2.1. Site
The Lincoln University agroforestry experiment has been described in detail by Mead et al. (1993). The experiment was established in 1990 on fertile arable soils (Templeton silt loam or Dystric Ustochrept in Soil Taxonomy) on the Canterbury Plains, New Zealand. These loessal soils are free draining with moderate water holding capacity and are underlain by fluvio-glacial outwash gravels at 1.1–2 m depth (mean 1.3 m).
The climate is temperate and subhumid with a long-term mean annual precipitation of 660 mm which is about 60% of potential evapotranspiration, and the mean annual temperature is 11.4 °C. In spring and summer strong, dry föhn winds sometimes occur. Summer drought typically limits plant growth by mid-summer. During the study period, the October to March growing season for year 5 was dryer than other years, followed by year 6 (Table 2). Year 4 was the least dry year. The growing season average monthly temperatures ranged from 13.4 to 14.6 °C. Between May and September mean monthly temperatures usually fall below 10 °C and ground frosts are common