Progression of Sugarberry (Celtis laevigata) Dieback and Mortality in the Southeastern United States

The southeastern United States has been experiencing unexplained sugarberry (Celtis laevigata) mortality for over a decade, representing one of the most severe and widespread Celtis mortality episodes ever reported from North America. Here we describe external symptoms, progression of mortality, and the known geographic extent of the problem. More than half of all trees monitored at one site within the affected area died over five years of observation. Although many trees died within a year of first exhibiting symptoms (e.g., small yellow leaves, branch dieback, premature leaf fall), many others continued living for years after becoming symptomatic. A preliminary insecticide trial found no improvements in survivorship among trees treated with insecticides, emamectin benzoate and imidacloprid, relative to control trees. Our findings suggest the problem will likely continue and become more widespread in the coming years. Study Implications Sugarberry mortality in urban and forested environments is an ongoing problem that has the potential to spread throughout the southeastern United States and perhaps more widely, depending on the susceptibility of other native Celtis species. Many trees die within a year of first showing external symptoms, whereas others can live for many years after appearing symptomatic. Declining trees in rights-of-way and public spaces are presenting costly hazards to cities, and canopy gaps in natural areas are likely to facilitate the establishment and spread of invasive plants. Studies aimed at determining the cause of this problem are urgently needed.

Mechanical Properties of Native Tree Species for Soil Bioengineering in Northeastern Mexico

<p>In recent years, the effect of soil bioengineering has played a very important role on slope stability. However, our area of study is constantly under the influence of small-scale earthquakes and extreme events of heavy rainfall which cause potentially unstable conditions on the slopes. The mechanical properties of the root systems tensile strength (T<sub>s</sub>) and modulus of elasticity (E<sub>root</sub>) of four native species were analyzed for a potential use as soil bioengineering elements. We investigated if tensile strength (N/mm<sup>2</sup>) and modulus of elasticity of roots (N/mm<sup>2</sup>) was different between studied species: <em>Cercis canadensis</em>, <em>Celtis laevigata</em>, <em>Quercus rysophylla</em> and <em>Ligustrum lucidum</em>. The species considered were selected based on their native characteristics and widespread existence on the slopes. Regarding tree forest species, the tests were conducted with the Universal Testing Machine Shimadzu type SLFL-100KN. The relationships among root diameter, tensile strength (T<sub>s</sub>), and modulus of elasticity (E<sub>root</sub>) was negative and could be fitted with a power regression equation, showing highly significant   values p<0.01.Celtis laevigata showed the maximum value of tensile strength (T<sub>s</sub>) 28.11 N/mm<sup>2</sup> while the minimum value of tensile strength was observed in <em>Ligustrum lucidum</em> 5.27 N/mm<sup>2</sup>. For the variable modulus of elasticity (E<sub>root</sub>) <em>Celtis laevigata</em>  showed the maximum value of 90.01N/mm<sup>2</sup> while the minimum value of modulus of elasticity was observed in <em>Ligustrum lucidum</em> 29.16 N/mm<sup>2</sup>.Results of mechanical proprieties are showed the following ascending order: <em>Ligustrum lucidum</em> < <em>Quercus rysophylla</em> < <em>Cercis canadensis</em> < <em>Celtis laevigata</em>. Likewise, <em>Celtis laevigata</em> showed the highest tensile strength and modulus of elasticity of all investigated species.</p><p> </p><p>Key words: root, tensile strength, modulus or elasticity.</p><p> </p><p> </p>

Torus Structure and Development in the Woods of Ulmus Alata Michx., Celtis Laevigata Willd., and Celtis Occidentalis L.

Pit membranes between tracheary elements of Ulmus alata, Celtis laevigata, and Celtis occidentalis often contained tori. The degree of development of tori varied and was greatest in those membranes connecting elements of small diameter. Complete tori consisted of two wall thickenings adjoined by a central layer. In three dimensions the shape of the torus often approximated a grooved wheel. Initiation of thickening in the pit membrane occurred first on the side of the older cell and was well underway prior to the beginning of secondary wall synthesis. Torus formation resulted from the thickening of the primary walls of the pit membrane. Development of the torus was associated with membranous vesicles and cisternae but not with microtubule complexes as was reported in Osmanthus. The pit membranes in this study are capable of aspiration, and the tori may prevent rupture of the pit membrane during this process.

Clearcutting Not Enough for Early Establishment of Desirable Species in Santee River Swamp

Woody species in a Santee River Swamp area were sampled before and three growing seasons after a summer clearcut. Basal area before harvest was 140 ft², 72% of which was sweetgum (Liquidambar styraciflua), sugarberry (Celtis laevigata), ash (Fraxinus spp.), laurel oak (Quercus laurifolia), and water oak (Q. nigra). Sugarberry dominated the regeneration 3 years after harvest in all but the larger size classes. Reproduction less than 3-feet tall occurred on 39% of the sampled area while 69% of the sampled area contained one or more stems 3 feet or taller. Regeneration species composition and spatial distribution was not considered acceptable and was attributed to the lack of postharvest treatment. Shearing or prescribed fire is recommended to dispose of residual stems and logging slash. Subsequent planting seed or seedlings of cherrybark oak (Q. falcata var. pagodifolia), water oak, or sweetgum should ensure an acceptable species composition.