Legacy effects in prairie restoration: part 2
This is a follow-up/extension of my Oct. 24, 2014 post on “Legacyeffects in prairie restoration”.
which was based on the paper I gave/published in the 2012 NorthAmerican Prairie Conference.
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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