1997 Ornamentals Research Report - AUrora - Auburn University

I0 ALABAMA AGRICULTURAL ExPERIMENT STATION
ALABAMA AGRICULTURAL EXPERIMENT STATION
I0
METHODS
Two tree species, 'October Glory' red maple and water
oak were transplanted in two balled and burlapped tree sizes, 1.5
and three inches caliper, in Mobile at either a park or residential
site. The 1.5-inch trunk diameter transplants had root balls 18
inches in diameter, while three-inch trunk diameter transplants
had root balls 32 inches in diameter. All trees were hand dug.
Both tree species were planted in Mobile Municipal
Park, which consists of playgrounds, picnic areas, and has a
history of plant vandalism. This area receives heavy weekend
use. Residential plantings included 'October Glory' red maples
planted in an older, medium-income area, while water oaks were
planted in a nearby, low-income area. Trees were planted in May
1993 by city personnel. Particle size for soil at Municipal Park
was 78% sand, 19% silt, and 3% clay in areas where both species
were planted. Particle size for soil at the red maple residential
site was 80% sand, 18% silt, and 2% clay, while soil at the
willow oak residential site consisted of 81% sand, 15% silt, and
4% clay. Soil pH in the park ranged from 5.4 to 7.1, while soil
pH in both residential areas ranged from 5.7 to 6.
Planting holes were dug twice the width and the same
depth as the root ball. Trees were placed in the planting holes,
burlap and cord removed, and two-thirds of the soil was
backfilled. Trees were then watered in and the remaining soil
was added. Trees were hand irrigated twice per week during the
summer of 1993. No irrigation was applied during 1994 other
than natural rainfall. During March 1994 all trees were fertilized
with 0.4 pounds of 13-13-13 (one pound N per caliper inch
measured at six inches above the soil surface).
Growth data collected during the first and second
growing seasons included: height increase (determined each
year as the increase in height from the previous year on trees
with less than 25% crown dieback), trunk diameter increase
(determined each year as the increase in trunk diameter from the
previous year at six inches above the soil surface), and shoot
elongation (based on growth from dormant bud to terminal and
taken as an average of three randomly selected shoots).
Red maples were selected for gas exchange and water
potential evaluation. Gas exchange on clear to partly cloudy days
was monitored on a single, randomly selected, fully expanded
leaf from the side of the canopy with LI-COR 6250 Portable
Photosynthesis Systems (LI-COR, Inc., Lincoln, Neb.) on Aug.
25-26, 1993; June 13-14, 1994; and Aug. 11-12, 1994. Maples at
park and residential sites were monitored over the same period of
time by utilizing two LI-COR portable Pn systems. Each tree was
evaluated using a different leaf starting at 9 a.m., 11 a.m., 1 p.m.,
and 3 p.m. for a total of four observations per tree per day.
During the course of this study trees were visually
evaluated in August 1993 and September 1994 for general health,
as well as specifics such as percent crown dieback and death.
RESULTS
GROWTH. During 1994, an interaction occurred
between location and transplant size for maples. Although maple
transplant size had no effect at the residential site, small maples
at the park site had height increases of 12 centimeters (4.7
inches), compared to two centimeters (0.7 inches) for large
maples. Transplant size had no effect on maple caliper increases
during 1993, while lateral shoot elongation was greater for small
maples (Table 1). During 1994, small maples had height
increases six times greater than that of large maples. Trunk
diameter increases in 1994 were about twice as great with small
maples compared to large maples. Shoot elongation for small
maples during 1993 and 1994 was two and four times,
respectively, greater than that of large maples. Greater shoot
elongation for small maple transplants may indicate that they
were under less stress than large transplants.
Small willow oaks had height increases greater than
that of large oaks during 1993, but not in 1994. Willow oak shoot
elongation and trunk diameter increase were not affected by
transplant size in either year (Table 1). These data indicate that
field-grown willow oaks can be transplanted in these sizes with
similar success.
Greater height increases, trunk diameter increase, and
shoot elongation for small maple transplants support other work
which showed that 13 years after transplanting, a four-inch trunk
diameter tree transplanted at the same time as a 10-inch diameter
tree may have a shoot system of similar size. These data also
support research which reported that small transplants have
better shoot growth after transplanting due to a higher root to
shoot ratio compared to large transplants.
GAS EXCHANGE. Small maples had greater net
photosynthesis (Pn) rates than large transplants during August
1993, June 1994, and August 1994 observations (data not
shown). Greater Pn for small maples indicates that they were
under less stress than large maples during the first two growing
seasons. Higher Pn for small maples than large maples may
partially explain greater shoot elongation. Higher Pn during the
first growing season likely contributed to the capacity of smaller
trees to store more carbohydrates, which aided growth the
second year. Regardless of transplant size maples had greater Pn
rates during 1994 than 1993.
Transpiration of small maples was greater than that of
large maples on all sampling dates (data not shown). More
transpirational water loss by small maples indicate a greater
potential for water and nutrient uptake by the root system if they
were available. Storage of carbohydrates and nutrients one year
may aid growth the following year. Transpiration and
photosynthesis, regardless of transplant size during 1994, was
greater than in 1993, possibly due to greater rainfall in 1994.
Monthly precipitation was 2.03, 1.21, and 3.52 inches below
normal in June, July, and August 1993, respectively. However,
during the summer of 1994, precipitation was above normal in
June and July (0.43 and 3.54 inches), compared to 4.94 inches
below normal in August 1994.
WATER POTENTIAL. Mean daily leaf water potentials
taken during gas exchange observations and pre-dawn leaf
water potentials in August 1993 were greater for small than large
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