Assessing the use of bison for savanna restoration at Cedar Creek Ecosystem Science Reserve: Species Percent Cover

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.

橡稀树草原（oak savanna）是明尼苏达州受威胁最严重的生态系统，仅靠火烧无法实现其恢复与保护。我们的稀树草原恢复研究始于半个多世纪前，开展于锡达溪（Cedar Creek）曾为原生稀树草原的区域。研究表明，每十年进行4至7次火烧，可清除灌木与非稀树草原树种，并恢复草原草本物种。但我们长达50年的研究同时发现，这类高频高强度火烧会阻碍橡树的自然更新。目前已知美洲野牛（bison）是恢复与保护草原的关键物种（keystone species），但其在稀树草原生态系统中的作用仍未明确。在草原生态系统中，美洲野牛优先取食优势暖季草本植物——这类草本若不受干扰会压制野生花卉的生长，因此野牛放牧可促进植物共存并提升植物多样性。本研究拟通过减少火灾可燃草本植被、压制优势草本竞争者的方式，验证经火烧处理的稀树草原中，美洲野牛放牧是否能促进橡树幼苗的生长与存活。我们将保留现有火烧频率与长期火烧实验的设计方案，同时在该场地东南部的部分火烧单元中增设野牛放牧作为额外实验因子。野牛放牧将在夏季与早秋时段开展。研究团队将设置放牧排除区并栽植橡树幼苗，以此验证野牛放牧对橡树早期生长与存活的影响。本研究预期达成以下目标：（1）探索更高效的稀树草原生态系统恢复与保护技术方案；（2）明确上述技术对稀树草原生物多样性的影响机制；（3）向明尼苏达州民众普及该州的生态遗产，包括美洲野牛、火与生物多样性在稀树草原及明尼苏达州其他生态系统运行中发挥的作用。我们将通过以下途径实现上述目标：（1）在200英亩的橡稀树草原区域恢复野牛放牧；（2）通过实验验证野牛放牧对稀树草原生物多样性的提升作用；（3）将研究成果分享给K12阶段学生及到访游客。