Thick bark can protect trees from a severe ambrosia beetle attack

Thick bark has been shown to protect trees from wildfires, but can it protect trees from an ambrosia beetle attack? We addressed this question by examining the distribution of holes of the invasive Kuroshio Shot Hole Borer (KSHB, Euwallacea kuroshio; Coleoptera: Scolytinae) in the bark of Goodding’s black willow (Salix gooddingii), one of the KSHB’s most-preferred hosts. The study was conducted in the Tijuana River Valley, California, in 2016–17, during the peak of the KSHB infestation there. Using detailed measurements of bark samples cut from 27 infested trees, we tested and found support for two related hypotheses: (1) bark thickness influences KSHB attack densities and attack locations, i.e., the KSHB bores abundantly through thin bark and avoids boring through thick bark; and (2) bark thickness influences KSHB impacts, i.e., the KSHB causes more damage to thinner-barked trees than to thicker-barked trees. Our results indicate that thick bark protects trees because it limits the density of KSHB entry points and thereby limits internal structural damage to low, survivable levels. This is the first study to identify bark thickness as a factor that influences the density of KSHB—or any ambrosia beetle—in its host tree, and the first to link bark thickness to rates of host tree mortality.

Determining an Optimum Tree Species for the Phytoremediation of Cumene and 4-Cumylphenol in Groundwater

Cumene and 4-cumylphenol are the primary constituents of concern in a groundwater plume at a chemical facility located in Plaquemine, Louisiana. Phytoremediation, a method that uses plants to remove contaminants from water and soil, was posed as a solution to removing the constituents of concern and creating hydraulic control of the plume. Five tree species, eastern redcedar, bald cypress, black willow, eastern cottonwood, and water oak, were chosen as potential remediators. Eastern redcedar and water oak did not tolerate the saline, contaminated water. Bald cypress, black willow, and eastern cottonwood trees were irrigated with deionized water, deionized water containing 0.5 mg·L−1 (0.5 ppm) cumene and 1 mg·L−1 (1 ppm) 4-cumylphenol as the low concentration, or deionized water containing 1 mg·L−1 (1 ppm) cumene and 4 mg·L−1 (4 ppm) 4-cumylphenol referred to as the high concentration. Both bald cypress and black willow were the best tree species for remediation of the groundwater as they were able to sequester the constituents of concern in their lower root tissue. Mean concentration of 4-cumylphenol detected in bald cypress roots at the end of the study were 1.72 mg·kg−1 in the low concentration water treatment and 1.50 mg·kg−1 in the high concentration water treatment. Mean concentration of 4-cumylphenol detected in black willow roots at the end of the study were 16.58 mg·kg−1 in the low concentration water treatment and 25.65 mg·kg−1 in the high concentration water treatment. Bald cypress was ultimately chosen for full scale planting in the fall of 2008.

Screening Selected Gulf Coast and Southeastern Forest Species for Susceptibility to Phytophthora ramorum

Phytophthora ramorum, the causal agent of sudden oak death, poses a threat to woody plants in the rest of the United States. Several plant species native to Gulf Coast and southeastern US forests were tested for reaction to P. ramorum, including eastern baccharis (Baccharis halmifolia), spicebush (Lindera benzoin), yaupon (Ilex vomitoria), southern magnolia (Magnolia grandiflora), sweetbay magnolia (M. virginiana), Virginia creeper (Parthenocissus quinquefolia), black willow (Salix nigra), and baldcypress (Taxodium distichum). The foliage of each species was inoculated with a zoospore suspension and placed in a dew chamber for 5 days. The average percentage of leaf area necrosis was 0.2, 4.9, 27.9, 32.1, 8.6, 1.5, 1.1, 0.2, and 5.0% for inoculated eastern baccharis, spicebush, yaupon, southern magnolia, sweetbay magnolia, Virginia creeper (Louisiana), Virginia creeper (Maryland), black willow, and baldcypress, respectively. Comparison of the percent necrotic leaf area between inoculated and non-inoculated plants showed significant differences (P ≤ 0.05) for yaupon (P = 0.0008), southern magnolia (P = 0.001), and sweetbay magnolia (P = 0.0009). The other species did not show significant differences although infection was confirmed on spicebush, Virginia creeper, and baldcypress. This is a first report of yaupon, sweetbay magnolia, and baldcypress being hosts of P. ramorum. Accepted for publication 2 April 2013. Published 30 July 2013.