Tom's Blog

Monday, October 27, 2014

Legacy effects in prairie restoration: part 2

To review: at the time the Nature Conservancy acquired Black Earth Rettenmund Prairie, the site had become about 50% wooded, including two major aspen clones, and lots of honeysuckle and other shrubs. Over the next 25 years, all of the major woody material was removed. Despite these efforts, woody vegetation has continued to appear.

In the research I am reporting here, I have used sumac as a surrogate for woody vegetation, since its distinctive fall coloration makes it very easy to locate. Using GPS, I recorded the coordinates of sumac in October of 2010 and 2011. The map below (based on GIS work) shows sumac locations overlayed on a map of the woody vegetation in 1987, before restoration had begun. The correspondence between the present-day sumac populations and the historic woody vegetation is striking. Recall that biennial burns have been carried out since restoration work began in 1987. Also, all visible woody vegetation was removed in the original restoration work in the period 1987-1998.

Another legacy effect is the difficulty of establishing prairie grass in former aspen areas. The photo below shows a comparison between a former aspen area (eradicated from trees in 1987-1988) and the same area in 2010. The dearth of grass in this former aspen area is striking. This area has been burned at least every other year since the aspen were removed. Also, the area  has been planted with grass seeds several times. Again, a legacy effect.

An important conclusion from my study is that despite the fact that the tree/shrub areas have been eliminated, the legacy of their former vegetation remains. Thus, what there is today is a result of what was there in the past. Despite the extensive restoration work that has been carried out, woody shrubs still arise, in locations that correspond to the original woody vegetation. The “land remembers”.

This conclusion has critical implications for restoration ecology, and emphasizes how important it is to understand the history of a site when devising restoration strategies. This concept has now been well accepted in restoration ecology. For instance: “site history is embedded in the structure and function of all ecosystems, environmental history is an integral part of ecological science, and historical perspectives inform policy development and the management of systems…” (Foster, David; Swanson, Frederick; Aber, John; Burke, Ingrid; Brokaw, Nicholas; Tilman, David; and Knapp, Alan. 2003. The importance of land-use legacies to ecology and conservation. BioScience 53: 77-88.)

My work could not have been done without the historic air photos, as well as the extensive written records found in the Nature Conservancy and Wisconsin Department of Natural Areas files. I strongly urge that restoration work be carefully documented and that written records as well as digital ones be archived for use by future generations.


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