Topping, C.J. NERI Technical report no. 527, 2005

 

Summary

 

Five scenarios of potential ways of implementing reductions in pesticide usage were evaluated against a baseline scenario for the impact that they would have on skylark populations. These scenarios were a general decrease in all pesticides (P), a larger (H) and smaller (DH) decrease in herbicides used, a 5m unsprayed margin around all fields (UM), and the impact of increasing the current area of organic farming by 25% (O). In addition 14 technical scenarios were constructed designed to illustrate the effect of assumptions and parameter inputs to the model. All scenarios were run using a derivative of NERI’s ALMaSS model which is designed to integrate animal ecology with landscape structure and management. The results of the scenarios indicated that the general reductions in pesticides scenarios (P, H, DH) would have a negative impact on skylarks. Scenario O had no significant impact since the area altered was very small in percentage terms. Scenario UM had the largest positive impact.

 

The cause of the decline under decreased pesticide was two-fold. Firstly the response of the farmer was predicted to be to increase the area of winter cropping, which is typically detrimental to skylarks. Secondly, the reduction in number of times the farmer opens the tramlines in the crops leads to decreased accessibility for the birds, and therefore reduced foraging possibilities. The increased food biomass as a result of reduced pesticide applications did not outweigh these negative effects because access to the food was not improved and may be decreased. The technical scenarios indicated that the greatest benefit to skylarks is by altering the structure of the crop such that they have access for nesting and feeding. Large benefits could also be achieved using unsprayed margins even if they were not added to all fields. Unsprayed field margins will also have other significant benefits to wildlife by protecting the non-cultivated areas from spray drift.

 

A crucial assumption in the modelling work is that given the limited reduction in pesticide usage, there will not be a significant increase in weeds or a decrease in the impenetrability of crops. Further simulations could be carried out in collaboration with agronomists to improve the basis for this assumption.

 

Full report in PDF format (2,511 kB).