/10.1016/j.biocon.2014.01.007
Hansson, M. 1991. Management of semi-natural grassland. Results of a fifteen-year- old field experiment in south and central Sweden. – Swedish University of Agricultural Sciences, Uppsala. Department of Ecology and Environmental Research. Report No. 45. In Swedish with English summary.
Hansson M, Fogelfors (2000) Management of semi-natural grassland; results from a 15-year old experiment in southern Sweden. Journal of Vegetation Science 11, 31-38. http://dx.doi.org/10.2307/3236772
Milberg P (1995) Seed bank after eighteen years of succession from grassland to forest. Oikos 72, 3-13. http://dx.doi.org/10.2307/3546031
Milberg P, Hansson ML (1994) Soil seed bank and species turnover in a limestone grassland. Journal of Vegetation Science 5, 35-42. http://www.jstor.org/stable/3235635
Milberg P (2014) Evidence-based vegetation management: prospects and challenges. Applied Vegetation Science 17, 604–608. http://dx.doi.org/10.1111/avsc.12114
Milberg P, Bergman K-O, Johansson H, Jansson N (2014a) Low host-tree preferences among saproxylic beetles: a comparison of four deciduous species. Insect Conservation & Diversity 7, 508–522. http://dx.doi.org/10.1111/icad.12074
Milberg P, Akoto B, Bergman K-O, Fogelfors H, Paltto H, Tälle M (2014b) Is spring burning a viable management tool for species-rich grasslands? Applied Vegetation Science 17, 429–441. http://dx.doi.org/10.1111/avsc.12091
Milberg P, Bergman K-O, Norman H, Pettersson RB, Westerberg L, Wikars L-O, Jansson N (2015) A burning desire for smoke? Sampling insects favoured by forest fire in the absence of fire. Journal of Insect Conservation 19, 55-65 http://dx.doi.org/10.1007/s10841-014-9742-5
Tälle M, Bergman K-O, Paltto H, Pihlgren A, Svensson R, Westerberg L, Wissman J, Milberg P (2014) Mowing for biodiversity: knife mower with grass trimmer perform equally well. Biodiversity & Conservation 23, 3073-3089. http://dx.doi.org/10.1007/s10531-014-0765-8
Tälle M, Fogelfors H, Westerberg L, Milberg P (2015) The conservation benefit of mowing vs. grazing for management of species-rich grasslands: a multi-site, multi-year field experiment. Nordic Journal of Botany, in press. http://dx.doi.org/10.1111/njb.00966
Wahlman H, Milberg P (2002) Management of semi-natural grassland vegetation: evaluation of a long-term experiment in southern Sweden. Annales Botanici Fennici 39, 159-166. http://www.sekj.org/PDF/anbf39/anbf39-159p.pdf