Arboriculture & Urban Forestry 36(4): July 2010 not sliced, and field-grown), in each of 30 blocks. The 120 trees were planted in five rows 2.7 m apart. Weeds in a 1.8 m wide strip down each row were kept in check with periodic applications of Gly- phosate. Surface between weed-free strips was mowed regularly. Maintenance Trees were irrigated (Table 1) roughly in accordance with the ir- rigation schedule shown to encourage post-planting survival in Florida (Gilman et al. 1998). Irrigation for 170 L containers and field-grown trees was delivered to the root ball surface through three low-volume Roberts spray stakes (Roberts Irrigation Pro- duces, Inc., San Marcos, CA), equally spaced at the edge of the root ball and directed toward the trunk. Irrigation for 57 L con- tainers was delivered to the root ball surface through one low-vol- ume Roberts spray stake positioned at edge of root ball directed toward the trunk. Immediately after planting, strategy for the first three months was to periodically interrupt the irrigation schedule designed to encourage survival with short periods of moderate stress. Stress was induced by withholding irrigation for two or more days beginning 12, 28, 76, and 104 days after planting. Trees were irrigated in late afternoon on each of these four days follow- ing stress measurement. Live oak trees of this size receiving daily irrigation in the nursery—such as trees in this study—are known to stress, drop foliage, or die without regular irrigation following planting in Florida (Gilman 2001). Trees were stressed consid- erably beginning 104 DAP by withholding all irrigation for 33 days. Rainfall during that period was 13 cm, which was 20 cm be- low normal. Trees were irrigated daily beginning 137 DAP (July 26, 2005) through 186 DAP (September 13, 2005) to help them overcome obvious water stress that resulted from this extended 33-day dry period. No irrigation was applied in 2006 or 2007 through end of the study in November 2007 with two exceptions because of exceptionally dry weather. One irrigation occurred 423 days after planting (May 29, 2006), and one 433 days after planting (June 8, 2006), when trees appeared moderate to severely stressed (foliage drop on some trees was measured as described below) due to drought in the normally hot dry weather of May. Trees were fertilized after planting into landscape field soil with 100 g of 16-4-8 (N:P:K) per tree, applied to a 91 cm diam- eter area around the trunk in March, April, and September 2005. In 2006, 400 g of 16-4-8 were similarly applied to each tree in April, June, and September. In April 2006, lower trunks were cleaned of all branches from the ground up to lower crown 1.4 m from ground; no other pruning was conducted during the study. 185 Measurements Trunk caliper, tree height (height from ground to top of crown), and crown spread [(maximum crown spread + crown spread perpendicular to maximum) ÷ 2] on each tree were measured when planted into landscape field soil and in September of each year. Roots were excavated nondestructively April 2006 (386 DAP), in the east and west directions (i.e., within weed- free soil in rows), until root tips farthest from trunk were found. Preliminary excavations indicated that roots farthest from trunk were growing just under soil surface. Root spread was record- ed as distance from trunk to edge of root system. Defoliation in drought was evaluated May 18, 2006 (400 DAP) on all four trees in 14 randomly selected replicate blocks due to consider- able foliage discoloration and leaf drop. Visual estimates of de- foliation were made by two assessors standing next to each tree. Both assessors had to agree on defoliation amount: None (1) = no defoliation; some (2) = up to about one-third of foliage on ground; medium (3) = between one-thirds and two-thirds of foli- age on ground; heavy defoliation (4) = most foliage on ground. Xylem water potential 12:00 to 14:00 hour on sunny or mostly sunny days was measured on all four trees in eight ran- domly selected blocks (four planting treatments x eight replicate blocks = 32 trees), periodically (Figure 1), for 463 DAP with a pressure bomb (Soil Moisture Inc., Santa Barbara, CA). Ter- minal portions of stems of current year twigs in full sun on the south side of crown half way up crown were cut roughly 10 cm long. Pressure in the air-tight chamber was increased at a con- stant rate of 30 seconds per MPa. Pressure was recorded when cut stem surface became uniformly wet. Water stress on trees in the same eight blocks was measured at each measurement date. Statistical Analysis Trunk caliper, tree height, crown diameter, defoliation rat- ing, root system radius, and root:crown spread were compared among four landscape planting treatments using one-way analy- sis of variance (ANOVA) in a randomized complete block de- sign. Xylem water potential means were analyzed with one-way ANOVA for each point in time. Means were compared using Duncan’s multiple range test. Defoliation severity data was ana- lyzed as a Poisson distribution and log transformed for analysis using GENMOD procedure because data was discrete; means were compared using CONTRAST statement. SAS Institute Inc. (Cary, NC) analytical software was used for all analysis. Table 1. Irrigation schedule in the 432 days following landscape installationz Days after planting 1–11y Irrigationw Irrigationv volume 76 (L) per tree for 57 L containers volume 76 (L) per tree for field grown and 170 L containers z 57 28 28 28 28 57 28 Trees planted into field soil March 24 through April 3, 2005. Day 1 was April 4, 2005. y Applied every other day. x Applied daily. w Irrigation delivered in late afternoon to root ball surface through one low-volume Roberts spray stake (Roberts Irrigation Produces, Inc., San Marcos, CA). v Irrigation delivered in late afternoon to root ball surface through three low-volume Roberts spray stakes. ©2010 International Society of Arboriculture 28 28 28 57 680 57 4304 12 15 18–28y 10 10 10 40 42 46 48–90y 10 10 20 10 of Cathedral Oak live oak trees. 98 102 104 137–186x 10 10 10 20 423 432 Total irrigation applied 227 20 1434
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