Hardwood Species Show Wide Variability in Response to Silviculture during Reclamation of Coal Mine Sites

Coal is a significant energy source for the United States, and reclamation of surface mined lands is required under the Surface Mining Control and Reclamation Act of 1977. Reforestation of mined lands is challenging due to soil substrate properties including soil compaction, herbaceous competition, and animal browse, necessitating silvicultural treatments to help overcome such limiting factors. We investigated the field performance of black walnut (Juglans nigra L.), northern red oak (Quercus rubra L.), and swamp white oak (Quercus bicolor Willd.) planted on two mine reclamation sites in southern Indiana, USA, and evaluated the interactions of nursery stocktypes (container and bareroot), herbicide application, and tree shelters. Two-year survival averaged 80% across all species and stocktypes. Container stocktype had greater relative height and diameter growth (i.e., relative to initial size at planting), whereas bareroot had greater absolute height and diameter growth corresponding to initial stocktype differences. Shelter use increased height growth and reduced diameter growth across both stocktypes. Swamp white oak (Q. bicolor) had the highest survival rate and field performance regardless of silvicultural treatment, whereas red oak (Q. rubra) and black walnut (J. nigra) showed strong early regeneration responses to silvicultural treatments. Container seedlings showed promise as an alternative to bareroot seedlings to promote early growth on mine reclamation sites. Species-specific responses documented here indicate the need to consider the ecology and stress resistance of target species in developing cost-effective silvicultural prescriptions.

Comparing the Missouri Gravel Bed and a Wood Chip Production Method for Tree Growth

Tree root defects from current nursery production practices influence short- and long-term tree performance and survivability. The Missouri Gravel Bed (MGB) system, a production method using gravel as a substrate, has been used to prevent many of these defects from occurring. MGB production involves planting bare root stock into a bed of gravel with frequent drip irrigation in order to produce a root system with relatively few defects. MGB production methods have also been purported to allow for summer transplanting of many species, as opposed to traditional dormant transplanting.Because gravel has low water- and nutrient-holding capacity, biochar (5% by volume) was incorporated into one plot as a possible means of improving both water- and nutrient-holding capacity over gravel alone. Wood chip mulch was also investigated as a growing substrate in place of the gravel in a growing system. In 2015, three species, Quercus bicolor (swamp white oak), Taxodium distichum (baldcypress), and Tilia cordata (littleleaf linden), were studied in pea gravel (PG), biochar-amended pea gravel (BC), and wood chip mulch bed (MB) growing environments. Very few differences occurred over the growing season with above- or belowground parameters indicating that the minimal-to-no-cost, more readily available substrate of wood chip mulch should be considered in these growing systems.

Screening Oak Hybrids for Tolerance to Alkaline Soils

This study evaluated a diverse range of oak (Quercus) hybrids for tolerance to alkaline soils, which is a common site condition in urban landscapes that often limits the growth and longevity of many tree species. Different oak hybrids display varying severities of iron-deficiency induced leaf chlorosis when grown in a highly alkaline medium. Severity of leaf chlorosis was found to vary between different maternal parent species, with the results suggesting that hybrids with the maternal parents Q. macrocarpa (bur oak), possibly Q. muehlenbergii (chinkapin oak), and Q. ‘Ooti’ (ooti oak), are more likely to maintain healthy green leaf color when growing in a highly alkaline medium. These findings suggest that breeders interested in developing oak hybrids that are both cold-hardy and tolerant of alkaline soils should utilize these species in their crosses, and avoid Q. bicolor (swamp white oak), hybrids of which were generally found to be intolerant of alkaline soil. This study is one phase of a long-term project underway at Cornell University's Urban Horticulture Institute to select superior urban-tolerant cultivars of oak hybrids for future introduction into the horticulture industry.

Cutting Back Stock Plants Promotes Adventitious Rooting of Stems of Quercus bicolor and Quercus macrocarpa

Studies were conducted to investigate the severity of cutting back stock plants on adventitious rooting of layered stems and stem cuttings of Quercus bicolor Willd. (swamp white oak) and Quercus macrocarpa Michx. (bur oak). Rooting averaged 77% in Q. bicolor and 70% in Q. macrocarpa layered stems from the cutback stock plant group, compared to air layered stems from intact plants which averaged 1% in Q. bicolor and 0% in Q. macrocarpa. In another experiment cuttings were taken from three stock plant heights [4 cm (1.6 in), or 100 cm (39.4 in) stumps and intact plants ∼ 170 cm (66.9 in)] which were either etiolated or grown in natural light and rooted under mist. The best rooting (59%) and average number of roots (9.3) were found in etiolated Q. bicolor cuttings taken from 4 cm (1.6 in) stumps. Q. macrocarpa cuttings rooted poorly with only 7% of the cuttings rooting. By taking cuttings a week earlier for rooting (2 weeks, at the softwood stage), rooting in Q. macrocarpa was possible, with the best rooting (46%) found in etiolated cuttings taken from 4 cm (1.6 in) stumps. Overall, the highest rooting and greatest number of roots occurred in etiolated layers and cuttings from the 4 cm cutback group. Rooting generally increased with increasing extent of stock plant cutback

The Effects of Pruning on Drag and Bending Moment of Shade Trees

Arborists assume that pruning can help reduce the risk of tree failure by reducing the pressure exerted on trunks by wind (drag-induced bending moment), but there are few studies that quantify this effect. We simulated wind by driving trees in the back of a pickup truck from 0 to 24.5 m/s (0 to 55 mph) and measured drag-induced bending moment as well as tree morphometric data for Freeman maple (Acer × freemanii), swamp white oak (Quercus bicolor Willd.), and shingle oak (Quercus imbricaria Michx.). Measurements were taken before and after application of one of three American National Standards Institute A300 pruning types (raising, reduction pruning, thinning). Reduction of drag-induced bending moment differed by pruning type, largely in accordance with the mass of foliage and twigs removed. The effectiveness of pruning types was also species-dependent because crown architecture affected how much mass each pruning type removed. In general, per unit of mass removed, reduction pruning more effectively reduced the drag-induced bending moment than thinning or raising. Reduction pruning reduced the center of pressure height and, presumably, increased crown porosity after pruning. Prediction of the reduction of drag-induced bending moment was not reliable based on reduction in crown area after pruning. We discuss the practical applications of our findings.

Growth of three oak species during establishment of an agroforestry practice for watershed protection

Tree species that provide early benefits for farmers can serve to increase the adoption of temperate agroforestry practices. Growth of pin (Quercus palustris Muenchh.), swamp white (Quercus bicolor Willd.), and bur oak (Quercus macrocarpa Michx.) saplings was evaluated in an agroforestry practice designed for watershed protection in northern Missouri, USA, to identify species that provide early productive and protective functions. Large, containerized oak seedlings were planted in the center of 4.5-m-wide contour grass-legume strips established at 22.8- to 36.5-m intervals on a 4.44-ha watershed with a corn (Zea mays L.) – soybean (Glycine max (L.) Merr.) rotation. Sapling survival, height, and diameter growth were annually recorded during five growing seasons. Branch and leaf mass were also recorded in the two last measuring years. Preliminary assessment of rooting pattern was made based on the relative abundance of horizontal and vertical main roots. Mean shoot growth rate of pin oak was the highest during the whole study period, while swamp white and bur oak grew at the same rate until the fourth growing season. During the fifth growing season, growth rate of bur oak was the lowest. The root system of pin oak appears to be concentrated close to the tree, thus strengthening the buffer strips and competing least with the crop. The shallow root system of swamp white oak may best scavenge leaching nutrients from subsurface flow, thus reducing nonpoint source pollution. Sapling survival, growth rate, and rooting pattern suggest that pin oak and swamp white oak have a better potential for agroforestry practices in the Midwest than bur oak.