Effect of different grazing systems on dynamics of grassland weedy species
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Journal of Plant Diseases and Protection Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz Sonderheft XX, 377-383 (2006), ISSN 1861-4051 © Eugen Ulmer KG, Stuttgart Effect of different grazing systems on dynamics of grassland weedy species V. PAVLǓ1*, J. GAISLER1, M. HEJCMAN2, L. PAVLǓ3 1 Research Institute of Crop Production Prague-Ruzyně, Grassland Research Station, Rolnická 6, CZ-460 01, Liberec 11, Czech Republic, e-mail: pavlu@vurv.cz, jan.gaisler@volny.cz 2 Czech University of Agriculture, Department of Ecology and Environment, Kamýcká 1176, CZ-165 21, Praha 6 – Suchdol, Czech Republic, e-mail: hejcman@fle.czu.cz 3 Jizerské Mts. Protected Landscape Area Administration, U Jezu, CZ-460 01 Liberec 1, Czech Republic, e-mail: lenka.pavlu@schkocr.cz * Corresponding author Summary The effect of different grazing regimes on dynamics of weedy species was studied in an upland grassland in the Jizerské Mountains. We applied continuous stocking and rotational grazing. The experiment included three replicate pairs of plots. Cover of the most abundant weedy species was estimated in 100 m2 permanent plots. Weedy vegetation varied as a result of time and differences between treatments. We revealed higher cover of broad-leaved dock (Rumex obtusifolius) and tall weedy grasses (Holcus mollis, Poa trivialis) under rotational grazing, whereas continuous grazing supported successively increase of dandelion (Taraxacum spp.). The results demonstrate that not only grazing itself but also different grazing system alters the composition of weedy vegetation in grasslands. Keywords: Rotational grazing, set stocking, weed control, Taraxacum spp., Rumex obtusifolius Zusammenfassung Einfluss verschiedener Weidesysteme auf die Entwicklung von Grünlandunkräutern Der Einfluss verschiedener Weidesysteme auf die Dynamik der Unkrautentwicklung wurde in einem Berglandgrünland im Isergebirge studiert. Es wurden Stand- und Umtriebsweiden miteinander verglichen. Die Varianten waren dreifach wiederholt. Der Deckungsgrad der häufigsten Unkräuter wurde in dauerhaft markierten 100 m2-Flächen aufgenommen. Die Unkrautvegetation veränderte sich mit der Zeit und variierte zwischen den Behandlungen. In der Umtriebsweide war der Deckungsgrad breitblättriger Unkräuter (Rumex obtusifolius) und hochwachsender Gräser (Holcus mollis, Poa trivialis) erhöht, wohingegen auf der Standweide der Anteil von Löwenzahn (Taraxacum spp.) mit der Zeit zunahm. Die Ergebnisse zeigen, dass nicht nur durch die Weidewirtschaft an sich sondern auch durch das Weidesystem die Zusammen- setzung der Unkrautflora des Grünlandes beeinflusst wird. Stichwörter: Umtriebsweide, Standweide, Unkrautkontrolle, Taraxacum spp., Rumex obtusifolius Introduction Weeds have always been tolerated in grassland to a grater extent than in arable crops (FRAME 1992), because many of them have relatively good quality and can be used as a fodder of herbivores. Grassland weeds can be effectively controlled by chemical, biological, mechanical and cultural measures. Grazing management is one of the most important factors, which affect sward structure of pastures (PAVLǓ et al. 2003). Farmers use two basically different systems of grazing: continuous and rotational. Under rotational
378 PAVLǓ, GAISLER, HEJCMAN, PAVLǓ grazing the area is divided into a series of fields or paddocks that are grazed in sequence, each use being followed by a rest period (FRAME 1992), whereas under continuous stocking (set stocking) the animals are in the grazing area for the whole grazing season or year (HODGSON 1979). In spite of the importance of the practiced management only a little is still known about the effects of different grazing systems on weedy species in pasture ecosystems (ZALLER 2004). Several studies have focused primarily to high productive sown pastures only, but data from widespread seminatural grasslands are missing. Therefore, the objective of this study was to examine the effect of rotational grazing and continuous stocking on weedy plants in common upland grassland. Materials and methods Site description The experiment was carried out in an experimental pasture near the town of Liberec in uplands of the Jizerské hory mountains (50°49' N, 15° 02' E), Czech Republic. The altitude of the study site is 420 m a. s. l. Mean annual temperature is 7.2°C and the average annual precipitation is 803 mm (Liberec meteorological station). The geological substratum is granite underlying medium deep brown soil (cambisol) with the following attributes: pH/KCl = 4.8, Cox = 3 %, available P content = 43 mg kg-1, available K content = 70 mg kg-1, and available Mg content = 68 mg kg-1. The dominant species before the start of the experiment were Elytrigia repens, Agrostis capillaris, Lolium perenne, Trifolium repens and Taraxacum spp. No fertilisers have been applied since 1992. The productivity of pasture varied from 5 to 7 t.ha-1 of dry biomass. Nomenclature of vascular plant species follows KUBÁT el al. (2002). Design of the experiment and data collection The experiment was set up in the spring of 1993. The treatments were rotational grazing (R) and continuous stocking (C). The R treatment consisted of six paddocks, each with 0.166 ha. Four to six heifers were moved from one paddock to another, when the sward height was reduced to about 7 cm. The grazing period was 2-7 days in summer and autumn or in spring, respectively. The C treatment was established in one large paddock of 1 ha. The average sward height of 5-7.5 cm was maintained by varying the grazing area available for the treatment and by reducing the number of animals in late summer. Both treatments were grazed by two separate herds of young heifers. The grazing season started in early May and ended in September or mid-October. In September the stocking rate in both treatments was around 1000 kg ha -1. Three pairs of permanent plots 10 x 10 m were established in 1993. The percentage cover of all vascular species was visually estimated in permanent plots before the start of grazing in May each year from 1993 to 1997. We present only the most abundant weedy grass and forbs species here. Repeated measures ANOVA was used to evaluate cover data. Results The results of ANOVA analyses of the most abundant weedy species are presented in Tabs. 1 and 2. Species associated with R treatment were Holcus mollis, Poa trivialis and Rumex obtusifolius (Figs 1 and 2). Weed forb species thriving in C treatment was Taraxacum spp. There was also recorded remarkable successional development of Agrostis capillaris, Holcus mollis, Poa trivialis and Taraxacum spp. independent of experimental treatments. A consecutive decrease of tall grasses (Elytrigia repens, Poa trivialis) and on other hand an increase of short (Agrostis capillaris) and tall (Holcus mollis) grass was recorded in both treatments during run of the experiment. We revealed neither treatment nor time effect on Aegopodium podagraria and Ranunculus repens. Their representation in sward was relative stable during the whole study period. Cover of Taraxacum spp. gradually increased under both grazing treatments particularly in continuously grazed plot.
% cover % cover
0
5
10
15
20
25
0
5
10
15
20
Years
Years
Elytrigia repens
Agrostis capillaris
1993 1994 1995 1996 1997
1993 1994 1995 1996 1997
R
C
R
C
% cover % cover
0
2
4
6
8
0
5
10
15
20
25
Years
Years
Poa trivialis
Holcus mollis
1993 1994 1995 1996 1997
1993 1994 1995 1996 1997
R
C
R
C
Dynamics of grassland weeds
Fig. 1: Changes in cover (%) of weedy grasses under rotational (R) and continuous (C) grazing for years 1993-97.
Abb. 1 Veränderungen des Deckungsgrades (%) von Ungräsern bei Umtriebsweide (R) und Standweide (C) über die Jahre 1993-1997.
379380
% cover % cover
0
1
2
3
0
1
2
3
4
5
6
Years
Years
Ranunculus repens
Aegopodium podagraria
1993 1994 1995 1996 1997
1993 1994 1995 1996 1997
PAVLǓ, GAISLER, HEJCMAN, PAVLǓ
R
C
R
C
% cover % cover
0
1
2
3
4
0
5
10
15
20
25
Years
Years
Taraxacum spp.
Rumex obtusifolius
1993 1994 1995 1996 1997
1993 1994 1995 1996 1997
R
C
R
C
Fig. 2: Changes in cover (%) of weedy forbs under rotational (R) and continuous (C) grazing for years 1993-97.
Abb. 2. Veränderungen des Deckungsgrades (%) von Unkräutern bei Umtriebsweide und Standweide (C) über die Jahre 1993-1997.Dynamics of grassland weeds 381
Tab. 1: Results of repeated measurements – ANOVA analyses of weedy forbs. Significant differences
are boldfaced.
Tab. 1: Ergebnisse der Varianzanalysen (ANOVA, repeated measurements) für die Unkräuter. Signifi-
kante Unterschiede sind fett gedruckt.
Species Effect Degrees of F-ratio P-value
freedom
Aegopodium podagraria Treatment 1 0.28 0.6020
Year 4 0.07 0.9903
Treatment*Year 4 0.02 0.9993
Ranunculus repens Treatment 1 1.84 1.9000
Year 4 0.99 0.4338
Treatment*Year 4 0.47 0.7561
Taraxacum spp. Treatment 1 5.11 0.0350
Year 4 5.28 0.0045
Treatment*Year 4 0.25 0.9008
Rumex obtusifolius Treatment 1 8.44 0.0087
Year 4 0.31 0.8682
Treatment*Year 4 0.47 0.7576
Tab. 2: Results of repeated measurements – ANOVA analyses of weedy grasses. Significant differences
are boldfaced.
Tab. 2: Ergebnisse der Varianzanalysen (ANOVA, repeated measurements) für Ungräser. Signifikante
Unterschiede sind fett gedruckt.
Species Effect Degrees of F-ratio P-value
freedom
Agrostis capillaris Treatment 1 0.62 0.4400
Year 4 3.00 0.0432
Treatment*Year 4 0.09 0.9850
Elytrigia repens Treatment 1 0.41 0.5255
Year 4 2.23 0.1019
Treatment*Year 4 0.10 0.9828
Holcus mollis Treatment 1 6.51 0.0190
Year 4 6.16 0.0021
Treatment*Year 4 0.75 0.5664
Poa trivialis Treatment 1 9.13 0.0067
Year 4 39.51 0.0000
Treatment*Year 4 3.47 0.0261
Discussion
Continuous stocking resulted in a decrease in abundance of tall weedy grasses (Elytrigia repens, Poa
trivialis). The overall increase of rhizomatous Holcus mollis is surprising, because it does not usually
persist in heavily grazed swards (GRIME et al. 1988), however its regenerative strategies is evidently
subject to disturbance as a grazing. In practise the cover of all presented tall grasses can be simply
reduced by the intensity of grazing (e.g. MITCHLEY 1988, BELSKY 1992, PAVLǓ 2006).
Short grass A. capillaris was indifferent to applied treatment and in terms of coverage, the grazing
itself seems to be more important then the grazing system used (e.g. PAVLǓ 2003, HELLSTRÖM et al.
2003; HEJCMAN et al. 2005). Although all these grasses are included to the list of grassland weeds in the382 PAVLǓ, GAISLER, HEJCMAN, PAVLǓ
Czech Republic (KNEIFLOVÁ and MIKULKA 2003), their dangerousness in grassland is relative low.
Especially under grazing management they are relatively palatable and well ingest by animals.
The most abundant prostrate forb Taraxacum spp. increased in cover in continuously grazed treatment
during the run of the experiment similarly as in other studies testing grazing intensity (BULLOCK et al.
2001; PAVLǓ et al. 2003, PYKÄLÄ 2005, LOUAULT et al. 2005). Although dandelion is comprised into the
list of grassland weed species its content of nutrients is relatively high (ISSELSTEIN 1994, WILMAN and
DERRICK 1994) and it is well accepted by grazers. Lower yield of grasslands infested by dandelion is not
detrimental in many cases because of grasslands surplus in the Czech Republic and further due to process
of grassland extensification arisen in Europe in the last decade.
R. obtusifolius, the most important worldwide pasture weed, seems to be sensitive to frequent
defoliation under continuous grazing in our experiment. A possible explanation is probably grazing of
broad-lived dock plants in very young developmental stages (ZALLER 2004) and also higher competition
ability of other plants in frequently defoliated sward. However sward disturbation created by excessive
trampling and a higher availability of easily accessible nutrients for seedlings usually can result in
succesional increase of R. obtusifolius densities (MIKULKA and KNEIFLOVÁ 2004). Nevertheless we have
to count in to seasonality as an important factor of its biology (MARTÍNKOVÁ and HONĚK 2001).
We can conclude that not only grazing itself but also different grazing system alters the composition of
weedy vegetation in grasslands. This is consistent with the review of FRECKLETON and WATKINSON
(2002), which found that weed population dynamics is a result of the broad-scale type of management.
Acknowledgement
This work was supported by the Ministry of Agriculture of the Czech Republic 0002700601.
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