United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-164 Sept. 1981
Project Summary
Critical Factors Controlling
Vegetation Growth on
Completed Sanitary Landfills
Edward F. Gilman, Ida A. Leone, and Franklin B. Flower
This study summarized here identi-
fies some of the critical factors that
affect tree and shrub growth on
reclaimed sanitary landfill sites and
determines which woody species are
adaptable to the adverse growth
conditions of such sites. Trees planted
at the Edgeboro landfill. East Bruns-
wick. NJ, produced less shoot and
stem growth and shallower roots than
trees on the adjacent control plot. Of
19 woody species planted 4 years ago
on the 14-year-old landfill, black gum
and Japanese black pine proved to be
the most tolerant and green ash and
hybrid poplar the least tolerant to
landfill conditions. Root systems of
the more tolerant species proved to be
shallower than those of the landfill-
intolerant species. Smaller planting
stock (30 to 60 cm tall) appeared to be
better suited for landfill planting than
large trees (3 to 4 m tall). Balled and
burlapped trees showed better growth
on the landfill plot than bare-rooted
material. Of five gas barrier systems
tested, three proved effective: a soil
trench underlaid by plastic sheeting
over gravel and vented by means of
vertical PVC pipes, a 0.9-m mound of
soil underlaid with 30 cm of clay, and a
0.9-m soil mound with no clay barrier.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory. Cincin-
nati. OH, to announce key findings of
the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The sanitary landfill is presently the
least expensive environmentally ac-
ceptable means of municipal waste
disposal available. Advantages attributed
to landfilling are neatness, safety, and
relatively low cost. Though early landfill
sites were located far from residential
areas, rapid urban and suburban expan-
sion has brought many once-remote
sites within developed areas. As such,
they provide attractive sources of much
needed land for recreational uses, and
some municipalities have even consid-
ered them acceptable for commercial
purposes.
Regardless of the ultimate use of
landfill sites, certain disadvantages
exist, including groundwater pollution,
production of explosive gases, surface
settlement, and high ground tempera-
tures. Because abnormally high inci-
dences of plant mortality were found on
many landfills, a nationwide mail survey
was initiated to determine whether such
occurrences were common throughout
the United States (Flower et al., 1978).
Results indicated that the problem was
indeed of national magnitude.
The goal of this project was to help
develop the scientific knowledge neces-
sary to convert former landfill sites into
recreational areas by determining:
1. the relative adaptability of 19
woody species to landfill condi-
tions,
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2. the relationship of rooting depth to
the tree's tolerance of landfill soil,
3. whether small planting stock can
survive on completed landfills
better than large specimens,
4. whether balled and' burlapped
plant material is better suited for
landfill plantings than bare-rooted
material,
5. the effects of irrigation on tree
growth in landfill soil, and
6. the feasibility of constructing
barriers to the passage of toxic
gases from the refuse into the root
zone of gas-sensitive species.
The full report also includes information
on whether the leaf tissue nutrient
content of trees in landfill soil differs
from that of trees in nonlandfill soil and
the effects of high concentrations of
landfill gas (carbon dioxide and methane)
on the availability of soil nutrients.
Methods and Materials
Literature Review
A literature review was conducted to
determine the extent of existing data on
vegetation growth on landfills and to
study the effects of soil moisture on
plant growth, environmental factors on
leaf transpiration, "soil conditions on
nutrient uptake, and soil conditions on
root growth. Detailed reports describing
vegetation on landfills were scarce.
Many attempts to vegetate completed
sanitary refuse landfills with trees and
shrubs have been unsuccessful (Flower
et at., 1978). Gilman et al. (1980) report
that tree and shrub species have varied
tolerances to commonly occurring
landfill gases in the soil.
Tree Planting
The tree-planting segment of the
study included a species screening
experiment and studies of gas barrier
techniques, irrigation and tree growth:,
and planting stock size and type. Landfill
and control plots were used to plant
specimens and observe results. Cultural
methods included applications of 10-6-
4 granular fertilizer, liming, irrigation,
pest control (Sevin* and malathion), use
of chicken wire to protect against rabbit
damage of young seedlings, and weed
control by mowing, pulling, and chemi-
cal applications (Princep).
Sampling methods used in this study
included soil measurements (gas con-
tent, temperature, bulk density, moisture
content, and nutrient concentrations),
tree measurements (shoot length, stem
area, root biomass, leaf weight, tissue
nutrient content, and transpiration
rate), and meteorologic measurements
(air temperature, humidity, and total
wind movement). Various chemical
analyses were conducted to determine
leaf tissue content. Roots were examined
by excavating each root system com-
pletely with a small hand trowel from
the point of emergence at the main
stump to the root tips.
Results and Discussion
Species Screening Experiment
During the spring of 1976, 10
replicates of 19 woody species (Table 1)
were planted on both the completed 14-
year-old Edgeboro sanitary landfill in
East Brunswick, NJ, and on a nea'rby
control site that had not been landfilled.
Data presented in this report were
collected during 1978 and 1979, and
compiled with portions of data collected
in 1976 and 1977 (Gilman 1978).
Relative Viability of Plants-
Plant viability after 4 years of growth
on the completed landfill varied greatly
among species. By the end of 1979, all
of the weeping willows, rhododendrons,
and euonymus had died on the landfill
plot. Willows and rhododendrons were
obviously unable to withstand the
periods of desiccation characteristic 01
such sites during midsummer. The
euonymus shrubs on the site that were
not girdled by rabbits during the winter
of 1977-78 also appeared to have
become desiccated during midsummer
from lack of soil moisture. Several
sweet gum, black gum, bayberry, and
pin oak died from undetermined causes.
Landfill gas contamination of the root
zone and low soil moisture during mid-
July 1978 were suspected as contribu-
ting factors in the sweet gum deaths.
Since the concentrations of carbon
dioxide, oxygen, and methane at the 20-
cm (8-in.) soil depth can reportedly vary
from day to day, some tree deaths may
have resulted from undetected landfill
gas migrations into the root zone (i.e.,
samples might have been collected only
on days of low concentrations). Arthur
(1978) indicates that short periods of
high landfill gas concentrations may
adversely affect tree growth. Also,
gases other than carbon dioxide and
methane may have migrated into the
cover soil of the Edgeboro landfill and
adversely affected plant growth. In spite
of the numerous plant deaths, enough
replicates of 16 of the original 19
species remained alive during 1978 and
1979 to evaluate statistically their
ability to tolerate landfill soil conditions.
Relative Growth of Surviving
Plants-
Determination of landfill tolerance of
the surviving trees was based on shoot
length and stem area increase for each
Table 1. Species Selected for Vegetation Growth Experiment at Edgeboro Landfill
Latin name Common name
•Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use by the U.S. Environmental Protection
Agency.
Acer rubrum
Euonymus alatus
Fraxinus lanceolate
Ginkgo
Gleditsia triancanthos
Liquidambar styraciflua
Myrica pensylvanica
Nyssa sylvatica
Picea excelsa
Populus spp.
Populus spp.
Plantanus occidentalis
Pinus strobus
Pinus thunbergi
Quercus palustris
Rhododendron hyb. 'Roseum Elagans'
Salix babylonica
Tilia americana
Taxus cuspidata var. capitata
Red maple
Euonymus
Green ash
Ginkgo
Honey locust
Sweet gum
Bayberry
Black gum
Norway spruce
Hybrid poplar (saplings)
Hybrid poplar (from rooted cuttings)
American sycamore
White pine
Black pine
Pin oak
Rhododendron
Weeping willow
American basswood
Japanese yew
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species on both the landfill and control
plots. Relative tolerance of landfill
conditions depended both on the growth
parameter measured and the growing
season in which measurements were
collected. During the 1978 growing
season when landfill plot growth was
compared with that of the control plot,
black pine shoot and stem growth was
better than that for any other species.
During 1979, however, shoot growth of
black pine on the landfill was fourth and
stem growth was tenth best of all
species. Thus, black pine appeared to be
less tolerant of landfill conditions in
1979 than in 1978. In'the 1978
comparison, honey locust shoot and
stem growth were fifteenth and sixteenth
in rank, respectively, among the species
tested; but during 1979, honey locust
shoot growth was best, and stem
growth was fifth best of all species
tested. Evidently, a tolerance list based
on growth measurements during one
particular growing season does not
necessarily*epresent a reliable estimate
of an overall tolerance to landfill
conditions.
Since landfill tolerance also appears
to depend on the particular growth
measurement in question, the critical
growth criteria must be identified when.
selecting species. For example, either
shoot growth, stem growth, or both may
be critical for a particular vegetation
project.
When the total amount of shoot
growth produced on the landfill from
1976 through 1979 was compared with
that in the control plot, ginkgo, black
gum, and Japanese yew appeared to be
most tolerant; green ash, sweet gum,
and hybrid poplar saplings appeared
least tolerant of landfill conditions. But
.comparisons.of percent stem area
increase show Japanese yew, white
pine, and Norway spruce to be most
tolerant and hybrid poplar cuttings,
hybrid poplar saplings, and green ash to
be least tolerant of landfill conditions.
Since no single growth parameter is
best suited for comparing tree growth
on the landfill with that on the control
plot, shoot and stem growth data were
combined for 1976, 1977, 1978, and
1979 and analyzed as a unit. Two
different statistical methods were
chosen to analyze the combined growth
rate to rank the test species for overall
tolerance to landfill conditions.
One method consisted of averaging*
hoot growth during 1976 (when stem
rowth was not available) and shoot and
stem growth for 1977 through 1979
control plot. A rank of one was given the
species that produced the greatest
amount of shoot or stem growth on the
landfill as compared with that on the
control plot. The species that grew most
poorly on the landfill as compared with
its growth on the control plot was
ranked last (16th). Thus seven rank lists
were formed, and the tolerance rank
values from the lists were totaled for
each species for an overall landfill
tolerance rank (Table 2).
Principal components analyses of
shoot and stem data from 1976 through
1979 made up the second method
(Table 3). A factor score was calculated
for each species on each plot. The
differences in scores between plots
were aligned from smallest to largest.
The ranking of species from most to
least landfill tolerant by this system was
similar to the first analytical method.
Only two species changed positions
dramatically; Japanese yew moved
from most tolerant by the first method to
eighth according to the principal com-
ponents analysis, and hybrid poplar
cuttings moved from eighth in tolerance
by the first method to least tolerant by
the second analysis. As a result of both
methods of analysis, black gum, black
pine, and bayberry appeared to be most
tolerant, and hybrid poplar saplings.
green ash, and honey locust appeared
least tolerant of landfill conditions.
A final way of assessing relative
tolerance to landfill conditions is to total
the rank values from the two methods of
analysis (Table 4). Black gum appears
most tolerant and Japanese yew is
second most tolerant of landfill condi-
tions. Japanese yew appears to have
been ranked very tolerant because
growth on the control was inhibited by
"wet feet" conditions.
In all the landfill tolerance lists, the
species were generally distributed in a
similar manner throughout tolerance
ranks: That is, those at the top of one list
generally appeared toward the top of the
other lists and vice versa.
Stress on the intolerant trees provided
by low moisture, or elevated carbon
dioxide and methane concentrations, or
both was reflected in greater variability
in growth on the landfill plot than on the
control. Since tolerant species were
apparently more capable than the
intolerant species of withstanding the
low soil moisture and elevated gas
levels of the landfill plot, the lower
variability among tolerant trees on the
landfill comes as no surprise.
From the previous discussion, the
following questions must be answered
before plant material is selected: Should
the plant produce a quick vegetative
Table 2. Sum of Landfill Tolerance Ranks* for Shoot and Stem Measurements
1976-1979
Species
Japanese yew
Japanese black pine
Black gum
Bayberry
Ginkgo
White pine
Norway spruce
Hybrid poplar (rooted cuttings)
American basswood
American sycamore
Red maple
Honey locust
Pin oak
Sweet gum
Green ash
Hybrid poplar (saplings)
Sum of
Tolerance
Rank Values*
37
42
45
45
46
49
50
50
54
60
60
72
77
83
87
102
Landfill
Tolerance
Rank
1
2
3
3
5
6
7
7
9
10
10
12
13
14
15
16
*Each number is the sum of that species' rank in seven rank lists relative to the other
species. The seven rank lists are the following: stem area increase measurements
from 1977, 1978, and 1979, and shoot length measurements from 1976, 1977,
1978, and 1979.
*The lower the number, the more tolerant the species is to landfill conditions.
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Table3. Average Factor Scores* for 16 Species from Landfill and Control Plot
Data, 1976-1979
Species
Black gum
Japanese black pine
Bayberry
Ginkgo
White pine
American basswood
Norway spruce
Japanese yew
Sweet gum
American sycamore
Red maple
Pin oak
Hybrid poplar
(saplings)
Green ash
Honey locust
Hybrid poplar
(rooted cuttings)
Landfill
-0.02
-0.23
-0.65
-1.08
-0.61
-0.57
-0.57
-0.43
0.18
0.02
0.15
-0.22
0.12
-0.57
0.31
2.96
Control
-0.14
-0.28
-0.69
-1.11
-0.63
-0.54
-0.50
-0.36
0.31
0.17
0.53
0.36
0.71
0.30
1.33
4.04
Difference
(control-landfill)
-0.12
-0.05
-0.04
-0.03
-0.02
-0.03
-0.07
-0.07
0.13
0.15
0.38
0.58$
0.59%
0.57$
1.02%
2.96%
Landfill
Tolerance
Rank*
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
* Principal Axis Factor Method was used to calculate factor patterns and factor scores
for shoot and stem data from 1976 through 1979.
"The lower the number, the more tolerant the species is to landfill conditions.
^Significant @ P< 0.05.
cover? Must it grow in a manner similar
to trees on sites that are not landfilled?
Should it produce good shoot growth,
good stem area increase, or both?
Tolerance of Rapid Versus
Slow Growers
Seven of the eight most intolerant
species have been classified as rapid
growers (Table 4); most of the tolerant
species are slow growers. Apparently,
those species with the capacity to grow
very-quickly cannot maintain this rapid
growth rate on completed landfills,
whereas species that naturally have a
slower growth rate can maintain a rate
on the landfill comparable with that on
the control. Since fast growing trees are
likely to withdraw more moisture from
the soil, they may-become subjected to
water stress more quickly than the slow
growers, and irrigation may be more
essential for their establishment. Thus
when growth on the landfill was
compared with growth on the control,
rapidly growing trees proved intolerant
of landfill conditions. But many of these
supposedly intolerant (based on landfill
growth compared with control growth)
rapid-growing species (hybrid poplar
rooted cuttings, honey locust, and
American sycamore) actually produced
more absolute vegetative growth on the
landfill than other so-called tolerant
species growing on the landfill.
Tolerance of Drought-Sensitive
and Flood-Tolerant Species
The characteristic low-moisture-
holding capacity of landfill cover soils
was demonstrated on the experimental
landfill plot during the years 1977 and
1978. Species most likely to be affected
by water stress are those that naturally
grow in areas associated with a high
water table. Five of the eight species
(green ash, honey locust, sweet gum,
pin oak, and red maple) observed to be
landfill-stressed in these investigations
(Table 4) cannot tolerate drought,
whereas only one of the eight tolerant
species is reported drought sensitive.
Several of these intolerant species
(green ash, red maple, honey locust)
may have proved to be landfill tolerant if
adequate amounts of water had been
provided.
A reasonable assumption may be that
those species that can withstand periods
of flooding can also tolerate landfill
conditions, since both environments
generally lack sufficient oxygen for
normal root respiration. But since the
soil on the Edgeboro landfill was often
lacking in moisture, these species were
probably not afforded the opportunity to
exhibit their low-oxygen adaptability.
Thus their growth on the landfill was
much reduced compared with the
control.
Effect of pH on Tolerance
Evidence exists to show that soil pH
may affect species tolerance to landfill
conditions. Stem area increase data
indicated that acid-loving plants (Japa-
nese black pine, Norway spruce, black
gum, and bayberry) were more tolerant
of landfill soil with a low pH (4.5 as
opposed to 6.2). Shoot-length data,
however, showed no recognizable rela-
tionship between soil pH and landfill
tolerance. Stem area increase may thus
be a more sensitive indicator for the
tolerance of woody species to landfill
conditions.
Effect of Soil Compaction on
Tolerance
High soil bulkdensity isanotherfactor
that may have influenced the response
of a number of the test species to the soil
environment created on the landfill plot.
Optimum levels of soil bulk density for a
variety of crops vary between 1.3 and
1.5 g/cm3. Since bulk density on the
landfill plot during the current investiga-.
tions was 1.8 g/cm3, the lowered oxygen
content of the soil may have affected
some species.
Tolerance of Shallow-
Versus Deep-Rooted Species
The species that adapted to the
landfill plot most quickly (Japanese
black pine, Norway spruce) had shal-
lower and more extensive root systems
on the landfill than did the intolerant
species (honey locust, green ash, hybrid
poplar). This study presents evidence
that the root systems of these presently
intolerant species are making their way
toward the soil surface and may in
several years be able to tolerate landfill
conditions. Their root systems will
probably grow away from the high
carbon dioxide and methane concentra-
tions (and, consequently, low oxygen
concentrations) in the deeper soil strata,
and they will probably require extensive
irrigation to maintain growth comparable
with the control.
Root Adaptations
The root adaptation mechanism of
hybrid poplar associated with landfill
tolerance appeared to be different from
that of green ash. Deep poplar roots (30,
cm) grew toward the soil surface and]
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Table 4. Relative Tolerance of 16 Species to Landfill Conditions*
Species
Sum of Landfill
Tolerance Rank Values
Black gum (4, 8f -R$
Japanese yew (9, 4) -
Japanese black pine (10, 9) -
Ginkgo (7, 9) -S
White pine (10. 10) -S
Bayberry (9, 9) -
Norway spruce (8, 8) -S
American basswood (9, 10) -S
American sycamore (10, 10) -R
Red maple (9, 10) -I
Hybrid poplar (rooted cuttings) (10, 5) -R
Pin oak (9, 10) -R
Sweet gum (1, 6) -R
Honey locust (10, 10) -R
Green ash (10, 10) -R
Hybrid poplar (saplings) (2, 7) -R
10
13
14
17
21
23
26
31
34
41
44
48
51
52
59
60
*Tolerance was established by totaling the landfill tolerance rank values for each
species from Tables 8, 9, 10, and 11.
^Number of replicates living on the landfill and control plots respectively at the end of
1979.
\R=rapid growth rate, ^intermediate growth rate, S=slow growth rate, N=data not
available - from Powells (1965).
proliferated there, whereas ash roots at
the same depth did not extend to the soil
surface. Instead, a shallow root system
was provided for by roots that sprouted
from the root collar 2 cm below the soil
surface. The ash roots proliferated at
this depth, resulting in a shallow root
system.
American basswoods suffered a
decrease in total root length and a
reduction in the depth of maximum root
penetration when levels of soil carbon
dioxide and methane were high and
oxygen concentrations were low. This
result indicates that at least 1 in. of
irrigation per week is needed on
completed landfills to maintain good
tree growth. Though American bass-
wood roots did not maintain good
growth when landfill gas concentrations
were high, moderate gas concentrations
permitted roots to grow toward the soil
surface and avoid the contaminated soil
environment below.
Tolerance of Small Versus
Large Trees
Small trees(30 to 60cm tall)appearto
be more adaptable to landfills than large
trees (3 to 4 m tall). Shoot growth for
small trees of four (pin oak, green ash,
sugar maple, hybrid poplar) out of five
species tested was as good on the
andfill as on the control, but shoot
growth on the large specimens (saplings)
was significantly lower (P <0.10) on the
landfill.
Tolerance of Balled and
Burlapped Versus Bare-
Hooted Material
Another practice involving root char-
acteristics that may help trees adapt to
stressed environments is the use of
balled and burlapped material rather
than bare-rooted stock. In this investi-
gation with a single species (sugar
maple), balled and burlapped trees
produced longer shoots and greater leaf
volume than bare-rooted trees on the
landfill plot, but not on the control plot.
Obviously there was some advantage in
having a less pruned root stock. Better
mycorrhizae inoculum may also have
existed in the soil ball. Whether this is a
characteristic of one species or many
remains to be determined.
Tolerance of Irrigated Versus
Nonirrigated Plants
Sugar maple was used to assess the
value of supplemental irrigation in
adapting trees to landfill cover soils.
This species generally grew better in the
control soil, with its higher moisture and
oxygen and lower carbon dioxide, than
in the landfill. Irrigated maples produced
significantly more (P < 0.01) leaf tissue
than nonirrigated trees on the landfill,
but not on the control plot during 1978
and 1979. Shoot length was enhanced
by irrigation in both plots, but the
increase was not statistically signifi-
cant. Possibly the failure of irrigation to
stimulate growth in the control plot was
a result of the sufficient rainfall that
occurred during the growing season;
thus moisture was not a limiting factor
for growth of sugar maple on the control
as it was on the landfill.
Decreased height of sugar maples on
the landfill plot was undoubtedly
because of the combined effects of low
soil moisture, slightly elevated soil
carbon dioxide, and depressed oxygen
concentration. Also, the elevated carbon
dioxide levels may have caused the
production of a shallower root system
on the landfill than on the control and
may therefore have predisposed the
maples to drought damage. Gingrich
and Russell (1957) report that oxygen
and moisture content interact so that at
high oxygen concentrations, low mois-
ture content has a more deleterious
effect on corn growth than at low
oxygen contents. Since the oxygen
concentration in the landfill soil was
only slightly depressed, low soil moisture
could have had a strong effect on maple
development.
Arthur (1978) observed an increase in
stomatal resistance and hence reduced
transpiration of sugar maples after
several days of exposure to simulated
landfill gas mixtures. A similar effect
was observed in sugar maples growing
in the landfill plot. Elevated soil carbon
dioxide concentrations (7.8%) in the
nonirrigated portion of the landfill
caused significantly increased stomatal
resistance in the sugar maples from late
morning until early evening over that of
the trees located on the landfill where
carbon dioxide averaged 2.8%. Irrigation
throughout the growing season did not
significantly reduce the stomatal resist-
ance below that of the nonirrigated
area.
Air temperature, relative humidity,
and other meteorological parameters
are also known to affect stomatal
aperture. But the effects of an adverse
gas environment and reduced moisture
content on stomatal aperture in the
landfill plot apparently overrode the
recognized effects of temperature,
humidity, and wind.
Gas Barrier Experiment
Landfill gases (primarily carbon diox-
ide and methane) must be kept away
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from the root system of trees and shrubs
to promote good vegetation growth. Five
gas barrier systems were tested, and
three proved to be effective: (a) a soil
trench underlaid with plastic sheeting
over gravel and vented by means of
vertical PVC pipes, (b) a 0.9-m mound of
soil underlaid with 30 cm of clay, and (c)
a 0.9-m soil mound with no clay barrier.
Concentrations of carbon dioxide,
oxygen, and methane in the two mounds
and in the trench were similar to those
in the control plots, thus indicating that
these gas barrier techniques are suitable
for application in landfill vegetation
projects.
Evaluations were made of the effects
of varied soil environments on American
basswood growth and on the total
nutrients they accumulated in each gas
barrier test area. American basswoods
growing in 0.9-m (36-in.) soil mounds
(either unlined or lined with a 30-cm
(12-in.) clay barrier) and in the gravel/
plastic/vents trench generally produced
more stem and shoot growth than trees
in unmodified landfill soil. The other two
gas barrier trench systems did not
promote better tree growth than the
unmodified landfill areas. Basswoods in
the gravel/plastic/vents trench and in
the clay-lined mound accumulated
more of eight plant nutrients (nitrogen,
potassium, magnesium, calcium, man-
ganese, iron, zinc, and copper) than did
the trees in the unmodified landfill
screening area.
Conclusions
1. Woody species differ in their adapta-
bility to landfill soil.
2. Slow-growing trees appear to be
better adapted to landfill conditions
than rapid-growing trees.
3. Trees and shrubs planted as small
specimens appear to be better
adapted to landfill conditions than
large specimens.
4. Species with a natural propensityfor
producing shallow roots are better
suited for landfill vegetation projects
than naturally deeper-rooted species.
5. Species reportedly tolerant to low
oxygen environments will not grow
well on landfills unless they are
irrigated very thoroughly.
6. Balled and burlapped plant material
appears to be better adapted than
bare-rooted material to landfill soil.
7. Landfill gases (primarily carbon
dioxide and methane) must be kept
away from the root system of trees
and shrubs to promote good vegeta-
tion growth. Two types of methods
shown to be effective are (a) a mound
of soil (0.9 m) over existing cover
(with or without a clay liner), and (b) a
lined and vented trench backfilled
with suitable soil.
The full report was submitted in
fulfillment of Contract No. R-805907-
01 by Rutgers University under the
sponsorship of the U.S. Environmental
Protection Agency.
References
Arthur, J.J. The Effect of Simulated
Sanitary Landfill Generated Gas Con-
tamination of the Root Zone of Tomato
Plants and Two Maple Species.
Masters Thesis, Rutgers University,
N.J. 1978.
Flower, F.B., I.A. Leone, E.F. Gilmanand
J.J. Arthur. A Study of Vegetation
Problems Associated with Refuse
Landfills. EPA-600/2-78-094. U.S.
Environmental Protection Agency,
Cincinnati, Ohio, 1978.
Powells, H.A. Silvics of Forest Trees
of the United States. USDA Handbook
No. 271. U.S. Department of Agricul-
ture, Washington, D.C. 762 pp. 1965.
Gilman, E.F. Screening of Woody Species
and Planting Techniques for Suitabil-
ity in Vegetating Completed Sanitary
Refuse Landfills. M.S. Thesis, Rutgers
University, N.J. 130 pp., 1978.
Gilman, E.F., I.A. Leone and F.B. Flower.
Determining the Adaptability of Woody
Species for Vegetating Completed
Refuse Landfill Sites. For. Sci. (in
press). 1980.
Gingrich, J.R. and M.B. Russell. A
Comparison of Effects of Soil Mois-
ture Tension and Osmotic Stress on
Root Growth. Soil Science. 84:185-
194, 1957.
Edward F. Gilman, Ida A. Leone, and Franklin B. Flower are with Cook College,
Rutgers University, New Brunswick, NJ 08903.
Robert E. Landreth is the EPA Project Officer (see below).
The complete report, entitled "Critical Factors Controlling Vegetation Growth
on Completed Sanitary Landfills," (Order No. PB 81-246 324; Cost: $17.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
•ft U.S. GOVERNMENT PRINTING OFFICE. 1981 - 757-012/7351
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Environmental Protection Information C aia
Agency Cincinnati OH 45268
Agency
EPA 335
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