Northeast Natural History Conference 2011: Selected Papers
2012 Northeastern Naturalist 19(Special Issue 6):181–193
Long-term Management of an Invasive Plant:
Lessons from Seven Years of Phragmites australis Control
Karen B. Lombard1,*, Dena Tomassi1,2, and John Ebersole3
Abstract - We treated the invasive wetland grass, Phragmites australis (Common Reed),
with herbicide in 99 (total of 14 ha) interdunal wetland swales of Sandy Neck barrier
beach on Cape Cod, MA from 2002–2008. The herbicide applications have significantly
reduced the number of Phragmites stems within invaded swales, with parallel reductions
in personnel and chemical costs of the control program. After seven years of treatment,
we have achieved substantial containment and suppression of Phragmites, but the plant
persists in all but a few of the treated swales. Whether eradication or near-eradication can
be ultimately achieved remains uncertain.
Introduction
Phragmites australis (Cav.) Trin. ex Steud. (Common Reed, hereafter referred
to as Phragmites), a perennial grass, is historically native to the eastern United
States, including New England. However, a non-native lineage of Phragmites
from Europe has aggressively invaded coastal marshes and inland wetlands of the
United States over the past century (Chambers et al. 1999; Meyerson et al. 2009,
2000; Saltonstall 2002). The invasive lineage is most common where wetlands
have been altered, but it also invades both tidal and freshwater wetlands where
anthropogenic disturbance seems minimal (Meyerson et al. 2009). Phragmites
stands expand by sprouting from rhizomes to form extensive monocultures, and
new stands can be established by both dispersal of rhizome fragments and seed
(Bart and Hartman 2002, 2003; Belzile et al. 2010; Farnsworth and Meyerson
2003; McCormick et al. 2010; Meyerson et al. 2000; Saltonstall 2003). Phragmites
grows rapidly, with high biomass production above and below ground,
and its litter decomposes slowly, which hinders the growth of other species by
reducing nutrients, light, and space availability (Coleman 2003, Meyerson et al.
2000, Minchinton et al. 2006). As a result, Phragmites invasions often decrease
the diversity of plant communities (Back and Holomuzki 2008, Hocking et al.
1983, Meyerson et al. 2009, Rice et al. 2000, Whyte et al. 2008).
On Sandy Neck barrier beach in Barnstable, Cape Cod, MA, several habitats
have established stands of Phragmites. Sandy Neck (620 ha) is six miles long
and ranges from 60 m to 1 km wide (Fig. 1). Although comprised of migrating
sand dunes, the spit is relatively stable, which has facilitated the development of
1The Nature Conservancy, 99 Bedford Street, 5th floor, Boston, MA 02111. 2Current address
- 25 Diamond Street, Plymouth, MA 02360. 3University of Massachusetts-Boston,
Biology Department, 100 Morrissey Blvd., Boston, MA 02125-3393. *Corresponding
author - klombard@tnc.org.
182 Northeastern Naturalist Vol. 19, Special Issue 6
several natural communities including maritime forest, cranberry bogs, and over
170 interdunal wetland swales (totaling >28 ha) (Fig. 2). Despite being first offi
cially documented in 1971, the majority of the non-native Phragmites invasions
on Sandy Neck is in the wetland swales and is believed to have occurred after
two large storms in 1990 and 1991 that caused extensive flooding in the dune
system (Coleman 2003). Further, large, healthy stands of Phragmites are present
across the Great Marsh (which borders Sandy Neck to the south; labeled as “salt
marsh” in Fig. 1) and probably became established due to disturbances created by
shoreline development (Silliman and Bertness 2004) and hydrological alteration
(Chambers et al. 1999).
Swales are isolated wetland habitats that develop in the low-lying areas between
surrounding dunes. They access water through accumulated precipitation
or groundwater and are characteristically nutrient-poor (Shumway and Banks
2001, Swain and Kearsley 2001). Sandy Neck swales range in size from 0.004
to 1.3 ha and contain common species such as: Vaccinium macrocarpon Aiton
(Cranberry), Morella pensylvanica (Mirb.) Kartesz (Northern Bayberry), Juncus
canadensis J. Gay ex Laharpe (Canadian Rush), and Toxicodendron radicans
(L.) Kuntze (Poison Ivy) (Shumway 1996). Native Phragmites, a subspecies that
historically has been part of freshwater and brackish marshes in New England,
has not been recorded in these natural communities (Coleman 2003, Saltonstall
2002). Colonization of swales by Phragmites propagules at Sandy Neck likely
occurs by wind, by movement of wrack during storm surges, and by humans
via recreational activities (Minchinton 2006). A previous study at Sandy Neck
documented that Phragmites litter reduced the density of native plants by 94.5%
in several of the swales due to the reduction of light transmission to the soil surface
(Coleman 2003). Such negative effects of non-native Phragmites in these
Figure 1. Swales treated for Phragmites invasion and uninvaded swales in Sandy Neck,
Cape Cod, MA. Inset shows a close up of some of the interdunal swales.
2012 K.B. Lombard, D. Tomassi, and J. Ebersole 183
swales threaten the diversity of native plants and the habitat quality for several
state-threatened or special-concern species that inhabit these swales, including
Scaphiopus holbrookii (Eastern Spadefoot Toad) and Sabatia kennedyana Fernald
(Plymouth Rose Gentian) (Anderson et al. 2006).
In 2002, The Nature Conservancy initiated a long-term herbicide-based
control program of Phragmites at Sandy Neck, with the goal of reducing Phragmites
to levels where it would presumably have limited effects on native swale
communities and future control would require limited (1–2 weeks) staff time
per year. Although herbicide application reduces Phragmites cover greatly in
the short term (after 1–2 years of treatment), research indicates that reapplication
of herbicide is required for long-term effectiveness (Ailstock et al. 2001,
Back and Holomuzki 2008, Carlson and Kowalski 2009, Jones 1987, Modzer
et al. 2008, Moreira et al. 1999), and control is generally most successful when
herbicide application is combined with other techniques (burning, flooding,
cutting, etc.; Marks et al.1994). Consequently, it may take many years to either
reduce the invasion to a maintenance level or eradicate the species from a particular
location.
Methods
In a previous study at Sandy Neck, Coleman (2003) mapped most of the
swale plant communities at Sandy Neck using GPS, characterized them by
Figure 2. A typical wetland swale without Phragmites invasion at Sandy Neck. Photograph
© Nina Coleman.
184 Northeastern Naturalist Vol. 19, Special Issue 6
recording prevalent native plants, and surveyed them for the presence of
Phragmites. The patchy distribution of Phragmites makes detailed assessment
of density or abundance logistically unfeasible, so we continued the method
developed by Coleman (2003) of using broad categories to score Phragmites
density and abundance (Tables 1, 2; see supplemental appendix 1, available
online at https://www.eaglehill.us/NENAonline/suppl-files/n19-sp6-1032b-
Lomabard-s1, and, for BioOne subscribers, at http://dx.doi.org/10.1656/
N1032b.s1 for descriptions of other monitoring techniques evaluated for their
usefulness but not ultimately chosen for data collection). In subsequent years
of the project (2002–2008), we trained seasonal staff to score density and
abundance of Phragmites according to Coleman’s methods.
We also trained seasonal staff in herbicide application, using the method
of hand cutting Phragmites stems with clippers and then dripping a 50% solution
of RodeoTM or AquamasterTM (active ingredient: isopropylamine salt of
glyphosate) into the center of each stem (cut and drip). We used 2- to 4-person
crews hired from late August to early October each year, except when we applied
treatments for only two weeks in 2002 and only two days in 2006, due to
personnel and funding constraints. We expanded treatment methods after 2003
to include plants too small for the cut and drip method, which were swiped with
a cotton glove dipped in 33% solution of glyphosate herbicide. We also used
backpack sprayers to apply 2% glyphosate in high-density Phragmites stands
with limited native vegetation.
We found Phragmites in 55 (9 ha) of the 133 swales that were assessed in
2001–2002, and treated 14 of these swales (3 ha) with herbicide in 2002. Up to
2008, we attempted to retreat previously treated swales and initiate treatment in
Table 1. Phragmites density scores used to estimate the total number of Phragmites stems per swale
area for yearly classification of swales before treatment.
Phragmites density scores Description
0 No live Phragmites stems present
1 Light: ≤200 stems per swale, native vegetation appears normal
under Phragmites
2 Moderate: >200 stems per swale, patchy Phragmites with some
dense areas, but also some areas with native vegetation
3 Heavy: Phragmites and poison ivy dominant in swale, significant
Phragmites thatch present
Table 2. Phragmites abundance scores used to estimate the percent cover of Phragmites stems for
yearly classification of swales before treatment.
Phragmites abundance scores Description
0 No live Phragmites stems present
1 <25% of swale covered
2 25-49% of swale covered
3 50%-75% of swale covered
4 >75% of swale covered
2012 K.B. Lombard, D. Tomassi, and J. Ebersole 185
as many new swales as could be reached during the treatment period. By 2009,
the last year of assessment, we located and treated Phragmites in an additional 44
swales for a total of 99 treated swales (14 ha). The invaded swales varied in initial
level of Phragmites infestation and have different treatment histories, since we
were not able to treat all swales in all possible years.
To examine the impact of herbicide applications on Phragmites infestations
in swales, we analyzed how the estimated densities (total number of
Phragmites stems per swale area) and abundance (percent cover) changed
over time in the 133 swales originally mapped in 2001/2002. To determine
whether herbicide application had a significant impact on Phragmites infestations,
we performed linear mixed model regressions on estimated density and
abundance scores from 2002–2009, with time (year) and number of treatments
as independent variables. Mixed model regression takes into consideration the
repeated measures that may have a significant effect on the estimated density
and abundance of a Phragmites infestation. All monitoring data were analyzed
using PASW® Statistics 18 (IBM.com).
In addition to tracking swales treated, we examined the personnel hours required
for a treatment period and annual costs of the project, including supplies,
transportation, communication, labor, data analysis, and report writing; indirect
costs and housing (donated) were not included.
Results
Over the seven years of the control project, we found that Phragmites was
steadily reduced in terms of both density and abundance in the 133 swales first
mapped in 2001–2002 (Fig. 3), with the highest reductions in areas that initially
had high abundance and/or high density of Phragmites. More specifically,
just before herbicide applications had begun in 2002, 15% of swales received
the highest score for estimated Phragmites density (score of 3), indicating
a heavy invasion (Fig. 3A); however, only 1.5% of these swales were given
the highest density ranking in 2009. The number of swales in the moderately
dense category (score of 2) decreased during the same time period: about 16%
were moderately dense swales in 2002, compared to 8% in 2009. During this
treatment period, the proportion of swales described as having a light invasion
or no invasion (density score of 0 or 1) rose from 68% to 90%. Although
Phragmites density decreased in the swales, the swales show only a slightly
decreasing trend in the proportion with Phragmites over time (Fig. 3). Comparing
2002 (pre-treatment) to 2009 (last year of data showing 2008 treatment
results) shows little change in the proportion of swales infested with Phragmites
(41% versus 35%).
This pattern of Phragmites reduction over the course of the control project is
also evident from the estimated abundance data (Fig. 3B). In 2002, 16% of swales
were given the highest abundance score of 4, indicating heavy invasion, while
none of the swales were given this maximum score in 2008 and 2009. Similarly,
the number of swales in the second highest abundance category (score of 3) fell
186 Northeastern Naturalist Vol. 19, Special Issue 6
from 7% in 2002 to 0% in 2009. Finally, swales given an abundance score of 1
increased over time, from ≈13% in 2002, to almost 30% in 2009. During the same
Figure 3. Phragmites density scores (A) and Phragmites abundance scores (B) from
2002–2009 for swales initially mapped in 2001 or 2002.
2012 K.B. Lombard, D. Tomassi, and J. Ebersole 187
seven-year period, the proportion of swales described as having a light invasion
or no invasion (abundance score 0 or 1) increased from 71.5% to 93.2%.
The linear mixed model regressions show that year (time) and the number of herbicide
applications are both highly significant predictors of Phragmites abundance
and Phragmites density scores. Phragmites was significantly reduced with repeated
herbicide treatments over the years of the program (Tables 3, 4). The parameter
estimates of both independent variables are negative, indicating a decreasing
relationship with the dependent variable. In other words, as time and the number
of treatments increase, the estimated density and abundance scores decrease. Five
years of treatment were needed before every invaded swale was treated at least
once, and large numbers of treated swales begin to have no Phragmites stems only
after seven years of treatment (Fig. 4). In several cases, we observed that Phragmites
appeared again in a swale after it was recorded as absent in a previous year.
For example, in 2007, four swales that had previously been treated had no Phragmites;
however, in 2008 two of these had Phragmites stems and had to be retreated.
In 2008, twelve swales were reported with no Phragmites, but, in two of these,
Phragmites was present again in 2009. In both cases, the re-invasion was a small
number of stems that were presumed to be from rhizomes not killed by herbicide.
As the invasion was controlled and Phragmites levels declined at Sandy
Neck, personnel hours, chemical amounts, and cost generally decreased
(Fig. 5). The cost of the project ranged from almost $3000/ha in the early
years to less than $1000/ha, with the overall cost to date being approximately
$110,000 USD (not including indirect costs). When we started the project, we
used a crew of 3–4 people for 8 weeks or 131 hrs/ha (not including the first
year of treatment). By 2009, we reduced the crew to 2 people for 2–6 weeks or
77 hrs/ha. In addition, we reduced the liters of glyphosate used from 10 l/ha to
1 l/ha over the same time period.
Table 4. Linear mixed model regressions for estimated abundance scoring from 2002-2009
(** indicates a result below an alpha level of 5%).
95%
confidence interval
Parameter Estimate Std. Error df t P Lower Upper
Intercept 94.80 23.20 998.0 4.1 less than 0.001 49.40 140.20
**Number of treatments -0.20 0.02 1070.9 -9.7 less than 0.001 -0.28 -0.20
**Year -0.05 0.012 998.0 -4.05 less than 0.001 -0.07 -0.02
Table 3. Linear mixed model regressions for estimated density scoring from 2002-2009 (** indicates
a result below an alpha level of 5%).
95%
confidence interval
Parameter Estimate Std. Error df t P Lower Upper
Intercept 50.90 19.00 989 2.7 0.008 13.60 88.20
**Number of treatments -0.20 0.02 1059 -8.8 less than 0.001 -0.20 -0.10
**Year -0.03 0.01 989 -2.6 0.009 -0.04 -0.01
188 Northeastern Naturalist Vol. 19, Special Issue 6
Discussion
Our analysis of the 2002–2008 Phragmites treatment data demonstrates the
control project’s success in reducing the density and abundance of Phragmites
plants in interdunal swales of Sandy Neck. By 2009, 79% of the swales treated
had either no Phragmites or were at a low density in 2009—levels less likely to
affect native vegetation. Although the Sandy Neck project did not include untreated
swales as experimental controls, it is likely that without these chemical
treatments, many of the wetland swales at Sandy Neck would now be heavily
invaded by Phragmites. In Virginia, along the seaside of the eastern shore, comparisons
between untreated and treated landholdings showed that in areas of no
treatment, Phragmites acreage expanded 68% (130 acres) over four years from
2004–2008, whereas Phragmites acreage in aerially treated areas decreased 34%
(238 acres) (Myers et al. 2009). On Lake Erie, seven years of herbicide applications
reduced Phragmites from 18 to 6 percent of emergent vegetation (Back and
Holomuzki 2008).
Although the control efforts have resulted in a significant reduction in
Phragmites stems, the plant persists in all but a few swales. The influence
of application methods and timing on herbicide effectiveness may help explain
this continued persistence. Glyphosate may be most effective when
applied in the fall (Cross and Fleming 1989, Derr 2008, Moreira et al. 1999;
Figure 4. Number of previously treated swales without live Phragmites stems in succeeding
years. No data were collected in 2006.
2012 K.B. Lombard, D. Tomassi, and J. Ebersole 189
Figure 5. Resources per hectare needed, including: A) liters of herbicide used/ha (Rodeo
® or Aquamaster®), B) person hours/ha, and C) costs/ha. In year one, we only
treated for two weeks, and in year five, we used a contractor to treat just a few highdensity
swales. The majority (over 85%) of costs is for personnel; indirect costs are not
included in these estimates.
190 Northeastern Naturalist Vol. 19, Special Issue 6
but see Mozdzer et al. 2008), when Phragmites is preparing for dormancy
and nutrients are being directed to the horizontal rhizomes (Haslam 1969a,
1969b, 1969c; Norris et al. 2002); herbicide applied during this period can be
transferred throughout the entire root system to produce a high mortality rate
(Derr 2008). Prior to 2006, the small work crew at Sandy Neck had to begin
herbicide applications in summer to have enough time to treat the many, widespread,
heavily infested swales before the first frost. In more recent years,
the Sandy Neck control project has shifted to fall treatments, which likely is
why we saw substantially reduced Phragmites invasions since 2006. Initiating
treatments earlier in some years may have limited the effectiveness of the herbicide,
allowing Phragmites to re-emerge.
Logistical considerations also prevented the use of the most effective herbicide
application method, cut-and-drip, in heavily infested swales during the
early years of the control project. Although this method is both time- and laborintensive,
cut–and-drip minimizes non-target negative effects, and provides a
high probability that the herbicide will be translocated from the plant stem to the
belowground system of roots and rhizomes (Norris et al. 2002). Application of
herbicide by swiping or backpack spraying instead of cut-and-drip in some heavily
infested swales at Sandy Neck may have reduced the impact of herbicide and
allowed sprouting of new Phragmites individuals from these extensive belowground
systems. Since application technique and timing have such a strong effect
on the success of herbicide treatments, repeat herbicide applications are usually
required to gain complete control and eventually eradicate expanding Phragmites
stands (Havens et al. 1997, Marks et al. 1993, Warren et al. 2001), and this may
be the case on Sandy Neck.
Maintenance of currently low Phragmites density and abundance as well as
further reductions will continue to require time and resources into the future. Although
we did not reach our original goal of getting the invasion to a point that
could be treated in 1–2 weeks each year, we did substantially reduce the number
of personnel hours and cost, so that two staff members working over four weeks
could treat all swales. This project was funded for many years with a combination
of federal, state, and private grants; however, identifying new funding sources for
necessary maintenance of these gains will continue to be a major challenge.
Other studies indicate that eradication of a plant species is possible (Gardener
et al. 2009; Panetta and Timmins 2004; Rejmánek and Pitcairn 2002; Simberloff
2003, 2008), but will likely require over 10 years to achieve (Mack and Lonsdale
2002). In this case, we did not start seeing many swales with no Phragmites stems
until 5–7 years into the project, and many swales still exhibited low numbers of
stems. Follow-up monitoring and treatment will probably be needed in perpetuity
because stems are still present and re-invasion is likely due to adjacent source
populations and continued anthropogenic impacts. Given the challenging site
logistics of locating, monitoring, and potentially treating the large number of
swales each year, containment of Phragmites at low densities in the currently
invaded swales may be a more pragmatic goal, with near-eradication possible
with continued treatments.
2012 K.B. Lombard, D. Tomassi, and J. Ebersole 191
Acknowledgments
This work was funded by the Massachusetts Environmental Trust, the NRCS Wildlife
Habitat Incentive Program, the USFWS Partners Program, the William Wharton Trust,
and Entrust Fund. We thank the Town of Barnstable and in particular Sandy Neck Beach
Managers, Nina Coleman and Ken Alfieri, for critical support during this project. We appreciated
the assistance of the Massachusetts Audubon Society; Cape Cod AmeriCorps;
as well as the numerous invasives crewmembers that provided many hours of dedicated
work to control this invasion. Appreciation also goes to The Nature Conservancy’s Eastern
Invasives Network and Rich McHorney for assistance in early stages of the project
and to Erik Kiviat who encouraged us to tell this story to a wider audience. This paper
also benefitted from the excellent input of Jessica Dyson, Peter Kareiva, Dan Majka,
Laura Marx, Karen Poiani, and Stacey Solie.
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