Impact of dairy farming on soil, plants and earthworms in a Canterbury dryland reserve

Less than 60 hectares of protected native dryland habitat remain in the Canterbury Plains of New Zealand. These few remaining dryland areas are surrounded by farms that dominate the landscape. Due to their small size, their isolation and the increasing presence of dairy farming around them, these dryland remnants and the native communities they contain are likely to be affected by irrigation, nutrient inputs and the colonisation by exotic plant and animal species. We surveyed soil nitrate and phosphate, earthworms and vegetation in the 2.6 ha Bankside Reserve using a series of nine transects from the adjacent dairy farm into the reserve. We also compared plant species found in the reserve with a survey 40 years earlier. We found that the adjacent dairy farm had significant edge effects on soils biochemistry, earthworm communities and plant diversity within Bankside Reserve. Mean phosphate values in the reserve were significantly higher (P=0.018) closer to the paddock boundary. Mean phosphate and nitrate values on the boundary were two-fold higher than in the paddock. Four species of endemic earthworms were found and at least six species of exotic earthworms. Endemics mainly occur in high areas and away from the fence (and adjacent dairy pasture). Drainage from the dairy farm through the reserve also has a significant detrimental effect on the reserve with lower lying areas with significantly higher mean phosphate levels, higher exotic plants and exotic earthworms. Protective and remedial action for management of this reserve and implications for other dryland reserves are discussed