This paper presents the results of 3 years (1994–96) work on the effect of shelter created by a 9 m high Aleppo pine (Pinus halepensis) windbreak in the Mediterranean environment of South Australia on the productivity of wheat, canola, faba beans and oats. Elements of the classic windbreak signature could be detected in the yield responses of 6 of 8 crop years. For example, in the dry year of 1994, yields in the sheltered zone (3–6 H) were 44, 49 and 81% greater than in the exposed zone (18–24 H) for wheat, faba beans and canola, respectively. In 1995, a wet year, only faba beans showed a response (18% increase). In 1996, oats showed an apparent 25% yield increase in the sheltered zone compared with the unsheltered zone. However, these yield differences were not due to shelter alone. For example, covariate analysis of 1995 wheat and bean yield data with soil texture indicated that yield variation across the paddock could be explained by variation in depth to calcareous clay loam. Cumulative water use of wheat was greater in the 3–12 H zone in 1994 (dry year) but less in 1995 (wet year); however, these differences are likely to be also due to soil variation in the 2 plots used. Nevertheless, the windbreak effectively altered the microclimate. Cumulative temperature was measured at 4 distances on the leeward side of the windbreak and used to predict the time taken for wheat to reach anthesis at each location. The correlation between normalised values of observed and predicted times to anthesis was found for 3 wheat crops with different times of sowing in 1995 (r2 = 0.62). It was concluded that (i) shelter will affect the physiology of crops grown in this environment, (ii)�the shelter effect on enhancing crop yield is relatively subtle compared with other sources of yield variation and (iii)�the evidence for a water-saving mechanism in enhancing crop yield is inconclusive.
The association of childhood exposure to crop yield variation and survival in a subsistence farming population in Burkina Faso
