Cloudiness can lower tree lines because it decreases the photosynthesis-to-respiration ratio, causing a carbon deficit. For example, the tree line is lower on the warmer, cloudier western coast of Scotland than it is on the colder, clearer eastern coast because on the west the cloudy weather limits photosynthesis, while the warmer temperatures promote respiration.

The factors that limit tree growth at high elevation and extreme latitude indirectly promote longevity, as in the case of the Great Basin bristlecone pine (P. longaeva). The factors involved are smaller tree size, slower growth rate (possibly mediated by lower night temperatures), larger allocation of carbon to roots as opposed to tops (stems and leaves), cold hardiness, efficient use of water, more reliance on asexual reproduction, and fewer pathogens in the environment.

Some long-lived trees, such as the Douglas fir (Pseudotsuga menziesii), have been found in lava beds, suggesting that reduced competition and the presence of fewer pathogens in this environment might be factors in the long life spans. This harsh environment probably also reduces the developmental rate, which is correlated with increased life span in some species.

The major difference between subarctic and subalpine timberline environments is that the subalpine environment has greater light intensity and more ultraviolet light, less variation in the length of the day, lower carbon dioxide, and more daily temperature variation. The subalpine also has higher precipitation, especially snow, but the soil is generally drier because of better soil drainage and the mountainous topography. The factors that are common to both are the short growing season, low temperatures, and high winds. Mountains located in arid areas may show additional complexity along elevational gradients owing to marked changes in both water availability and temperature. In the southwestern United States, small piñon pines may grow at the base of mountains, and, as elevation increases, temperature decreases along with water stress. Tree height increases as the larger ponderosa pines dominate; these in turn may give way to Douglas fir. At higher altitudes, spruce and fir predominate, and they decrease in height with altitude, forming tree lines at the upper limits.