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  1. Semi-natural grassland are widely considered as high-value ecosystems due to their species-rich habitat, particularly in traditional landscapes. These low-input grasslands furthermore also are inhabited by many threatened insect taxa (Veen et al. 2009) Invertebrates are considered of incredible importance to ecosystem processes, in particular herbivory, nutrient cycling and pollination (Humbert et al. 2009) However, there have been a lot of recent concern over invertebrate population declines, associated with landscape transformation and intensification (Hendrickx et al. 2007) In particular grasslands, which are of utmost importance to various invertebrate species, have been systematically converted into arable lands, intensified or abandoned (Poschlod et al. 2002) Such conversion and intensification are achieved by the use of fertilizer input, application of pesticides, and reseeding. While in itself these measures are not to blame for threatening insect populations, they set in motion a series of events by enabling more frequent cuts and higher grazing intensity. This has led to grassland cultivation becoming a more lucrative business. Together with the development of mechanization and expanding field sizes for farms, this has led to a very high degree of homogenization of the agricultural landscape (Robinson et al, 2002) and the intensification of agriculture is not expected to change in the future if no land-use changes are made (Tilman et al, 2001) Although several management plans have been developed in recent history, the scientific knowledge available on the impact of agricultural cutting techniques and fauna diversity is still very limited (Humbert et al. 2009) Species are expected to react in a different manner to the various agricultural cutting techniques (as fauna as a whole, and as species). Therefore, to design innovative policies that can be implemented by farmers and land managers to deal with this issue, there is a need for extensive scientific knowledge on the case (Humbert et al. 2009)
  2. Three key reasons how cutting regimes interact with invertebrate populations can be identified (Kiel, 1999)
  3. (1) A cutting can result in direct mortality in species. Individuals can be killed by the cutting operation itself or be removed from their environment during harvesting.
  4. (2) Cuttings lead to a drastic change in the environment. Besides the physical structure, factors such as temperature, humidity, food availability and predation pressure are also changed. Depending on the adapting capacity of a species this can have dire consequences for some species.
  5. (3) As a result of the previous two reasons, the composition of species diversity will change within the ecosystem. Species that depend on other species to survive (e.g. predation, protection) could either go extinct, or overpopulate an area and supress other species
  6. Therefore, maintenance and restoration of them is a top priority in conservation policies. Nevertheless however, they represent a real conservation challenge especially regarding invertebrates assemblages (Buri et al. 2013)
  7. On the topic of direct mortality in species during cutting, studies that focussed on mammals and amphibians, show that an important determinant factor is the cutting height of the equipment that’s used; the damage caused by rotary-mowers was quantified at 27% for a cutting height of 7-8cm, but decreased to only 5% when the cutting height was set at 12cm (Classen et al. 1996) Furthermore, other studies have shown that mortality also strongly correlates to the type of equipment that is used. For example, rotary disc mowers have been found to result in almost twice as many deaths among invertebrates compared to double-blade mowers. (Oppermann et al, 2000) In another study, rotary drum mowers had a casualty-rate of 14.1%, with double-blade mowers and finger cutter bar mowers reported at respectively 11.4% and 8.7% (Humbert et al. 2009) Finally, the use of a conditioner (used in agriculture to crush newly cut hay to promote faster and more even drying) also is shown to have a negative effect on the mortality count during cutting (Humbert et al. 2009)
  8. Additional confirmation that the type of equipment and cutting height are determinant factors in cutting mortality among invertebrates is provided by a set of studies that quantified the. The studies made use of invertebrates models placed on the ground to simulate actual organisms. During the studies, other factors such as wind, temperature and time of harvesting were reported as not having much of an effect on the direct mortality
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  10. Table 1: percentage mortality or damage rates for the invertebrate models, due to different common mowing techniques on diverse taxa (Humbert et al. 2009)
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  12. What becomes clear from this study is that flail mowers and rotary mowers with conditioner had much higher mortality rates (59.7 ± 23 and 34.9 ± 12 ) compared to bar mowers and rotary mowers (27.3 ± 16 and 18.3 ± 15). Furthermore, the research also shows that depending on the type of equipment the cutting height can have a massive effect on the mortality rate as well. For bar mowers, increasing the cutting height from 5cm to 10cm led to a decrease in mortality both for the models that were placed on the ground and the cut horizon (respectively a 70% and 20% reduction) Flail mowers showed similar statistics (84% and 37% reduction) Interestingly however, no notable effect was found for rotary mowers (0% and 11% reduction)
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  14. One of the issues rooted in this is the fact that generally mowing is regarded as actually being beneficial to fulfil the needs of plant populations (Grime, 2001) The effects of mowing on plant communities has been extensively studied by conservation experts and this has led to a large base to support the need for grassland mowing. Regular disturbance is required to avoid vegetation succession, which promotes a high degree of plant diversity. Ways in how this can be achieved include grazing regimes, cutting and burning (Grime 2001) From this list, cutting is the most regular and regular intervention that is taking place in grasslands/meadows. While the relevance of plant conservation is considered when doing this (in fact, often it is the most important reason why it is taking place) it is not known whether the plant diversity correlates with invertebrates diversity under the same management regime. The effect of mowing on insect populations has received little attention up until recently. As an example, the exact impact of cutting regimes on invertebrates was only quantified 2009 (Humbert et al, 2009) Although in general the effect of grassland harvesting on invertebrate populations still remains largely unexplored, it is argued that the effect is most likely to be negative (Morris, 2000) Whereas one or two cuts per year have been proven to be beneficial to meadow plant diversity (Huston, 1994) for grassland invertebrates it has been confirmed that it reduces the diversity and abundance for most species, while promoting it for only a few species. For example, beetles are considered more resistant to cutting regimes when compared to butterflies and spiders.
  15. Several key factors in cutting regimes are considered as follow:
  16. (1) The time of the year at which cutting commences. Due to the life cycle of many invertebrates depending on the time of the year a cutting may be disastrous for a specific species. For example, if a spring cut was to commence, it would greatly affect the less-mobile developmental stage of caterpillars, whereas for spiders, summer cuts are most detrimental.
  17. (2) The frequency at which cuttings take place. Obviously, the higher the frequency of cuttings, the stronger the effect of the cutting regime will be on invertebrate populations. However, while keeping in mind the importance of avoidance of vegetation succession in plant populations, a balance should be found to avoid degradation in both plant and invertebrate species.
  18. (3) The time in between different cuttings. In general, it is argued that if multiple cuttings take place in a too short time lapse, invertebrate do not have sufficient time to recover and therefore the impact of the cutting regime amplifies itself.
  19. (4) The type of the meadow where the cutting regime takes place. In wetlands, late mowing on a supra-annual cycle is recommended for the conservation of arthropods (Wettstein, 1999)
  20. One interesting notion that has be mentioned here, is that due to the differences between invertebrate species, there is not one specific cutting regime that is ideal for all species. Due to difference in life cycles, different mating seasons and difference in response to cuttings the most favourable cutting regimes for species conflict on a regular basis. Therefore, cuttings are always going to take place at a time that are detrimental for some species (Humbert et al. 2009) Despite this, however, there is still considered to be a lot of improvement left that can be done on cutting regimes in relation to insect conservation.
  21. In 2010, a research programme was launched with the objectives to (1) better appraise the influence of different mowing regimes on invertrebates (2) propose management measures that can easily be implemented by farmers.
  22. In a 2013 research paper, Buri et al. reflects back on this initiative by evaluating the different mowing regimes on orthopterans (e.g. grasshoppers, crickets, locusts) The following three cutting regimes were investigated during the research:
  23. (1) Delaying the first cut by one month, moving it from early summer to mid-summer. The influence of a delayed cutting regime on insect populations have shown to be neutral or somewhat positive in previous studies.
  24. (2) Limiting the cuts per year down to two, with a minimum of eight weeks in between them.
  25. (3) Each time a meadow was mown, an uncut grass area had to be left as refuge for insect populations, improving their fitness as land that previously offered shelter and food resources suddenly disappears.
  26. The research conducted by Buri et al. shown that measures such as delaying mowing and leaving uncut refuge areas can make a very signification contribution to better conservation of insect populations. The orthopteran density was observed as five times higher when mowing was delayed by one month (measure 1) In the case of leaving refuge land, the orthopteran density was observed as two times higher (measure 3) Furthermore, leaving the method of leaving refuge land also contributed to an increase of species diversity, probably due to heterogenization of the landscape. Finally, increasing the population size of orthopterans will also allow to sustain a higher amount of other taxa levels. According to Buri et al., the adaption of either of these measures does not require additional work or money from the farmers and therefore could be easily implemented in agri-environmental policies. Based on their research findings, they make the following recommendations:
  27. (1) A fraction of extensively harvested grasslands should have the first mowing commence in mid-summer (July),
  28. (2) Another fraction of the grasslands should maintain an uncut grass refuge of approximately 10-20%
  29. It is the researchers’ prospect that implementation of these two measures would alleviate the issue of insect conservation by mediation through spatial habitat heterogeneity (Benton et al. 2003).
  30. Recommendations
  31. Something that remains unexplored even within the domain of insect ecology studies is whether managed meadows represent source or sink environments for insects. Understanding this concept would contribute to a better understanding in the long-term viability of insect populations. Furthermore, the socio-economic incentives for low-impact meadow management with the purpose of promoting biodiversity is also something worth investigating in future research. After all, conservation policies cannot succeed if the people involved in the domain are not willing to cooperate with the implementation of them.
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