Assessing the use of bison for savanna restoration at Cedar Creek Ecosystem Science Reserve: Oak sapling growth

Oak savanna is the most threatened ecosystem in Minnesota and fire, alone, is not restoring and preserving it. Our savanna restoration research started more than a half century ago in what had once been native savanna at Cedar Creek. It has shown that burning about 4 to 7 times per decade eliminates shrubs and non-savanna tree species and restores prairie grassland species. However, our 50 years of research is also showing that these frequent and intense fires are preventing oaks from regenerating. Bison are now known to be a keystone species for restoring and preserving grasslands, but their roles in savanna ecosystems remain unknown. In grasslands, bison preferentially graze the dominant warm season grasses that would otherwise outcompete wildflowers, thereby promoting plant coexistence and enhancing plant diversity. Here we propose to test whether bison grazing might promote the growth and survivorship of oak seedlings in burned savannas by reducing grass fuel for fires and by knocking back dominant grass competitors. We will maintain the existing fire frequencies and the design of the long-term burning experiment, while adding bison grazing as an additional factor in part of several burn units on the southeast side of the property. Bison will graze during the summer and early fall seasons. Grazing exclosures will be established, and oak seedlings will be planted, to test effects of bison grazing on early oak growth and survivorship. The outcomes we plan to achieve are to: (1) discover better restoration and preservation practices for savanna ecosystems; (2) determine how these practices impact savanna biodiversity; and (3) educate Minnesotans about the ecological heritage of their state, including the roles that bison, fire and biodiversity play in the functioning of savannas and other Minnesota ecosystems. We will achieve these goals and outcomes by: (1) restoring bison grazing to 200 acres of oak savanna; (2) experimentally testing whether bison grazing promotes savanna biodiversity; and (3) disseminating results to K-12 students and visitors.栎树稀树草原（oak savanna）是明尼苏达州受威胁最严重的生态系统，仅依靠火烧手段无法实现其修复与保护目标。本团队的稀树草原修复研究始于半个多世纪前，选址于锡达克里克（Cedar Creek）曾为原生稀树草原的区域。研究表明，每十年实施4至7次火烧，可清除灌木与非稀树草原树种，并恢复北美草原（prairie）草本物种。然而，长达50年的研究同时发现，这类高频高强度火烧会阻碍栎树的自然更新。 目前学界已证实美洲野牛（bison）是草原生态系统修复与保护的关键种（keystone species），但其在稀树草原生态系统中的作用仍不明朗。在草原生态系统中，美洲野牛优先取食优势暖季草本植物——这类植物若不受干扰会竞争排斥野生花卉，从而促进植物共存并提升植物多样性。本研究拟验证：在经火烧处理的稀树草原中，美洲野牛放牧是否可通过减少火灾的草本燃料量、抑制优势草本竞争者，从而促进栎树幼苗的生长与存活。 我们将维持现有火烧频率与长期火烧实验的设计方案，在研究地块东南部的数个火烧样地（burn units）中增设野牛放牧作为额外实验因子。野牛将在夏季与早秋季进行放牧。本研究将设置放牧排除区（grazing exclosures）并栽植栎树幼苗，以检验野牛放牧对栎树早期生长与存活的影响。 本研究预期达成以下目标：（1）探索更优化的稀树草原生态系统修复与保护实践模式；（2）明确此类实践对稀树草原生物多样性的影响；（3）向明尼苏达州民众科普本州的生态遗产，包括美洲野牛、火生态与生物多样性在稀树草原及明尼苏达州其他生态系统的功能运转中所发挥的作用。 我们将通过以下路径实现上述目标：（1）在200英亩的栎树稀树草原区域恢复野牛放牧；（2）通过实验检验野牛放牧是否可提升稀树草原生物多样性；（3）将研究成果传播给K-12阶段学生与到访者。