Pictures below are of spiral Ponderosa pine trees and logs, they were shot at the rim of Bryce Canyon , probably the weirdest place at Earth. As you may see from the photos, the angle of spirals is typically about 30 o to the vertical, but may vary. The elevation is 8,000-9,000 feet. July is the warmest month, with an average daytime high temperature of 83 o F and a nighttime low of 47 o F. Spring and fall weather is highly variable. Cold winter days are offset by high altitude sun and dry climate.
Winter nights are sub-freezing.
During some winters, Alaskan cold fronts descend on the Colorado Plateau region bringing temperatures as low as -30 o F. Annual snowfall averages 95 inches. Much of the area's precipitation comes as afternoon thundershowers during mid to late summer. One may guess that the spirals increase survivability of trees, that is its resistibility to strong winds, sharp temperature change, etc. The mechanical properties of the trunks can be reliably modeled and the loading conditions can be calculated too. Therefore, the survivability can be viewed as a problem of mechanics of fracture.