Erosion, Geological History, and Indigenous Agriculture: A Tale of Two Valleys
Erosion, Geological History, and Indigenous Agriculture: A Tale of Two Valleys
复制标题
侵蚀、地质历史和本土农业：两个山谷的故事
作者：
P. Vitousek;O. Chadwick;G. Hilley;P. Kirch;T. Ladefoged
在与欧洲人接触之前，灌溉池塘田和雨养田系统代表了农业集约化的另一种途径，它们在夏威夷群岛上不均匀地分布，池塘田在较湿润的土壤和较老的岛屿上，雨养田系统在较年轻的岛屿上肥沃、雨量适中的高地上。这些系统的空间分离被认为促成了接触前夏威夷社会和政治组织的动态。然而，在古老的夏威夷群岛上，深溪谷的低坡上经常保留着旱地农业的遗迹。我们通过比较夏威夷年轻岛屿pololi谷和莫洛卡伊岛Hālawa谷的土壤，评估了为什么旱作农业在古老岛屿的山谷斜坡上发展，而不是在年轻岛屿的山谷斜坡上。与周围高地相比，冲积谷底和崩塌坡土壤的碱性饱和度和可风化磷含量丰富4 - 5倍，树脂可提取磷和可风化钙含量丰富10倍以上。然而，由于年轻的夏威夷岛的火山沉降与冰川后海平面上升的相互作用，pololi谷的侧壁直接陷入平坦的谷底，而Hālawa谷的冲积层被一带肥沃的崩积土包围，那里集中了雨育农业特征。只有5%的pololi山谷支持斜坡在5°到12°之间（适合雨养农业）的崩积土，而16%的Hālawa山谷这样做。较老的夏威夷岛屿的池塘田/雨养河谷系统的综合潜力增加了它们在生产力和可持续性方面的优势，而不是年轻岛屿的主要雨养系统。
Irrigated pondfields and rainfed field systems represented alternative pathways of agricultural intensification that were unevenly distributed across the Hawaiian Archipelago prior to European contact, with pondfields on wetter soils and older islands and rainfed systems on fertile, moderate-rainfall upland sites on younger islands. The spatial separation of these systems is thought to have contributed to the dynamics of social and political organization in pre-contact Hawai’i. However, deep stream valleys on older Hawaiian Islands often retain the remains of rainfed dryland agriculture on their lower slopes. We evaluated why rainfed agriculture developed on valley slopes on older but not younger islands by comparing soils of Pololū Valley on the young island of Hawai’i with those of Hālawa Valley on the older island of Moloka’i. Alluvial valley-bottom and colluvial slope soils of both valleys are enriched 4–5-fold in base saturation and in P that can be weathered, and greater than 10-fold in resin-extractable P and weatherable Ca, compared to soils of their surrounding uplands. However, due to an interaction of volcanically driven subsidence of the young island of Hawai’i with post-glacial sea level rise, the side walls of Pololū Valley plunge directly into a flat valley floor, whereas the alluvial floor of Hālawa Valley is surrounded by a band of fertile colluvial soils where rainfed agricultural features were concentrated. Only 5% of Pololū Valley supports colluvial soils with slopes between 5° and 12° (suitable for rainfed agriculture), whereas 16% of Hālawa Valley does so. The potential for integrated pondfield/rainfed valley systems of the older Hawaiian Islands increased their advantage in productivity and sustainability over the predominantly rainfed systems of the younger islands.