Pruning Severity and Crown Position Influence Aspect Ratio Change

Growth on one branch is suppressed in proportion to pruning severity, resulting in a predictable reduction in branch:trunk diameter (aspect) ratio. However, little is known about response to pruning multiple branches. Several of the largest branches on live oak (15.3 cm trunk diameter) were pruned with four severities (0%, 25%, 50%, and 75%), then branch, nearby stem, and trunk diameter were measured for five subsequent years. Rate of trunk diameter increase five years after pruning was greatest for trees pruned with the 25% severity. Aspect ratio on all three pruned and measured branches decreased with time after pruning, pruning severity, and increasing height in the crown. Mean aspect ratio ceased declining between three and five years after pruning. The decrease in aspect ratio over time and with increasing severity on pruned branches was less pronounced in the lower crown than in the upper crown. Smaller change in aspect ratio on pruned branches in the lower crown suggests that when structurally pruning trees, branches in the lower crown may require a higher pruning severity to effect the same change in aspect ratio as upper branches.

Use of Cast Post-and-cores for the Alteration of Crown Position for the Esthetically Compromised Patient

SUMMARY The authors describe the use of cast post-and-cores, which allow a change in position of the clinical crown to permit the fabrication of two fixed partial dentures. The two fixed partial dentures change the clinical appearance of the patient.

Effect of population size, tree diameter and crown position on viable seed output per cone of the tropical conifer Widdringtonia whytei in Malawi

The tropical montane conifer tree Widdringtonia whytei is found in small fragments on Mulanje Mountain in Malawi. A study was conducted with the objectives of determining the effect of population size, tree stem diameter and crown position on the proportion of viable seeds per cone produced by W. whytei at three sites (Sombani, Chambe and Lichenya) on Mulanje Mountain. Three population sizes, namely small (fragments with ≤10 cone-bearing trees), medium (fragments with 11–20 cone-bearing trees) and large (fragments with >20 cone-bearing trees) and isolated trees were sampled at each study site. In each fragment, four cone-bearing trees were randomly located, 20 mature cones were collected from each tree and the viability of seeds was tested. Only 23% of the seeds per cone were viable but seed viability per cone was highly variable among fragments. Large fragment populations produced the highest proportion of viable seeds per cone (30%), followed by similar proportions in small fragments (28.3%) and isolated trees (26.1%), with the lowest proportions in medium-sized fragments (18.7%), indicating a non-linear relationship between viable seed output per cone and population size. Tree stem diameter and crown position had no effect on the proportion of viable seeds per cone. Further studies are needed to identify the factors that lead to the low viable seed output per cone, and how this influences whole-tree seed production in W. whytei.

Grafting Fraser Fir (Abies fraseri): Effect of Scion Origin (Crown Position and Branch Order)

Success and subsequent growth of fraser fir [Abies fraseri (Pursh) Poir.] cleft grafts were studied in relation to origin and type of scion material in the tree crown. First- and second-order shoots (current-year) were collected from five zones in the crown, ranging from top to bottom, and grafted to 5-year-old fraser fir transplants in April. Success rates were similar for first- and second-order scions, whereas budbreak and subsequent growth were best for first-order scions. In general, results were best for first-order scions taken from the upper crown. Plagiotropism of grafts was similar for all crown zones and shoot types.

Soil and light effects on the sapling performance of the shade-tolerant speciesBrosimum alicastrum(Moraceae) in a Mexican tropical rain forest

Many studies conclude that light is the most important resource that determines plant performance of tree saplings in tropical rain forests, and implicitly suggest that soil resources are less important. To provide a quantitative test for soil versus light effects on sapling performance, we studied how saplings of the shade-tolerant tree speciesBrosimum alicastrumresponded to contrasting levels of light availability and soil fertility in a Mexican tropical rain forest. Therefore saplings were selected from ten low-light exposure (crown position index <1.5) and ten high-light exposure (crown position index ≥2.5) sites either on productive alluvial soils, or on poor sandy soils on adjacent hills. Annual growth responses were scored for 58 saplings. The soil–light interaction had a strong positive effect on branching rate and leaf area production, rather than light or soil alone. Height growth only increased at higher light availability. Herbivore damage was higher on the more productive soil and, to a lesser extent, at higher light availability. Our results suggest that saplings (1) responded differently to soil and light availability, (2) expanded in overall size when both soil and light limitations are released, but only increased in height with increasing light intensity (3) and faced a trade-off between expansion and defence along both soil and light gradients. This study emphasizes the role of soil resources, in interaction with light availability, on the plastic responses in saplings living in a tropical forest understorey.