Restoring the Cullen Nature Preserve to its Historic Oak Savanna Habitat
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PART ONE Cultural and Ecological History |
PART ONE: Cultural and Ecological History
Cullen Nature Preserve - A Family Gift and Legacy
The Cullen Nature Preserve is a City-owned property protected in perpetuity under a Minnesota Land Trust Conservation Easement. Ann Cullen Smith and her husband William Cullen purchased the 30-acre property in Minnetonka in 1935. After the couple built a house and moved to the property in 1937, Ann resided in the home for 77 years until 2014. Ann and William often discussed their desire to have the property remain in its natural state so it could be appreciated and enjoyed by the public. After working with the Minnesota Land Trust to develop a conservation easement for the property, Ann approached the City of Minnetonka and arranged to sell the property to the City for half its value. After Ann passed away in 2015 at the age of 105, the property was transferred to the City of Minnetonka.
The Cullen Nature Preserve is a City-owned property protected in perpetuity under a Minnesota Land Trust Conservation Easement. Ann Cullen Smith and her husband William Cullen purchased the 30-acre property in Minnetonka in 1935. After the couple built a house and moved to the property in 1937, Ann resided in the home for 77 years until 2014. Ann and William often discussed their desire to have the property remain in its natural state so it could be appreciated and enjoyed by the public. After working with the Minnesota Land Trust to develop a conservation easement for the property, Ann approached the City of Minnetonka and arranged to sell the property to the City for half its value. After Ann passed away in 2015 at the age of 105, the property was transferred to the City of Minnetonka.
Ann Cullen's vision for the property, detailed in the conservation easement, includes the protection of the property with a goal of preserving its key conservation values. These values are to preserve and restore the open and natural character of the property, create natural habitat for wildlife and plants, and provide an opportunity for public education and passive use such as nature observation, study, and reflection.
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Minnetonka’s Historic Ecological Landscape
Minnetonka lies in the tension zone where prairies, oak savannas, oak woodlands, and big woods (late successional, maple-dominated closed canopy forests) historically converged. In Minnetonka, prairies and oak ecosystems (oak savannas and oak woodlands) were once the prevalent plant communities prior to Euro-American settlement. Just west of Minnetonka in communities such as Excelsior or Wayzata, big woods was the primary plant community. The Cullen Nature Preserve likely was a transition zone between oak savanna and oak woodland, as evidenced by the age of the white and bur oaks as opposed to the much younger fire-intolerant trees on the property. |
Pre-European Settlement Map of Plant Communities in Minnetonka. The pink area was oak savanna. Source: City of Minnetonka 2021 Natural Resources Master Plan
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Cultural Uses of the Land in Minnetonka - A Timeline of Ecological Change
When Ann and William Cullen purchased the land in the 1930s, profound ecological changes had already taken place in Minnetonka and the surrounding region. By 1930, seventy years had passed since treaties were signed by local Native American tribes that resulted in the tribes being driven from their ancestral land they had managed for thousands of years.
Euro-American settlers began to convert these managed prairies and oak ecosystems for agricultural use, log the oaks for lumber and fuel, and ultimately played a primary role in extirpating grazing animals and their predators from the area. The open, oak savannas and oak woodlands became degraded from overgrazing by introduced cattle or lost for other uses as more settlers arrived and continued to convert land for cultivation. Fire suppression by Euro-American settlers led to a significant change in the oak ecosystems; the areas not in cultivation soon became invaded by shade tolerant, fire-intolerant trees. Fire suppression created cool, moist conditions where evaporation decreased, promoting succession toward forests.
When Ann and William Cullen purchased the land in the 1930s, profound ecological changes had already taken place in Minnetonka and the surrounding region. By 1930, seventy years had passed since treaties were signed by local Native American tribes that resulted in the tribes being driven from their ancestral land they had managed for thousands of years.
Euro-American settlers began to convert these managed prairies and oak ecosystems for agricultural use, log the oaks for lumber and fuel, and ultimately played a primary role in extirpating grazing animals and their predators from the area. The open, oak savannas and oak woodlands became degraded from overgrazing by introduced cattle or lost for other uses as more settlers arrived and continued to convert land for cultivation. Fire suppression by Euro-American settlers led to a significant change in the oak ecosystems; the areas not in cultivation soon became invaded by shade tolerant, fire-intolerant trees. Fire suppression created cool, moist conditions where evaporation decreased, promoting succession toward forests.
The damp, shaded closed-canopy conditions provided the ideal welcome mat for European buckthorn to become established, furthering the decline in diversity of the ground layer vegetation, resulting in even more shaded conditions, and ultimately a self-reinforcing feedback loop.
By the mid-1960s, shade-tolerant mesophytic tree species such as ironwood, basswood, elm, maple, black cherry, and red oak had fully invaded these white and bur oak ecosystems. At Cullen Nature Preserve, several of the large harvested specimens of these mesophytic trees were assessed for age, and most were between 45 and 55 years old. In other words, the white and bur oak ecosystems at Cullen began to transition to closed canopy forests in the mid-1960s. Many of these fast-growing canopy trees were similar in size to the white oaks; however, the white oak and bur oaks at the Preserve are much older.
Around the same decade, the seeds of invasive plant species such as European buckthorn were being spread from homeowner yards to natural areas by birds. The damp, shaded closed-canopy conditions provided the ideal welcome mat for European buckthorn to become established, furthering the decline in diversity of the ground layer vegetation, resulting in even more shaded conditions, and ultimately a self-reinforcing feedback loop.
Around the same decade, the seeds of invasive plant species such as European buckthorn were being spread from homeowner yards to natural areas by birds. The damp, shaded closed-canopy conditions provided the ideal welcome mat for European buckthorn to become established, furthering the decline in diversity of the ground layer vegetation, resulting in even more shaded conditions, and ultimately a self-reinforcing feedback loop.