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DNR Works to Restore Rare, But Historically Important Habitat

RUTHVEN – An ambitious effort to restore one of Iowa’s rarest natural habitats is being undertaken throughout northwest and north central Iowa.

Known as a bur oak savanna, these grasslands are dominated by large bur oak trees that once grew with little competition from neighboring trees. This complex network of sun and shade patches created by an overstory of primarily open-grown oak trees leads to an amazing diversity of grasses, sedges, and flowering plants.

And there’s a good reason if many people are not familiar with bur oak savannas and their value to a variety of wildlife species – it is estimated that less than 1/100th of 1 percent of this type of habitat remains of what originally existed in the northern region of Iowa.

The effort to restore this rare and native habitat, however, requires the removal of existing, non-compatible trees that outcompete and shade out young oaks and native prairie understory that is being re-established. The reintroduction of prescribed fires will also aide in reducing many fire-intolerant species that have invaded historic bur oak savanna ecosystems, which have a superior and unique ability to tolerate fire.

One of the areas where the effort to remove existing trees and re-establish oak savanna is currently occurring on a three-acre area at Smith’s Slough along a portion of Trumbull Lake. The weedy trees and shrubs are being removed to restore an important and almost forgotten historical habitat that once bordered most of Iowa’s natural shallow lakes.

This particular area is a part of the Dewey’s Pasture Bird Conservation Area that was dedicated in 2006 recognizing its importance for nesting and migratory grassland (which includes oak savanna) and wetland birds.

While the sight of seeing trees removed may be unsettling at first, extensive scientific research and data support the long-term benefits to restoration of a natural habitat that once covered hundreds of thousands of acres in Iowa, but is now extremely rare.

A 2004 study of grassland birds in North Dakota found that 11 of 15 grassland bird species declined when woody cover increased 5-20 percent in the prairies.  When woody cover exceeded 25 percent the grasslands became entirely unsuitable for nine species.  It has become obvious that active measures must be taken to reduce trees in Midwestern grassland habitats. 

Scattered non-compatible trees on public grasslands only provides seed trees that will continue to impact the landscape in the future.  Overtime if not managed grassland species and ecosystems will be suppressed and potentially eliminated by tree invasion.  Some of the best remaining grassland and wetland complexes can eventually be dominated by invasive trees that can eliminate plants species that are required for the best water quality benefits.

In the northwestern 2/3 of Iowa, wildlife managers are removing more trees and burning more prairie to restore valuable grassland habitats for declining birds.  But in other parts of the state, efforts are focused upon creating more woodlands by planting trees to connect or enlarge existing but fragmented blocks of forest.  There, area sensitive forest birds will benefit from tree planting, just as grassland birds benefit by tree removal in the prairie pothole region of Iowa.

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