It's a privet thing, okay? Controlling invasive privet at Hoffler Creek Wildlife Preserve

Situated far back into the quiet and dull suburban subdivisions of Portsmouth, Virginia is a somewhat unexpected place; it is a place that easily breaks the monotony of neatly trimmed lawns and dated cookie-cutter houses.  The Hoffler Creek Wildlife Preserve protects one of the last remaining undeveloped tracts of land in the Portsmouth city limits (see map below).  This protects the water quality of the Hoffler Creek tidal estuary (see Photo A), and the land-areas of the preserve are filled with lush Mid-Atlantic maritime forest (Photo B).


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Photo A: The Hoffler Creek tidal estuary

Photo B:  A milder climate and a lack of urban development has helped preserve the maritime forest community at Hoffler Creek Wildlife Preserve.

In the middle of the wildlife preserve is a natural-looking, mostly freshwater lake (Photo C).  Prior to the establishment of the wildlife preserve, the land was a sand and gravel pit that was quarried to provide a foundation for the nearby Virginia-164 freeway.  Once operations were completed at the quarry, the city of Portsmouth zoned the area for residential development.  

This angered local residents, who wanted to protect the woods and salt marshes in and around the old quarry site, and eventually the Hoffler Creek Wildlife Foundation was formed to manage the newly created wildlife sanctuary.  

Photo C:  The convincingly natural lake in the middle of the preserve is a filled-in sand pit.  

While nature has certainly done a nice job of filling in the former quarry site, clues of the large-scale disturbance in this area are still evident.  One particular aspect of ecological degradation that I am going to attempt to address is that of an invasive species present in the preserve.  An invasive species is an animal (or a plant in this case) that was introduced from somewhere else and out-competes native species.  Invasive species are brought over sometimes by accident (such as sticking to someones shoe or carried in the ballast water of cargo ships) and sometimes they are introduced purposely (such as for ornamental purposes or to help control crop pests).  Invasive species often exhibit two characteristics:  (1) they have evolved in another region or continent, and therefore have no natural controls such as predators or diseases, and (2) they thrive in disturbed or polluted environments.  Both these points are the case for the invasive shrub that I am hoping to gain some control of in this preserve.  

European Privet (Ligustrum ovalifolium) is a woody shrub native to Europe that was frequently planted as a hedge shrub in agricultural lands and suburban housing lots.  The plant does well in open sunny areas and tolerates poor and "ruffled-up" soils and waste sites.  At Hoffler Creek, this shrub forms a near monoculture (a landscape dominated by one single species, in this case, privet) around areas near the quarry...which makes sense considering this is where the harshest disturbance occurred during quarrying and mining operations.  Privet growth has become so thick and dense in these areas of the preserve that native trees, shrubs, and wildflowers become shaded and rooted out.  The density of shrub growth can also create an impasse for the movement of wildlife.  

One of my goals is to experiment with controlling the growth and cover of privet in the preserve.  I am essentially going to have three test plots to determine which method (if any) is effective in controlling the growth of privet.  The plots will be small.  Each plot will be 3 square feet in size.  

Plot 1

Believe it or not, natural resource managers DO use chemical herbicides when doing ecological restoration.  Now before you have a heart-attack, let me explain to you that unlike the agricultural or industrial industries, conservationists use only a sparing amount of chemicals.  In this case, I will be using an herbicide that will be sprayed ONLY on the tips of the cut stumps of the individual privet bushes in this plot.  This method is called cut-stump spraying and it involves cutting the shrub down as far as I can go towards the ground and then immediately putting herbicide on the stump that I just cut.  Figure 1 shows a larger shrub that was cut down with a chain saw.  The blue rim around the edge of the stump is herbicide with dye in it so that the person applying the chemical can see where they sprayed.  I will likely be using Rodeo, a glyphosate-based solution.  

Figure 1:  A cut stump of a shrub with blue-colored
herbicide sprayed on the outer edge.
Photo retrieved 19 October 2012 from
 <http://forestry.about.com/od/forestresourceinformation/tp/Tree-Herbicide-Application-Methods.htm>

Plot 2

This plot will test the effectiveness in killing privet bushes using the cut-stump method just described, but will instead test an herbicide made with household ingredients.  The recipe that I will put together is:

• 1 gallon white vinegar
• 1 pound salt
• 8 drops of Dawn dish soap

In a big pot heat 1 gallon of white vinegar, dissolve one pound of salt. After salt dissolves, remove from heat and add 8 drops of dish soap. Wait until it cools down and pour into a squirt bottle. 

Plot 3

This plot will be a control plot.  In an experiment, a control is something where you don't do anything to manipulate the outcome.  In this case, I will cut down the privet shrubs but I will not spray the stumps with anything. 

Once the cutting and spaying tasks have been accomplished, I will return to the plot sites and check to see of there is any regrowth of the cut shrubs.  The hope is that at least one of these techniques will work and that at least one of the plots will have stumps that do not re-sprout.

Check back soon to see if this works!