High Elevation Forest Discovered

On a steep, boulder-strewn mountainside in the Himalaya, clings a stand of juniper trees that holds the record for the highest forest growing north of the equator. The dense cluster of Juniperus tibetica was recently discovered at 4900 metres (16,076 feet) elevation in southeast Tibet.

Its largest trees reach just over 3 m in height and have single stems of 0.25 m diameter at breast height. This particular west-facing site might be conducive to trees surviving at an exceptionally high altitude because the deep valley below funnels dry winds from the south.

Laying claim to the highest-elevation treeline is fraught with controversy over defining what constitutes a tree. In this case, a woody plant with a single stem at least 3 m tall is considered a tree. Although the junipers extend another 30 m up the slope, there they are shaped more like bushes than trees, with gnarly form and multiple stems. Lower down, the junipers grow up to 6 m tall, and it appears even larger trees were once felled.

There are only a few other records of trees surviving anywhere close to this elevation in the northern hemisphere. Individual Juniperus tibetica trees have been discovered growing at 4850 m at scattered locations in southern Tibet, the only region where this species exists. A related species, Juniperus indica was found at 4750 m where a 3-metre tall, single-stemmed tree stands rooted to a precipitous, southeast-facing slope in northern Bhutan.

The rarefied Himalayan junipers persist in an ecotone pattern seen elsewhere at high-elevation treelines, such as in southern Ethiopia. At their uppermost reach, closed stands of upright trees give way to a few scattered, short and shrubby individuals.