2007) and experimental (Caldeira et al. 2001; Tracy and Sanderson 2004; van Peer et al. 2004; Weigelt et al. 2009), found a positive effect (Table 1). Despite initially positive impacts on plant production, Tracy and Faulkner (2006) did not measure increased daily liveweight gains of cattle nor could they increase stocking rates in more diverse pastures. Also Soder et al. (2006) found no effects on herbage intake or milk production of dairy
cattle with increased plant diversity. In a survey of 854 meadows and pastures in Inner Mongolia, Bai et al. (2007) observed increased primary production with increased plant diversity. However, the authors pointed out that FDA-approved Drug Library in vitro this coincided with patterns of annual rainfall and soil nitrogen. Furthermore, conditions in this area were representative selleck inhibitor of those in the Eurasian steppe, but not necessarily directly comparable with managed temperate grassland. The voluntary daily dry matter intake of sheep has been found to increase with species richness up to eight species out of 11 in an indoor cafeteria trial (Wang et al. 2010). This should translate into weight gains of the animal, which were however not determined. In a field experiment, no difference in intake was observed between fields with four to six and with more than eight plant species. The authors discuss that this might be due to
supplementary corn offered in the field (Wang et al. 2010). Interestingly, the studies finding positive effects were mainly carried out in experimental plots, not in agricultural grassland (Caldeira et al. 2001; Tracy and Sanderson 2004; van Peer et al. 2004; Weigelt et al. 2009). In other studies of experimental plots, positive effects on production were found when the number of sown species was considered. However, based on the total number of species present (i.e. including weeds), no consistent effects were found (Bezemer and van der Putten 2007; Dodd et al. 2004). It has been a principle of ecological theory that the assembly of species
in a given habitat depends on the niches present. Therefore, within the limits of historical influences and site accessibility for propagules, the available resources determine phytodiversity in the first place. Here, diversity has been found to be maximal at intermediate resource availability (Critchley et al. 2002; Janssens et al. 1998; Schmid 2002). Hautier Teicoplanin et al. (2009) could show that a negative effect of fertilisation on phytodiversity of fertilised grassland communities was mainly due to increased competition for light and restriction of light reaching the lower layers of vegetation. In contrast to this, Rajaniemi (2002) did not find an effect of shading on species richness or diversity in an unproductive former field and concluded that the observed significant effects of fertilisation were due to increased total above- and belowground competition. The importance of belowground competition in such a system where light is not limiting could later be confirmed (Rajaniemi et al.