Abstract
Parallel declines in insect-pollinated plants and their pollinators have been reported as a result of agricultural intensification. Intensive arable plant communities have previously been shown to contain higher proportions of self-pollinated plants compared to natural or semi-natural plant communities. Though intensive grasslands are widespread, it is not known whether they show similar patterns to arable systems nor whether local and/or landscape factors are influential. We investigated plant community composition in 10 pairs of organic and conventional dairy farms across Ireland in relation to the local and landscape context. Relationships between plant groups and local factors (farming system, position in field and soil parameters) and landscape factors (e.g. landscape complexity) were investigated. The percentage cover of unimproved grassland was used as an inverse predictor of landscape complexity, as it was negatively correlated with habitat-type diversity. Intensive grasslands (organic and conventional) contained more insect-pollinated forbs than non-insect pollinated forbs. Organic field centres contained more insect-pollinated forbs than conventional field centres. Insect-pollinated forb richness in field edges (but not field centres) increased with increasing landscape complexity (% unimproved grassland) within 1, 3, 4 and 5km radii around sites, whereas non-insect pollinated forb richness was unrelated to landscape complexity. Pollination systems within intensive grassland communities may be different from those in arable systems. Our results indicate that organic management increases plant richness in field centres, but that landscape complexity exerts strong influences in both organic and conventional field edges. Insect-pollinated forb richness, unlike that for non-insect pollinated forbs, showed positive relationships to landscape complexity reflecting what has been documented for bees and other pollinators. The insect-pollinated forbs, their pollinators and landscape context are clearly linked. This needs to be taken into account when managing and conserving insect-pollinated plant and pollinator communities.
Highlights
Animal-mediated pollination is required for successful reproduction in many angiosperms [1]
There was a significant interaction between farm type and edge/ centre (Pseudo-F = 1.320, P = 0.042) (Fig. 3) with the centres of conventional fields mainly characterised by graminoids (89% contribution to community, Lolium perenne and Agrostis stolonifera) while organic centres were characterised by a large percentage of insectpollinated forbs (42% contribution to community, Trifolium repens and Ranunculus repens) and much fewer non-insect-pollinated forbs (2% contribution to community, Taraxacum spp.) as well as graminoids (46% contribution to community, Lolium perenne, Holcus lanatus and Agrostis spp.)
Community composition in organic and conventional field edges was similar but all edges were significantly different from all field centres (Pseudo-F = 20.899, P = 0.001) (Fig. 3) as they contained varying mixtures of insect-pollinated forbs (10–14% contribution to community), non-insect pollinated forbs (6–7% contribution to community) and graminoids (70–75% contribution to community)
Summary
Animal-mediated pollination is required for successful reproduction in many angiosperms [1]. Natural or semi-natural systems tend to have lower proportions of self-pollinated plants [6]. It is not clear whether intensive grasslands have reduced proportions of insect-pollinated plants. Intensive grasslands receive high fertilizer application rates and frequent defoliation [8]. This results in degraded species pools and structurally homogenous swards. The majority of agricultural land in the Republic of Ireland is intensive grassland [9]; these intensive grasslands support considerably fewer plant [10] and pollinator [11,12] species compared to the communities of plants [13,14] and pollinators [15,16] found in semi-natural grasslands. Declines in insect-pollinated plant numbers may, in turn, have further knock-on impacts on pollinators and plant-pollinator interaction networks
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