Microclimatic Effects of Ko (Sugarcane, Saccharum officinarum) Row Planting in the Leeward Kohala Field System, Hawai'i Island

The Leeward Kohala Field System (LKFS) on Hawai'i Island once featured over 60 [km.sup.2] 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 ko (Saccharum officinarum, sugarcane). These raised ko 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 ko rows within the LKFS. Ko rows proved effective windbreaks, reducing near-surface 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.sup.-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 ko. A zone of low turbulence leeward of each ko row also appeared to benefit 'uala growth. Additional measurements are needed to investigate the landscape-level hydrologic effects of ko row planting. Our findings will help guide ongoing efforts to expand agricultural and educational activities in the LKFS. Keywords: sugarcane, sweet potato, traditional agriculture, windbreaks, row planting, microclimates, traditional ecological knowledge, land stewardship
HAWAIIANS WERE UNIQUE within pre-contact Polynesia for their reliance on--and mastery of--dryland agriculture (Lincoln and Vitousek 2017). After beginning to farm in fertile lowlands and river valleys, Hawaiians expanded their [...]