Comparison of Structural and Noncompacted Soils for Trees Surrounded by Pavement

Abstract

Trees in areas surrounded by pavement often have inhospitable rooting environments, which shorten their useful life expectancy. This trial was established to compare five different soil treatment options under pavement. Snowgoose cherry (Prunus serrulata) and Bosque lacebark elm (Ulmus parvifolia) were planted into 5.4 m3 (189 ft3) of medium containing compacted soil, gravel/soil mixture, Stalite, Stalite/soil mixture, or noncompacted soil and covered with con- crete. A variety of growth and health parameters were measured after 14 months. It was found that there was more trunk diameter growth with the noncompacted treatment than the Stalite and Stalite/soil treatments; more twig growth in the noncompacted and gravel/soil treatments than all others; higher relative chlorophyll rating in the noncompacted treatment than all others; and more root growth in the noncompacted treatment (elms only). Suspended pavement over noncompacted soils provided the greatest amount of tree growth and health and should be considered when designing urban planting sites for trees.

Full text

Comparison of Structural and Noncompacted Soils for
Trees Surrounded by Pavement
E. Thomas Smiley, Lisa Calfee, Bruce R. Fraedrich, and Emma J. Smiley
Abstract. Trees in areas surrounded by pavement often have inhospitable rooting environments, which shorten their useful
life expectancy. This trial was established to compare five different soil treatment options under pavement. Snowgoose
cherry (Prunus serrulata) and Bosque lacebark elm (Ulmus parvifolia) were planted into 5.4 m
3
(189 ft
3
) of medium
containing compacted soil, gravel/soil mixture, Stalite, Stalite/soil mixture, or noncompacted soil and covered with con-
crete. A variety of growth and health parameters were measured after 14 months. It was found that there was more trunk
diameter growth with the noncompacted treatment than the Stalite and Stalite/soil treatments; more twig growth in the
noncompacted and gravel/soil treatments than all others; higher relative chlorophyll rating in the noncompacted treatment
than all others; and more root growth in the noncompacted treatment (elms only). Suspended pavement over noncompacted
soils provided the greatest amount of tree growth and health and should be considered when designing urban planting sites
for trees.
Key Words. Biobarrier; Bosque lacebark elm; CU Soil; geotextile; planting pits; Prunus serrulata; skeletal soil;
Snowgoose cherry; soil compaction; Stalite; structural soil; suspended pavement; suspended sidewalks; Ulmus parvifolia;
urban plaza; urban tree planting.
Although the benefits of trees to the urban environment are
widely acknowledged, highly developed urban areas are det-
rimental to the trees themselves. Many factors such as air
pollution, poor drainage, and damage by people or vehicles
contribute to the short life expectancy for urban trees. How-
ever, the most limiting factor in the growth of urban trees is
the lack of usable soil for root growth (Craul 1992).
To meet this challenge, several “structural” or “skeletal
soils” have been developed as alternatives to the typical com-
pacted soil required to bear the weight of pavement and ve-
hicular traffic in urban areas. Researchers at Cornell Univer-
sity have experimented with a gravel and soil medium, con-
sisting of 80% stone 20% soil (by weight) and a small amount
of hydrogel to prevent the two from separating during mix-
ing. Research suggests that this mixture, known as CU Soil is
more beneficial to urban trees than standard compacted soil
(Grabosky and Bassuk 1995; Grabosky et al. 1998; Grabosky
et al. 2002).
Likewise, Carolina Stalite Company (Salisbury, NC, U.S.)
developed a structural soil treatment using a porous expanded
slate rock known as Stalite. This material can take the place
of the solid rock used in the CU Soil and provide additional
water and air storage capacity when mixed with 20% sandy
clay loam (Costello and Jones 2003). Stalite and gravel/soil
mixtures are both capable of meeting engineering require-
ments in urban areas by forming a stone matrix under the
pavement. Meanwhile the soil found between the stones is
noncompacted, leaving room for air exchange, water holding,
and root growth. Research has shown that this model encour-
ages roots to penetrate deeper into the ground rather than
shifting the structural soil upward and causing pavement fail-
ures (Grabosky et al. 1998).
Another option is suspended pavement over noncompacted
soil; this construction technique allows the use of higher us-
able soil volume under the pavement. The pavement may be
either precast concrete lowered onto footers or concrete
poured in place (Don McSween and James Urban, pers.
comm.). Although structural soils only contain approximately
20% soil by volume, which may affect water and nutrient
availability, suspended pavement can have nearly 100% of
the soil volume in noncompacted soil.
Although research has been conducted on these structural
soils individually, no comparison has been made of their
gravel/soil mixture, Stalite, Stalite/soil mixture, and noncom-
pacted soil installed under a suspended sidewalk. This ex-
perimental was developed to compare the ease of installation
of each product, the impact of each treatment on tree growth,
required maintenance practices, and the impact on the pave-
ment over time. The results of the treatments in the first year
of growth are reported in this article.
MATERIALS AND METHODS
Three trenches6×24m(19.8 × 79.2 ft) were completely
excavated to a depth of 0.6 m (1.98 ft) at the Bartlett Tree
Research Laboratory in Charlotte, North Carolina, U.S. dur-
ing the spring of 2004. The trenches were lined with a thick
164 Smiley et al.: Structural and Noncompacted Soils for Trees
©2006 International Society of Arboriculture

geotextile (Typar Style 3801 g; BBA Fiberweb, Old Hickory,
TN) to contain root growth. In addition, sections 3 ×3 m (9.9
×9.9 ft) were delineated using Biobarrier (BBA Fiberweb) to
contain root growth from individual trees. Four adjacent 3 ×
3 m (9.9 ×9.9 ft) sections were filled with the same soil
medium to compose a treatment. One tree was planted in each
3×3 m (9.9 ×9.9 ft) section giving each tree approximately
5.4 m
3
(189 ft
3
) of medium to grow in. Trees were set in the
middle of each 3 ×3 m (9.9 ×9.9 ft) plot and soil was added
in lifts around them and compacted using either a plate vi-
brator or impact compactor (Wacker Packer WP1550 vibra-
tory plate compactor, Wacker Rammer BS600Y jumping jack
compactor, respectively). Soil density was independently de-
termined by S&ME Inc., Charlotte, NC.
Treatments were as follows:
1. Gravel/soil mixture—comprised of 80% gravel 2.5 to
3.5 cm (1 to 1.4 in) diameter and 20% sandy clay loam
soil. A hydrogel (Terrasorb, fine) was sprayed on the
gravel before mixing with soil. Lifts were 20.3 cm (8.12
in) thick and were compacted with an impact compactor
to 95% Proctor.
2. Stalite/soil mixture—comprised of 80% Stalite 2 to 3.5
cm (0.8 to 1.4 in) diameter mixed with 20% sandy clay
loam. Stalite was wetted before mixing with soil. Lifts
were 30.5 cm (12.2 in) thick and compacted with a
vibratory plate compactor to the manufacturer’s speci-
fications.
3. Stalite alone was installed in 30.5 cm (12.2 in) lifts and
compacted with a vibratory plate compactor to the
manufacturer’s specifications.
4. Compacted soil—sandy clay loam was installed in 20.3
cm (8.12 in) lifts and compacted with an impact com-
pactor to 95% Proctor.
5. Noncompacted soil with suspended pavement was in-
stalled in the existing sandy clay loam soil. Biobarrier
was trenched 61 cm (24.4 in) deep to make 3 ×3 m (9.9
×9.9 ft) plots. The soil at this site was decompacted
using a backhoe excavator after tree planting using the
method proposed by Rolf (1994).
With the exception of the noncompacted treatment, each
treatment was randomly assigned within a row, creating a
randomized block design. As a result of the different con-
struction techniques used in the noncompacted treatment, all
of the noncompacted treatments were confined to a single
row.
Concrete was installed over the plots leaving an 80 cm
(32 in) round hole centered on each tree trunk. The concrete
was 5 cm (2 in) thick near the center hole and gradually
thickened toward the outside edge of the plot to 10 cm (4 in).
In the noncompacted soil plot, 15.2 cm (6.1 in) diameter
holes were augured 61 cm (24.4 in) deep to act as footer
pilings, and 5 cm (2 in) of gravel was applied to the soil
surface before installing the concrete.
In each treatment plot, two trees of two different species
were planted for a total of four trees per treatment plot
blocked by rows and randomly replicated three times for a
total of 60 trees. The trees were Snowgoose cherry (Prunus
serrulata) and Bosque lacebark elm (Ulmus parvifolia).
These species were selected because they are medium-sized
at maturity and root aggressively. Tree caliper was 5 cm (2
in) when installed. Wire baskets and burlap were removed
from the top of the root balls at planting.
Bubbler irrigation was installed above the root ball, two
bubblers on opposite sides of the trunk. Bubblers on treat-
ments 1 and 2 were 0.5 gal per minute, treatment 3 were 1.0
gal per minute, and treatments 4 and 5 were 0.25 gal per
minute. These flow rates were selected to maximize the water
input and minimize soil surface runoff. Root ball soil mois-
ture was monitored with tensiometers (Soil Moisture Equip-
ment Corp., Santa Barbara, CA), one per treatment. When
any two tensiometers reached 50 centibars of vacuum, the
irrigation system was turned on for 5 minutes. During periods
of drought, irrigation was applied daily. A drainage pipe was
installed below the lower side of each row and run downhill
to daylight.
Trunk caliper was measured with a diameter tape 30.5 cm
(12.2 in) above grade. Twig growth was measured on five
randomly selected branches of each tree. A Minolta SPAD
502 chlorophyll meter was used to determine relative chlo-
rophyll content on five leaves selected at random around the
crown of each tree. Foliar color and crown dieback were
visually rated on a scale of 0 to 5, with 0 being dead and 5
being completely healthy. Trunk borer counts were made by
visual assessment and carefully cutting into the outer bark
when necessary to determine if a borer was present. Borer
counts are total number per treatment. Scale insects were
rated on a visual scale of 1 to 5, with 1 being scale-free and
5 being twigs completely covered with scale insects.
Rhizotrons were installed on one tree of each species per
treatment. For the cherries, rhizotron windows were in direct
contact with the treatment media. For elms, a 1.9 cm (0.76 in)
layer of sand and peat mixture was installed between the
clear Lexan window and the treatment media. This mixture
was used to avoid clay and silt buildup on the window so as
not to obscure root visibility over a long period of time.
Rhizotrons were 61 cm (24.4 in) deep and 114 cm (45.6 in)
wide, installed 1.5 m (4.95 ft) from the center of the tree
trunk. Windows were kept covered with 1.9 cm (0.76 in)
Styrofoam and 1.9 cm (0.76 in) plywood when not being
assessed. Covers were used to keep light off the window and
to buffer the temperature differences. Roots that grew to the
point of touching the windows were diverted and grew along
the surface of the glass. These roots were traced with a
Arboriculture & Urban Forestry 32(4): July 2006 165
©2006 International Society of Arboriculture

marker and measured with a rotary measuring wheel (Alvin,
Germany).
Statistical analysis was conducted using SPSS (SPSS Inc.,
Chicago, IL) analysis of variance with Student-Newman-
Keuls separation of mean (P⳱0.05).
RESULTS
The fastest and simplest treatment to install was the Stalite
treatment. It required only pouring the stone and using a
vibratory compactor with fairly large lifts according to the
manufacturer’s instructions.
The noncompacted/suspended concrete treatments were
second in speed and ease of installation. As a result of the
location of this treatment, it was necessary to drive equipment
over the existing soil. However, just before paving, the soil
was decompacted with a backhoe. There was the additional
step of drilling the footer holes and pouring concrete footer
pilings, which adds to the time and cost of the treatment.
In the Stalite/soil mix treatment, the use of Stalite rather
than a nonporous rock allowed wetting of the stone before
mixing without the use of a hydrogel. This made mixing soil
and stone much faster. Mixing and compacting the gravel/soil
treatment was the most time-consuming.
Fourteen months after planting, there were distinct differ-
ences in tree growth, color, root growth, and crown dieback
(Figure 1). With the cherries (Table 1), there was signifi-
cantly more trunk diameter growth in the noncompacted/
suspended pavement treatment than with the Stalite and
Stalite/soil treatments. Twig growth rates were significantly
higher in the noncompacted/suspended pavement treatment
than all other treatments. Visually, the foliar rating of the
noncompacted/suspended pavement treatment, gravel/soil
treatment, Stalite/soil treatment, and compacted treatment
were all significantly better than the Stalite treatment. The
mean SPAD reading of foliar color was significantly higher
on the noncompacted/suspended pavement treatment than all
Figure 1. Research plot photographed from above in July 2005, approximately 14 months after plot establishment,
labeled to show the different treatments: compacted soil, Stalite, Stalite/soil mixture, gravel/soil mixture, and suspended
pavement over noncompacted soil.
166 Smiley et al.: Structural and Noncompacted Soils for Trees
©2006 International Society of Arboriculture

other treatments. There was significantly more dieback in the
compacted treatment than any other treatment. Root length at
the rhizotrons was much higher in the noncompacted/
suspended pavement, gravel/soil, and Stalite treatments than
in the remaining two treatments. Rhizotron root growth data
were not statistically analyzed because there was only one
rhizotron per treatment.
With the elms (Table 2), there was also significantly more
trunk diameter growth in the noncompacted/suspended pave-
ment treatment than with the Stalite and Stalite/soil treat-
ments. Twig growth rates were significantly higher in the
noncompacted/suspended pavement and gravel/soil treat-
ments than the other treatments. Visually, the foliar rating of
the noncompacted/suspended pavement treatment was sig-
nificantly better than the Stalite treatment. The SPAD reading
of foliar color was significantly higher on the noncompacted/
suspended pavement treatment than all other treatments.
There was significantly more dieback in the Stalite treatment
than any other treatment. Root length at the rhizotrons was much
higher in the noncompacted/suspended pavement treatment.
There were no significant differences in the number of
borers or scale insect ratings among treatments. There was no
damage to the concrete associated with any tree.
Trees in the Stalite and Stalite/soil treatments exhibited a
severe chlorosis within a month of planting. Foliar nutrient
analysis found deficiencies in manganese and iron. These
micronutrient deficiencies were induced by the high pH of the
Stalite. A mixture of sulfur, iron chelate, and manganese chelate
was applied to these treatments. A second application of sulfur
was required the next spring on the Stalite treatment. No other
fertilizers were applied before measurements were taken.
DISCUSSION
The trees in the noncompacted/suspended pavement treat-
ment were larger, faster growing, had better color, and more
root growth than most of the other treatments. This treatment
was followed in tree quality by the gravel/soil treatment.
Stalite/soil and compacted soil treatments were overall
slightly worse than the gravel/soil treatment. The Stalite treat-
ment was the easiest to install; however, it did not provide a
favorable environment for tree growth. The manufacturer of
Stalite is investigating the possibility of washing the carbon-
ates from the product to reduce the pH of the product and
potentially improve tree growth quality in the future.
Twig growth data in previous research (Grabosky et al.
2002) found equal or better growth in the CU Soil as com-
Table 1. Snowgoose cherry (Prunus serrulata) conditions 14 months after planting in 200 ft
3
of soil medium covered
with concrete.
Treatment
Average
trunk
diameter
(cm)
Average
diameter
change
since
planting
(cm)
Average
twig
growth
2005 (cm)
Average
visual
foliar
rating
(0–5 scale)
Average
SPAD
Average
SPAD
change
since
planting
Average
visual
dieback
(percentage
of crown)
Total root
length at
rhizotron
window
(cm)
Gravel/soil 2.77 a* 0.433 a 10.13 b 3.83 ab 42.35 b −6.3 ab 5.83 a 1580
Stalite/soil 2.68 a 0.283 bc 9.37 b 3.17 bc 40.63 bc −2.3 ab 12.50 a 24
Stalite 2.53 b 0.183 c 2.23 b 2.67 c 36.05 c −6.7 ab 15.83 a 774
Compacted soil 2.75 a 0.350 ab 7.80 b 3.17 bc 39.15 bc −8.6 b 31.67 b 37
Noncompacted soil 2.80 a 0.417 a 21.70 a 4.33 a 47.47 a −0.25 a 9.17 a 1415
*Means with the same letter were not significantly different as determined by analysis of variance with Student-Newman-Keuls separation of mean (P⳱0.05).
Table 2. Bosque lacebark elm (Ulmus parvifolia) conditions 14 months after planting in 200 ft
3
of soil medium covered
with concrete.
Treatment
Average
trunk
diameter
(cm)
Average
diameter
change
since
planting
(cm)
Average
twig
growth 2005
(cm)
Average
visual
foliar
rating
(0–5 scale)
Average
SPAD
Average
SPAD
change
since
planting
Average
visual
dieback
(percentage
of crown)
Total
root
length at
rhizotron
window
(cm)
Gravel/soil 2.35 a* 0.52 ab 23.97 a 3.5 ab 37.93 b −7.48 ab 0 a 3
Stalite/soil 2.12 b 0.28 bc 11.33 c 3.0 b 36.48 b −0.35 a 0 a 0
Stalite 1.97 b 0.15 c 3.13 d 1.0 c 13.30 c −16.80 b 6.7 b 0
Compacted soil 2.38 a 0.52 ab 17.33 b 2.8 b 33.95 b −6.28 ab 0 a 0
Noncompacted soil 2.57 a 0.65 a 24.73 a 4.0 a 44.00 a −0.88 a 0 a 61
*Means with the same letter were not significantly different as determined by analysis of variance with Student-Newman-Keuls separation of mean (P⳱0.05).
Arboriculture & Urban Forestry 32(4): July 2006 167
©2006 International Society of Arboriculture

pared with close by tree lawn plantings. This sharply con-
trasts the findings in this study in which twig growth in the
noncompacted/suspended pavement treatment was nearly
double the second best gravel/soil mix treatment in the cher-
ries. With the elm, the second best twig growth rate was also
found in the gravel/soil treatment and was nearly equal to the
noncompacted treatment. These differences point to species
variability in the response to the soil medium.
Relative chlorophyll content, as measured with a SPAD
meter, in a previous study (Grabosky et al. 1998) found
slightly higher chlorophyll levels in field grown Acer and
Malus that in a CU Soil. However, a higher chlorophyll level
was found in the CU Soil treatment than field-grown Tilia.
Chlorophyll levels were lower with all three species in the
adjacent compacted standard sidewalk profile treatment in
that study. Soil pH (8.8 to 9.1) found in the sidewalk base was
thought to contribute to the lower chlorophyll content with
the compacted sidewalk treatment. In this study, SPAD levels
were significantly higher, meaning more chlorophyll, in the
noncompacted/suspended pavement treatment than all other
treatments with both tree species. Media pH (ⱕ8.5) was also
a factor in the Stalite treatment and to a lesser degree in the
Stalite/soil treatment. The reason for the differences between
the two studies in not obvious.
When designing for planting in spaces that require a solid
surface for vehicles and pedestrians, the option of using
suspended pavement over noncompacted soil has not re-
ceived much attention over the past few years. It has been
used successfully in places like downtown Charlotte, North
Carolina. The differences in tree growth among treatments
was dramatic; trees growing in the noncompacted soil sus-
pended pavement treatment are visually healthier in appear-
ance and provide more shade more quickly than any of the
other treatments. If suspended pavement is to be used, the
pavement will need to be engineered to take expected loads
without fracturing. This may require greater reinforcement
than pavement installed over structural soil and installation of
footers.
The tree growth, maintenance requirements, and pavement
damage from the trees in this plot need to be monitored for 10
years.
Acknowledgments. We thank Robert Bartlett, Jr., and the F.A.
Bartlett Tree Expert Co. for support of this project; James Urban, Dr.
Jason Grabosky, Neil Harley, Dan Thompson, and Don
McSween, for technical advice in the layout and construction of the
research plot; Jerry Dunaway and Bill Hawkins of BBA Fiberweb
and Chuck Fredrick and Debbie Stringer, Carolina Stalite Co., for
contributing materials used in the project; Ethan Stewart, Imogene
Mole, and Elden LeBrun for assistance with the construction of the
plot; Dr. Donald C. Booth for insect evaluations; Dr. Christina Wells
at Clemson University for assistance with data analysis; and Laura
Johnson and Greg Paige for plot maintenance.
LITERATURE CITED
Costello, L.R., and K.S. Jones. 2003. Reducing Infrastructure
Damage by Tree Roots: A Compendium of Strategies.
ISA Western Chapter, Cohasset, CA.
Craul, P.J. 1992. Urban Soil in Landscape Design. John
Wiley and Sons, New York, NY.
Grabosky, J., and N. Bassuk. 1995. A new urban tree soil to
safely increase rooting volumes under sidewalks. Journal
of Arboriculture 21:187–201.
Grabosky, J., N. Bassuk, and B.Z. Marranca. 2002. Prelimi-
nary findings from measuring street tree shoot growth in
two skeletal soil installations compared to tree lawn plant-
ings. Journal of Arboriculture 28:106–108.
Grabosky, J., N. Bassuk, L. Irwin, and H. van Es. 1998. Pilot
study of structural soil materials in pavement profiles. In
Watson, G. (Ed.) The Landscape Below Ground II. Inter-
national Society of Arboriculture, Champaign, IL.
Rolf, K. 1994. Soil compaction and loosening effects on soil
physics and tree growth. In Watson, G.W. and D. Neely
(Eds.). The Landscape Below Ground. International So-
ciety of Arboriculture, Champaign, IL.
E. Thomas Smiley, Ph.D. (corresponding author)
Arboricultural Researcher
Bartlett Tree Research Laboratory
Adjunct Professor, Clemson University
13768 Hamilton Road
Charlotte, NC 28278, U.S.
tsmiley@bartlettlab.com
Lisa Calfee, Ph.D.
Assistant Professor
Queens University
Charlotte, NC, U.S.
Bruce R. Fraedrich, Ph.D.
Director
Bartlett Tree Research Laboratory
Charlotte, NC, U.S.
Emma J. Smiley
Research Technician
Bartlett Tree Research Laboratory
Charlotte, NC, U.S.
Résume. Les arbres entourés de surfaces pavées ont souvent des
environnements inhospitaliers pour leur enracinement, ce qui di-
minue leur espérance de vie. Cet essai a étéconçu pour comparer
cinq options différentes de type de sol sous les milieux pavés.
Ces cerisiers àfleurs japonais (Prunus serrulata) et des ormes à
petites feuilles (Ulmus parvifolia) ont étéplantés dans des milieux
168 Smiley et al.: Structural and Noncompacted Soils for Trees
©2006 International Society of Arboriculture

de 5,4 m
3
contenant du sol compacté,unmélange sol-gravier, du
Stalite™,unmélange de sol avec Stalite, un sol non compacté,etqui
aétérecouvert d’une couche de béton. Une variétéde paramètres de
santéet de croissance ont étémesurés 14 mois après. On a découvert
que l’accroissement en diamètre du tronc était plus important avec le
sol non compactéqu’avec les milieux en Stalite ou en sol-Stalite;
que la croissance des pousses était plus importante avec le sol non
compactéou le milieu sol-gravier que tous les autres types de mi-
lieux; qu’il y avait un plus haut taux de chlorophylle avec le sol non
compactéqu’avec tous les autre types de milieux; et que la crois-
sance racinaire était plus importante avec le sol non compacté(dans
le cas de l’orme seulement). La présence de pavage suspendu au-
dessus des sols non compactés produisait les plus importantes aug-
mentation de croissance et résultait en des arbres plus en santé; ces
aspects devraient de ce fait être pris en considération lors du design
de sites de plantation d’arbres en milieu urbain.
Zusammenfassung. Bäume, die von Pflaster und Straßenbelegen
umgeben sind, haben oft ungastliche Wurzelräume, die die Leb-
enserwartung sehr einschränken. Diese Untersuchung wurde durch-
geführt, um 5 verschiedene Bodenkonditionen unter dem Belag zu
testen. Prunus serrulata und Ulmus parvifolia wurden in 5,4 qm
Pflanzlöcher gepflanzt mit 1. verdichtetem Boden, 2. Kies/Boden-
Gemisch, 3. Stalit, 4. Stalit/Boden oder nicht verdichteten Boden,
bedeckt mit Beton. Eine Reihe von Wachstum- und Gesundheitspa-
rametern wurden nach 14 Monaten gemessen. Man fand heraus, dass
es mehr Stammdurchmesser bei unverdichtetem Boden als bei Stalit
oder Stalit/Boden-Mischungen und mehr Zweigwachstum bei un-
verdichteten und Kies-Mischungen gab als bei allen anderen. Es gab
höhere Chlorophyllraten bei unverdichteten Böden und mehr Wur-
zelwachstum. Aufgenommenes Pflaster über nicht verdichteten
Böden bewirkte größte Freiheit beim Wachstum und Gesundheit der
Bäume und sollte bei der Planung künftiger Standort berücksichtigt
werden.
Resumen. Los árboles en áreas rodeadas de pavimento con fre-
cuencia tienen ambientes que acortan su esperanza de vida. Este
ensayo fue establecido para comparar cinco diferentes opciones de
tratamientos al suelo bajo pavimento. El cerezo (Prunus serrulata)
y el olmo Bosque®(Ulmus parvifolia) fueron plantados en espacios
de 5.4 metros cúbicos (200 cubic feet) con suelo compactado, mez-
cla de grava/suelo, Stalite™, y mezcla de Stalite/suelo o suelo no
compactado y cubierto con concreto. Una variedad de parámetros de
crecimiento y salud fueron medidos después de 14 meses. Se en-
contróque hubo más crecimiento del diámetro del tronco con trata-
miento no compactado que los tratamientos Stalite™y mezcla de
Stalite/suelo; más crecimiento de rebrotes en suelo no compactado y
grava/suelo que en todos los otros; más alta tasa de clorofila en el
tratamiento no compactado que en todos los otros; y mayor creci-
miento de raíces en los tratamientos no compactados (solamente
olmos). El pavimento suspendido sobre suelo no compactado pro-
porcionóuna mayor cantidad de crecimiento del árbol y salud y
debería ser considerado cuando se diseñen sitios de plantaciones
urbanas para árboles.
Arboriculture & Urban Forestry 32(4): July 2006 169
©2006 International Society of Arboriculture