Helen Allison Savanna
Helen Allison Savanna
Anoka Sandplain, Minnesota, USA
Helen Allison Savanna on the Anoka Sandplain formed by the glacial Mississippi River, is owned by The Nature Conservancy (TNC) and administered as a Scientific and Natural Area by the Minnesota Department of Natural Resources. I can hike the eighty-acre savanna from one end to the other in around twenty minutes. It is possible to know every square foot of a landscape of this scale and I often spend entire days as the light changes from dawn to dusk photographing plants and the 100-year old bur oak trees with their distinctive forms and individual character.
The savanna was the site of TNC’s first prescribed burn nationwide in 1962. Using fire as a management tool was a new concept – calculated to promote the growth of native plants and especially grasses with deep roots that regenerate quickly after fires, and to kill competitors and reduce invasive species. For millions of years fire had shaped the world’s forests and grasslands but suppression through the mid-20th century led to decades of degradation and accumulated biomass.
The savanna is named in honor of Helen Lowry Allison. Trained as a botanist at the University of Minnesota, earning an MA in 1951, she spent twenty years studying grasses, writing The Key to the Grasses of Minnesota, Found in the Wild or Commonly Cultivated Crops.
In 1991, Barbara C. Delaney, one of the co-authors of Minnesota’s St. Croix River Valley and Anoka Sandplain: A Guide to Native Habitats updated the savanna’s plant list. She introduced me to the site during a field trip coordinated by the TNC and Allison Savanna became my first study site for investigating native plant communities.
For twenty-five years, I have visited the savanna throughout the seasons to document the changes in vegetation, and have kept plant observation lists. This once remote prairie remnant, discontinuous with nearby tracts including the Cedar Creek Natural History Area and Carlos Avery Wildlife Refuge, is now bounded by exurban development. The view to the south across one of the meadows is terminated by a backyard lawn strewn with play equipment and I often encounter people walking their dogs through the preserve.
One-third of the site is burned each year to maintain the grassy prairie and create inviting open vistas in this one-tree-per-acre savanna. The park-like character attracts residents who now likely view this Scientific Area and Natural Area as their neighborhood park.