The effect of tree windbreaks on the microclimate and crop yields in the Western Cape Region of South Africa

[摘要] ENGLISH ABSTRACT:The windbreak species near Wolseley (WoSl and WoS3) was Casuarinacunninghamiana. The windbreak species near Saron (SaSl) and Villiersdorp (ViSl) wasEucalyptus cladocalyx and Pinus radiata respectively. A shelter effect was indicated atViSI (from northerly winds in winter/early spring 1999), and WoS3 (from southerly windsin late spring 1999).Wind speeds were consistently reduced in the leeward sheltered zone ofViSl and WoS3.To improve the correlation of the shelter effect, mild contaminating winds (comprisingapproximately 28% of the total data recorded at each site) were excluded for theprediction equations of the shelter effect at each site.Compared to the more exposed wind speeds at 1.0 H to the windward side, wind speedsat ViS] were reduced by 32% at 3.0 H. Compared to 11.0 H, wind speeds at ViSl werereduced by 49 and 46% at 3.0 and 1.0 H respectively. With r2 values above 93%,accurate linear prediction equations were produced. The early barley damage assessmentsindicated that damage was absent or negligible at 11.1 H to the lee, and significantlyhighest (X < 0.05) at 13.7 H to the lee and beyond. The crop shelter effect significantlyincreased (p < 0.05) barley head number, transformed proportion of total barley head massfrom above-ground mass, potato tuber mass, potato above-ground mass total potato tubernumber, small tuber number, and disproportionate tissue damage to the windward sectionof each plant.For WoS3, the shelter effect became pronounced with severe south-easterly winds. Theaverage hourly wind speeds at 3.0 H dropped from 0.9 m / s (in the previous and lesswindy sampling period) to 0.8 m / s, despite the sharp increase in exposed wind speeds.Compared to 13.0 H, wind speeds were reduced by 73 and 32% at 3.0 and 7.0 Hrespectively. With r2 values above 94%, accurate linear prediction equations wereproduced. The crop shelter effect significantly increased (p < 0.05) sub-sample mass of lOOgrains. At WoS3, strong and sustained wind speeds caused leeward soil temperature increases ofup to 4°C at 3.0 H, compared to 11.0 H. Brief strong winds (characteristic of winds atViSl) had little effect on the soil temperature differences. At ViSl, a deviation of soilmoisture content between 3.0 and 11.0 H, following periods of recharge, indicated apotential soil-moisture conservation effect in the sheltered zone. This did not occur atWoS3, due partly to a very low soil moisture content that had little scope for variation;From the crop variations and the microclimate variations at both ViS 1 and WoS3, themaximum shelter effect extended to approximately 4.0 H, followed by an intermediatezone of diminishing shelter that extended to approximately 9.0 H.For ViSl, WoS3 and SaSl, a shading effect significantly reduced yields (p<0.05) at1.0 H from the respective northern windbreak, compared to yields at 2.0 H. At ViS 1 andWoS3, soil probes did not indicate a depletion of soil moisture resulting from therespective windbreaks. Soil moisture competition was indicated on the northern side ofthe WoSl windbreak with drier conditions; where soil moisture levels at 1.0 and 3.0 Hdiverged from a negligible level to a 22% lower level (p > 0.05) at 1.0 H, compared to3.0H.

[发布机构] Stellenbosch University