Tree Removal

"If WPAs are for wildlife, why do you cut down the trees?"  This is a common question we are asked.  

Historically, Rainwater Basin wetlands were located in a treeless, grassland ecosystem.  Fire, bison, and lack of seed source kept trees from becoming established.  In modern times, conditions are very favorable for volunteer trees if land is left idle for a few years.  The moist, bare hydric soils along the edge of wetlands are ideal for seed germination.  Frequent flooding can keep trees from invading into the center of wetlands, but trees will eventually ring the wetland and cover the uplands.  

Grassland birds have experienced dramatic declines because of the loss of grasslands. The North American Breeding Bird Survey reports that 70% of the 29 species characteristic of North American prairies have experienced a decline in population. A portion of that decline is attributed to the small acreage of remaining grassland parcels and the increasing number of trees found within the grasslands (Bakker 2003). Cowbird parasitism is especially concerning in the district due to planted shelterbelts and scattered volunteer trees that are numerous at the WPAs. 

It is within the directive of the Service to manage areas according to their historical conditions for the benefit of multiple species of plants, animals, and insects.  Because of the small amount of remaining native grassland, it is important to manage the uplands in this manner.  For most of the grassland bird species, the percentage of woody cover should be less than 5% of the plant community (McKee et al. 1998). Prairie chickens prefer less than 1% woody vegetation for lek sites (Merrill et al. 1999).  McCarthy et al. (1997) found woody cover encroachment directly decreased adequate nesting cover for prairie chickens.  Burger et al. (1994) found prairie fragmentation directly affected predation rates on bobwhite quail, noting that nests found more than 60 meters from woody cover were three times more successful than those found less than 60 meters from woody cover.  Therefore, tree and shrub removal is critically important for those WPAs that have a high percentage of trees or shrubs.  Bakker (2000) recommends removing woodland habitat within or adjacent to grassland and acquiring or preserving grassland patches large enough (300–600 acres) to attract the majority of grassland-dependent species.

Fire is the preferred method to control tree invasion on grasslands.  Haying is done on some occasions but can only be used on drier soils.  Land that is left undisturbed for even a few years, can establish a cluster of trees that begin to shade out the grasses below.  With low fuel levels in the understory, fire is not effective at killing the trees, especially those larger than three inches in diameter.  At that stage of growth, trees have to be physically removed by chainsaw or tree shearer.  Once trees are cut, a herbicide is applied to the cambium layer to prevent regrowth.  

On occasion we are forced to use a large rotary mower to shred the small seedlings.  This does not kill the tree, but hampers tree growth to allow us to use fire in a future year.

Clearing volunteer trees that surround wetland basin.

Literature Cited:

Bakker, K.K. 2000. Avian occurrence in woodlands and grasslands on public areas throughout eastern South Dakota [PhD dissertation]. Brookings, SD: South Dakota State University. [Number of pages unknown].

Bakker, K.K. 2003. The effect of woody vegetation on grassland nesting birds: an annotated bibliography. In: The Proceedings of the South Dakota Academy of Sciences;  82:119–41.

Burger, L.D.; Burger, L.W., Jr.; Faaborg, J. 1994. Effects of prairie fragmentation predation on artifi cial nests. Journal of Wildlife Management 58(2):249–54.

McKee, G.M.; Ryan, R.; Mechlin, L.M. 1998. Predicting greater prairie-chicken nest success from vegetation and landscape characteristics. Journal of Wildlife Management 62:314–21.

Merrill, M.D.; Chapman, K.A.; Poiani, K.A. [et al.] 1999. Land-use patterns surrounding greater prairie-chicken leks in northwestern Minnesota. Journal of Wildlife Management 63:189–98.

McCarthy, C.; Pella, T.; Link, G. [et al.] 1997. Greater prairie chicken nesting habitat, Sheyenne National Grassland, North Dakota. [Place of publication unknown]: U.S. Department of Agriculture, Forest Service. General Technical Report RM-GTR-298. [Pages unknown].

Last updated: September 23, 2008

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