THÈSE - Université de Franche-Comté

Fig. 3 shows the results of a principle component analysis carried out on the matrix “13
farming practice variables” x “46 parcels”. The two first components represented here
accounted for 49.8 % of the total inertia. Nitrogen fertilisation and mowing variables (yield
and number of annual cuttings) were the variables most correlated to Axis 1 (Fig. 3). The first
principal component was thus interpreted as a gradient of intensification. This gradient
opposed two types of parcel management: one where fertilisation and mowing are the main
features and the other grazing.
A. terrestris dynamics in relation to farming practices and to T. europaea relative abundance
Among all variables of practices and T. europaea relative abundance, only those correlated to
an A. terrestris population dynamic variables at a risk lower than 0.15 were kept (Table 3).
Figs 4a and 4b are based on a redundancy analysis and show the overall canonical relationship
according to the two first axes between the table “farming practices and T. europaea relative
abundance” and the table “A. terrestris population dynamic variables”. This relationship was
found to be globally significant (P < 0.01 after 999 permutations). The canonical axes
explained 18.7 % and 5.5 % of the variance of the A. terrestris population dynamics,
respectively (total 24.2 %). Fig. 4a represents the maximum values for each parcel in the
canonical space: they were clearly larger in the parcels where the relative abundance of T.
europaea was higher at the beginning of the study period (spring 2002) and where grazing
took place in the fall. Furthermore, the parcels for which the increase of A. terrestris
populations began later in a commune were those with the lowest number of cuttings and
addition of organic nitrogen fertiliser (Fig. 4b). The four variables (tesp2, autgraz, organ and
cutting) account for less than 30 per cent of total variance, suggesting another explanatory
variable also affected the A. terrestris population kinetics.
THE HIGH DENSITY PHASE OF AN A. TERRESTRIS POPULATION CYCLE
The A. terrestris relative abundance decreased with increasing grazing intensity (P < 0.001)
and soil work intensity (P < 0.001).
Influence of livestock grazing on A. terrestris relative abundance
Significant differences were found between intensive pastures and permanent grassland and
between intensive pastures and traditional pastures (Fig. 5a).
Thèse C. Morilhat 2005 105