Tree-Ring Data of Shurb Species of the Tibetan Platean Faithfully Record Climatic Warming Signal During Past Decades

Abstract

The Tibetan Plateau is regarded as the "roof of the world of the Earth", and its warming rate is much higher than the global average level in the same period, so it is a hot area to study the relationship between vegetation and climate. Alpine shrubs are widely distributed in the Tibetan Plateau and the shrub distribution area is also the population distribution concentration area of the Tibetan Plateau, which is of great significance for assessing the climate change in the main population distribution area of the Tibetan Plateau. At present, the related work of using tree ring materials in Tibetan Plateau is mainly based on the climate sensitivity and ecological adaptability of a single species or sample scale, but the comparative research under the conditions of various points and multi-species needs to be developed. In order to reveal the response of the radial growth of alpine shrubs in the Tibetan Plateau to climate change in recent 40 years and the difference of their ability to cope with extreme drought, the standard chronology of tree ring width of 8 shrubs in 13 sample plots in this area was constructed, and the extreme drought events were defined by Palmer Drought Index (PDSI). The tree ring width is used to quantify the resistance (Rt), recovery (Rc) and resilience (Rs) of radial growth to extreme drought events. The results showed that: (1) The radial growth of most shrubs showed a significant growth trend. Under the background of warm and humid climate, the growth dynamics of most shrubs are consistent, showing an upward trend, and the upward trend is more significant after 1998. All the shrubs suffering from drought showed obvious narrow ring width in 2007. (2) The correlation between typical shrubs and temperature in Tibetan Plateau is obviously stronger than that of precipitation. Among them, Juniperus squamata has the strongest correlation with temperature, and compared with the maximum temperature and mean temperature, the positive correlation between Juniperus squamata and the minimum temperature in the growing season (June-August) is the most significant; The correlation between Cotoneaster multiflorus, Caragana korshinskii and Salix integra and climate is inferior to that of Juniperus squamata, and it is weakly positively correlated with the temperature in most months (from June of last year to October of that year) and negatively correlated with precipitation. However, Potentilla fruticosa, Sibiraea angustata, Potentilla glabra and Berberis wilsoniae were weakly negatively correlated with the temperature in last winter (October-December) and spring (March-May). (3) The ecological and climatic conditions of Tibetan Plateau are suitable for the growth of alpine shrubs. With the aggravation of drought, the resistance of shrubs increased, and the recovery and resilience weakened. In the drought events in 2007, the resistance, recovery and resilience of Juniperus squamata in Baqing, Nangqian and Basu county were better than other shrub species. The growth level of Juniperus squamata in Zaduo County further decreased after drought, followed by Cotoneaster multiflorus and the ecological resilience of Caragana korshinskii was the worst. On the whole, the ecological adaptability of alpine shrubs in Tibetan Plateau is strong, and the climatic conditions in this area are more suitable for the growth of alpine shrubs.

Keywords: Tibetan Plateau, Shrub, Radial growth, Extreme weather, Ecological elasticity