Weeds or wild plants?

What is your impression of the weeds listed on the left: pernicious weeds or important for farmland biodiversity? Click on them to find if you're right.

Weeds have a conflicting role in agro-ecosystems: they compete with the crop, reducing yields, whilst at the same time providing food for farmland wildlife. Weed management today has to reconcile these two conflicting elements. Studies at Rothamsted Research are aimed at assessing the competitive abilities of weeds and their contribution to farmland biodiversity so that targeted weed management decisions can be made.

Concern about the decline in farmland birds in the UK

Farmland bird species	Decline 1970-1998
Corn bunting	85%
Gray partridge	82%
Yellow hammer	54%
Linnet	54%
Skylark	52%
Lapwing	40%
Data recorded by British Trust for Ornithology 'Common Bird Census'

Farmland bird decline is a result of changes at a landscape scale

The decline in bird species that are specialists of farmland in the UK has been driven mainly by two related factors - 1) reduction in the availablilty of insect and plant seed food and 2) reduction or changes in available habitat. These changes have happened on a landscape scale and patterns of pesticide use are only one of the factors involved. Changes in cropping rotations for example have played an important role, a move to more profitable rotations dominated by autmn sown crops has reduce spring-sown crops and the weed species associated with them, and also decrease the occurrence of valueable over-winter stubble habitats.

Halting the decline

If we are going to halt the decline we need to make changes to both the management within individual crops, but also to make changes to rotations and to landscape management. One thing is certain if we want to encourage farmland birds and animals an absolute pre-requisite is farmland and the farmers to manage it.

References / Acknowledgments

1. Most of the information provided here has been compiled from the DEFRA-PSD funded review PN0940 'The impact of herbicides on weed abundance and biodiversity', Marshall et al (2001) (available to be downloaded from the PSD website).
2. As part of the review the CEH provided access to their Phytophagous Insect Data Base (PIDB), that information is reproduced here and is gratefully acknowledged.
3. Weed occurrence data is available in the paper 'Changes in the arable flora of central southern England since the 1960s' by Sutcliff & Kay (2000).
4. Information about competitive effects of weeds has been compiled from DEFRA funded work undertaken in the UK over a number of years e.g. Cussans et al (1998)