Quandaries of a Decade-Long Restoration Experiment Trying to Reduce Invasive Species: Beat Them, Joi
Friday, August 26, 2016
Susan Cordell, PhD
Institute of Pacific Islands Forestry
USDA Forest Service
The historical and continued degradation of Hawaiian and Pacific Island environment has opened the door to species invasions that have transformed entire ecosystems and altered historic disturbance regimes. Once transformed, these habitats are often at a point of no return. A new paper from the Institute of Pacific Islands Forestry suggests a non-traditional hybrid restoration approach of using both native and non-native, but non-invasive species may be the best way to protect the Hawaiian and Pacific Island’s native bio-diversity.
The study looked at the Keaukaha Military Reservation (KMR) as it still has native species in its canopy capable of regenerating. However, the presence of a multitude of invasive plants and animals means few-if-any of the seedlings survive into adulthood. Susan Cordell, lead author of the study explains, “When the existing adults die, the forest will become wholly made up of exotic species. At KMR those are mainly highly invasive species which put such a great pressure on native biodiversity that restoration using traditional passive approaches of tropical forest restoration is not feasible.”
In 2002, Cordell and her colleagues established their initial study to determine how KMR responds to invasive species removal. The crew spent countless hours and removed more than 5000 pounds of material from the plots. They kept these plots weed free and calculated the weight of the weeds removed approximately once a year. Despite a dramatic decrease in invasive species from 2004-2009, Cordell and her group began to see a precipitous increase from 2010-2015 indicating that short term success did not equate to a long term positive outcome. In 2010 they changed the approach and began actively outplanting native species into the plots. In spite of relatively high survival rates, the relative growth rates of these seedlings two years later were not greater than those of the naturally recruited non-native species.
“We initially felt a sense of failure," says Cordell, "because not only did the forest not revert to a native-dominated system but our efforts actually recruited new non-native species.”
But, the setback provided an opportunity. The researchers started over and began using both native and non-invasive but non-native species and named this “hybrid” approach the Liko Na Pilina project, which loosely translated from Hawaiian means “growing new partnerships”
They chose species whose traits foster reduced carbon and nutrient cycling because this mimics native Hawaiian systems. The researchers now predict native biodiversity will be favored and the vicious cycle which favors invasive species will be discouraged by this new species choice approach.
One of the main goals of this project was to build invasion-resistance into the lowland wet forest by incorporating a greater diversity of functional trait expression. Results of the study will provide a quantitative assessment of the value of designing self-sustaining combinations of species that balance tradeoffs between supporting native biodiversity, resistance to invasion by non-desirable plants, and fostering human needs (such as carbon storage or food availability).
Says Cordell, “We fully expect to recapitulate our previous experience—there will be a series of successes and failures, and adaptive restoration practiced—but at least this time we can set more realistic criteria.”
Reference: Susan Cordell, Rebecca Ostertag, Jené Michaud and Laura Warman, 2016. Quandaries of a decade-long restoration experiment trying to reduce invasive species: beat them, join them, give up, or start over? Restoration Ecology DOI: 10.1111/rec.12321
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