Under global warming, expectations for woody biomass as a renewable energy are increasing. Short rotation coppice willow is the most widely planted energy wood crop. In this study, we examined the effect of harvest frequency on willow yield across multiple harvest rotations, something which is poorly understood. We planted 18 clones of Salix pet-susu and S. sachalinensis at a density of 25,000 or 16,667 cuttings ha⁻¹ in Hokkaido, northern Japan, and harvested either annually or biennially for 10 years (2009–2018). Annual variation in willow yield per stool was analyzed using five linear mixed-effect models incorporating the number of rotations, harvest interval, and weather parameters during the growing season with clones and plant density as random factors. Number of rotations had a significant negative effect on annual yield in all five models. We estimated that yield could be halved over 10 consecutive years of harvesting. In three out of the five models, biennial harvesting had a significant positive effect on yield in comparison with annual harvesting. In addition, we found that weather conditions, such as hours of sunshine during growing season, air temperature in May (when leaf flushing occurs), and precipitation in July (when vigorous height growth occurs) have significant positive effects on willow yield. These results suggest that, to maintain willow vigor for longer time periods biennial, or more than two-year-harvest, cycle is recommended rather than annual harvest.

在全球变暖的背景下，人们对木质生物质作为可再生能源的期望不断提高。短轮伐木柳是种植最多的能源木本作物。在这项研究中，我们研究了收获频率对多轮收获后柳树产量的影响，这一点目前尚不清楚。我们种的18个克隆柳宠物素素和S.红景天在25000个或16667屑公顷的密度^-1在日本北部的北海道，每年或每两年收获十年（2009-2018年）。使用五个线性混合效应模型分析了每粪柳产量的年度变化，该模型结合了转数，收获间隔和生长季节中的天气参数，其中克隆和植物密度为随机因素。在所有五个模型中，轮换数均对年收益产生显着的负面影响。我们估计连续10年收获后产量可能减半。在五种模式中的三种中，与年度收获相比，两年期收获对单产具有显着的积极影响。此外，我们发现天气情况，例如生长季节的日照时间，五月的气温（发生叶子潮红），7月份的降水量和降水量（发生高度高度增长时）对柳树产量具有显着的积极影响。这些结果表明，要在更长的时期内（每两年一次或超过两年）保持柳树活力，建议采用周期而不是每年收获。