Management of invasive Phragmites australis in the Adirondacks: a cautionary tale about prospects of eradication

Abstract

Invasive plant management (largely mechanical and chemical) consumes an ever-increasing portion of budgets for land management organizations, but metrics of success, other than extent of areas treated or resources expended is rarely available. Here we assess success of managing 346 populations of invasive Phragmites australis (range 0.36-4134 m 2 ; cover 37-75%) in the Adirondack Park in upstate New York, USA. We began by treating 18 patches in 2010 using herbicide; gradually adding patches treated annually or intermittently for a total of 334 by the end of the project period. We monitored each population annually and if P. australis was present mapped its spatial extent and estimated cover. We considered P. australis eradicated when live stems were absent from a site for at least three consecutive years. Our treatments reduced size and cover of P. australis populations and eradication was achieved at 104 of 294 sites. However, probability of eradicating P. australis over a 7-year project timeframe was 0.83 for the smallest patches (0.36 m 2 ), whereas at medium (45 m 2 ) and large patches ([3000 m 2 ) probability of eradication decreased to 0.26 and 0.02, respectively. Our results question efficacy of managing large P. australis populations with the goal of eradication. We urge conservation organizations to clearly articulate management objectives beyond short-term suppression of target plants and to promote accountability by providing quantitative measurements of outcomes.

Invasive Phragmites australis management outcomes and native plant recovery are context dependent

“…Knowing the environmental circumstances that promote restoration success can help inform this decision‐making and allow for the most cost‐effective management. Our multi‐site study found wide variability in Phragmites management outcomes and native plant recovery, which indicates success in the restoration of Phragmites ‐invaded wetlands is highly context dependent, a finding consistent with studies in other regions of North America (Carlson et al, ; Hazelton, ; Quirion et al, ). We found that site hydrology played an important role in determining outcomes, but there were likely other unmeasured factors that contributed to divergent results such as landscape setting, site history, and age of invasion, which should be further explored.…”

Nitrogen immobilization may reduce invasibility of nutrient enriched plant community invaded by Phragmites australis

“…The tissue chemistry of Phragmites and its extensive production alters nutrient pools 21 and availability in soils 16,18 . Together with its negative effects on ecology, Phragmites can impose considerable financial loss 22 . For example, invasive species management costs about $25 billion/year in the USA 23 .…”

“…Current methods to control Phragmites invasions are aimed at eradication of existing populations, which are effective only in short term 31 . The recent study raises the question about the efficacy of managing large populations invaded by Phragmites through the method 22 . Generally, Phragmites populations can be treated using herbicide applications in combination with cutting, burning and covering with plastic 32 .…”

Suppression of established invasivePhragmites australisleads to secondary invasion

“…Most studies that used herbicide report success in reducing the abundance of P. australis locally, but none suggest eradication was achieved. Some report short-term reductions in P. australis, and most caution that repeated control measures are needed to suppress re-growth (e.g., Lombard et al 2012;Quirion et al 2017). Fewer suggest that herbicide application led to the recovery of native vegetation.…”

“…Ideally, recovery should target a vegetation community that resembles the community present in equivalent edaphic and hydrologic conditions where P. australis never invaded (i.e., the reference condition, sensu Stoddard et al 2006). Management outcomes for P. australis suppression techniques have received extensive study (e.g., Farnsworth and Meyerson 1999;Ailstock et al 2001;Derr 2008;Mozdzer et al 2008;Lombard et al 2012;Rapp et al 2012;Hunt et al 2017;Quirion et al 2017;Zimmerman et al 2018;Judd and Francoeur 2019;Rohal et al 2019a, b). Yet there are inconsistencies in the literature regarding information on baseline conditions, experimental controls, or adequately characterized recovery targets, making differences in outcomes difficult to reconcile.…”