Over three growing seasons (2003 through 2005) we investigated stem area increase and shoot growth of field-grown (FG) trident maple (Acer buergeranum), hedge maple (A. campestre), autumn blaze maple (A. × freemanii ‘Autumn Blaze’), shantung maple (A. truncatum), Mexican redbud (Cercis canadensis mexicana), Texas redbud (C. canadensis texensis), white Texas redbud (C. canadensis texensis ‘Alba’), Oklahoma redbud (C. canadensis texensis ‘Oklahoma’), Washington hawthorn (Crataegus phaenopyrum), Arizona ash (Fraxinus velutina coriacea ‘Bonita’), Mexican plum (Prunus mexicana), chinquapin oak (Quercus muehlenbergii), English oak (Q. robur) trees subjected to three reference evapotranspiration (ETo) based irrigation regimes (100, 60, and 30% ETo). For maple trees, stem area increase did not differ between irrigation treatments. However, except for trident maple shoot elongation varied with irrigation level and species. Stem area did not differ between irrigation regimes for redbud trees, and shoot elongation was generally greatest for trees that received lower irrigation treatments. Depending upon species, oak stem area increase did not differ, or was greatest for trees that received greater irrigation. For each oak species, shoot elongation was influenced by irrigation level. For two of the three remaining species, stem area increase and shoot elongation differed according to irrigation volume. Despite three differing irrigation volumes, greatest growth was not always associated with increased irrigation volume. In addition, each species appears to be suited for regions with low precipitation and high pH soils.

Experiments investigated the influence of drought conditioning stock plants and an auxin-based plant growth regulator (PGR) on adventitious root formation of terminal stem cuttings taken from containerized firebush and Fraser's photinia stock plants. Drought conditioning (DC) treatments were initiated in a glass greenhouse and included: irrigation every day (no DC), irrigation every other day (medium DC), and irrigation every fourth day (high DC). Plants were subjected to DC for 16 consecutive days. Following DC treatments, all plants were irrigated and left overnight. Terminal stem cuttings were taken the following day and an 0.3% auxin talc formulation was used as the PGR. Plant growth regulator/DC treatments included: no DC ± PGR, medium DC ± PGR, and high DC ± PGR. Cuttings were placed under intermittent mist and heating pads maintained media temperature. After 21 and 78 days cuttings were evaluated for rooting percentage, number of roots, and length of the longest root. For firebush, rooting percentage was near 100% for all treatments. Number of roots and length of longest root for firebush cuttings was greatest for cuttings treated with PGR. For Fraser's photinia cuttings, rooting percentage was highest for cuttings treated with high DC + no PGR treatments. Cuttings treated with medium DC or high DC ± PGR treatment produced the greatest number of roots, while mean root length was longest for cuttings treated with medium DC + PGR and high DC + no PGR.

For three growing seasons (2003–2005) two newly planted, field-grown redbud (Cercis canadensis L.) varieties were subjected to three reference evapotranspiration (ETo)-based irrigation regimes (100, 66, and 33% ETo). Over this time period, water relations (pre-dawn leaf water potential), gas exchange (mid-day stomatal conductance), and growth data (trunk cross sectional area increase, tree leaf area, and shoot elongation) were measured. Pre-dawn leaf water potential (ψl) was more negative for trees receiving the least amount of irrigation, and for Mexican redbud [C. canadensis var. mexicana (Rose) M. Hopkins] trees. However, mid-day stomatal conductance (gs) was similar for Texas redbud (C. canadensis var. texensis S. Watson) trees across the three irrigation regimes, and was highest for Mexican redbud trees receiving the greatest amount of irrigation volume. Growth varied by variety and irrigation regime. Trunk cross sectional area increase was greatest for Mexican redbud trees, leaf area was highest for trees receiving the greatest amount of irrigation, and shoot elongation was greatest for trees receiving the 66% ETo irrigation regime. However, despite differing irrigation volumes, greatest gas exchange and growth was not necessarily associated with greatest irrigation volume. When considering conservation of precious water resources, these redbud varieties maintain adequate growth and appearance under reduced irrigation.

Gas exchange and growth of transplanted and nontransplanted, mulched and nonmulched field-grown Shumard red oak trees (Quercus shumardii Buckli.) were investigated in a semiarid climate. In Spring 2003, 12 field-grown trees were selected for uniformity. Six trees were moved with a tree spade and six trees were undisturbed. In addition, pine bark mulch was applied around three randomly selected transplant and nontransplant trees. Soil volumetric water content, predawn leaf water potential, midday stomatal conductance (g S) and leaf temperature, and growth data were collected over three consecutive growing seasons. Throughout the experiment, weekly predawn leaf water potential and g S data indicate transplanted trees with and without mulch were under greater water stress when compared with nontransplanted trees. In addition, nontransplanted trees with mulch were under greater stress when compared with nontransplanted trees without mulch. Each year, transplanted trees and nontransplanted trees with mulch had less apical growth when compared with nontransplanted trees without mulch. Although gas exchange and apical growth of transplanted trees and nontransplanted mulched trees tended to increase each growing season, by experiment termination, gas exchange and apical growth for transplanted trees and nontransplanted trees with mulch did not recover to nontransplanted, nonmulch tree levels.

Recent droughts and depleted water tables across many regions have elevated the necessity to irrigate field-grown (FG) nursery trees. At the same time, ordinances restricting nursery irrigation volume (often without regard to plant water requirements) have been implemented. This research investigated gas exchange and growth of two FG maple tree species (Acer × freemanii `Autumn Blaze' and A. truncatum) subjected to three reference evapotranspiration (ETo) irrigation regimes (100%, 60%, and 30% of ETo) in a semi-arid climate. During Spring 2002, nine containerized (11.3 L) trees of each species were field planted in a randomized block design. Each year trees were irrigated through a drip irrigation system. During the first growing season, all trees were irrigated at 100% ETo. Irrigation treatments began Spring of 2003. Gas exchange data (pre-dawn leaf water potential and midday stomatal conductance) were collected during the 2003 and 2004 growing seasons and growth data (shoot elongation, caliper increase, and leaf area) were collected at the end of each growing season. For each species, yearly data indicates irrigation regime influenced gas exchange and growth of these FG trees. However, it is interesting to note gas exchange and growth of these FG maple trees were not necessarily associated with trees receiving the high irrigation treatment. In addition, it appears the influence of irrigation volume on the growth of these FG trees is plant structure and species specific. Our data suggests irrigation of FG trees based upon local ETo measurements and soil surface root area may be a means to conserve irrigation water and produce FG trees with adequate growth. However, continued research on the influence of reduced irrigation on FG tree species is needed.