Five tree species, Platanus occidentalis L., Fraxinus americana L., Quercus palustris Muench., Liriodendron tulipifera L., and Gleditsia triacanthos L. f. inermis (L.) Zabel were wounded for 4 consecutive years. Four whorls of circular wounds or one whorl of elliptical wounds were cut into the trunk at widths of 10, 13, 17, and 25 mm. Tree growth was not measurably reduced by trunk wounding. Wound closure per unit of radial growth differed by species and annual growth.
Trunk wounds and branch pruning wounds were made on 5 to 7 m tall white ashes, honey locusts, and pin oaks. The amount of healing of each wound and the amount of trunk growth of each tree were measured for 3 years. The rate of healing of wounds was directly correlated with radial growth of the tree. Elliptical wounds, originally 50 mm wide, on all 3 tree species, decreased in width each year by 2.6 mm per 1 mm radial growth. The single most important dimension of a wound affecting rate of healing was width. The variables of wound shape, facing direction, height, and type of wound dressing affected rate of healing little, if at all. Healing of wounds occurred during the season of the year when trunk growth occurred.
The hypothesis that wounds on all species and sizes of trees heal equal amounts per unit of radial growth was not confirmed by this experiment. Tree species affected rate of healing as did size of wound. The rate of healing for soft maple and American elm (Ulmus americana L.) was significantly greater than for white ash (Fraxinus americana L.), pin oak (Quercus palustris Muench.), tulip tree (Liriodendron tulipifera L.), and honey locust [Gleditsia triacanthos f inermis (L.) Zabel].
The wound-healing process in cuttings of Pelargonium X hortorum L.H. Bailey cv. Yours Truly was studied using histological and histochemical techniques. Anatomical changes at the wounded surface of cuttings within 24 hours included deposition of a granular, amber-colored substance identified as suberin on the cell walls, in the intercellular spaces, and in the lumina of xylem vessels. Wound xylem, adventitious root primordia, and wound callus developed within 7 days. A periderm developed 14 to 21 days after wounding and its cell walls were suberized.
Seventeen commercial products containing 11 herbicides used to control weeds in lawns were tested at rates recommended by the manufacturers and at three times the recommended rate in plots of established white ash and pin oak trees for three consecutive seasons. Bandane, benefin, bensulide, 2,4-D, DCPA, DSMA, siduron, silvex, 2,4,5-T, and trifluralin were not phytotoxic but dicamba consistently caused phytotoxic symptoms especially at the high dosage. Tree species sensitivity to dicamba varied with rate of application, soil type, and amount of rainfall. White and blue spruce trees were readily killed; tulip trees, honey locust, pin oak, and linden trees suffered twig die back; walnut, ash, maple, and redbud trees suffered leaf distortion and red cedar trees were unaffected.