Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
CASE STUDY: RESTORING REMNANT HARDWOOD FOREST
IMPACTED BY INVASIVE TREE-OF-HEAVEN (AILANTHUS
ALTISSIMA)1
C. M. Peugh2, J.M. Bauman, and S. M. Byrd
Abstract: Tree-of-heaven (Ailanthus altissima) is a fast growing tree native to
China. Introduced as an ornamental plant, A. altissima has spread throughout
North American landscapes, imposing a threat to the biodiversity of native
ecosystems. Recommended control methods include basal bark treatments using
herbicide with an oil-based carrier around the base of Ailanthus stems. Land
managers value application methods that maximize efficiency while also reducing
environmental impacts when applied over landscape scales. The focus of this
study was to assess the efficiency of herbicide concentrations and carriers on the
mortality of A. altissima. This study was conducted in a 105 ha hardwood forest
at the Wilds Conservation Center in Cumberland, OH. The forest is directly
adjacent to areas mined for coal and reclaimed in the 1980s. Twenty-five plots
were established consisting of 732 target trees. Two carriers (AX-IT™ basal oil
and diesel fuel) mixed with Garlon® 4 Ultra herbicide were tested at two different
concentrations: 1) 10% Garlon® in 90% diesel fuel carrier, 2) 20% Garlon® with
80% diesel carrier, 3) 10% Garlon® with 90% AX-IT™ carrier, and 4) 20%
Garlon® with 80% AX-IT™ carrier. Basal bark treatments were applied using a
backpack sprayer. After one year, treatments were similar (89-100% mortality)
with one exception, the 10% Garlon® in 90% diesel treatment was least effective
(69% mortality; P< 0.0001). This was more apparent as the diameter at breast
height (DBH) increased (P < 0.0001). When canopy dieback was compared
across treatments, AX-IT™ basal oil remained more effective regardless of the
DBH or concentration. Cost comparisons show 10% Garlon® solution in AX-IT™
oil base can be the most economically and ecologically beneficial treatment when
applied on a large scale. Long-term monitoring will determine the occurrence of
re-sprouts (via seed and root sprouting) and the impact each treatment has on the
plant communities within this forest system.
Additional Key Words: Garlon® 4 Ultra, triclopyr, diesel fuel, AX-IT™ basal oil, basal
spray, invasive species, herbicide control, allelopathy.
________________________
1
Poster paper was presented at the 2013 National Meeting of the American Society of Mining
and Reclamation, Laramie, WY Reclamation Across Industries, June 1 – 6, 2013 and accepted
for the online Journal of The American Society of Mining and Reclamation, Volume 2, No. 2,
2013. R.I. Barnhisel (Ed.) Published by ASMR, 3134 Montavesta Rd., Lexington, KY 40502.
2
Corine M. Peugh, Restoration Ecology Project Manager, the Wilds, Cumberland, OH 43732;
Jenise M. Bauman, Professor, Miami University, Oxford, OH 45056; Shana M. Byrd, Director
of Restoration Ecology, the Wilds, Cumberland, OH 43732.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
Introduction
Ailanthus altissima (Tree-of-Heaven) is a non-native, aggressive species that readily
establishes along roadways, utility lines, pastures, mine lands, and in disturbed forests (Burch
and Zedaker, 2003; Meloche and Murphy, 2006; DiTomaso and Kyser, 2007). Native to China,
this species was first introduced to the eastern U.S. as an ornamental in 1784 from Europe, and
was later brought into the western U.S. by Chinese immigrants as a cultural and medicinal plant
(Feret, 1985). Ailanthus has spread throughout the landscapes of North America imposing a
threat to the biodiversity of native ecosystems. Today, this tree is found from Ontario, Canada,
south to northern Florida, and west to Texas, becoming sparse along the west coast, south of
Washington and west of New Mexico (Burns and Honkala, 1990).
Ailanthus is capable of growing up to 3 m in the first year and is well suited to a wide variety
of climates, elevations, pH levels, and soil types (Burns and Honkala, 1990; Feret, 1985). It is
able to survive in the understory as a seedling, replacing native tree species when canopy gaps
are created (Heisey, 1990; Knapp and Canham, 2000; Runkle, 1985). This species forms dense
stands through vigorous stump and root-sprouts and prolific seed production; a mature female
tree can produce over 300,000 samaras that are dispersed by wind and water (Kowarik and
Sämuel, 2008; Landenberger et al., 2007; Miller et al., 2010; Pannill, 2000). Ailanthus also
releases allelopathic chemicals from its roots that hinder the growth of other tree species, further
increasing the ability of this noxious weed to suppress native tree regeneration (Heisey, 1990;
Gomez-Aparicio and Canham, 2008).
These aggressive attributes make Ailanthus a formidable competitor on disturbed sites, such
as surface-mined land. Often, reclaimed surface mines have poor, rocky soils with a very thin
layer of topsoil that is unsuitable for many native species, but more than adequate for Ailanthus.
Plass (1975) found that tree-of-heaven is well suited to growing on acidic spoils with low
phosphorus levels on a mine site in eastern Kentucky. Ailanthus also produces many allelopathic
compounds including the phytotoxic compound, ailanthone, which has been shown to be toxic to
many gymnosperms and angiosperms, possibly impeding the progression of natural succession
on surface-mined lands (Heisey, 1996; Hoshovsky, 1988; Mergen 1959). This competitive
growth habit allows for this species to dominate reclaimed mine land sites. Unfortunately, these
source populations on mine sites are invading neighboring woodland habitats and displacing
native hardwood species.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
Important for land managers are application methods that maximize efficiency while
reducing environmental impacts when applied over landscape scales.
There are several
recommended control methods for Ailanthus including manual, mechanical, and chemical
controls; each method has seen varying levels of success. Manually pulling or digging out stems
can be successful for removing small seedlings that have not yet established a taproot. However,
this laborious method requires ongoing follow-up treatments due to vigorous re-sprouting and reinvasion by Ailanthus or other undesirable species (Pannill, 2002). Mechanical methods, such as
cut-stump removal, without the use of herbicide often exacerbate the problem by causing
multiple root and stump sprouts per felled tree (Pannill, 2002). Some studies have looked at
prescribed burning as a control method, but this has limited success when used in conjunction
with forest thinning methods (Asaro et al., 2009; Rebbeck et al., 2005). Chemical management
methods such as foliar spray, stem injection, and basal bark treatment have been shown to
achieve the best control with the lowest occurrence of re-sprouts. However, these methods can
also be expensive and sometimes labor intensive when used in areas of heavy infestations
(Bowker and Stringer, 2011; Burch and Zedaker, 2003; DiTomaso and Kyser, 2007; Johnson et
al., 2001; Meloche and Murphy, 2006).
This study evaluated low-volume basal spray herbicide formulas to control Ailanthus in
remnant forest patches.
Our study plot was located in a remnant forest at the Wilds, a
conservation and research facility located on 3700 ha of reclaimed, surface-mined land in
southeastern Ohio. We used basal-bark application of herbicide in two types of carriers and with
two different concentrations. We selected a commercially available carrier, AX-IT™ basal oil,
and a more readily accessible and less expensive carrier, diesel fuel, which is commonly used by
private landowners as both an herbicide and a carrier. The overall objective was to assess the
efficiency of herbicide concentrations and carriers on the mortality of A. altissima in order to
develop a recommendation based on cost assessment for landowners.
Methods
This research is part of a three-year study initiated in 2011 at the Wilds conservation center.
Our study site is located in a 105 ha hardwood forest in Cumberland, OH (39°49’29.02”N,
81°44’56.82”W). This remnant forest site is directly adjacent to areas mined for coal and
reclaimed under the Surface Mining Control and Reclamation Act (SMCRA) in the 1980s. This
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
forest was not directly surface mined. However, this remnant forest was undermined and logged,
which may have caused the introduction of invasive species such as A. altissima and Elaeagnus
umbellata. The forest is dominated primarily by Fraxinus americana, Ulmus rubra, and Acer
rubrum, with a varied understory ranging from open to a dense cover of Lindera benzoin, Rosa
multiflora, Rubus occidentalis, and various other woody and herbaceous species.
Twenty-five plots, averaging 0.5 ha, in areas with notable populations of Ailanthus were
mapped and assigned treatments (Fig. 1). Within each plot, 25 healthy trees were tagged for
treatment and assigned a size class based on (DBH; Table 1). Even distributions of all size
classes were included in each plot. Individual treatments were assigned to each plot rather than
in a randomized design to simplify treatment applications. This allowed for one applicator to be
present and avoided contamination between treatments via translocation or drift, as many treated
trees are located in close proximity to one another. Some variation in site conditions was noted
between sites, but overall sites were similar. A GPS point was recorded for each tree, including
trees representing all treatments and untreated controls. All trees were numbered with a metal
tag attached approximately 40-55 cm from the base on the north facing aspect of the tree. Data
such as height, DBH, and canopy cover were recorded at this time. Size classes 1-3 were later
combined into size class 3 because of the uniform mortality noted among all seedlings that were
< 7 cm DBH. This simplified the results and allowed for a balance among individuals per size
class (Table 1).
Table 1. Individuals were assigned to a size class using
diameter at breast height (DBH).
DBH
Size Class
n
3
0.05– 6.9 cm
112
4
7 – 10.9 cm
128
5
11 – 14.9 cm
125
6
15 – 21.9 cm
134
7
22 - 38.8 cm
170
Basal bark treatments were applied during late summer in 2011 using Garlon® 4 Ultra
herbicide, a trade name for triclopyr, as this was found to have a high rate of success and is
widely available to land managers (Bowker and Stringer, 2011; Burch and Zedaker, 2003;
DiTomaso and Kyser, 2007; Johnson et al., 2001).
Mixtures were based on 15.0 liters of
solution and concentrations were prepared as follows: 1) 20% Garlon® 4 Ultra with 80%
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
Figure 1. Map of the study site illustrating the location of the treatment
plots and controls within the 105 hectare hardwood forest.
AX-IT™ oil-surfactant , 2) Garlon® 4 Ultra with 80% diesel fuel, 3) 10% Garlon® 4 Ultra with
90% AX-IT™ oil-surfactant and, 4) 10% Garlon® 4 Ultra with 90% diesel fuel. Each 15.0 L
treatment using diesel fuel included 118.3 milliliters of TrailLite 264™ dye, as an application
marker, the AX-IT™ oil came pre-mixed with dye (Table 2).
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Table 2. Treatments consisted of two concentrations of herbicide and two different carriers to
test the lowest effective concentration of herbicide in the most effective carrier (the
ratios were based on preparation of 15.0 liters of solution).
Carrier
TrailLite 264™
1
Herbicide Concentration
(Garlon® 4 Ultra)
20 % (3.0 L)
80% AX-IT™ oil (12.0 L)
0 ml
2
20 % (3.0 L)
80% Diesel fuel (12.0 L)
118.3 ml
3
10 % (1.5 L)
90% AX-IT™ oil (13.5 L)
0 ml
4
10 % (1.5 L)
90% Diesel fuel (13.5 L)
118.3 ml
Treatment
Basal-bark treatments were applied using a low volume hand pump backpack sprayer at
30 psi. Treatments were applied completely around the circumference of the tree, up to 3040 cm from the base. Bark was sprayed until substrate was visibly wet and just to the point of
runoff using approximately 1ml of herbicide per 32.3cm diameter (Nelson et al., 2007). After
treatment with herbicide, each tree was sprayed with a fluorescent blaze and marked with
flagging tape to facilitate locating individuals for follow-up assessment. Although previous
studies have documented that rain following basal-bark treatments does not impair the
effectiveness of the application (Pannill and Swearingen, 2009), we were cautious and did not
apply our treatments when precipitation was forecasted. Therefore, basal bark treatments were
applied during clear days and the bark was allowed to dry completely after application.
In the summer of 2012, trees were scored as alive or dead. Differences in mortality were
detected using Pearson’s Chi-Square (X2). In addition, each tree was evaluated for percent
canopy dieback and reported as percent mortality. This was done by recording the estimated
percent cover by visual inspection before and after treatment by standing at the base of the target
tree and looking directly up. The percent dieback per tree was averaged per size class and helped
determine the efficiency of the treatments with regard to canopy mortality. Percent canopy
dieback among treatments was assessed using an analysis of variance (ANOVA) followed by
Tukey’s HSD. Differences were considered significant when P< 0.05 according to the F test.
Log (n + 1) transformations were used to control for unequal variance. All statistics were
performed using JMP (8.0, SAS Institute, Cary, NC, USA).
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
Results
Results illustrate that after one year there was a significant difference among treatments with
regard to Ailanthus mortality (X2 =288.495, P≤ 0.0001). The treatment using 10% herbicide in
90% diesel fuel had the lowest mortality (69%).
This was significantly lower than 20%
herbicide in 80% AX-IT™ (100% mortality), 10% herbicide in 90% AX-IT™ (93% mortality),
and 20% herbicide in 80% diesel fuel (89% mortality; Fig. 2).
When herbicide application was compared to size class, significant differences were noted
with regard to mortality (X2 =71.84, P≤ 0.0001). For example, mortality significantly decreased
with increased size class. Mortality percentages are as follows: size class 3 (97%), size class 4
(87%), size class 5 (76%), size class 6 (66%), and size class 7 (58%; Fig. 3).
Figure 2. Graph illustrating mortality of Ailanthus after basal-bark treatments on the y axis.
Treatments are shown as bars from the x axis with specific carrier and
concentration names below, corresponding with bar. Of the treatments, the 90%
diesel was least effective with 69% mortality.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
Figure 3. Graph illustrates percent mortality of Ailanthus after basal-bark
treatment per size class. Mortality is illustrated on the y axis with size
classes on the x axis with corresponding bar. As size of Ailanthus
increased mortality decreased.
When canopy dieback was compared (size classes pooled) one difference existed. The 10%
herbicide in 90% diesel fuel was again significantly lower (78%; Fig. 4, first panel). In contrast,
herbicide in both concentrations of AX-IT™ (80 and 90%) had very high canopy dieback, 100
and 99%, respectively. This was closely followed by the 20% herbicide in 80% diesel (98%
canopy dieback).
When seedlings were separated by size class, there were no differences among treatments for
individuals that were in size class 3; all were similar as canopy dieback ranged between 99 and
100%. However, differences among treatments became apparent for size classes 4-7 when 10%
herbicide in 90% diesel fuel was used (F = 38.89, P < 0.0001). Again, canopy dieback was
significantly higher for both AX-IT™ treatments and the 20% herbicide in 80% diesel (D), all
ranging between 95-100% canopy dieback. It was the 10% herbicide in 90% diesel fuel that
resulted in significantly lower dieback in all size classes 4 and above; class 4 (79%), class 5
(73%), class 6 (70%), and class 7 (68%) (Fig. 4).
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
Figure 4. Bar graph illustrates percent (%) canopy dieback of A. altissima after basalbark treatments. Basal-bark treatments are shown as bars from the x axis as:
AX-IT 90 and 80%, Diesel (D) 90 and 80%, and the untreated control trees
(C). Error bars are ± 1 SE. Bars with different letters are significantly
different at P < 0.05 as determined by Tukey's HSD. The 10% herbicide in
90% diesel fuel demonstrated significantly lower canopy dieback when size
classes where pooled (78%) and in all size classes 4 and above: class 4
(79%), class 5 (73%), class 6 (70%), and class 7 (68%). Canopy dieback was
much higher among the size classes in the other treatments (95-100%
dieback).
Discussion
While other chemical applications have been shown to be effective (Bowker and Stringer,
2011; DiTomaso and Kyser, 2007), the basal-bark application method was chosen because it
requires less time and labor when compared to some other removal methods. Bowker and
Stringer (2011) experienced a 100% canopy reduction of Ailanthus when using 25% triclopyr in
75% non-polar carrier as a basal-bark treatment, while DiTomaso and Kyser (2007) showed that
20% Garlon® 4 in Hasten oil achieved a 86.7% canopy reduction on individuals with <4 cm
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
diameter and 100% dieback on individuals with >4 cm diameter when used as a basal-bark
treatment. Johnson et al. (2001) used a 15% triclopyr herbicide solution as a basal-bark spray,
achieving 99-100% canopy dieback of A. altissima.
This method allowed for a more controlled application of herbicide, minimized the risk of
non-target mortality, and reduced the amount of Garlon® 4 Ultra that was used (Nelson et al.,
2006). Additionally, this method allows for treated trees to remain standing, further reducing the
resources required for removal while providing snags for wildlife in a forest stand. Lastly, in
comparable studies, this method has been shown to be very effective, resulting in complete dieback with relatively few incidences of re-sprouting when similar formulations were used
(Bowker and Stringer, 2011; Burch and Zedaker, 2003; DiTomaso and Kyser, 2007;
Johnson et al., 2001).
Other studies recommend that the DBH be no greater than 8 to 10 cm when applying basal
herbicide (Nelson et al., 2006; Pannill, 2002). However, our study illustrates that basal-bark
spray can be very effective for controlling mature Ailanthus trees, with consistent occurrence of
mortality when using AX-IT™ oil as a carrier for individuals up to 30 cm DBH. Neither of the
treatments using AX-IT™ basal oil saw a significant change in effectiveness as the DBH
increased. In addition, we note that neither AX-IT™ treatment experienced re-sprouts when
study was assessed after one year (C. Peugh, Per. Obs.). In contrast, the 90% diesel solution
illustrated significant changes, with noticeable loss of effectiveness as the size of the trees
increased. This could be attributed to a variety of factors, but because diesel is thought to be a
less effective carrier than commercial oils, it is possible that the concentration of herbicide was
too low to effectively penetrate the bark with enough herbicide to kill the trees.
Because of the similarities in the AX-IT™ treatments and consistency among the size classes,
this was the better herbicide carrier when used with Garlon® 4 Ultra to promote Ailanthus
mortality. This treatment also utilized a more environmentally responsible carrier, basal oil, as
opposed to diesel fuel which can be harmful to non-target vegetation, wildlife, and the applicator.
Diesel fuel was chosen as a carrier to determine its effectiveness when compared to a
commercially available carrier such as AX-IT™ oil. While diesel is initially less expensive than
AX-IT™ oil, it is less likely to achieve full control of Ailanthus when used as a carrier for basal-
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
bark spray treatments, and will require additional treatments, increasing long-term management
costs.
The increase in the Garlon® 4 Ultra concentration to 20% in AX-IT™ oil resulted in 100%
mortality, compared to 93% mortality in a 10% Garlon® 4 Ultra and AX-IT™ solution. Although
not statistically similar, this 7% survival rate can be significant or manageable, depending on the
site conditions. When considering which herbicide treatment to use, it is important to consider
several factors. If the site is difficult to access or has high densities of Ailanthus present, it may
be more suitable to use the 80% AX-IT™ solution. However if the site is relatively easy to
access, such as in a park or along roadsides and has relatively low densities, the 7% survival
associated with the 90% AX-IT™ solution may be manageable when the cost and environment
impacts are considered. However, this technique requires continued follow-up surveys to treat
any re-sprouts in order to achieve full control. For land managers whose priority is efficiency,
this study indicates that use of the basal-bark method with 20% Garlon® 4 Ultra in AX-IT™ basal
oil may be effective at achieving complete removal and reduce the likelihood of re-invasion posttreatment.
The costs per gallon of herbicide treatments were calculated, showing that the 90% diesel
treatment was the least expensive, but was also the least effective (69% mortality). The 90%
AX-IT™ solution was the next least expensive treatment with a high level of effectiveness (93%
mortality). The 80% diesel solution was only slightly more expensive than the 90% AX-IT™
solution, but achieved only 89% mortality. The 80% AX-IT™ solution was the most expensive
treatment, while also achieving the highest mortality rate (100%). These results indicate
AX-IT™ oil as a carrier for Garlon® 4 Ultra is the most economically mindful while producing
the highest mortality rate (Table 3.)
Table 3. Cost comparison for 3.8 liters of each treatment*
Treatment
80% AX-IT™
80% Diesel
90% AX-IT™
90% Diesel
Garlon® 4 Ultra
Qty.
Price
(L)
(USD)
0.8
$22.32
0.8
$22.32
0.4
$11.16
0.4
$11.16
AX-IT™
Qty.
Price
(L)
(USD)
3.0
$10.93
0
$0.00
3.4
$12.29
0
$0.00
Diesel
Qty.
Price
(L)
(USD)
0
$0.00
3.0
$3.05
0
$0.00
3.4
$3.43
TrailLite™
Qty.
Price
(ml)
(USD)
0
$0.00
29.6
$0.34
0
$0.00
29.6
$0.34
Total
$33.25
$25.71
$23.45
$14.93
*(Prices were calculated using the cost of herbicides and carriers in August 2011.) 3.8 liters of
any mixture can be used to treat an average of 75 trees with an average DBH of 32.3cm.
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Journal American Society of Mining and Reclamation, 2013 Volume 2, Issue 2
Additional follow-up surveys will be conducted in the summer of 2013 to determine the
effectiveness of the treatments over time and re-evaluate the occurrence of re-sprouts. Future
phases of this study will also determine the long-term effect of treatments on the succession of
vegetation in the areas where canopy gaps are formed due to Ailanthus death. It is predicted that
without establishing a cover of competitive vegetation, re-invasion will occur by additional
Ailanthus and possibly other invasive species such as R. multiflora. Therefore, the next phase of
this study will help determine if replanting using native species is necessary to aid native forest
recovery after Ailanthus removal. In addition, we will also test the hack-and-squirt and cutstump technique. The hack-and-squirt method will involve making equally spaced, downward
cuts into the vascular tissue of the tree and applying 100% Garlon® 4 Ultra into the cuts, which
will significantly reduce the amount of herbicide necessary to treat individual trees. The cutstump treatment will utilize 20% Garlon® 4 Ultra, in an oil-based carrier, on the freshly cut
stumps of Ailanthus. Treatment methods will quantify the percent canopy dieback, total number
of root/stump-sprouts, and change in vegetation correlated with light availability. Results will be
combined with those of this study and additional recommendations will be formed for
landowners.
Acknowledgements
The authors would like to acknowledge Casey Brooks, Caitlin Byrne, Zack Canter, Rebecca
Fehn, Patrick Piecynski and Jessica Spencer for their assistance gathering data in the field, as
well as the United States Department of Agriculture Natural Resources Conservation Service
(USDA-NRCS) for providing cost share assistance from the Environmental Quality Incentives
Program (EQIP), which allowed for implementation of the forest management techniques that
this study sought to evaluate.
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