N.B. Tim Clune was unable to present this paper at the conference, but delegates are welcome to contact him regarding the project.

Ninety eight percent of the original native vegetation in the Riverina Bioregion has been displaced for intensive agriculture. Integrating native tree shelterbelts in intensive agricultural landscapes is one option for meeting both productivity and biodiversity demands in this landscape. This paper reports some important learnings from a case study examining the impact of the introduction of native tree shelterbelts to an intensive lucerne production system.

There has been little investigation into the effects of trees on crops and pastures in irrigated environments. We examined the interactions between an irrigated lucerne stand and adjacent shelterbelts of indigenous native species established 12 to 15 years ago as part of the Superb Parrot conservation program. Measurements were conducted over three irrigation seasons and included lucerne production, soil water content, soil fertility, soil salinity and pH. Lucerne production adjacent to the trees (within 10m of the fence line) was approximately half that of the remaining paddock. Differences in production were not related to soil fertility, soil type, salinity or pH. Whilst soil water content varied markedly with soil profile depth, there did not appear to be competition between the trees and the irrigated lucerne. Soil water content in the top 60cm of the lucerne profile was greater than that under the trees. In contrast the lucerne was increasingly drier at depths greater than 1m. In the absence of climatic and edaphic contributors to reduced lucerne production we argue that paddock management (largely traffic associated with the movement of irrigation infrastructure), and not the adjacent trees, was the cause of reduced lucerne production.

The key learning from this project was that establishment of trees in farming systems needs to take place as part of a broader farm planning exercise, in which future management activities are considered. In the absence of recognising management activities as a factor, trees will continue to be associated with negative impacts on crop and pasture productivity.