Tree Shape and Resistance to Uprooting : A Simple Model Analysis

We examined tree resistance to uprooting in relation to tree shape using a simple, qualitative model for the ratio of the resistive moment to the overturning moment. For this analysis, we used model trees and varied the crown size for a fixed stem size for a ratio of crown mass to stem mass that varied from 0.1 to 1. The results predicted the phase transition in the resistance trend in relation to the crown mass/stem mass ratio. Resistance increased on both sides of the crown mass/stem mass ratio, and was minimized at intermediate ratios. This indicates that crown expansion contributes to resistance to the right side of minimum, and vice versa. The same trend was recognized for actual Sitka spruce tree data. These results were consistent with previous observations of tree resistance to uprooting: trees with a small slenderness ratio (ratio of height to diameter at breast height) are resistant to uprooting, and trees/stands are vulnerable to uprooting after thinning, especially after belated thinning. We recommend sparse tree densities in plantations to manage the risk of physical tree damage such as overturning and stem failure. However, quantitative analyses of wind damage to trees and stands are necessary to improve risk management of plantations. The results of this study can be incorporated into such quantitative analyses

Both stem and crown mass affect tree resistance to uprooting

To examine the hypothesis that both stem and crown mass affect the resistance of a tree to uprooting and that tree resistance increases with the increase in crown mass, we conducted tree-pulling experiments on three Picea glehnii plantations (stands A, B, and C: 27-32 years old) that differed in tree density and slenderness ratio. Allometries between crown and stem masses and between the critical uprooting moment and stem mass differed significantly among the three stands, with the crown mass and critical moment significantly larger in Stand C than in Stands A or B, despite the same stem mass. These results quantitatively verified our hypothesis. Allometries between crown and stem masses and between critical uprooting moment and stem mass were highly significant in each stand but were stand specific. Therefore, these allometries can be used to estimate tree resistance to uprooting in a given stand but not for data compiled from stands of various conditions and tree shapes. The allometry between critical moment and aboveground mass did not differ among the three Picea stands; thus, it is not stand specific and is generally appropriate to use for estimating tree resistance. To increase tree resistance to uprooting, we recommend light management for Picea glehnii plantations and probably other coniferous plantations as well

Observation of Diurnal Ground Surface Changes Due to Freeze-Thaw Action by Real-Time Kinematic Unmanned Aerial Vehicle

Ground surface changes caused by freeze-thaw action affect agriculture and forestry, as well as artificial structures such as roads. In this study, an area is examined in which reforestation is urgently needed but the growth of naturally restored seedlings and planted trees is impaired by freeze-thaw action. Thus, a method of measuring freeze-thaw induced ground surface changes and mitigating their negative impacts is needed. Real-time kinematic unmanned aerial vehicle and structure-from-motion multiview stereophotogrammetry are used on slope-failure sites in forest areas to observe the ground surface changes caused by freeze-thaw action over a wide area, in a nondestructive manner. The slope characteristics influencing the ground-surface changes were examined, and it was confirmed that it is possible to observe minute topographical changes of less than ±5 cm resulting from freeze-thaw action. Statistical models show that the amount of freeze-thaw action is mostly linked to the cumulative solar radiation, daily ground-surface temperature range, and topographic-wetness index, which influence the microscale dynamics of the ground surface. The proposed method will be useful for future quantitative assessments of ground-surface conditions. Further, efficient reforestation could be implemented by considering the effects of the factors identified on the amount of freeze-thaw action