1. Intra-annual patch stability Inter-annual patch stability
Selective grazing, patch stability and vegetation dynamics in a rotationally-grazed pasture
B. Dumont, P. Carrère, N. Rossignol, J. Chadoeuf, A. Farruggia, C. Ginane, F. Louault
INRA, UR Herbivores, Ecosystème Prairial & Biostatistiques et Processus Spatiaux
Lack of data on interactions between grazing intensity and livestock species  Difficulty to propose recommendations for the management of biodiversity and production in grassland ecosystems
Study area: a productive grassland divided into 12 plots that were rotationally grazed by cattle at a high (Ca+) or a low (Ca-) stocking rate or by sheep at the same low stocking rate (Sh-)
Measurements: diet selection and patch stability, we aim to relate to the initial direction of community changes in a long-term ecosystem manipulation experiment
Forbs -1
-0.5
0.5 1 R1 R2 R3 R4 R5
Legumes
Ca+
Ca-
Sh-
Jacobs’ Index
Tall grasses
Short grasses *
* : missing data
Diet selection
Direct observation of bites
For both sheep and cattle,
Selection for legumes, forbs and short rather than tall grass patches, consistent with their higher nutritive value
Avoidance of tall grasses increasing over the grazing season as grass becomes mature, especially after the 3rd rotation (R3) early July
Intra-annual patch stability
Fine-scale measurements on permanent grids
Inter-annual patch stability
Large-scale measurements (25 x 20m²)
Respective proportions of vegetation types in stable 1.6 x 0.8 m² grids after the 3rd (Early July) and 4th (September) rotations of 2006 & 2007
Ca-: inter-annual stability of grazing patterns at the peak of biomass (R3; P < 0.05), but more ‘fluctuating’ patch boundaries in the autumn (R4) *
Ca+: high degree of inter-annual patch stability after R4 (P < 0.001) due to repellent items
Use of covariograms to assess the effect of local sward composition on patch stability over the grazing season
Sh-: no inter-annual stability (R3: P = 0.83; R4: P = 0.23)
Ca-
Ca+
Sh-
Vegetation dynamics
Point quadrats
Ca- & Sh-: positive link between the initial local abundance of legumes and forbs, and the stability of grazing patterns
Ca- & Ca+: positive link between the initial abundance of reproductive grasses and the stability of ungrazed patches
2004
2006
2007
2008
Ca-
 Greater effect of stocking rate than of grazer species in affecting the initial direction of community changes
Sh-
Ca+
Grasses Legumes Forbs
Selective grazing at a fine scale can create relatively stable patches within the pasture
Plots grazed by sheep showed some level of patch stability between the peak of biomass and the autumn, but no inter-annual stability.
Grazing by cattle seems more likely to locally maintain relatively short cover over successive years, and would consequently favour functional vegetation diversity by creating relatively stable open patches enabling prostrate forbs and legumes to compete with tall grasses.
In the long term, this could result in divergent vegetation dynamics within plots, and may lead to an effect of grazer species on sward botanical composition, beyond the strong effect of stocking rate
INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE
UR1213 Herbivores • F • Saint-Genès-Champanelle • France
UR874 Ecosystème Prairial • F Clermont-Fd & UR546 Biostatistique et Processus Spatiaux • F Avignon
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