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The impact of different cutting regimes on population density of Jacobaea aquatica (Hill) G. Gaertn., B. Mey. & Scherb. and grassland vegetation
Agriculture, Ecosystems and Environment 226 (2016) 18–24
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The impact of different cutting regimes on population density of Jacobaea aquatica (Hill) G. Gaertn., B. Mey. & Scherb. and grassland vegetation Gabriele Basslera,b,* , Gerhard Karrera , Monika Kriechbaumb a b
Institute of Botany, University of Natural Resources and Life Sciences, Gregor Mendel Straße 33, A-1180 Vienna, Austria Institute for Integrative Nature Conservation Research, University of Natural Resources and Life Sciences, Gregor Mendel Straße 33, A-1180 Vienna, Austria
A R T I C L E I N F O
Article history: Received 15 January 2016 Received in revised form 13 April 2016 Accepted 22 April 2016 Available online xxx Keywords: Senecio aquaticus Management Marsh ragwort Poisonous plant Toxicity Weed control
A B S T R A C T
Jacobaea aquatica is a monocarpic Asteraceae growing in wet grasslands of low management intensity. It is considered a noxious weed because it contains pyrrolizidine alkaloids, which cause health problems to livestock. The aim of this study was to develop management options to reduce the population density of J. aquatica in meadows of high nature conservation value without negative impacts on plant species diversity. The study site is located at the Hercynian part of Lower Austria near the city of Gmünd. The effect of five different cutting regimes on population density and seed production of J. aquatica as well as on species richness of the surrounding vegetation was tested on permanent plots from 2007 to 2012. One cut in October diminished J. aquatica but species richness decreased. Two cuts during the peak flowering period (July and August) and October reduced the population density of J. aquatica by c. 70% without obvious loss of species richness. Traditionally practiced two cuts in June and September lead to a rapid population growth of J. aquatica. According to our results, a first cut in June providing non-toxic fodder and two additional cuts during peak flowering are appropriate to reduce J. aquatica and to maintain biodiversity. ã 2016 Elsevier B.V. All rights reserved.
1. Introduction Like many other species of the genera Senecio and Jacobaea, J. aquatica (marsh ragwort) contains pyrrolizidine alkaloids, which are toxic for most vertebrates, particularly for mammals. The toxic compounds are not or insufficiently decomposed in hay and silage (Berendonk et al., 2010; Chizzola et al., 2015b). They are mutagenic, cause cancer (Chen et al., 2010) and destroy the liver tissue (Mattocks, 1968). Health problems for humans consuming intoxicated milk or honey cannot be excluded (Hoogenboom et al., 2011; Kempf et al., 2010). Therefore, some species of this genus are treated as noxious weeds, notably Jacobaea vulgaris (syn. Senecio jacobaea). Jacobaea aquatica is a close relative of J. vulgaris (Pelser et al., 2002, 2003). In consequence of recent phylogenetic analyses, the species with the former name Senecio aquaticus was
* Corresponding author. E-mail addresses: [email protected] (G. Bassler), [email protected] (G. Karrer), [email protected] (M. Kriechbaum). http://dx.doi.org/10.1016/j.agee.2016.04.018 0167-8809/ã 2016 Elsevier B.V. All rights reserved.
incorporated into the genus Jacobaea and named Jacobaea aquaticus (Hill) P. Gaertn., B. Mey. and Scherb. (Pelser et al., 2006). As a plant inhabiting grasslands of medium to low management intensity, it has diminished with the industrialisation of agriculture during the second half of the 20th century (Rich and Woodruff 1995; Rosenthal 2000). Encouraged by agri-environmental programs, farmers have ceased fertilisation and reduced the cutting frequency on formerly ameliorated wet grasslands during the last decades. This has caused an increase in J. aquatica population density (Liehl et al., 2012; Suter and Lüscher, 2007, 2008). Since the early 21st century, this species has become a serious issue as a toxic grassland plant in Switzerland (Bohren et al., 2008; Bosshard et al., 2003), Germany (Berendonk et al., 2010; Conradi and Zehm, 2011) and Austria. The abundance of J. aquatica and specific management options were investigated in Orkney by Forbes (1976), in Switzerland by Suter and Lüscher (2007, 2008) and in Austria by Liehl et al. (2012). In a review by Roberts and Pullin (2007), the effectiveness of management interventions to control ragwort species was analysed, but there was insufficient experimental evidence to assess manual or mechanical treatments. Also a review by Leiss (2011) on management practices for control of ragwort species
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does not mention any mechanical treatment against J. aquatica. Recently, Suter and Lüscher (2011) performed experiments in Switzerland testing various management types (cutting, ploughing, harrowing, pulling and combination of all these treatments with overseed) to control the species. The aim of a study in the UK (Sargent, 2008) was to develop management tools for meadows of high nature conservation value to reduce population density of J. aquatica by mechanical control. This paper focuses on population density under five different cutting regimes in Austria. We addressed the following research questions: Which cutting treatment is most effective in reducing mature seeds and population density of J. aquatica? Do plant species diversity and composition change under different cutting treatments? 2. Materials and methods 2.1. Study species J. aquatica is a short-lived perennial and usually monocarpic Asteraceae (Bassler, unpublished; Schmidt, 1983) native to many European countries. It germinates in autumn or spring and after two to seven years of vegetative growth as a rosette, flower shoots with yellow capitula are elongated from July to August. If the main shoot is cut, lateral shoots will immediately develop from the base and form new capitula. After fruit ripening (from end of July to September) most plants die off. The soil seed bank of J. aquatica belongs to the long-term persistent type (Bassler et al., 2010; Suter and Lüscher, 2012; Thompson et al., 1997). According to Schmidt (1983), J. aquatica reproduces by seeds. It is a grassland species that is restricted to wet meadows and pastures (Bartelheimer et al., 2010; Bassler, unpublished) mostly on acidic soils at low fertilisation levels (Dierschke and Briemle, 2002). 2.2. Study site The study took place in the Hercynian part of Lower Austria (Bohemian Massif), called Waldviertel, in Kleedorf close to the Czech border at an altitude of 470 m. The climate is characterised by a mean annual temperature of 6.8 C and a mean annual precipitation of 660 mm. The soil type is a strongly acidic gley developed from granite substrate. The A-horizon is middle to rich in humus (BFW). The experimental plots were located in a flat, frequently waterlogged meadow affiliated to the community type Lychnido floris cuculi-Festucetum rubrae Lichtenecker, Bassler, Karrer 2003 subass. juncetosum filiformis. Dominant graminoids were Anthoxanthum odoratum, Festuca rubra, Juncus filiformis and, in some plots, Deschampsia cespitosa, Carex nigra or C. brizoides; widespread herbs were Cardamine pratensis, Lychnis flos-cuculi, Plantago lanceolata, Ranuculus acris, R. flammula and R. indecorus. J. aquatica covered between 10 and 40 % at the study site in 2007 (Supplementary material). The annual mean productivity of the meadows (aboveground dry mass) was 4 t/ha. Before the beginning of the experiment in 2007, the meadow was mown once or twice a year after 15 June without applying fertiliser. 2.3. Experimental design and data analyses
Table 1 Cutting dates from 2007 to 2011; roman numbers indicate the month of cutting. Date of cutting Year
VI
VIIa
VIIb
VIII
IX
X
2007 2008 2009 2010 2011
05 June 02 June 03 June 07 June 14 June
03 28 03 05 05
16 July 21 July 17 July 16 July 25 July
06 August 02 August 05 August 10 August 16 August
03 September 09 September 30 August 15 September 06 September
03 October 07 October 29 September 15 October 30 September
July June July July July
weight of 0.32 mg (Fitter and Peat, 1994). Five different cutting regimes (=treatments) were applied to study their effect on population growth rates of J. aquatica (Tables 1 and 2): (1) “ October” (standard): cut once per year in early October (X); (2)“June–September” (representing the traditional cutting regime for extensive meadows in the Waldviertel region): cut in early June (VI), when all plants were still in rosette stage and in early September (IX), when seed dispersal was nearly finished; (3) “June–July–October”: managed as “June–September” plus an additional cut in late July (VIIb), when adult individuals were flowering a second time; (4) “July-October”: cut in early July (VIIa), when J. aquatica flowered but no seeds were mature and in early October (X); (5) “July–August–October”: cut at full flowering in early July (VIIa) as well as in early August (VIII) and in early October (X). The exact date was dependent on the forage growth (Table 1). The number of replicates per treatment was five. Plots were cut manually with a scythe, implicating a low cutting height (c. 3 cm). The following measurements were taken before every cutting date at every 1 m2 plot from 2007 to 2011: number of rosettes larger than 1 cm in diameter, number of flowering individuals and number of capitula with mature seeds of every flowering individual; seeds were regarded as mature when capitula were in release stage or seeds were already released from the capitula. Counting of the number of vegetative and generative individuals was extended to year 2012. The vegetation was documented in 2007 and 2010 in June before the first cut. Relevés included complete species lists of vascular plants per plot; coverage of plants was estimated using the scale of Londo (1976). The nomenclature of vascular plants follows Fischer et al. (2008). Statistical analyses were conducted with SPSS 18.0 (IBM, Somers, NY, USA). Graphs were drawn with STATISTICA 10 (StatSoft, Tulsa, OK, USA). Changes in species diversity were tested by comparing the number of vascular plants per m2 in 2007 and 2010 by single t-tests for dependent variables for every treatment. A repeated measures ANOVA was calculated to detect changes in consecutive years under different treatments of the following parameters: density of J. aquatica, mean number of flowering individuals per m2 and mean number of capitula per individual plant per m2. One outlier was removed in treatment “June– September” in order to achieve normally distributed residuals.
Table 2 Cutting regimes (=treatments) and developmental stages of J. aquatica individuals at time of mowing: r = rosette, f = flowering plant, s = seed release, d = dead (additional vegetative rosettes are present all over the year.); Roman numerals indicate dates (months) of cutting (Table 1). Treatment code
Twenty five permanent plots of one square meter were arranged in a randomised complete block design in the meadow described above. The distance from one plot to another was one meter. The area around the plots was mown regularly to avoid seed rain from the direct neighbourhood of the experimental plots. Seed exchange between experimental plots was assumed to be low, because J. aquatica seeds generally are not dispersed over long distances (Bassler et al., 2011; Forbes 1976), despite their light
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Date of cutting VI
VIIa
VIIb
VIII
IX
X d
October June–September
r
June–July–October
r
s f
July–October
f
July–August–October
f
s/d r/d f
r/d
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The J. aquatica population was very dense at the beginning of the experiment. On average, 90 individuals per m2 were counted in 2007, corresponding to a coverage of 10–40%. A repeated measures ANOVA (SPSS) revealed that the within-subject effect “year” (sphericity assumed: p < 0.001) the between subject effect “treatment” (p = < 0.001) and their interaction (p < 0.001) were significant. Between 2007 and 2012, the number of individuals per plot remained more or less stable in treatments “June–July– October” and “July–October” (Fig. 1). In treatment “June–September”, the density increased from 84 to 124.2 individuals per plot; density increase was more or less linear until 2011 and decreased in 2012 (Fig. 1). This treatment differed significantly from all other treatments (multiple comparisons). Under treatment “July– August–October”, the population declined. Coverage was reduced from 2007 onwards by c. 70%, resulting in a density of 40 individuals/m2, on average. In treatment “October”, the density of ragwort individuals decreased mainly in 2011 and 2012 (18 individuals per m2 referring to 29% of 2007). It differed significantly from treatment “July–October” and “June–September”. The repeated measures ANOVA shows that the number of flowering individuals per m2 varied significantly (p < 0.001) from year to year: On average, 16.7 individuals flowered in 2007, 24.3 in 2008, 11.1 in 2009, 15.2 in 2010, 8.7 in 2011, and 9.8 in 2012. Variation was generally high, ranging from 0 to 64 flowering individuals per plot. This referred to 19% flowering individuals in the year 2007, 30% in 2008 and only 12–16% from 2009 to 2012 (Fig. 2). The number of flowering individuals per m2 were not significantly influenced by the treatments (p = 0.131).
September and lasted until October. In treatment “June–September” and “June–July–October” ripening was slightly delayed. For treatment “June–September” the main time for seed ripening was during the second half of July and August. In treatment “June–July– October” ripening was prevented by two cuts until August. In treatment “July–October” seed ripening started and culminated in August and lasted until October. In treatment “July–August– October” seed ripening was almost totally prevented. Only in years with a warm autumn (e.g. 2009) seeds succeeded to ripen in September or October. The repeated measures ANOVA revealed that the mean number of capitula with mature seeds per individual and plot differed significantly by treatments (p < 0.001). The highest number of capitula with mature seeds (on average, 9.5 capitula per individual for all years 2008–2011) were counted in treatment “October”. Treatment “June–September” followed with a mean of 5.7 capitula per individual. An additional cut in July in treatment “June–July– October” reduced the mean number of capitula with mature seeds to 1.3. Treatment “July–October” with one cut in the main flowering period resulted in a mean of 4.5 capitula per individual. The best suppression of seed production was observed in treatment “July–August–October”, where only 0.1 capitula per individual contained mature seeds (Fig. 3). Year to year variation of seed production was also high (p < 0.001): In the years 2008 and 2011 most capitula with mature seeds were produced (5.3 respectively 5.7), while in the years 2009 and 2010 the number was only 2.7 resp. 5.74. In 2008 and 2011 prevention of seed production in treatment “June–July–October” was almost as effective as in treatment “July– August–October”. Apart from that, the relative differences in seed production between the different treatments were stable in all years.
3.2. Production of mature seeds of J. aquatica
3.3. Development of species richness and vegetation composition
Fig. 3 shows the phenology of seed ripening with regard to different cutting regimes averaged for the years 2008–2011; 2007 was not considered because of insufficient data. Treatment “October” was mown only once in autumn and allowed the undisturbed development of mature seeds. Under these conditions, seed ripening started in mid-July, was highest in early
The overall mean number of vascular plants per m2 was 16.3 in 2007 and 16.6 in 2010. Regarding the different treatments, no significant changes in species number between the first and the second survey could be observed (Table 3). However, some notable changes in species composition were found. In all October-plots graminoid species (especially Scirpus sylvaticus, Juncus filiformis,
3. Results 3.1. Development of population density of J. aquatica
Fig. 1. Number of J. aquatica individuals per m2 and different treatments from 2007 to 2012 (means, 95% confidence interval).
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Fig. 2. Number of flowering individuals of J. aquatica per m2 and different treatments from 2007 to 2011 (means, 95% confidence interval).
Fig. 3. Number of capitula containing mature seeds per J. aquatica individual regarding five different treatments at five different dates (VIIa to X, Table 1). Values are averaged over the years 2008–2011 (means, s.e. of the mean).
Table 3 Comparison of the number of species per m2 of the years 2007 and 2010 (mean standard error). Treatment
Number of species/m2 2007
October June–September June–Jul–October July–October July–August–October
17.8 16.6 14.4 16.4 16.4
2010 0.4 1.4 1.4 1.1 0.7
17.0 18.2 15.4 15.8 16.8
0.9 1.2 1.0 0.9 1.2
Deschampsia cespitosa and Carex. brizoides) enhanced their cover from 63 to 92%, while the cover of forbs (legumes included) decreased from 53 to 42%. In three out of five Oct-plots the cover of J. aquatica decreased from 2007 to 2010 and vanished completely until 2012. Comparing relevés from 2007 and 2010, some shifts in species dominancy in other treatments were detected (Supplementary material): In the late mowing treatments “October”, “July– October” and “July–August–October”, the cover of Festuca rubra decreased, which was in contrast to results of Gaisler et al. (2013), who observed that F. rubra is indifferent to different cutting and mulching regimes. The cover of Trifolium repens was generally low in 2010. Anthoxanthum odoratum increased in 2010 in treatment “June–September”. The cover of J. aquatica decreased in treatment
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“July–August–October” but increased in treatment “June–September”; no changes were recorded in treatment “June–July–October” and “July–October”. The cover of the other species remained more or less stable. 4. Discussion The aim of this study was to find a management strategy that reduces the abundance of J. aquatica in grassland with high nature conservation value without endangering biodiversity. This should be achieved by adequate cutting regimes, avoiding management practices like ploughing or herbicides. Those vegetation disturbing practices, anyhow, did not work well, when applied only once (Suter and Lüscher, 2011). As J. aquatica reproduces only by seeds (Schmidt, 1983), it was assumed that breaking the life cycle by prevention of seed ripening should help to empty the seed bank and consequently lead to a decrease of population density. Seedlings were not considered in this experiment, but seedling density was highly fluctuating with up to 340 seedlings per m2. It was not only influenced by the number of seeds of the previous year, but also by the number of seeds in the seed bank, the weather conditions of the year and the percentage of bare ground (Bassler, unpublished). In the majority of years, J. aquatica individuals under treatment “Oct”, which were undisturbed during flowering and seed ripening in July and August, produced most seeds. However, although seed production was highest, the population density ranged from stable to strongly decreasing (Fig. 4). In 2011 and 2012 the decrease of population density was remarkable in most “October”-plots and J. aquatica vanished completely in three out of five plots. Tall graminoids (Scirpus sylvaticus, Carex brizoides) increased because of the late cutting and lead to a dense vegetation canopy, which prevented the light penetrating to the ground. Thus in “October”plots, mortality of older J. aquatica rosettes increased and seeds of J. aquatica could not germinate and establish. Population density remained stable in only one plot, where vigour was less and the plant composition did not change. This indicates that a late single cut regime is not feasible to reduce J. aquatica on oligotrophic sites. In their study about long term effects of grassland management, Gaisler et al. (2013) also observed an increase of tall grasses and a
decrease of small forbs when mulching was applied only once in September. In a fallow experiment, J. aquatica completely disappeared after a period of five years without any cutting (Rosenthal, 2010). Suter and Lüscher (2011) stated that one cut in autumn performed best in suppressing J. aquatica compared to their control treatment, though the total number of J. aquatica plants increased in their experiment. They recommend one cut for sites with less favourable topography and fodder quality by arguing that this comes close to the treatment of traditional fens, which are also characterised by high species diversity. In our experiments, the species number per plot remarkably decreased only in one plot after four years of a very late cut in October. However, there is a high risk that the late cutting in the long run also suppresses other species, especially if the site is not extremely nutrient-poor (cf. Gaisler et al., 2013; Rosenthal, 2010; Smith et al., 1996). Considering possible economic consequences, this cutting regime cannot be recommended, because late mown fodder has insuffi cient quality (Cop et al., 2009). The two cut treatment “June-September”, which is usually applied by farmers receiving agri-environmental compensation payments in the Waldviertel region, did not harm the flowering of J. aquatica very much. At the first cut in early June, most J. aquatica individuals were still in the rosette stage and were hardly affected by mowing (Fig. 1). In this treatment flowering started only about one week later than in the treatment with undisturbed flowering individuals (“October”). At the second cut in September, seed release was more or less finished. The total number of mature seeds of treatment “June-September” reached on average 78% of the treatment “October”. Population density increased rapidly in this treatment and reached more than 200% after four years, possibly as a consequence of dense juvenile rosettes. The slight decline of J. aquatica density in 2011 and 2012 (Fig. 1) might be due to intraspecific competition of the growing rosettes. Suter and Lüscher (2011) also reported an increase in vegetative individuals in a comparable regime (first cut in Mid-June and second cut in late October, in the Swiss Prealps). They also found that different control options (ploughing, harrowing, herbicide application) combined with this cutting regime did not change the overall tendency of population growth.
Fig. 4. Mean number of capitula containing mature seeds per J. aquatica individual and m2 with regard to different treatments from 2008 to 2011(means, 95% confidence interval).
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In cutting regimes like treatments “June–July–October” and “July–October”, where J. aquatica was mown at least once when it was flowering, seed production was reduced (24–54%), but population density of J. aquatica remained stable. These treatments prevented J. aquatica populations to spread by seeds, but were not able to diminish its density within four years. Treatment “July– October” is partly comparable to the cutting regime of Sargent (2008) with one cut in mid-June, which prevented seed ripening under the climatic conditions of the UK. In contrast to our experiment, she reported a strong decline of J. aquatica individuals after two years. Perhaps this decrease in density might rather be due to unfavourable conditions for germination than to a reduction of seed production. Maybe these differences are the result of a short-lived soil seed bank of J. aquatica in the UK compared to Austria (Bassler et al., 2010) or Switzerland (Suter and Lüscher, 2012), where J. aquatica builds up a permanent seed bank. This fact could also be a consequence of shorter-lived individuals in the UK. In Austria individuals reach a maximum age of at least seven years (Bassler, unpublished). In treatment “July–August–October” (two cuts at peak flowering in July and August) seed ripening was almost completely prevented; only a mean of 30 mature seeds per individual were produced, which is 3% of treatment “October”. This treatment led to a significant linear reduction of the total number of individuals. After 5 years, the number of individuals decreased by about 70% resulting in 40 individuals/m2 on average. This is still quite a lot, but if the decrease will continue in future (see trend in Fig. 1), J. aquatica might be controlled in the long term. Though the plots of treatment “July–August–October” were mown three times a year, no reduction of plant species diversity was observed until 2010. Negative trends are not very probable because most species present are rather sensitive to early cuts (e.g. in May) but less harmed by cuts during summer. Especially at the October cut, plant height was very low and mowing did not significantly reduce total biomass (Chizzola et al., 2015a). The comparison of treatment “June–July–October” and “July– August–October” shows the importance of the nearly total prevention of seed production in at least five consecutive years: In treatment “July–August–October”, in every year seed production was prevented almost totally, whereas in treatment “June–July– October” the prevention was only effective in some years. Nevertheless, treatment “June–July–October” did not lead to a reduction of the total number of individuals. Another problem is that herbage mown at peak flowering contains a high proportion of toxic J. aquatica (Chizzola et al., 2015a) and should not be used as fodder, but has to be disposed of. 5. Conclusions All cutting regimes tested in our study did not harm the vegetation composition and richness of vascular plants, except for the regime with one cut in October, in which graminoids started to dominate and suppress other species. On the other hand, this “ October” cutting regime performed well in suppressing J. aquatica. This is valid, at least at moderate nutrient-rich sites, whereas on very nutrient-poor sites vegetation composition did not change and the density of J. aquatica remained stable. The cutting regime with two cuts at peak flowering in July and August lead to a slow decrease of J. aquatica density after six years. The disadvantage of this mowing regime, however, is the infestation of the fodder with highly toxic plants. The following management regime can be a compromise: The fodder of a cutting before flowering with low proportions of J. aquatica is suited best for feeding. If it is cut in early June, it does not negatively affect biodiversity goals. Two consecutive cuts at peak flowering diminish the J. aquatica population, but should not be used as fodder. This costly management could be partly compensated by agri-environmental
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measures, as it is also intended for invasive species in the recent agri-environmental scheme “ÖPUL 2015” in Austria (Suske and Huber, 2014). A regime with cuts in June and September should be avoided, because it leads to a rapid increase of J. aquatica density. Using a cutting regime, as outlined above, can be a good alternative to time consuming hand pulling or digging out J. aquatica plants. The results of our experiment are valid at least at the local and regional scale. Experiments have to be expanded to climatically different sites. Acknowledgements This work was funded by the Federal Ministry of Agriculture, Forestry, Environment and Water Management in cooperation with Federal States of Austria and the Jubiläumsfonds of the Austrian Nationalbank. We thank the farmers for providing their meadows, Desirée Bruhin for assistance in the field and Bernhard Spangl for statistical support. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.agee.2016.04.018. References Bartelheimer, M., Gowing, D., Silvertown, J., 2010. Explaining hydrological niches: the decisive role of below-ground competition in two closely related Senecio species. J. Ecol. 98, 126–136. Bassler, G., Karrer, G., Kriechbaum, M., 2010. The fate of Senecio aquaticus seeds. In: Jongejans, E., Macel, M., Vergeer, P., Verhoeven, K. (Eds.), Plant Population Biology—Crossing Borders. Institute for Water and Wetland Research, Radboud University Nijmegen, Nijmegen, Netherlands p. 92. Bassler, G., Karrer, G., Grabmaier, A., Kriechbaum, M., 2011. Spread and control options of the poisonous grassland weed Senecio aquaticus. 3rd International Symposium on Environmental Weeds and Invasive Plants, Ascona, Switzerland. Berendonk, C., Cerff, D., Hünting, K., Wiedenfeld, H., Becerra, J., Kuschak, M., 2010. Pyrrolizidine alkaloid level in Senecio jacobaea and Senecio erraticus the effect of plant organ and forage conservation. Grassland Science in Europe 15, 669– 671. BFW (Bundesforschungs- und Ausbildungszentrum für Wald, Naturgefahren und Landschaft) Digitale Bodenkarte von Österreich; http://gis.lebensministerium. at/eBOD/ (accessed 28.07.14.). Bohren, C., Delabays, N., Rometsch, S., 2008. Invasive Pflanzen: Herausforderung für die Landwirtschaft? Agrarforschung 15, 314–319. Bosshard, A., Joshi, J., Lüscher, A., Schaffner, U., 2003. Jakobs- und andere Kreuzkraut-Arten: eine Standortbestimmung. Agrarforschung 10, 231–235. Chen, T., Mei, N., Fu, P.P., 2010. Genotoxicity of pyrrolizidine alkaloids. J. Appl. Toxicol. 30, 183–196. Chizzola, R., Bassler, G., Kriechbaum, M., Karrer, G., 2015a. Pyrrolizidine alkaloid production of Jacobaea aquatica under different cutting regimes. J. Agric. Food Chem. 63, 1293–1299. Chizzola, R., Bassler, G., Winter, S., Zebeli, Q., Kriechbaum, M., 2015b. Persistence of alkaloids of typical poisonous plants autumn crocus and marsh ragwort in grass silage. Wiener Tierärztliche Monatsschrift—Veterinary Medicine Austria 102, 285–292. Cop, J., Vidrih, M., Hacin, J., 2009. Influence of cutting regime and fertilizer application on the botanical composition, yield and nutritive value of herbage of wet grasslands in Central Europe. Grass Forage Sci. 64, 454–465. Conradi, T., Zehm, A., 2011. Zusammenstellung zur Kreuzkraut-Situation (Gattung Senecio)—aktueller Kenntnisstand zum Management. Informationsblatt der Regierung von Schwaben und des Bayerischen Landesamtes für Umwelt, Augsburg, p. 16 https://www.lfu.bayern.de/natur/streuwiesen/kreuzkraeuter/ doc/conradi_zehm_senecio_management.pdf (accessed 01.13.16.). Dierschke, H., Briemle, G., 2002. Kulturgrasland Wiesen, Weiden und verwandte Staudenfluren. Reihe Ökosysteme Mitteleuropas aus geobotanischer Sicht. Verlag Eugen Ulmer Stuttgart, pp. 239. Fischer, M.A., Oswald, K., Adler, W., 2008. Exkursionsflora für Österreich, Lichtenstein und Südtirol. Biologiezentrum der Österreichischen Landesmuseen. Linz. Fitter, A.H., Peat, H.J., 1994. The ecological flora databaseJ. Ecol. 82, 415–425. . (accessed 03.03.2014.) http://www.ecoflora.co.uk/index.php. Forbes, J.C., 1976. Influence of management and environmental factors on the distribution of the marsh ragwort (Senecio aquaticus Huds.) in agricultural grassland in Orkney. J. Appl. Ecol. 13, 985–990. Gaisler, J., Pavlu, V., Pavlu, L., Hejcman, M., 2013. Long-term effects of different mulching and cutting regimes on plant species composition of Festuca rubra grassland. Agric. Ecosyst. Environ. 178, 10–17.
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Hoogenboom, L.A.P., Mulder, P.P.J., Zeilmaker, M.J., Van den Top, H.J., Remmelink, G. J., Brandon, E.F.A., Klijnstra, M., Meijer, G.A.L., Schothorst, R., Van Egmond, H.P., 2011. Carry-over of pyrrolizidine alkaloids from feed to milk in dairy cows. Food Addit. Contam. 28, 359–372. Kempf, M., Schreier, P., Reinhard, A., Beuerle, T., 2010. Pyrrolizidine alkaloids in honey and pollen. J. Consum. Protect. Food Saf. 5, 393–406. Leiss, K.A., 2011. Management practices for control of ragwort species. Phythocem. Rev. 10, 153–163. Liehl, M., Bassler, G., Kriechbaum, M., 2012. Das Wasser-Greiskraut (Senecio aquaticus) im Bezirk Gmünd, Niederösterreich—Verbreitung, Standortpräferenzen und Bewirtschaftungseinflüsse, vol. 23. Wiss. Mitt. Niederösterr. Landesmuseum, pp. 119–160. Londo, G., 1976. The decimal scale for releves of permanent quadrats. Vegetatio 33, 61–64. Mattocks, A.R., 1968. Toxicity of pyrrolizine alkaloids. Nature 217, 723–728. Pelser, P.B., Gravendeel, B., Van der Meijden, R., 2002. Tackling speciose genera: species composition and phylogenetic position of Senecio sect. Jacobaea (Asteraceae) based on plastid and nrDNA sequences. Am. J. Bot. 89, 929–939. Pelser, P.B., Gravendeel, B., Van der Meijden, R., 2003. Phylogeny reconstruction in the gap between too little and too much divergence: the closest relatives of Senecio jacobaea (Asteraceae) according to DANN sequences and AFLPs. Mol. Phylogenet. Evol. 29, 613–628. Pelser, P.B., Veldkamp, J.-F., Van der Meijden, R., 2006. New combinations in Jacobaea Mill (Asteraceae-Senecioneae). Compos. Newslett. 44, 1–11. Rich, T.C.G., Woodruff, E.R., 1995. Changes in the vascular plant floras of England and Scottland between 1930–1960 and 1987–1988: the BSBI monitoring scheme. Biol. Conserv. 75, 217–229. Roberts, P.D., Pullin, A.S., 2007. The effectiveness of management interventions used to control Ragwort species. Environ. Manage. 39, 691–706. Rosenthal, G., 2000. Zielkonzeptionen und Erfolgsbewertung von Renaturierungsversuchen in nordwestdeutschen Niedermooren anhand
vegetationskundlicher und ökologischer Kriterien. Habilitation. Universität Stuttgart, Germany. Rosenthal, G., 2010. Secondary succession in a fallow central European wet grassland. Flora 205, 153–160. Sargent, E., 2008. The non chemical control of marsh ragwort (Senecio aquaticus Huds.)Leaflet. RSPB, Bedfordshire, UK, pp. 2. . (accessed 13.01.16.) http://www. floodplainmeadows.org.uk/files/floodplain/Marsh%20Ragworth%20Trial% 20RSPB%20Leaflet.pdf. Schmidt, R., 1983. Über Wuchsform und Arealdifferenzierung zentraleuropäischer Senecioneae: I. Wuchsform und Lebensgeschichte der Senecionoiden. Wissenschaftliche Zeitschrift der Martin-Luther-Universität Halle-Wittenberg: Mathematisch-naturwissenschaftliche Reihe 32, 113–132. Smith, R.S., Buckingham, H., Bullard, R.S., Shiel, R.S., Younger, A., 1996. The conservation management of mesotrophic (meadow) grassland in northern England . 1. Effects of grazing, cutting date and fertilizer on the vegetation of a traditionally managed sward. Grass Forage Sci. 51, 278–291. Suske, W., Huber, J., 2014. ÖPUL-Naturschutzmaßnahmen 2015+. Bundesministerium für Land- und Forstwirtschaft, Umwelt und Wasserwirtschaft, Wien, pp. 118. Suter, M., Lüscher, A., 2007. Beeinflusst die Bewirtschaftung das WasserKreuzkraut? Agrarforschung 14, 22–27. Suter, M., Lüscher, A., 2008. Occurrence of Senecio aquaticus in relation to grassland management. Appl. Veg. Sci. 11, 317–324. Suter, M., Lüscher, A., 2011. Measures for the control of Senecio aquaticus in managed grassland. Weed Res. 51, 601–611. Suter, M., Lüscher, A., 2012. Rapid and high seed germination and large soil seed bank of Senecio aquaticus in managed grassland. Sci. World J. 2012, 1–8. Thompson, K., Bakker, J.P., Bekker, R.M., 1997. The Soil Seed Banks of North West Europe: Methodology, Density and Longevity. University Press Cambridge, pp. 276.
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Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee
The impact of different cutting regimes on population density of Jacobaea aquatica (Hill) G. Gaertn., B. Mey. & Scherb. and grassland vegetation Gabriele Basslera,b,* , Gerhard Karrera , Monika Kriechbaumb a b
Institute of Botany, University of Natural Resources and Life Sciences, Gregor Mendel Straße 33, A-1180 Vienna, Austria Institute for Integrative Nature Conservation Research, University of Natural Resources and Life Sciences, Gregor Mendel Straße 33, A-1180 Vienna, Austria
A R T I C L E I N F O
Article history: Received 15 January 2016 Received in revised form 13 April 2016 Accepted 22 April 2016 Available online xxx Keywords: Senecio aquaticus Management Marsh ragwort Poisonous plant Toxicity Weed control
A B S T R A C T
Jacobaea aquatica is a monocarpic Asteraceae growing in wet grasslands of low management intensity. It is considered a noxious weed because it contains pyrrolizidine alkaloids, which cause health problems to livestock. The aim of this study was to develop management options to reduce the population density of J. aquatica in meadows of high nature conservation value without negative impacts on plant species diversity. The study site is located at the Hercynian part of Lower Austria near the city of Gmünd. The effect of five different cutting regimes on population density and seed production of J. aquatica as well as on species richness of the surrounding vegetation was tested on permanent plots from 2007 to 2012. One cut in October diminished J. aquatica but species richness decreased. Two cuts during the peak flowering period (July and August) and October reduced the population density of J. aquatica by c. 70% without obvious loss of species richness. Traditionally practiced two cuts in June and September lead to a rapid population growth of J. aquatica. According to our results, a first cut in June providing non-toxic fodder and two additional cuts during peak flowering are appropriate to reduce J. aquatica and to maintain biodiversity. ã 2016 Elsevier B.V. All rights reserved.
1. Introduction Like many other species of the genera Senecio and Jacobaea, J. aquatica (marsh ragwort) contains pyrrolizidine alkaloids, which are toxic for most vertebrates, particularly for mammals. The toxic compounds are not or insufficiently decomposed in hay and silage (Berendonk et al., 2010; Chizzola et al., 2015b). They are mutagenic, cause cancer (Chen et al., 2010) and destroy the liver tissue (Mattocks, 1968). Health problems for humans consuming intoxicated milk or honey cannot be excluded (Hoogenboom et al., 2011; Kempf et al., 2010). Therefore, some species of this genus are treated as noxious weeds, notably Jacobaea vulgaris (syn. Senecio jacobaea). Jacobaea aquatica is a close relative of J. vulgaris (Pelser et al., 2002, 2003). In consequence of recent phylogenetic analyses, the species with the former name Senecio aquaticus was
* Corresponding author. E-mail addresses: [email protected] (G. Bassler), [email protected] (G. Karrer), [email protected] (M. Kriechbaum). http://dx.doi.org/10.1016/j.agee.2016.04.018 0167-8809/ã 2016 Elsevier B.V. All rights reserved.
incorporated into the genus Jacobaea and named Jacobaea aquaticus (Hill) P. Gaertn., B. Mey. and Scherb. (Pelser et al., 2006). As a plant inhabiting grasslands of medium to low management intensity, it has diminished with the industrialisation of agriculture during the second half of the 20th century (Rich and Woodruff 1995; Rosenthal 2000). Encouraged by agri-environmental programs, farmers have ceased fertilisation and reduced the cutting frequency on formerly ameliorated wet grasslands during the last decades. This has caused an increase in J. aquatica population density (Liehl et al., 2012; Suter and Lüscher, 2007, 2008). Since the early 21st century, this species has become a serious issue as a toxic grassland plant in Switzerland (Bohren et al., 2008; Bosshard et al., 2003), Germany (Berendonk et al., 2010; Conradi and Zehm, 2011) and Austria. The abundance of J. aquatica and specific management options were investigated in Orkney by Forbes (1976), in Switzerland by Suter and Lüscher (2007, 2008) and in Austria by Liehl et al. (2012). In a review by Roberts and Pullin (2007), the effectiveness of management interventions to control ragwort species was analysed, but there was insufficient experimental evidence to assess manual or mechanical treatments. Also a review by Leiss (2011) on management practices for control of ragwort species
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does not mention any mechanical treatment against J. aquatica. Recently, Suter and Lüscher (2011) performed experiments in Switzerland testing various management types (cutting, ploughing, harrowing, pulling and combination of all these treatments with overseed) to control the species. The aim of a study in the UK (Sargent, 2008) was to develop management tools for meadows of high nature conservation value to reduce population density of J. aquatica by mechanical control. This paper focuses on population density under five different cutting regimes in Austria. We addressed the following research questions: Which cutting treatment is most effective in reducing mature seeds and population density of J. aquatica? Do plant species diversity and composition change under different cutting treatments? 2. Materials and methods 2.1. Study species J. aquatica is a short-lived perennial and usually monocarpic Asteraceae (Bassler, unpublished; Schmidt, 1983) native to many European countries. It germinates in autumn or spring and after two to seven years of vegetative growth as a rosette, flower shoots with yellow capitula are elongated from July to August. If the main shoot is cut, lateral shoots will immediately develop from the base and form new capitula. After fruit ripening (from end of July to September) most plants die off. The soil seed bank of J. aquatica belongs to the long-term persistent type (Bassler et al., 2010; Suter and Lüscher, 2012; Thompson et al., 1997). According to Schmidt (1983), J. aquatica reproduces by seeds. It is a grassland species that is restricted to wet meadows and pastures (Bartelheimer et al., 2010; Bassler, unpublished) mostly on acidic soils at low fertilisation levels (Dierschke and Briemle, 2002). 2.2. Study site The study took place in the Hercynian part of Lower Austria (Bohemian Massif), called Waldviertel, in Kleedorf close to the Czech border at an altitude of 470 m. The climate is characterised by a mean annual temperature of 6.8 C and a mean annual precipitation of 660 mm. The soil type is a strongly acidic gley developed from granite substrate. The A-horizon is middle to rich in humus (BFW). The experimental plots were located in a flat, frequently waterlogged meadow affiliated to the community type Lychnido floris cuculi-Festucetum rubrae Lichtenecker, Bassler, Karrer 2003 subass. juncetosum filiformis. Dominant graminoids were Anthoxanthum odoratum, Festuca rubra, Juncus filiformis and, in some plots, Deschampsia cespitosa, Carex nigra or C. brizoides; widespread herbs were Cardamine pratensis, Lychnis flos-cuculi, Plantago lanceolata, Ranuculus acris, R. flammula and R. indecorus. J. aquatica covered between 10 and 40 % at the study site in 2007 (Supplementary material). The annual mean productivity of the meadows (aboveground dry mass) was 4 t/ha. Before the beginning of the experiment in 2007, the meadow was mown once or twice a year after 15 June without applying fertiliser. 2.3. Experimental design and data analyses
Table 1 Cutting dates from 2007 to 2011; roman numbers indicate the month of cutting. Date of cutting Year
VI
VIIa
VIIb
VIII
IX
X
2007 2008 2009 2010 2011
05 June 02 June 03 June 07 June 14 June
03 28 03 05 05
16 July 21 July 17 July 16 July 25 July
06 August 02 August 05 August 10 August 16 August
03 September 09 September 30 August 15 September 06 September
03 October 07 October 29 September 15 October 30 September
July June July July July
weight of 0.32 mg (Fitter and Peat, 1994). Five different cutting regimes (=treatments) were applied to study their effect on population growth rates of J. aquatica (Tables 1 and 2): (1) “ October” (standard): cut once per year in early October (X); (2)“June–September” (representing the traditional cutting regime for extensive meadows in the Waldviertel region): cut in early June (VI), when all plants were still in rosette stage and in early September (IX), when seed dispersal was nearly finished; (3) “June–July–October”: managed as “June–September” plus an additional cut in late July (VIIb), when adult individuals were flowering a second time; (4) “July-October”: cut in early July (VIIa), when J. aquatica flowered but no seeds were mature and in early October (X); (5) “July–August–October”: cut at full flowering in early July (VIIa) as well as in early August (VIII) and in early October (X). The exact date was dependent on the forage growth (Table 1). The number of replicates per treatment was five. Plots were cut manually with a scythe, implicating a low cutting height (c. 3 cm). The following measurements were taken before every cutting date at every 1 m2 plot from 2007 to 2011: number of rosettes larger than 1 cm in diameter, number of flowering individuals and number of capitula with mature seeds of every flowering individual; seeds were regarded as mature when capitula were in release stage or seeds were already released from the capitula. Counting of the number of vegetative and generative individuals was extended to year 2012. The vegetation was documented in 2007 and 2010 in June before the first cut. Relevés included complete species lists of vascular plants per plot; coverage of plants was estimated using the scale of Londo (1976). The nomenclature of vascular plants follows Fischer et al. (2008). Statistical analyses were conducted with SPSS 18.0 (IBM, Somers, NY, USA). Graphs were drawn with STATISTICA 10 (StatSoft, Tulsa, OK, USA). Changes in species diversity were tested by comparing the number of vascular plants per m2 in 2007 and 2010 by single t-tests for dependent variables for every treatment. A repeated measures ANOVA was calculated to detect changes in consecutive years under different treatments of the following parameters: density of J. aquatica, mean number of flowering individuals per m2 and mean number of capitula per individual plant per m2. One outlier was removed in treatment “June– September” in order to achieve normally distributed residuals.
Table 2 Cutting regimes (=treatments) and developmental stages of J. aquatica individuals at time of mowing: r = rosette, f = flowering plant, s = seed release, d = dead (additional vegetative rosettes are present all over the year.); Roman numerals indicate dates (months) of cutting (Table 1). Treatment code
Twenty five permanent plots of one square meter were arranged in a randomised complete block design in the meadow described above. The distance from one plot to another was one meter. The area around the plots was mown regularly to avoid seed rain from the direct neighbourhood of the experimental plots. Seed exchange between experimental plots was assumed to be low, because J. aquatica seeds generally are not dispersed over long distances (Bassler et al., 2011; Forbes 1976), despite their light
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Date of cutting VI
VIIa
VIIb
VIII
IX
X d
October June–September
r
June–July–October
r
s f
July–October
f
July–August–October
f
s/d r/d f
r/d
20
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The J. aquatica population was very dense at the beginning of the experiment. On average, 90 individuals per m2 were counted in 2007, corresponding to a coverage of 10–40%. A repeated measures ANOVA (SPSS) revealed that the within-subject effect “year” (sphericity assumed: p < 0.001) the between subject effect “treatment” (p = < 0.001) and their interaction (p < 0.001) were significant. Between 2007 and 2012, the number of individuals per plot remained more or less stable in treatments “June–July– October” and “July–October” (Fig. 1). In treatment “June–September”, the density increased from 84 to 124.2 individuals per plot; density increase was more or less linear until 2011 and decreased in 2012 (Fig. 1). This treatment differed significantly from all other treatments (multiple comparisons). Under treatment “July– August–October”, the population declined. Coverage was reduced from 2007 onwards by c. 70%, resulting in a density of 40 individuals/m2, on average. In treatment “October”, the density of ragwort individuals decreased mainly in 2011 and 2012 (18 individuals per m2 referring to 29% of 2007). It differed significantly from treatment “July–October” and “June–September”. The repeated measures ANOVA shows that the number of flowering individuals per m2 varied significantly (p < 0.001) from year to year: On average, 16.7 individuals flowered in 2007, 24.3 in 2008, 11.1 in 2009, 15.2 in 2010, 8.7 in 2011, and 9.8 in 2012. Variation was generally high, ranging from 0 to 64 flowering individuals per plot. This referred to 19% flowering individuals in the year 2007, 30% in 2008 and only 12–16% from 2009 to 2012 (Fig. 2). The number of flowering individuals per m2 were not significantly influenced by the treatments (p = 0.131).
September and lasted until October. In treatment “June–September” and “June–July–October” ripening was slightly delayed. For treatment “June–September” the main time for seed ripening was during the second half of July and August. In treatment “June–July– October” ripening was prevented by two cuts until August. In treatment “July–October” seed ripening started and culminated in August and lasted until October. In treatment “July–August– October” seed ripening was almost totally prevented. Only in years with a warm autumn (e.g. 2009) seeds succeeded to ripen in September or October. The repeated measures ANOVA revealed that the mean number of capitula with mature seeds per individual and plot differed significantly by treatments (p < 0.001). The highest number of capitula with mature seeds (on average, 9.5 capitula per individual for all years 2008–2011) were counted in treatment “October”. Treatment “June–September” followed with a mean of 5.7 capitula per individual. An additional cut in July in treatment “June–July– October” reduced the mean number of capitula with mature seeds to 1.3. Treatment “July–October” with one cut in the main flowering period resulted in a mean of 4.5 capitula per individual. The best suppression of seed production was observed in treatment “July–August–October”, where only 0.1 capitula per individual contained mature seeds (Fig. 3). Year to year variation of seed production was also high (p < 0.001): In the years 2008 and 2011 most capitula with mature seeds were produced (5.3 respectively 5.7), while in the years 2009 and 2010 the number was only 2.7 resp. 5.74. In 2008 and 2011 prevention of seed production in treatment “June–July–October” was almost as effective as in treatment “July– August–October”. Apart from that, the relative differences in seed production between the different treatments were stable in all years.
3.2. Production of mature seeds of J. aquatica
3.3. Development of species richness and vegetation composition
Fig. 3 shows the phenology of seed ripening with regard to different cutting regimes averaged for the years 2008–2011; 2007 was not considered because of insufficient data. Treatment “October” was mown only once in autumn and allowed the undisturbed development of mature seeds. Under these conditions, seed ripening started in mid-July, was highest in early
The overall mean number of vascular plants per m2 was 16.3 in 2007 and 16.6 in 2010. Regarding the different treatments, no significant changes in species number between the first and the second survey could be observed (Table 3). However, some notable changes in species composition were found. In all October-plots graminoid species (especially Scirpus sylvaticus, Juncus filiformis,
3. Results 3.1. Development of population density of J. aquatica
Fig. 1. Number of J. aquatica individuals per m2 and different treatments from 2007 to 2012 (means, 95% confidence interval).
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Fig. 2. Number of flowering individuals of J. aquatica per m2 and different treatments from 2007 to 2011 (means, 95% confidence interval).
Fig. 3. Number of capitula containing mature seeds per J. aquatica individual regarding five different treatments at five different dates (VIIa to X, Table 1). Values are averaged over the years 2008–2011 (means, s.e. of the mean).
Table 3 Comparison of the number of species per m2 of the years 2007 and 2010 (mean standard error). Treatment
Number of species/m2 2007
October June–September June–Jul–October July–October July–August–October
17.8 16.6 14.4 16.4 16.4
2010 0.4 1.4 1.4 1.1 0.7
17.0 18.2 15.4 15.8 16.8
0.9 1.2 1.0 0.9 1.2
Deschampsia cespitosa and Carex. brizoides) enhanced their cover from 63 to 92%, while the cover of forbs (legumes included) decreased from 53 to 42%. In three out of five Oct-plots the cover of J. aquatica decreased from 2007 to 2010 and vanished completely until 2012. Comparing relevés from 2007 and 2010, some shifts in species dominancy in other treatments were detected (Supplementary material): In the late mowing treatments “October”, “July– October” and “July–August–October”, the cover of Festuca rubra decreased, which was in contrast to results of Gaisler et al. (2013), who observed that F. rubra is indifferent to different cutting and mulching regimes. The cover of Trifolium repens was generally low in 2010. Anthoxanthum odoratum increased in 2010 in treatment “June–September”. The cover of J. aquatica decreased in treatment
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“July–August–October” but increased in treatment “June–September”; no changes were recorded in treatment “June–July–October” and “July–October”. The cover of the other species remained more or less stable. 4. Discussion The aim of this study was to find a management strategy that reduces the abundance of J. aquatica in grassland with high nature conservation value without endangering biodiversity. This should be achieved by adequate cutting regimes, avoiding management practices like ploughing or herbicides. Those vegetation disturbing practices, anyhow, did not work well, when applied only once (Suter and Lüscher, 2011). As J. aquatica reproduces only by seeds (Schmidt, 1983), it was assumed that breaking the life cycle by prevention of seed ripening should help to empty the seed bank and consequently lead to a decrease of population density. Seedlings were not considered in this experiment, but seedling density was highly fluctuating with up to 340 seedlings per m2. It was not only influenced by the number of seeds of the previous year, but also by the number of seeds in the seed bank, the weather conditions of the year and the percentage of bare ground (Bassler, unpublished). In the majority of years, J. aquatica individuals under treatment “Oct”, which were undisturbed during flowering and seed ripening in July and August, produced most seeds. However, although seed production was highest, the population density ranged from stable to strongly decreasing (Fig. 4). In 2011 and 2012 the decrease of population density was remarkable in most “October”-plots and J. aquatica vanished completely in three out of five plots. Tall graminoids (Scirpus sylvaticus, Carex brizoides) increased because of the late cutting and lead to a dense vegetation canopy, which prevented the light penetrating to the ground. Thus in “October”plots, mortality of older J. aquatica rosettes increased and seeds of J. aquatica could not germinate and establish. Population density remained stable in only one plot, where vigour was less and the plant composition did not change. This indicates that a late single cut regime is not feasible to reduce J. aquatica on oligotrophic sites. In their study about long term effects of grassland management, Gaisler et al. (2013) also observed an increase of tall grasses and a
decrease of small forbs when mulching was applied only once in September. In a fallow experiment, J. aquatica completely disappeared after a period of five years without any cutting (Rosenthal, 2010). Suter and Lüscher (2011) stated that one cut in autumn performed best in suppressing J. aquatica compared to their control treatment, though the total number of J. aquatica plants increased in their experiment. They recommend one cut for sites with less favourable topography and fodder quality by arguing that this comes close to the treatment of traditional fens, which are also characterised by high species diversity. In our experiments, the species number per plot remarkably decreased only in one plot after four years of a very late cut in October. However, there is a high risk that the late cutting in the long run also suppresses other species, especially if the site is not extremely nutrient-poor (cf. Gaisler et al., 2013; Rosenthal, 2010; Smith et al., 1996). Considering possible economic consequences, this cutting regime cannot be recommended, because late mown fodder has insuffi cient quality (Cop et al., 2009). The two cut treatment “June-September”, which is usually applied by farmers receiving agri-environmental compensation payments in the Waldviertel region, did not harm the flowering of J. aquatica very much. At the first cut in early June, most J. aquatica individuals were still in the rosette stage and were hardly affected by mowing (Fig. 1). In this treatment flowering started only about one week later than in the treatment with undisturbed flowering individuals (“October”). At the second cut in September, seed release was more or less finished. The total number of mature seeds of treatment “June-September” reached on average 78% of the treatment “October”. Population density increased rapidly in this treatment and reached more than 200% after four years, possibly as a consequence of dense juvenile rosettes. The slight decline of J. aquatica density in 2011 and 2012 (Fig. 1) might be due to intraspecific competition of the growing rosettes. Suter and Lüscher (2011) also reported an increase in vegetative individuals in a comparable regime (first cut in Mid-June and second cut in late October, in the Swiss Prealps). They also found that different control options (ploughing, harrowing, herbicide application) combined with this cutting regime did not change the overall tendency of population growth.
Fig. 4. Mean number of capitula containing mature seeds per J. aquatica individual and m2 with regard to different treatments from 2008 to 2011(means, 95% confidence interval).
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In cutting regimes like treatments “June–July–October” and “July–October”, where J. aquatica was mown at least once when it was flowering, seed production was reduced (24–54%), but population density of J. aquatica remained stable. These treatments prevented J. aquatica populations to spread by seeds, but were not able to diminish its density within four years. Treatment “July– October” is partly comparable to the cutting regime of Sargent (2008) with one cut in mid-June, which prevented seed ripening under the climatic conditions of the UK. In contrast to our experiment, she reported a strong decline of J. aquatica individuals after two years. Perhaps this decrease in density might rather be due to unfavourable conditions for germination than to a reduction of seed production. Maybe these differences are the result of a short-lived soil seed bank of J. aquatica in the UK compared to Austria (Bassler et al., 2010) or Switzerland (Suter and Lüscher, 2012), where J. aquatica builds up a permanent seed bank. This fact could also be a consequence of shorter-lived individuals in the UK. In Austria individuals reach a maximum age of at least seven years (Bassler, unpublished). In treatment “July–August–October” (two cuts at peak flowering in July and August) seed ripening was almost completely prevented; only a mean of 30 mature seeds per individual were produced, which is 3% of treatment “October”. This treatment led to a significant linear reduction of the total number of individuals. After 5 years, the number of individuals decreased by about 70% resulting in 40 individuals/m2 on average. This is still quite a lot, but if the decrease will continue in future (see trend in Fig. 1), J. aquatica might be controlled in the long term. Though the plots of treatment “July–August–October” were mown three times a year, no reduction of plant species diversity was observed until 2010. Negative trends are not very probable because most species present are rather sensitive to early cuts (e.g. in May) but less harmed by cuts during summer. Especially at the October cut, plant height was very low and mowing did not significantly reduce total biomass (Chizzola et al., 2015a). The comparison of treatment “June–July–October” and “July– August–October” shows the importance of the nearly total prevention of seed production in at least five consecutive years: In treatment “July–August–October”, in every year seed production was prevented almost totally, whereas in treatment “June–July– October” the prevention was only effective in some years. Nevertheless, treatment “June–July–October” did not lead to a reduction of the total number of individuals. Another problem is that herbage mown at peak flowering contains a high proportion of toxic J. aquatica (Chizzola et al., 2015a) and should not be used as fodder, but has to be disposed of. 5. Conclusions All cutting regimes tested in our study did not harm the vegetation composition and richness of vascular plants, except for the regime with one cut in October, in which graminoids started to dominate and suppress other species. On the other hand, this “ October” cutting regime performed well in suppressing J. aquatica. This is valid, at least at moderate nutrient-rich sites, whereas on very nutrient-poor sites vegetation composition did not change and the density of J. aquatica remained stable. The cutting regime with two cuts at peak flowering in July and August lead to a slow decrease of J. aquatica density after six years. The disadvantage of this mowing regime, however, is the infestation of the fodder with highly toxic plants. The following management regime can be a compromise: The fodder of a cutting before flowering with low proportions of J. aquatica is suited best for feeding. If it is cut in early June, it does not negatively affect biodiversity goals. Two consecutive cuts at peak flowering diminish the J. aquatica population, but should not be used as fodder. This costly management could be partly compensated by agri-environmental
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measures, as it is also intended for invasive species in the recent agri-environmental scheme “ÖPUL 2015” in Austria (Suske and Huber, 2014). A regime with cuts in June and September should be avoided, because it leads to a rapid increase of J. aquatica density. Using a cutting regime, as outlined above, can be a good alternative to time consuming hand pulling or digging out J. aquatica plants. The results of our experiment are valid at least at the local and regional scale. Experiments have to be expanded to climatically different sites. Acknowledgements This work was funded by the Federal Ministry of Agriculture, Forestry, Environment and Water Management in cooperation with Federal States of Austria and the Jubiläumsfonds of the Austrian Nationalbank. We thank the farmers for providing their meadows, Desirée Bruhin for assistance in the field and Bernhard Spangl for statistical support. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.agee.2016.04.018. References Bartelheimer, M., Gowing, D., Silvertown, J., 2010. Explaining hydrological niches: the decisive role of below-ground competition in two closely related Senecio species. J. Ecol. 98, 126–136. Bassler, G., Karrer, G., Kriechbaum, M., 2010. The fate of Senecio aquaticus seeds. In: Jongejans, E., Macel, M., Vergeer, P., Verhoeven, K. (Eds.), Plant Population Biology—Crossing Borders. Institute for Water and Wetland Research, Radboud University Nijmegen, Nijmegen, Netherlands p. 92. Bassler, G., Karrer, G., Grabmaier, A., Kriechbaum, M., 2011. Spread and control options of the poisonous grassland weed Senecio aquaticus. 3rd International Symposium on Environmental Weeds and Invasive Plants, Ascona, Switzerland. Berendonk, C., Cerff, D., Hünting, K., Wiedenfeld, H., Becerra, J., Kuschak, M., 2010. Pyrrolizidine alkaloid level in Senecio jacobaea and Senecio erraticus the effect of plant organ and forage conservation. Grassland Science in Europe 15, 669– 671. BFW (Bundesforschungs- und Ausbildungszentrum für Wald, Naturgefahren und Landschaft) Digitale Bodenkarte von Österreich; http://gis.lebensministerium. at/eBOD/ (accessed 28.07.14.). Bohren, C., Delabays, N., Rometsch, S., 2008. Invasive Pflanzen: Herausforderung für die Landwirtschaft? Agrarforschung 15, 314–319. Bosshard, A., Joshi, J., Lüscher, A., Schaffner, U., 2003. Jakobs- und andere Kreuzkraut-Arten: eine Standortbestimmung. Agrarforschung 10, 231–235. Chen, T., Mei, N., Fu, P.P., 2010. Genotoxicity of pyrrolizidine alkaloids. J. Appl. Toxicol. 30, 183–196. Chizzola, R., Bassler, G., Kriechbaum, M., Karrer, G., 2015a. Pyrrolizidine alkaloid production of Jacobaea aquatica under different cutting regimes. J. Agric. Food Chem. 63, 1293–1299. Chizzola, R., Bassler, G., Winter, S., Zebeli, Q., Kriechbaum, M., 2015b. Persistence of alkaloids of typical poisonous plants autumn crocus and marsh ragwort in grass silage. Wiener Tierärztliche Monatsschrift—Veterinary Medicine Austria 102, 285–292. Cop, J., Vidrih, M., Hacin, J., 2009. Influence of cutting regime and fertilizer application on the botanical composition, yield and nutritive value of herbage of wet grasslands in Central Europe. Grass Forage Sci. 64, 454–465. Conradi, T., Zehm, A., 2011. Zusammenstellung zur Kreuzkraut-Situation (Gattung Senecio)—aktueller Kenntnisstand zum Management. Informationsblatt der Regierung von Schwaben und des Bayerischen Landesamtes für Umwelt, Augsburg, p. 16 https://www.lfu.bayern.de/natur/streuwiesen/kreuzkraeuter/ doc/conradi_zehm_senecio_management.pdf (accessed 01.13.16.). Dierschke, H., Briemle, G., 2002. Kulturgrasland Wiesen, Weiden und verwandte Staudenfluren. Reihe Ökosysteme Mitteleuropas aus geobotanischer Sicht. Verlag Eugen Ulmer Stuttgart, pp. 239. Fischer, M.A., Oswald, K., Adler, W., 2008. Exkursionsflora für Österreich, Lichtenstein und Südtirol. Biologiezentrum der Österreichischen Landesmuseen. Linz. Fitter, A.H., Peat, H.J., 1994. The ecological flora databaseJ. Ecol. 82, 415–425. . (accessed 03.03.2014.) http://www.ecoflora.co.uk/index.php. Forbes, J.C., 1976. Influence of management and environmental factors on the distribution of the marsh ragwort (Senecio aquaticus Huds.) in agricultural grassland in Orkney. J. Appl. Ecol. 13, 985–990. Gaisler, J., Pavlu, V., Pavlu, L., Hejcman, M., 2013. Long-term effects of different mulching and cutting regimes on plant species composition of Festuca rubra grassland. Agric. Ecosyst. Environ. 178, 10–17.
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