Abstract

Abstract:

Abstract: The Leeward Kohala Field System (LKFS) on Hawai'i Island once featured over 60 km2 of productive, rain-fed croplands. For several centuries, its occupants cultivated 'uala (Ipomoea batatas, sweet potato) as a staple crop between kuaiwi (earthen or rock walls) planted with kō (Saccharum officinarum, sugarcane). These raised kō rows could have influenced 'uala growth through an array of microclimatic processes, including wind abatement, shading, and the redistribution of moisture. While such effects are frequently mentioned in the literature, efforts to directly quantify them and relate them to 'uala production have been lacking. We measured wind speeds, precipitation rates, solar illuminance, soil moisture, and 'uala yields along a transect through three kō rows within the LKFS. Kō rows proved effective windbreaks, reducing nearsurface wind speeds by up to 90% and for distances of up to 10 m. The rows also concentrated wind-blown moisture at their upwind edges while creating rain shadows 5–6 m in length. 'Uala yields peaked at 3.8–6.0 kg m–2 near the center of inter-row space, probably because 'uala were energy-limited during the wet study period and grew slowly when shaded by the kō. A zone of low turbulence leeward of each kō row also appeared to benefit 'uala growth. Additional measurements are needed to investigate the landscape-level hydrologic effects of kō row planting. Our findings will help guide ongoing efforts to expand agricultural and educational activities in the LKFS.

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