The Height Trap: Why Growing Taller Spells Decline for a High-Altitude Shrub

For many organisms, growing tall is a sign of success. Yet for the widespread Hippophae rhamnoides shrub on the Qinghai-Tibetan Plateau, height is a fatal flaw. Scientists investigating its decline found that it suffers from a problem usually documented in towering trees: hydraulic limitation.

The study reveals that as these shrubs grow taller, their internal plumbing struggles. The efficiency of water transport from roots to leaves—known as hydraulic conductivity—decreases significantly. This, in turn, hampers their ability to photosynthesise and create energy. The plant has a coping mechanism—reducing its sapwood density to improve water flow—which allows it to survive for decades even after decay begins.

However, this adaptation is not enough. The research also uncovered a fascinating difference between the sexes. During their decline, taller male shrubs showed poorer hydraulic function than females. Ultimately, despite its compensatory strategies, the physical strain of lifting water proves too much, driving the decline of this important shrub.