Past the climate optimum: Recruitment is declining at the world's highest juniper shrublines on the Tibetan Plateau

Abstract

Alpine biomes are climate change hotspots, and treeline dynamics in particular have received much attention as visible evidence of climate‐induced shifts in species distributions. Comparatively little is known, however, about the effects of climate change on alpine shrubline dynamics. Here, we reconstruct decadally resolved shrub recruitment history (age structure) through the combination of field surveys and dendroecology methods at the world's highest juniper (Juniperus pingii var. wilsonii) shrublines on the south‐central Tibetan Plateau. A total of 1,899 shrubs were surveyed at 12 plots located in four regions along an east‐to‐west declining precipitation gradient. We detected synchronous recruitment with 9 out of 12 plots showing a gradual increase from 1600 to 1900, a peak at 1900–1940, and a subsequent decrease from the 1930s onward. Shrub recruitment was significantly and positively correlated with reconstructed summer temperature from 1600 to 1940, whereas it was negatively associated with temperature in recent decades (1930–2000). Recruitment was also positively correlated with precipitation, except in the 1780–1830 period, when a trend toward wetter climate conditions began. Warming‐induced drought limitation has likely reduced the recruitment potential of alpine juniper shrubs in recent decades. Ongoing warming without a simultaneous increase in precipitation is expected to further impair recruitment at the world's highest juniper shrublines and alter the dynamics and competitive balance between woody plant species throughout these alpine biomes.

Growth response of Abies spectabilis to climate along an elevation gradient of the Manang valley in the central Himalayas

“…It is one of the world's most vulnerable regions to global warming, with a warming rate higher than the global average (Shrestha et al 2012). Warming-induced drought stress has caused a higher occurrence of missing annual rings of high-elevation forests in the central Himalayas (Liang et al 2014), and declining recruitment at the world's highest juniper shrublines in recent decades on the Tibetan Plateau (Lu et al 2019). Thus, ongoing warming is expected to further alter drought-sensitive forest ecosystems along elevations.…”

Climate response of Salix oritrepha growth along a latitudinal gradient on the northeastern Tibetan Plateau

“…The Tibetan Plateau is characterized by a large-area of alpine ecosystem and relatively little is known about the influence of climate change on this biome (Shen et al, 2015;Lu et al, 2019). Taller shrubs are considered to be more sensitive to climate change than low statured shrub species (Myers-Smith et al, 2015).…”

An unusually high shrubline on the Tibetan Plateau

“…The genus Juniperus , composed of about 76 species, has a broad altitudinal distribution over the northern hemisphere (Adams 2014). For instance, some juniper shrub species grow in coastal sites (García‐Cervigón et al 2019), whereas others grow in alpine regions at ˃5,000 m above sea level [a. s. l.] in the Himalayas (Huang et al 2019, Lu et al 2019). In the so‐called “Third Pole” region, Juniperus species form some of the highest alpine treelines worldwide (ca.…”