[Pollinator] Enhancing pollinator biodiversity in intensive grasslands

[David Inouye]

Potts, S. G., B. A. Woodcock, S. P. M. Roberts, 
T. T., E. S. Pilgrim, V. K. Brown, and J. R. 
Tallowin. 2009. Enhancing pollinator biodiversity 
in intensive grasslands. Journal of Applied Ecology 46:369-379.


ABSTRACT

    * 1. Increased agricultural intensification 
has led to well-documented declines in the fauna 
and flora associated with intensive grasslands in 
the UK. We aimed to quantify the effectiveness of 
different field margin management strategies for 
putting bumblebee and butterfly biodiversity back into intensive grasslands.
    * 2. Using four intensive livestock farms in 
south-west England, we manipulated conventional 
management practices (addition of inorganic 
fertilizer, cutting frequency and height, and 
aftermath grazing) to generate seven grass-based 
treatments along a gradient of decreasing 
management intensity. We also tested two more 
interventionist treatments which introduced sown 
components into the sward: (i) a cereal, grass 
and legume mix, and (ii) a diverse conservation 
mix with kale, mixed cereals, linseed and 
legumes. These crop mixtures were intended to 
provide forage and structural resources for 
pollinators but were not intended to have 
agronomic value as livestock feed. Using a 
replicated block design, we monitored bumblebee 
and butterfly responses in 27 plots (10 × 50 m) 
in each farm from 2003 to 2006.
    * 3. Bumblebees were most abundant, 
species-rich and diverse in the sown treatments 
and virtually absent from the grass-based 
treatments. The diverse conservation mix 
treatment supported larger and more diverse 
bumblebee assemblages than the cereal, grass and 
legume mix treatment. The sown treatments, and 
the most extensively managed grass-based 
treatments, had the highest abundance, species 
richness and diversity of adult butterflies, 
whereas butterfly larvae were only found in the grass-based treatments.
    * 4.  Bumblebee and butterfly assemblage 
structure was driven by floral abundance, floral 
richness, the availability of nectar resources, 
and sward structure. Only vegetation cover was 
correlated with butterfly larval abundance.
    * 5.  Synthesis and applications. This study 
has identified management options in the margins 
of intensive grasslands which can enhance 
bumblebee and butterfly biodiversity. 
Extensification of conventional grass management 
by stopping fertilization, reducing cutting 
frequency and not grazing, benefits butterflies. 
However, to enhance bumblebees requires a more 
interventionist approach in the form of sowing 
flower-rich habitat. Both approaches are 
potentially suitable for adoption in 
agri-environment schemes in the UK and Europe.