Arboriculture & Urban Forestry 35(5): September 2009 MATERIALS AND METHODS Study 1: Organic Mulches, Inorganic Mulches, and Living Groundcovers Impact Eastern Redbud Establishment Forty planting pits of 1.1 m x 1.5 m (3.5 ft x 5 ft) dimensions were established at the Texas A&M University Horticulture Gar- dens (lat. 30E37.78’N. long. 96E20.51’W.) in College Station, Texas, U.S., on May 29, 1998. Cells were established in exist- ing 3.7 m x 12.2 m (12 ft x 40 ft) beds filled with a Silawa fine sandy loam (siliceous, thermic ultic haplustalfs, 73% sand, 9% clay, 18% silt) surrounded by treated landscape timbers. Soils in the pits were tilled to a 25.4 cm (10 in) depth. Cells were di- vided by sinking sheet metal edging 20.3 cm (8 in) deep to con- tain surface roots beneath the individual soil surface treatments. Irrigation was provided via stationary risers installed at 30.4 cm (12 in) above grade level with a 100% overlapping spray pat- tern. Irrigation was applied twice weekly to maintain adequate moisture by pulse irrigating for 20 min. intervals until tensiom- eter readings in the soil returned to below -15 kPa (-0.15 bars). Forty 23.3 L (#7) container grown Cercis canadensis var. texensis ‘Alba’ grafted on C. canadensis var. texensis seedling rootstocks were obtained in advance from Turkey Creek Farms, Humble, TX, and acclimated on site for 10 days prior to transplanting to the planting pits. Trees were established one to the center of each planting pit prior to the imposition of soil surface treatments. Eight soil surface treatments were imposed with five repli- cates each. The control consisted of bare soil with no cover. The remaining seven treatments consisted of 7.6 cm (3 in) depth of pine bark mulch; Trachelospermum asiaticum on 30 cm (12 in) centers mulched with 7.6 cm of pine bark; solid-sodded Steno- taphrum secundatum; 7.6 cm of white decorative gravel (Parkers River Pebbles, Pursell Industries, Inc., Sylacauga, AL); 2.5 cm (1 in) of recycled paper mulch (EnviroGuard™ landscape mulch, Tascon, Inc., Houston, TX); 9.8 cm x 19.8 cm x 6 cm (3.89 in x 7.8 in x 2.36 in) brick pavers underlied with 5.1 cm (2 in) of coarse builder’s sand (brick-on-sand); and seasonal color mulched with 7.6 cm of pine bark. The seasonal herbaceous color plant rotation for summer, fall/winter, and spring was Catharanthus roseus (L.) G. Don ‘Raspberry Cooler’, Viola × wittrockiana Gams. ‘Crown Yellow’, and Petunia × hybrida Hort. Vilm.-Andr. ‘Dreams Red’, respectively. Plots containing turfgrass were mown weekly at a height of 5.1 cm (2 in) throughout the growing season using hand- held clippers. Plots were fertilized with a 13N-5.7P-10.8K granu- lar fertilizer (Pursell Industries, Inc., Sylacauga, AL) at the rate of 0.45 kg (1 lb) of actual N per 92.9 m2 (1000 ft2 ) of bed surface in April, June, August, and October. Just prior to installation of the soil surface treatments, five randomly distributed soil core samples were extracted using a 2.5 cm internal diameter soil corer (Arts Manufacturing & Supply, American Falls, ID). At harvest of the experiment, five replicate samples were taken from beneath each of the eight soil surface treatments. Cores were extracted from 1.3 cm (0.5 in) below the mulch layer to a depth of 10 cm (3.9 in) and dried at 50°C (122°F) to a constant mass. These cores were used to estimate soil bulk density. A duplicate set was extracted at the same time and used to measure soil pH (Accumet® , Model 20, pH/conductivity meter, Fisher Scientific, Pittsburgh, PA). Soil moisture potential was measured weekly from April through September using tensiometers (Model 2725 JetFill Ten- siometers, Soil Moisture Equipment Corp., Santa Barbara, CA) 233 with mean PPFD, leaf temperatures, and relative humidity of 956 mmols·-1 ·m-2 Analyzer Model 6250, Li-Cor, Lincoln, NE), , 27.2°C (81.0°F), 20.8%, respectively. Root-zone [0 inserted to a 15.2 cm (6 in) depth. Midday xylem water potentials to estimate maximal water stress and subsequent pre-dawn xylem water potentials to estimate recovery from water stress were de- termined monthly for each tree using a pressure chamber (Model 610, PMS Instrument Company, Albany, Ore). A single, recently fully expanded leaf was detached and immediately placed in the chamber for measurement in the field for each tree. Midday water potentials were determined between noon and 2:00 pm. Pre-dawn water potentials were determined between 3:30 am and dawn. Tree height, trunk diameter at 15.2 cm above the soil surface, and foliar stress ratings were recorded monthly during the growing season. Foliar stress ratings, as described in Arnold et al. 2005 and Ar- nold et al. 2007, were estimated as the proportion of the canopy to the nearest 10% exhibiting chlorosis, necrosis or abscission in the canopy. Transpiration and stomatal conductance were measured on October 21, 1999 (Portable Photosynthesis System Model Li- 6200 with a CO2 to 10.2 cm (0 to 4 in) depth] and trunk temperatures (15.2 cm height) were monitored on May 6–18, 1999, using 10.2 cm (4 in) Cole-Parmer 400 series thermistor penetration probes attached to a logging Digi-Sense® scanning thermocouple thermometer (Cole- Parmer, Vernon Hills, IL). Three recently fully expanded leaves were selected from the south side of each tree for transpiration and stomatal conductance measurements. Throughout the second growing season, percent of the soil covered by the soil surface covers and the percentage of the soil surface covered by weeds were estimated monthly during the growing season to assess the efficacy of the soil surface cover in suppressing weed establish- ment. After weed estimates were recorded, the weeds were re- moved by hand weeding. Tree height, caliper at 15.2 cm above the soil surface, and foliar stress ratings were measured monthly dur- ing the growing season. Trees were harvested in December 1999. The statistical design was a completely random design and was analyzed using Proc GLM procedures in SAS system for Windows, Release 9.1 (SAS Institute Inc., Cary, NC). Dead trees were treat- ed as missing data points for measurements taken on dates after death. A oneway analysis of variance was used for measures taken on a single date, while those taken on multiple dates were analyzed as a two-way analysis of variance with soil surface treatments and dates as the main effects. When they were significant (P ≤ 0.05), treatment by time interactions were presented. If interactions were not found to be significant, then the main effects of treatments were tested. Where significant (P ≤ 0.05) effects were found, means were compared using the least squares means procedures. Study 2: Masonry Color Affects on Tree Establish- ment with Brick-on-Sand Pavement Texas Redbud Responses In April 2001, twenty of the planting pits were reestablished with Cercis canadensis var. texensis ‘Alba’ using four surface cover- age treatments with five randomly distributed replications of each treatment. The control was a bare or fallow soil surface. The other treatments consisted of three colors of decorative concrete brick- shaped pavers (Bermuda design pavers, Matt Stone, Inc., Tampa, FL) on a 5.1 cm deep bed of builder’s sand with an open space in the center for the tree. Brick colors ranged from a pale blond tan, red-brown, to a dark charcoal color. Bricks were chosen with the ©2009 International Society of Arboriculture
September 2009
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