Procerum root disease (PRD) is a serious problem in eastern white pine (Pinus strobus L.) Christmas tree plantations in VIrginia. Procerum root disease is caused by Leptographium procerum (Kendr.) Wingf which is believed to be transmitted by the pales weevil Hylobius pales (Herbst). Symptoms of procerum root disease include reduced shoot elongation, reduced leaf conductance, low photosynthetic activity, low pre-dawn water potential and chlorosis of foliage. Resinous occlusion of the sapwood at the root collar is the likely cause of the suite of symptoms that resemble water stress. Increased incidence ofPRD has been associated with trees growing in poorly drained soils in low lying areas. Two studies were undertaken to explore the relationship of site factors and vascular conductivity of sapwood to the expression ofPRD symptoms in P. strobus. In the first study, plots were established in a variety of drainage classes in two Christmas tree plantations. Leaf conductance was monitored periodically in conjunction with measurements of soil factors to assess the role of abiotic factors on foliar symptom expression. At the termination of the field monitoring, trees were harvested and three vascular disease severity variables were measured: hydraulic conductivity of sapwood, percent basal occlusion and sapwood moisture content. These disease severity variables describe the permeability of sapwood to water and the relative hydration of the sapwood. Reduced leaf conductance was associated with reduced stem hydraulic conductivity, reduced sapwood moisture content and increased basal occlusion. Increased vascular disease severity and foliar symptom expression were associated with increased soil moisture content and several other factors that relate to soil moisture retention (percent slope, total porosity, textural class and bulk density). The second study was initiated to study the development of PRD in artificially inoculated P. strobus seedlings exposed to three soil water classes: droughty, optimum and saturated. Seedlings in the optimum soil water class exhibited the greatest biomass accumulation and shoot elongation, while seedlings in droughty showed the least. No negative effects of L. procerum inoculation and no symptoms ofPRD were observed eight months after inoculation regardless of the soil water class. / Master of Science

To evaluate the compression wood response in eastern white pine (Pinus strobus L.) following a severe ice storm in 1994, 47 trees were felled in 2007 and cross-sectional samples were collected at 0.5 (±0.2) m stem height. The disks were sanded and digitally scanned, and the cross-sectional area (mm2) of compression wood within each tree-ring was quantified using image analysis software. Topographic data (slope, aspect, and elevation) were also recorded for each P. strobus tree, along with a modified competition index. Wood anatomical features were also quantified in the three years before and after the storm along a tree diameter gradient. Although tree age was relatively constant in this stand, tree size was influenced by topographic position; larger trees grew in the valley while smaller trees were found growing in thin soils at the mid-slope position. When the cohort was about 25 years old, ice deposition caused a heterogeneous compression wood response which was highly related to tree size. In the thirteen years following the ice storm, the 6 – 9 cm (2007) diameter class formed significantly more compression wood area than any other, followed by the 10 – 13 cm (2007) diameter class. The tree diameter range that formed the most post-storm compression wood was 4 – 8 cm at the time of the storm, suggesting that this diameter range was most affected by 8.5 cm of ice loading in P. strobus. Trees > 18 cm in 1994 did not form any compression wood after the storm, but many experienced a growth release to fill canopy gaps. Topographic variables did not influence compression wood formation directly, but only one plot was sampled so these results are tenuous. However, topography did influence tree size which was the most important predictor in compression wood. There was no relationship between compression wood area and competition index. Due to compression wood formation after the ice storm, cell wall thickness and cell circularity were significantly higher in the 1994 tree-ring than in other rings examined (1991 – 1993, 1995, and 1996). Tracheid and lumen diameters were significantly smaller in compression wood cells (30.5 and 19.5 μm, respectively) than in normal wood (36.8 and 28.4 μm, respectively); opposite wood cells were intermediate in size (32.4 and 24.4 μm, respectively). Due to small tracheid size, compression wood contained significantly more cells mm⁻¹ (33) than normal wood (27), but no significant differences in cell wall area. Therefore, cumulative cell wall area occupied 47% of the cross-section in compression wood tissue on average, compared to 31% in normal wood. Dispersing tree weight across a greater surface area may help compression wood to prop up a bent tree, but reduced lumen area may also impact hydraulic conductivity in the stem. / Master of Science

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