FA10 Weeds on spring cereal fields
|All non-cultivated plant species growing on cultivated fields can considered as weeds. The most abundant weeds are efficient propagators and tolerate reoccurring tillage well. Examples include the Field Pansy, Fat-hen and Couch Grass. Weeds provide food for farmland birds as well for pollinating and herbivorous insects and therefore contribute to the diversity of many other farmland species groups.|
Trends in the abundance of weeds
The abundance of weeds on spring cereal fields fell steeply between the surveys made in 1961–1964 and 1982–1984. The most important factor behind this development was the large scale use of pesticides that started in the 1960s and reached its peak in the early 1980s. By the latest surveys conducted in 1997–1999 the density of weeds had started to recover, although still remaining at only 50% of the level in the 1960s.
No chemical pesticides are allowed in organic farming, which started to become more farming practice common in the 1990s. The weed densities on organically grown fields in 1990s were even higher than on regularly cultivated fields in the 1960s. On the whole, however, the significance of organic farming has remained quite low since the share of organically grown fields of the total area of fields is small. At the end of 1990s six percent of the total field area has under organic farming.Partly the low diversity of weeds is also due to the intensified competition against cultivated species, which results from the cultivation of species with a higher yield, the proliferation of monocultures and growing amounts of nitrogen fertilization. Species that have benefitted from these changes include the Couch Grass.
Weeds as a source of nutrition
|An index has been developed at Agrifood Research Finland to describe trends in the amount of food provided by the weed community to other farmland species groups. The index is based on the number of interactions between weeds and the populations of species that utilize them. The three indices for different species groups behave in a similar fashion over time: there was a steep decline between 1960s and 1980s and a slight increase between 1980s and 1990s.|
The strongest change can be seen in the index for farmland birds. This is mainly due to the significant changes in the abundance of the species, such as the Fat-hen, that are especially important as food items for birds. Bees depend more on the insect pollinated perennial plants such as the Yarrows, Creeping Thistle and Field Sow Thistle. For herbivorous insects the differences between species are the most pronounced. Some species, which are of little importance for other species groups (including Couch Grass and Bedstraws), are important for herbivores.
|The next update of this indicator will be in 2010.|
- Updated (14.05.2013)