Leaf and Stem Cold Hardiness of 17 Broadleaf Evergreen Taxa

The leaves and stems of 17 broadleaf evergreen taxa were screened for cold hardiness in laboratory tests. Leaves of Ilex were generally less cold hardy than stems. However, the leaves of I. × koehneana ‘Wirt L. Winn’, Ilex latifolia and Ilex ‘Lydia Morris’ were equal to or more cold hardy than the stems. Maximum cold hardiness of most taxa occurred in mid-January. Ilex opaca, Ilex opaca, ‘Greenleaf’, and Ilex × attenuata ‘Foster's #2,’ were the most cold hardy. Among the Ilex × attenuata cultivars, ‘Foster's #2’ was more cold tolerant than ‘Savannah’ and ‘East Palatka.’ Ilex latifolia and Ilex ‘Lydia Morris’ were least cold hardy. I. ‘Nellie Stevens’ and I. × koehneana ‘Wirt L. Winn’ were intermediate. Osmanthus heterophyllus ‘Gulftide’ was the hardiest tea-olive, followed by Osmanthus americanus, Osmanthus × fortunei and Osmanthus heterophyllus ‘Rotundifolius’. Prunus laurocerasus ‘Zabeliana’ was hardier than ‘Schipkaensis’ than ‘Otto Luyken’. The actual differences, however, were slight.

Comparative field water relations of four co-occurring forest tree species

Diurnal patterns of stomatal resistance and leaf water potentials were measured in individuals of Ilex opaca Ait., Cornus florida L., Liriodendron tulipifera L., and Acer rubrum L. growing in close proximity on the same field site. The field measurements indicated patterns of stomatal performance and water potentials which differed diurnally, seasonally, differed between species, and differed by tissue age class in Ilex opaca. Liriodendron and Cornus developed patterns of midday stomatal closure as a drought period progressed; Ilex and Acer did not undergo marked midday stomatal closure. Young Ilex leaves consistently showed higher stomatal resistances than older leaves on the same plant early in the season; these differences were gone by the time the young leaves were about 2 months old in mid-July. Cornus developed the most negative water potentials, and Ilex showed the highest water potentials during the drought period.The measured differences suggested differences in water-use patterns among the species such that they may have temporally segregated water-related activity patterns, and may thus temporally partition the water resource.