|Kyrgyzstan - Yeti Oguz valley|
(N 42.30168°; E 78.30188°)
This mountain landscape shows the two main climatic constraints that limit tree growth on earth: low temperature and moisture deficit.
The white line marks the upper limit of north-exposed, dense stands of Picea shrenkiana, the Asian spruce. The treeline is located here at 2950 m.
By contrast, there is no visible treeline on south-exposed slopes and this is just because there are no trees there ! Why ? Remind we are in a semi arid continental climate and the most plausible explanation is water shortage (possibly in combination with grazing).
This striking distribution of forests can be seen in many different areas of the Tian Shan mountains : the spruce is restricted to a narrow elevational band and almost exclusively on north-exposed slope or deep valleys. The lower it would be too dry, the higher it would be too cold.